lessonID,lessonName,ID,content,media_type,ImagePath
L_0002,earth science and its branches,T_0016,"Geology is the study of the solid Earth. Geologists study how rocks and minerals form. The way mountains rise up is part of geology. The way mountains erode away is another part. Geologists also study fossils and Earths history. There are many other branches of geology. There is so much to know about our home planet that most geologists become specialists in one area. For example, a mineralogist studies minerals, as seen in (Figure 1.11). Some volcanologists brave molten lava to study volcanoes. Seismologists monitor earthquakes worldwide to help protect people and property from harm (Figure 1.11). Paleontologists are interested in fossils and how ancient organisms lived. Scientists who compare the geology of other planets to Earth are planetary geologists. Some geologists study the Moon. Others look for petroleum. Still others specialize in studying soil. Some geologists can tell how old rocks are and determine how different rock layers formed. There is probably an expert in almost anything you can think of related to Earth! Geologists might study rivers and lakes, the underground water found between soil and rock particles, or even water that is frozen in glaciers. Earth scientists also need geographers who explore the features of Earths surface and work with cartographers, who make maps. Studying the layers of rock beneath the surface helps us to understand the history of planet Earth (Figure 1.12). ",text,
L_0002,earth science and its branches,T_0017,"Oceanography is the study of the oceans. The word oceanology might be more accurate, since ology is the study of. Graph is to write and refers to map making. But mapping the oceans is how oceanography started. More than 70% of Earths surface is covered with water. Almost all of that water is in the oceans. Scientists have visited the deepest parts of the ocean in submarines. Remote vehicles go where humans cant. Yet much of the ocean remains unexplored. Some people call the ocean the last frontier. Humans have had a big impact on the oceans. Populations of fish and other marine species have been overfished. Contaminants are polluting the waters. Global warming is melting the thick ice caps and warming the water. Warmer water expands and, along with water from the melting ice caps, causes sea levels to rise. There are many branches of oceanography. Physical oceanography is the study of water movement, like waves and ocean currents (Figure 1.13). Marine geology looks at rocks and structures in the ocean basins. Chemical oceanography studies the natural elements in ocean water. Marine biology looks at marine life. ",text,
L_0002,earth science and its branches,T_0017,"Oceanography is the study of the oceans. The word oceanology might be more accurate, since ology is the study of. Graph is to write and refers to map making. But mapping the oceans is how oceanography started. More than 70% of Earths surface is covered with water. Almost all of that water is in the oceans. Scientists have visited the deepest parts of the ocean in submarines. Remote vehicles go where humans cant. Yet much of the ocean remains unexplored. Some people call the ocean the last frontier. Humans have had a big impact on the oceans. Populations of fish and other marine species have been overfished. Contaminants are polluting the waters. Global warming is melting the thick ice caps and warming the water. Warmer water expands and, along with water from the melting ice caps, causes sea levels to rise. There are many branches of oceanography. Physical oceanography is the study of water movement, like waves and ocean currents (Figure 1.13). Marine geology looks at rocks and structures in the ocean basins. Chemical oceanography studies the natural elements in ocean water. Marine biology looks at marine life. ",text,
L_0002,earth science and its branches,T_0018,"Meteorologists dont study meteors they study the atmosphere! The word meteor refers to things in the air. Meteorology includes the study of weather patterns, clouds, hurricanes, and tornadoes. Meteorology is very important. Using radars and satellites, meteorologists work to predict, or forecast, the weather (Figure 1.14). The atmosphere is a thin layer of gas that surrounds Earth. Climatologists study the atmosphere. These scientists work to understand the climate as it is now. They also study how climate will change in response to global warming. The atmosphere contains small amounts of carbon dioxide. Climatologists have found that humans are putting a lot of extra carbon dioxide into the atmosphere. This is mostly from burning fossil fuels. The extra carbon dioxide traps heat from the Sun. Trapped heat causes the atmosphere to heat up. We call this global warming (Figure 1.15). ",text,
L_0002,earth science and its branches,T_0018,"Meteorologists dont study meteors they study the atmosphere! The word meteor refers to things in the air. Meteorology includes the study of weather patterns, clouds, hurricanes, and tornadoes. Meteorology is very important. Using radars and satellites, meteorologists work to predict, or forecast, the weather (Figure 1.14). The atmosphere is a thin layer of gas that surrounds Earth. Climatologists study the atmosphere. These scientists work to understand the climate as it is now. They also study how climate will change in response to global warming. The atmosphere contains small amounts of carbon dioxide. Climatologists have found that humans are putting a lot of extra carbon dioxide into the atmosphere. This is mostly from burning fossil fuels. The extra carbon dioxide traps heat from the Sun. Trapped heat causes the atmosphere to heat up. We call this global warming (Figure 1.15). ",text,
L_0002,earth science and its branches,T_0019,Environmental scientists study the ways that humans affect the planet we live on. We hope to find better ways of living that can also help the environment. Ecologists study lifeforms and the environments they live in (Figure 1.16). They try to predict the chain reactions that could occur when one part of the ecosystem is disrupted. ,text,
L_0002,earth science and its branches,T_0020,"Astronomy and astronomers have shown that the planets in our solar system are not the only planets in the universe. Over 530 planets were known outside our solar system in 2011. And there are billions of other planets! The universe also contains black holes, other galaxies, asteroids, comets, and nebula. As big as Earth seems, the entire universe is vastly more enormous. Earth is just a tiny part of our universe. Astronomers use many tools to study things in space. Earth-orbiting telescopes view stars and galaxies from the darkness of space (Figure 1.17). They may have optical and radio telescopes to see things that the human eye cant see. Spacecraft travel great distances to send back information on faraway places. Astronomers ask a wide variety of questions. How do strong bursts of energy from the Sun, called solar flares, affect communications? How might an impact from an asteroid affect life on Earth? What are the properties of black holes? Astronomers ask bigger questions too. How was the universe created? Is there life on other planets? Are there resources on other planets that people could use? Astronomers use what Earth scientists know to make comparisons with other planets. ",text,
L_0003,erosion and deposition by flowing water,T_0021,"Flowing water is a very important agent of erosion. Flowing water can erode rocks and soil. Water dissolves minerals from rocks and carries the ions. This process happens really slowly. But over millions of years, flowing water dissolves massive amounts of rock. Moving water also picks up and carries particles of soil and rock. The ability to erode is affected by the velocity, or speed, of the water. The size of the eroded particles depends on the velocity of the water. Eventually, the water deposits the materials. As water slows, larger particles are deposited. As the water slows even more, smaller particles are deposited. The graph in Figure 10.1 shows how water velocity and particle size influence erosion and deposition. ",text,
L_0003,erosion and deposition by flowing water,T_0022,"Faster-moving water has more energy. Therefore, it can carry larger particles. It can carry more particles. What causes water to move faster? The slope of the land over which the water flows is one factor. The steeper the slope, the faster the water flows. Another factor is the amount of water thats in the stream. Streams with a lot of water flow faster than streams that are nearly dry. ",text,
L_0003,erosion and deposition by flowing water,T_0023,"The size of particles determines how they are carried by flowing water. This is illustrated in Figure 10.2. Minerals that dissolve in water form salts. The salts are carried in solution. They are mixed thoroughly with the water. Small particles, such as clay and silt, are carried in suspension. They are mixed throughout the water. These particles are not dissolved in the water. Somewhat bigger particles, such as sand, are moved by saltation. The particles move in little jumps near the stream bottom. They are nudged along by water and other particles. The biggest particles, including gravel and pebbles, are moved by traction. In this process, the particles roll or drag along the bottom of the water. ",text,
L_0003,erosion and deposition by flowing water,T_0024,"Flowing water slows down when it reaches flatter land or flows into a body of still water. What do you think happens then? The water starts dropping the particles it was carrying. As the water slows, it drops the largest particles first. The smallest particles settle out last. ",text,
L_0003,erosion and deposition by flowing water,T_0025,"Water that flows over Earths surface includes runoff, streams, and rivers. All these types of flowing water can cause erosion and deposition. ",text,
L_0003,erosion and deposition by flowing water,T_0026,"When a lot of rain falls in a short period of time, much of the water is unable to soak into the ground. Instead, it runs over the land. Gravity causes the water to flow from higher to lower ground. As the runoff flows, it may pick up loose material on the surface, such as bits of soil and sand. Runoff is likely to cause more erosion if the land is bare. Plants help hold the soil in place. The runoff water in Figure 10.3 is brown because it eroded soil from a bare, sloping field. Can you find evidence of erosion by runoff where you live? What should you look for? Much of the material eroded by runoff is carried into bodies of water, such as streams, rivers, ponds, lakes, or oceans. Runoff is an important cause of erosion. Thats because it occurs over so much of Earths surface. ",text,
L_0003,erosion and deposition by flowing water,T_0027,"Streams often start in mountains, where the land is very steep. You can see an example in Figure 10.4. A mountain stream flows very quickly because of the steep slope. This causes a lot of erosion and very little deposition. The rapidly falling water digs down into the stream bed and makes it deeper. It carves a narrow, V-shaped channel. ",text,
L_0003,erosion and deposition by flowing water,T_0027,"Streams often start in mountains, where the land is very steep. You can see an example in Figure 10.4. A mountain stream flows very quickly because of the steep slope. This causes a lot of erosion and very little deposition. The rapidly falling water digs down into the stream bed and makes it deeper. It carves a narrow, V-shaped channel. ",text,
L_0003,erosion and deposition by flowing water,T_0028,"Mountain streams may erode waterfalls. As shown in Figure 10.5, a waterfall forms where a stream flows from an area of harder to softer rock. The water erodes the softer rock faster than the harder rock. This causes the stream bed to drop down, like a step, creating a waterfall. As erosion continues, the waterfall gradually moves upstream. ",text,
L_0003,erosion and deposition by flowing water,T_0029,"Rivers flowing over gentle slopes erode the sides of their channels more than the bottom. Large curves, called meanders, form because of erosion and deposition by the moving water. The curves are called meanders because they slowly wander over the land. You can see how this happens in Figure 10.6. As meanders erode from side to side, they create a floodplain. This is a broad, flat area on both sides of a river. Eventually, a meander may become cut off from the rest of the river. This forms an oxbow lake, like the one in Figure 10.6. ",text,
L_0003,erosion and deposition by flowing water,T_0029,"Rivers flowing over gentle slopes erode the sides of their channels more than the bottom. Large curves, called meanders, form because of erosion and deposition by the moving water. The curves are called meanders because they slowly wander over the land. You can see how this happens in Figure 10.6. As meanders erode from side to side, they create a floodplain. This is a broad, flat area on both sides of a river. Eventually, a meander may become cut off from the rest of the river. This forms an oxbow lake, like the one in Figure 10.6. ",text,
L_0003,erosion and deposition by flowing water,T_0030,"When a stream or river slows down, it starts dropping its sediments. Larger sediments are dropped in steep areas, but smaller sediments can still be carried. Smaller sediments are dropped as the slope becomes less steep. Alluvial Fans In arid regions, a mountain stream may flow onto flatter land. The stream comes to a stop rapidly. The deposits form an alluvial fan, like the one in Figure 10.7. Deltas Deposition also occurs when a stream or river empties into a large body of still water. In this case, a delta forms. A delta is shaped like a triangle. It spreads out into the body of water. An example is shown in Figure 10.7. ",text,
L_0003,erosion and deposition by flowing water,T_0031,"A flood occurs when a river overflows it banks. This might happen because of heavy rains. Floodplains As the water spreads out over the land, it slows down and drops its sediment. If a river floods often, the floodplain develops a thick layer of rich soil because of all the deposits. Thats why floodplains are usually good places for growing plants. For example, the Nile River in Egypt provides both water and thick sediments for raising crops in the middle of a sandy desert. Natural Levees A flooding river often forms natural levees along its banks. A levee is a raised strip of sediments deposited close to the waters edge. You can see how levees form in Figure 10.8. Levees occur because floodwaters deposit their biggest sediments first when they overflow the rivers banks. ",text,
L_0003,erosion and deposition by flowing water,T_0032,"Some water soaks into the ground. It travels down through tiny holes in soil. It seeps through cracks in rock. The water moves slowly, pulled deeper and deeper by gravity. Underground water can also erode and deposit material. ",text,
L_0003,erosion and deposition by flowing water,T_0033,"As groundwater moves through rock, it dissolves minerals. Some rocks dissolve more easily than others. Over time, the water may dissolve large underground holes, or caves. Groundwater drips from the ceiling to the floor of a cave. This water is rich in dissolved minerals. When the minerals come out of solution, they are deposited. They build up on the ceiling of the cave to create formations called stalactites. A stalactite is a pointed, icicle-like mineral deposit that forms on the ceiling of a cave. They drip to the floor of the cave and harden to form stalagmites. A stalagmite is a more rounded mineral deposit that forms on the floor of a cave (Figure 10.9). Both types of formations grow in size as water keeps dripping and more minerals are deposited. ",text,
L_0003,erosion and deposition by flowing water,T_0034,"As erosion by groundwater continues, the ceiling of a cave may collapse. The rock and soil above it sink into the ground. This forms a sinkhole on the surface. You can see an example of a sinkhole in Figure 10.10. Some sinkholes are big enough to swallow vehicles and buildings. ",text,
L_0004,erosion and deposition by waves,T_0035,"All waves are the way energy travels through matter. Ocean waves are energy traveling through water. They form when wind blows over the surface of the ocean. Wind energy is transferred to the sea surface. Then, the energy is carried through the water by the waves. Figure 10.11 shows ocean waves crashing against rocks on a shore. They pound away at the rocks and anything else they strike. Three factors determine the size of ocean waves: 1. The speed of the wind. 2. The length of time the wind blows. 3. The distance the wind blows. The faster, longer, and farther the wind blows, the bigger the waves are. Bigger waves have more energy. ",text,
L_0004,erosion and deposition by waves,T_0036,"Runoff, streams, and rivers carry sediment to the oceans. The sediment in ocean water acts like sandpaper. Over time, they erode the shore. The bigger the waves are and the more sediment they carry, the more erosion they cause. ",text,
L_0004,erosion and deposition by waves,T_0037,Erosion by waves can create unique landforms (Figure 10.12). Wave-cut cliffs form when waves erode a rocky shoreline. They create a vertical wall of exposed rock layers. Sea arches form when waves erode both sides of a cliff. They create a hole in the cliff. Sea stacks form when waves erode the top of a sea arch. This leaves behind pillars of rock. ,text,
L_0004,erosion and deposition by waves,T_0038,"Eventually, the sediment in ocean water is deposited. Deposition occurs where waves and other ocean motions slow. The smallest particles, such as silt and clay, are deposited away from shore. This is where water is calmer. Larger particles are deposited on the beach. This is where waves and other motions are strongest. ",text,
L_0004,erosion and deposition by waves,T_0039,"In relatively quiet areas along a shore, waves may deposit sand. Sand forms a beach, like the one in Figure 10.13. Many beaches include bits of rock and shell. You can see a close-up photo of beach deposits in Figure 10.14. ",text,
L_0004,erosion and deposition by waves,T_0039,"In relatively quiet areas along a shore, waves may deposit sand. Sand forms a beach, like the one in Figure 10.13. Many beaches include bits of rock and shell. You can see a close-up photo of beach deposits in Figure 10.14. ",text,
L_0004,erosion and deposition by waves,T_0040,Most waves strike the shore at an angle. This causes longshore drift. Longshore drift moves sediment along the shore. Sediment is moved up the beach by an incoming wave. The wave approaches at an angle to the shore. Water then moves straight offshore. The sediment moves straight down the beach with it. The sediment is again picked up by a wave that is coming in at an angle. This motion is show in Figure 10.15 and at the link below. ,text,
L_0004,erosion and deposition by waves,T_0041,Deposits from longshore drift may form a spit. A spit is a ridge of sand that extends away from the shore. The end of the spit may hook around toward the quieter waters close to shore. You can see a spit in Figure 10.16. Waves may also deposit sediments to form sandbars and barrier islands. You can see examples of these landforms in Figure 10.17. ,text,
L_0004,erosion and deposition by waves,T_0042,"Shores are attractive places to live and vacation. But development at the shore is at risk of damage from waves. Wave erosion threatens many homes and beaches on the ocean. This is especially true during storms, when waves may be much larger than normal. ",text,
L_0004,erosion and deposition by waves,T_0043,"Barrier islands provide natural protection to shorelines. Storm waves strike the barrier island before they reach the shore. People also build artificial barriers, called breakwaters. Breakwaters also protect the shoreline from incoming waves. You can see an example of a breakwater in Figure 10.18. It runs parallel to the coast like a barrier island. ",text,
L_0004,erosion and deposition by waves,T_0044,"Longshore drift can erode the sediment from a beach. To keep this from happening, people may build a series of groins. A groin is wall of rocks or concrete that juts out into the ocean perpendicular to the shore. It stops waves from moving right along the beach. This stops the sand on the upcurrent side and reduces beach erosion. You can see how groins work in Figure 10.19. ",text,
L_0006,erosion and deposition by glaciers,T_0054,"Glaciers form when more snow falls than melts each year. Over many years, layer upon layer of snow compacts and turns to ice. There are two different types of glaciers: continental glaciers and valley glaciers. Each type forms some unique features through erosion and deposition. An example of each type is pictured in Figure 10.27. A continental glacier is spread out over a huge area. It may cover most of a continent. Today, continental glaciers cover most of Greenland and Antarctica. In the past, they were much more extensive. A valley glacier is long and narrow. Valley glaciers form in mountains and flow downhill through mountain river valleys. ",text,
L_0006,erosion and deposition by glaciers,T_0055,"Like flowing water, flowing ice erodes the land and deposits the material elsewhere. Glaciers cause erosion in two main ways: plucking and abrasion. Plucking is the process by which rocks and other sediments are picked up by a glacier. They freeze to the bottom of the glacier and are carried away by the flowing ice. Abrasion is the process in which a glacier scrapes underlying rock. The sediments and rocks frozen in the ice at the bottom and sides of a glacier act like sandpaper. They wear away rock. They may also leave scratches and grooves that show the direction the glacier moved. ",text,
L_0006,erosion and deposition by glaciers,T_0056,"Valley glaciers form several unique features through erosion. You can see some of them in Figure 10.28. As a valley glacier flows through a V-shaped river valley, it scrapes away the sides of the valley. It carves a U-shaped valley with nearly vertical walls. A line called the trimline shows the highest level the glacier reached. A cirque is a rounded hollow carved in the side of a mountain by a glacier. The highest cliff of a cirque is called the headwall. An arte is a jagged ridge that remains when cirques form on opposite sides of a mountain. A low spot in an arte is called a col. A horn is a sharp peak that is left behind when glacial cirques are on at least three sides of a mountain. ",text,
L_0006,erosion and deposition by glaciers,T_0057,"Glaciers deposit their sediment when they melt. They drop and leave behind whatever was once frozen in their ice. Its usually a mixture of particles and rocks of all sizes, called glacial till. Water from the melting ice may form lakes or other water features. Figure 10.29 shows some of the landforms glaciers deposit when they melt. Moraine is sediment deposited by a glacier. A ground moraine is a thick layer of sediments left behind by a retreating glacier. An end moraine is a low ridge of sediments deposited at the end of the glacier. It marks the greatest distance the glacier advanced. A drumlin is a long, low hill of sediments deposited by a glacier. Drumlins often occur in groups called drumlin fields. The narrow end of each drumlin points in the direction the glacier was moving when it dropped the sediments. An esker is a winding ridge of sand deposited by a stream of meltwater. Such streams flow underneath a retreating glacier. A kettle lake occurs where a chunk of ice was left behind in the sediments of a retreating glacier. When the ice melted, it left a depression. The meltwater filled it to form a lake. ",text,
L_0008,fossils,T_0064,"Fossils are preserved remains or traces of organisms that lived in the past. Most preserved remains are hard parts, such as teeth, bones, or shells. Examples of these kinds of fossils are pictured in Figure 11.1. Preserved traces can include footprints, burrows, or even wastes. Examples of trace fossils are also shown in Figure 11.1. ",text,
L_0008,fossils,T_0065,The process by which remains or traces of living things become fossils is called fossilization. Most fossils are preserved in sedimentary rocks. ,text,
L_0008,fossils,T_0066,Most fossils form when a dead organism is buried in sediment. Layers of sediment slowly build up. The sediment is buried and turns into sedimentary rock. The remains inside the rock also turn to rock. The remains are replaced by minerals. The remains literally turn to stone. Fossilization is illustrated in Figure 11.2. ,text,
L_0008,fossils,T_0066,Most fossils form when a dead organism is buried in sediment. Layers of sediment slowly build up. The sediment is buried and turns into sedimentary rock. The remains inside the rock also turn to rock. The remains are replaced by minerals. The remains literally turn to stone. Fossilization is illustrated in Figure 11.2. ,text,
L_0008,fossils,T_0067,"Fossils may form in other ways. With complete preservation, the organism doesnt change much. As seen below, tree sap may cover an organism and then turn into amber. The original organism is preserved so that scientists might be able to study its DNA. Organisms can also be completely preserved in tar or ice. Molds and casts are another way organisms can be fossilized. A mold is an imprint of an organism left in rock. The organisms remains break down completely. Rock that fills in the mold resembles the original remains. The fossil that forms in the mold is called a cast. Molds and casts usually form in sedimentary rock. With compression, an organisms remains are put under great pressure inside rock layers. This leaves behind a dark stain in the rock. You can read about them in Figure 11.3. ",text,
L_0008,fossils,T_0068,"Its very unlikely that any given organism will become a fossil. The remains of many organisms are consumed. Remains also may be broken down by other living things or by the elements. Hard parts, such as bones, are much more likely to become fossils. But even they rarely last long enough to become fossils. Organisms without hard parts are the least likely to be fossilized. Fossils of soft organisms, from bacteria to jellyfish, are very rare. ",text,
L_0008,fossils,T_0069,"Of all the organisms that ever lived, only a tiny number became fossils. Still, scientists learn a lot from fossils. Fossils are our best clues about the history of life on Earth. ",text,
L_0008,fossils,T_0070,"Fossils give clues about major geological events. Fossils can also give clues about past climates. Fossils of ocean animals are found at the top of Mt. Everest. Mt. Everest is the highest mountain on Earth. These fossils show that the area was once at the bottom of a sea. The seabed was later uplifted to form the Himalaya mountain range. An example is shown in the Figure 11.4. Fossils of plants are found in Antarctica. Currently, Antarctica is almost completely covered with ice. The fossil plants show that Antarctica once had a much warmer climate. ",text,
L_0008,fossils,T_0071,"Fossils are used to determine the ages of rock layers. Index fossils are the most useful for this. Index fossils are of organisms that lived over a wide area. They lived for a fairly short period of time. An index fossil allows a scientist to determine the age of the rock it is in. Trilobite fossils, as shown in Figure 11.5, are common index fossils. Trilobites were widespread marine animals. They lived between 500 and 600 million years ago. Rock layers containing trilobite fossils must be that age. Different species of trilobite fossils can be used to narrow the age even more. ",text,
L_0009,relative ages of rocks,T_0072,The study of rock strata is called stratigraphy. The laws of stratigraphy can help scientists understand Earths past. The laws of stratigraphy are usually credited to a geologist from Denmark named Nicolas Steno. He lived in the 1600s. The laws are illustrated in Figure 11.6. Refer to the figure as you read about the laws below. ,text,
L_0009,relative ages of rocks,T_0073,"Superposition refers to the position of rock layers and their relative ages. Relative age means age in comparison with other rocks, either younger or older. The relative ages of rocks are important for understanding Earths history. New rock layers are always deposited on top of existing rock layers. Therefore, deeper layers must be older than layers closer to the surface. This is the law of superposition. You can see an example in Figure 11.7. ",text,
L_0009,relative ages of rocks,T_0073,"Superposition refers to the position of rock layers and their relative ages. Relative age means age in comparison with other rocks, either younger or older. The relative ages of rocks are important for understanding Earths history. New rock layers are always deposited on top of existing rock layers. Therefore, deeper layers must be older than layers closer to the surface. This is the law of superposition. You can see an example in Figure 11.7. ",text,
L_0009,relative ages of rocks,T_0074,"Rock layers extend laterally, or out to the sides. They may cover very broad areas, especially if they formed at the bottom of ancient seas. Erosion may have worn away some of the rock, but layers on either side of eroded areas will still match up. Look at the Grand Canyon in Figure 11.8. Its a good example of lateral continuity. You can clearly see the same rock layers on opposite sides of the canyon. The matching rock layers were deposited at the same time, so they are the same age. ",text,
L_0009,relative ages of rocks,T_0075,"Sediments were deposited in ancient seas in horizontal, or flat, layers. If sedimentary rock layers are tilted, they must have moved after they were deposited. ",text,
L_0009,relative ages of rocks,T_0076,"Rock layers may have another rock cutting across them, like the igneous rock in Figure 11.9. Which rock is older? To determine this, we use the law of cross-cutting relationships. The cut rock layers are older than the rock that cuts across them. ",text,
L_0009,relative ages of rocks,T_0077,"Geologists can learn a lot about Earths history by studying sedimentary rock layers. But in some places, theres a gap in time when no rock layers are present. A gap in the sequence of rock layers is called an unconformity. Look at the rock layers in Figure 11.10. They show a feature called Huttons unconformity. The unconformity was discovered by James Hutton in the 1700s. Hutton saw that the lower rock layers are very old. The upper layers are much younger. There are no layers in between the ancient and recent layers. Hutton thought that the intermediate rock layers eroded away before the more recent rock layers were deposited. Huttons discovery was a very important event in geology! Hutton determined that the rocks were deposited over time. Some were eroded away. Hutton knew that deposition and erosion are very slow. He realized that for both to occur would take an extremely long time. This made him realize that Earth must be much older than people thought. This was a really big discovery! It meant there was enough time for life to evolve gradually. ",text,
L_0009,relative ages of rocks,T_0077,"Geologists can learn a lot about Earths history by studying sedimentary rock layers. But in some places, theres a gap in time when no rock layers are present. A gap in the sequence of rock layers is called an unconformity. Look at the rock layers in Figure 11.10. They show a feature called Huttons unconformity. The unconformity was discovered by James Hutton in the 1700s. Hutton saw that the lower rock layers are very old. The upper layers are much younger. There are no layers in between the ancient and recent layers. Hutton thought that the intermediate rock layers eroded away before the more recent rock layers were deposited. Huttons discovery was a very important event in geology! Hutton determined that the rocks were deposited over time. Some were eroded away. Hutton knew that deposition and erosion are very slow. He realized that for both to occur would take an extremely long time. This made him realize that Earth must be much older than people thought. This was a really big discovery! It meant there was enough time for life to evolve gradually. ",text,
L_0009,relative ages of rocks,T_0078,"When rock layers are in the same place, its easy to give them relative ages. But what if rock layers are far apart? What if they are on different continents? What evidence is used to match rock layers in different places? ",text,
L_0009,relative ages of rocks,T_0079,"Some rock layers extend over a very wide area. They may be found on more than one continent or in more than one country. For example, the famous White Cliffs of Dover are on the coast of southeastern England. These distinctive rocks are matched by similar white cliffs in France, Belgium, Holland, Germany, and Denmark (see Figure 11.11). It is important that this chalk layer goes across the English Channel. The rock is so soft that the Channel Tunnel connecting England and France was carved into it! ",text,
L_0009,relative ages of rocks,T_0080,"Like index fossils, key beds are used to match rock layers. A key bed is a thin layer of rock. The rock must be unique and widespread. For example, a key bed from around the time that the dinosaurs went extinct is very important. A thin layer of clay was deposited over much of Earths surface. The clay has large amount of the element iridium. Iridium is rare on Earth but common in asteroids. This unusual clay layer has been used to match rock up layers all over the world. It also led to the hypothesis that a giant asteroid struck Earth and caused the dinosaurs to go extinct. ",text,
L_0009,relative ages of rocks,T_0081,Index fossils are commonly used to match rock layers in different places. You can see how this works in Figure ,text,
L_0009,relative ages of rocks,T_0082,Earth formed 4.5 billion years ago. Geologists divide this time span into smaller periods. Many of the divisions mark major events in life history. ,text,
L_0009,relative ages of rocks,T_0083,"Divisions in Earth history are recorded on the geologic time scale. For example, the Cretaceous ended when the dinosaurs went extinct. European geologists were the first to put together the geologic time scale. So, many of the names of the time periods are from places in Europe. The Jurassic Period is named for the Jura Mountains in France and Switzerland, for example. ",text,
L_0009,relative ages of rocks,T_0084,"To create the geologic time scale, geologists correlated rock layers. Stenos laws were used to determine the relative ages of rocks. Older rocks are at the bottom and younger rocks are at the top. The early geologic time scale could only show the order of events. The discovery of radioactivity in the late 1800s changed that. Scientists could determine the exact age of some rocks in years. They assigned dates to the time scale divisions. For example, the Jurassic began about 200 million years ago. It lasted for about 55 million years. ",text,
L_0009,relative ages of rocks,T_0085,"The largest blocks of time on the geologic time scale are called eons. Eons are split into eras. Each era is divided into periods. Periods may be further divided into epochs. Geologists may just use early or late. An example is late Jurassic, or early Cretaceous. Figure 11.13 shows you what the geologic time scale looks like. ",text,
L_0009,relative ages of rocks,T_0086,The geologic time scale may include illustrations of how life on Earth has changed. Major events on Earth may also be shown. These include the formation of the major mountains or the extinction of the dinosaurs. Figure 11.14 is a different kind of the geologic time scale. It shows how Earths environment and life forms have changed. ,text,
L_0009,relative ages of rocks,T_0087,"We now live in the Phanerozoic Eon, the Cenozoic Era, the Quaternary Period, and the Holocene Epoch. Phanero- zoic means visible life. During this eon, rocks contain visible fossils. Before the Phanerozoic, life was microscopic. The Cenozoic Era means new life. It encompasses the most recent forms of life on Earth. The Cenozoic is sometimes called the Age of Mammals. Before the Cenozoic came the Mesozoic and Paleozoic. The Mesozoic means middle life. This is the age of reptiles, when dinosaurs ruled the planet. The Paleozoic is old life. Organisms like invertebrates and fish were the most common lifeforms. ",text,
L_0010,absolute ages of rocks,T_0088,"Radioactive decay is the breakdown of unstable elements into stable elements. To understand this process, recall that the atoms of all elements contain the particles protons, neutrons, and electrons. ",text,
L_0010,absolute ages of rocks,T_0089,"An element is defined by the number of protons it contains. All atoms of a given element contain the same number of protons. The number of neutrons in an element may vary. Atoms of an element with different numbers of neutrons are called isotopes. Consider carbon as an example. Two isotopes of carbon are shown in Figure 11.15. Compare their protons and neutrons. Both contain 6 protons. But carbon-12 has 6 neutrons and carbon-14 has 8 neutrons. Almost all carbon atoms are carbon-12. This is a stable isotope of carbon. Only a tiny percentage of carbon atoms are carbon-14. Carbon-14 is unstable. Figure 11.16 shows carbon dioxide, which forms in the atmosphere from carbon-14 and oxygen. Neutrons in cosmic rays strike nitrogen atoms in the atmosphere. The nitrogen forms carbon- 14. Carbon in the atmosphere combines with oxygen to form carbon dioxide. Plants take in carbon dioxide during photosynthesis. In this way, carbon-14 enters food chains. ",text,
L_0010,absolute ages of rocks,T_0089,"An element is defined by the number of protons it contains. All atoms of a given element contain the same number of protons. The number of neutrons in an element may vary. Atoms of an element with different numbers of neutrons are called isotopes. Consider carbon as an example. Two isotopes of carbon are shown in Figure 11.15. Compare their protons and neutrons. Both contain 6 protons. But carbon-12 has 6 neutrons and carbon-14 has 8 neutrons. Almost all carbon atoms are carbon-12. This is a stable isotope of carbon. Only a tiny percentage of carbon atoms are carbon-14. Carbon-14 is unstable. Figure 11.16 shows carbon dioxide, which forms in the atmosphere from carbon-14 and oxygen. Neutrons in cosmic rays strike nitrogen atoms in the atmosphere. The nitrogen forms carbon- 14. Carbon in the atmosphere combines with oxygen to form carbon dioxide. Plants take in carbon dioxide during photosynthesis. In this way, carbon-14 enters food chains. ",text,
L_0010,absolute ages of rocks,T_0090,"Like other unstable isotopes, carbon-14 breaks down, or decays. For carbon-14 decay, each carbon-14 atom loses an alpha particle. It changes to a stable atom of nitrogen-14. This is illustrated in Figure 11.17. The decay of an unstable isotope to a stable element occurs at a constant rate. This rate is different for each isotope pair. The decay rate is measured in a unit called the half-life. The half-life is the time it takes for half of a given amount of an isotope to decay. For example, the half-life of carbon-14 is 5730 years. Imagine that you start out with 100 grams of carbon-14. In 5730 years, half of it decays. This leaves 50 grams of carbon-14. Over the next 5730 years, half of the remaining amount will decay. Now there are 25 grams of carbon-14. How many grams will there be in another 5730 years? Figure 11.18 graphs the rate of decay of carbon-14. ",text,
L_0010,absolute ages of rocks,T_0091,The rate of decay of unstable isotopes can be used to estimate the absolute ages of fossils and rocks. This type of dating is called radiometric dating. ,text,
L_0010,absolute ages of rocks,T_0092,"The best-known method of radiometric dating is carbon-14 dating. A living thing takes in carbon-14 (along with stable carbon-12). As the carbon-14 decays, it is replaced with more carbon-14. After the organism dies, it stops taking in carbon. That includes carbon-14. The carbon-14 that is in its body continues to decay. So the organism contains less and less carbon-14 as time goes on. We can estimate the amount of carbon-14 that has decayed by measuring the amount of carbon-14 to carbon-12. We know how fast carbon-14 decays. With this information, we can tell how long ago the organism died. Carbon-14 has a relatively short half-life. It decays quickly compared to some other unstable isotopes. So carbon- 14 dating is useful for specimens younger than 50,000 years old. Thats a blink of an eye in geologic time. But radiocarbon dating is very useful for more recent events. One important use of radiocarbon is early human sites. Carbon-14 dating is also limited to the remains of once-living things. To date rocks, scientists use other radioactive isotopes. ",text,
L_0010,absolute ages of rocks,T_0093,"The isotopes in Table 11.1 are used to date igneous rocks. These isotopes have much longer half-lives than carbon- 14. Because they decay more slowly, they can be used to date much older specimens. Which of these isotopes could be used to date a rock that formed half a million years ago? Unstable Isotope Decays to At a Half-Life of (years) Potassium-40 Uranium-235 Uranium-238 Argon-40 Lead-207 Lead-206 1.3 billion 700 million 4.5 billion Dates Rocks Aged (years old) 100 thousand - 1 billion 1 million - 4.5 billion 1 million - 4.5 billion ",text,
L_0011,the origin of earth,T_0094,"Our solar system began about 5 billion years ago. The Sun, planets and other solar system objects all formed at about the same time. ",text,
L_0011,the origin of earth,T_0095,"The Sun and planets formed from a giant cloud of gas and dust. This was the solar nebula. The cloud contracted and began to spin. As it contracted, its temperature and pressure increased. The cloud spun faster, and formed into a disk. Scientists think the solar system at that time looked like these disk-shaped objects in the Orion Nebula (Figure ",text,
L_0011,the origin of earth,T_0096,"Temperatures and pressures at the center of the cloud were extreme. It was so hot that nuclear fusion reactions began. In these reactions hydrogen fuses to make helium. Extreme amounts of energy are released. Our Sun became a star! Material in the disk surrounding the Sun collided. Small particles collided and became rocks. Rocks collided and became boulders. Eventually planets formed from the material (Figure 12.2). Dwarf plants, comets, and asteroids formed too (Figure 12.3). ",text,
L_0011,the origin of earth,T_0096,"Temperatures and pressures at the center of the cloud were extreme. It was so hot that nuclear fusion reactions began. In these reactions hydrogen fuses to make helium. Extreme amounts of energy are released. Our Sun became a star! Material in the disk surrounding the Sun collided. Small particles collided and became rocks. Rocks collided and became boulders. Eventually planets formed from the material (Figure 12.2). Dwarf plants, comets, and asteroids formed too (Figure 12.3). ",text,
L_0011,the origin of earth,T_0096,"Temperatures and pressures at the center of the cloud were extreme. It was so hot that nuclear fusion reactions began. In these reactions hydrogen fuses to make helium. Extreme amounts of energy are released. Our Sun became a star! Material in the disk surrounding the Sun collided. Small particles collided and became rocks. Rocks collided and became boulders. Eventually planets formed from the material (Figure 12.2). Dwarf plants, comets, and asteroids formed too (Figure 12.3). ",text,
L_0011,the origin of earth,T_0097,Material at a similar distances from the Sun collided together to form each of the planets. Earth grew from material in its part of space. Moons origin was completely different from Earths. ,text,
L_0011,the origin of earth,T_0098,"Earth formed like the other planets. Different materials in its region of space collided. Eventually the material made a planet. All of the collisions caused Earth to heat up. Rock and metal melted. The molten material separated into layers. Gravity pulled the denser material into the center. The lighter elements rose to the surface (Figure 12.4). Because the material separated, Earths core is made mostly of iron. Earths crust is made mostly of lighter materials. In between the crust and the core is Earths mantle, made of solid rock. ",text,
L_0011,the origin of earth,T_0099,"This model for how the Moon formed is the best fit of all of the data scientists have about the Moon. In the early solar system there was a lot of space debris. Asteroids flew around, sometimes striking the planets. An asteroid the size of Mars smashed into Earth. The huge amount of energy from the impact melted most of Earth. The asteroid melted too. Material from both Earth and the asteroid was thrown out into orbit. Over time, this material smashed together to form our Moon. The lunar surface is about 4.5 billion years old. This means that the collision happened about 70 million years after Earth formed. ",text,
L_0011,the origin of earth,T_0100,An atmosphere is the gases that surround a planet. The early Earth had no atmosphere. Conditions were so hot that gases were not stable. ,text,
L_0011,the origin of earth,T_0101,"Earths first atmosphere was different from the current one. The gases came from two sources. Volcanoes spewed gases into the air. Comets carried in ices from outer space. These ices warmed and became gases. Nitrogen, carbon dioxide, hydrogen, and water vapor, or water in gas form, were in the first atmosphere (Figure 12.5). Take a look at the list of gases. Whats missing? The early atmosphere had almost no oxygen. ",text,
L_0011,the origin of earth,T_0102,"Earths atmosphere slowly cooled. Once it was cooler, water vapor could condense. It changed back to its liquid form. Liquid water could fall to Earths surface as rain. Over millions of years water collected to form the oceans. Water began to cycle on Earth as water evaporated from the oceans and returned again as rainfall. ",text,
L_0012,early earth,T_0103,"The earliest crust was probably basalt. It may have resembled the current seafloor. This crust formed before there were any oceans. More than 4 billion years ago, continental crust appeared. The first continents were very small compared with those today. ",text,
L_0012,early earth,T_0104,"Continents grow when microcontinents, or small continents, collide with each other or with a larger continent. Oceanic island arcs also collide with continents to make them grow. ",text,
L_0012,early earth,T_0105,"There are times in Earth history when all of the continents came together to form a supercontinent. Supercontinents come together and then break apart. Pangaea was the last supercontinent on Earth, but it was not the first. The supercontinent before Pangaea is called Rodinia. Rodinia contained about 75% of the continental landmass that is present today. The supercontinent came together about 1.1 billion years ago. Rodinia was not the first supercontinent either. Scientists think that three supercontinents came before Rodina, making five so far in Earth history. ",text,
L_0012,early earth,T_0106,"Since the early Earth was very hot, mantle convection was very rapid. Plate tectonics likely moved very quickly. The early Earth was a very active place with abundant volcanic eruptions and earthquakes. The remnants of these early rocks are now seen in the ancient cores of the continents. ",text,
L_0012,early earth,T_0107,For the first 4 billion years of Earth history there is only a little evidence of life. Organisms were tiny and soft and did not fossilize well. But scientists use a variety of ways to figure out what this early life was like. ,text,
L_0012,early earth,T_0108,"Life probably began in the oceans. No one knows exactly how or when. Life may have originated more than once. If life began before the Moon formed, that impact would have wiped it out and it would have had to originate again. Eventually conditions on Earth became less violent. The planet could support life. The first organisms were made of only one cell (Figure 12.6). The earliest cells were prokaryotes. Prokaryotic cells are surrounded by a cell membrane, but they do not have a nucleus. The cells got their nutrients directly from the water. The cells needed to use these nutrients to live and grow. The cells also needed to be able to make copies of themselves. To do this they stored genetic information in nucleic acids. The two nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Nucleic acids pass ",text,
L_0012,early earth,T_0109,"Early cells took nutrients from the water. Eventually the nutrients would have become less abundant. Around 3 billion years ago, photosynthesis began. Organisms could make their own food from sunlight and inorganic molecules. From these ingredients they made chemical energy that they used. Oxygen is a waste product of photosynthesis. That first oxygen combined with iron to create iron oxide. Later on, the oxygen entered the atmosphere. Some of the oxygen in the atmosphere became ozone. The ozone layer formed to protect Earth from harmful ultraviolet radiation. This made the environment able to support more complex life forms. ",text,
L_0012,early earth,T_0110,The first organisms to photosynthesize were cyanobacteria. These organisms may have been around as far back as 3.5 billion years and are still alive today (Figure 12.7). Now they are called blue-green algae. They are common in lakes and seas and account for 20% to 30% of photosynthesis today. ,text,
L_0012,early earth,T_0111,"Eukaryotes evolved about 2 billion years ago. Unlike prokaryotes, eukaryotes have a cell nucleus. They have more structures and are better organized. Organelles within a eukaryote can perform certain functions. Some supply energy; some break down wastes. Eukaryotes were better able to live and so became the dominant life form. ",text,
L_0012,early earth,T_0112,"For life to become even more complex, multicellular organisms needed to evolve. Prokaryotes and eukaryotes can be multicellular. Toward the end of the Precambrian, the Ediacara Fauna evolved (Figure 12.8). These are the fossils discovered by Walcott in the introduction to the next section. The Ediacara was extremely diverse. They appeared after Earth defrosted from a worldwide glaciation. The Ediacara fauna seem to have died out. Other multicellular organisms appeared in the Phanerozoic. ",text,
L_0014,water on earth,T_0131,"Water is a simple chemical compound. Each molecule of water contains two hydrogen atoms (H2 ) and one oxygen atom (O). Thats why the chemical formula for water is H2 O. If water is so simple, why is it special? Water is one of the few substances that exists on Earth in all three states of matter. Water occurs as a gas, a liquid and a solid. You drink liquid water and use it to shower. You breathe gaseous water vapor in the air. You may go ice skating on a pond covered with solid water ice in the winter. ",text,
L_0014,water on earth,T_0132,"Earth is often called the water planet. Figure 13.1 shows why. If astronauts see Earth from space, this is how it looks. Notice how blue the planet appears. Thats because oceans cover much of Earths surface. Water is also found in the clouds that rise above the planet. Most of Earths water is salt water in the oceans. As Figure 13.2 shows, only 3 percent of Earths water is fresh. Freshwater is water that contains little or no dissolved salt. Most freshwater is frozen in ice caps and glaciers. Glaciers cover the peaks of some tall mountains. For example, the Cascades Mountains in North America and the Alps Mountains in Europe are capped with ice. Ice caps cover vast areas of Antarctica and Greenland. Chunks of ice frequently break off ice caps. They form icebergs that float in the oceans. ",text,
L_0014,water on earth,T_0132,"Earth is often called the water planet. Figure 13.1 shows why. If astronauts see Earth from space, this is how it looks. Notice how blue the planet appears. Thats because oceans cover much of Earths surface. Water is also found in the clouds that rise above the planet. Most of Earths water is salt water in the oceans. As Figure 13.2 shows, only 3 percent of Earths water is fresh. Freshwater is water that contains little or no dissolved salt. Most freshwater is frozen in ice caps and glaciers. Glaciers cover the peaks of some tall mountains. For example, the Cascades Mountains in North America and the Alps Mountains in Europe are capped with ice. Ice caps cover vast areas of Antarctica and Greenland. Chunks of ice frequently break off ice caps. They form icebergs that float in the oceans. ",text,
L_0014,water on earth,T_0133,"Did you ever wonder where the water in your glass came from or where its been? The next time you take a drink of water, think about this. Each water molecule has probably been around for billions of years. Thats because Earths water is constantly recycled. ",text,
L_0014,water on earth,T_0134,"Water is recycled through the water cycle. The water cycle is the movement of water through the oceans, atmo- sphere, land, and living things. The water cycle is powered by energy from the Sun. Figure 13.3 diagrams the water cycle. ",text,
L_0014,water on earth,T_0135,"Water keeps changing state as it goes through the water cycle. This means that it can be a solid, liquid, or gas. How does water change state? How does it keep moving through the cycle? As Figure 13.3 shows, several processes are involved. Evaporation changes liquid water to water vapor. Energy from the Sun causes water to evaporate. Most evaporation is from the oceans because they cover so much area. The water vapor rises into the atmosphere. Transpiration is like evaporation because it changes liquid water to water vapor. In transpiration, plants release water vapor through their leaves. This water vapor rises into the atmosphere. Condensation changes water vapor to liquid water. As air rises higher into the atmosphere, it cools. Cool air can hold less water vapor than warm air. So some of the water vapor condenses into water droplets. Water droplets may form clouds. Precipitation is water that falls from clouds to Earths surface. Water droplets in clouds fall to Earth when they become too large to stay aloft. The water falls as rain if the air is warm. If the air is cold, the water may freeze and fall as snow, sleet, or hail. Most precipitation falls into the oceans. Some falls on land. Runoff is precipitation that flows over the surface of the land. This water may travel to a river, lake, or ocean. Runoff may pick up fertilizer and other pollutants and deliver them to the water body where it ends up. In this way, runoff may pollute bodies of water. Infiltration is the process by which water soaks into the ground. Some of the water may seep deep under- ground. Some may stay in the soil, where plants can absorb it with their roots. In all these ways, water keeps cycling. The water cycle repeats over and over again. Who knows? Maybe a water molecule that you drink today once quenched the thirst of a dinosaur. ",text,
L_0015,surface water,T_0136,Look at the pictures of flowing water in Figure 13.4. A waterfall tumbles down a mountainside. A brook babbles through a forest. A river slowly meanders through a broad valley. What do all these forms of flowing water have in common? They are all streams. ,text,
L_0015,surface water,T_0137,"A stream is a body of freshwater that flows downhill in a channel. The channel of a stream has a bottom, or bed, and sides called banks. Any size body of flowing water can be called a stream. Usually, though, a large stream is called a river. ",text,
L_0015,surface water,T_0138,"All streams and rivers have several features in common. These features are shown in (Figure 13.5). The place where a stream or river starts is its source. The source might be a spring, where water flows out of the ground. Or the source might be water from melting snow on a mountain top. A single stream may have multiple sources. A stream or river probably ends when it flows into a body of water, such as a lake or an ocean. A stream ends at its mouth. As the water flows into the body of water, it slows down and drops the sediment it was carrying. The sediment may build up to form a delta. Several other features of streams and rivers are also shown in Figure 13.5. Small streams often flow into bigger streams or rivers. The small streams are called tributaries. A river and all its tributaries make up a river system. At certain times of year, a stream or river may overflow its banks. The area of land that is flooded is called the floodplain. The floodplain may be very wide where the river flows over a nearly flat surface. A river flowing over a floodplain may wear away broad curves. These curves are called meanders. ",text,
L_0015,surface water,T_0139,"All of the land drained by a river system is called its basin, or watershed. One river systems basin is separated from another river systems basin by a divide. The divide is created by the highest points between the two river basins. Precipitation that falls within a river basin always flows toward that river. Precipitation that falls on the other side of the divide flows toward a different river. Figure 13.6 shows the major river basins in the U.S. You can watch an animation of water flowing through a river basin at this link: http://trashfree.org/btw/graphics/watershed_anim.gif ",text,
L_0015,surface water,T_0139,"All of the land drained by a river system is called its basin, or watershed. One river systems basin is separated from another river systems basin by a divide. The divide is created by the highest points between the two river basins. Precipitation that falls within a river basin always flows toward that river. Precipitation that falls on the other side of the divide flows toward a different river. Figure 13.6 shows the major river basins in the U.S. You can watch an animation of water flowing through a river basin at this link: http://trashfree.org/btw/graphics/watershed_anim.gif ",text,
L_0015,surface water,T_0140,"After a heavy rain, you may find puddles of water standing in low spots. The same principle explains why water collects in ponds and lakes. Water travels downhill, so a depression in the ground fills with standing water. A pond is a small body of standing water. A lake is a large body of standing water. Most lakes have freshwater, but a few are salty. The Great Salt Lake in Utah is an example of a saltwater lake. The water in a large lake may be so deep that sunlight cannot penetrate all the way to the bottom. Without sunlight, water plants and algae cannot live on the bottom of the lake. Thats because plants need sunlight for photosynthesis. The largest lakes in the world are the Great Lakes. They lie between the U.S. and Canada, as shown in Figure 13.7. How great are they? They hold 22 percent of all the worlds fresh surface water! ",text,
L_0015,surface water,T_0141,Ponds and lakes may get their water from several sources. Some falls directly into them as precipitation. Some enters as runoff and some from streams and rivers. Water leaves ponds and lakes through evaporation and also as outflow. ,text,
L_0015,surface water,T_0142,"The depression that allows water to collect to form a lake may come about in a variety of ways. The Great Lakes, for example, are glacial lakes. A glacial lake forms when a glacier scrapes a large hole in the ground. When the glacier melts, the water fills the hole and forms a lake. Over time, water enters the lake from the sources mentioned above as well. Other lakes are crater lakes or rift lakes, which are pictured in Figure 13.8. Crater lakes form when volcanic eruptions create craters that fill with water. Rift lakes form when movements of tectonic plates create low places that fill with water. ",text,
L_0015,surface water,T_0143,"Some of Earths freshwater is found in wetlands. A wetland is an area that is covered with water, or at least has very soggy soil, during all or part of the year. Certain species of plants thrive in wetlands, and they are rich ecosystems. Freshwater wetlands are usually found at the edges of steams, rivers, ponds, or lakes. Wetlands can also be found at the edges of seas. ",text,
L_0015,surface water,T_0144,"Not all wetlands are alike, as you can see from Figure 13.9. Wetlands vary in how wet they are and how much of the year they are soaked. Wetlands also vary in the kinds of plants that live in them. This depends mostly on the climate where the wetland is found. Types of wetlands include marshes, swamps, and bogs. A marsh is a wetland that is usually under water. It has grassy plants, such as cattails. A swamp is a wetland that may or may not be covered with water but is always soggy. It has shrubs or trees. A bog is a wetland that has soggy soil. It is generally covered with mosses. ",text,
L_0015,surface water,T_0145,"People used to think that wetlands were useless. Many wetlands were filled in with rocks and soil to create lands that were then developed with roads, golf courses, and buildings. Now we know that wetlands are very important. Laws have been passed to help protect them. Why are wetlands so important? Wetlands have great biodiversity. They provide homes or breeding sites to a huge variety of species. Because so much wetland area has been lost, many of these species are endangered. Wetlands purify water. They filter sediments and toxins from runoff before it enters rivers, lakes, and oceans. Wetlands slow rushing water. During hurricanes and other extreme weather, wetlands reduce the risk of floods. Although the rate has slowed, wetlands are still being destroyed today. ",text,
L_0015,surface water,T_0146,"A flood occurs when so much water enters a stream or river that it overflows its banks. Flood waters from a river are shown in Figure 13.10. Like this flood, many floods are caused by very heavy rains. Floods may also occur when deep snow melts quickly in the spring. Floods are a natural part of the water cycle, but they can cause a lot of damage. Farms and homes may be lost, and people may die. In 1939, millions of people died in a flood in China. Although freshwater is needed to grow crops and just to live, too much freshwater in the same place at once can be deadly. ",text,
L_0016,groundwater,T_0147,"Freshwater below Earths surface is called groundwater. The water infiltrates, or seeps down into, the ground from the surface. How does this happen? And where does the water go? ",text,
L_0016,groundwater,T_0148,"Water infiltrates the ground because soil and rock are porous. Between the grains are pores, or tiny holes. Since water can move through this rock it is permeable. Eventually, the water reaches a layer of rock that is not porous and so is impermeable. Water stops moving downward when it reaches this layer of rock. Look at the diagram in Figure 13.11. It shows two layers of porous rock. The top layer is not saturated; it is not full of water. The next layer is saturated. The water in this layer has nowhere else to go. It cannot seep any deeper into the ground because the rock below it is impermeable. ",text,
L_0016,groundwater,T_0149,"The top of the saturated rock layer in Figure 13.11 is called the water table. The water table isnt like a real table. It doesnt remain firmly in one place. Instead, it rises or falls, depending on how much water seeps down from the surface. The water table is higher when there is a lot of rain and lower when the weather is dry. ",text,
L_0016,groundwater,T_0150,"An underground layer of rock that is saturated with groundwater is called an aquifer. A diagram of an aquifer is shown in Figure 13.12. Aquifers are generally found in porous rock, such as sandstone. Water infiltrates the aquifer from the surface. The water that enters the aquifer is called recharge. ",text,
L_0016,groundwater,T_0151,"Most land areas have aquifers beneath them. Many aquifers are used by people for freshwater. The closer to the surface an aquifer is, the easier it is to get the water. However, an aquifer close to the surface is also more likely to become polluted. Pollutants can seep down through porous rock in recharge water. An aquifer that is used by people may not be recharged as quickly as its water is removed. The water table may lower and the aquifer may even run dry. If this happens, the ground above the aquifer may sink. This is likely to damage any homes or other structures built above the aquifer. ",text,
L_0016,groundwater,T_0152,"One of the biggest aquifers in the world is the Ogallala aquifer. As you can see from Figure 13.13, this aquifer lies beneath parts of eight U.S. states. It covers a total area of 451,000 square kilometers (174,000 square miles). In some places, it is less than a meter deep. In other places, it is hundreds of meters deep. The Ogallala aquifer is an important source of freshwater in the American Midwest. This is a major farming area, and much of the water is used to irrigate crops. The water in this aquifer is being used up ten times faster than it is recharged. If this continues, what might happen to the Ogallala aquifer? ",text,
L_0016,groundwater,T_0153,"The top of an aquifer may be high enough in some places to meet the surface of the ground. This often happens on a slope. The water flows out of the ground and creates a spring. A spring may be just a tiny trickle, or it may be a big gush of water. One of the largest springs in the world is Big Spring in Missouri, seen in Figure 13.14. Water flowing out of the ground at a spring may flow downhill and enter a stream. Thats what happens to the water that flows out of Big Spring in Missouri. If the water from a spring cant flow downhill, it may spread out to form a pond or lake instead. Lake George in New York State, which is pictured in Figure 13.15, is a spring-fed lake. The lake basin was carved by a glacier. ",text,
L_0016,groundwater,T_0153,"The top of an aquifer may be high enough in some places to meet the surface of the ground. This often happens on a slope. The water flows out of the ground and creates a spring. A spring may be just a tiny trickle, or it may be a big gush of water. One of the largest springs in the world is Big Spring in Missouri, seen in Figure 13.14. Water flowing out of the ground at a spring may flow downhill and enter a stream. Thats what happens to the water that flows out of Big Spring in Missouri. If the water from a spring cant flow downhill, it may spread out to form a pond or lake instead. Lake George in New York State, which is pictured in Figure 13.15, is a spring-fed lake. The lake basin was carved by a glacier. ",text,
L_0016,groundwater,T_0154,"Some springs have water that contains minerals. Groundwater dissolves minerals out of the rock as it seeps through the pores. The water in some springs is hot because it is heated by hot magma. Many hot springs are also mineral springs. Thats because hot water can dissolve more minerals than cold water. Grand Prismatic Spring, shown in Figure 13.16, is a hot mineral spring. Dissolved minerals give its water a bright blue color. The edge of the spring is covered with thick orange mats of bacteria. The bacteria use the minerals in the hot water to make food. ",text,
L_0016,groundwater,T_0155,"Heated groundwater may become trapped in spaces within rocks. Pressure builds up as more water seeps into the spaces. When the pressure becomes great enough, the water bursts out of the ground at a crack or weak spot. This is called a geyser. When the water erupts from the ground, the pressure is released. Then more water collects and the pressure builds up again. This leads to another eruption. Old Faithful is the best-known geyser in the world. You can see a picture of it in Figure 13.17. The geyser erupts faithfully every 90 minutes, day after day. During each eruption, it may release as much as 30,000 liters of water! ",text,
L_0016,groundwater,T_0156,"Most groundwater does not flow out of an aquifer as a spring or geyser. So to use the water thats stored in an aquifer people must go after it. How? They dig a well. A well is a hole that is dug or drilled through the ground down to an aquifer. This is illustrated in Figure 13.18. People have depended on water from wells for thousands of years. To bring water to the surface takes energy because the force of gravity must be overcome. Today, many wells use electricity to pump water to the surface. However, in some places, water is still brought to the surface the old-fashioned way  with human labor. The well pictured in Figure 13.19 is an example of this type of well. A hand-cranked pulley is used to lift the bucket of water to the surface. ",text,
L_0017,introduction to the oceans,T_0157,"When Earth formed 4.6 billion years ago, it would not have been called the water planet. There were no oceans then. In fact, there was no liquid water at all. Early Earth was too hot for liquid water to exist. Earths early years were spent as molten rock and metal. ",text,
L_0017,introduction to the oceans,T_0158,"Over time, Earth cooled. The surface hardened to become solid rock. Volcanic eruptions, like the one in Figure 14.1, brought lava and gases to the surface. One of the gases was water vapor. More water vapor came from asteroids and comets that crashed into Earth. As Earth cooled still more, the water vapor condensed to make Earths first liquid water. At last, the oceans could start to form. ",text,
L_0017,introduction to the oceans,T_0159,"Earths crust consists of many tectonic plates that move over time. Due to plate tectonics, the continents changed their shapes and positions during Earth history. As the continents changed, so did the oceans. About 250 million years ago, there was one huge land mass known as Pangaea. There was also one huge ocean called Panthalassa. You can see it in Figure 14.2. By 180 million years ago, Pangaea began to break up. The continents started to drift apart. They slowly moved to where they are today. The movement of the continents caused Panthalassa to break into smaller oceans. These oceans are now known as the Pacific, Atlantic, Indian, and Arctic Oceans. The waters of all the oceans are connected. ",text,
L_0017,introduction to the oceans,T_0160,"Oceans cover more than 70 percent of Earths surface and hold 97 percent of its surface water. Its no surprise that the oceans have a big influence on the planet. The oceans affect the atmosphere, climate, and living things. ",text,
L_0017,introduction to the oceans,T_0161,"Oceans are the major source of water vapor in the atmosphere. Sunlight heats water near the sea surface, as shown in Figure 14.3. As the water warms, some of it evaporates. The water vapor rises into the air, where it may form clouds and precipitation. Precipitation provides the freshwater needed by plants and other living things. Ocean water also absorbs gases from the atmosphere. The most important are oxygen and carbon dioxide. Oxygen is needed by living things in the oceans. Much of the carbon dioxide sinks to the bottom of the seas. Carbon dioxide is a major cause of global warming. By absorbing carbon dioxide, the oceans help control global warming. ",text,
L_0017,introduction to the oceans,T_0162,"Coastal areas have a milder climate than inland areas. They are warmer in the winter and cooler in the summer. Thats because land near an ocean is influenced by the temperature of the oceans. The temperature of ocean water is moderate and stable. Why? There are two major reasons: 1. Water is much slower to warm up and cool down than land. As a result, oceans never get as hot or as cold as land. 2. Water flows through all the worlds oceans. Warm water from the equator mixes with cold water from the poles. The mixing of warm and cold water makes the water temperature moderate. Even inland temperatures are milder because of oceans. Without oceans, there would be much bigger temperature swings all over Earth. Temperatures might plunge hundreds of degrees below freezing in the winter. In the summer, lakes and seas might boil! Life as we know it could not exist on Earth without the oceans. ",text,
L_0017,introduction to the oceans,T_0163,"The oceans provide a home to many living things. In fact, a greater number of organisms lives in the oceans than on land. Coral reefs, like the one in Figure 14.4, have more diversity of life forms than almost anywhere else on Earth. ",text,
L_0017,introduction to the oceans,T_0164,You know that ocean water is salty. But do you know why? How salty is it? ,text,
L_0017,introduction to the oceans,T_0165,"Ocean water is salty because water dissolves minerals out of rocks. This happens whenever water flows over or through rocks. Much of this water and its minerals flow in rivers that end up in the oceans. Minerals dissolved in water form salts. When the water evaporates, it leaves the salts behind. As a result, ocean water is much saltier than other water on Earth. ",text,
L_0017,introduction to the oceans,T_0166,"Have you ever gone swimming in the ocean? If you have, then you probably tasted the salts in the water. By mass, salts make up about 3.5 percent of ocean water. Figure 14.5 shows the most common minerals in ocean water. The main components are sodium and chloride. Together they form the salt known as sodium chloride. You may know the compound as table salt or the mineral halite. The amount of salts in ocean water varies from place to place. For example, near the mouth of a river, ocean water may be less salty. Thats because river water contains less salt than ocean water. Where the ocean is warm, the water may be more salty. Can you explain why? (Hint: More water evaporates when the water is warm.) ",text,
L_0017,introduction to the oceans,T_0167,"In addition to the amount of salts, other conditions in ocean water vary from place to place. One is the amount of nutrients in the water. Another is the amount of sunlight that reaches the water. These conditions depend mainly on two factors: distance from shore and depth of water. Oceans are divided into zones based on these two factors. The ocean floor makes up another zone. Figure 14.6 shows all the ocean zones. ",text,
L_0017,introduction to the oceans,T_0168,"There are three main ocean zones based on distance from shore. They are the intertidal zone, neritic zone, and oceanic zone. Distance from shore influences how many nutrients are in the water. Why? Most nutrients are washed into ocean water from land. Therefore, water closer to shore tends to have more nutrients. Living things need nutrients. So distance from shore also influences how many organisms live in the water. ",text,
L_0017,introduction to the oceans,T_0169,"Two main zones based on depth of water are the photic zone and aphotic zone. The photic zone is the top 200 meters of water. The aphotic zone is water deeper than 200 meters. The deeper you go, the darker the water gets. Thats because sunlight cannot penetrate very far under water. Sunlight is needed for photosynthesis. So the depth of water determines whether photosynthesis is possible. There is enough sunlight for photosynthesis only in the photic zone. Water also gets colder as you go deeper. The weight of the water pressing down from above increases as well. At great depths, life becomes very difficult. The pressure is so great that only specially adapted creatures can live there. ",text,
L_0018,ocean movements,T_0170,"Most ocean waves are caused by winds. A wave is the transfer of energy through matter. A wave that travels across miles of ocean is traveling energy, not water. Ocean waves transfer energy from wind through water. The energy of a wave may travel for thousands of miles. The water itself moves very little. Figure 14.9 shows how water molecules move when a wave goes by. ",text,
L_0018,ocean movements,T_0170,"Most ocean waves are caused by winds. A wave is the transfer of energy through matter. A wave that travels across miles of ocean is traveling energy, not water. Ocean waves transfer energy from wind through water. The energy of a wave may travel for thousands of miles. The water itself moves very little. Figure 14.9 shows how water molecules move when a wave goes by. ",text,
L_0018,ocean movements,T_0171,"Figure 14.9 also shows how the size of waves is measured. The highest point of a wave is the crest. The lowest point is the trough. The vertical distance between a crest and a trough is the height of the wave. Wave height is also called amplitude. The horizontal distance between two crests is the wavelength. Both amplitude and wavelength are measures of wave size. The size of an ocean wave depends on how fast, over how great a distance, and how long the wind blows. The greater each of these factors is, the bigger a wave will be. Some of the biggest waves occur with hurricanes. A hurricane is a storm that forms over the ocean. Its winds may blow more than 150 miles per hour! The winds also travel over long distances and may last for many days. ",text,
L_0018,ocean movements,T_0172,"Figure 14.10 shows what happens to waves near shore. As waves move into shallow water, they start to touch the bottom. The base of the waves drag and slow. Soon the waves slow down and pile up. They get steeper and unstable as the top moves faster than the base. When they reach the shore, the waves topple over and break. ",text,
L_0018,ocean movements,T_0173,"Not all waves are caused by winds. A shock to the ocean can also send waves through water. A tsunami is a wave or set of waves that is usually caused by an earthquake. As we have seen in recent years, the waves can be enormous and extremely destructive. Usually tsunami waves travel through the ocean unnoticed. But when they reach the shore they become enormous. Tsunami waves can flood entire regions. They destroy property and cause many deaths. Figure 14.11 shows the damage caused by a tsunami in the Indian Ocean in 2004. ",text,
L_0018,ocean movements,T_0174,"Tides are daily changes in the level of ocean water. They occur all around the globe. High tides occur when the water reaches its highest level in a day. Low tides occur when the water reaches its lowest level in a day. Tides keep cycling from high to low and back again. In most places the water level rises and falls twice a day. So there are two high tides and two low tides approximately every 24 hours. In Figure 14.12, you can see the difference between high and low tides. This is called the tidal range. ",text,
L_0018,ocean movements,T_0175,"Figure 14.13 shows why tides occur. The main cause of tides is the pull of the Moons gravity on Earth. The pull is greatest on whatever is closest to the Moon. Although the gravity pulls the land, only the water can move. As a result: Water on the side of Earth facing the Moon is pulled hardest by the Moons gravity. This causes a bulge of water on that side of Earth. That bulge is a high tide. Earth itself is pulled harder by the Moons gravity than is the ocean on the side of Earth opposite the Moon. As a result, there is bulge of water on the opposite side of Earth. This creates another high tide. With water bulging on two sides of Earth, theres less water left in between. This creates low tides on the other two sides of the planet. ",text,
L_0018,ocean movements,T_0176,"The Suns gravity also pulls on Earth and its oceans. Even though the Sun is much larger than the Moon, the pull of the Suns gravity is much less because the Sun is much farther away. The Suns gravity strengthens or weakens the Moons influence on tides. Figure 14.14 shows the position of the Moon relative to the Sun at different times during the month. The positions of the Moon and Sun relative to each other determines how the Sun affects tides. This creates spring tides or neap tides. Spring tides occur during the new moon and full moon. The Sun and Moon are in a straight line either on the same side of Earth or on opposite sides. Their gravitational pull combines to cause very high and very low tides. Spring tides have the greatest tidal range. Neap tides occur during the first and third quarters of the Moon. The Moon and Sun are at right angles to each other. Their gravity pulls on the oceans in different directions so the highs and lows are not as great. Neap tides have the smallest tidal range. This animation shows the effect of the Moon and Sun on the tides: ",text,
L_0018,ocean movements,T_0176,"The Suns gravity also pulls on Earth and its oceans. Even though the Sun is much larger than the Moon, the pull of the Suns gravity is much less because the Sun is much farther away. The Suns gravity strengthens or weakens the Moons influence on tides. Figure 14.14 shows the position of the Moon relative to the Sun at different times during the month. The positions of the Moon and Sun relative to each other determines how the Sun affects tides. This creates spring tides or neap tides. Spring tides occur during the new moon and full moon. The Sun and Moon are in a straight line either on the same side of Earth or on opposite sides. Their gravitational pull combines to cause very high and very low tides. Spring tides have the greatest tidal range. Neap tides occur during the first and third quarters of the Moon. The Moon and Sun are at right angles to each other. Their gravity pulls on the oceans in different directions so the highs and lows are not as great. Neap tides have the smallest tidal range. This animation shows the effect of the Moon and Sun on the tides: ",text,
L_0018,ocean movements,T_0177,"Another way ocean water moves is in currents. A current is a stream of moving water that flows through the ocean. Surface currents are caused mainly by winds, but not the winds that blow and change each day. Surface currents are caused by the major wind belts that blow in the same direction all the time. The major surface currents are shown in Figure 14.15. They flow in a clockwise direction in the Northern Hemi- sphere. In the Southern Hemisphere, they flow in the opposite direction. ",text,
L_0018,ocean movements,T_0178,"Winds and surface currents tend to move from the hot equator north or south toward the much cooler poles. Thats because of differences in the temperature of air masses over Earths surface. But Earth is spinning on its axis underneath the wind and water as they move. The Earth rotates from west to east. As a result, winds and currents actually end up moving toward the northeast or southeast. This effect of Earths rotation on the direction of winds and currents is called the Coriolis effect. ",text,
L_0018,ocean movements,T_0179,"Large ocean currents can have a big impact on the climate of nearby coasts. The Gulf Stream, for example, carries warm water from near the equator up the eastern coast of North America. Look at the map in Figure 14.16. It shows how the Gulf Stream warms both the water and land along the coast. ",text,
L_0018,ocean movements,T_0180,"Currents also flow deep below the surface of the ocean. Deep currents are caused by differences in density at the top and bottom. Density is defined as the amount of mass per unit of volume. More dense water takes up less space than less dense water. It has the same mass but less volume. Water that is more dense sinks. Less dense water rises. What can make water more dense? Water becomes more dense when it is colder and when it has more salt. In the North Atlantic Ocean, cold winds chill the water at the surface. Sea ice grows in this cold water, but ice is created from fresh water. The salt is left behind in the seawater. This cold, salty water is very dense, so it sinks to the bottom of the North Atlantic. Downwelling can take place in other places where surface water becomes very dense (see Figure 14.17). When water sinks it pushes deep water along at the bottom of the ocean. This water circulates through all of the ocean basins in deep currents. ",text,
L_0018,ocean movements,T_0180,"Currents also flow deep below the surface of the ocean. Deep currents are caused by differences in density at the top and bottom. Density is defined as the amount of mass per unit of volume. More dense water takes up less space than less dense water. It has the same mass but less volume. Water that is more dense sinks. Less dense water rises. What can make water more dense? Water becomes more dense when it is colder and when it has more salt. In the North Atlantic Ocean, cold winds chill the water at the surface. Sea ice grows in this cold water, but ice is created from fresh water. The salt is left behind in the seawater. This cold, salty water is very dense, so it sinks to the bottom of the North Atlantic. Downwelling can take place in other places where surface water becomes very dense (see Figure 14.17). When water sinks it pushes deep water along at the bottom of the ocean. This water circulates through all of the ocean basins in deep currents. ",text,
L_0018,ocean movements,T_0181,"Sometimes deep ocean water rises to the surface. This is called upwelling. Figure 14.18 shows why it happens. Strong winds blow surface water away from shore. This allows deeper water to flow to the surface and take its place. When water comes up from the deep, it brings a lot of nutrients with it. Why is deep water so full of nutrients? Over time, dead organisms and other organic matter settle to the bottom water and collect. The nutrient-rich water that comes to the surface by upwelling supports many living things. ",text,
L_0019,the ocean floor,T_0182,Scientists study the ocean floor in various ways. Scientists or their devices may actually travel to the ocean floor. Or they may study the ocean floor from the surface. One way is with a tool called sonar. ,text,
L_0019,the ocean floor,T_0183,"Did you ever shout and hear an echo? If you did, thats because the sound waves bounced off a hard surface and back to you. The same principle explains how sonar works. A ship on the surface sends sound waves down to the ocean floor. The sound waves bounce off the ocean floor and return to the surface, like an echo. Figure 14.19 show how this happens. Sonar can be used to measure how deep the ocean is. A device records the time it takes sound waves to travel from the surface to the ocean floor and back again. Sound waves travel through water at a known speed. Once scientists know the travel time of the wave, they can calculate the distance to the ocean floor. They can then combine all of these distances to make a map of the ocean floor. Figure 14.20 shows an example of this type of map. ",text,
L_0019,the ocean floor,T_0183,"Did you ever shout and hear an echo? If you did, thats because the sound waves bounced off a hard surface and back to you. The same principle explains how sonar works. A ship on the surface sends sound waves down to the ocean floor. The sound waves bounce off the ocean floor and return to the surface, like an echo. Figure 14.19 show how this happens. Sonar can be used to measure how deep the ocean is. A device records the time it takes sound waves to travel from the surface to the ocean floor and back again. Sound waves travel through water at a known speed. Once scientists know the travel time of the wave, they can calculate the distance to the ocean floor. They can then combine all of these distances to make a map of the ocean floor. Figure 14.20 shows an example of this type of map. ",text,
L_0019,the ocean floor,T_0184,"Only a specially designed vehicle can venture beneath the sea surface. But only very special vehicles can reach the ocean floor. Three are described here and pictured in Figure 14.21: In 1960, scientists used the submersible Trieste to travel into the Mariana Trench. They succeeded, but the trip was very risky. Making humans safe at such depths costs a lot of money. People have not traveled to this depth again. In 2012, the film director, James Cameron, dove to the bottom of the Mariana Trench by himself in a submersible that he had built for the purpose. The vehicle named Alvin was developed soon after Trieste. The submersible has made over 4,000 dives deep into the ocean. People can stay underwater for up to 9 hours. Alvin has been essential for developing a scientific understanding the worlds oceans. Today, remote-control vehicles, called remotely operated vehicles (ROVs) go to the deepest ocean floor. They dont have any people on board. However, they carry devices that record many measurements. They also collect sediments and take photos. ",text,
L_0019,the ocean floor,T_0185,"Scientists have learned a lot about the ocean floor. For example, they know that Earths tallest mountains and deepest canyons are on the ocean floor. The major features on the ocean floor are described below. They are also shown in Figure 14.22. The continental shelf is the ocean floor nearest the edges of continents. It has a a gentle slope. The water over the continental shelf is shallow. The continental slope lies between the continental shelf and the abyssal plain. It has a steep slope with a sharp drop to the deep ocean floor. The abyssal plain forms much of the floor under the open ocean. It lies from 3 to 6 kilometers (1.9 to 3.7 miles) below the surface. Much of it is flat. An oceanic trench is a deep canyon on the ocean floor. Trenches occur where one tectonic plate subducts under another. The deepest trench is the Mariana Trench in the Pacific Ocean. It plunges more than 11 kilometers (almost 7 miles) below sea level. A seamount is a volcanic mountain on the ocean floor. Seamounts that rise above the water surface are known as islands. There are many seamounts dotting the seafloor. The mid-ocean ridge is a mountain range that runs through all the worlds oceans. It is almost 64,000 kilometers (40,000 miles) long! It forms where tectonic plates pull apart. Magma erupts through the ocean floor to make new seafloor. The magma hardens to create the ridge. ",text,
L_0019,the ocean floor,T_0186,The ocean floor is rich in resources. The resources include both living and nonliving things. ,text,
L_0019,the ocean floor,T_0187,"The ocean floor is home to many species of living things. Some from shallow water are used by people for food. Clams and some fish are among the many foods we get from the ocean floor. Some living things on the ocean floor are sources of human medicines. For example, certain bacteria on the ocean floor produce chemicals that fight cancer. ",text,
L_0019,the ocean floor,T_0188,"Oil and natural gas lie below some regions of the seafloor. Large drills on floating oil rigs must be used to reach them. This is risky for workers on the rigs. It is also risky for the ocean and its living things. An oil rig explosion caused a massive oil leak in the Gulf of Mexico in 2010. Oil poured into the water for several months. The oil caused great harm to habitats and living things, both in the water and on the coast. The oil spill also hurt the economy of Gulf Coast states. The effects of the oil spill are still being tallied. There are many minerals on the ocean floor. Some settle down from the water above. Some are released in hot water through vents, or cracks, in the seafloor. The minerals in hot water settle out and form metallic chimneys, as in Figure 14.23. These metals could be mined, but they are very deep in the sea and very far from land. This means that mining them would be too expensive and not worth the effort. Some types of minerals form balls called nodules. Nodules may be tiny or as big as basketballs. They contain manganese, iron, copper, and other useful minerals. As many as 500 billion tons of nodules lie on the ocean floor! However, mining them would be very costly and could be harmful to the ocean environment. ",text,
L_0020,ocean life,T_0189,"When you think of life in the ocean, do you think of fish? Actually, fish are not the most common life forms in the ocean. Plankton are the most common. Plankton make up one of three major groups of marine life. The other two groups are nekton and benthos. Figure 14.24 shows the three groups. ",text,
L_0020,ocean life,T_0190,Plankton are living things that float in the water. Most plankton are too small to see with the unaided eye. Some examples are shown in Figure 14.25. Plankton are unable to move on their own. Ocean motions carry them along. There are two main types of plankton: 1. Phytoplankton are plant-like plankton. They make food by photosynthesis. They live in the photic zone. Most are algae. 2. Zooplankton are animal-like plankton. They feed on phytoplankton. They include tiny animals and fish larvae. ,text,
L_0020,ocean life,T_0190,Plankton are living things that float in the water. Most plankton are too small to see with the unaided eye. Some examples are shown in Figure 14.25. Plankton are unable to move on their own. Ocean motions carry them along. There are two main types of plankton: 1. Phytoplankton are plant-like plankton. They make food by photosynthesis. They live in the photic zone. Most are algae. 2. Zooplankton are animal-like plankton. They feed on phytoplankton. They include tiny animals and fish larvae. ,text,
L_0020,ocean life,T_0191,"Nekton are living things that swim through the water. They may live at any depth, in the photic or aphotic zone. Most nekton are fish, although some are mammals. Fish have fins and streamlined bodies to help them swim. Fish also have gills to take oxygen from the water. Figure 14.26 shows examples of nekton. ",text,
L_0020,ocean life,T_0192,Benthos are living things on the ocean floor. Many benthic organisms attach themselves to rocks and stay in one place. This protects them from crashing waves and other water movements. Some benthic organisms burrow into sediments for food or protection. Benthic animals may crawl over the ocean floor. Examples of benthos include clams and worms. Figure 14.27 shows two other examples. Some benthos live near vents on the deep ocean floor. Tubeworms are an example (see Figure 14.28). Scalding hot water pours out of the vents. The hot water contains chemicals that some specialized bacteria can use to make food. Tubeworms let the bacteria live inside them. The bacteria get protection and the tubeworms get some of the food. ,text,
L_0020,ocean life,T_0192,Benthos are living things on the ocean floor. Many benthic organisms attach themselves to rocks and stay in one place. This protects them from crashing waves and other water movements. Some benthic organisms burrow into sediments for food or protection. Benthic animals may crawl over the ocean floor. Examples of benthos include clams and worms. Figure 14.27 shows two other examples. Some benthos live near vents on the deep ocean floor. Tubeworms are an example (see Figure 14.28). Scalding hot water pours out of the vents. The hot water contains chemicals that some specialized bacteria can use to make food. Tubeworms let the bacteria live inside them. The bacteria get protection and the tubeworms get some of the food. ,text,
L_0020,ocean life,T_0193,"Figure 14.29 shows a marine food chain. Phytoplankton form the base of the food chain. Phytoplankton are the most important primary producers in the ocean. They use sunlight and nutrients to make food by photosynthesis. Small zooplankton consume phytoplankton. Larger organisms eat the small zooplankton. Larger predators eat these consumers. In an unusual relationship, some enormous whales depend on plankton for their food. They filter tremendous amounts of these tiny creatures out of the water. The bacteria that make food from chemicals are also primary producers. These organisms do not do photosynthesis since there is no light at the vents. They do something called chemosynthesis. They break down chemicals to make food. When marine organisms die, decomposers break them down. This returns their nutrients to the water. The nutrients can be used again to make food. Decomposers in the oceans include bacteria and worms. Many live on the ocean floor. Do you know why? ",text,
L_0022,energy in the atmosphere,T_0210,What explains all of these events? The answer can be summed up in one word: energy. Energy is defined as the ability to do work. Doing anything takes energy. A campfire obviously has energy. You can feel its heat and see its light. ,text,
L_0022,energy in the atmosphere,T_0211,"Heat and light are forms of energy. Other forms are chemical and electrical energy. Energy cant be created or destroyed. It can change form. For example, a piece of wood has chemical energy stored in its molecules. When the wood burns, the chemical energy changes to heat and light energy. ",text,
L_0022,energy in the atmosphere,T_0212,Energy can move from one place to another. It can travel through space or matter. Thats why you can feel the heat of a campfire and see its light. These forms of energy travel from the campfire to you. ,text,
L_0022,energy in the atmosphere,T_0213,Almost all energy on Earth comes from the Sun. The Suns energy heats the planet and the air around it. Sunlight also powers photosynthesis and life on Earth. ,text,
L_0022,energy in the atmosphere,T_0214,The Sun gives off energy in tiny packets called photons. Photons travel in waves. Figure 15.7 models a wave of light. Notice the wavelength in the figure. Waves with shorter wavelengths have more energy. ,text,
L_0022,energy in the atmosphere,T_0215,"Energy from the Sun has a wide range of wavelengths. The total range of energy is called the electromagnetic spectrum. You can see it in Figure 15.8. Visible light is the only light that humans can see. Different wavelengths of visible light appear as different colors. Radio waves have the longest wavelengths. They also have the least amount of energy. Infrared light has wavelengths too long for humans to see, but we can feel them as heat. The atmosphere absorbs the infrared light. Ultraviolet (UV) light is in wavelengths too short for humans to see. The most energetic UV light is harmful to life. The atmosphere absorbs most of this UV light from the Sun. Gamma rays have the highest energy and they are the most damaging rays. Fortunately, gamma rays dont penetrate Earths atmosphere. ",text,
L_0022,energy in the atmosphere,T_0215,"Energy from the Sun has a wide range of wavelengths. The total range of energy is called the electromagnetic spectrum. You can see it in Figure 15.8. Visible light is the only light that humans can see. Different wavelengths of visible light appear as different colors. Radio waves have the longest wavelengths. They also have the least amount of energy. Infrared light has wavelengths too long for humans to see, but we can feel them as heat. The atmosphere absorbs the infrared light. Ultraviolet (UV) light is in wavelengths too short for humans to see. The most energetic UV light is harmful to life. The atmosphere absorbs most of this UV light from the Sun. Gamma rays have the highest energy and they are the most damaging rays. Fortunately, gamma rays dont penetrate Earths atmosphere. ",text,
L_0022,energy in the atmosphere,T_0216,"Energy travels through space or material. Heat energy is transferred in three ways: radiation, conduction, and convection. ",text,
L_0022,energy in the atmosphere,T_0217,"Radiation is the transfer of energy by waves. Energy can travel as waves through air or empty space. The Suns energy travels through space by radiation. After sunlight heats the planets surface, some heat radiates back into the atmosphere. ",text,
L_0022,energy in the atmosphere,T_0218,"In conduction, heat is transferred from molecule to molecule by contact. Warmer molecules vibrate faster than cooler ones. They bump into the cooler molecules. When they do they transfer some of their energy. Conduction happens mainly in the lower atmosphere. Can you explain why? ",text,
L_0022,energy in the atmosphere,T_0219,"Convection is the transfer of heat by a current. Convection happens in a liquid or a gas. Air near the ground is warmed by heat radiating from Earths surface. The warm air is less dense, so it rises. As it rises, it cools. The cool air is dense, so it sinks to the surface. This creates a convection current, like the one in Figure 15.9. Convection is the most important way that heat travels in the atmosphere. ",text,
L_0022,energy in the atmosphere,T_0220,"Different parts of Earths surface receive different amounts of sunlight. You can see this in Figure 15.10. The Suns rays strike Earths surface most directly at the equator. This focuses the rays on a small area. Near the poles, the Suns rays strike the surface at a slant. This spreads the rays over a wide area. The more focused the rays are, the more energy an area receives and the warmer it is. ",text,
L_0022,energy in the atmosphere,T_0221,"When sunlight heats Earths surface, some of the heat radiates back into the atmosphere. Some of this heat is absorbed by gases in the atmosphere. This is the greenhouse effect, and it helps to keep Earth warm. The greenhouse effect allows Earth to have temperatures that can support life. Gases that absorb heat in the atmosphere are called greenhouse gases. They include carbon dioxide and water vapor. Human actions have increased the levels of greenhouse gases in the atmosphere. This is shown in Figure 15.11. The added gases have caused a greater greenhouse effect. How do you think this affects Earths temperature? ",text,
L_0023,layers of the atmosphere,T_0222,"Air temperature changes as altitude increases. In some layers of the atmosphere, the temperature decreases. In other layers, it increases. You can see this in Figure 15.12. Refer to this figure as you read about the layers below. ",text,
L_0023,layers of the atmosphere,T_0223,"The troposphere is the lowest layer of the atmosphere. In it, temperature decreases with altitude. The troposphere gets some of its heat directly from the Sun. Most, however, comes from Earths surface. The surface is heated by the Sun and some of that heat radiates back into the air. This makes the temperature higher near the surface than at higher altitudes. ",text,
L_0023,layers of the atmosphere,T_0224,"Look at the troposphere in Figure 15.12. This is the shortest layer of the atmosphere. It rises to only about 12 kilometers (7 miles) above the surface. Even so, this layer holds 75 percent of all the gas molecules in the atmosphere. Thats because the air is densest in this layer. ",text,
L_0023,layers of the atmosphere,T_0225,"Air in the troposphere is warmer closer to Earths surface. Warm air is less dense than cool air, so it rises higher in the troposphere. This starts a convection cell. Convection mixes the air in the troposphere. Rising air is also a main cause of weather. All of Earths weather takes place in the troposphere. ",text,
L_0023,layers of the atmosphere,T_0226,"Sometimes air doesnt mix in the troposphere. This happens when air is cooler close to the ground than it is above. The cool air is dense, so it stays near the ground. This is called a temperature inversion. An inversion can trap air pollution near the surface. Temperature inversions are more common in the winter. Can you explain why? ",text,
L_0023,layers of the atmosphere,T_0227,At the top of the troposphere is a thin layer of air called the tropopause. You can see it in Figure 15.12. This layer acts as a barrier. It prevents cool air in the troposphere from mixing with warm air in the stratosphere. ,text,
L_0023,layers of the atmosphere,T_0228,The stratosphere is the layer above the troposphere. The layer rises to about 50 kilometers (31 miles) above the surface. ,text,
L_0023,layers of the atmosphere,T_0229,"Air temperature in the stratosphere layer increases with altitude. Why? The stratosphere gets most of its heat from the Sun. Therefore, its warmer closer to the Sun. The air at the bottom of the stratosphere is cold. The cold air is dense, so it doesnt rise. As a result, there is little mixing of air in this layer. ",text,
L_0023,layers of the atmosphere,T_0230,"The stratosphere contains a layer of ozone gas. Ozone consists of three oxygen atoms (O3 ). The ozone layer absorbs high-energy UV radiation. As you can see in Figure 15.14, UV radiation splits the ozone molecule. The split creates an oxygen molecule (O2 ) and an oxygen atom (O). This split releases heat that warms the stratosphere. By absorbing UV radiation, ozone also protects Earths surface. UV radiation would harm living things without the ozone layer. ",text,
L_0023,layers of the atmosphere,T_0231,At the top of the stratosphere is a thin layer called the stratopause. It acts as a boundary between the stratosphere and the mesosphere. ,text,
L_0023,layers of the atmosphere,T_0232,The mesosphere is the layer above the stratosphere. It rises to about 85 kilometers (53 miles) above the surface. Temperature decreases with altitude in this layer. ,text,
L_0023,layers of the atmosphere,T_0233,There are very few gas molecules in the mesosphere. This means that there is little matter to absorb the Suns rays and heat the air. Most of the heat that enters the mesosphere comes from the stratosphere below. Thats why the mesosphere is warmest at the bottom. ,text,
L_0023,layers of the atmosphere,T_0234,"Did you ever see a meteor shower, like the one in Figure 15.15? Meteors burn as they fall through the mesosphere. The space rocks experience friction with the gas molecules. The friction makes the meteors get very hot. Many meteors burn up completely in the mesosphere. ",text,
L_0023,layers of the atmosphere,T_0235,At the top of the mesosphere is the mesopause. Temperatures here are colder than anywhere else in the atmosphere. They are as low as -100 C (-212 F)! Nowhere on Earths surface is that cold. ,text,
L_0023,layers of the atmosphere,T_0236,The thermosphere is the layer above the mesosphere. It rises to 600 kilometers (372 miles) above the surface. The International Space Station orbits Earth in this layer as in Figure 15.16. ,text,
L_0023,layers of the atmosphere,T_0237,"Temperature increases with altitude in the thermosphere. Surprisingly, it may be higher than 1000 C (1800 F) near the top of this layer! The Suns energy there is very strong. The molecules absorb the Suns energy and are heated up. But there are so very few gas molecules, that the air still feels very cold. Molecules in the thermosphere gain or lose electrons. They then become charged particles called ions. ",text,
L_0023,layers of the atmosphere,T_0238,"Have you ever seen a brilliant light show in the night sky? Sometimes the ions in the thermosphere glow at night. Storms on the Sun energize the ions and make them light up. In the Northern Hemisphere, the lights are called the northern lights, or aurora borealis. In the Southern Hemisphere, they are called southern lights, or aurora australis. ",text,
L_0023,layers of the atmosphere,T_0238,"Have you ever seen a brilliant light show in the night sky? Sometimes the ions in the thermosphere glow at night. Storms on the Sun energize the ions and make them light up. In the Northern Hemisphere, the lights are called the northern lights, or aurora borealis. In the Southern Hemisphere, they are called southern lights, or aurora australis. ",text,
L_0023,layers of the atmosphere,T_0239,"The exosphere is the layer above the thermosphere. This is the top of the atmosphere. The exosphere has no real upper limit; it just gradually merges with outer space. Gas molecules are very far apart in this layer, but they are really hot. Earths gravity is so weak in the exosphere that gas molecules sometimes just float off into space. ",text,
L_0030,world climates,T_0304,"Major climate types are based on temperature and precipitation. These two factors determine what types of plants can grow in an area. Animals and other living things depend on plants. So each climate is associated with certain types of living things. A major type of climate and its living things make up a biome. As you read about the major climate types below, find them on the map in Figure 17.9. ",text,
L_0030,world climates,T_0305,"Tropical climates are found around the equator. As youd expect, these climates have warm temperatures year round. Tropical climates may be very wet or wet and dry. Tropical wet climates occur at or very near the equator. They have high rainfall year round. Tropical rainforests grow in this type of climate. Tropical wet and dry climates occur between 5 and 20 latitude and receive less rainfall. Most of the rain falls in a single season. The rest of the year is dry. Few trees can withstand the long dry season, so the main plants are grasses (see Figure 17.10). ",text,
L_0030,world climates,T_0306,"Dry climates receive very little rainfall. They also have high rates of evaporation. This makes them even drier. The driest climates are deserts. Most occur between about 15 and 30 latitude. This is where dry air sinks to the surface in the global circulation cells. Deserts receive less than 25 centimeters (10 inches) of rain per year. They may be covered with sand dunes or be home to sparse but hardy plants (see Figure 17.11). With few clouds, deserts have hot days and cool nights. Other dry climates get a little more precipitation. They are called steppes. These regions have short grasses and low bushes (see Figure 17.11). Steppes occur at higher latitudes than deserts. They are dry because they are in continental interiors or rain shadows. ",text,
L_0030,world climates,T_0306,"Dry climates receive very little rainfall. They also have high rates of evaporation. This makes them even drier. The driest climates are deserts. Most occur between about 15 and 30 latitude. This is where dry air sinks to the surface in the global circulation cells. Deserts receive less than 25 centimeters (10 inches) of rain per year. They may be covered with sand dunes or be home to sparse but hardy plants (see Figure 17.11). With few clouds, deserts have hot days and cool nights. Other dry climates get a little more precipitation. They are called steppes. These regions have short grasses and low bushes (see Figure 17.11). Steppes occur at higher latitudes than deserts. They are dry because they are in continental interiors or rain shadows. ",text,
L_0030,world climates,T_0307,"Temperate climates have moderate temperatures. These climates vary in how much rain they get and when the rain falls. You can see different types of temperate climates in Figure 17.12. Mediterranean climates are found on the western coasts of continents. The latitudes are between 30 and 45. The coast of California has a Mediterranean climate. Temperatures are mild and rainfall is moderate. Most of the rain falls in the winter, and summers are dry. To make it through the dry summers, short woody plants are common. Marine west coast climates are also found on the western coasts of continents. They occur between 45 and 60 latitude. The coast of Washington State has this type of climate. Temperatures are mild and theres plenty of rainfall all year round. Dense fir forests grow in this climate. Humid subtropical climates are found on the eastern sides of continents between about 20 and 40 latitude. The southeastern U.S. has this type of climate. Summers are hot and humid, but winters are chilly. There is moderate rainfall throughout the year. Pine and oak forests grow in this climate. ",text,
L_0030,world climates,T_0308,"Continental climates are found in inland areas. They are too far from oceans to experience the effects of ocean water. Continental climates are common between 40 and 70 north latitude. There are no continental climates in the Southern Hemisphere. Can you guess why? The southern continents at this latitude are too narrow. All of their inland areas are close enough to a coast to be affected by the ocean! Humid continental climates are found between 40 and 60 north latitude. The northeastern U.S. has this type of climate. Summers are warm to hot, and winters are cold. Precipitation is moderate, and it falls year round. Deciduous trees grow in this climate. They lose their leaves in the fall and grow new ones in the spring. Subarctic climates are found between 60 and 70 north latitude. Much of Canada and Alaska have this type of climate. Summers are cool and short. Winters are very cold and long. Little precipitation falls, and most of it falls during the summer. Conifer forests grow in this climate (see Figure 17.13). ",text,
L_0030,world climates,T_0309,"Polar climates are found near the North and South Poles. They also occur on high mountains at lower latitudes. The summers are very cool, and the winters are frigid. Precipitation is very low because its so cold. You can see examples of polar climates in Figure 17.14. Polar tundra climates occur near the poles. Tundra climates have permafrost. Permafrost is layer of ground below the surface that is always frozen, even in the summer. Only small plants, such as mosses, can grow in this climate. Alpine tundra climates occur at high altitudes at any latitude. They are also called highland climates. These regions are very cold because they are so far above sea level. The alpine tundra climate is very similar to the polar tundra climate. Ice caps are areas covered with thick ice year round. Ice caps are found only in Greenland and Antarctica. Temperatures and precipitation are both very low. What little snow falls usually stays on the ground. It doesnt melt because its too cold. ",text,
L_0030,world climates,T_0310,"A place might have a different climate than the major climate type around it. This is called a microclimate. Look at Figure 17.15. The south-facing side of the hill gets more direct sunlight than the north side of a hill. This gives the south side a warmer microclimate. A microclimate can be due to a place being deeper. Since cold air sinks, a depression in the land can be a lot colder than the land around it. ",text,
L_0031,climate change,T_0311,Earths climate has changed many times through Earths history. Its been both hotter and colder than it is today. ,text,
L_0031,climate change,T_0312,"Over much of Earths past, the climate was warmer than it is today. Picture in your mind dinosaurs roaming the land. Theyre probably doing it in a pretty warm climate! But ice ages also occurred many times in the past. An ice age is a period when temperatures are cooler than normal. This causes glaciers to spread to lower latitudes. Scientists think that ice ages occurred at least six times over the last billion years alone. How do scientists learn about Earths past climates? ",text,
L_0031,climate change,T_0313,"The last major ice age took place in the Pleistocene. This epoch lasted from 2 million to 14,000 years ago. Earths temperature was only 5 C (9 F) cooler than it is today. But glaciers covered much of the Northern Hemisphere. In Figure 17.17, you can see how far south they went. Clearly, a small change in temperature can have a big impact on the planet. Humans lived during this ice age. ",text,
L_0031,climate change,T_0314,"Since the Pleistocene, Earths temperature has risen. Figure 17.18 shows how it changed over just the last 1500 years. There were minor ups and downs. But each time, the anomaly (the difference from average temperature) was less than 1 C (1.8 F). Since the mid 1800s, Earth has warmed up quickly. Look at Figure 17.19. The 14 hottest years on record have all occurred since 1900. Eight of them have occurred since 1998! This is what is usually meant by global warming. ",text,
L_0031,climate change,T_0314,"Since the Pleistocene, Earths temperature has risen. Figure 17.18 shows how it changed over just the last 1500 years. There were minor ups and downs. But each time, the anomaly (the difference from average temperature) was less than 1 C (1.8 F). Since the mid 1800s, Earth has warmed up quickly. Look at Figure 17.19. The 14 hottest years on record have all occurred since 1900. Eight of them have occurred since 1998! This is what is usually meant by global warming. ",text,
L_0031,climate change,T_0315,Natural processes caused earlier climate changes. Human beings are the main cause of recent global warming. ,text,
L_0031,climate change,T_0316,"Several natural processes may affect Earths temperature. They range from sunspots to Earths wobble. Sunspots are storms on the Sun. When the number of sunspots is high, the Sun gives off more energy than usual. Still, there is little evidence for climate changing along with the sunspot cycle. Plate movements cause continents to drift closer to the poles or the equator. Ocean currents also shift when continents drift. All these changes can affect Earths temperature. Plate movements trigger volcanoes. A huge eruption could spew so much gas and ash into the air that little sunlight would reach the surface for months or years. This could lower Earths temperature. A large asteroid hitting Earth would throw a lot of dust into the air. This could block sunlight and cool the planet. Earth goes through regular changes in its position relative to the Sun. Its orbit changes slightly. Earth also wobbles on its axis of rotation. The planet also changes the tilt on its axis. These changes can affect Earths temperature. ",text,
L_0031,climate change,T_0317,Recent global warming is due mainly to human actions. Burning fossil fuels adds carbon dioxide to the atmosphere. Carbon dioxide is a greenhouse gas. Its one of several that human activities add to the atmosphere. An increase in greenhouse gases leads to greater greenhouse effect. The result is increased global warming. Figure 17.20 shows the increase in carbon dioxide since 1960. ,text,
L_0031,climate change,T_0318,"As Earth has gotten warmer, sea ice has melted. This has raised the level of water in the oceans. Figure 17.21 shows how much sea level has risen since 1880. ",text,
L_0031,climate change,T_0319,"Earths temperature will keep rising unless greenhouse gases are curbed. The temperature in 2100 may be as much as 5 C (9 F) higher than it was in 2000. Since the glacial periods of the Pleistocene, average temperature has risen about 4 C. Thats just 4 C from abundant ice to the moderate climate we have today. How might a 5 C increase in temperature affect Earth in the future? Warming will affect the entire globe by the end of this century. The map in Figure 17.22 shows the average temperature in the 2050s. This is compared with the average temperature in 1971 to 2000. In what place is the temperature increase the greatest? Where in the United States is the temperature increase the highest? As temperature rises, more sea ice will melt. Figure 17.23 shows how much less sea ice there may be in 2050 if temperatures keep going up. This would cause sea level to rise even higher. Some coastal cities could be under water. Millions of people would have to move inland. How might other living things be affected? ",text,
L_0031,climate change,T_0320,"Youve probably heard of El Nio and La Nia. These terms refer to certain short-term changes in climate. The changes are natural and occur in cycles. To understand the changes, you first need to know what happens in normal years. This is shown in Figure 17.24. ",text,
L_0031,climate change,T_0321,"During an El Nio, the western Pacific Ocean is warmer than usual. This causes the trade winds to change direction. The winds blow from west to east instead of east to west. This is shown in Figure 17.25. The warm water travels east across the equator, too. Warm water piles up along the western coast of South America. This prevents upwelling. Why do you think this is true? These changes in water temperature, winds, and currents affect climates worldwide. The changes usually last a year or two. Some places get more rain than normal. Other places get less. In many locations, the weather is more severe. ",text,
L_0031,climate change,T_0321,"During an El Nio, the western Pacific Ocean is warmer than usual. This causes the trade winds to change direction. The winds blow from west to east instead of east to west. This is shown in Figure 17.25. The warm water travels east across the equator, too. Warm water piles up along the western coast of South America. This prevents upwelling. Why do you think this is true? These changes in water temperature, winds, and currents affect climates worldwide. The changes usually last a year or two. Some places get more rain than normal. Other places get less. In many locations, the weather is more severe. ",text,
L_0031,climate change,T_0322,La Nia generally follows El Nio. It occurs when the Pacific Ocean is cooler than normal. Figure 17.26 shows what happens. The trade winds are like they are in a normal year. They blow from east to west. But in a La Nia the winds are stronger than usual. More cool water builds up in the western Pacific. These changes can also affect climates worldwide. ,text,
L_0031,climate change,T_0322,La Nia generally follows El Nio. It occurs when the Pacific Ocean is cooler than normal. Figure 17.26 shows what happens. The trade winds are like they are in a normal year. They blow from east to west. But in a La Nia the winds are stronger than usual. More cool water builds up in the western Pacific. These changes can also affect climates worldwide. ,text,
L_0031,climate change,T_0323,Some scientists think that global warming is affecting the cycle of El Nio and La Nia. These short-term changes seem to be cycling faster now than in the past. They are also more extreme. ,text,
L_0033,cycles of matter,T_0337,"Carbon is an element. By itself, its a black solid. You can see a lump of carbon in Figure 18.10. Carbon is incredibly important because of what it makes when it combines with many other elements. Carbon can form a wide variety of substances. For example, in the air, carbon combines with oxygen to form the gas carbon dioxide. In living things, carbon combines with several other elements. For example, it may combine with nitrogen and ",text,
L_0033,cycles of matter,T_0338,"In the carbon cycle, carbon moves through living and nonliving things. Carbon actually moves through two cycles that overlap. One cycle is mainly biotic; the other cycle is mainly abiotic. Both cycles are shown in Figure 18.11. ",text,
L_0033,cycles of matter,T_0339,Producers such as plants or algae use carbon dioxide in the air to make food. The organisms combine carbon dioxide with water to make sugar. They store the sugar as starch. Both sugar and starch are carbohydrates. Consumers get carbon when they eat producers or other consumers. Carbon doesnt stop there. Living things get energy from food in a process called respiration. This releases carbon dioxide back into the atmosphere. The cycle then repeats. ,text,
L_0033,cycles of matter,T_0340,"Carbon from decaying organisms enters the ground. Some carbon is stored in the soil. Some carbon may be stored underground for millions of years. This will form fossil fuels. When volcanoes erupt, carbon from the mantle is released as carbon dioxide into the air. Producers take in the carbon dioxide to make food. Then the cycle repeats. The oceans also play an important role in the carbon cycle. Ocean water absorbs carbon dioxide from the air. In fact, the oceans contain 50 times more carbon than the atmosphere. Much of the carbon sinks to the bottom of the oceans, where it may stay for hundreds of years. ",text,
L_0033,cycles of matter,T_0341,"Human actions are influencing the carbon cycle. Burning of fossil fuels releases the carbon dioxide that was stored in ancient plants. Carbon dioxide is a greenhouse gas and is a cause of global warming. Forests are also being destroyed. Trees may be cut down for their wood, or they may be burned to clear the land for farming. Burning wood releases more carbon dioxide into the atmosphere. You can see how a tropical rainforest was cleared for farming in Figure 18.12. With forests shrinking, there are fewer trees to remove carbon dioxide from the air. This makes the greenhouse effect even worse. ",text,
L_0033,cycles of matter,T_0342,"Living things also need nitrogen. Nitrogen is a key element in proteins. Like carbon, nitrogen cycles through ecosystems. You can see the nitrogen cycle in Figure 18.13. ",text,
L_0033,cycles of matter,T_0343,"Air is about 78 percent nitrogen. Decomposers release nitrogen into the air from dead organisms and their wastes. However, producers such as plants cant use these forms of nitrogen. Nitrogen must combine with other elements before producers can use it. This is done by certain bacteria in the soil. Its called fixing nitrogen. ",text,
L_0033,cycles of matter,T_0344,"Nitrogen is one of the most important nutrients needed by plants. Thats why most plant fertilizers contain nitrogen. Adding fertilizer to soil allows more plants to grow. As a result, a given amount of land can produce more food. So far, so good. But what happens next? Rain dissolves fertilizer in the soil. Runoff carries it away. The fertilizer ends up in bodies of water, from ponds to oceans. The nitrogen is a fertilizer in the water bodies. Since there is a lot of nitrogen it causes algae to grow out of control. Figure 18.14 shows a pond covered with algae. Algae may use up so much oxygen in the water that nothing else can grow. Soon, even the algae die out. Decomposers break down the dead tissue and use up all the oxygen in the water. This creates a dead zone. A dead zone is an area in a body of water where nothing grows because there is too little oxygen. There is a large dead zone in the Gulf of Mexico. You can see it Figure 18.14. ",text,
L_0034,the human population,T_0345,"A population usually grows when it has what it needs. If theres plenty of food and other resources, the population will get bigger. Look at Table 18.1. It shows how a population of bacteria grew. A single bacteria cell was added to a container of nutrients. Conditions were ideal. The bacteria divided every 30 minutes. After just 10 hours, there were more than a million bacteria! Assume the bacteria population keeps growing at this rate. How many bacteria will there be at 10.5 hours? Or at 12 hours? Time (hours) 0 0.5 Number of Bacteria 1 2 Time (hours) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10 Number of Bacteria 4 8 16 32 64 128 256 512 1,024 2,048 4,096 8,192 16,384 32,768 65,536 131,072 262,144 524,288 1,048,576 ",text,
L_0034,the human population,T_0346,"The population growth rate is how fast a population is growing. The letter r stands for the growth rate. The growth rate equals the number of new members added to the population in a year for each 100 members already in the population. The growth rate includes new members added to the population and old members removed from the population. Births add new members to the population. Deaths remove members from the population. The formula for population growth rate is: r = b - d, where b = birth rate (number of births in 1 year per 100 population members) d = death rate (number of deaths in 1 year per 100 population members) If the birth rate is greater than the death rate, r is positive. This means that the population is growing bigger. For example, if b = 10 and d = 8, r = 2. This means that the population is growing by 2 individuals per year for every 100 members of the population. This may not sound like much, but its a fairly high rate of growth. A population growing at this rate would double in size in just 35 years! If the birth rate is less than the death rate, r is negative. This means that the population is becoming smaller. What do you think might cause this to happen? ",text,
L_0034,the human population,T_0347,"A population cant keep growing bigger and bigger forever. Sooner or later, it will run out of things it needs. For a given species, there is a maximum population that can be supported by the environment. This maximum is called the carrying capacity. When a population gets close to the carrying capacity, it usually grows more slowly. You can see this in Figure 18.16. When the population reaches the carrying capacity, it stops growing. ",text,
L_0034,the human population,T_0348,"Figure 18.17 shows how the human population has grown. It grew very slowly for tens of thousands of years. Then, in the 1800s, something happened to change all that. The human population started to grow much faster. ",text,
L_0034,the human population,T_0349,"The industrial revolution is what happened. The industrial revolution began in the late 1700s in Europe, North America, and a few other places. In these places, the human population grew faster. While there had always been a lot of births, the population grew because the death rate fell. It fell for several reasons: 1. New farm machines were invented. They increased the amount of food that could be produced. With more food, people were healthier and could live longer. 2. Steam engines and railroads were built. These machines could quickly carry food long distances. This made food shortages less likely. 3. Sanitation was improved. Sewers were dug to carry away human wastes (see Figure 18.18). This helped reduce the spread of disease. With better food and less chance of disease, the death rate fell. More children lived long enough to reach adulthood and have children of their own. As the death rate fell, the birth rate stayed high for a while. This caused rapid population growth. However, the birth rate in these countries has since fallen to a rate close to that of the low death rate. The result was slow population growth once again. These changes are called the demographic transition. ",text,
L_0034,the human population,T_0350,"More recently, the death rate has fallen because of the availability of more food and medical advances: A green revolution began in the mid 1900s. New methods and products increased how much food could be grown. For example, chemicals were developed that killed weeds without harming crops. Pesticides were developed that killed pests that destroyed crops. Vaccinations were developed that could prevent many diseases (see Figure 18.19). Antibiotics were discov- ered that could cure most infections caused by bacteria. Together, these two advances saved countless lives. Today in many countries, death rates have gone down but birth rates remain high. This means that the population is growing. Figure 18.20 shows the growth rates of human populations all over the world. ",text,
L_0034,the human population,T_0350,"More recently, the death rate has fallen because of the availability of more food and medical advances: A green revolution began in the mid 1900s. New methods and products increased how much food could be grown. For example, chemicals were developed that killed weeds without harming crops. Pesticides were developed that killed pests that destroyed crops. Vaccinations were developed that could prevent many diseases (see Figure 18.19). Antibiotics were discov- ered that could cure most infections caused by bacteria. Together, these two advances saved countless lives. Today in many countries, death rates have gone down but birth rates remain high. This means that the population is growing. Figure 18.20 shows the growth rates of human populations all over the world. ",text,
L_0034,the human population,T_0351,The growth of the human population has started to slow down. You can see this in Figure 18.21. It may stop growing by the mid 2000s. Scientists think that the human population will peak at about 9 billion people. What will need to change for the population to stop growing then? ,text,
L_0034,the human population,T_0352,"Are 9 billion people the human carrying capacity? It looks that way in Figure 18.21. But some people think there are too many of us already. Thats because we are harming the environment. Supplying all those people with energy creates a lot of pollution. For example, huge oil spills have killed millions of living things. Burning fossil fuels pollutes the air. This also increases causes global warming. Fossil fuels and other resources are being used up. We may run out of oil by the mid 2000s. Many other resources will run out sooner or later. People are killing too many animals for food. For example, some of the best fishing grounds in the oceans have almost no fish left. People have destroyed many habitats. For example, theyve drained millions of acres of wetlands. Wetlands have a great diversity of species. As wetlands shrink, species go extinct. People have allowed alien or invasive species - species originally from a different area - to invade new habitats. Often, the aliens have no natural enemies in their new home. They may drive native species extinct. Figure People themselves are also affected by the large size of the human population. A minority of people use most of the worlds energy and other resources. Many other people lack resources. Many dont have enough to eat or live with ",text,
L_0034,the human population,T_0352,"Are 9 billion people the human carrying capacity? It looks that way in Figure 18.21. But some people think there are too many of us already. Thats because we are harming the environment. Supplying all those people with energy creates a lot of pollution. For example, huge oil spills have killed millions of living things. Burning fossil fuels pollutes the air. This also increases causes global warming. Fossil fuels and other resources are being used up. We may run out of oil by the mid 2000s. Many other resources will run out sooner or later. People are killing too many animals for food. For example, some of the best fishing grounds in the oceans have almost no fish left. People have destroyed many habitats. For example, theyve drained millions of acres of wetlands. Wetlands have a great diversity of species. As wetlands shrink, species go extinct. People have allowed alien or invasive species - species originally from a different area - to invade new habitats. Often, the aliens have no natural enemies in their new home. They may drive native species extinct. Figure People themselves are also affected by the large size of the human population. A minority of people use most of the worlds energy and other resources. Many other people lack resources. Many dont have enough to eat or live with ",text,
L_0034,the human population,T_0353,"Is it possible for all the worlds people to live well and still protect the planet? Thats the aim of sustainable development. Its goals are to: 1. Distribute resources fairly. 2. Conserve resources so they wont run out. 3. Use resources in ways that wont harm ecosystems. A smaller human population may be part of the solution. Better use of resources is another part. For example, when forests are logged, new trees should be planted. Everyone can help in the effort. What will you do? ",text,
L_0036,pollution of the land,T_0362,Love Canal gained worldwide attention in the late 1970s when the press started covering its story. The story is outlined below and illustrated in Figure 19.9. ,text,
L_0036,pollution of the land,T_0363,"The Love Canal disaster actually began back in the mid 1900s. The disaster continues even today. Starting in the early 1940s, a big chemical company put thousands of barrels of chemical waste into an old canal. Over the next 10 years, the company dumped almost 22,000 tons of chemicals into the ground! In the early 1950s, the company covered over the barrels in the canal with soil. Then they sold the land to the city for just a dollar. The city needed the land in order to build an elementary school. The company warned the city that toxic waste was buried there. But they thought the waste was safe. The school and hundreds of homes were also built over the old canal. As it turned out, the cheap price was no bargain. Chemicals started leaking from the barrels. Chemicals seeped into basements. Chemicals bubbled up to the surface of the ground. In some places, plants wouldnt even grow on the soil. People noticed bad smells. Many got sick, especially the children. Residents wanted to know if the old chemicals were the cause. But they had a hard time getting officials to listen. So they demonstrated and demanded answers. Finally, the soil was tested and was found to be contaminated with harmful chemicals. For example, it contained a lot of lead and mercury. Both can cause permanent damage to the human nervous system. The school was closed. More than 200 homes were evacuated. Much of the Love Canal neighborhood was bulldozed away. The area had a massive clean-up effort. The cleanup cost millions of dollars. More than three decades later, much of Love Canal is still too contaminated to be safe for people. ",text,
L_0036,pollution of the land,T_0364,"Love Canal opened peoples eyes to toxic waste burial. They realized there must be other Love Canals all over the country. Thousands of contaminated sites were found. The Superfund Act was passed in 1980. The law required that money be set aside for cleanup of toxic waste sites, like the Elizabeth Copper Mine in Vermont (see the far-right image in Figure 19.9). The law also required safer disposal of hazardous waste in the future. ",text,
L_0036,pollution of the land,T_0365,"Love Canal highlighted the problem of pollution by hazardous waste. Hazardous waste is any waste that is dangerous to the health of people or the environment. It may be dangerous because it is toxic, corrosive, flammable, or explosive. Toxic waste is poisonous. Toxic waste may cause cancer or birth defects in people. It may also harm other living things. Corrosive waste is highly reactive with other substances. Corrosive waste may cause burns or destroy other materials that it touches. Flammable waste can burn easily. It may also give off harmful fumes when it burns. Explosive waste is likely to explode. The risk of explosion may be greater if the waste is mixed with other substances. Table 19.1 shows some examples of hazardous waste. Look closely. Are any of these examples lurking around your home? Example Description Cars contain toxic fluids such as brake fluid. The fluids may also be corrosive and flammable. This photo shows one way the fluids can end up in the ground. Cars use gas and oil. These materials are toxic and flammable. They pollute the land when they leak or spill. Batteries contain toxic and corrosive materials. People often toss them in the trash, but they should be disposed of properly. Electronics, such as old computers, contain toxic chem- icals. They may be sent to landfills where the toxic materials end up in the ground. Medical waste can contain many hazards: Human body fluids may cause disease; old thermometers may contain toxic mercury; and pharmaceuticals may be toxic to people and other living things. Example Description Paints can be both toxic and flammable. Paints may spill on the ground or be thrown improperly in the trash. Chemicals are applied to farm fields and lawns. They include fertilizers, herbicides, and pesticides. Many of these chemicals are toxic to people and other animals. ",text,
L_0036,pollution of the land,T_0366,The greatest source of hazardous waste is industry. Agriculture is another major source. Even households produce a lot of hazardous waste. ,text,
L_0036,pollution of the land,T_0367,"Thanks to the lessons of Love Canal, the U.S. now has laws requiring the safe disposal of hazardous waste. Companies must ensure that hazardous waste is not allowed to enter the environment in dangerous amounts. They must also protect their workers from hazardous materials. For example, they must provide employees with the proper safety gear and training (see Figure 19.10). ",text,
L_0036,pollution of the land,T_0368,"Cleaning products, lawn chemicals, paints, batteries, motor oil these are just some of the many hazardous materials that may be found in households. You might think that a household doesnt produce enough hazardous waste to worry about. But when you add up all the waste from all the households in a community, its a different story. A city of just 50,000 people might produce more than 40 tons of hazardous waste each year! Clearly, how households deal with hazardous waste matters. What can your family do? Reduce, reuse, recycle, or properly dispose of the wastes. 1. Reduce the amount of hazardous products you buy. For example, if you only need a quart of paint for a job, dont buy a gallon. 2. Use less hazardous products if you can. For example, clean windows with vinegar and water instead of toxic window cleaners. 3. Reuse products if its safe to do so. For example, paint thinner that has been used to clean paint brushes can be strained and reused. 4. Recycle whenever possible. For example, some service stations allow you to drop off used motor oil, car batteries, or tires for recycling. 5. Always properly dispose of hazardous waste. For example, let liquid waste evaporate before placing the container in the trash. Proper disposal depends on the waste. Many hazardous products have disposal guidelines on the label. Thats one reason why you should keep the products in their original containers. The labels also explain how to use the products safely. Follow the instructions to protect yourself and the environment. Most communities have centers for disposing of household hazardous waste (see Figure 19.11). Do you know how to dispose of hazardous waste in your community? ",text,
L_0036,pollution of the land,T_0368,"Cleaning products, lawn chemicals, paints, batteries, motor oil these are just some of the many hazardous materials that may be found in households. You might think that a household doesnt produce enough hazardous waste to worry about. But when you add up all the waste from all the households in a community, its a different story. A city of just 50,000 people might produce more than 40 tons of hazardous waste each year! Clearly, how households deal with hazardous waste matters. What can your family do? Reduce, reuse, recycle, or properly dispose of the wastes. 1. Reduce the amount of hazardous products you buy. For example, if you only need a quart of paint for a job, dont buy a gallon. 2. Use less hazardous products if you can. For example, clean windows with vinegar and water instead of toxic window cleaners. 3. Reuse products if its safe to do so. For example, paint thinner that has been used to clean paint brushes can be strained and reused. 4. Recycle whenever possible. For example, some service stations allow you to drop off used motor oil, car batteries, or tires for recycling. 5. Always properly dispose of hazardous waste. For example, let liquid waste evaporate before placing the container in the trash. Proper disposal depends on the waste. Many hazardous products have disposal guidelines on the label. Thats one reason why you should keep the products in their original containers. The labels also explain how to use the products safely. Follow the instructions to protect yourself and the environment. Most communities have centers for disposing of household hazardous waste (see Figure 19.11). Do you know how to dispose of hazardous waste in your community? ",text,
L_0037,introduction to earths surface,T_0369,"To describe your location wherever you are on Earths surface, you could use a coordinate system. For example, you could say that you are at 1234 Main Street, Springfield, Ohio. Or you could use a point of reference. If you want to meet up with a friend, you could tell him the distance and direction you are from the reference point. An example is, I am at the corner of Maple Street and Main Street, about two blocks north of your apartment. When studying Earths surface, scientists must be able to pinpoint a feature they are interested in. Scientists and others have a system to describe the location of any feature. Usually they use latitude and longitude as a coordinate system. Lines of latitude and longitude form a grid. The grid is centered on a reference point. You will learn about this type of grid when we discuss maps later in this chapter. ",text,
L_0037,introduction to earths surface,T_0370,"When an object is moving, it is not enough to describe its location. We also need to know direction. Direction is important for describing moving objects. For example, a wind blows a storm over your school. Where is that storm coming from? Where is it going? The most common way to describe direction is by using a compass. A compass is a device with a floating needle (Figure 2.1). The needle is a small magnet that aligns itself with the Earths magnetic field. The compass needle always points to magnetic north. If you have a compass and you find north, you can then know any other direction. See the directions, such as east, south, west, etc., on a compass rose. A compass needle lines up with Earths magnetic north pole. This is different from Earths geographic north pole, or true north. The geographic north pole is the top of the imaginary axis around which Earth rotates. The geographic north pole is much like the spindle of a spinning top. The location of the geographic north pole does not change. However, the magnetic north pole shifts in location over time. Depending on where you live, you can correct for the difference between the two poles when you use a map and a compass (Figure 2.2). Some maps have a double compass rose. This allows users to make the corrections between magnetic north and true north. An example is a nautical chart that boaters use to chart their positions at sea (Figure 2.3). ",text,
L_0037,introduction to earths surface,T_0371,"As you know, the surface of Earth is not flat. Some places are high and some places are low. For example, mountain ranges like the Sierra Nevada in California or the Andes in South America are high above the surrounding areas. We can describe the topography of a region by measuring the height or depth of that feature relative to sea level (Figure mountains, while others are more like small hills! Relief, or terrain, includes all the landforms of a region. A topographic map shows the height, or elevation, of features in an area. This includes mountains, craters, valleys, and rivers. For example, Figure 2.5 shows the San Francisco Peaks in northern Arizona. Features on the map include mountains, hills and lava flows. You can recognize these features from the differences in elevation. We will talk about some different landforms in the next section. ",text,
L_0037,introduction to earths surface,T_0371,"As you know, the surface of Earth is not flat. Some places are high and some places are low. For example, mountain ranges like the Sierra Nevada in California or the Andes in South America are high above the surrounding areas. We can describe the topography of a region by measuring the height or depth of that feature relative to sea level (Figure mountains, while others are more like small hills! Relief, or terrain, includes all the landforms of a region. A topographic map shows the height, or elevation, of features in an area. This includes mountains, craters, valleys, and rivers. For example, Figure 2.5 shows the San Francisco Peaks in northern Arizona. Features on the map include mountains, hills and lava flows. You can recognize these features from the differences in elevation. We will talk about some different landforms in the next section. ",text,
L_0037,introduction to earths surface,T_0371,"As you know, the surface of Earth is not flat. Some places are high and some places are low. For example, mountain ranges like the Sierra Nevada in California or the Andes in South America are high above the surrounding areas. We can describe the topography of a region by measuring the height or depth of that feature relative to sea level (Figure mountains, while others are more like small hills! Relief, or terrain, includes all the landforms of a region. A topographic map shows the height, or elevation, of features in an area. This includes mountains, craters, valleys, and rivers. For example, Figure 2.5 shows the San Francisco Peaks in northern Arizona. Features on the map include mountains, hills and lava flows. You can recognize these features from the differences in elevation. We will talk about some different landforms in the next section. ",text,
L_0037,introduction to earths surface,T_0371,"As you know, the surface of Earth is not flat. Some places are high and some places are low. For example, mountain ranges like the Sierra Nevada in California or the Andes in South America are high above the surrounding areas. We can describe the topography of a region by measuring the height or depth of that feature relative to sea level (Figure mountains, while others are more like small hills! Relief, or terrain, includes all the landforms of a region. A topographic map shows the height, or elevation, of features in an area. This includes mountains, craters, valleys, and rivers. For example, Figure 2.5 shows the San Francisco Peaks in northern Arizona. Features on the map include mountains, hills and lava flows. You can recognize these features from the differences in elevation. We will talk about some different landforms in the next section. ",text,
L_0037,introduction to earths surface,T_0372,"If you take away the water in the oceans (Figure 2.6), Earth looks really different. You see that the surface has two main features: continents and ocean basins. Continents are large land areas. Ocean basins extend from the edges of continents to the ocean floor and into deep trenches. Continents are much older than ocean basins. Some rocks on the continents are billions of years old. Ocean basins are only millions of years old at their oldest. Because the continents are so old, a lot has happened to them! As we view the land around us we see landforms. Landforms are physical features on Earths surface. Landforms are introduced in this section but will be discussed more in later chapters. Constructive forces cause landforms to grow. Lava flowing into the ocean can build land outward. A volcano can be a constructive force. Destructive forces may blow landforms apart. A volcano blowing its top off is a destructive force. The destructive forces of weathering and erosion change landforms more slowly. Over millions of years, mountains are worn down by rivers and streams. Constructive and destructive forces work together to create landforms. Constructive forces create mountains and erosion may wear them away. Mountains are very large landforms. Mountains may wear away into a high flat area called a plateau, or a lower-lying plain. Interior plains are in the middle of continents. Coastal plains are on the edge of a continent, where it meets the ocean. Rivers and streams flow across continents. They cut away at rock, forming river valleys (Figure 2.8). These are ",text,
L_0037,introduction to earths surface,T_0372,"If you take away the water in the oceans (Figure 2.6), Earth looks really different. You see that the surface has two main features: continents and ocean basins. Continents are large land areas. Ocean basins extend from the edges of continents to the ocean floor and into deep trenches. Continents are much older than ocean basins. Some rocks on the continents are billions of years old. Ocean basins are only millions of years old at their oldest. Because the continents are so old, a lot has happened to them! As we view the land around us we see landforms. Landforms are physical features on Earths surface. Landforms are introduced in this section but will be discussed more in later chapters. Constructive forces cause landforms to grow. Lava flowing into the ocean can build land outward. A volcano can be a constructive force. Destructive forces may blow landforms apart. A volcano blowing its top off is a destructive force. The destructive forces of weathering and erosion change landforms more slowly. Over millions of years, mountains are worn down by rivers and streams. Constructive and destructive forces work together to create landforms. Constructive forces create mountains and erosion may wear them away. Mountains are very large landforms. Mountains may wear away into a high flat area called a plateau, or a lower-lying plain. Interior plains are in the middle of continents. Coastal plains are on the edge of a continent, where it meets the ocean. Rivers and streams flow across continents. They cut away at rock, forming river valleys (Figure 2.8). These are ",text,
L_0037,introduction to earths surface,T_0372,"If you take away the water in the oceans (Figure 2.6), Earth looks really different. You see that the surface has two main features: continents and ocean basins. Continents are large land areas. Ocean basins extend from the edges of continents to the ocean floor and into deep trenches. Continents are much older than ocean basins. Some rocks on the continents are billions of years old. Ocean basins are only millions of years old at their oldest. Because the continents are so old, a lot has happened to them! As we view the land around us we see landforms. Landforms are physical features on Earths surface. Landforms are introduced in this section but will be discussed more in later chapters. Constructive forces cause landforms to grow. Lava flowing into the ocean can build land outward. A volcano can be a constructive force. Destructive forces may blow landforms apart. A volcano blowing its top off is a destructive force. The destructive forces of weathering and erosion change landforms more slowly. Over millions of years, mountains are worn down by rivers and streams. Constructive and destructive forces work together to create landforms. Constructive forces create mountains and erosion may wear them away. Mountains are very large landforms. Mountains may wear away into a high flat area called a plateau, or a lower-lying plain. Interior plains are in the middle of continents. Coastal plains are on the edge of a continent, where it meets the ocean. Rivers and streams flow across continents. They cut away at rock, forming river valleys (Figure 2.8). These are ",text,
L_0037,introduction to earths surface,T_0373,"The ocean basin begins where the ocean meets the land. The continental margin begins at the shore and goes down to the ocean floor. It includes the continental shelf, slope, and rise. The continental shelf is part of the continent, but it is underwater today. It is about 100-200 meters deep, much shallower than the rest of the ocean. The continental shelf usually goes out about 100 to 200 kilometers from the shore (Figure 2.9). The continental slope is the slope that forms the edge of the continent. It is seaward of the continental shelf. In some places, a large pile of sediments brought from rivers creates the continental rise. The continental rise ends at the Besides seamounts, there are long, very tall (about 2 km) mountain ranges. These ranges are connected so that they form huge ridge systems called mid-ocean ridges (Figure 2.11). The mid-ocean ridges form from volcanic eruptions. Lava from inside Earth breaks through the crust and creates the mountains. The deepest places of the ocean are the ocean trenches. Many trenches line the edges of the Pacific Ocean. The Mariana Trench is the deepest place in the ocean. (Figure 2.12). At about 11 km deep, it is the deepest place on Earth! To compare, the tallest place on Earth, Mount Everest, is less than 9 km tall. ",text,
L_0037,introduction to earths surface,T_0373,"The ocean basin begins where the ocean meets the land. The continental margin begins at the shore and goes down to the ocean floor. It includes the continental shelf, slope, and rise. The continental shelf is part of the continent, but it is underwater today. It is about 100-200 meters deep, much shallower than the rest of the ocean. The continental shelf usually goes out about 100 to 200 kilometers from the shore (Figure 2.9). The continental slope is the slope that forms the edge of the continent. It is seaward of the continental shelf. In some places, a large pile of sediments brought from rivers creates the continental rise. The continental rise ends at the Besides seamounts, there are long, very tall (about 2 km) mountain ranges. These ranges are connected so that they form huge ridge systems called mid-ocean ridges (Figure 2.11). The mid-ocean ridges form from volcanic eruptions. Lava from inside Earth breaks through the crust and creates the mountains. The deepest places of the ocean are the ocean trenches. Many trenches line the edges of the Pacific Ocean. The Mariana Trench is the deepest place in the ocean. (Figure 2.12). At about 11 km deep, it is the deepest place on Earth! To compare, the tallest place on Earth, Mount Everest, is less than 9 km tall. ",text,
L_0037,introduction to earths surface,T_0373,"The ocean basin begins where the ocean meets the land. The continental margin begins at the shore and goes down to the ocean floor. It includes the continental shelf, slope, and rise. The continental shelf is part of the continent, but it is underwater today. It is about 100-200 meters deep, much shallower than the rest of the ocean. The continental shelf usually goes out about 100 to 200 kilometers from the shore (Figure 2.9). The continental slope is the slope that forms the edge of the continent. It is seaward of the continental shelf. In some places, a large pile of sediments brought from rivers creates the continental rise. The continental rise ends at the Besides seamounts, there are long, very tall (about 2 km) mountain ranges. These ranges are connected so that they form huge ridge systems called mid-ocean ridges (Figure 2.11). The mid-ocean ridges form from volcanic eruptions. Lava from inside Earth breaks through the crust and creates the mountains. The deepest places of the ocean are the ocean trenches. Many trenches line the edges of the Pacific Ocean. The Mariana Trench is the deepest place in the ocean. (Figure 2.12). At about 11 km deep, it is the deepest place on Earth! To compare, the tallest place on Earth, Mount Everest, is less than 9 km tall. ",text,
L_0038,modeling earths surface,T_0374,"Imagine you are going on a road trip. Perhaps you are going on vacation. How do you know where to go? Most likely, you will use a map. A map is a picture of specific parts of Earths surface. There are many types of maps. Each map gives us different information. Lets look at a road map, which is the probably the most common map that you use (Figure 2.13). ",text,
L_0038,modeling earths surface,T_0375,"Look for the legend on the top left side of the map. It explains how this map records different features. You can see the following: The boundaries of the state show its shape. Black dots represent the cities. Each city is named. The size of the dot represents the population of the city. Red and brown lines show major roads that connect the cities. Blue lines show rivers. Their names are written in blue. Blue areas show lakes and other waterways the Gulf of Mexico, Biscayne Bay, and Lake Okeechobee. Names for bodies of water are also written in blue. A line or scale of miles shows the distance represented on the map an inch or centimeter on the map represents a certain amount of distance (miles or kilometers). The legend explains other features and symbols on the map. It is the convention for north to be at the top of a map. For this reason, a compass rose is not needed on most maps. You can use this map to find your way around Florida and get from one place to another along roadways. ",text,
L_0038,modeling earths surface,T_0376,"There are many other types of maps besides road maps. Some examples include: Political or geographic maps show the outlines and borders of states and/or countries. Satellite view maps show terrains and vegetation forests, deserts, and mountains. Relief maps show elevations of areas, but usually on a larger scale, such as the whole Earth, rather than a local area. Topographic maps show detailed elevations of features on the map. Climate maps show average temperatures and rainfall. Precipitation maps show the amount of rainfall in different areas. Weather maps show storms, air masses, and fronts. Radar maps show storms and rainfall. Geologic maps detail the types and locations of rocks found in an area. These are but a few types of maps that various Earth scientists might use. You can easily carry a map around in your pocket or bag. Maps are easy to use because they are flat or two-dimensional. However, the world is three- dimensional. So, how do map makers represent a three-dimensional world on flat paper? ",text,
L_0038,modeling earths surface,T_0377,"Earth is a round, three-dimensional ball. In a small area, Earth looks flat, so it is not hard to make accurate maps of a small place. When map makers want to map the round Earth on flat paper, they use projections. What happens if you try to flatten out the skin of a peeled orange? Or if you try to gift wrap a soccer ball? To flatten out, the orange peel must rip and its shape must become distorted. To wrap around object with flat paper requires lots of extra cuts and folds. A projection is a way to represent Earths curved surface on flat paper (Figure 2.14). There are many types of projections. Each uses a different way to change three dimensions into two dimensions. There are two basic methods that the map maker uses in projections: The map maker slices the sphere in some way and unfolds it to make a flat map, like flattening out an orange peel. The map maker can look at the sphere from a certain point and then translate this view onto a flat paper. Lets look at a few commonly used projections. ",text,
L_0038,modeling earths surface,T_0378,"In 1569, Gerardus Mercator (1512-1594) (Figure 2.15) figured out a way to make a flat map of our round world, called the Mercator projection (Figure 2.16). Imagine wrapping the round, ball-shaped Earth with a big, flat piece of paper. First you make a tube or a cylinder. The cylinder will touch Earth at its fattest part, the equator. The equator is the imaginary line running horizontally around the middle of Earth. The poles are the farthest points from the cylinder. If you shine a light from the inside of your model Earth out to the cylinder, the image projected onto the paper is a Mercator projection. Where does the projection represent Earth best? Where is it worst? Your map would be most correct at the equator. The shapes and sizes of continents become more stretched out near the poles. Early sailors and navigators found the Mercator map useful because most explorations were located near the equator. Many world maps still use the Mercator projection. The Mercator projection is best within 15 degrees north or south of the equator. Landmasses or countries outside that zone get stretched out of shape. The further the feature is from the equator, the more out of shape it is stretched. For example, if you look at Greenland on a globe, you see it is a relatively small country near the North Pole. Yet, on a Mercator projection, Greenland looks almost as big the United States. Because Greenland is closer to the pole, the continents shape and size are greatly increased. The United States is closer to its true dimensions. In a Mercator projection, all compass directions are straight lines. This makes it a good type of map for navigation. The top of the map is north, the bottom is south, the left side is west and the right side is east. However, because it is a flat map of a curved surface, a straight line on the map is not the shortest distance between the two points it connects. ",text,
L_0038,modeling earths surface,T_0378,"In 1569, Gerardus Mercator (1512-1594) (Figure 2.15) figured out a way to make a flat map of our round world, called the Mercator projection (Figure 2.16). Imagine wrapping the round, ball-shaped Earth with a big, flat piece of paper. First you make a tube or a cylinder. The cylinder will touch Earth at its fattest part, the equator. The equator is the imaginary line running horizontally around the middle of Earth. The poles are the farthest points from the cylinder. If you shine a light from the inside of your model Earth out to the cylinder, the image projected onto the paper is a Mercator projection. Where does the projection represent Earth best? Where is it worst? Your map would be most correct at the equator. The shapes and sizes of continents become more stretched out near the poles. Early sailors and navigators found the Mercator map useful because most explorations were located near the equator. Many world maps still use the Mercator projection. The Mercator projection is best within 15 degrees north or south of the equator. Landmasses or countries outside that zone get stretched out of shape. The further the feature is from the equator, the more out of shape it is stretched. For example, if you look at Greenland on a globe, you see it is a relatively small country near the North Pole. Yet, on a Mercator projection, Greenland looks almost as big the United States. Because Greenland is closer to the pole, the continents shape and size are greatly increased. The United States is closer to its true dimensions. In a Mercator projection, all compass directions are straight lines. This makes it a good type of map for navigation. The top of the map is north, the bottom is south, the left side is west and the right side is east. However, because it is a flat map of a curved surface, a straight line on the map is not the shortest distance between the two points it connects. ",text,
L_0038,modeling earths surface,T_0379,"Instead of a cylinder, you could wrap the flat paper into a cone. Conic map projections use a cone shape to better represent regions near the poles (Figure 2.17). Conic projections are best where the cone shape touches the globe. This is along a line of latitude, usually the equator. ",text,
L_0038,modeling earths surface,T_0380,What if want to wrap a different approach? Lets say you dont want to wrap a flat piece of paper around a round object? You could put a flat piece of paper right on the area that you want to map. This type of map is called a gnomonic map projection (Figure 2.18). The paper only touches Earth at one point. The sizes and shapes of countries near that point are good. The poles are often mapped this way to avoid distortion. A gnomic projection is best for use over a small area. ,text,
L_0038,modeling earths surface,T_0380,What if want to wrap a different approach? Lets say you dont want to wrap a flat piece of paper around a round object? You could put a flat piece of paper right on the area that you want to map. This type of map is called a gnomonic map projection (Figure 2.18). The paper only touches Earth at one point. The sizes and shapes of countries near that point are good. The poles are often mapped this way to avoid distortion. A gnomic projection is best for use over a small area. ,text,
L_0038,modeling earths surface,T_0381,"In 1963, Arthur Robinson made a map with more accurate sizes and shapes of land areas. He did this using mathematical formulas. The formulas could directly translate coordinates onto the map. This type of projection is shaped like an oval rather than a rectangle (Figure 2.19). Robinsons map is more accurate than a Mercator projection. The shapes and sizes of continents are closer to true. Robinsons map is best within 45 degrees of the equator. Distances along the equator and the lines parallel to it are true. However, the scales along each line of latitude are different. In 1988, the National Geographic Society began to use Robinsons projection for its world maps. Whatever map projection is used, maps help us find places and to be able to get from one place to another. So how do you find your location on a map? ",text,
L_0038,modeling earths surface,T_0382,"Most maps use a grid of lines to help you to find your location. This grid system is called a geographic coordinate system. Using this system you can define your location by two numbers, latitude and longitude. Both numbers are angles between your location, the center of Earth, and a reference line (Figure 2.20). ",text,
L_0038,modeling earths surface,T_0383,"Lines of latitude circle around Earth. The equator is a line of latitude right in the middle of the planet. The equator is an equal distance from both the North and South Pole. If you know your latitude, you know how far you are north or south of the equator. ",text,
L_0038,modeling earths surface,T_0384,"Lines of longitude are circles that go around Earth from pole to pole, like the sections of an orange. Lines of longitude start at the Prime Meridian. The Prime Meridian is a circle that runs north to south and passes through Greenwich, England. Longitude tells you how far you are east or west from the Prime Meridian (Figure 2.21). You can remember latitude and longitude by doing jumping jacks. When your hands are above your head and your feet are together, say longitude (your body is long!). When you put your arms out to the side horizontally, say latitude (your head and arms make a cross, like the t in latitude). While you are jumping, your arms are going the same way as each of these grid lines: horizontal for latitude and vertical for longitude. ",text,
L_0038,modeling earths surface,T_0385,"If you know the latitude and longitude of a place, you can find it on a map. Simply place one finger on the latitude on the vertical axis of the map. Place your other finger on the longitude along the horizontal axis of the map. Move your fingers along the latitude and longitude lines until they meet. For example, say the location you want to find is at 30o N and 90o W. Place your right finger along 30o N at the right of the map. Place your left finger along the bottom at 90o W. Move your fingers along the lines until they meet. Your location should be near New Orleans, Louisiana, along the Gulf coast of the United States. What if you want to know the latitude and longitude of your location? If you know where you are on a map, point to the place with your fingers. Take one finger and move it along the latitude line to find your latitude. Then move another finger along the longitude line to find your and longitude. ",text,
L_0038,modeling earths surface,T_0386,"You can also use a polar coordinate system. Your location is marked by an angle and distance from some reference point. The angle is usually the angle between your location, the reference point, and a line pointing north. The distance is given in meters or kilometers. To find your location or to move from place to place, you need a map, a compass, and some way to measure your distance, such as a range finder. Suppose you need to go from your location to a marker that is 20o E and 500 m from your current position. You must do the following: Use the compass and compass rose on the map to orient your map with north. Use the compass to find which direction is 20o E. Walk 500 meters in that direction to reach your destination. Polar coordinates are used in a sport called orienteering. People who do orienteering use a compass and a map with polar coordinates. Participants find their way along a course across wilderness terrain (Figure 2.22). They move to various checkpoints along the course. The winner is the person who completes the course in the fastest time. ",text,
L_0038,modeling earths surface,T_0387,"Earth is a sphere and so is a globe. A globe is the best way to make a map of the whole Earth. Because both the planet and a globe have curved surfaces, the sizes and shapes of countries are not distorted. Distances are true to scale. (Figure 2.23). Globes usually have a geographic coordinate system and a scale. The shortest distance between two points on a globe is the length of the portion of a circle that connects them. Globes are difficult to make and carry around. They also cannot be enlarged to show the details of any particular area. Globes are best sitting on your desk for reference. Google Earth is a neat site to download to your computer. This is a link that you can follow to get there: http://w tilt your image and lots more. ",text,
L_0039,topographic maps,T_0388,"Mapping is an important part of Earth Science. Topographic maps use a line, called a contour line, to show different elevations on a map. Contour lines show the location of hills, mountains and valleys. A regular road map shows where a road goes. But a road map doesnt show if the road goes over a mountain pass or through a valley. A topographic map shows you the features the road is going through or past. Lets look at topographic maps. Look at this view of the Swamp Canyon Trail in Bryce Canyon National Park, Utah (Figure 2.25). You can see the rugged canyon walls and valley below. The terrain has many steep cliffs with high and low points between the cliffs. Now look at the same section of the visitors map (Figure 2.26). You can see a green line that is the main road. The black dotted lines are trails. You see some markers for campsites, a picnic area, and a shuttle bus stop. The map does not show the height of the terrain. Where are the hills and valleys located? What is Natural Bridge? How high are the canyon walls? Which way do streams flow? A topographic map represents the elevations in an area (Figure 2.27). We mentioned topographic maps in the section on orienteering above. ",text,
L_0039,topographic maps,T_0388,"Mapping is an important part of Earth Science. Topographic maps use a line, called a contour line, to show different elevations on a map. Contour lines show the location of hills, mountains and valleys. A regular road map shows where a road goes. But a road map doesnt show if the road goes over a mountain pass or through a valley. A topographic map shows you the features the road is going through or past. Lets look at topographic maps. Look at this view of the Swamp Canyon Trail in Bryce Canyon National Park, Utah (Figure 2.25). You can see the rugged canyon walls and valley below. The terrain has many steep cliffs with high and low points between the cliffs. Now look at the same section of the visitors map (Figure 2.26). You can see a green line that is the main road. The black dotted lines are trails. You see some markers for campsites, a picnic area, and a shuttle bus stop. The map does not show the height of the terrain. Where are the hills and valleys located? What is Natural Bridge? How high are the canyon walls? Which way do streams flow? A topographic map represents the elevations in an area (Figure 2.27). We mentioned topographic maps in the section on orienteering above. ",text,
L_0039,topographic maps,T_0389,Contour lines connect all the points on the map that have the same elevation. Lets take a closer look at this (Figure Each contour line represents a specific elevation. The contour line connects all the points that are at the same elevation. Every fifth contour line is made bold. The bold contour lines have numbers to show elevation. Contour lines run next to each other and NEVER cross one another. If the lines crossed it would mean that one place had two different elevations. This cannot happen. ,text,
L_0039,topographic maps,T_0390,"Since each contour line represents a specific elevation, two different contour are separated by the same difference in elevation (e.g. 20 ft or 100 ft.). This difference between contour lines is called the contour interval. You can calculate the contour interval by following these steps: a. Take the difference in elevation between 2 bold lines. b. Divide that difference by the number of contour lines between them. Imagine that the difference between two bold lines is 100 feet and there are five lines between them. What is the contour interval? If you answered 20 feet, then you are correct (100 ft/5 lines = 20 ft between lines). The legend on the map also gives the contour interval. ",text,
L_0039,topographic maps,T_0391,"How does a topographic map tell you about the terrain? Lets consider the following principles: 1. The spacing of contour lines shows the slope of the land. Contour lines that are close together indicate a steep slope. This is because the elevation changes quickly in a small area. Contour lines that seem to touch indicate a very steep slope, like a cliff. When contour lines are spaced far apart the slope is gentle. So contour lines help us see the three-dimensional shape of the land. Look at the topographic map of Stowe, Vermont (Figure 2.28). There is a steep hill rising just to the right of the city of Stowe. You can tell this because the contour lines there are closely spaced. The contour lines also show that the hill has a sharp rise of about 200 feet. Then the slope becomes less steep toward the right. 2. Concentric circles indicate a hill. Figure 2.29 shows another side of the topographic map of Stowe, Vermont. When contour lines form closed loops, there is a hill. The smallest loops are the higher elevations on the hill. The larger loops encircling the smaller loops are downhill. If you look at the map, you can see Cady Hill in the lower left and another, smaller hill in the upper right. 3. Hatched concentric circles indicate a depression. The hatch marks are short, perpendicular lines inside the circle. The innermost hatched circle represents the deepest part of the depression. The outer hatched circles represent higher elevations (Figure 2.30). 4. V-shaped portions of contour lines indicate stream valleys. The V shape of the contour lines point uphill. There is a V shape because the stream channel passes through the point of the V. The open end of the V represents the downstream portion. A blue line indicates that there is water running through the valley. If there is not a blue line the V pattern indicates which way water flows. In Figure 2.31, you can see examples of V-shaped markings. Try to find the direction a stream flows. 5. Like other maps, topographic maps have a scale so that you can find the horizontal distance. You can use the horizontal scale to calculate the slope of the land (vertical height/horizontal distance). Common scales used in United States Geological Service (USGS) maps include the following: 1:24,000 scale - 1 inch = 2000 ft 1:100,000 scale - 1 inch = 1.6 miles 1:250,000 scale - 1 inch = 4 miles Including contour lines, contour intervals, circles, and V-shapes allows a topographic map to show three-dimensional information on a flat piece of paper. A topographic map gives us a good idea of the shape of the land. ",text,
L_0039,topographic maps,T_0391,"How does a topographic map tell you about the terrain? Lets consider the following principles: 1. The spacing of contour lines shows the slope of the land. Contour lines that are close together indicate a steep slope. This is because the elevation changes quickly in a small area. Contour lines that seem to touch indicate a very steep slope, like a cliff. When contour lines are spaced far apart the slope is gentle. So contour lines help us see the three-dimensional shape of the land. Look at the topographic map of Stowe, Vermont (Figure 2.28). There is a steep hill rising just to the right of the city of Stowe. You can tell this because the contour lines there are closely spaced. The contour lines also show that the hill has a sharp rise of about 200 feet. Then the slope becomes less steep toward the right. 2. Concentric circles indicate a hill. Figure 2.29 shows another side of the topographic map of Stowe, Vermont. When contour lines form closed loops, there is a hill. The smallest loops are the higher elevations on the hill. The larger loops encircling the smaller loops are downhill. If you look at the map, you can see Cady Hill in the lower left and another, smaller hill in the upper right. 3. Hatched concentric circles indicate a depression. The hatch marks are short, perpendicular lines inside the circle. The innermost hatched circle represents the deepest part of the depression. The outer hatched circles represent higher elevations (Figure 2.30). 4. V-shaped portions of contour lines indicate stream valleys. The V shape of the contour lines point uphill. There is a V shape because the stream channel passes through the point of the V. The open end of the V represents the downstream portion. A blue line indicates that there is water running through the valley. If there is not a blue line the V pattern indicates which way water flows. In Figure 2.31, you can see examples of V-shaped markings. Try to find the direction a stream flows. 5. Like other maps, topographic maps have a scale so that you can find the horizontal distance. You can use the horizontal scale to calculate the slope of the land (vertical height/horizontal distance). Common scales used in United States Geological Service (USGS) maps include the following: 1:24,000 scale - 1 inch = 2000 ft 1:100,000 scale - 1 inch = 1.6 miles 1:250,000 scale - 1 inch = 4 miles Including contour lines, contour intervals, circles, and V-shapes allows a topographic map to show three-dimensional information on a flat piece of paper. A topographic map gives us a good idea of the shape of the land. ",text,
L_0039,topographic maps,T_0391,"How does a topographic map tell you about the terrain? Lets consider the following principles: 1. The spacing of contour lines shows the slope of the land. Contour lines that are close together indicate a steep slope. This is because the elevation changes quickly in a small area. Contour lines that seem to touch indicate a very steep slope, like a cliff. When contour lines are spaced far apart the slope is gentle. So contour lines help us see the three-dimensional shape of the land. Look at the topographic map of Stowe, Vermont (Figure 2.28). There is a steep hill rising just to the right of the city of Stowe. You can tell this because the contour lines there are closely spaced. The contour lines also show that the hill has a sharp rise of about 200 feet. Then the slope becomes less steep toward the right. 2. Concentric circles indicate a hill. Figure 2.29 shows another side of the topographic map of Stowe, Vermont. When contour lines form closed loops, there is a hill. The smallest loops are the higher elevations on the hill. The larger loops encircling the smaller loops are downhill. If you look at the map, you can see Cady Hill in the lower left and another, smaller hill in the upper right. 3. Hatched concentric circles indicate a depression. The hatch marks are short, perpendicular lines inside the circle. The innermost hatched circle represents the deepest part of the depression. The outer hatched circles represent higher elevations (Figure 2.30). 4. V-shaped portions of contour lines indicate stream valleys. The V shape of the contour lines point uphill. There is a V shape because the stream channel passes through the point of the V. The open end of the V represents the downstream portion. A blue line indicates that there is water running through the valley. If there is not a blue line the V pattern indicates which way water flows. In Figure 2.31, you can see examples of V-shaped markings. Try to find the direction a stream flows. 5. Like other maps, topographic maps have a scale so that you can find the horizontal distance. You can use the horizontal scale to calculate the slope of the land (vertical height/horizontal distance). Common scales used in United States Geological Service (USGS) maps include the following: 1:24,000 scale - 1 inch = 2000 ft 1:100,000 scale - 1 inch = 1.6 miles 1:250,000 scale - 1 inch = 4 miles Including contour lines, contour intervals, circles, and V-shapes allows a topographic map to show three-dimensional information on a flat piece of paper. A topographic map gives us a good idea of the shape of the land. ",text,
L_0039,topographic maps,T_0391,"How does a topographic map tell you about the terrain? Lets consider the following principles: 1. The spacing of contour lines shows the slope of the land. Contour lines that are close together indicate a steep slope. This is because the elevation changes quickly in a small area. Contour lines that seem to touch indicate a very steep slope, like a cliff. When contour lines are spaced far apart the slope is gentle. So contour lines help us see the three-dimensional shape of the land. Look at the topographic map of Stowe, Vermont (Figure 2.28). There is a steep hill rising just to the right of the city of Stowe. You can tell this because the contour lines there are closely spaced. The contour lines also show that the hill has a sharp rise of about 200 feet. Then the slope becomes less steep toward the right. 2. Concentric circles indicate a hill. Figure 2.29 shows another side of the topographic map of Stowe, Vermont. When contour lines form closed loops, there is a hill. The smallest loops are the higher elevations on the hill. The larger loops encircling the smaller loops are downhill. If you look at the map, you can see Cady Hill in the lower left and another, smaller hill in the upper right. 3. Hatched concentric circles indicate a depression. The hatch marks are short, perpendicular lines inside the circle. The innermost hatched circle represents the deepest part of the depression. The outer hatched circles represent higher elevations (Figure 2.30). 4. V-shaped portions of contour lines indicate stream valleys. The V shape of the contour lines point uphill. There is a V shape because the stream channel passes through the point of the V. The open end of the V represents the downstream portion. A blue line indicates that there is water running through the valley. If there is not a blue line the V pattern indicates which way water flows. In Figure 2.31, you can see examples of V-shaped markings. Try to find the direction a stream flows. 5. Like other maps, topographic maps have a scale so that you can find the horizontal distance. You can use the horizontal scale to calculate the slope of the land (vertical height/horizontal distance). Common scales used in United States Geological Service (USGS) maps include the following: 1:24,000 scale - 1 inch = 2000 ft 1:100,000 scale - 1 inch = 1.6 miles 1:250,000 scale - 1 inch = 4 miles Including contour lines, contour intervals, circles, and V-shapes allows a topographic map to show three-dimensional information on a flat piece of paper. A topographic map gives us a good idea of the shape of the land. ",text,
L_0039,topographic maps,T_0392,"As we mentioned above, topographic maps show the shape of the land. You can determine a lot of information about the landscape using a topographic map. These maps are invaluable for Earth scientists. ",text,
L_0039,topographic maps,T_0393,"Earth scientists use topographic maps for many things: Describing and locating surface features, especially geologic features. Determining the slope of the Earths surface. Determining the direction of flow for surface water, groundwater, and mudslides. Hikers, campers, and even soldiers use topographic maps to locate their positions in the field. Civil engineers use topographic maps to determine where roads, tunnels, and bridges should go. Land use planners and architects use topographic maps when planning development projects, such as housing projects, shopping malls, and roads. ",text,
L_0039,topographic maps,T_0394,"Oceanographers use a type of topographic map that shows water depths (Figure 2.32). On this map, the contour lines represent depth below the surface. Therefore, high numbers are deeper depths and low numbers are shallow depths. These maps are made from depth soundings or sonar data. They help oceanographers understand the shape of bottoms of lakes, bays, and the ocean. This information also helps boaters navigate safely. ",text,
L_0039,topographic maps,T_0395,"A geologic map shows the different rocks that are exposed at the surface of a region. Rock units are shown in a color identified in a key. On the geologic map of the Grand Canyon, for example, different rock types are shown in different colors. Some people call the Grand Canyon layer cake geology because most of the rock units are in layers. Rock units show up on both sides of a stream valley. A geologic map looks very complicated in a region where rock layers have been folded, like the patterns in marble cake. Faults are seen on this geologic map cutting across rock layers. When rock layers are tilted, you will see stripes of each layer on the map. There are symbols on a geologic map that tell you which direction the rock layers slant, and often there is a cut away diagram, called a cross section, that shows what the rock layers look like below the surface. A large-scale geologic map will just show geologic provinces. They do not show the detail of individual rock layers. ",text,
L_0040,using satellites and computers,T_0396,"To understand what satellites can do, lets look at an example. One of the deadliest hurricanes in United States history hit Galveston, Texas in 1900. The storm was first spotted at sea on Monday, August 27th , 1900. It was a tropical storm when it hit Cuba on September 3rd . By September 8th , it had intensified to a hurricane over the Gulf of Mexico. It came ashore at Galveston (Figure 2.34). Because there was not advanced warning, more than 8000 people lost their lives. Today, we have satellites with many different types of instruments that orbit the Earth. With these satellites, satellites can see hurricanes form at sea. They can follow hurricanes as they move from far out in the oceans to shore. Weather forecasters can warn people who live along the coasts. These advanced warning give people time to prepare for the storm. They can find a safe place or even evacuate the area, which helps save lives. ",text,
L_0040,using satellites and computers,T_0397,Satellites orbit high above the Earth in several ways. Different orbits are important for viewing different things about the planet. ,text,
L_0040,using satellites and computers,T_0398,"A satellite in a geostationary orbit flies above the planet at a distance of 36,000 km. It takes 24 hours to complete one orbit. The satellite and the Earth both complete one rotation in 24 hours. This means that the satellite stays over the same spot. Weather satellites use this type of orbit to observe changing weather conditions over a region. Communications satellites, like satellite TV, use this type of orbit to keep communications going full time. ",text,
L_0040,using satellites and computers,T_0399,"Another useful orbit is the polar orbit (Figure 2.35). The satellite orbits at a distance of several hundred kilometers. It makes one complete orbit around the Earth from the North Pole to the South Pole about every 90 minutes. In this same amount of time, the Earth rotates only slightly underneath the satellite. So in less than a day, the satellite can see the entire surface of the Earth. Some weather satellites use a polar orbit to see how the weather is changing globally. Also, some satellites that observe the land and oceans use a polar orbit. ",text,
L_0040,using satellites and computers,T_0400,"The National Aeronautics and Space Administration (NASA) has launched a fleet of satellites to study the Earth (Figure 2.36). The satellites are operated by several government agencies, including NASA, the National Oceano- graphic and Atmospheric Administration (NOAA), and the United States Geological Survey (USGS). By using different types of scientific instruments, satellites make many kinds of measurements of the Earth. Some satellites measure the temperatures of the land and oceans. Some record amounts of gases in the atmosphere, such as water vapor and carbon dioxide. Some measure their height above the oceans very precisely. From this information, they can measure sea level. Some measure the ability of the surface to reflect various colors of light. This information tells us about plant life. Some examples of the images from these types of satellites are shown in Figure 2.37. ",text,
L_0040,using satellites and computers,T_0400,"The National Aeronautics and Space Administration (NASA) has launched a fleet of satellites to study the Earth (Figure 2.36). The satellites are operated by several government agencies, including NASA, the National Oceano- graphic and Atmospheric Administration (NOAA), and the United States Geological Survey (USGS). By using different types of scientific instruments, satellites make many kinds of measurements of the Earth. Some satellites measure the temperatures of the land and oceans. Some record amounts of gases in the atmosphere, such as water vapor and carbon dioxide. Some measure their height above the oceans very precisely. From this information, they can measure sea level. Some measure the ability of the surface to reflect various colors of light. This information tells us about plant life. Some examples of the images from these types of satellites are shown in Figure 2.37. ",text,
L_0040,using satellites and computers,T_0400,"The National Aeronautics and Space Administration (NASA) has launched a fleet of satellites to study the Earth (Figure 2.36). The satellites are operated by several government agencies, including NASA, the National Oceano- graphic and Atmospheric Administration (NOAA), and the United States Geological Survey (USGS). By using different types of scientific instruments, satellites make many kinds of measurements of the Earth. Some satellites measure the temperatures of the land and oceans. Some record amounts of gases in the atmosphere, such as water vapor and carbon dioxide. Some measure their height above the oceans very precisely. From this information, they can measure sea level. Some measure the ability of the surface to reflect various colors of light. This information tells us about plant life. Some examples of the images from these types of satellites are shown in Figure 2.37. ",text,
L_0040,using satellites and computers,T_0401,"In order to locate your position on a map, you must know your latitude and your longitude. But you need several instruments to measure latitude and longitude. What if you could do the same thing with only one instrument? Satellites can also help you locate your position on the Earths surface. By 1993, the United States military had launched 24 satellites to help soldiers locate their positions on battlefields. This system of satellites was called the Global Positioning System (GPS). Later, the United States government allowed the public to use this system. Heres how it works. You must have a GPS receiver to use the system (Figure 2.38). You can buy many types of these in stores. The ",text,
L_0040,using satellites and computers,T_0402,"Prior to the late 20th and early 21st centuries, mapmakers sent people out in the field to determine the boundaries and locations for various features for maps. State or county borders were used to mark geological features. Today, people in the field use GPS receivers to mark the locations of features. Map-makers also use various satellite images and computers to draw maps. Computers are able to break apart the fine details of a satellite image, store the pieces of information, and put them back together to make a map. In some instances, computers can make 3-D images of the map and even animate them. For example, scientists used computers and satellite images from Mars to create a 3-D image of Mars ice cap (Figure 2.39). The image makes you feel as if you are looking at the ice cap from the surface of Mars. When you link any type of information to a location, you can put together incredibly useful maps and images. The information could be numbers of people living in an area, types of plants or soil, locations of groundwater or levels of rainfall. As long as you can link the information to a position with a GPS receiver, you can store it in a computer for later processing and map-making. This type of mapping is called a Geographic Information System (GIS). Geologists can use GIS to make maps of natural resources. City leaders might link these resources to where people live and help plan the growth of cities or communities. Other types of data can be linked by GIS. For example, Figure 2.40 shows a map of the counties where farmers made insurance claims for crop damage in 2008. Computers have improved how maps are made. They have also increased the amount of information that can be displayed. During the 21st century, computers will be used more and more in mapping. ",text,
L_0040,using satellites and computers,T_0402,"Prior to the late 20th and early 21st centuries, mapmakers sent people out in the field to determine the boundaries and locations for various features for maps. State or county borders were used to mark geological features. Today, people in the field use GPS receivers to mark the locations of features. Map-makers also use various satellite images and computers to draw maps. Computers are able to break apart the fine details of a satellite image, store the pieces of information, and put them back together to make a map. In some instances, computers can make 3-D images of the map and even animate them. For example, scientists used computers and satellite images from Mars to create a 3-D image of Mars ice cap (Figure 2.39). The image makes you feel as if you are looking at the ice cap from the surface of Mars. When you link any type of information to a location, you can put together incredibly useful maps and images. The information could be numbers of people living in an area, types of plants or soil, locations of groundwater or levels of rainfall. As long as you can link the information to a position with a GPS receiver, you can store it in a computer for later processing and map-making. This type of mapping is called a Geographic Information System (GIS). Geologists can use GIS to make maps of natural resources. City leaders might link these resources to where people live and help plan the growth of cities or communities. Other types of data can be linked by GIS. For example, Figure 2.40 shows a map of the counties where farmers made insurance claims for crop damage in 2008. Computers have improved how maps are made. They have also increased the amount of information that can be displayed. During the 21st century, computers will be used more and more in mapping. ",text,
L_0040,using satellites and computers,T_0403,5. What would have happened if there had been satellites during the time of the 1900 Galveston earthquake? 6. What would have happened if there had been no satellites when hurricane Katrina struck the Gulf of Mexico coast in 2005? ,text,
L_0041,use and conservation of resources,T_0404,"We need natural resources for just about everything we do. We need them for food and clothing, for building materials and energy. We even need them to have fun. Table 20.1 gives examples of how we use natural resources. Can you think of other ways we use natural resources? Use Vehicles Resources Rubber for tires from rubber trees Steel frames and other metal parts from minerals such as iron Example iron ore Use Electronics Resources Plastic cases from petroleum prod- ucts Glass screens from minerals such as lead Example lead ore Homes Nails from minerals such as iron Timber from trees spruce timber Jewelry Gemstones such as diamonds Minerals such as silver silver ore Food Sunlight, water, and soil Minerals such as phosphorus corn seeds in soil Clothing Wool from sheep Cotton from cotton plants cotton plants Recreation Water for boating and swimming Forests for hiking and camping pine forest Some natural resources are renewable. Others are not. It depends in part on how we use them. ",text,
L_0041,use and conservation of resources,T_0405,"Renewable resources can be renewed as they are used. An example is timber, which comes from trees. New trees can be planted to replace those that are cut down. Sunlight is a renewable resource. It seems we will never run out of that! Just because a resource is renewable, it doesnt mean we should use it carelessly. If we arent careful, we can pollute resources. Then they may no longer be fit for use. Water is one example. If we pollute a water source it may not be usable for drinking, bathing or any other type of use. We can also overuse resources that should be renewable. In this case the resources may not be able to recover. For example, fish are renewable resources. Thats because they can reproduce and make more fish. But water pollution and overfishing can cause them to die out if their population becomes too low. Figure 20.1 shows another example. ",text,
L_0041,use and conservation of resources,T_0406,"Some resources cant be renewed. At least, they cant be renewed fast enough to keep up with use. Fossil fuels are examples. It takes millions of years for them to form. We are using them up much more quickly. Elements that are used to produce nuclear power are other examples. They include uranium. This element is already rare. Sooner or later, it will run out. Supplies of non-renewable resources are shrinking. This makes them harder to get. Oil is a good example. Oil reserves beneath land are running out. So oil companies have started to drill for oil far out in the ocean. This costs more money. Its also more dangerous. Figure 20.2 shows an oil rig that exploded in 2010. The explosion killed 11 people. Millions of barrels of oil spilled into the water. It took months to plug the leak. ",text,
L_0041,use and conservation of resources,T_0407,"Rich nations use more natural resources than poor nations. In fact, the richest 20 percent of people use 85 percent of the worlds resources. What about the poorest 20 percent of people? They use only 1 percent of the worlds resources. You can see this unequal distribution of oil resources in Figure 20.3. Imagine a world in which everybody had equal access to resources. Some people would have fewer resources than they do now. But many people would have more. In the real world, the difference between rich and poor just keeps growing. ",text,
L_0041,use and conservation of resources,T_0408,"Every 20 minutes, the human population adds 3,500 more people. More people need more resources. For example, we now use five times more fossil fuels than we did in 1970. The human population is expected to increase for at least 40 years. What will happen to resource use? ",text,
L_0041,use and conservation of resources,T_0409,"How can we protect Earths natural resources? One answer is conservation. This means saving resources. We need to save resources so some will be left for the future. We also need to protect resources from pollution and overuse. When we conserve resources, we also cut down on the trash we produce. Americans throw out 340 million tons of trash each year. We throw out 2.5 million plastic bottles alone every hour! Most of what we throw out ends up in landfills. You can see a landfill in Figure 20.4. In a landfill, all those plastic bottles take hundreds of years to break down. What are the problems caused by producing so much trash? Natural resources must be used to produce the materials. Land must be given over to dump the materials. If the materials are toxic, they may cause pollution. ",text,
L_0041,use and conservation of resources,T_0410,"You probably already know about the three Rs. They stand for reduce, reuse, and recycle. The third R recycle has caught on in a big way. Thats because its easy. There are thousands of places to drop off items such as aluminum cans for recycling. Many cities allow you to just put your recycling in a special can and put it at the curb. We havent done as well with the first two Rs reducing and reusing. But they arent always as easy as recycling. Recycling is better than making things from brand new materials. But it still takes some resources to turn recycled items into new ones. It takes no resources at all to reuse items or not buy them in the first place. ",text,
L_0041,use and conservation of resources,T_0411,"Reducing resource use means just what it says using fewer resources. There are lots of ways to reduce our use of resources. Buy durable goods. Choose items that are well made so they will last longer. Youll buy fewer items in the long run, so youll save money as well as resources. Thats a win-win! Repair rather than replace. Fix your bike rather than buying a new one. Sew on a button instead of buying a new shirt. Youll use fewer resources and save money. Buy only what you need. Dont buy a gallon of milk if you can only drink half of it before it spoils. Instead, buy a half gallon and drink all of it. You wont be wasting resources (or money!). Buy local. For example, buy local produce at a farmers market, like the one in Figure 20.5. A lot of resources are saved by not shipping goods long distances. Products bought at farmers markets use less packaging, too! About a third of what we throw out is packaging. Try to buy items with the least amount of packaging. For example, buy bulk items instead of those that are individually wrapped. Also, try to select items with packaging that can be reused or recycled. This is called precycling. Pop cans and plastic water bottles, for example, are fairly easy to recycle. Some types of packaging are harder to recycle. You can see examples in Figure 20.6. If it cant be reused or recycled, its a waste of resources. Many plastics: The recycling symbol on the bottom of plastic containers shows the type of plastic they contain. Numbers 1 and 2 are easier to recycle than higher numbers. Mixed materials: Packaging that contains more than one material may be hard to recycle. This carton is made mostly of cardboard. But it has plastic around the opening. ",text,
L_0041,use and conservation of resources,T_0411,"Reducing resource use means just what it says using fewer resources. There are lots of ways to reduce our use of resources. Buy durable goods. Choose items that are well made so they will last longer. Youll buy fewer items in the long run, so youll save money as well as resources. Thats a win-win! Repair rather than replace. Fix your bike rather than buying a new one. Sew on a button instead of buying a new shirt. Youll use fewer resources and save money. Buy only what you need. Dont buy a gallon of milk if you can only drink half of it before it spoils. Instead, buy a half gallon and drink all of it. You wont be wasting resources (or money!). Buy local. For example, buy local produce at a farmers market, like the one in Figure 20.5. A lot of resources are saved by not shipping goods long distances. Products bought at farmers markets use less packaging, too! About a third of what we throw out is packaging. Try to buy items with the least amount of packaging. For example, buy bulk items instead of those that are individually wrapped. Also, try to select items with packaging that can be reused or recycled. This is called precycling. Pop cans and plastic water bottles, for example, are fairly easy to recycle. Some types of packaging are harder to recycle. You can see examples in Figure 20.6. If it cant be reused or recycled, its a waste of resources. Many plastics: The recycling symbol on the bottom of plastic containers shows the type of plastic they contain. Numbers 1 and 2 are easier to recycle than higher numbers. Mixed materials: Packaging that contains more than one material may be hard to recycle. This carton is made mostly of cardboard. But it has plastic around the opening. ",text,
L_0041,use and conservation of resources,T_0412,"Reusing resources means using items again instead of throwing them away. A reused item can be used in the same way by someone else. Or it can be used in a new way. For example, Shana has a pair of jeans she has outgrown. She might give them to her younger sister to wear. Or she might use them to make something different for herself, say, a denim shoulder bag. Some other ideas for reusing resources are shown in Figure 20.7. ",text,
L_0041,use and conservation of resources,T_0413,"Many things can be recycled. The materials in them can be reused in new products. For example, plastic water bottles can be recycled. The recycled material can be made into t-shirts! Old phone books can also be recycled and made into textbooks. When you shop for new products, look for those that are made of recycled materials (see Figure 20.8). Even food scraps and lawn waste can be recycled. They can be composted and turned into humus for the garden. At most recycling centers, you can drop off metal cans, cardboard and paper products, glass containers, and plastic bottles. Recycling stations like the one in Figure 20.9 are common. Curbside recycling usually takes these items too. Do you know how to recycle in your community? Contact your local solid waste authority to find out. If you dont already recycle, start today. Its a big way you can help the planet! ",text,
L_0042,use and conservation of energy,T_0414,Think about your typical day. How do you use energy? Do you take a shower when you first get out of bed? What about taking a shower uses energy? It takes energy to heat the water and to pump the water to your home. Do you eat a hot breakfast? Energy is used to cook your food. Do you ride a bus or have someone drive you to school? Motor vehicles need energy from fossil fuels to run. ,text,
L_0042,use and conservation of energy,T_0415,"Figure 20.10 shows the major ways energy is used in the U.S. A lot of energy is used in homes. In fact, more energy is used in homes than in stores and businesses. Even more energy is used for transportation. A lot of fuel is necessary to move people and goods around the country. Industry uses the most energy. Industrial uses account for one-third of all the energy used in the U.S. ",text,
L_0042,use and conservation of energy,T_0416,"Figure 20.11 shows the energy resources used in the U.S. The U.S. depends mainly on fossil fuels. Petroleum is used more than any other resource. Renewable energy resources, such as solar and wind energy, could provide all the energy we need, but they are not yet widely used in the U.S. ",text,
L_0042,use and conservation of energy,T_0417,"We must use energy to get energy resources. This is true of non-renewable and renewable energy. Getting fossil fuels so that they can be used takes many steps. All of these steps use energy. 1. 2. 3. 4. 5. Fossil fuels must be found. The resources must be removed from the ground. These resources need to be refined, some more than others. Fossil fuels may need to be changed to a different form of energy. Energy resources must be transported from where they are produced to where they are sold or used. Consider petroleum as an example. Oil companies explore for petroleum in areas where they think it might be. When they find it, they must determine how much is there. They must also know how hard it will be to get. If theres enough to make it worthwhile, they will decide to go for it. To extract petroleum, companies they must build huge rigs, like the one in Figure 20.12. An oil rig drills deep into the ground and pumps the oil to the surface. The oil is then transported to a refinery. At the refinery, the oil is heated. It will then separate into different products, such as gasoline and motor oil. Finally, the oil products are transported to gas stations, stores, and industries. At every step, energy is used. For every five barrels of oil we use, it takes at least one barrel to get the oil. Less energy is needed to get renewable energy sources. Solar energy is a good example. Sunlight is everywhere, so no one needs to go out and find it. We dont have to drill for it or pump it to the surface. We just need to install solar panels like the ones in Figure 20.13 and let sunlight strike them. The energy from the sunlight is changed to electricity. The electricity is used to power lights and appliances in the house. So solar energy doesnt have to be transported. ",text,
L_0042,use and conservation of energy,T_0418,"Nonrenewable energy resources will run out before long. Using these energy resources also produces pollution and increases global warming. For all these reasons, we need to use less of these energy sources. We also need to use them more efficiently. ",text,
L_0042,use and conservation of energy,T_0418,"Nonrenewable energy resources will run out before long. Using these energy resources also produces pollution and increases global warming. For all these reasons, we need to use less of these energy sources. We also need to use them more efficiently. ",text,
L_0042,use and conservation of energy,T_0418,"Nonrenewable energy resources will run out before long. Using these energy resources also produces pollution and increases global warming. For all these reasons, we need to use less of these energy sources. We also need to use them more efficiently. ",text,
L_0042,use and conservation of energy,T_0419,"There are many ways to use less energy. Table 20.2 lists some of them. Can you think of other ways to use less energy? For example, how might schools use less energy? Use of Energy Transportation How to Use Less Plan ahead to reduce the number of trips you make. Take a bus or train instead of driving. Walk or bike rather than ride. Home Unplug appliances when not in use. Turn off lights when you leave a room. Put on a sweater instead of turning up the heat. Run the dishwasher and washing machine only when full. ",text,
L_0042,use and conservation of energy,T_0420,"We can get more work out of the energy we use. Table 20.3 show some ways to use energy more efficiently. By getting more bang for the buck, we wont need to use as much energy overall. Does your family use energy efficiently? How could you find out? Use of Energy More Efficient Use Another way to use energy more efficiently is with Energy Star appliances. They carry the Energy Star logo, shown in Figure 20.14. To be certified as Energy Star, the appliance must use less energy. Energy Star appliances save a lot of energy over their lifetime. What if millions of households used Energy Star appliances? How much energy would it save? ",text,
L_0043,humans and the water supply,T_0421,"Figure 21.1 shows how people use water worldwide. The greatest use is for agriculture and then industry. Municipal use is last, but is also important. Municipal use refers to water used by homes and businesses in communities. ",text,
L_0043,humans and the water supply,T_0422,"Many crops are grown where there isnt enough rainfall for plants to thrive. For example, crops are grown in deserts of the American southwest. How is this possible? The answer is irrigation. Irrigation is any way of providing extra water to plants. Most of the water used in agriculture is used for irrigation. Livestock also use water, but they use much less. Irrigation can waste a lot of water. The type of irrigation shown in Figure 21.2 is the most wasteful. The water is sprayed into the air and then falls to the ground. But much of the water never reaches the crops. Instead, it evaporates in the air or runs off the fields. Irrigation water may cause other problems. The water may dissolve agricultural chemicals such as pesticides. When the water soaks into the ground, the dissolved chemicals do, too. They may enter groundwater or run off into rivers or lakes. Salts in irrigation water can also collect in the soil. The soil may get too salty for plants to grow. ",text,
L_0043,humans and the water supply,T_0422,"Many crops are grown where there isnt enough rainfall for plants to thrive. For example, crops are grown in deserts of the American southwest. How is this possible? The answer is irrigation. Irrigation is any way of providing extra water to plants. Most of the water used in agriculture is used for irrigation. Livestock also use water, but they use much less. Irrigation can waste a lot of water. The type of irrigation shown in Figure 21.2 is the most wasteful. The water is sprayed into the air and then falls to the ground. But much of the water never reaches the crops. Instead, it evaporates in the air or runs off the fields. Irrigation water may cause other problems. The water may dissolve agricultural chemicals such as pesticides. When the water soaks into the ground, the dissolved chemicals do, too. They may enter groundwater or run off into rivers or lakes. Salts in irrigation water can also collect in the soil. The soil may get too salty for plants to grow. ",text,
L_0043,humans and the water supply,T_0423,Almost a quarter of the water used worldwide is used in industry. Industries use water for many purposes. Chemical processes need a lot of water. Water is used to generate electricity. An important way that industries use water is to cool machines and power plants. ,text,
L_0043,humans and the water supply,T_0424,"Think about all the ways people use water at home. Besides drinking it, they use it for cooking, bathing, washing dishes, doing laundry, and flushing toilets. The water used inside homes goes down the drain. From there it usually ends up in a sewer system. At the sewage treatment plant, water can be is treated and prepared for reuse. Households may also use water outdoors. If your family has a lawn or garden, you may water them with a hose or sprinkler. You probably use water to wash the car, like the teen in Figure 21.3. Much of the water used outdoors evaporates or runs off into the gutter. The runoff water may end up in storm sewers that flow into a body of water, such as the ocean. ",text,
L_0043,humans and the water supply,T_0425,"There are many ways to use water for fun, from white water rafting to snorkeling. When you do these activities you dont actually use water. You are doing the activity on or in the water. What do you think is the single biggest use of water for fun? Believe it or not, its golf! Keeping golf courses green uses an incredible amount of water. Since many golf courses are in sunny areas, much of the water is irrigation water. Many golf courses, like the one in Figure 21.4, have sprinkler systems. Like any similar sprinkler system, much of this water is wasted. It evaporates or runs off the ground. ",text,
L_0043,humans and the water supply,T_0426,"Most Americans have plenty of fresh, clean water. But many people around the world do not. In fact, water scarcity is the worlds most serious resource problem. How can that be? Water is almost everywhere. More than 70 percent of Earths surface is covered by water. ",text,
L_0043,humans and the water supply,T_0427,"One problem is that only a tiny fraction of Earths water is fresh, liquid water that people can use. More than 97 percent of Earths water is salt water in the oceans. Just 3 percent is freshwater. Most of the freshwater is frozen in ice sheets, icebergs, and glaciers (see Figure 21.5). ",text,
L_0043,humans and the water supply,T_0428,"Rainfall varies around the globe. About 40 percent of the land gets very little rain. About the same percentage of the worlds people dont have enough water. You can compare global rainfall with the worldwide freshwater supply at the two URLs below. Drier climates generally have less water for people to use. In some places, people may have less water available to them for an entire year than many Americans use in a single day! How much water is there where you live? Global rainfall: http://commons.wikimedia.org/wiki/File:World_precip_annual.png Freshwater supply: http://commons.wikimedia.org/wiki/File:2006_Global_Water_Availability.svg ",text,
L_0043,humans and the water supply,T_0429,"Richer nations can drill deep wells, build large dams or supply people with water in other ways. In these countries, just about everyone has access to clean running water in their homes. Its no surprise that people in these countries also use the most water. In poorer nations, there is little money to develop water supplies. Look at the people in Figure 21.6. These people must carry water home in a bucket from a distant pump. ",text,
L_0043,humans and the water supply,T_0430,"Water shortages are common in much of the world. People are most likely to run short of water during droughts. A drought is a period of unusually low rainfall. Human actions have increased how often droughts occur. One way people can help to bring on drought is by cutting down trees. Trees add a lot of water vapor to the air. With fewer trees, the air is drier and droughts are more common. We already use six times as much water today as we did a hundred years ago. As the number of people rises, our need for water will grow. By the year 2025, only half the worlds people will have enough clean water. Water is such a vital resource that serious water shortages may cause other problems. Crops and livestock may die, so people will have less food available. Other uses of water, such as industry, may have to stop. This reduces the jobs people can get and the products they can buy. People and nations may fight over water resources. In extreme cases, people may die from lack of water. The Figure 21.7 shows the global water situation in the 2030s with water stress and water scarcity on the map. ",text,
L_0043,humans and the water supply,T_0431,"The water Americans get from their faucets is generally safe. This water has been treated and purified. But at least 20 percent of the worlds people do not have clean drinking water. Their only choice may be to drink water straight from a river (see Figure 21.8). If the river is polluted with wastes, it will contain bacteria and other organisms that cause disease. Almost 9 out of 10 cases of disease worldwide are caused by unsafe drinking water. Diseases from unsafe drinking water are the leading cause of death in young children. ",text,
L_0044,water pollution,T_0432,"Pollution that enters water at just one point is called point source pollution. For example, chemicals from a factory might empty into a stream through a pipe or set of pipes (see Figure 21.9). Pollution that enters in many places is called non-point source pollution. This means that the pollution is from multiple sources. With non-point source pollution, runoff may carry the pollution into a body of water. Which type of pollution do you think is harder to control? ",text,
L_0044,water pollution,T_0433,"There are three main sources of water pollution: 1. Agriculture. 2. Industry. 3. Municipal, or community, sources. ",text,
L_0044,water pollution,T_0434,"Huge amounts of chemicals, such as fertilizers and pesticides, are applied to farm fields (see Figure 21.10). Some of the chemicals are picked up by rainwater. Runoff then carries the chemicals to nearby rivers or lakes. Dissolved fertilizer causes too much growth of water plants and algae. This can lead to dead zones where nothing can live in lakes and at the mouths of rivers. Some of the chemicals can infiltrate into groundwater. The contaminated water comes up in water wells. If people drink the polluted water, they may get sick. Waste from livestock can also pollute water. The waste contains bacteria and other organisms that cause disease. In fact, more than 40 human diseases can be caused by water polluted with animal waste. Many farms in the U.S. have thousands of animals. These farms produce millions of gallons of waste. The waste is stored in huge lagoons, like the one in Figure 21.11. Unfortunately, many leaks from these lagoons have occurred. Two examples are described below. In North Carolina, 25 million gallons of hog manure spilled into a nearby river. The contaminated water killed ",text,
L_0044,water pollution,T_0434,"Huge amounts of chemicals, such as fertilizers and pesticides, are applied to farm fields (see Figure 21.10). Some of the chemicals are picked up by rainwater. Runoff then carries the chemicals to nearby rivers or lakes. Dissolved fertilizer causes too much growth of water plants and algae. This can lead to dead zones where nothing can live in lakes and at the mouths of rivers. Some of the chemicals can infiltrate into groundwater. The contaminated water comes up in water wells. If people drink the polluted water, they may get sick. Waste from livestock can also pollute water. The waste contains bacteria and other organisms that cause disease. In fact, more than 40 human diseases can be caused by water polluted with animal waste. Many farms in the U.S. have thousands of animals. These farms produce millions of gallons of waste. The waste is stored in huge lagoons, like the one in Figure 21.11. Unfortunately, many leaks from these lagoons have occurred. Two examples are described below. In North Carolina, 25 million gallons of hog manure spilled into a nearby river. The contaminated water killed ",text,
L_0044,water pollution,T_0435,"Factories and power plants may pollute water with harmful substances. Many industries produce toxic chemicals. Some of the worst are arsenic, lead, and mercury. Nuclear power plants produce radioactive chemicals. They cause cancer and other serious health problems. Oil tanks and pipelines can leak. Leaks may not be noticed until a lot of oil has soaked into the ground. The oil may pollute groundwater so it is no longer fit to drink. ",text,
L_0044,water pollution,T_0436,Municipal refers to the community. Households and businesses in a community are also responsible for polluting the water supply. For example: People apply chemicals to their lawns. The chemicals may be picked up by rainwater. The contaminated runoff enters storm sewers and ends up in nearby rivers or lakes. Underground septic tanks can develop leaks. This lets household sewage seep into groundwater. Municipal sewage treatment plants dump treated wastewater into rivers or lakes. Sometimes the wastewater is not treated enough and contains bacteria or toxic chemicals. ,text,
L_0044,water pollution,T_0437,The oceans are vast. You might think they are too big to be harmed by pollution. But thats not the case. Ocean water is becoming seriously polluted. ,text,
L_0044,water pollution,T_0438,"The oceans are most polluted along coasts. Why do you think thats the case? Of course, its because most pollution enters the oceans from the land. Runoff and rivers carry the majority of pollution into the ocean. Many cities dump their wastewater directly into coastal waters. In some parts of the world, raw sewage and trash may be thrown into the water (see Figure 21.12). Coastal water may become so polluted that people get sick if they swim in it or eat seafood from it. The polluted water may also kill fish and other ocean life. ",text,
L_0044,water pollution,T_0439,"Oil spills are another source of ocean pollution. To get at oil buried beneath the seafloor, oil rigs are built in the oceans. These rigs pump oil from beneath the ocean floor. Huge ocean tankers carry oil around the world. If something goes wrong with a rig on a tanker, millions of barrels of oil may end up in the water. The oil may coat and kill ocean animals. Some of the oil will wash ashore. This oil may destroy coastal wetlands and ruin beaches. Figure 21.13 shows an oil spill on a beach. The oil washed ashore after a deadly oil rig explosion in the Gulf of Mexico in 2010. ",text,
L_0044,water pollution,T_0440,"Thermal pollution is pollution that raises the temperature of water. This is caused by power plants and factories that use the water to cool their machines. The plants pump cold water from a lake or coastal area through giant cooling towers, like those in Figure 21.14. As it flows through the towers, the cold water absorbs heat. This warmed water is returned to the lake or sea. Thermal pollution can kill fish and other water life. Its not just the warm temperature that kills them. Warm water cant hold as much oxygen as cool water. If the water gets too warm, there may not be enough oxygen for living things. ",text,
L_0045,protecting the water supply,T_0441,"In the mid 1900s, people were startled to see the Cuyahoga River in Cleveland, Ohio, burst into flames! The river was so polluted with oil and other industrial wastes that it was flammable. Nothing could live in it. You can see the Cuyahoga River in Figure 21.16 ",text,
L_0045,protecting the water supply,T_0442,"Disasters such as rivers burning led to new U.S. laws to protect the water. For example, the Environmental Protection Agency (EPA) was established, and the Clean Water Act was passed. Now, water is routinely tested. Pollution is tracked to its source, and polluters are forced to fix the problem and clean up the pollution. They are also fined. These consequences have led industries, agriculture, and communities to pollute the water much less than before. ",text,
L_0045,protecting the water supply,T_0443,"Most water pollution comes from industry, agriculture, and municipal sources. Homes are part of the municipal source and the individuals and families that live in them can pollute the water supply. What can you do to reduce water pollution? Read the tips below. Properly dispose of motor oil and household chemicals. Never pour them down the drain. Also, dont let them spill on the ground. This keeps them out of storm sewers and bodies of water. Use fewer lawn and garden chemicals. Use natural products instead. For example, use compost instead of fertilizer. Or grow plants that can thrive on their own without any extra help. Repair engine oil leaks right away. A steady drip of oil from an engine can quickly add up to gallons. When the oil washes off driveways and streets it can end up in storm drains and pollute the water supply. Dont let pet litter or pet wastes get into the water supply (see Figure 21.17). The nitrogen they contain can cause overgrowth of algae. The wastes may also contain bacteria and other causes of disease. ",text,
L_0045,protecting the water supply,T_0444,"Water treatment is a series of processes that remove unwanted substances from water. The goal of water treatment is to make the water safe to return to the natural environment or to the human water supply. Treating water for other purposes may not include all the same steps. Thats because water used in agriculture or industry may not have to be as clean as drinking water. You can see how water for drinking is treated in Figure 21.18. Treating drinking water requires at least four processes: 1. Chemicals are added to untreated water. They cause solids in the water to clump together. This is called coagulation. 2. The water is moved to tanks. The clumped solids sink to the bottom of the water. This is called sedimentation. 3. The water is passed through filters that remove smaller particles from the water. This is called filtration. 4. Chlorine is added to the water to kill bacteria and other microbes. This is called disinfection. Finally, the water is pure enough to drink. ",text,
L_0045,protecting the water supply,T_0445,"Conserving water means using less of it. Of course, this mostly applies to people in the wealthy nations that have the most water and also waste the most. ",text,
L_0045,protecting the water supply,T_0446,Irrigation is the single biggest use of water. Overhead irrigation wastes a lot of water. Drip irrigation wastes a lot less. Figure 21.19 shows a drip irrigation system. Water pipes run over the surface of the ground. Tiny holes in the pipes are placed close to each plant. Water slowly drips out of the holes and soaks into the soil around the plants. Very little of the water evaporates or runs off the ground. ,text,
L_0045,protecting the water supply,T_0447,"Some communities save water with rationing. Much rationing takes place only during times of drought. During rationing, water may not be used for certain things. For example, communities may ban lawn watering and car washing. People may be fined if they use water in these ways. You can do your part. Follow any bans where you live. ",text,
L_0045,protecting the water supply,T_0448,"Its easy to save water at home. If you save even a few gallons a day you can make a big difference over the long run. The best place to start saving water is in the bathroom. Toilet flushing is the single biggest use of water in the home. Showers and baths are the next biggest use. Follow the tips below to save water at home. Install water-saving toilets. They use only about half as much water per flush. A single household can save up to 20,000 gallons a year with this change alone! Take shorter showers. You can get just as clean in 5 minutes as you can in 10. And youll save up to 50 gallons of water each time you shower. Thats thousands of gallons each year. Use low-flow shower heads. They use about half as much water as regular shower heads. They save thousands of gallons of water. Fix leaky shower heads and faucets. All those drips really add up. At one drip per second, more than 6,000 gallons go down the drain in a year per faucet! Dont leave the water running while you brush your teeth. You could save as much as 10 gallons each time you brush. That could add up to 10,000 gallons in a year. Landscape your home with plants that need little water. This could result in a huge savings in water use. Look at the garden in Figure 21.20. It shows that you dont have to sacrifice beauty to save water. ",text,
L_0047,air pollution,T_0452,"Air quality is a measure of the pollutants in the air. More pollutants mean poorer air quality. Air quality, in turn, depends on many factors. Some natural processes add pollutants to the air. For example, forest fires and volcanoes add carbon dioxide and soot. In dry areas, the air often contains dust. However, human actions cause the most air pollution. The single biggest cause is fossil fuel burning. ",text,
L_0047,air pollution,T_0453,"Poor air quality started to become a serious problem after the Industrial Revolution. The machines in factories burned coal. This released a lot of pollutants into the air. After 1900, motor vehicles became common. Cars and trucks burn gasoline, which adds greatly to air pollution. ",text,
L_0047,air pollution,T_0454,"By the mid-1900s, air quality in many big cities was very bad. The worst incident came in December 1952. A temperature inversion over London, England, kept cold air and pollutants near the ground. The air became so polluted that thousands of people died in just a few days. This event was called the Big Smoke. ",text,
L_0047,air pollution,T_0455,"At the same time, many U.S. cities had air pollution problems. Some of the worst were in California. Cars were becoming more popular. Oil refineries and power plants also polluted the air. Mountain ranges trapped polluted air over cities. The California sunshine caused chemical reactions among the pollutants. These reactions produced many more harmful compounds. ",text,
L_0047,air pollution,T_0456,"By 1970, it was clear that something needed to be done to protect air quality. In the U.S., the Clean Air Act was passed. It limits what can be released into the air. As a result, the air in the U.S. is much cleaner now than it was 50 years ago. But air pollution has not gone away. Vehicles, factories, and power plants still release more than 150 million tons of pollutants into the air each year. ",text,
L_0047,air pollution,T_0457,There are two basic types of pollutants in air. They are known as primary pollutants and secondary pollutants. ,text,
L_0047,air pollution,T_0458,"Primary pollutants enter the air directly. Some are released by natural processes, like ash from volcanoes. Most are released by human activities. They pour into the air from vehicles and smokestacks. Several of these pollutants are described below. Carbon oxides include carbon monoxide (CO) and carbon dioxide (CO2 ). Carbon oxides are released when fossil fuels burn. Nitrogen oxides include nitric oxide (NO) and nitrogen dioxide (NO2 ). Nitrogen oxides form when nitrogen and oxygen combine at high temperatures. This occurs in hot exhausts from vehicles, factories, and power plants. Sulfur oxides include sulfur dioxide (SO2 ) and sulfur trioxide (SO3 ). Sulfur oxides are produced when sulfur and oxygen combine. This happens when coal burns. Coal can contain up to 10 percent sulfur. Toxic heavy metals include mercury and lead. Mercury is used in some industrial processes. It is also found in fluorescent light bulbs. Lead was once widely used in gasoline, paint, and pipes. It is still found in some products. Volatile organic compounds (VOCs) are carbon compounds such as methane. VOCs are released in many human activities, such as raising livestock. Livestock wastes produce a lot of methane. Particulates are solid particles. These particles may be ash, dust, or even animal wastes. Many are released when fossil fuels burn (see Figure 22.1). ",text,
L_0047,air pollution,T_0459,"Secondary pollutants form when primary pollutants undergo chemical reactions after they are released. Many occur as part of photochemical smog. This type of smog is seen as a brown haze in the air. Photochemical smog forms when certain pollutants react together in the presence of sunlight. You can see smog hanging in the air over San Francisco in Figure 22.2. Photochemical smog consists mainly of ozone (O3 ). The ozone in smog is the same compound as the ozone in the ozone layer,(O3 ). But ozone in smog is found near the ground. Figure 22.3 shows how it forms. When nitrogen oxides and VOCs are heated by the Sun, they lose oxygen atoms. The oxygen atoms combine with molecules of oxygen to form ozone. Smog ozone is harmful to humans and other living things. ",text,
L_0047,air pollution,T_0460,Most pollutants enter the air when fossil fuels burn. Some are released when forests burn. Others evaporate into the air. ,text,
L_0047,air pollution,T_0461,"Burning fossil fuels releases many pollutants into the air. These pollutants include carbon monoxide, carbon dioxide, nitrogen dioxide, and sulfur dioxide. Motor vehicles account for almost half of fossil fuel use. Most vehicles run on gasoline, which comes from petroleum. Power plants and factories account for more than a quarter of fossil fuel use. Power plants burn fossil fuels to generate electricity. Factories burn fossil fuels to power machines. Homes and other buildings also burn fossil fuels. The energy they release is used for heating, cooking, and other purposes. ",text,
L_0047,air pollution,T_0462,Millions of acres of forest have been cut and burned to make way for farming. Figure 22.4 shows an example. Burning trees produces most of the same pollutants as burning fossil fuels. ,text,
L_0047,air pollution,T_0463,"VOCs enter the air by evaporation. VOCs are found in many products, like paints and petroleum products. Methane is a VOC that evaporates from livestock waste and landfills. ",text,
L_0048,effects of air pollution,T_0464,All air pollutants are harmful. Thats why theyre called pollutants. Some air pollutants damage the environment as well as the health of living things. The type of damage depends on the pollutant. ,text,
L_0048,effects of air pollution,T_0465,Particulates cause lung diseases. They can also increase the risk of heart disease and the number of asthma attacks. Particulates block sunlight from reaching Earths surface. This means there is less energy for photosynthesis. Less photosynthesis means that plants and phytoplankton produce less food. This affects whole ecosystems. ,text,
L_0048,effects of air pollution,T_0466,"The ozone in smog may damage plants. The effects of ozone add up over time. Plants such as trees, which normally live a long time, are most affected. Entire forests may die out if ozone levels are very high. Other plants, including crop plants, may also be damaged by ozone. You can see evidence of ozone damage in Figure 22.5. The ozone in smog is also harmful to human health. Figure 22.6 shows the levels of ozone to watch out for. Some people are especially sensitive to ozone. They can be harmed by levels of ozone that would not affect most other people. These people include those with lung or heart problems. ",text,
L_0048,effects of air pollution,T_0466,"The ozone in smog may damage plants. The effects of ozone add up over time. Plants such as trees, which normally live a long time, are most affected. Entire forests may die out if ozone levels are very high. Other plants, including crop plants, may also be damaged by ozone. You can see evidence of ozone damage in Figure 22.5. The ozone in smog is also harmful to human health. Figure 22.6 shows the levels of ozone to watch out for. Some people are especially sensitive to ozone. They can be harmed by levels of ozone that would not affect most other people. These people include those with lung or heart problems. ",text,
L_0048,effects of air pollution,T_0467,"Both nitrogen and sulfur oxides are toxic to humans. These compounds can cause lung diseases or make them worse. Nitrogen and sulfur oxides form acid rain, which is described below. ",text,
L_0048,effects of air pollution,T_0468,"Carbon monoxide (CO) is toxic to both plants and animals. CO is deadly to people in a confined space, such as a closed home. Carbon monoxide is odorless and colorless, so people cant tell when they are breathing it. Thats why homes should have carbon monoxide detectors. You can see one in Figure 22.7. ",text,
L_0048,effects of air pollution,T_0469,"Heavy metals, such as mercury and lead, are toxic to living things. They can enter food chains from the atmosphere. The metals build up in the tissues of organisms by bioaccumulation. Bioaccumulation is illustrated in Figure 22.8. As heavy metals are passed up a food chain they accumulate. Imagine a low-level consumer eating a producer. That consumer takes in all of the heavy metals from all of the producers that it eats. Then a higher-level consumer eats it and accumulates all the heavy metals from all of the lower-level consumers that it eats. In this way, heavy metals may accumulate. At high levels in the food chain, the heavy metals may be quite become quite concentrated. The higher up a food chain that humans eat, the greater the levels of toxic metals they take in. Thats why people should avoid eating too much of large fish such as tuna. Tuna are predators near the top of their food chains. They have been shown to contain high levels of mercury. In people, heavy metals can damage the brain and other organs. Unborn babies and young children are most affected. Thats because their organs are still developing. ",text,
L_0048,effects of air pollution,T_0469,"Heavy metals, such as mercury and lead, are toxic to living things. They can enter food chains from the atmosphere. The metals build up in the tissues of organisms by bioaccumulation. Bioaccumulation is illustrated in Figure 22.8. As heavy metals are passed up a food chain they accumulate. Imagine a low-level consumer eating a producer. That consumer takes in all of the heavy metals from all of the producers that it eats. Then a higher-level consumer eats it and accumulates all the heavy metals from all of the lower-level consumers that it eats. In this way, heavy metals may accumulate. At high levels in the food chain, the heavy metals may be quite become quite concentrated. The higher up a food chain that humans eat, the greater the levels of toxic metals they take in. Thats why people should avoid eating too much of large fish such as tuna. Tuna are predators near the top of their food chains. They have been shown to contain high levels of mercury. In people, heavy metals can damage the brain and other organs. Unborn babies and young children are most affected. Thats because their organs are still developing. ",text,
L_0048,effects of air pollution,T_0470,"VOCs are toxic to humans and other living things. In people, they can cause a wide range of problems, from eye and nose irritation to brain damage and cancer. Levels of VOCs are often higher indoors than out. Thats because they are released by products such as paints, cleaning solutions, and building materials. How might you reduce your exposure to VOCs? ",text,
L_0048,effects of air pollution,T_0471,"Acid rain is rain that has a pH less than 5 (see Figure 22.9). The pH of normal rain is 5.6. Its slightly acidic because carbon dioxide in the air dissolves in rain. This forms carbonic acid, a weak acid. ",text,
L_0048,effects of air pollution,T_0472,Acid rain forms when nitrogen and sulfur oxides in air dissolve in rain (see Figure 22.10). This forms nitric and sulfuric acids. Both are strong acids. Acid rain with a pH as low as 4.0 is now common in many areas. Acid fog may be even more acidic than acid rain. Fog with a pH as low as 1.7 has been recorded. Thats the same pH as toilet bowl cleaner! ,text,
L_0048,effects of air pollution,T_0473,"Figure 22.11 shows some of the damage done by acid rain. Acid rain ends up in soil and bodies of water. This can make them very acidic. The acid strips soil of its nutrients. These changes can kill trees, fish, and other living things. Acid rain also dissolves limestone and marble. This can damage buildings, monuments, and statues. ",text,
L_0048,effects of air pollution,T_0474,Ozone near the ground harms human health. But the ozone layer in the stratosphere protects us from solar rays. Thats why people were alarmed in the 1980s to learn that there was a hole in the ozone layer. ,text,
L_0048,effects of air pollution,T_0475,"Whats destroying the ozone layer? The chief cause is chlorofluorocarbons (CFCs). These are human-made chemicals that contain the element chlorine (Cl). In the past, CFCs were widely used in spray cans, refrigerators, and many other products. CFCs are stable compounds that can remain in the atmosphere for hundreds of years. Once CFCs are in the air, they float up into the stratosphere. What happens next is shown in Figure 22.12. Sunlight breaks apart the molecules. This releases their chlorine atoms (Cl). The free chlorine atoms may then combine with oxygen atoms in ozone. This breaks down the ozone molecules into an oxygen molecule and an oxygen atom. One CFC molecule can break down as many as 100,000 ozone molecules in this way! These forms of oxygen do not protect the planet from ultraviolet radiation. ",text,
L_0048,effects of air pollution,T_0476,"Most ozone loss it taking place over the South Pole and Antarctica. This is the location of the ozone hole. The ozone hole is also seasonal. The hole forms during the early part spring in the Southern Hemisphere and then grows northward. You can see the hole in Figure 22.13. Besides the ozone hole, the ozone layer is thinner over the Northern Hemisphere. ",text,
L_0048,effects of air pollution,T_0476,"Most ozone loss it taking place over the South Pole and Antarctica. This is the location of the ozone hole. The ozone hole is also seasonal. The hole forms during the early part spring in the Southern Hemisphere and then grows northward. You can see the hole in Figure 22.13. Besides the ozone hole, the ozone layer is thinner over the Northern Hemisphere. ",text,
L_0048,effects of air pollution,T_0477,"With less ozone in the stratosphere, more UV rays reach the ground. More UV rays increase skin cancer rates. Just a 1 percent loss of ozone causes a 5 percent increase in skin cancer. More UV rays also harm plants and phytoplankton. As a result, they produce less food. This may affect entire ecosystems. ",text,
L_0049,reducing air pollution,T_0478,"There are two basic types of strategies for reducing pollution from fossil fuels: 1. Use less fossil fuel to begin with. 2. When fossil fuels must be used, prevent the pollution from entering the air. ",text,
L_0049,reducing air pollution,T_0479,"We can reduce our use of fossil fuels in several ways: Conserve fossil fuels. For example, turning out lights when we arent using them saves electricity. Why does this help? A lot of the electricity we use comes from coal-burning power plants. Use fossil fuels more efficiently. For example, driving a fuel-efficient car lets you go farther on each gallon of gas. This can add up to a big savings in fossil fuel use. Change to alternative energy sources that produce little or no air pollution. For example, hybrid cars run on electricity that would be wasted during braking. These cars use gas only as a backup fuel. As a result, they produce just 10 percent of the air pollution produced by cars that run only on gas. Cars that run on hydrogen and produce no pollution at all have also been developed (see Figure 22.14). ",text,
L_0049,reducing air pollution,T_0480,"Some of the pollutants from fossil fuels can be filtered out of exhaust before it is released into the air. Other pollutants can be changed to harmless compounds before they are released. Two widely used technologies are scrubbers and catalytic converters. Scrubbers are used in factories and power plants. They remove particulates and waste gases from exhaust before it is released to the air. You can see how a scrubber works in Figure 22.15. Catalytic converters are used on motor vehicles. They break down pollutants in exhaust to non-toxic com- pounds. For example, they change nitrogen oxides to harmless nitrogen and oxygen gasses. ",text,
L_0049,reducing air pollution,T_0481,"The problems of ozone loss and global warming were unknown in 1970. When they were discovered, worldwide efforts were made to reduce CFCs and carbon dioxide emissions. ",text,
L_0049,reducing air pollution,T_0482,"The Montreal Protocol is a worldwide agreement on air pollution. It focuses on CFCs. It was signed by many countries in 1987. It controls almost 100 chemicals that can damage the ozone layer. Its aim is to return the ozone layer to its normal state. The Montreal Protocol has been effective in controlling CFCs. By 1995, few CFCs were still being used. But the ozone hole kept growing for several years after that because of the CFCs already in the atmosphere. It peaked in 2006. Since then, it has been somewhat smaller. ",text,
L_0049,reducing air pollution,T_0483,"The Kyoto Protocol is another worldwide agreement on air pollution. It was passed in 1997. The Protocol focuses on controlling greenhouse gas emissions. Its aim is to control global warming. Carbon dioxide is the main greenhouse gas causing global warming. There are several possible ways to reduce carbon dioxide emissions. They include cap-and-trade systems, carbon taxes, and carbon sequestration In a cap-and-trade system, each nation is given a cap, or upper limit, on carbon dioxide emissions. If a nation needs to go over its cap, it can trade with another nation that is below its cap. Figure 22.16 shows how this works. Carbon taxes are taxes placed on gasoline and other products that produce carbon dioxide. The taxes encourage people to use less fossil fuel, which reduces carbon dioxide emissions. Carbon sequestration is any way of removing carbon dioxide from the atmosphere and storing it in another form. Carbon is sequestered naturally by forests. Trees take in carbon dioxide for photosynthesis. Artificial methods of sequestering carbon underground are being researched. The Kyoto Protocol has not been as successful as the Montreal Protocol. One reason is that the worlds biggest producer of greenhouse gases, the U.S., did not sign the Kyoto Protocol. Of the nations that signed it, few are ",text,
L_0050,telescopes,T_0484,Earth is just a tiny speck in the universe. Our planet is surrounded by lots of space. Light travels across empty space. Astronomers can study light from stars to learn about the universe. Light is the visible part of the electromagnetic spectrum. Astronomers use the light that comes to us to gather information about the universe. ,text,
L_0050,telescopes,T_0485,"In space, light travels at about 300,000,000 meters per second (670,000,000 miles per hour). How fast is that? A beam of light could travel from New York to Los Angeles and back again nearly 40 times in just one second. Even at that amazing rate, objects in space are so far away that it takes a lot of time for their light to reach us. Even light from the nearest star, our Sun, takes about 8 minutes to reach Earth. ",text,
L_0050,telescopes,T_0486,"We need a really big unit to measure distances out in space because distances between stars are so great. A light- year, 9.5 trillion kilometers (5.9 trillion miles), is the distance that light travels in one year. Thats a long way! Out in space, its actually a pretty short distance. Proxima Centauri is the closest star to us after the Sun. This near neighbor is 4.22 light-years away. That means the light from Proxima Centauri takes 4.22 years to reach us. Our galaxy, the Milky Way Galaxy, is about 100,000 light-years across. So it takes light 100,000 years to travel from one side of the galaxy to the other! It turns out that even 100,000 light years is a short distance. The most distant galaxies we have detected are more than 13 billion light-years away. Thats over a hundred-billion-trillion kilometers! ",text,
L_0050,telescopes,T_0487,"When we look at stars and galaxies, we are seeing over great distances. More importantly, we are also seeing back in time. When we see a distant galaxy, we are actually seeing how the galaxy used to look. For example, the Andromeda Galaxy, shown in Figure 23.1, is about 2.5 million light-years from Earth. When you see an image of the galaxy what are you seeing? You are seeing the galaxy as it was 2.5 million years ago! Since scientists can look back in time they can better understand the Universes history. Check out http://science.n ",text,
L_0050,telescopes,T_0488,"Light is one type of electromagnetic radiation. Light is energy that travels in the form of an electromagnetic wave. Figure 23.2 shows a diagram of an electromagnetic wave. An electromagnetic (EM) wave has two parts: an electric field and a magnetic field. The electric and magnetic fields vibrate up and down, which makes the wave. The wavelength is the horizontal distance between two of the same points on the wave, like wave crest to wave crest. A waves frequency measures the number of wavelengths that pass a given point every second. As wavelength increases, frequency decreases. This means that as wavelengths get shorter, more waves move past a particular spot in the same amount of time. ",text,
L_0050,telescopes,T_0488,"Light is one type of electromagnetic radiation. Light is energy that travels in the form of an electromagnetic wave. Figure 23.2 shows a diagram of an electromagnetic wave. An electromagnetic (EM) wave has two parts: an electric field and a magnetic field. The electric and magnetic fields vibrate up and down, which makes the wave. The wavelength is the horizontal distance between two of the same points on the wave, like wave crest to wave crest. A waves frequency measures the number of wavelengths that pass a given point every second. As wavelength increases, frequency decreases. This means that as wavelengths get shorter, more waves move past a particular spot in the same amount of time. ",text,
L_0050,telescopes,T_0489,"Visible light is the part of the electromagnetic spectrum (Figure 23.3) that humans can see. Visible light includes all the colors of the rainbow. Each color is determined by its wavelength. Visible light ranges from violet wavelengths of 400 nanometers (nm) through red at 700 nm. There are parts of the electromagnetic spectrum that humans cannot see. This radiation exists all around you. You just cant see it! Every star, including our Sun, emits radiation of many wavelengths. Astronomers can learn a lot from studying the details of the spectrum of radiation from a star. Many extremely interesting objects cant be seen with the unaided eye. Astronomers use telescopes to see objects at wavelengths all across the electromagnetic spectrum. Some very hot stars emit light primarily at ultraviolet wavelengths. There are extremely hot objects that emit X-rays and even gamma rays. Some very cool stars shine mostly in the infrared light wavelengths. Radio waves come from the faintest, most distant objects. To learn more about stars spectra, visit ",text,
L_0050,telescopes,T_0490,,text,
L_0050,telescopes,T_0491,"Humans have been making and using magnifying lenses for thousands of years. The first telescope was built by Galileo in 1608. His telescope used two lenses to make distant objects appear both nearer and larger. Telescopes that use lenses to bend light are called refracting telescopes, or refractors (Figure 23.4). The earliest telescopes were all refractors. Many amateur astronomers still use refractors today. Refractors are good for viewing details within our solar system. Craters on the surface of Earths Moon or the rings around Saturn are two such details. Around 1670, Sir Isaac Newton built a different kind of telescope. Newtons telescope used curved mirrors instead of lenses to focus light. This type of telescope is called a reflecting telescope, or reflector (see Figure 23.5). The mirrors in a reflecting telescope are much lighter than the heavy glass lenses in a refractor. This is important because a refracting telescope must be much stronger to support the heavy glass. Its much easier to precisely make mirrors than to precisely make glass lenses. For that reason, reflectors can be made larger than refractors. Larger telescopes can collect more light. This means that they can study dimmer or more distant objects. The largest optical telescopes in the world today are reflectors. Telescopes can also be made to use both lenses and mirrors. For more on how telescopes were developed, visit http://galileo.rice.edu/sci/instruments/telescope.html . ",text,
L_0050,telescopes,T_0492,"Radio telescopes collect radio waves. These telescopes are even larger telescopes than reflectors. Radio telescopes look a lot like satellite dishes. In fact, both are designed to collect and focus radio waves or microwaves from space. The largest single radio telescope in the world is at the Arecibo Observatory in Puerto Rico (see Figure 23.6). This telescope is located in a natural sinkhole. The sinkhole formed when water flowing underground dissolved the limestone. This telescope would collapse under its own weight if it were not supported by the ground. There is a big disadvantage to this design. The telescope can only observe the part of the sky that happens to be overhead at a given time. A group of radio telescopes can be linked together with a computer. The telescopes observe the same object. The computer then combines the data from each telescope. This makes the group function like one single telescope. An example is shown in Figure 23.7. To learn more about radio telescopes and radio astronomy in general, go to ",text,
L_0050,telescopes,T_0492,"Radio telescopes collect radio waves. These telescopes are even larger telescopes than reflectors. Radio telescopes look a lot like satellite dishes. In fact, both are designed to collect and focus radio waves or microwaves from space. The largest single radio telescope in the world is at the Arecibo Observatory in Puerto Rico (see Figure 23.6). This telescope is located in a natural sinkhole. The sinkhole formed when water flowing underground dissolved the limestone. This telescope would collapse under its own weight if it were not supported by the ground. There is a big disadvantage to this design. The telescope can only observe the part of the sky that happens to be overhead at a given time. A group of radio telescopes can be linked together with a computer. The telescopes observe the same object. The computer then combines the data from each telescope. This makes the group function like one single telescope. An example is shown in Figure 23.7. To learn more about radio telescopes and radio astronomy in general, go to ",text,
L_0050,telescopes,T_0492,"Radio telescopes collect radio waves. These telescopes are even larger telescopes than reflectors. Radio telescopes look a lot like satellite dishes. In fact, both are designed to collect and focus radio waves or microwaves from space. The largest single radio telescope in the world is at the Arecibo Observatory in Puerto Rico (see Figure 23.6). This telescope is located in a natural sinkhole. The sinkhole formed when water flowing underground dissolved the limestone. This telescope would collapse under its own weight if it were not supported by the ground. There is a big disadvantage to this design. The telescope can only observe the part of the sky that happens to be overhead at a given time. A group of radio telescopes can be linked together with a computer. The telescopes observe the same object. The computer then combines the data from each telescope. This makes the group function like one single telescope. An example is shown in Figure 23.7. To learn more about radio telescopes and radio astronomy in general, go to ",text,
L_0050,telescopes,T_0492,"Radio telescopes collect radio waves. These telescopes are even larger telescopes than reflectors. Radio telescopes look a lot like satellite dishes. In fact, both are designed to collect and focus radio waves or microwaves from space. The largest single radio telescope in the world is at the Arecibo Observatory in Puerto Rico (see Figure 23.6). This telescope is located in a natural sinkhole. The sinkhole formed when water flowing underground dissolved the limestone. This telescope would collapse under its own weight if it were not supported by the ground. There is a big disadvantage to this design. The telescope can only observe the part of the sky that happens to be overhead at a given time. A group of radio telescopes can be linked together with a computer. The telescopes observe the same object. The computer then combines the data from each telescope. This makes the group function like one single telescope. An example is shown in Figure 23.7. To learn more about radio telescopes and radio astronomy in general, go to ",text,
L_0050,telescopes,T_0493,"Telescopes on Earth all have one big problem: Incoming light must pass through the atmosphere. This blocks some wavelengths of radiation. Also, motion in the atmosphere distorts light. You see this when you see stars twinkling in the night sky. Many observatories are built on high mountains. There is less air above the telescope, so there is less interference from the atmosphere. Space telescopes avoid such problems completely since they orbit outside the atmosphere. The Hubble Space Telescope is the best known space telescope. Hubble is shown in Figure 23.8. Hubble began operations in 1994. Since then it has provided huge amounts of data. The telescope has helped astronomers answer many of the biggest questions in astronomy. The National Aeronautics and Space Administration (NASA) has placed three other major space telescopes in orbit. Each uses a different part of the electromagnetic spectrum. The James Webb Space Telescope will launch in 2014. The telescope will replace the aging Hubble. To learn more about NASAs great observatories, check out ",text,
L_0050,telescopes,T_0493,"Telescopes on Earth all have one big problem: Incoming light must pass through the atmosphere. This blocks some wavelengths of radiation. Also, motion in the atmosphere distorts light. You see this when you see stars twinkling in the night sky. Many observatories are built on high mountains. There is less air above the telescope, so there is less interference from the atmosphere. Space telescopes avoid such problems completely since they orbit outside the atmosphere. The Hubble Space Telescope is the best known space telescope. Hubble is shown in Figure 23.8. Hubble began operations in 1994. Since then it has provided huge amounts of data. The telescope has helped astronomers answer many of the biggest questions in astronomy. The National Aeronautics and Space Administration (NASA) has placed three other major space telescopes in orbit. Each uses a different part of the electromagnetic spectrum. The James Webb Space Telescope will launch in 2014. The telescope will replace the aging Hubble. To learn more about NASAs great observatories, check out ",text,
L_0050,telescopes,T_0494,,text,
L_0050,telescopes,T_0495,"Humans have been studying the night sky for thousands of years. Knowing the motions of stars helped people keep track of seasons. With this information they could know when to plant crops. Stars were so important that the patterns they made in the sky were named. These patterns are called constellations. Even now, constellations help astronomers know where they are looking in the night sky. The ancient Greeks carefully observed the locations of stars in the sky. They noticed that some of the stars moved across the background of other stars. They called these bright spots in the sky planets. The word in Greek means wanderers. Today we know that the planets are not stars. They are objects in the solar system that orbit the Sun. Ancient astronomers made all of their observations without the aid of a telescope. ",text,
L_0050,telescopes,T_0496,"In 1610, Galileo looked at the night sky through the first telescope. This tool allowed him to make the following discoveries (among others): There are more stars in the night sky than the unaided eye can see. The band of light called the Milky Way consists of many stars. The Moon has craters (see Figure 23.10). Venus has phases like the Moon. Jupiter has moons orbiting around it. There are dark spots that move across the surface of the Sun. Galileos observations made people think differently about the universe. They made them think about the solar system and Earths place in it. Until that time, people believed that the Sun and planets revolved around Earth. One hundred years before Galileo, Copernicus had said that the Earth and the other planets revolved around the Sun. No one would believe him. But Galileos observations through his telescope proved that Copernicus was right. ",text,
L_0050,telescopes,T_0497,"Galileos telescope got people to think about the solar system in the right way. Modern tools have also transformed our way of thinking about the universe. Imagine this: Today you can see all of the things Galileo saw using a good pair of binoculars. You can see sunspots if you have special filters on the lenses. (Never look directly at the Sun without using the proper filters!) With the most basic telescope, you can see polar caps on Mars, the rings of Saturn, and bands in the atmosphere of Jupiter. You can see many times more stars with a telescope than without a telescope. Still, stars seen in a telescope look like single points of light. They are so far away. Only the red supergiant star Betelgeuse is large enough to appear as a disk. Except for our Sun, of course. Today, astronomers attach special instruments to telescopes. This allows them to collect a wide variety of data. The data is fed into computers so that it can be studied. An astronomer may take weeks to analyze all of the data collected from just a single night! ",text,
L_0050,telescopes,T_0498,"A spectrometer is a special tool that astronomers commonly use. Spectrometers allow them to study the light from a star or galaxy. A spectrometer produces a spectrum, like the one shown in Figure 23.11. A prism breaks light into all its colors. Gases from the outer atmosphere of a star absorb light. This forms dark lines in the spectrum. These dark lines reveal what elements the star contains. Astronomers use the spectrum to learn even more about the star. One thing they learn is how hot the star is. They also learn the direction the star is going and how fast. By carefully studying light from many stars, astronomers know how stars evolve. They have learned about the distribution and kinds of matter found throughout the universe. They even know something about how the universe might have formed. To find out what you can expect to see when looking through a telescope, check out ",text,
L_0051,early space exploration,T_0499,Humans did not reach space until the second half of the 20th century. They needed somehow to break past Earths gravity. A rocket moves rapidly in one direction. The device is propelled by particles flying out of it at high speed in the other direction. There are records of the Chinese using rockets in war against the Mongols as early as the 13th century. The Mongols then used rockets to attack Eastern Europe. Early rockets were also used to launch fireworks. ,text,
L_0051,early space exploration,T_0500,"Rockets were used for centuries before anyone could explain how they worked. The theory came about in 1687. Isaac Newton (16431727) described three basic laws of motion, now referred to as Newtons Laws of Motion: 1. An object in motion will remain in motion unless acted upon by a force. 2. Force equals mass multiplied by acceleration. 3. To every action, there is an equal and opposite reaction. Which of these three best explains how a rocket works? Newtons third law of motion. When a rockets propulsion pushes in one direction, the rocket moves in the opposite direction, as seen in the Figure 23.12. For a long time, many people believed that a rocket wouldnt work in space. There would be nothing for the rocket to push against. But they do work! Fuel is ignited in a chamber. The gases in the chamber explode. The explosion creates pressure that forces the gases out of one side of the rocket. The rocket moves in the opposite direction, as shown in Figure 23.13. The force pushing the rocket is called thrust. ",text,
L_0051,early space exploration,T_0501,"For centuries, rockets were powered by gunpowder or other solid fuels. These rockets could travel only short distances. Around the turn of the 20th century, several breakthroughs took place. These breakthroughs led to rockets that could travel beyond Earth. Liquid fuel gave rockets enough power to escape Earths gravity (Figure 23.14). By using multiple stages, empty fuel containers could drop away. This reduced the mass of the rocket so that it could fly higher. Rockets were used during World War II. The V2 was the first human-made object to travel high enough to be considered in space (Figure 23.15). Its altitude was 176 km (109 miles) above Earths surface. Wernher von Braun was a German rocket scientist. After he fled Germany in WWII, he helped the United States develop missile weapons. After the war, von Braun worked for NASA. He designed the Saturn V rocket (Figure ",text,
L_0051,early space exploration,T_0502,One of the first uses of rockets in space was to launch satellites. A satellite is an object that orbits a larger object. An orbit is a circular or elliptical path around an object. Natural objects in orbit are called natural satellites. The Moon is a natural satellite. Human-made objects in orbit are called artificial satellites. There are more and more artificial satellites orbiting Earth all the time. They all get into space using some sort of rocket. ,text,
L_0051,early space exploration,T_0502,One of the first uses of rockets in space was to launch satellites. A satellite is an object that orbits a larger object. An orbit is a circular or elliptical path around an object. Natural objects in orbit are called natural satellites. The Moon is a natural satellite. Human-made objects in orbit are called artificial satellites. There are more and more artificial satellites orbiting Earth all the time. They all get into space using some sort of rocket. ,text,
L_0051,early space exploration,T_0502,One of the first uses of rockets in space was to launch satellites. A satellite is an object that orbits a larger object. An orbit is a circular or elliptical path around an object. Natural objects in orbit are called natural satellites. The Moon is a natural satellite. Human-made objects in orbit are called artificial satellites. There are more and more artificial satellites orbiting Earth all the time. They all get into space using some sort of rocket. ,text,
L_0051,early space exploration,T_0502,One of the first uses of rockets in space was to launch satellites. A satellite is an object that orbits a larger object. An orbit is a circular or elliptical path around an object. Natural objects in orbit are called natural satellites. The Moon is a natural satellite. Human-made objects in orbit are called artificial satellites. There are more and more artificial satellites orbiting Earth all the time. They all get into space using some sort of rocket. ,text,
L_0051,early space exploration,T_0503,"Why do satellites stay in orbit? Why dont they crash into Earth due to the planets gravity? Newtons law of universal gravitation describes what happens. Every object in the universe is attracted to every other object. Gravity makes an apple fall to the ground. Gravity also keeps you from floating away into the sky. Gravity holds the Moon in orbit around Earth. It keeps Earth in orbit around the Sun. Newton used an example to explain how gravity makes orbiting possible. Imagine a cannonball launched from a high mountain, as shown in Figure 23.17. If the cannonball is launched at a slow speed, it will fall back to Earth. This is shown as paths (A) and (B). Something different happens if the cannonball is launched at a fast speed. The Earth below curves away at the same rate that the cannonball falls. The cannonball then goes into a circular orbit, as in path (C). If the cannonball is launched even faster, it could go into an elliptical orbit (D). It might even leave Earths gravity and go into space (E). Unfortunately, Newtons idea would not work in real life. A cannonball launched at a fast speed from Mt. Everest would not go into orbit. The cannonball would burn up in the atmosphere. However, a rocket can launch straight up, then steer into orbit. It wont burn up in the orbit. A rocket can carry a satellite above the atmosphere and then release the satellite into orbit. ",text,
L_0051,early space exploration,T_0504,"The first artificial satellite was launched just over 50 years ago. Thousands are now in orbit around Earth. Satellites have orbited other objects in the solar system. These include the Moon, the Sun, Venus, Mars, Jupiter, and Saturn. Satellites have many different purposes. Imaging satellites take pictures Earths surface. These images are used for military or scientific purposes. Astronomers use imaging satellites to study and make maps of the Moon and other planets. Communications satellites, such as the one in Figure 23.18, are now extremely common. These satellites receive and send signals for telephone, television, or other types of communications. Navigational satellites are used for navigation systems, such as the Global Positioning System (GPS). The largest artificial satellite is the International Space Station. The ISS is designed for humans to live in space while conducting scientific research. ",text,
L_0051,early space exploration,T_0505,"Dozens of satellites collect data about the Earth. One example is NASAs Landsat satellites. These satellites make detailed images of Earths continents and coastal areas. Other satellites study the oceans, atmosphere, polar ice sheets, and other Earth systems. This data helps us to monitor climate change. Other long-term changes in the planet are also best seen from space. Satellite images help scientists understand how Earths systems affect one another. Different satellites monitor different wavelengths of energy, as in Figure 23.19. ",text,
L_0051,early space exploration,T_0506,Satellites have different views depending on their orbit. Satellites may be put in a low orbit. These satellites orbit from north to south over the poles. These satellites view a different part of Earth each time they circle. Imaging and weather satellites need this type of view. Satellite may be placed so that they orbit at the same rate the Earth spins. The satellite then remains over the same location on the surface. Communications satellites are often placed in these orbits. ,text,
L_0051,early space exploration,T_0507,The Cold War was between the Soviet Union (USSR) and the United States. The war lasted from the end of World War II in 1945 to the breakup of the USSR in 1991. The hallmark of the Cold War was an arms race. The two nations spared no expense to create new and more powerful weapons. The development of better missiles fostered better rocket technologies. ,text,
L_0051,early space exploration,T_0508,"The USSR launched Sputnik 1 on October 4, 1957. This was the first artificial satellite ever put into orbit. Sputnik 1, shown in Figure 23.20, sent out radio signals, which were detected by scientists and amateur radio operators around the world. The satellite stayed in orbit for about 3 months, until it burned up as a result of friction with Earths atmosphere. The launch of Sputnik 1 started the Space Race between the USSR and the USA. Americans were shocked that the Soviets had the technology to put the satellite into orbit. They worried that the Soviets might also be winning the arms race. On November 3, 1957, the Soviets launched Sputnik 2. This satellite carried the first living creature into orbit, a dog named Laika. ",text,
L_0051,early space exploration,T_0509,"In response to Sputnik program, the U.S. launched two satellites. Explorer I was launched on January 31, 1958 and Vanguard 1 on March 17, 1958. National Aeronautics and Space Administration (NASA) was established that same year. The race was on! On April 12, 1961, a Soviet cosmonaut became the first human in space and in orbit. Less than one month later May 5, 1961 the U.S. sent its first astronaut into space: Alan Shepherd. The first American in orbit was John Glenn, in February 1962. And on it went. ",text,
L_0051,early space exploration,T_0510,"On May 25, 1961, President John F. Kennedy challenged the U.S. Congress: I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him back safely to the Earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space; and none will be so difficult or expensive to accomplish. The Soviets were also trying to reach the Moon. Who would win? The answer came eight years after Kennedys challenge, on July 20, 1969. NASAs Apollo 11 mission put astronauts Neil Armstrong and Buzz Aldrin on the Moon, as shown in Figure 23.21. A total of five American missions put astronauts on the Moon. The last was Apollo 17. This mission landed on December 11, 1972. No other country has yet put a person on the Moon. Today, most space missions are done by ",text,
L_0051,early space exploration,T_0510,"On May 25, 1961, President John F. Kennedy challenged the U.S. Congress: I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him back safely to the Earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space; and none will be so difficult or expensive to accomplish. The Soviets were also trying to reach the Moon. Who would win? The answer came eight years after Kennedys challenge, on July 20, 1969. NASAs Apollo 11 mission put astronauts Neil Armstrong and Buzz Aldrin on the Moon, as shown in Figure 23.21. A total of five American missions put astronauts on the Moon. The last was Apollo 17. This mission landed on December 11, 1972. No other country has yet put a person on the Moon. Today, most space missions are done by ",text,
L_0051,early space exploration,T_0511,"Both the United States and the Soviet Union sent space probes to other planets. A space probe is an unmanned spacecraft. The craft collects data by flying near or landing on an object in space. This could be a planet, moon, asteroid, or comet. The USSR sent several probes to Venus in the Venera missions. Some landed on the surface and sent back data. The U.S. sent probes to Mercury, Venus, and Mars in the Mariner missions. Two probes landed on Mars during the Viking missions. The U.S. also sent probes to the outer solar system. These probes conducted fly-bys of Jupiter, Saturn, Uranus, and Neptune. The Pioneer and Voyager probes are now out beyond the edges of our solar system. We have lost contact with the two Pioneer probes. We hope to maintain contact with the two Voyager probes until at least 2020. ",text,
L_0052,recent space exploration,T_0512,"While the United States continued missions to the Moon in the early 1970s, the Soviets worked to build a space station. A space station is a large spacecraft. People can live on this craft for a long period of time. ",text,
L_0052,recent space exploration,T_0513,"Between 1971 and 1982, the Soviets put a total of seven Salyut space stations into orbit. Figure 23.22 shows the last of these, Salyut 7. These were all temporary stations. They were launched and later inhabited by a human crew. Three of the Salyut stations were used for secret military purposes. The others were used to study the problems of living in space. Cosmonauts aboard the stations performed a variety of experiments in astronomy, biology, and Earth science. Salyut 6 and Salyut 7 each had two docking ports. One crew could dock a spacecraft to one end. A replacement crew could dock to the other end. The U.S. only launched one space station during this time. It was called Skylab. Skylab was launched in May 1973. Three crews visited Skylab, all within its first year in orbit. Skylab was used to study the effects of staying in space for long period. Devices on board were and for studying the Sun. Skylab reentered Earths atmosphere in 1979, sooner than expected. ",text,
L_0052,recent space exploration,T_0514,The first space station designed for long-term use was the Mir space station (Figure 23.23). Mir was launched in several separate pieces. These pieces were put together in space. Mir holds the current record for the longest continued presence in space. There were people living on Mir continuously for almost 10 years! Mir was the first major space project in which the United States and Russia worked together. American space shuttles transported supplies and people to and from Mir. American astronauts lived on Mir for many months. This cooperation allowed the two nations to learn from each other. The U.S. learned about Russias experiences with long-duration space flights. Mir was taken out of orbit in 2001. It fell into the Pacific Ocean. ,text,
L_0052,recent space exploration,T_0514,The first space station designed for long-term use was the Mir space station (Figure 23.23). Mir was launched in several separate pieces. These pieces were put together in space. Mir holds the current record for the longest continued presence in space. There were people living on Mir continuously for almost 10 years! Mir was the first major space project in which the United States and Russia worked together. American space shuttles transported supplies and people to and from Mir. American astronauts lived on Mir for many months. This cooperation allowed the two nations to learn from each other. The U.S. learned about Russias experiences with long-duration space flights. Mir was taken out of orbit in 2001. It fell into the Pacific Ocean. ,text,
L_0052,recent space exploration,T_0515,"The International Space Station, shown in Figure 23.24 is a joint project between the space agencies of many nations These include the United States (NASA), Russia (RKA), Japan (JAXA), Canada (CSA), several European countries (ESA) and the Brazilian Space Agency. The International Space Station is a very large station. It has many different sections and is still being assembled. The station has had people on board since 2000. American space shuttles deliver most of the supplies and equipment to the station. Russian Soyuz spacecraft carry people. The primary purpose of the station is scientific research. This is important because the station has a microgravity environment. Experiments are done in the fields of biology, chemistry, physics, physiology and medicine. ",text,
L_0052,recent space exploration,T_0516,"NASA wanted a new kind of space vehicle. This vehicle had to be reusable. It had to able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The new vehicle was called a space shuttle, shown in Figure 23.25. There have been five space shuttles: Columbia, Challenger, Discovery, Atlantis, and Endeavor. A space shuttle has three main parts. You are probably most familiar with the orbiter. This part has wings like At the end of the mission, the orbiter re-enters Earths atmosphere. The outside heats up as it descends. Pilots have to steer the shuttle to the runway very precisely. Space shuttles usually land at Kennedy Space Center or at Edwards Air Force Base in California. The orbiter is later hauled back to Florida on the back of a jet airplane. ",text,
L_0052,recent space exploration,T_0516,"NASA wanted a new kind of space vehicle. This vehicle had to be reusable. It had to able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The new vehicle was called a space shuttle, shown in Figure 23.25. There have been five space shuttles: Columbia, Challenger, Discovery, Atlantis, and Endeavor. A space shuttle has three main parts. You are probably most familiar with the orbiter. This part has wings like At the end of the mission, the orbiter re-enters Earths atmosphere. The outside heats up as it descends. Pilots have to steer the shuttle to the runway very precisely. Space shuttles usually land at Kennedy Space Center or at Edwards Air Force Base in California. The orbiter is later hauled back to Florida on the back of a jet airplane. ",text,
L_0052,recent space exploration,T_0517,"The space shuttle program has been very successful. Over 100 mission have been flown. Space shuttle missions have made many scientific discoveries. Crews have launched many satellites. There have been other great achievements in space. However, the program has also had two tragic disasters. The first came just 73 seconds after launch, on January 28, 1986. The space shuttle Challenger disintegrated in mid-air, as shown in Figure 23.27. On board were seven crew members. All of them died. One of them was Christa McAuliffe, who was to be the first teacher in space. The problem was later shown to be an O-ring. This small part was in one of the rocket boosters. Space shuttle missions were put on hold while NASA improved the safety of the shuttles. The second occurred during the takeoff of the Columbia on January 16, 2003. A small piece of insulating foam broke off the fuel tank. The foam smashed into a tile on the shuttles wing. The tile was part of the shuttles heat shield. The shield protects the shuttle from extremely high temperatures as it reenters the atmosphere. When Columbia returned to Earth on February 3, 2003, it could not withstand the high temperatures. The shuttle broke apart. Again, all seven crew members died. The space shuttle will be retired in 2011. All the remaining shuttle missions will be to the ISS. Orion will replace the shuttle. Known as a Crew Exploration Vehicle, Orion is expected to be ready by 2016. ",text,
L_0052,recent space exploration,T_0518,The disasters have caused NASA to focus on developing unmanned missions. Missions without a crew are less expensive and less dangerous. These missions still provide a great deal of valuable information. ,text,
L_0052,recent space exploration,T_0519,"Incredible images have come from the Hubble Space Telescope (HST). Even more incredible scientific discoveries have come from HST. The Hubble was the first telescope in space. It was put into orbit by the space shuttle Discovery in 1990. Since then, four shuttle missions have gone to the Hubble to make repairs and upgrades. The last repair mission to the Hubble happened in 2009. An example of a HST image is in Figure 23.28, ",text,
L_0052,recent space exploration,T_0520,"We continue to explore the solar system. A rover is like a spacecraft on wheels (Figure 23.29). It can wheel around on the surface. Scientists on Earth tell it where to go. The craft then collects and sends back data from that locations. The Mars Pathfinder studied the red planet for nearly three months in 1997. Two more rovers, Spirit and Opportunity, landed on Mars in 2004. Both were only designed to last 90 days, but have lasted many times longer. Spirit sent back data until it became stuck in January 2010. Opportunity continues to explore Mars. Several spacecraft are currently in orbit, studying the Martian surface and thin atmosphere. ",text,
L_0052,recent space exploration,T_0520,"We continue to explore the solar system. A rover is like a spacecraft on wheels (Figure 23.29). It can wheel around on the surface. Scientists on Earth tell it where to go. The craft then collects and sends back data from that locations. The Mars Pathfinder studied the red planet for nearly three months in 1997. Two more rovers, Spirit and Opportunity, landed on Mars in 2004. Both were only designed to last 90 days, but have lasted many times longer. Spirit sent back data until it became stuck in January 2010. Opportunity continues to explore Mars. Several spacecraft are currently in orbit, studying the Martian surface and thin atmosphere. ",text,
L_0052,recent space exploration,T_0521,Budget concerns have impacted NASA in recent years. Many scientists have come together to discuss the goals of the U.S. space program. Some would like to further explore the Moon. Others are interested in landing on Mars. A variety of destinations in the inner solar system may also be visited. Private aerospace companies will play more of a role in the coming years. ,text,
L_0052,recent space exploration,T_0522,"How to Discover a New Planet Thousands of planets - ones that look totally different than what were used to, and possibly could support life, exist outside of our solar system. But were only just now starting to find them. In the video below, Ashley takes you behind the simple technique that astronomers have been using to discover these curious new planets. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0053,planet earth,T_0523,"As you walk, the ground usually looks pretty flat, even though the Earth is round. How do we know this? We have pictures of Earth taken from space that show that Earth is round. Astronauts aboard the Apollo 17 shuttle took this one, called The Blue Marble (Figure 24.1). Earth looks like a giant blue and white ball. Long before spacecraft took photos of Earth from space, people knew that Earth was round. How? One way was to look at ships sailing off into the distance. What do you see when you watch a tall ship sail over the horizon of the Earth? The bottom part of the ship disappears faster than the top part. What would that ship look like if Earth was flat? No part of it would disappear before the other. It would all just get smaller as it moved further away. In the solar system, the planets orbit around the Sun. The Sun and each of the planets of our solar system are round. Earth is the third planet from the Sun. It is one of the inner planets. Jupiter is an outer planet. It is the largest planet in the solar system at about 1,000 times the size of Earth. The Sun is about 1,000 times bigger than Jupiter! (Figure The outer planets in the solar system are giant balls of swirling gas. Earth and the other inner planets are relatively small, dense, and rocky. Most of Earths surface is covered with water. As far as we know, Earth is also the only planet that has liquid water. Earths atmosphere has oxygen. The water and oxygen are crucial to life as we know it. Earth appears to be the only planet in the solar system with living creatures. You can learn more about the planets in the Our Solar System chapter. Some of the different parts of the Earth are our: Since Earth is round, the layers all have the word sphere at the end (Figure 24.3). All of Earths layers interact. Therefore, Earths surface is constantly undergoing change. ",text,
L_0053,planet earth,T_0523,"As you walk, the ground usually looks pretty flat, even though the Earth is round. How do we know this? We have pictures of Earth taken from space that show that Earth is round. Astronauts aboard the Apollo 17 shuttle took this one, called The Blue Marble (Figure 24.1). Earth looks like a giant blue and white ball. Long before spacecraft took photos of Earth from space, people knew that Earth was round. How? One way was to look at ships sailing off into the distance. What do you see when you watch a tall ship sail over the horizon of the Earth? The bottom part of the ship disappears faster than the top part. What would that ship look like if Earth was flat? No part of it would disappear before the other. It would all just get smaller as it moved further away. In the solar system, the planets orbit around the Sun. The Sun and each of the planets of our solar system are round. Earth is the third planet from the Sun. It is one of the inner planets. Jupiter is an outer planet. It is the largest planet in the solar system at about 1,000 times the size of Earth. The Sun is about 1,000 times bigger than Jupiter! (Figure The outer planets in the solar system are giant balls of swirling gas. Earth and the other inner planets are relatively small, dense, and rocky. Most of Earths surface is covered with water. As far as we know, Earth is also the only planet that has liquid water. Earths atmosphere has oxygen. The water and oxygen are crucial to life as we know it. Earth appears to be the only planet in the solar system with living creatures. You can learn more about the planets in the Our Solar System chapter. Some of the different parts of the Earth are our: Since Earth is round, the layers all have the word sphere at the end (Figure 24.3). All of Earths layers interact. Therefore, Earths surface is constantly undergoing change. ",text,
L_0053,planet earth,T_0523,"As you walk, the ground usually looks pretty flat, even though the Earth is round. How do we know this? We have pictures of Earth taken from space that show that Earth is round. Astronauts aboard the Apollo 17 shuttle took this one, called The Blue Marble (Figure 24.1). Earth looks like a giant blue and white ball. Long before spacecraft took photos of Earth from space, people knew that Earth was round. How? One way was to look at ships sailing off into the distance. What do you see when you watch a tall ship sail over the horizon of the Earth? The bottom part of the ship disappears faster than the top part. What would that ship look like if Earth was flat? No part of it would disappear before the other. It would all just get smaller as it moved further away. In the solar system, the planets orbit around the Sun. The Sun and each of the planets of our solar system are round. Earth is the third planet from the Sun. It is one of the inner planets. Jupiter is an outer planet. It is the largest planet in the solar system at about 1,000 times the size of Earth. The Sun is about 1,000 times bigger than Jupiter! (Figure The outer planets in the solar system are giant balls of swirling gas. Earth and the other inner planets are relatively small, dense, and rocky. Most of Earths surface is covered with water. As far as we know, Earth is also the only planet that has liquid water. Earths atmosphere has oxygen. The water and oxygen are crucial to life as we know it. Earth appears to be the only planet in the solar system with living creatures. You can learn more about the planets in the Our Solar System chapter. Some of the different parts of the Earth are our: Since Earth is round, the layers all have the word sphere at the end (Figure 24.3). All of Earths layers interact. Therefore, Earths surface is constantly undergoing change. ",text,
L_0053,planet earth,T_0524,"Earth and Moon orbit each other. This Earth-Moon system orbits the Sun in a regular path (Figure 24.4). Gravity is the force of attraction between all objects. Gravity keeps the Earth and Moon in their orbits. Earths gravity pulls the Moon toward Earths center. Without gravity, the Moon would continue moving in a straight line off into space. All objects in the universe have a gravitational attraction to each other (Figure 24.5). The strength of the force of gravity depends on two things. They are the mass of the objects and the distance between them. The greater the objects mass, the greater the force of attraction. As the distance between the objects increases, the force of attraction decreases. ",text,
L_0053,planet earth,T_0525,"Earth has a magnetic field (Figure 24.6). The magnetic field has north and south poles. The field extends several thousand kilometers into space. Earths magnetic field is created by the movements of molten metal in the outer core. Earths magnetic field shields us from harmful radiation from the Sun (Figure 24.7). If you have a large bar magnet, you can hang it from a string. Then watch as it aligns itself in a north-south direction, in response to Earths magnetic field. A compass needle also aligns with Earths magnetic field. People can navigate by finding magnetic north (Figure 24.8). ",text,
L_0053,planet earth,T_0525,"Earth has a magnetic field (Figure 24.6). The magnetic field has north and south poles. The field extends several thousand kilometers into space. Earths magnetic field is created by the movements of molten metal in the outer core. Earths magnetic field shields us from harmful radiation from the Sun (Figure 24.7). If you have a large bar magnet, you can hang it from a string. Then watch as it aligns itself in a north-south direction, in response to Earths magnetic field. A compass needle also aligns with Earths magnetic field. People can navigate by finding magnetic north (Figure 24.8). ",text,
L_0053,planet earth,T_0525,"Earth has a magnetic field (Figure 24.6). The magnetic field has north and south poles. The field extends several thousand kilometers into space. Earths magnetic field is created by the movements of molten metal in the outer core. Earths magnetic field shields us from harmful radiation from the Sun (Figure 24.7). If you have a large bar magnet, you can hang it from a string. Then watch as it aligns itself in a north-south direction, in response to Earths magnetic field. A compass needle also aligns with Earths magnetic field. People can navigate by finding magnetic north (Figure 24.8). ",text,
L_0053,planet earth,T_0525,"Earth has a magnetic field (Figure 24.6). The magnetic field has north and south poles. The field extends several thousand kilometers into space. Earths magnetic field is created by the movements of molten metal in the outer core. Earths magnetic field shields us from harmful radiation from the Sun (Figure 24.7). If you have a large bar magnet, you can hang it from a string. Then watch as it aligns itself in a north-south direction, in response to Earths magnetic field. A compass needle also aligns with Earths magnetic field. People can navigate by finding magnetic north (Figure 24.8). ",text,
L_0053,planet earth,T_0525,"Earth has a magnetic field (Figure 24.6). The magnetic field has north and south poles. The field extends several thousand kilometers into space. Earths magnetic field is created by the movements of molten metal in the outer core. Earths magnetic field shields us from harmful radiation from the Sun (Figure 24.7). If you have a large bar magnet, you can hang it from a string. Then watch as it aligns itself in a north-south direction, in response to Earths magnetic field. A compass needle also aligns with Earths magnetic field. People can navigate by finding magnetic north (Figure 24.8). ",text,
L_0053,planet earth,T_0526,"Earths axis is an imaginary line passing through the North and South Poles. Earthsrotation is its spins on its axis. Rotation is what a top does around its spindle. As Earth spins on its axis, it also orbits around the Sun. This is called Earths revolution. These motions lead to the cycles we see. Day and night, seasons, and the tides are caused by Earths motions. ",text,
L_0053,planet earth,T_0527,"In 1851, Lon Foucault, a French scientist, hung a heavy iron weight from a long wire. He pulled the weight to one side and then released it. The weight swung back and forth in a straight line. If Earth did not rotate, the pendulum would not change direction as it was swinging. But it did, or at least it appeared to. The direction of the pendulum appeared to change because Earth rotated beneath it. Figure 24.9 shows how this might look. A Turn of the Earth In this video, MIT students demonstrate how a Foucault Pendulum is used to prove that the Earth is rotating. See the video at  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0053,planet earth,T_0528,"How long does it take Earth to spin once on its axis? One rotation is 24 hours. That rotation is the length of a day! Whatever time it is, the side of Earth facing the Sun has daylight. The side facing away from the Sun is dark. If you look at Earth from the North Pole, the planet spins counterclockwise. As the Earth rotates, you see the Sun moving across the sky from east to west. We often say that the Sun is rising or setting. The Sun rises in the east and sets in the west. Actually, it is the Earths rotation that makes it appear that way. The Moon and the stars at night also seem to rise in the east and set in the west. Earths rotation is also responsible for this too. As Earth turns, the Moon and stars change position in the sky. ",text,
L_0053,planet earth,T_0529,"The Earth is tilted 23 1/2 on its axis (Figure 24.10). This means that as the Earth rotates, one hemisphere has longer days with shorter nights. At the same time the other hemisphere has shorter days and longer nights. For example, in the Northern hemisphere summer begins on June 21. On this date, the North Pole is pointed directly toward the Sun. This is the longest day and shortest night of the year in the Northern Hemisphere. The South Pole is pointed away from the Sun. This means that the Southern Hemisphere experiences its longest night and shortest day (Figure 24.11). The hemisphere that is tilted away from the Sun is cooler because it receives less direct rays. As Earth orbits the Sun, the Northern Hemisphere goes from winter to spring, then summer and fall. The Southern Hemisphere does the opposite from summer to fall to winter to spring. When it is winter in the Northern hemisphere, it is summer in the Southern hemisphere, and vice versa. ",text,
L_0053,planet earth,T_0529,"The Earth is tilted 23 1/2 on its axis (Figure 24.10). This means that as the Earth rotates, one hemisphere has longer days with shorter nights. At the same time the other hemisphere has shorter days and longer nights. For example, in the Northern hemisphere summer begins on June 21. On this date, the North Pole is pointed directly toward the Sun. This is the longest day and shortest night of the year in the Northern Hemisphere. The South Pole is pointed away from the Sun. This means that the Southern Hemisphere experiences its longest night and shortest day (Figure 24.11). The hemisphere that is tilted away from the Sun is cooler because it receives less direct rays. As Earth orbits the Sun, the Northern Hemisphere goes from winter to spring, then summer and fall. The Southern Hemisphere does the opposite from summer to fall to winter to spring. When it is winter in the Northern hemisphere, it is summer in the Southern hemisphere, and vice versa. ",text,
L_0053,planet earth,T_0530,"Earths revolution around the Sun takes 365.24 days. That is equal to one year. The Earth stays in orbit around the Sun because of the Suns gravity (Figure 24.12). Earths orbit is not a circle. It is somewhat elliptical. So as we travel around the Sun, sometimes we are a little farther away from the Sun. Sometimes we are closer to the Sun. Students sometimes think the slightly oval shape of our orbit causes Earths seasons. Thats not true! The seasons are due to the tilt of Earths axis, as discussed above. ",text,
L_0054,earths moon,T_0531,"The Moon is Earths only natural satellite. The Moon is about one-fourth the size of Earth, 3,476 kilometers in diameter. Gravity on the Moon is only one-sixth as strong as it is on Earth. If you weigh 120 pounds on Earth, you would only weigh 20 pounds on the Moon. You can jump six times as high on the Moon as you can on Earth. The Moon makes no light of its own. Like every other body in the solar system, it only reflects light from the Sun. The Moon rotates on its axis once for every orbit it makes around the Earth. What does this mean? This means that the same side of the Moon always faces Earth. The side of the Moon that always faces Earth is called the near side. The side of the Moon that always faces away from Earth is called the far side (Figure 24.13). All people for all time have only seen the Moons near side. The far side has only been seen by spacecraft. The Moon has no atmosphere. With no atmosphere, the Moon is not protected from extreme temperatures. The average surface temperature during the day is approximately 107C (225F). Daytime temperatures can reach as high as 123C (253F). At night, the average temperature drops to -153C (-243F). The lowest temperatures measured are as low as -233C (-397F). ",text,
L_0054,earths moon,T_0532,"We all know what the Moon looks like. Its always looked the same during our lifetime. In fact, the Moon has looked the same to every person who has looked up at it for all time. Even the dinosaurs and trilobites, should they have looked up at it, would have seen the same thing. This is not true of Earth. Natural processes continually alter the Earths surface. Without these processes, would Earths surface resemble the Moons? Even though we cant see it from Earth, the Moon has changed recently too. Astronauts footprints are now on the Moon. They will remain unchanged for thousands of years, because there is no wind, rain, or living thing to disturb them. Only a falling meteorite could destroy them. ",text,
L_0054,earths moon,T_0533,"The landscape of the Moon - its surface features - is very different from Earth. The lunar landscape is covered by craters caused by asteroid impacts (Figure 24.14). The craters are bowl-shaped basins on the Moons surface. Because the Moon has no water, wind, or weather, the craters remain unchanged. The Moons coldest temperatures are found deep in the craters. The coldest craters are at the south pole on the Moons far side, where the Sun never shines. These temperatures are amongst the coldest in our entire solar system. ",text,
L_0054,earths moon,T_0534,"When you look at the Moon from Earth, you notice dark and light areas. The maria are dark, solid, flat areas of lava. Maria covers around 16% of the Moons surface, mostly on the near side. The maria formed about 3.0 to 3.5 billion years ago, when the Moon was continually bombarded by meteorites (Figure 24.15). Large meteorites broke through the Moons newly formed surface. This caused magma to flow out and fill the craters. Scientists estimate volcanic activity on the Moon ended about 1.2 billion years ago. The lighter parts on the Moon are called terrae, or highlands (Figure 24.15). They are higher than the maria and include several high mountain ranges. The rock that makes up the highlands is lighter in color and crystallized more slowly than the maria. The rock looks light because it reflects more of the Suns light. ",text,
L_0054,earths moon,T_0534,"When you look at the Moon from Earth, you notice dark and light areas. The maria are dark, solid, flat areas of lava. Maria covers around 16% of the Moons surface, mostly on the near side. The maria formed about 3.0 to 3.5 billion years ago, when the Moon was continually bombarded by meteorites (Figure 24.15). Large meteorites broke through the Moons newly formed surface. This caused magma to flow out and fill the craters. Scientists estimate volcanic activity on the Moon ended about 1.2 billion years ago. The lighter parts on the Moon are called terrae, or highlands (Figure 24.15). They are higher than the maria and include several high mountain ranges. The rock that makes up the highlands is lighter in color and crystallized more slowly than the maria. The rock looks light because it reflects more of the Suns light. ",text,
L_0054,earths moon,T_0535,"There are no lakes, rivers, or even small puddles anywhere to be found on the Moons surface. So there is no running water and no atmosphere. This means that there is no erosion. Natural processes continually alter the Earths surface. Without these processes, our planets surface would be covered with meteorite craters just like the Moon. Many moons in our solar system have cratered surfaces. NASA scientists have discovered a large number of water molecules mixed in with lunar dirt. There is also surface water ice. Even though there is a very small amount of water, there is no atmosphere. Temperatures are extreme. So it comes as no surprise that there has not been evidence of life on the Moon. ",text,
L_0054,earths moon,T_0536,"Like Earth, the Moon has a distinct crust, mantle, and core. The crust is composed of igneous rock. This rock is rich in the elements oxygen, silicon, magnesium, and aluminum. On the near side, the Moons crust is about 60 kilometers thick. On the far side, the crust is about 100 kilometers thick. The mantle is made of rock like Earths mantle. The Moon has a small metallic core, perhaps 600 to 800 kilometers in diameter. The composition of the core is probably mostly iron with some sulfur and nickel. We learned this both from the rock samples gathered by astronauts and from spacecraft sent to the Moon. ",text,
L_0055,the sun,T_0537,"The Sun is made almost entirely of the elements hydrogen and helium. The Sun has no solid material. Most atoms in the Sun exist as plasma. Plasma is superheated gas with an electrical charge. Because the Sun is made of gases, it does not have a defined outer boundary. Like Earth, the Sun has an internal structure. The inner three layers make up what we would actually call the Sun. ",text,
L_0055,the sun,T_0538,"The core is the Suns innermost layer. The core is plasma. It has a temperature of around 15 million degrees Celsius (C). Nuclear fusion reactions create the immense temperature. In these reactions, hydrogen atoms fuse to form helium. This releases vast amounts of energy. The energy moves towards the outer layers of the Sun. Energy from the Suns core powers most of the solar system. ",text,
L_0055,the sun,T_0539,"The radiative zone is the next layer out. It has a temperature of about 4 million degrees C. Energy from the core travels through the radiative zone. The rate the energy travels is extremely slow. Light particles, called photons, can only travel a few millimeters before they hit another particle. The particles are absorbed and then released again. It may take 50 million years for a photon to travel all the way through the radiative zone. ",text,
L_0055,the sun,T_0540,"The convection zone surrounds the radiative zone. In the convection zone, hot material from near the Suns center rises. This material cools at the surface, and then plunges back downward. The material then receives more heat from the radiative zone. ",text,
L_0055,the sun,T_0541,The three outer layers of the Sun are its atmosphere. ,text,
L_0055,the sun,T_0542,"The photosphere is the visible surface of the Sun (Figure 24.17). Its the part that we see shining. Surprisingly, the photosphere is also one of the coolest layers of the Sun. It is only about 6000 degrees C. ",text,
L_0055,the sun,T_0543,"The chromosphere lies above the photosphere. It is about 2,000 km thick. The thin chromosphere is heated by energy from the photosphere. Temperatures range from about 4000 degrees C to about 10,000 degrees C. The chromosphere is not as hot as other parts of the Sun, and it glows red. Jets of gas sometimes fly up through the chromosphere. With speeds up to 72,000 km per hour, the jets can fly as high as 10,000 kilometers. ",text,
L_0055,the sun,T_0544,"The corona is the outermost part of the Suns atmosphere. It is the Suns halo, or crown. With a temperature of 1 to 3 million K, the corona is much hotter than the photosphere. The corona extends millions of kilometers into space. Sometime you should try to see a total solar eclipse. If you do you will see the Suns corona shining out into space. ",text,
L_0055,the sun,T_0545,The Sun has many incredible surface features. Dont try to look at them though! Looking directly at the Sun can cause blindness. Find the appropriate filters for a pair of binoculars or a telescope and enjoy! ,text,
L_0055,the sun,T_0546,"The most noticeable magnetic activity of the Sun is the appearance of sunspots. Sunspots are cooler, darker areas on the Suns surface (Figure 24.18). Sunspots occur in an 11 year cycle. The number of sunspots begins at a minimum. The number gradually increases to the maximum. Then the number returns to a minimum again. Sunspots form because loops of the Suns magnetic field break through the surface. Sunspots usually occur in pairs. The loop breaks through the surface where it comes out of the Sun. It breaks through again where it goes back into the Sun. Sunspots disrupt the transfer of heat from the Suns lower layers. ",text,
L_0055,the sun,T_0547,"A loop of the Suns magnetic field may break. This creates solar flares. Solar flares are violent explosions that release huge amounts of energy (Figure 24.19). The streams of high energy particles they emit make up the solar wind. Solar wind is dangerous to spacecraft and astronauts. Solar flares can even cause damage on Earth. They have knocked out entire power grids and can disturb radio, satellite, and cell phone communications. ",text,
L_0055,the sun,T_0548,"Another amazing feature on the Sun is solar prominences. Plasma flows along the loop that connects sunspots. This plasma forms a glowing arch. The arch is a solar prominence. Solar prominences can reach thousands of kilometers into the Suns atmosphere. Prominences can last for a day to several months. Prominences can be seen during a total solar eclipse. NASAs Solar Dynamics Observatory (SDO) was launched on February 11, 2010. SDO is studying the Suns magnetic field. This includes how the Sun affects Earths atmosphere and climate. SDO provides extremely high resolution images. The craft gathers data faster than anything that ever studied the Sun. To learn more about the SDO mission, visit: http://sdo.gsfc.nasa.gov To find these videos for download, check out:  There are other ways to connect with NASA. Subscribe to NASAs Goddard Shorts HD podcast (http://svs.gsfc.nasa ",text,
L_0056,the sun and the earthmoon system,T_0549,"When a new moon passes directly between the Earth and the Sun, it causes a solar eclipse (Figure 24.20). The Moon casts a shadow on the Earth and blocks our view of the Sun. This happens only all three are lined up and in the same plane. This plane is called the ecliptic. The ecliptic is the plane of Earths orbit around the Sun. The Moons shadow has two distinct parts. The umbra is the inner, cone-shaped part of the shadow. It is the part in which all of the light has been blocked. The penumbra is the outer part of Moons shadow. It is where the light is only partially blocked. When the Moons shadow completely blocks the Sun, it is a total solar eclipse (Figure 24.21). If only part of the Sun is out of view, it is a partial solar eclipse. Solar eclipses are rare events. They usually only last a few minutes. That is because the Moons shadow only covers a very small area on Earth and Earth is turning very rapidly. Solar eclipses are amazing to experience. It appears like night only strange. Birds may sing as they do at dusk. Stars become visible in the sky and it gets colder outside. Unlike at night, the Sun is out. So during a solar eclipse, its easy to see the Suns corona and solar prominences. This NASA page will inform you on when solar eclipses are expected: http://eclipse.gsfc.nasa.gov/solar.html ",text,
L_0056,the sun and the earthmoon system,T_0549,"When a new moon passes directly between the Earth and the Sun, it causes a solar eclipse (Figure 24.20). The Moon casts a shadow on the Earth and blocks our view of the Sun. This happens only all three are lined up and in the same plane. This plane is called the ecliptic. The ecliptic is the plane of Earths orbit around the Sun. The Moons shadow has two distinct parts. The umbra is the inner, cone-shaped part of the shadow. It is the part in which all of the light has been blocked. The penumbra is the outer part of Moons shadow. It is where the light is only partially blocked. When the Moons shadow completely blocks the Sun, it is a total solar eclipse (Figure 24.21). If only part of the Sun is out of view, it is a partial solar eclipse. Solar eclipses are rare events. They usually only last a few minutes. That is because the Moons shadow only covers a very small area on Earth and Earth is turning very rapidly. Solar eclipses are amazing to experience. It appears like night only strange. Birds may sing as they do at dusk. Stars become visible in the sky and it gets colder outside. Unlike at night, the Sun is out. So during a solar eclipse, its easy to see the Suns corona and solar prominences. This NASA page will inform you on when solar eclipses are expected: http://eclipse.gsfc.nasa.gov/solar.html ",text,
L_0056,the sun and the earthmoon system,T_0550,"Sometimes a full moon moves through Earths shadow. This is a lunar eclipse (Figure 24.22). During a total lunar eclipse, the Moon travels completely in Earths umbra. During a partial lunar eclipse, only a portion of the Moon enters Earths umbra. When the Moon passes through Earths penumbra, it is a penumbral eclipse. Since Earths shadow is large, a lunar eclipse lasts for hours. Anyone with a view of the Moon can see a lunar eclipse. Partial lunar eclipses occur at least twice a year, but total lunar eclipses are less common. The Moon glows with a dull red coloring during a total lunar eclipse. ",text,
L_0056,the sun and the earthmoon system,T_0551,"The Moon does not produce any light of its own. It only reflects light from the Sun. As the Moon moves around the Earth, we see different parts of the Moon lit up by the Sun. This causes the phases of the Moon. As the Moon revolves around Earth, it changes from fully lit to completely dark and back again. A full moon occurs when the whole side facing Earth is lit. This happens when Earth is between the Moon and the Sun. About one week later, the Moon enters the quarter-moon phase. Only half of the Moons lit surface is visible from Earth, so it appears as a half circle. When the Moon moves between Earth and the Sun, the side facing Earth is completely dark. This is called the new moon phase. Sometimes you can just barely make out the outline of the new moon in the sky. This is because some sunlight reflects off the Earth and hits the Moon. Before and after the quarter-moon phases are the gibbous and crescent phases. During the crescent moon phase, the Moon is less than half lit. It is seen as only a sliver or crescent shape. During the gibbous moon phase, the Moon is more than half lit. It is not full. The Moon undergoes a complete cycle of phases about every 29.5 days. ",text,
L_0056,the sun and the earthmoon system,T_0552,,text,
L_0057,introduction to the solar system,T_0553,"The Sun and all the objects that are held by the Suns gravity are known as the solar system. These objects all revolve around the Sun. The ancient Greeks recognized five planets. These lights in the night sky changed their position against the background of stars. They appeared to wander. In fact, the word planet comes from a Greek word meaning wanderer. These objects were thought to be important, so they named them after gods from their mythology. The names for the planets Mercury, Venus, Mars, Jupiter, and Saturn came from the names of gods and a goddess. ",text,
L_0057,introduction to the solar system,T_0554,"The ancient Greeks thought that Earth was at the center of the universe, as shown in Figure 25.1. The sky had a set of spheres layered on top of one another. Each object in the sky was attached to one of these spheres. The object moved around Earth as that sphere rotated. These spheres contained the Moon, the Sun, and the five planets they recognized: Mercury, Venus, Mars, Jupiter, and Saturn. An outer sphere contained all the stars. The planets appear to move much faster than the stars, so the Greeks placed them closer to Earth. Ptolemy published this model of the solar system around 150 AD. ",text,
L_0057,introduction to the solar system,T_0555,"About 1,500 years after Ptolemy, Copernicus proposed a startling idea. He suggested that the Sun is at the center of the universe. Copernicus developed his model because it better explained the motions of the planets. Figure 25.2 shows both the Earth-centered and Sun-centered models. Copernicus did not publish his new model until his death. He knew that it was heresy to say that Earth was not the center of the universe. It wasnt until Galileo developed his telescope that people would take the Copernican ",text,
L_0057,introduction to the solar system,T_0556,"Today we know that we have eight planets, five dwarf planets, over 165 moons, and many, many asteroids and other small objects in our solar system. We also know that the Sun is not the center of the universe. But it is the center of the solar system. Figure 25.3 shows our solar system. The planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Table 25.1 gives some data on the mass and diameter of the Sun and planets relative to Earth. Object Mass (Relative to Earth) Sun Mercury Venus Earth Mars Jupiter Saturn Uranus 333,000 Earths mass 0.06 Earths mass 0.82 Earths mass 1.00 Earths mass 0.11 Earths mass 317.8 Earths mass 95.2 Earths mass 14.6 Earths mass Diameter of Planet (Relative to Earth) 109.2 Earths diameter 0.39 Earths diameter 0.95 Earths diameter 1.00 Earths diameter 0.53 Earths diameter 11.21 Earths diameter 9.41 Earths diameter 3.98 Earths diameter Neptune 17.2 Earths mass ",text,
L_0057,introduction to the solar system,T_0557,"Youve probably heard about Pluto. When it was discovered in 1930, Pluto was called the ninth planet. Astronomers later found out that Pluto was not like other planets. For one thing, what they were calling Pluto was not a single object. They were actually seeing Pluto and its moon, Charon. In older telescopes, they looked like one object. This one object looked big enough to be a planet. Alone, Pluto was not very big. Astronomers also discovered many objects like Pluto. They were rocky and icy and there were a whole lot of them. Astronomers were faced with a problem. They needed to call these other objects planets. Or they needed to decide that Pluto was something else. In 2006, these scientists decided what a planet is. According to the new definition, a planet must: Orbit a star. Be big enough that its own gravity causes it to be round. Be small enough that it isnt a star itself. Have cleared the area of its orbit of smaller objects. If the first three are true but not the fourth, then that object is a dwarf planet. We now call Pluto a dwarf planet. There are other dwarf planets in the solar system. They are Eris, Ceres, Makemake and Haumea. There are many other reasons why Pluto does not fit with the other planets in our solar system. ",text,
L_0057,introduction to the solar system,T_0558,"Figure 25.4 shows the Sun and planets with the correct sizes. The distances between them are way too small. In general, the farther away from the Sun, the greater the distance from one planets orbit to the next. In Figure 25.5, you can see that the orbits of the planets are nearly circular. Plutos orbit is a much longer ellipse. Some astronomers think Pluto was dragged into its orbit by Neptune. Distances in the solar system are often measured in astronomical units (AU). One astronomical unit is defined as the distance from Earth to the Sun. 1 AU equals about 150 million km (93 million miles). Table 25.2 shows the distance from the Sun to each planet in AU. The table shows how long it takes each planet to spin on its axis. It also shows how long it takes each planet to complete an orbit. Notice how slowly Venus rotates! A day on Venus is actually longer than a year on Venus! Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Average Distance from Sun (AU) 0.39 AU 0.72 1.00 1.52 5.20 9.54 19.22 30.06 Length of Day (In Earth Days) 56.84 days 243.02 1.00 1.03 0.41 0.43 0.72 0.67 Length of Year Earth Years) 0.24 years 0.62 1.00 1.88 11.86 29.46 84.01 164.8 (In ",text,
L_0057,introduction to the solar system,T_0558,"Figure 25.4 shows the Sun and planets with the correct sizes. The distances between them are way too small. In general, the farther away from the Sun, the greater the distance from one planets orbit to the next. In Figure 25.5, you can see that the orbits of the planets are nearly circular. Plutos orbit is a much longer ellipse. Some astronomers think Pluto was dragged into its orbit by Neptune. Distances in the solar system are often measured in astronomical units (AU). One astronomical unit is defined as the distance from Earth to the Sun. 1 AU equals about 150 million km (93 million miles). Table 25.2 shows the distance from the Sun to each planet in AU. The table shows how long it takes each planet to spin on its axis. It also shows how long it takes each planet to complete an orbit. Notice how slowly Venus rotates! A day on Venus is actually longer than a year on Venus! Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Average Distance from Sun (AU) 0.39 AU 0.72 1.00 1.52 5.20 9.54 19.22 30.06 Length of Day (In Earth Days) 56.84 days 243.02 1.00 1.03 0.41 0.43 0.72 0.67 Length of Year Earth Years) 0.24 years 0.62 1.00 1.88 11.86 29.46 84.01 164.8 (In ",text,
L_0057,introduction to the solar system,T_0559,"Planets are held in their orbits by the force of gravity. What would happen without gravity? Imagine that you are swinging a ball on a string in a circular motion. Now let go of the string. The ball will fly away from you in a straight line. It was the string pulling on the ball that kept the ball moving in a circle. The motion of a planet is very similar to the ball on a string. The force pulling the planet is the pull of gravity between the planet and the Sun. Every object is attracted to every other object by gravity. The force of gravity between two objects depends on the mass of the objects. It also depends on how far apart the objects are. When you are sitting next to your dog, there is a gravitational force between the two of you. That force is far too weak for you to notice. You can feel the force of gravity between you and Earth because Earth has a lot of mass. The force of gravity between the Sun and planets is also very large. This is because the Sun and the planets are very large objects. Gravity is great enough to hold the planets to the Sun even though the distances between them are enormous. Gravity also holds moons in orbit around planets. ",text,
L_0057,introduction to the solar system,T_0560,"Since the early 1990s, astronomers have discovered other solar systems. A solar system has one or more planets orbiting one or more stars. We call these planets extrasolar planets, or exoplanets. They are called exoplanets because they orbit a star other than the Sun. As of June 2013, 891 exoplanets have been found. More exoplanets are found all the time. You can check out how many we have found at http://planetquest.jpl.nasa.gov/. We have been able to take pictures of only a few exoplanets. Most are discovered because of some tell-tale signs. One sign is a very slight motion of a star that must be caused by the pull of a planet. Another sign is the partial dimming of a stars light as the planet passes in front of it. ",text,
L_0057,introduction to the solar system,T_0561,"To figure out how the solar system formed, we need to put together what we have learned. There are two other important features to consider. First, all the planets orbit in nearly the same flat, disk-like region. Second, all the planets orbit in the same direction around the Sun. These two features are clues to how the solar system formed. ",text,
L_0057,introduction to the solar system,T_0562,"Scientists think the solar system formed from a big cloud of gas and dust, called a nebula. This is the solar nebula hypothesis. The nebula was made mostly of hydrogen and helium. There were heavier elements too. Gravity caused the nebula to contract (Figure 25.6). As the nebula contracted, it started to spin. As it got smaller and smaller, it spun faster and faster. This is what happens when an ice skater pulls her arms to her sides during a spin move. She spins faster. The spinning caused the nebula to form into a disk shape. This model explains why all the planets are found in the flat, disk-shaped region. It also explains why all the planets revolve in the same direction. The solar system formed from the nebula about 4.6 billion years ago ",text,
L_0057,introduction to the solar system,T_0563,"The Sun was the first object to form in the solar system. Gravity pulled matter together to the center of the disk. Density and pressure increased tremendously. Nuclear fusion reactions begin. In these reactions, the nuclei of atoms come together to form new, heavier chemical elements. Fusion reactions release huge amounts of nuclear energy. From these reactions a star was born, the Sun. Meanwhile, the outer parts of the disk were cooling off. Small pieces of dust started clumping together. These clumps collided and combined with other clumps. Larger clumps attracted smaller clumps with their gravity. Eventually, all these pieces grew into the planets and moons that we find in our solar system today. The outer planets Jupiter, Saturn, Uranus, and Neptune condensed from lighter materials. Hydrogen, helium, water, ammonia, and methane were among them. Its so cold by Jupiter and beyond that these materials can form solid particles. Closer to the Sun, they are gases. Since the gases can escape, the inner planets Mercury, Venus, Earth, and Mars formed from denser elements. These elements are solid even when close to the Sun. ",text,
L_0058,inner planets,T_0564,"Mercury is the smallest planet. It has no moon. The planet is also closest to the Sun and appears in Figure 25.7. As Figure 25.8 shows, the surface of Mercury is covered with craters, like Earths Moon. The presence of impact craters that are so old means that Mercury hasnt changed much geologically for billions of years. With only a trace of an atmosphere, it has no weather to wear down the ancient craters. Because Mercury is so close to the Sun, it is difficult to observe from Earth, even with a telescope. The Mariner 10 spacecraft did a flyby of Mercury in 19741975, which was the best data from the planet for decades. In 2004, the MESSENGER mission left Earth. On its way to Mercury it did one flyby of Earth, two of Venus and three of Mercury. In March 2011, MESSENGER became the first spacecraft to enter an orbit around Mercury. During its year-long mission, the craft will map the planets surface and conduct other studies. One of these images can be seen in Figure 25.9. ",text,
L_0058,inner planets,T_0564,"Mercury is the smallest planet. It has no moon. The planet is also closest to the Sun and appears in Figure 25.7. As Figure 25.8 shows, the surface of Mercury is covered with craters, like Earths Moon. The presence of impact craters that are so old means that Mercury hasnt changed much geologically for billions of years. With only a trace of an atmosphere, it has no weather to wear down the ancient craters. Because Mercury is so close to the Sun, it is difficult to observe from Earth, even with a telescope. The Mariner 10 spacecraft did a flyby of Mercury in 19741975, which was the best data from the planet for decades. In 2004, the MESSENGER mission left Earth. On its way to Mercury it did one flyby of Earth, two of Venus and three of Mercury. In March 2011, MESSENGER became the first spacecraft to enter an orbit around Mercury. During its year-long mission, the craft will map the planets surface and conduct other studies. One of these images can be seen in Figure 25.9. ",text,
L_0058,inner planets,T_0565,"Mercury is named for the Roman messenger god. Mercury was a messenger because he could run extremely fast. The Greeks gave the planet this name because Mercury moves very quickly in its orbit around the Sun. Mercury orbits the Sun in just 88 Earth days. Mercury has a very short year, but it also has very long days. Mercury rotates slowly on its axis, turning exactly three times for every two times it orbits the Sun. Therefore, each day on Mercury is 58 Earth days long. ",text,
L_0058,inner planets,T_0566,"Mercury is very close to the Sun, so it can get very hot. Mercury also has virtually no atmosphere. As the planet rotates very slowly, the temperature varies tremendously. In direct sunlight, the surface can be as hot as 427C (801F). On the dark side, the surface can be as cold as 183C (297F)! The coldest temperatures may be on the insides of craters. Most of Mercury is extremely dry. Scientists think that there may be a small amount of water, in the form of ice, at the planets poles. The poles never receive direct sunlight. ",text,
L_0058,inner planets,T_0567,Figure 25.10 shows a diagram of Mercurys interior. Mercury is one of the densest planets. Scientists think that the interior contains a large core made mostly of melted iron. Mercurys core takes up about 42% of the planets volume. Mercurys highly cratered surface is evidence that Mercury is not geologically active. ,text,
L_0058,inner planets,T_0568,"Named after the Roman goddess of love, Venus is the only planet named after a female. Venus is sometimes called Earths sister planet. But just how similar is Venus to Earth? Venus is our nearest neighbor. Venus is most like Earth in size. ",text,
L_0058,inner planets,T_0569,"Viewed through a telescope, Venus looks smooth and featureless. The planet is covered by a thick layer of clouds. You can see the clouds in pictures of Venus, such as Figure 25.11. We make maps of the surface using radar, because the thick clouds wont allow us to take photographs of the surface of Venus. Figure 25.12 shows the topographical features of Venus. The image was produced by the Magellan probe on a flyby. Radar waves sent by the spacecraft reveal mountains, valleys, vast lava plains, and canyons. Like Mercury, Venus does not have a moon. Clouds on Earth are made of water vapor. Venuss clouds are a lot less pleasant. They are made of carbon dioxide, sulfur dioxide and large amounts of corrosive sulfuric acid! The atmosphere of Venus is so thick that the pressure on the surface of Venus is very high. In fact, it is 90 times greater than the pressure at Earths surface! The thick atmosphere causes a strong greenhouse effect. As a result, Venus is the hottest planet. Even though it is farther from the Sun, Venus is much hotter even than Mercury. Temperatures at the surface reach 465C (860F). Thats hot enough to melt lead! ",text,
L_0058,inner planets,T_0570,"Venus has more volcanoes than any other planet. There are between 100,000 and one million volcanoes on Venus! Most of the volcanoes are now inactive. There are also a large number of craters. This means that Venus doesnt have tectonic plates. Plate tectonics on Earth erases features over time. Figure 25.13 is an image made using radar data. The volcano is Maat Mons. Lava beds are in the foreground. Scientists think the color of sunlight on Venus is ",text,
L_0058,inner planets,T_0570,"Venus has more volcanoes than any other planet. There are between 100,000 and one million volcanoes on Venus! Most of the volcanoes are now inactive. There are also a large number of craters. This means that Venus doesnt have tectonic plates. Plate tectonics on Earth erases features over time. Figure 25.13 is an image made using radar data. The volcano is Maat Mons. Lava beds are in the foreground. Scientists think the color of sunlight on Venus is ",text,
L_0058,inner planets,T_0570,"Venus has more volcanoes than any other planet. There are between 100,000 and one million volcanoes on Venus! Most of the volcanoes are now inactive. There are also a large number of craters. This means that Venus doesnt have tectonic plates. Plate tectonics on Earth erases features over time. Figure 25.13 is an image made using radar data. The volcano is Maat Mons. Lava beds are in the foreground. Scientists think the color of sunlight on Venus is ",text,
L_0058,inner planets,T_0571,"Venus is the only planet that rotates clockwise as viewed from its North Pole. All of the other planets rotate counterclockwise. Venus turns slowly, making only one turn every 243 days. This is longer than a year on Venus! It takes Venus only 225 days to orbit the Sun. Because the orbit of Venus is inside Earths orbit, Venus always appears close to the Sun. You can see Venus rising early in the morning, just before the Sun rises. For this reason, Venus is sometimes called the morning star. When it sets in the evening, just after the Sun sets, it may be called the evening star. Since planets only reflect the Suns light, Venus should not be called a star at all! Venus is very bright because its clouds reflect sunlight very well. Venus is the brightest object in the sky besides the Sun and the Moon. ",text,
L_0058,inner planets,T_0572,"Earth is the third planet out from the Sun, shown in Figure 25.14. Because it is our planet, we know a lot more about Earth than we do about any other planet. What are main features of Earth? ",text,
L_0058,inner planets,T_0573,"Earth is a very diverse planet, seen in Figure 25.14. Water appears as vast oceans of liquid. Water is also seen as ice at the poles or as clouds of vapor. Earth also has large masses of land. Earths average surface temperature is 14C (57F). At this temperature, water is a liquid. The oceans and the atmosphere help keep Earths surface temperatures fairly steady. Earth is the only planet known to have life. Conditions on Earth are ideal for life! The atmosphere filters out harmful radiation. Water is abundant. Carbon dioxide was available for early life forms. The evolution of plants introduced more oxygen for animals. ",text,
L_0058,inner planets,T_0574,"The Earth is divided into many plates. These plates move around on the surface. The plates collide or slide past each other. One may even plunge beneath another. Plate motions cause most geological activity. This activity includes earthquakes, volcanoes, and the buildup of mountains. The reason for plate movement is convection in the mantle. Earth is the only planet that we know has plate tectonics. ",text,
L_0058,inner planets,T_0575,"Earth rotates on its axis once every 24 hours. This is the length of an Earth day. Earth orbits the Sun once every 365.24 days. This is the length of an Earth year. Earth has one large moon. This satellite orbits Earth once every 29.5 days. This moon is covered with craters, and also has large plains of lava. The Moon came into being from material that flew into space after Earth and a giant asteroid collided. This moon is not a captured asteroid like other moons in the solar system. ",text,
L_0058,inner planets,T_0576,"Mars, shown in Figure 25.15, is the fourth planet from the Sun. The Red Planet is the first planet beyond Earths orbit. Mars atmosphere is thin compared to Earths. This means that there is much lower pressure at the surface. Mars also has a weak greenhouse effect, so temperatures are only slightly higher than they would be if the planet did not have an atmosphere. Mars is the easiest planet to observe. As a result, it has been studied more than any other planet besides Earth. People can stand on Earth and observe the planet through a telescope. We have also sent many space probes to Mars. In April 2011, there were three scientific satellites in orbit around Mars. The rover, Opportunity, was still moving around on the surface. No humans have ever set foot on Mars. NASA and the European Space Agency have plans to send people to Mars. The goal is to do it sometime between 2030 and 2040. The expense and danger of these missions are phenomenal. ",text,
L_0058,inner planets,T_0577,"Viewed from Earth, Mars is red. This is due to large amounts of iron in the soil. The ancient Greeks and Romans named the planet Mars after the god of war. The planets red color reminded them of blood. Mars has only a very thin atmosphere, made up mostly of carbon dioxide. ",text,
L_0058,inner planets,T_0578,"Mars is home to the largest volcano in the solar system. Olympus Mons is shown in Figure 25.16. Olympus Mons is a shield volcano. The volcano is similar to the volcanoes of the Hawaiian Islands. But Olympus Mons is a giant, about 27 km (16.7 miles/88,580 ft) tall. Thats three times taller than Mount Everest! At its base, Olympus Mons is about the size of the entire state of Arizona. Mars also has the largest canyon in the solar system, Valles Marineris (Figure 25.17). This canyon is 4,000 km (2,500 miles) long. Thats as long as Europe is wide! One-fifth of the circumference of Mars is covered by the canyon. Valles Marineris is 7 km (4.3 miles) deep. How about Earths Grand Canyon? Earths most famous canyon is only 446 km (277 miles) long and about 2 km (1.2 miles) deep. Mars has mountains, canyons, and other features similar to Earth. But it doesnt have as much geological activity as Earth. There is no evidence of plate tectonics on Mars. There are also more craters on Mars than on Earth. Buy there are fewer craters than on the Moon. What does this suggest to you regarding Mars plate tectonic history? ",text,
L_0058,inner planets,T_0578,"Mars is home to the largest volcano in the solar system. Olympus Mons is shown in Figure 25.16. Olympus Mons is a shield volcano. The volcano is similar to the volcanoes of the Hawaiian Islands. But Olympus Mons is a giant, about 27 km (16.7 miles/88,580 ft) tall. Thats three times taller than Mount Everest! At its base, Olympus Mons is about the size of the entire state of Arizona. Mars also has the largest canyon in the solar system, Valles Marineris (Figure 25.17). This canyon is 4,000 km (2,500 miles) long. Thats as long as Europe is wide! One-fifth of the circumference of Mars is covered by the canyon. Valles Marineris is 7 km (4.3 miles) deep. How about Earths Grand Canyon? Earths most famous canyon is only 446 km (277 miles) long and about 2 km (1.2 miles) deep. Mars has mountains, canyons, and other features similar to Earth. But it doesnt have as much geological activity as Earth. There is no evidence of plate tectonics on Mars. There are also more craters on Mars than on Earth. Buy there are fewer craters than on the Moon. What does this suggest to you regarding Mars plate tectonic history? ",text,
L_0058,inner planets,T_0579,"Water on Mars cant be a liquid. This is because the pressure of the atmosphere is too low. The planet does have a lot of water; it is in the form of ice. The south pole of Mars has a very visible ice cap. Scientists also have evidence that there is also a lot of ice just under the Martian surface. The ice melts when volcanoes erupt. At this times liquid water flows across the surface. Scientists think that there was once liquid water on the planet. There are many surface features that look like water- eroded canyons. The Mars rover collected round clumps of crystals that, on Earth, usually form in water. If there was liquid water on Mars, life might have existed there in the past. ",text,
L_0058,inner planets,T_0580,"Mars has two very small, irregular moons, Phobos (seen in Figure 25.18) and Deimos. These moons were discovered in 1877. They are named after the two sons of Ares, who followed their father into war. The moons were probably asteroids that were captured by Martian gravity. ",text,
L_0059,outer planets,T_0581,"Jupiter, shown in Figure 25.19, is the largest planet in our solar system. Jupiter is named for the king of the gods in Roman mythology. Jupiter is truly a giant! The planet has 318 times the mass of Earth, and over 1,300 times Earths volume. So Jupiter is much less dense than Earth. Because Jupiter is so large, it reflects a lot of sunlight. When it is visible, it is the brightest object in the night sky besides the Moon and Venus. Jupiter is quite far from the Earth. The planet is more than five times as far from Earth as the Sun. It takes Jupiter about 12 Earth years to orbit once around the Sun. ",text,
L_0059,outer planets,T_0582,"Since Jupiter is a gas giant, could a spacecraft land on its surface? The answer is no. There is no solid surface at all! Jupiter is made mostly of hydrogen, with some helium, and small amounts of other elements. The outer layers of the planet are gas. Deeper within the planet, the intense pressure condenses the gases into a liquid. Jupiter may have a small rocky core at its center. ",text,
L_0059,outer planets,T_0583,"Jupiters atmosphere is unlike any other in the solar system! The upper layer contains clouds of ammonia. The ammonia is different colored bands. These bands rotate around the planet. The ammonia also swirls around in tremendous storms. The Great Red Spot, shown in Figure 25.20, is Jupiters most noticeable feature. The spot is an enormous, oval-shaped storm. It is more than three times as wide as the entire Earth! Clouds in the storm rotate counterclockwise. They make one complete turn every six days or so. The Great Red Spot has been on Jupiter for at least 300 years. It may have been observed as early as 1664. It is possible that this storm is a permanent feature on Jupiter. No one knows for sure. ",text,
L_0059,outer planets,T_0584,"Jupiter has lots of moons. As of 2011, we have discovered over 60 natural satellites of Jupiter. Four are big enough and bright enough to be seen from Earth using a pair of binoculars. These four moons were first discovered by Galileo in 1610. They are called the Galilean moons. Figure 25.21 shows the four Galilean moons and their sizes relative to Jupiters Great Red Spot. These moons are named Io, Europa, Ganymede, and Callisto. The Galilean moons are larger than even the biggest dwarf planets, Pluto and Eris. Ganymede is the biggest moon in the solar system. It is even larger than the planet Mercury! Scientists think that Europa is a good place to look for extraterrestrial life. Europa is the smallest of the Galilean moons. The moons surface is a smooth layer of ice. Scientists think that the ice may sit on top of an ocean of liquid water. How could Europa have liquid water when it is so far from the Sun? Europa is heated by Jupiter. Jupiters tidal forces are so great that they stretch and squash its moon. This could produce enough heat for there to be liquid water. Numerous missions have been planned to explore Europa, including plans to drill through the ice and send a probe into the ocean. However, no such mission has yet been attempted. In 1979, two spacecrafts, Voyager 1 and Voyager 2, visited Jupiter and its moons. Photos from the Voyager missions ",text,
L_0059,outer planets,T_0584,"Jupiter has lots of moons. As of 2011, we have discovered over 60 natural satellites of Jupiter. Four are big enough and bright enough to be seen from Earth using a pair of binoculars. These four moons were first discovered by Galileo in 1610. They are called the Galilean moons. Figure 25.21 shows the four Galilean moons and their sizes relative to Jupiters Great Red Spot. These moons are named Io, Europa, Ganymede, and Callisto. The Galilean moons are larger than even the biggest dwarf planets, Pluto and Eris. Ganymede is the biggest moon in the solar system. It is even larger than the planet Mercury! Scientists think that Europa is a good place to look for extraterrestrial life. Europa is the smallest of the Galilean moons. The moons surface is a smooth layer of ice. Scientists think that the ice may sit on top of an ocean of liquid water. How could Europa have liquid water when it is so far from the Sun? Europa is heated by Jupiter. Jupiters tidal forces are so great that they stretch and squash its moon. This could produce enough heat for there to be liquid water. Numerous missions have been planned to explore Europa, including plans to drill through the ice and send a probe into the ocean. However, no such mission has yet been attempted. In 1979, two spacecrafts, Voyager 1 and Voyager 2, visited Jupiter and its moons. Photos from the Voyager missions ",text,
L_0059,outer planets,T_0585,"Saturn, shown in Figure 25.22, is famous for its beautiful rings. Saturn is the second largest planet in the solar system. Saturns mass is about 95 times Earths mass. The gas giant is 755 times Earths volume. Despite its large size, Saturn is the least dense planet in our solar system. Saturn is actually less dense than water. This means that if there were a bathtub big enough, Saturn would float! In Roman mythology, Saturn was the father of Jupiter. Saturn orbits the Sun once about every 30 Earth years. Saturns composition is similar to Jupiters. The planet is made mostly of hydrogen and helium. These elements are gases in the outer layers and liquids in the deeper layers. Saturn may also have a small solid core. Saturns upper atmosphere has clouds in bands of different colors. These clouds rotate rapidly around the planet. But Saturn has fewer storms than Jupiter. Thunder and lightning have been seen in the storms on Saturn (Figure 25.23). ",text,
L_0059,outer planets,T_0586,"There is a strange feature at Saturns north pole. The clouds form a hexagonal pattern, as shown in the infrared image in Figure 25.24. This hexagon was viewed by Voyager 1 in the 1980s. It was still there when the Cassini Orbiter visited in 2006. No one is sure why the clouds form this pattern. ",text,
L_0059,outer planets,T_0587,"Saturns rings were first observed by Galileo in 1610. He didnt know they were rings and thought that they were two large moons. One moon was on either side of the planet. In 1659, the Dutch astronomer Christiaan Huygens realized that they were rings circling Saturns equator. The rings appear tilted. This is because Saturn is tilted about 27 degrees to its side. The Voyager 1 spacecraft visited Saturn in 1980. Voyager 2 followed in 1981. These probes sent back detailed pictures of Saturn, its rings, and some of its moons. From the Voyager data, we learned that Saturns rings are made of particles of water and ice with a little bit of dust. There are several gaps in the rings. These gaps were cleared out by moons within the rings. Ring dust and gas are attracted to the moon by its gravity. This leaves a gap in the rings. Other gaps in the rings are caused by the competing forces of Saturn and its moons outside the rings. ",text,
L_0059,outer planets,T_0587,"Saturns rings were first observed by Galileo in 1610. He didnt know they were rings and thought that they were two large moons. One moon was on either side of the planet. In 1659, the Dutch astronomer Christiaan Huygens realized that they were rings circling Saturns equator. The rings appear tilted. This is because Saturn is tilted about 27 degrees to its side. The Voyager 1 spacecraft visited Saturn in 1980. Voyager 2 followed in 1981. These probes sent back detailed pictures of Saturn, its rings, and some of its moons. From the Voyager data, we learned that Saturns rings are made of particles of water and ice with a little bit of dust. There are several gaps in the rings. These gaps were cleared out by moons within the rings. Ring dust and gas are attracted to the moon by its gravity. This leaves a gap in the rings. Other gaps in the rings are caused by the competing forces of Saturn and its moons outside the rings. ",text,
L_0059,outer planets,T_0588,"As of 2011, over 60 moons have been identified around Saturn. Only seven of Saturns moons are round. All but one is smaller than Earths Moon. Some of the very small moons are found within the rings. All the particles in the rings are like little moons, because they orbit around Saturn. Someone must decide which ones are large enough to call moons. Saturns largest moon, Titan, is about one and a half times the size of Earths Moon. Titan is even larger than the planet Mercury. Figure 25.25 compares the size of Titan to Earth. Scientists are very interested in Titan. The moon has an atmosphere that is thought to be like Earths first atmosphere. This atmosphere was around before life developed on Earth. Like Jupiters moon, Europa, Titan may have a layer of liquid water under a layer of ice. Scientists now think that there are lakes on Titans surface. Dont take a dip, though. These lakes contain liquid methane and ethane instead of water! Methane and ethane are compounds found in natural gas. ",text,
L_0059,outer planets,T_0589,"Uranus, shown in Figure 25.26, is named for the Greek god of the sky, the father of Saturn. Astronomers pronounce the name YOOR-uh-nuhs. Uranus was not known to ancient observers. The planet was first discovered with a telescope by the astronomer William Herschel in 1781. Uranus is faint because it is very far away. Its distance from the Sun is 2.8 billion kilometers (1.8 billion miles). A photon from the Sun takes about 2 hours and 40 minutes to reach Uranus. Uranus orbits the Sun once about every 84 Earth years. ",text,
L_0059,outer planets,T_0590,"Uranus is a lot like Jupiter and Saturn. The planet is composed mainly of hydrogen and helium. There is a thick layer of gas on the outside. Further on the inside is liquid. But Uranus has a higher percentage of icy materials than Jupiter and Saturn. These materials include water, ammonia, and methane. Uranus is also different because of its blue-green color. Clouds of methane filter out red light. This leaves a blue-green color. The atmosphere of Uranus has bands of clouds. These clouds are hard to see in normal light. The result is that the planet looks like a plain blue ball. Uranus is the least massive outer planet. Its mass is only about 14 times the mass of Earth. Like all of the outer planets, Uranus is much less dense than Earth. Gravity is actually weaker than on Earths surface. If you were at the top of the clouds on Uranus, you would weigh about 10 percent less than what you weigh on Earth. ",text,
L_0059,outer planets,T_0591,All of the planets rotate on their axes in the same direction that they move around the Sun. Except for Uranus. Uranus is tilted on its side. Its axis is almost parallel to its orbit. So Uranus rolls along like a bowling ball as it revolves around the Sun. How did Uranus get this way? Scientists think that the planet was struck and knocked over by another planet-sized object. This collision probably took place billions of years ago. ,text,
L_0059,outer planets,T_0592,"Uranus has a faint system of rings, as shown in Figure 25.27. The rings circle the planets equator. However, Uranus is tilted on its side. So the rings are almost perpendicular to the planets orbit. We have discovered 27 moons around Uranus. All but a few are named for characters from the plays of William Shakespeare. The five biggest moons of Uranus, Miranda, Ariel, Umbriel, Titania, and Oberon, are shown in Figure ",text,
L_0059,outer planets,T_0592,"Uranus has a faint system of rings, as shown in Figure 25.27. The rings circle the planets equator. However, Uranus is tilted on its side. So the rings are almost perpendicular to the planets orbit. We have discovered 27 moons around Uranus. All but a few are named for characters from the plays of William Shakespeare. The five biggest moons of Uranus, Miranda, Ariel, Umbriel, Titania, and Oberon, are shown in Figure ",text,
L_0059,outer planets,T_0593,"Neptune is shown in Figure 25.29. It is the eighth planet from the Sun. Neptune is so far away you need a telescope to see it from Earth. Neptune is the most distant planet in our solar system. It is nearly 4.5 billion kilometers (2.8 billion miles) from the Sun. One orbit around the Sun takes Neptune 165 Earth years. Scientists guessed Neptunes existence before it was discovered. Uranus did not always appear exactly where it should. They said this was because a planet beyond Uranus was pulling on it. This gravitational pull was affecting its orbit. Neptune was discovered in 1846. It was just where scientists predicted it would be! Due to its blue color, the planet was named Neptune for the Roman god of the sea. Uranus and Neptune are often considered sister planets. They are very similar to each other. Neptune has slightly more mass than Uranus, but it is slightly smaller in size. ",text,
L_0059,outer planets,T_0594,"Like Uranus, Neptune is blue. The blue color is caused by gases in its atmosphere, including methane. Neptune is not a smooth looking ball like Uranus. The planet has a few darker and lighter spots. When Voyager 2 visited Neptune in 1986, there was a large dark-blue spot south of the equator. This spot was called the Great Dark Spot. When the Hubble Space Telescope photographed Neptune in 1994, the Great Dark Spot had disappeared. Another dark spot had appeared north of the equator. Astronomers believe that both of these spots represent gaps in the methane clouds on Neptune. Neptunes appearance changes due to its turbulent atmosphere. Winds are stronger than on any other planet in the solar system. Wind speeds can reach 1,100 km/h (700 mph). This is close to the speed of sound! The rapid winds surprised astronomers. This is because Neptune receives little energy from the Sun to power weather systems. It is not surprising that Neptune is one of the coldest places in the solar system. Temperatures at the top of the clouds are about 218C (360F). ",text,
L_0059,outer planets,T_0595,"Like the other outer planets, Neptune has rings of ice and dust. These rings are much thinner and fainter than Saturns. Neptunes rings may be unstable. They may change or disappear in a relatively short time. Neptune has 13 known moons. Only Triton, shown in Figure 25.30, has enough mass to be round. Triton orbits in the direction opposite to Neptunes orbit. Scientists think Triton did not form around Neptune. The satellite was captured by Neptunes gravity as it passed by. ",text,
L_0059,outer planets,T_0596,"Pluto was once considered one of the outer planets, but when the definition of a planet was changed in 2006, Pluto became one of the dwarf planets. It is one of the largest and brightest objects that make up this group. Look for Pluto in the next lesson, in the discussion of dwarf planets. ",text,
L_0060,other objects in the solar system,T_0597,"Asteroids are very small, irregularly shaped, rocky bodies. Asteroids orbit the Sun, but they are more like giant rocks than planets. Since they are small, they do not have enough gravity to become round. They are too small to have an atmosphere. With no internal heat, they are not geologically active. An asteroid can only change due to a collision. A collision may cause the asteroid to break up. It may create craters on the asteroids surface. An asteroid may strike a planet if it comes near enough to be pulled in by its gravity. Figure 25.31 shows a typical asteroid. ",text,
L_0060,other objects in the solar system,T_0598,"Hundreds of thousands of asteroids have been found in our solar system. They are still being discovered at a rate of about 5,000 new asteroids per month! The majority are located in between the orbits of Mars and Jupiter. This region is called the asteroid belt, as shown in Figure 25.32. There are many thousands of asteroids in the asteroid belt. Still, their total mass adds up to only about 4 percent of Earths Moon. Asteroids formed at the same time as the rest of the solar system. Although there are many in the asteroid belt, they were never were able to form into a planet. Jupiters gravity kept them apart. ",text,
L_0060,other objects in the solar system,T_0598,"Hundreds of thousands of asteroids have been found in our solar system. They are still being discovered at a rate of about 5,000 new asteroids per month! The majority are located in between the orbits of Mars and Jupiter. This region is called the asteroid belt, as shown in Figure 25.32. There are many thousands of asteroids in the asteroid belt. Still, their total mass adds up to only about 4 percent of Earths Moon. Asteroids formed at the same time as the rest of the solar system. Although there are many in the asteroid belt, they were never were able to form into a planet. Jupiters gravity kept them apart. ",text,
L_0060,other objects in the solar system,T_0599,"Near-Earth asteroids have orbits that cross Earths orbit. This means that they can collide with Earth. There are over 4,500 known near-Earth asteroids. Small asteroids do sometimes collide with Earth. An asteroid about 510 m in diameter hits about once per year. Five hundred to a thousand of the known near-Earth asteroids are much bigger. They are over 1 kilometer in diameter. When large asteroids hit Earth in the past, many organisms died. At times, many species became extinct. Astronomers keep looking for near-Earth asteroids. They hope to predict a possible collision early so they can to try to stop it. ",text,
L_0060,other objects in the solar system,T_0600,"Scientists are very interested in asteroids. Most are composed of material that has not changed since early in the solar system. Scientists can learn a lot from them about how the solar system formed. Asteroids may be important for space travel. They could be mined for rare minerals or for construction projects in space. Scientists have sent spacecraft to study asteroids. In 1997, the NEAR Shoemaker probe orbited the asteroid 433 Eros. The craft finally landed on its surface in 2001. The Japanese Hayabusa probe returned to Earth with samples of a small near-earth asteroid in 2010. The U.S. Dawn mission will visit Vesta in 2011 and Ceres in 2015. ",text,
L_0060,other objects in the solar system,T_0601,"If you look at the sky on a dark night, you may see a meteor, like in Figure 25.33. A meteor forms a streak of light across the sky. People call them shooting stars because thats what they look like. But meteors are not stars at all. The light you see comes from a small piece of matter burning up as it flies through Earths atmosphere. ",text,
L_0060,other objects in the solar system,T_0602,"Before these small pieces of matter enter Earths atmosphere, they are called meteoroids. Meteoroids are as large as boulders or as small as tiny sand grains. Larger objects are called asteroids; smaller objects are interplanetary dust. Meteoroids sometimes cluster together in long trails. They are the debris left behind by comets. When Earth passes through a comet trail, there is a meteor shower. During a meteor shower, there are many more meteors than normal for a night or two. ",text,
L_0060,other objects in the solar system,T_0603,"A meteoroid is dragged towards Earth by gravity and enters the atmosphere. Friction with the atmosphere heats the object quickly, so it starts to vaporize. As it flies through the atmosphere, it leaves a trail of glowing gases. The object is now a meteor. Most meteors vaporize in the atmosphere. They never reach Earths surface. Large meteoroids may not burn up entirely in the atmosphere. A small core may remain and hit the Earths surface. This is called a meteorite. Meteorites provide clues about our solar system. Many were formed in the early solar system (Figure 25.34). Some are from asteroids that have split apart. A few are rocks from nearby bodies like Mars. For this to happen, an asteroid smashed into Mars and sent up debris. A bit of the debris entered Earths atmosphere as a meteor. ",text,
L_0060,other objects in the solar system,T_0604,"Comets are small, icy objects that orbit the Sun. Comets have highly elliptical orbits. Their orbits carry them from close to the Sun to the solar systems outer edges. When a comet gets close to the Sun, its outer layers of ice melt and evaporate. The vaporized gas and dust forms an atmosphere around the comet. This atmosphere is called a coma. Radiation and particles streaming from the Sun push some of this gas and dust into a long tail. A comets tail always points away from the Sun, no matter which way the comet is moving. Why do you think that is? Figure Gases in the coma and tail of a comet reflect light from the Sun. Comets are very hard to see except when they have comas and tails. That is why they appear only when they are near the Sun. They disappear again as they move back to the outer solar system. The time between one visit from a comet and the next is called the comets period. The first comet whose period was known was Halleys Comet. Its period is 75 years. Halleys Comet last traveled through the inner solar system in 1986. The comet will appear again in 2061. Who will look up at it? ",text,
L_0060,other objects in the solar system,T_0605,"Some comets have periods of 200 years or less. They are called short-period comets. Short-period comets are from a region beyond the orbit of Neptune called the Kuiper Belt. Kuiper is pronounced KI-per, rhyming with viper. The Kuiper Belt is home to comets, asteroids, and at least two dwarf planets. Some comets have periods of thousands or even millions of years. Most long-period comets come from a very distant region of the solar system. This region is called the Oort cloud. The Oort cloud is about 50,000100,000 times the distance from the Sun to Earth. Comets carry materials in from the outer solar system. Comets may have brought water into the early Earth. Other substances could also have come from comets. ",text,
L_0060,other objects in the solar system,T_0606,"For several decades, Pluto was a planet. But new solar system objects were discovered that were just as planet-like as Pluto. Astronomers figured out that they were like planets except for one thing. These objects had not cleared their orbits of smaller objects. They didnt have enough gravity to do so. Astronomers made a category called dwarf planets. There are five dwarf planets in our solar system: Ceres, Pluto, Makemake, Haumea and Eris. Figure 25.36 shows Ceres. Ceres is a rocky body that orbits the Sun and is not a star. It could be an asteroid or a planet. Before 2006, Ceres was thought to be the largest asteroid. Is it an asteroid? Ceres is in the asteroid belt. But it is by far the largest object in the belt. Ceres has such high gravity that it is spherical. Is it a planet? Ceres only has about 1.3% of the mass of the Earths Moon. Its orbit is full of other smaller bodies. Its gravity was not high enough to clear its orbit. Ceres fails the fourth criterion for being a planet. Ceres is now considered a dwarf planet along with Pluto. ",text,
L_0060,other objects in the solar system,T_0607,"For decades Pluto was a planet. But even then, scientists knew it was an unusual planet. The other outer planets are all gas giants. Pluto is small, icy and rocky. With a diameter of about 2400 kilometers, it has only about 1/5 the mass of Earths Moon. The other planets orbit in a plane. Plutos orbit is tilted. The shape of the orbit is like a long, narrow ellipse. Plutos orbit is so elliptical that sometimes it is inside the orbit of Neptune. Plutos orbit is in the Kuiper belt. We have discovered more than 200 million Kuiper belt objects. Pluto has 3 moons of its own. The largest, Charon, is big. Some scientists think that Pluto-Charon system is a double dwarf planet (Figure 25.37). Two smaller moons, Nix and Hydra, were discovered in 2005. ",text,
L_0060,other objects in the solar system,T_0607,"For decades Pluto was a planet. But even then, scientists knew it was an unusual planet. The other outer planets are all gas giants. Pluto is small, icy and rocky. With a diameter of about 2400 kilometers, it has only about 1/5 the mass of Earths Moon. The other planets orbit in a plane. Plutos orbit is tilted. The shape of the orbit is like a long, narrow ellipse. Plutos orbit is so elliptical that sometimes it is inside the orbit of Neptune. Plutos orbit is in the Kuiper belt. We have discovered more than 200 million Kuiper belt objects. Pluto has 3 moons of its own. The largest, Charon, is big. Some scientists think that Pluto-Charon system is a double dwarf planet (Figure 25.37). Two smaller moons, Nix and Hydra, were discovered in 2005. ",text,
L_0060,other objects in the solar system,T_0608,"Haumea was named a dwarf planet in 2008. It is an unusual dwarf planet. The body is shaped like an oval! Haumeas longest axis is about the same as Plutos diameter, and its shortest axis is about half as long. The bodys orbit is tilted 28. Haumea is so far from the Sun that it takes 283 years to make one orbit (Figure 25.38). Haumea is the third-brightest Kuiper Belt object. It was named for the Hawaiian goddess of childbirth. Haumea has two moons, Hiiaka and Namaka, the names of the goddess Haumeas daughters. Haumeas odd oval shape is probably caused by its extremely rapid rotation. It rotates in just less than 4 hours! Like other Kuiper belt objects, Haumea is covered by ice. Its density is similar to Earths Moon, at 2.6 3.3 g/cm3 . This means that most of Haumea is rocky. Haumea is part of a collisional family. This is a group of astronomical objects that formed from an impact. This family has Haumea, its two moons, and five more objects. All of these objects are thought to have formed from a collision very early in the formation of the solar system. ",text,
L_0060,other objects in the solar system,T_0609,"Makemake is the third-largest and second-brightest dwarf planet we have discovered so far (Figure 25.39). Make- make is only 75 percent the size of Pluto. Its diameter is between 1300 and 1900 kilometers. The name comes from the mythology of the Eastern Islanders. Makemake was the god that created humanity. At a distance between 38.5 to 53 AU, this dwarf planet orbits the Sun in 310 years. Makemake is made of methane, ethane, and nitrogen ices. ",text,
L_0060,other objects in the solar system,T_0610,"Eris is the largest known dwarf planet in the solar system. It is 27 percent larger than Pluto (Figure 25.40). Like Pluto and Makemake, Eris is in the Kuiper belt. But Eris is about 3 times farther from the Sun than Pluto. Because of its distance, Eris was not discovered until 2005. Early on, it was thought that Eris might be the tenth planet. Its discovery helped astronomers realize that they needed a new definition of planet. Eris has a small moon, Dysnomia. Its moon orbits Eris once about every 16 days. Astronomers know there may be other dwarf planets far out in the solar system. Look for Quaoar, Varuna and Orcus to be possibly added to the list of dwarf planets in the future. We still have a lot to discover and explore! ",text,
L_0061,stars,T_0611,"The stars that make up a constellation appear close to each other from Earth. In reality, they may be very distant from one another. Constellations were important to people, like the Ancient Greeks. People who spent a lot of time outdoors at night, like shepherds, named them and told stories about them. Figure 26.1 shows one of the most easily recognized constellations. The ancient Greeks thought this group of stars looked like a hunter. They named it Orion, after a great hunter in Greek mythology. The constellations stay the same night after night. The patterns of the stars never change. However, each night the constellations move across the sky. They move because Earth is spinning on its axis. The constellations also move with the seasons. This is because Earth revolves around the Sun. Different constellations are up in the winter than in the summer. For example, Orion is high up in the winter sky. In the summer, its only up in the early morning. ",text,
L_0061,stars,T_0612,"Only a tiny bit of the Suns light reaches Earth. But that light supplies most of the energy at the surface. The Sun is just an ordinary star, but it appears much bigger and brighter than any of the other stars. Of course, this is just because it is very close. Some other stars produce much more energy than the Sun. How do stars generate so much energy? ",text,
L_0061,stars,T_0613,"Stars shine because of nuclear fusion. Fusion reactions in the Suns core keep our nearest star burning. Stars are made mostly of hydrogen and helium. Both are very lightweight gases. A star contains so much hydrogen and helium that the weight of these gases is enormous. The pressure at the center of a star is great enough to heat the gases. This causes nuclear fusion reactions. A nuclear fusion reaction is named that because the nuclei (center) of two atoms fuse (join) together. In stars like our Sun, two hydrogen atoms join together to create a helium atom. Nuclear fusion reactions need a lot of energy to get started. Once they begin, they produce even more energy. ",text,
L_0061,stars,T_0614,"Scientists have built machines called particle accelerators. These amazing tools smash particles that are smaller than atoms into each other head-on. This creates new particles. Scientists use particle accelerators to learn about nuclear fusion in stars. They can also learn about how atoms came together in the early universe. Two well-known accelerators are SLAC, in California, and CERN, in Switzerland. ",text,
L_0061,stars,T_0615,Stars shine in many different colors. The color relates to a stars temperature and often its size. ,text,
L_0061,stars,T_0616,"Think about the coil of an electric stove as it heats up. The coil changes in color as its temperature rises. When you first turn on the heat, the coil looks black. The air a few inches above the coil begins to feel warm. As the coil gets hotter, it starts to glow a dull red. As it gets even hotter, it becomes a brighter red. Next it turns orange. If it gets extremely hot, it might look yellow-white, or even blue-white. Like a coil on a stove, a stars color is determined by the temperature of the stars surface. Relatively cool stars are red. Warmer stars are orange or yellow. Extremely hot stars are blue or blue-white. ",text,
L_0061,stars,T_0617,"The most common way of classifying stars is by color as shown, in Table 26.1. Each class of star is given a letter, a color, and a range of temperatures. The letters dont match the color names because stars were first grouped as A through O. It wasnt until later that their order was corrected to go by increasing temperature. When you try to remember the order, you can use this phrase: Oh Be A Fine Good Kid, Man. Class O Color Blue Temperature range 30,000 K or more Sample Star An artists depiction of the O class star Zeta Pup- pis. B Blue-white 10,00030,000 K An artists depiction of Rigel, a Class B star. Class A Color White Temperature range 7,50010,000 K Sample Star Sirius A is the brightest star that we see in the night sky. The dot on the right, Sirius B, is a white dwarf. F Yellowish-white 6,0007,500 K There are two F class stars in this image, the super- giant Polaris A and Po- laris B. What we see in the night sky as the single star Polaris, we also known as the North Star. G Yellow 5,5006,000 K Our Sun: the most im- portant G class star in the Universe, at least for hu- mans. Class K M Color Orange Red Temperature range 3,5005,000 K 2,0003,500 K Sample Star Arcturus is a Class K star that looks like the Sun but is much larger. There are two types of Class M stars: red dwarfs and red giants. An artists concept of a red dwarf star. Most stars are red dwarfs. The red supergiant Betel- geuse is seen near Orions belt. The blue star in the lower right is the Class B star Rigel. The surface temperature of most stars is due to its size. Bigger stars produce more energy, so their surfaces are hotter. But some very small stars are very hot. Some very big stars are cool. ",text,
L_0061,stars,T_0618,"We could say that stars are born, change over time, and eventually die. Most stars change in size, color, and class at least once during their lifetime. ",text,
L_0061,stars,T_0619,"Stars are born in clouds of gas and dust called nebulas. Our Sun and solar system formed out of a nebula. A nebula is shown in Figure 26.2. In Figure 26.1, the fuzzy area beneath the central three stars contains the Orion nebula. For a star to form, gravity pulls gas and dust into the center of the nebula. As the material becomes denser, the pressure and the temperature increase. When the temperature of the center becomes hot enough, nuclear fusion begins. The ball of gas has become a star! ",text,
L_0061,stars,T_0620,"For most of a stars life, hydrogen atoms fuse to form helium atoms. A star like this is a main sequence star. The hotter a main sequence star is, the brighter it is. A star remains on the main sequence as long as it is fusing hydrogen to form helium. Our Sun has been a main sequence star for about 5 billion years. As a medium-sized star, it will continue to shine for about 5 billion more years. Large stars burn through their supply of hydrogen very quickly. These stars live fast and die young! A very large star may only be on the main sequence for 10 million years. A very small star may be on the main sequence for tens to hundreds of billions of years. ",text,
L_0061,stars,T_0621,"A star like our Sun will become a red giant in its next stage. When a star uses up its hydrogen, it begins to fuse helium atoms. Helium fuses into heavier atoms like carbon. At this time the stars core starts to collapse inward. The stars outer layers spread out and cool. The result is a larger star that is cooler on the surface, and red in color. Eventually a red giant burns up all of the helium in its core. What happens next depends on the stars mass. A star like the Sun stops fusion and shrinks into a white dwarf star. A white dwarf is a hot, white, glowing object about the size of Earth. Eventually, a white dwarf cools down and its light fades out. ",text,
L_0061,stars,T_0622,"A more massive star ends its life in a more dramatic way. Very massive stars become red supergiants, like Betelgeuse. In a red supergiant, fusion does not stop. Lighter atoms fuse into heavier atoms. Eventually iron atoms form. When there is nothing left to fuse, the stars iron core explodes violently. This is called a supernova explosion. The incredible energy released fuses heavy atoms together. Gold, silver, uranium and the other heavy elements can only form in a supernova explosion. A supernova can shine as brightly as an entire galaxy, but only for a short time, as shown in Figure 26.3. ",text,
L_0061,stars,T_0623,"After a supernova explosion, the stars core is left over. This material is extremely dense. If the core is less than about four times the mass of the Sun, the star will become a neutron star. A neutron star is shown in Figure 26.4. This type of star is made almost entirely of neutrons. A neutron star has more mass than the Sun, yet it is only a few kilometers in diameter. If the core remaining after a supernova is more than about 5 times the mass of the Sun, the core collapses to become a black hole. Black holes are so dense that not even light can escape their gravity. For that reason, we cant see black holes. How can we know something exists if radiation cant escape it? We know a black hole is there by the effect that it has on objects around it. Also, some radiation leaks out around its edges. A black hole isnt a hole at all. It is the tremendously dense core of a supermassive star. ",text,
L_0061,stars,T_0624,"Astronomers use light years as the unit to describe distances in space. Remember that a light year is the distance light travels in one year. How do astronomers measure the distance to stars? For stars that are close to us, they measure shifts in their position over time. This is called parallax. For distant stars, they use the stars brightness. For example, if a star is like the Sun, it should be about as bright as the Sun. They then figure out the stars distance from Earth by measuring how much less bright it is than expected. ",text,
L_0061,stars,T_0625,"Our solar system has only one star. But many stars are in systems of two or more stars. Two stars that orbit each other are called a binary star system. If more than two stars orbit each other, it is called a multiple star system. Figure 26.5 shows two binary star systems orbiting each other. This creates an unusual quadruple star system. ",text,
L_0062,galaxies,T_0626,"Star clusters are groups of stars smaller than a galaxy. There are two main types, open clusters and globular clusters. Open clusters are groups of up to a few thousand stars held together by gravity. The Jewel Box, shown in Figure an open cluster are young stars that all formed from the same nebula. Globular clusters are groups of tens to hundreds of thousands of stars held tightly together by gravity. Globular clusters have a definite, spherical shape. They contain mostly old, reddish stars. Near the center of a globular cluster, the stars are closer together. Figure 26.7 shows a globular cluster. The heart of the globular cluster M13 has hundreds of thousands of stars. M13 is 145 light years in diameter. The cluster contains red and blue giant stars. ",text,
L_0062,galaxies,T_0626,"Star clusters are groups of stars smaller than a galaxy. There are two main types, open clusters and globular clusters. Open clusters are groups of up to a few thousand stars held together by gravity. The Jewel Box, shown in Figure an open cluster are young stars that all formed from the same nebula. Globular clusters are groups of tens to hundreds of thousands of stars held tightly together by gravity. Globular clusters have a definite, spherical shape. They contain mostly old, reddish stars. Near the center of a globular cluster, the stars are closer together. Figure 26.7 shows a globular cluster. The heart of the globular cluster M13 has hundreds of thousands of stars. M13 is 145 light years in diameter. The cluster contains red and blue giant stars. ",text,
L_0062,galaxies,T_0627,"The biggest groups of stars are called galaxies. A few million to many billions of stars may make up a galaxy. With the unaided eye, every star you can see is part of the Milky Way Galaxy. All the other galaxies are extremely far away. The closest spiral galaxy, the Andromeda Galaxy, shown in Figure 26.8, is 2,500,000 light years away and contains one trillion stars! ",text,
L_0062,galaxies,T_0628,"Galaxies are divided into three types, according to shape. There are spiral galaxies, elliptical galaxies, and irregular galaxies. Spiral galaxies are a rotating disk of stars and dust. In the center is a dense bulge of material. Several arms spiral out from the center. Spiral galaxies have lots of gas and dust and many young stars. Figure 26.9 shows a spiral galaxy from the side. You can see the disk and central bulge. ",text,
L_0062,galaxies,T_0628,"Galaxies are divided into three types, according to shape. There are spiral galaxies, elliptical galaxies, and irregular galaxies. Spiral galaxies are a rotating disk of stars and dust. In the center is a dense bulge of material. Several arms spiral out from the center. Spiral galaxies have lots of gas and dust and many young stars. Figure 26.9 shows a spiral galaxy from the side. You can see the disk and central bulge. ",text,
L_0062,galaxies,T_0629,Figure 26.10 shows a typical elliptical galaxy. Elliptical galaxies are oval in shape. The smallest are called dwarf elliptical galaxies. Look back at the image of the Andromeda Galaxy. It has two dwarf elliptical galaxies as its companions. Dwarf galaxies are often found near larger galaxies. They sometimes collide with and merge into their larger neighbors. Giant elliptical galaxies contain over a trillion stars. Elliptical galaxies are red to yellow in color because they contain mostly old stars. Most contain very little gas and dust because the material has already formed into stars. ,text,
L_0062,galaxies,T_0630,"Look at the galaxy in Figure 26.11. Do you think this is a spiral galaxy or an elliptical galaxy? It doesnt look like either! If a galaxy is not spiral or elliptical, it is an irregular galaxy. Most irregular galaxies have been deformed. This can occur either by the pull of a larger galaxy or by a collision with another galaxy. ",text,
L_0062,galaxies,T_0631,"If you get away from city lights and look up in the sky on a very clear night, you will see something spectacular. A band of milky light stretches across the sky, as in Figure 26.12. This band is the disk of the Milky Way Galaxy. This is the galaxy where we all live. The Milky Way Galaxy looks different to us than other galaxies because our view is from inside of it! ",text,
L_0062,galaxies,T_0632,"The Milky Way Galaxy is a spiral galaxy that contains about 400 billion stars. Like other spiral galaxies, it has a disk, a central bulge, and spiral arms. The disk is about 100,000 light-years across. It is about 3,000 light years thick. Most of the galaxys gas, dust, young stars, and open clusters are in the disk. Some astronomers think that there is a gigantic black hole at the center of the galaxy. Figure 26.13 shows what the Milky Way probably looks like from the outside. Our solar system is within one of the spiral arms. Most of the stars we see in the sky are relatively nearby stars that are also in this spiral arm. We are a little more than halfway out from the center of the Galaxy to the edge, as shown in Figure 26.13. Our solar system orbits the center of the galaxy as the galaxy spins. One orbit of the solar system takes about 225 to 250 million years. The solar system has orbited 20 to 25 times since it formed 4.6 billion years ago. ",text,
L_0062,galaxies,T_0632,"The Milky Way Galaxy is a spiral galaxy that contains about 400 billion stars. Like other spiral galaxies, it has a disk, a central bulge, and spiral arms. The disk is about 100,000 light-years across. It is about 3,000 light years thick. Most of the galaxys gas, dust, young stars, and open clusters are in the disk. Some astronomers think that there is a gigantic black hole at the center of the galaxy. Figure 26.13 shows what the Milky Way probably looks like from the outside. Our solar system is within one of the spiral arms. Most of the stars we see in the sky are relatively nearby stars that are also in this spiral arm. We are a little more than halfway out from the center of the Galaxy to the edge, as shown in Figure 26.13. Our solar system orbits the center of the galaxy as the galaxy spins. One orbit of the solar system takes about 225 to 250 million years. The solar system has orbited 20 to 25 times since it formed 4.6 billion years ago. ",text,
L_0068,types of rocks,T_0685,"All rocks on Earth change, but these changes usually happen very slowly. Some changes happen below Earths surface. Some changes happen above ground. These changes are all part of the rock cycle. The rock cycle describes each of the main types of rocks, how they form and how they change. Figure 4.1 shows how the three main rock types are related to each other. The arrows within the circle show how one type of rock may change to rock of another type. For example, igneous rock may break down into small pieces of sediment and become sedimentary rock. Igneous rock may be buried within the Earth and become metamorphic rock. Igneous rock may also change back to molten material and re-cool into a new igneous rock. Rocks are made of minerals. The minerals may be so tiny that you can only see them with a microscope. The minerals may be really large. A rock may be made of only one type of mineral. More often rocks are made of a mixture of different minerals. Rocks are named for the combinations of minerals they are made of and the ways those minerals came together. Remember that different minerals form under different environmental conditions. So the minerals in a rock contain clues about the conditions in which the rock formed (Figure 4.2). ",text,
L_0068,types of rocks,T_0685,"All rocks on Earth change, but these changes usually happen very slowly. Some changes happen below Earths surface. Some changes happen above ground. These changes are all part of the rock cycle. The rock cycle describes each of the main types of rocks, how they form and how they change. Figure 4.1 shows how the three main rock types are related to each other. The arrows within the circle show how one type of rock may change to rock of another type. For example, igneous rock may break down into small pieces of sediment and become sedimentary rock. Igneous rock may be buried within the Earth and become metamorphic rock. Igneous rock may also change back to molten material and re-cool into a new igneous rock. Rocks are made of minerals. The minerals may be so tiny that you can only see them with a microscope. The minerals may be really large. A rock may be made of only one type of mineral. More often rocks are made of a mixture of different minerals. Rocks are named for the combinations of minerals they are made of and the ways those minerals came together. Remember that different minerals form under different environmental conditions. So the minerals in a rock contain clues about the conditions in which the rock formed (Figure 4.2). ",text,
L_0068,types of rocks,T_0686,"Geologists group rocks based on how they were formed. The three main kinds of rocks are: 1. Igneous rocks form when magma cools below Earths surface or lava cools at the surface (Figure 4.3). 2. Sedimentary rocks form when sediments are compacted and cemented together (Figure 4.4). These sediments may be gravel, sand, silt or clay. Sedimentary rocks often have pieces of other rocks in them. Some sedimentary rocks form the solid minerals left behind after a liquid evaporates. 3. Metamorphic rocks form when an existing rock is changed by heat or pressure. The minerals in the rock change but do not melt (Figure 4.5). The rock experiences these changes within the Earth. Rocks can be changed from one type to another, and the rock cycle describes how this happens. ",text,
L_0068,types of rocks,T_0686,"Geologists group rocks based on how they were formed. The three main kinds of rocks are: 1. Igneous rocks form when magma cools below Earths surface or lava cools at the surface (Figure 4.3). 2. Sedimentary rocks form when sediments are compacted and cemented together (Figure 4.4). These sediments may be gravel, sand, silt or clay. Sedimentary rocks often have pieces of other rocks in them. Some sedimentary rocks form the solid minerals left behind after a liquid evaporates. 3. Metamorphic rocks form when an existing rock is changed by heat or pressure. The minerals in the rock change but do not melt (Figure 4.5). The rock experiences these changes within the Earth. Rocks can be changed from one type to another, and the rock cycle describes how this happens. ",text,
L_0068,types of rocks,T_0687,"Any type of rock can change and become a new type of rock. Magma can cool and crystallize. Existing rocks can be weathered and eroded to form sediments. Rock can change by heat or pressure deep in Earths crust. There are three main processes that can change rock: Cooling and forming crystals. Deep within the Earth, temperatures can get hot enough to melt rock. This molten material is called magma. As it cools, crystals grow, forming an igneous rock. The crystals will grow larger if the magma cools slowly, as it does if it remains deep within the Earth. If the magma cools quickly, the crystals will be very small. Weathering and erosion. Water, wind, ice, and even plants and animals all act to wear down rocks. Over time they can break larger rocks into smaller pieces called sediments. Moving water, wind, and glaciers then carry these pieces from one place to another. The sediments are eventually dropped, or deposited, somewhere. The sediments may then be compacted and cemented together. This forms a sedimentary rock. This whole process can take hundreds or thousands of years. Metamorphism. This long word means to change form. A rock undergoes metamorphism if it is exposed to extreme heat and pressure within the crust. With metamorphism, the rock does not melt all the way. The rock changes due to heat and pressure. A metamorphic rock may have a new mineral composition and/or texture. An interactive rock cycle diagram can be found here:  The rock cycle really has no beginning or end. It just continues. The processes involved in the rock cycle take place over hundreds, thousands, or even millions of years. Even though for us rocks are solid and unchanging, they slowly change all the time. ",text,
L_0069,igneous rocks,T_0688,"Igneous rocks form when magma cools and forms crystals. These rocks can form at Earths surface or deep underground. Figure 4.7 shows a landscape in Californias Sierra Nevada that consists entirely of granite. Intrusive igneous rocks cool and form into crystals beneath the surface. Deep in the Earth, magma cools slowly. Slow cooling gives large crystals a chance to form. Intrusive igneous rocks have relatively large crystals that are easy to see. Granite is the most common intrusive igneous rock. Figure 4.8 shows four types of intrusive rocks. Extrusive igneous rocks form above the surface. The lava cools quickly as it pours out onto the surface (Figure ",text,
L_0069,igneous rocks,T_0688,"Igneous rocks form when magma cools and forms crystals. These rocks can form at Earths surface or deep underground. Figure 4.7 shows a landscape in Californias Sierra Nevada that consists entirely of granite. Intrusive igneous rocks cool and form into crystals beneath the surface. Deep in the Earth, magma cools slowly. Slow cooling gives large crystals a chance to form. Intrusive igneous rocks have relatively large crystals that are easy to see. Granite is the most common intrusive igneous rock. Figure 4.8 shows four types of intrusive rocks. Extrusive igneous rocks form above the surface. The lava cools quickly as it pours out onto the surface (Figure ",text,
L_0069,igneous rocks,T_0688,"Igneous rocks form when magma cools and forms crystals. These rocks can form at Earths surface or deep underground. Figure 4.7 shows a landscape in Californias Sierra Nevada that consists entirely of granite. Intrusive igneous rocks cool and form into crystals beneath the surface. Deep in the Earth, magma cools slowly. Slow cooling gives large crystals a chance to form. Intrusive igneous rocks have relatively large crystals that are easy to see. Granite is the most common intrusive igneous rock. Figure 4.8 shows four types of intrusive rocks. Extrusive igneous rocks form above the surface. The lava cools quickly as it pours out onto the surface (Figure ",text,
L_0069,igneous rocks,T_0688,"Igneous rocks form when magma cools and forms crystals. These rocks can form at Earths surface or deep underground. Figure 4.7 shows a landscape in Californias Sierra Nevada that consists entirely of granite. Intrusive igneous rocks cool and form into crystals beneath the surface. Deep in the Earth, magma cools slowly. Slow cooling gives large crystals a chance to form. Intrusive igneous rocks have relatively large crystals that are easy to see. Granite is the most common intrusive igneous rock. Figure 4.8 shows four types of intrusive rocks. Extrusive igneous rocks form above the surface. The lava cools quickly as it pours out onto the surface (Figure ",text,
L_0069,igneous rocks,T_0689,"Igneous rocks are grouped by the size of their crystals and the minerals they contain. The minerals in igneous rocks are grouped into families. Some contain mostly lighter colored minerals, some have a combination of light and dark minerals, and some have mostly darker minerals. The combination of minerals is determined by the composition of the magma. Magmas that produce lighter colored minerals are higher in silica. These create rocks such as granite and rhyolite. Darker colored minerals are found in rocks such as gabbro and basalt. There are actually more than 700 different types of igneous rocks. Diorite is extremely hard and is commonly used for art. It was used extensively by ancient civilizations for vases and other decorative art work (Figure 4.11). ",text,
L_0070,sedimentary rocks,T_0690,"Most sedimentary rocks form from sediments. Sediments are small pieces of other rocks, like pebbles, sand, silt, and clay. Sedimentary rocks may include fossils. Fossils are materials left behind by once-living organisms. Fossils can be pieces of the organism, like bones. They can also be traces of the organism, like footprints. Most often, sediments settle out of water (Figure 4.13). For example, rivers carry lots of sediment. Where the water slows, it dumps these sediments along its banks, into lakes and the ocean. When sediments settle out of water, they form horizontal layers. A layer of sediment is deposited. Then the next layer is deposited on top of that layer. So each layer in a sedimentary rock is younger than the layer under it. It is older than the layer over it. Sediments are deposited in many different types of environments. Beaches and deserts collect large deposits of sand. Sediments also continuously wind up at the bottom of the ocean and in lakes, ponds, rivers, marshes, and swamps. Avalanches produce large piles of sediment. The environment where the sediments are deposited determines the type of sedimentary rock that can form. ",text,
L_0070,sedimentary rocks,T_0691,Sedimentary rocks form in two ways. Particles may be cemented together. Chemicals may precipitate. ,text,
L_0070,sedimentary rocks,T_0692,"Over time, deposited sediments may harden into rock. First, the sediments are compacted. That is, they are squeezed together by the weight of sediments on top of them. Next, the sediments are cemented together. Minerals fill in the spaces between the loose sediment particles. These cementing minerals come from the water that moves through the sediments. These types of sedimentary rocks are called clastic rocks. Clastic rocks are rock fragments that are compacted and cemented together. Clastic sedimentary rocks are grouped by the size of the sediment they contain. Conglomerate and breccia are made of individual stones that have been cemented together. In conglomerate, the stones are rounded. In breccia, the stones are angular. Sandstone is made of sand-sized particles. Siltstone is made of smaller particles. Silt is smaller than sand but larger than clay. Shale has the smallest grain size. Shale is made mostly of clay-sized particles and hardened mud. ",text,
L_0070,sedimentary rocks,T_0693,"Chemical sedimentary rocks form when crystals precipitate out from a liquid. The mineral halite, also called rock salt, forms this way. You can make halite! Leave a shallow dish of salt water out in the Sun. As the water evaporates, salt crystals form in the dish. There are other chemical sedimentary rocks, like gypsum. Table 4.1 shows some common types of sedimentary rocks and the types of sediments that make them up. Picture Rock Name Conglomerate Type of Sedimentary Rock Clastic Breccia Clastic Sandstone Clastic Siltstone Clastic Limestone Bioclastic Coal Organic Picture Rock Name Rock Salt Type of Sedimentary Rock Chemical precipitate ",text,
L_0071,metamorphic rocks,T_0694,"Metamorphic rocks start off as some kind of rock. The starting rock can be igneous, sedimentary or even another metamorphic rock. Heat and/or pressure then change the rocks physical or chemical makeup. During metamorphism a rock may change chemically. Ions move and new minerals form. The new minerals are more stable in the new environment. Extreme pressure may lead to physical changes like foliation. Foliation forms as the rocks are squeezed. If pressure is exerted from one direction, the rock forms layers. This is foliation. If pressure is exerted from all directions, the rock usually does not show foliation. There are two main types of metamorphism: 1. Contact metamorphism results when magma contacts a rock, changing it by extreme heat (Figure 4.14). 2. Regional metamorphism occurs over a wide area. Great masses of rock are exposed to pressure from rock and sediment layers on top of it. The rock may also be compressed by other geological processes. Metamorphism does not cause a rock to melt completely. It only causes the minerals to change by heat or pressure. Hornfels is a rock with alternating bands of dark and light crystals. Hornfels is a good example of how minerals rearrange themselves during metamorphism (Figure 4.14). The minerals in hornfels separate by density. The result is that the rock becomes banded. Gneiss forms by regional metamorphism from extremely high temperature and pressure. ",text,
L_0071,metamorphic rocks,T_0694,"Metamorphic rocks start off as some kind of rock. The starting rock can be igneous, sedimentary or even another metamorphic rock. Heat and/or pressure then change the rocks physical or chemical makeup. During metamorphism a rock may change chemically. Ions move and new minerals form. The new minerals are more stable in the new environment. Extreme pressure may lead to physical changes like foliation. Foliation forms as the rocks are squeezed. If pressure is exerted from one direction, the rock forms layers. This is foliation. If pressure is exerted from all directions, the rock usually does not show foliation. There are two main types of metamorphism: 1. Contact metamorphism results when magma contacts a rock, changing it by extreme heat (Figure 4.14). 2. Regional metamorphism occurs over a wide area. Great masses of rock are exposed to pressure from rock and sediment layers on top of it. The rock may also be compressed by other geological processes. Metamorphism does not cause a rock to melt completely. It only causes the minerals to change by heat or pressure. Hornfels is a rock with alternating bands of dark and light crystals. Hornfels is a good example of how minerals rearrange themselves during metamorphism (Figure 4.14). The minerals in hornfels separate by density. The result is that the rock becomes banded. Gneiss forms by regional metamorphism from extremely high temperature and pressure. ",text,
L_0071,metamorphic rocks,T_0695,Quartzite and marble are the most commonly used metamorphic rocks. They are frequently chosen for building materials and artwork. Marble is used for statues and decorative items like vases (Figure 4.16). Quartzite is very hard and is often crushed and used in building railroad tracks. Schist and slate are sometimes used as building and landscape materials. ,text,
L_0072,earths energy,T_0696,"Almost all energy comes from the Sun. Plants make food energy from sunlight. Fossil fuels are made of the remains of plants and animals that stored the Suns energy millions of years ago. The Sun heats some areas more than others, which causes wind. The Suns energy also drives the water cycle, which moves water over the surface of the Earth. Both wind and water power can be used as renewable resources. Earths internal heat does not depend on the Sun for energy. This heat comes from remnant heat when the planet formed. It also comes from the decay of radioactive elements. Radioactivity is an important source of energy. ",text,
L_0072,earths energy,T_0697,"Energy provides the ability to move or change matter from one state to another (for example, from solid to liquid). Every living thing needs energy to live and grow. Your body gets its energy from food, but that is only a small part of the energy you use every day. Cooking your food takes energy, and so does keeping it cold in the refrigerator or the freezer. The same is true for heating or cooling your home. Whether you are turning on a light in the kitchen or riding in a car to school, you are using energy. Billions of people all around the world use energy, so there is a huge demand for resources to provide all of this energy. Why do we need so much energy? The main reason is that almost everything that happens on Earth involves energy. ",text,
L_0072,earths energy,T_0698,Energy changes form when something happens. But the total amount of energy always stays the same. The Law of Conservation of Energy says that energy cannot be created or destroyed. Scientists observed that energy could change from one form to another. They also observed that the overall amount of energy did not change. ,text,
L_0072,earths energy,T_0699,"Here is an example of how energy changes form: kicking a soccer ball. Your body gets energy from food. Where does the food get its energy? If youre eating a plant, then the energy comes directly from the Sun. If youre eating an animal, then the energy comes from a plant that got its energy from the Sun. Your body breaks down the food. It converts the food to chemical energy and stores it. When you are about to kick the ball, the energy must be changed again. Potential energy has the potential to do work. When your leg is poised to kick the ball but is not yet moving, your leg has potential energy. A ball at the top of a hill has the potential energy of location. Kinetic energy is the energy of anything in motion. Your muscles move your leg, your foot kicks the ball, and the ball gains kinetic energy (Figure 5.1). The kinetic energy was converted from potential energy that was in your leg before the kick. The action of kicking the ball is energy changing forms. The same is true for anything that involves change. ",text,
L_0072,earths energy,T_0700,Energy is the ability to do work. Fuel stores energy and can be released to do work. Heat is given off when fuel is burned. ,text,
L_0072,earths energy,T_0701,"What makes energy available whenever you need it? If you unplug a lamp, the light goes off. The lamp does not have a supply of energy to keep itself lit. The lamp uses electricity that comes through the outlet as its source of energy. The electricity comes from a power plant. The power plant has a source of energy to produce this electricity. ",text,
L_0072,earths energy,T_0702,"The energy to make the electricity comes from fuel. Fuel stores the energy and releases it when it is needed. Fuel is any material that can release energy in a chemical change. The food you eat acts as a fuel for your body. Gasoline and diesel fuel are fuels that provide the energy for most cars, trucks, and buses. But there are many different kinds of fuel. For fuel to be useful, its energy must be released in a way that can be controlled. ",text,
L_0072,earths energy,T_0703,"When fuel is burned, most of the energy is released as heat. Some of this heat can be used to do work. Heat cooks food or warms your house. Sometimes the heat is just waste heat. It still heats the environment, though. Heat from a fire can boil a pot of water. If you put an egg in the pot, you can eat a hard boiled egg in 15 minutes (cool it down first!). The energy to cook the egg was stored in the wood. The wood got that energy from the Sun when it was part of a tree. The Sun generated the energy by nuclear fusion. You started the fire with a match. The head of the match stores energy as chemical energy. That energy lights the wood on fire. The fire burns as long as there is energy in the wood. Once the wood has burned up, there is no energy left in it. The fire goes out. ",text,
L_0072,earths energy,T_0704,"Energy resources can be put into two categories renewable or non-renewable. Nonrenewable resources are used faster than they can be replaced. Renewable resources can be replaced as quickly as they are used. Renewable resources may also be so abundant that running out is impossible. The difference between non-renewable and renewable resources is like the difference between ordinary batteries and rechargeable ones. If a flashlight when ordinary batteries goes dead, the batteries need to be replaced. But if the flashlight has rechargeable batteries, the batteries can be placed in a charger. The charger transfers energy from an outlet into the batteries. Once recharged, the batteries can be put back into the flashlight. Rechargeable batteries can be used again and again (Figure 5.2). In this way, the energy in the rechargeable batteries is renewable. ",text,
L_0072,earths energy,T_0705,"Fossil fuels include coal, oil, and natural gas. Fossil fuels are the greatest energy source for modern society. Millions of years ago, plants used energy from the Sun to form carbon compounds. These compounds were later transformed into coal, oil, or natural gas. Fossil fuels take millions of years to form. For this reason, they are non-renewable. We will use most fossil fuels up in a matter of decades. Burning fossil fuels releases large amounts of pollution. The most important of these may be the greenhouse gas carbon dioxide. ",text,
L_0072,earths energy,T_0706,"Renewable energy resources include solar, water, wind, biomass, and geothermal power. These resources are usually replaced at the same rate that we use them. Scientists know that the Sun will continue to shine for billions of years. So we can use the solar energy without it ever running out. Water flows from high places to lower ones. Wind blows from areas of high pressure to areas of low pressure. We can use the flow of wind and water to generate power. We can count on wind and water to continue to flow! Burning wood is an example of biomass energy. Changing grains into biofuels is biomass energy. Biomass is renewable because we can plant new trees or crops to replace the ones we use. Geothermal energy uses water that was heated by hot rocks. There are always more hot rocks available to heat more water. Even renewable resources can be used unsustainably. We can cut down too many trees without replanting. We might need grains for food rather than biofuels. Some renewable resources are too expensive to be widely used. As the technology improves and more people use renewable energy, the prices will come down. The cost of renewable resources will go down relative to fossil fuels as we use fossil fuels up. In the long run renewable resources will need to make up a large amount of what we use. ",text,
L_0072,earths energy,T_0707,"Before we put effort into increasing the use of an energy source, we should consider two things. Is there a practical way to turn the resource into useful form of energy? For example, it is not practical if we dont get much more energy from burning a fuel than we put into making it. What happens when we turn the resource into energy? What happens when we use that resource? Mining the resource may cause a lot of health problems or environmental damage. Using the resource may create a large amount of pollution. In this case, that fuel may also not be the best choice for an energy resource. ",text,
L_0072,earths energy,T_0708,"Today we rely on electricity more than ever, but the resources that currently supply our power are finite. The race is on to harness more renewable resources, but getting all that clean energy from production sites to homes and businesses is proving to be a major challenge. Learn more by watching the resource below:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0073,nonrenewable energy resources,T_0709,"Fossil fuels are made from plants and animals that lived hundreds of millions of years ago. The plants and animals died. Their remains settled onto the ground and at the bottom of the sea. Layer upon layer of organic material was laid down. Eventually, the layers were buried very deeply. They experienced intense heat and pressure. Over millions of years, the organic material turned into fossil fuels. Fossil fuels are compounds of carbon and hydrogen, called hydrocarbons. Hydrocarbons can be solid, liquid, or gas. The solid form is coal. The liquid form is petroleum, or crude oil. The gaseous form is natural gas. ",text,
L_0073,nonrenewable energy resources,T_0710,"Coal is a solid hydrocarbon. Coal is useful as a fuel, especially for generating electricity. ",text,
L_0073,nonrenewable energy resources,T_0711,"Coal forms from dead plants that settled at the bottom of swamps millions of years ago. Water and mud in the swamp kept oxygen away from the plant material. Sand and clay settled on top of the decaying plants. The weight of this material squeezed out the water and some other substances. Over time, the organic material became a carbon-rich rock. This rock is coal. ",text,
L_0073,nonrenewable energy resources,T_0712,"Coal is a black or brownish-black rock that burns easily (Figure 5.3). Most coal is sedimentary rock. The hardest type of coal, anthracite, is a metamorphic rock. That is because it is exposed to higher temperature and pressure as it forms. Coal is mostly carbon, but some other elements can be found in coal, including sulfur. ",text,
L_0073,nonrenewable energy resources,T_0713,"Around the world, coal is the largest source of energy for electricity. The United States is rich in coal. Pennsylvania and the region to the west of the Appalachian Mountains are some of the most coal-rich areas of the United States. Coal has to be mined to get it out of the ground. Coal mining affects the environment and human health. Coal mining can take place underground or at the surface. Each method has some advantages and disadvantages. Surface mining exposes minerals that were underground to air and water at the surface. These minerals contain the chemical element sulfur. Sulfur mixes with air and water to make sulfuric acid. This acid is a highly corrosive chemical. Sulfuric acid gets into nearby streams and can kill fish, plants, and animals. Surface mining is safer for the miners. Coal mining underground is dangerous for the coal miners. Miners are sometimes killed if there is an explosion or a mine collapse. Miners breathe in coal dust and can get terrible lung diseases after a number of years in the mines. ",text,
L_0073,nonrenewable energy resources,T_0714,"To prepare coal for use, the coal is first crushed into powder and burned in a furnace. Like other fuels, coal releases most of its energy as heat when it burns. The heat from the burning coal is used to boil water. This makes steam. The steam spins turbines, which creates electricity. ",text,
L_0073,nonrenewable energy resources,T_0715,"Oil is a thick, dark brown or black liquid. It is found in rock layers of the Earths crust. Oil is currently the most commonly used source of energy in the world. ",text,
L_0073,nonrenewable energy resources,T_0716,"The way oil forms is similar in many ways to coal. Tiny organisms like plankton and algae die and settle to the bottom of the sea. Sediments settle over the organic material. Oxygen is kept away by the sediments. When the material is buried deep enough, it is exposed to high heat and pressure. Over millions of years, the organic material transforms into liquid oil. ",text,
L_0073,nonrenewable energy resources,T_0717,"The United States produces only about one-quarter as much oil as it uses. The main oil producing regions in the U.S. are the Gulf of Mexico, Texas, Alaska, and California. Geologists look for oil in folded layers of rock called anticlines. Oil moves through permeable rock and is trapped by the impermeable cap rock. ",text,
L_0073,nonrenewable energy resources,T_0718,"Oil comes out of the ground as crude oil. Crude oil is a mixture of many different hydrocarbons. Oil is separated into different compounds at an oil refinery (Figure 5.4). This is done by heating the oil. Each hydrocarbon compound in crude oil boils at a different temperature. We get gasoline, diesel, and heating oil, plus waxes, plastics, and fertilizers from crude oil. These fuels are rich sources of energy. Since they are mostly liquids they can be easily transported. These fuels provide about 90% of the energy used for transportation around the world. ",text,
L_0073,nonrenewable energy resources,T_0719,"Gasoline is a concentrated resource. It contains a large amount of energy for its weight. This is important because the more something weighs, the more energy is needed to move it. If gasoline could only provide a little energy, a car would have to carry a lot of it to be able to travel very far. Or the car would need to be filled up frequently. So a highly concentrated energy resource is a practical fuel to power cars and other forms of transportation. Lets consider how gasoline powers a car. As gasoline burns, it releases most of its energy as heat. It also releases carbon dioxide gas and water vapor. The heat makes the gases expand. This forces the pistons inside the engine to move. The engine makes enough power to move the car. ",text,
L_0073,nonrenewable energy resources,T_0720,Using gasoline to power automobiles affects the environment. The exhaust fumes from burning gasoline cause air pollution. These pollutants include smog and ground-level ozone. Air pollution is a big problem for cities where large numbers of people drive every day. Burning gasoline also produces carbon dioxide. This is a greenhouse gas and is a cause of global warming. Similar pollutants come from other forms of oil. ,text,
L_0073,nonrenewable energy resources,T_0721,Natural gas is mostly methane. ,text,
L_0073,nonrenewable energy resources,T_0722,Natural gas is often found along with coal or oil in underground deposits. This is because natural gas forms with these other fossil fuels. One difference between natural gas and oil is that natural gas forms at higher temperatures. ,text,
L_0073,nonrenewable energy resources,T_0723,"The largest natural gas reserves in the United States are located in the Rocky Mountain states, Texas, and the Gulf of Mexico region. California also has natural gas, mostly in the northern Sacramento Valley and the Sacramento Delta. Natural gas must be processed before it can be used as a fuel. Poisonous chemicals and water must be removed. Natural gas is delivered to homes, where it is used for cooking and heating. Natural gas is also a major energy source for powering turbines to make electricity. Natural gas releases most of its energy as heat when it burns. The power plant is able to use this heat, either in the form of hot gases or steam, to spin turbines. The spinning turbines turn generators, and the generators create electricity. ",text,
L_0073,nonrenewable energy resources,T_0724,"Processing natural gas has harmful effects on the environment, just like oil. Natural gas burns cleaner than other fossil fuels. As a result, it causes less air pollution. It also produces less carbon dioxide than the other fossil fuels. Still, natural gas does emit pollutants. ",text,
L_0073,nonrenewable energy resources,T_0725,"Fossil fuels present many problems. These fuels are non-renewable resources, so our supplies of them will eventually run out. Safety can be a problem, too. Since these fuels burn so easily, a natural gas leak in a building or an underground pipe can lead to a deadly explosion. Using fossil fuels affects the environment in a variety of ways. There are impacts to the environment when we extract these resources. Burning these fuels causes air pollution. These fuels release carbon dioxide, which is a major factor in global warming (Figure 5.5). Many of the problems with fossil fuels are worse for coal than for oil or natural gas. Burning coal releases more carbon dioxide than either oil or natural gas. Yet coal is the most common fossil fuel, so we continue to burn large amounts of it. That makes coal the biggest contributor to global warming. Another problem with coal is that most coal contains sulfur. As it burns, the sulfur goes into the air as sulfur dioxide. Sulfur dioxide is the main cause of acid rain. Acid rain can be deadly to plants, animals, and whole ecosystems. Burning coal also puts a large number of small solid particulates into the air. These particles are dangerous to people, especially those who have asthma. People with asthma may end up in the hospital on days when particulate pollution is high. ",text,
L_0073,nonrenewable energy resources,T_0726,Nuclear energy is produced by splitting the nucleus of an atom. This releases a huge amount of energy. ,text,
L_0073,nonrenewable energy resources,T_0727,"Nuclear power plants use uranium that has been concentrated in fuel rods (Figure 5.6). The uranium atoms are split apart when they are hit by other extremely tiny particles. These particles must be controlled or they would cause a dangerous explosion. Nuclear power plants use the energy they produce to heat water. The water turns into steam, which causes a turbine to spin. This in turn produces electricity. ",text,
L_0073,nonrenewable energy resources,T_0728,"Many countries around the world use nuclear energy as a source of electricity. For example, France gets about 80% of its electricity from nuclear energy. In the United States, a little less than 20% of electricity comes from nuclear energy. Nuclear energy does not pollute. If there are no accidents, a nuclear power plant releases nothing but steam into the air. But nuclear energy does create other environmental problems. Splitting atoms creates dangerous radioactive waste. These wastes can remain dangerous for hundreds of thousands of years. Scientists and engineers are still looking for ways to keep this waste safely away from people. ",text,
L_0073,nonrenewable energy resources,T_0729,"Nuclear power is a controversial subject in California and most other places. Nuclear power has no pollutants including carbon emissions, but power plants are not always safe and the long-term disposal of wastes is a problem that has not yet been solved. The future of nuclear power is murky. Find out more at: http://science.kqed.org/ques MEDIA Click image to the left or use the URL below. URL: ",text,
L_0074,renewable energy resources,T_0730,,text,
L_0074,renewable energy resources,T_0731,"The Sun is Earths main source of energy. The Sun gives us both light and heat. The Sun changes hydrogen into helium through nuclear fusion. This releases huge amounts of energy. The energy travels to the Earth mostly as visible light. The energy is carried through the empty space by radiation. We can use sunlight as an energy resource, called solar energy (Figure 5.7). ",text,
L_0074,renewable energy resources,T_0732,"Solar energy has been used on a small scale for hundreds of years. Today we are using solar energy for more of our power demands. Solar power plants are being built in many locations around the world. In the United States, the southwestern deserts are well suited for solar plants. ",text,
L_0074,renewable energy resources,T_0733,"Sunlight is turned into electricity at a solar power plant. These power plants use a large group of mirrors to focus sunlight on one place. This place is called a receiver (Figure 5.8). At the receiver, a liquid such as oil or water is heated to a high temperature. The liquid transfers its heat by conduction. In conduction, energy moves between two objects that are in contact. The higher temperature object transfers heat to the lower temperature object. For example, when you heat a pot of water on a stove top, energy moves from the pot to its metal handle by conduction. At a solar power plant, the energy conducted by the heated liquid is used to make electricity. ",text,
L_0074,renewable energy resources,T_0734,"Solar energy is used to heat homes and water, and to make electricity. Scientists and engineers have many ways to get energy from the Sun (Figure 5.9). One is by using solar cells. Solar cells are devices that turn sunlight directly into electricity. Lots of solar cells make up an individual solar panel. You may have seen solar panels on roof tops. The Suns heat can also be trapped in your home by using south facing windows and good insulation. ",text,
L_0074,renewable energy resources,T_0735,"Solar energy has many benefits. It does not produce any pollution. There is plenty of it available, much more than we could possibly use. But solar energy has problems. The Sun doesnt shine at night. A special battery is needed to store extra energy during the day for use at night. The technology for most uses of solar energy is still expensive. Until solar technology becomes more affordable, most people will prefer to get their energy from other sources. ",text,
L_0074,renewable energy resources,T_0735,"Solar energy has many benefits. It does not produce any pollution. There is plenty of it available, much more than we could possibly use. But solar energy has problems. The Sun doesnt shine at night. A special battery is needed to store extra energy during the day for use at night. The technology for most uses of solar energy is still expensive. Until solar technology becomes more affordable, most people will prefer to get their energy from other sources. ",text,
L_0074,renewable energy resources,T_0736,"Moving water has energy (Figure 5.10). That energy is used to make electricity. Hydroelectric power harnesses the energy of water moving down a stream. Hydropower is the most widely used form of renewable energy in the world. This abundant energy source provides almost one fifth of the worlds electricity. The energy of waves and tides can also be used to produce water power. At this time, wave and tidal power are rare. ",text,
L_0074,renewable energy resources,T_0737,"To harness water power, a stream must be dammed. Narrow valleys are the best for dams. While sitting in the reservoir behind the dam, the water has potential energy. Water is allowed to flow downhill into a large turbine. While flowing downhill, the water has kinetic energy. Kinetic energy makes the turbine spin. The turbine is connected to a generator, which makes electricity. ",text,
L_0074,renewable energy resources,T_0738,Many of the suitable streams in the United States have been developed for hydroelectric power. Many streams worldwide also have hydroelectric plants. Hydropower is a major source of Californias electricity. It accounts for about 14.5 percent of the total. Most of Californias nearly 400 hydroelectric power plants are located in the Sierra Nevada mountains. ,text,
L_0074,renewable energy resources,T_0739,"Water power does not burn a fuel. So it causes less pollution than many other kinds of energy. Water power is also a renewable resource. Water keeps flowing downhill. Although we use some of the energy from this movement, we are not using up the water. Water power does have problems. A large dam stops a streams flow, which floods the land upstream. A beautiful location may be lost. People may be displaced. The dams and turbines also change the downstream environment. Fish and other living things may not be able to survive. Dams slow the release of silt. Downstream deltas retreat and beaches may be starved of sand. Seaside cities may become exposed to storms and rising sea levels. Tidal power stations may need to close off a narrow bay or estuary. Wave power plants must withstand coastal storms and the corrosion of seawater. ",text,
L_0074,renewable energy resources,T_0740,"Although not yet widely used, many believe tidal power has more potential than wind or solar power for meeting alternative energy needs. Quest radio looks at plans for harnessing power from the sea by San Francisco and along the northern California coast. Learn more at: http://science.kqed.org/quest/audio/harnessing-power-from-the-sea/ MEDIA Click image to the left or use the URL below. URL: ",text,
L_0074,renewable energy resources,T_0741,"The energy from the Sun creates wind (Figure 5.11). Wind energy moves by convection. The Sun heats some locations more than others. Warm air rises, so other air rushes in to fill the hole left by the rising air. This horizontal movement of air is called wind. ",text,
L_0074,renewable energy resources,T_0742,"Wind power uses moving air as a source of energy. Some types of wind power have been around for a long time. People have used windmills to grind grain and pump water for hundreds of years. Sailing ships have depended on wind for millennia. Wind is now used to generate electricity. Moving air can make a turbine spin, just like moving water can. Moving air has kinetic energy. When wind hits the blades of the turbine, the kinetic energy makes the blades move. The turbine spins and creates electricity. ",text,
L_0074,renewable energy resources,T_0743,"Wind power has many advantages. It is clean: it does not release pollutants or carbon dioxide. It is plentiful almost everywhere. The technology to harness wind energy is being developed rapidly. Wind power also has problems. Wind does not blow all of the time, so wind energy must be stored for later use. Alternatively, another energy source needs to be available when the wind is not blowing. Wind turbines are expensive. They can wear out quickly. Finally, windmills are not welcomed by residents of some locations. They say that they are unattractive. Yet even with these problems, wind turbines are a competitive form of renewable energy. Many states are currently using wind power. Wind turbines are set up in mountain passes. This is common in California, where cool Pacific Ocean air is sucked across the passes and into the warmer inland valleys. ",text,
L_0074,renewable energy resources,T_0744,"Biomass is another renewable source of energy. Biomass includes wood, grains, and other plant materials or waste materials. People can burn wood directly for energy in the form of heat. Biomass can also be processed to make biofuel. Biofuel is a fairly new type of energy that is becoming more popular. Biomass is useful because it can be made liquid. This means that they can be used in cars and trucks. Some car engines can be powered by pure vegetable oil or even recycled vegetable oil. Sometimes the exhaust from these cars smells like French fries! By using biofuels, we can cut down on the amount of fossil fuel that we use. Because living plants take carbon dioxide out of the air, growing plants for biofuel can mean that we will put less of this gas into the air overall. This could help us do something about the problem of global warming. ",text,
L_0074,renewable energy resources,T_0745,"Geothermal energy comes the Earths internal heat. Hot springs and geysers are produced by water that is heated by magma or hot rock below the surface. At a geothermal power plant, engineers drill wells into the hot rocks. Hot water or steam may come up through the wells. Alternatively, water may be put down into the well to be heated. It then comes up. The hot water or steam makes a turbine spin. This makes electricity. ",text,
L_0074,renewable energy resources,T_0746,"Because the hot water or steam can be used directly to make a turbine spin, geothermal energy can be used without processing. Geothermal energy is clean and safe. It is renewable. There will always be hot rocks and water can be pumped down into a well. There, the water can be heated again to make more steam. Geothermal energy is an excellent resource in some parts of the world. Iceland is gets about one fourth of its electricity from geothermal sources. In the United States, California leads all states in producing geothermal energy. Geothermal energy in California is concentrated in the northern part of the state. The largest plant is in the Geysers Geothermal Resource Area. Geothermal energy is not economical everywhere. Many parts of the world do not have underground sources of heat that are close enough to the surface for building geothermal power plants. ",text,
L_0074,renewable energy resources,T_0747,"Where Earths internal heat gets close to the surface, geothermal power is a clean source of energy. In California, The Geysers supplies energy for many nearby homes and businesses. Learn more at: http://science.kqed.org/ques MEDIA Click image to the left or use the URL below. URL: ",text,
L_0076,continental drift,T_0757,"Alfred Wegener was an early 20th century German meteorologist. Wegener believed that the continents were once all joined together. He named the supercontinent Pangaea, meaning all earth. Wegener suggested that Pangaea broke up long ago. Since then, the continents have been moving to their current positions. He called his hypothesis continental drift. ",text,
L_0076,continental drift,T_0758,Wegener and his supporters collected a great deal of evidence for the continental drift hypothesis. Wegener found that this evidence was best explained if the continents had at one time been joined together. ,text,
L_0076,continental drift,T_0759,"Wegener found rocks of the same type and age on both sides of the Atlantic Ocean. He thought that the rocks formed side by side. These rocks then drifted apart on separate continents. Wegener also matched up mountain ranges across the Atlantic Ocean. The Appalachian Mountains were just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway. Wegener concluded that they formed as a single mountain range. This mountain range broke apart as the continents split up. The mountain range separated as the continents drifted. ",text,
L_0076,continental drift,T_0760,"Wegener also found evidence for continental drift from fossils (Figure 6.7). The same type of plant and animal fossils are found on continents that are now widely separated. These organisms would not have been able to travel across the oceans. Fossils of the seed fern Glossopteris are found across all of the southern continents. These seeds are too heavy to be carried across the ocean by wind. Mesosaurus fossils are found in South America and South Africa. Mesosaurus could swim, but only in fresh water. Cynognathus and Lystrosaurus were reptiles that lived on land. Both of these animals were unable to swim at all. Their fossils have been found across South America, Africa, India and Antarctica. Wegener thought that all of these organisms lived side by side. The lands later moved apart so that the fossils are separated. ",text,
L_0076,continental drift,T_0761,"Wegener also looked at evidence from ancient glaciers. Glaciers are found in very cold climates near the poles. The evidence left by some ancient glaciers is very close to the equator. Wegener knew that this was impossible! However, if the continents had moved, the glaciers would have been centered close to the South Pole. ",text,
L_0076,continental drift,T_0762,Coral reefs are found only in warm water. Coal swamps are also found in tropical and subtropical environments. Wegener discovered ancient coal seams and coral reef fossils in areas that are much too cold today. Wegener thought that the continents have moved since the time of Pangaea. ,text,
L_0076,continental drift,T_0763,"Some important evidence for continental drift came after Wegeners death. This is the magnetic evidence. Earths magnetic field surrounds the planet from pole to pole. If you have ever been hiking or camping, you may have used a compass to help you find your way. A compass points to the magnetic North Pole. The compass needle aligns with Earths magnetic field (Figure 6.8). Some rocks contain little compasses too! As lava cools, tiny iron-rich crystals line up with Earths magnetic field. ",text,
L_0079,stress in earths crust,T_0793,"Stress is the force applied to a rock. There are four types of stresses: Confining stress happens as weight of all the overlying rock pushes down on a deeply buried rock. The rock is being pushed in from all sides, which compresses it. The rock will not deform because there is no place for it to move. Compression stress squeezes rocks together. Compression causes rocks to fold or fracture (Figure 7.1). When two cars collide, compression causes them to crumple. Compression is the most common stress at convergent plate boundaries. Tension stress pulls rocks apart. Tension causes rocks to lengthen or break apart. Tension is the major type of stress found at divergent plate boundaries. Shear stress happens when forces slide past each other in opposite directions (Figure 7.2). This is the most common stress found at transform plate boundaries. The amount of stress on a rock may be greater than the rocks strength. In that case, the rock will change and deform (Figure 7.3). Deep within the Earth, the pressure is very great. A rock behaves like a stretched rubber band. When the stress stops, the rock goes back to its original shape. If more stress is applied to the rock, it bends and flows. It does not return to its original shape. Near the surface, if the stress continues, the rock will fracture and break. ",text,
L_0079,stress in earths crust,T_0794,"Sedimentary rocks are formed in horizontal layers. This is magnificently displayed around the southwestern United States. The arid climate allows rock layers to be well exposed (Figure 7.4). The lowest layers are the oldest and the higher layers are younger. Folds, joints and faults are caused by stresses. Figure 7.5 shows joints in a granite hillside. If a sedimentary rock is tilted or folded, we know that stresses have changed the rock (Figure 7.6). ",text,
L_0079,stress in earths crust,T_0794,"Sedimentary rocks are formed in horizontal layers. This is magnificently displayed around the southwestern United States. The arid climate allows rock layers to be well exposed (Figure 7.4). The lowest layers are the oldest and the higher layers are younger. Folds, joints and faults are caused by stresses. Figure 7.5 shows joints in a granite hillside. If a sedimentary rock is tilted or folded, we know that stresses have changed the rock (Figure 7.6). ",text,
L_0079,stress in earths crust,T_0795,"Deep within the Earth, as plates collide, rocks crumple into folds. You can model these folds by placing your hands on opposite edges of a piece of cloth and pushing your hands together. In sedimentary rocks, you can easily trace the folding of the layers. In the Figure 7.6, the rock layers are no longer horizontal. They tilt downhill from right to left in a monocline. Once rocks are folded, they do not return to their original shape. There are three types of folds: monoclines, anticlines, and synclines. A monocline is a simple one step bend in the rock layers (Figure 7.7). In a monocline, the oldest rocks are still at the bottom and the youngest are at the top. An anticline is a fold that arches upward. The rocks dip away from the center of the fold (Figure 7.8). The oldest rocks are found at the center of an anticline. The youngest rocks are draped over them at the top of the structure. When upward folding rocks form a circular structure, that structure is called a dome. If the top of the dome is eroded off, the oldest rocks are exposed at the center. A syncline is a fold that bends downward (Figure 7.9). In a syncline, the youngest rocks are at the center. The oldest rocks are at the outside edges. When rocks bend downward in a circular structure, it is called a basin. If the rocks are eroded, the youngest rocks are at the center. Basins can be enormous, like the Michigan Basin. ",text,
L_0079,stress in earths crust,T_0795,"Deep within the Earth, as plates collide, rocks crumple into folds. You can model these folds by placing your hands on opposite edges of a piece of cloth and pushing your hands together. In sedimentary rocks, you can easily trace the folding of the layers. In the Figure 7.6, the rock layers are no longer horizontal. They tilt downhill from right to left in a monocline. Once rocks are folded, they do not return to their original shape. There are three types of folds: monoclines, anticlines, and synclines. A monocline is a simple one step bend in the rock layers (Figure 7.7). In a monocline, the oldest rocks are still at the bottom and the youngest are at the top. An anticline is a fold that arches upward. The rocks dip away from the center of the fold (Figure 7.8). The oldest rocks are found at the center of an anticline. The youngest rocks are draped over them at the top of the structure. When upward folding rocks form a circular structure, that structure is called a dome. If the top of the dome is eroded off, the oldest rocks are exposed at the center. A syncline is a fold that bends downward (Figure 7.9). In a syncline, the youngest rocks are at the center. The oldest rocks are at the outside edges. When rocks bend downward in a circular structure, it is called a basin. If the rocks are eroded, the youngest rocks are at the center. Basins can be enormous, like the Michigan Basin. ",text,
L_0079,stress in earths crust,T_0796,"With enough stress, a rock will fracture, or break. The fracture is called a joint if the rock breaks but doesnt move, as shown in Figure 7.10. If the rocks on one or both sides of a fracture move, the fracture is called a fault (Figure 7.11). Faults can occur alone or in clusters, creating a fault zone. Earthquakes happen when rocks break and move suddenly. The energy released causes an earthquake. Slip is the distance rocks move along a fault, as one block of rock moves past the other. The angle of a fault is called When compression squeezes the crust into a smaller space, the hanging wall pushes up relative to the footwall. This creates a reverse fault. A thrust fault is a type of reverse fault where the angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 7.13). ",text,
L_0079,stress in earths crust,T_0796,"With enough stress, a rock will fracture, or break. The fracture is called a joint if the rock breaks but doesnt move, as shown in Figure 7.10. If the rocks on one or both sides of a fracture move, the fracture is called a fault (Figure 7.11). Faults can occur alone or in clusters, creating a fault zone. Earthquakes happen when rocks break and move suddenly. The energy released causes an earthquake. Slip is the distance rocks move along a fault, as one block of rock moves past the other. The angle of a fault is called When compression squeezes the crust into a smaller space, the hanging wall pushes up relative to the footwall. This creates a reverse fault. A thrust fault is a type of reverse fault where the angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 7.13). ",text,
L_0079,stress in earths crust,T_0796,"With enough stress, a rock will fracture, or break. The fracture is called a joint if the rock breaks but doesnt move, as shown in Figure 7.10. If the rocks on one or both sides of a fracture move, the fracture is called a fault (Figure 7.11). Faults can occur alone or in clusters, creating a fault zone. Earthquakes happen when rocks break and move suddenly. The energy released causes an earthquake. Slip is the distance rocks move along a fault, as one block of rock moves past the other. The angle of a fault is called When compression squeezes the crust into a smaller space, the hanging wall pushes up relative to the footwall. This creates a reverse fault. A thrust fault is a type of reverse fault where the angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 7.13). ",text,
L_0079,stress in earths crust,T_0796,"With enough stress, a rock will fracture, or break. The fracture is called a joint if the rock breaks but doesnt move, as shown in Figure 7.10. If the rocks on one or both sides of a fracture move, the fracture is called a fault (Figure 7.11). Faults can occur alone or in clusters, creating a fault zone. Earthquakes happen when rocks break and move suddenly. The energy released causes an earthquake. Slip is the distance rocks move along a fault, as one block of rock moves past the other. The angle of a fault is called When compression squeezes the crust into a smaller space, the hanging wall pushes up relative to the footwall. This creates a reverse fault. A thrust fault is a type of reverse fault where the angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 7.13). ",text,
L_0079,stress in earths crust,T_0796,"With enough stress, a rock will fracture, or break. The fracture is called a joint if the rock breaks but doesnt move, as shown in Figure 7.10. If the rocks on one or both sides of a fracture move, the fracture is called a fault (Figure 7.11). Faults can occur alone or in clusters, creating a fault zone. Earthquakes happen when rocks break and move suddenly. The energy released causes an earthquake. Slip is the distance rocks move along a fault, as one block of rock moves past the other. The angle of a fault is called When compression squeezes the crust into a smaller space, the hanging wall pushes up relative to the footwall. This creates a reverse fault. A thrust fault is a type of reverse fault where the angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 7.13). ",text,
L_0079,stress in earths crust,T_0796,"With enough stress, a rock will fracture, or break. The fracture is called a joint if the rock breaks but doesnt move, as shown in Figure 7.10. If the rocks on one or both sides of a fracture move, the fracture is called a fault (Figure 7.11). Faults can occur alone or in clusters, creating a fault zone. Earthquakes happen when rocks break and move suddenly. The energy released causes an earthquake. Slip is the distance rocks move along a fault, as one block of rock moves past the other. The angle of a fault is called When compression squeezes the crust into a smaller space, the hanging wall pushes up relative to the footwall. This creates a reverse fault. A thrust fault is a type of reverse fault where the angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 7.13). ",text,
L_0079,stress in earths crust,T_0796,"With enough stress, a rock will fracture, or break. The fracture is called a joint if the rock breaks but doesnt move, as shown in Figure 7.10. If the rocks on one or both sides of a fracture move, the fracture is called a fault (Figure 7.11). Faults can occur alone or in clusters, creating a fault zone. Earthquakes happen when rocks break and move suddenly. The energy released causes an earthquake. Slip is the distance rocks move along a fault, as one block of rock moves past the other. The angle of a fault is called When compression squeezes the crust into a smaller space, the hanging wall pushes up relative to the footwall. This creates a reverse fault. A thrust fault is a type of reverse fault where the angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 7.13). ",text,
L_0079,stress in earths crust,T_0797,"A strike-slip fault is a dip-slip fault where the dip of the fault plane is vertical. Strike-slip faults result from shear stresses. If you stand with one foot on each side of a strike-slip fault, one side will be moving toward you while the other side moves away from you. If your right foot moves toward you, the fault is known as a right-lateral strike-slip fault. If your left foot moves toward you, the fault is a left-lateral strike-slip fault (Figure 7.14). ",text,
L_0079,stress in earths crust,T_0798,"The San Andreas Fault in California is a right-lateral strike-slip fault (Figure 7.15). It is also a transform fault because the San Andreas is a plate boundary. As you can see, California will not fall into the ocean someday. The land west of the San Andreas Fault is moving northeastward, while the North American plate moves southwest. Someday, millions of years from now, Los Angeles will be a suburb of San Francisco! ",text,
L_0079,stress in earths crust,T_0798,"The San Andreas Fault in California is a right-lateral strike-slip fault (Figure 7.15). It is also a transform fault because the San Andreas is a plate boundary. As you can see, California will not fall into the ocean someday. The land west of the San Andreas Fault is moving northeastward, while the North American plate moves southwest. Someday, millions of years from now, Los Angeles will be a suburb of San Francisco! ",text,
L_0079,stress in earths crust,T_0798,"The San Andreas Fault in California is a right-lateral strike-slip fault (Figure 7.15). It is also a transform fault because the San Andreas is a plate boundary. As you can see, California will not fall into the ocean someday. The land west of the San Andreas Fault is moving northeastward, while the North American plate moves southwest. Someday, millions of years from now, Los Angeles will be a suburb of San Francisco! ",text,
L_0079,stress in earths crust,T_0799,"Many processes create mountains. Most mountains form along plate boundaries. A few mountains may form in the middle of a plate. For example, huge volcanoes are mountains formed at hotspots within the Pacific Plate. ",text,
L_0079,stress in earths crust,T_0800,"Most of the worlds largest mountains form as plates collide at convergent plate boundaries. Continents are too buoyant to get pushed down into the mantle. So when the plates smash together, the crust crumples upwards. This creates mountains. Folding and faulting in these collision zones makes the crust thicker. The worlds highest mountain range, the Himalayas, is growing as India collides with Eurasia. About 80 million years ago, India was separated from Eurasia by an ocean (Figure 7.16). As the plates collided, pieces of the old seafloor were forced over the Asian continent. This old seafloor is now found high in the Himalayas (Figure 7.17). ",text,
L_0079,stress in earths crust,T_0801,Volcanic mountain ranges form when oceanic crust is pushed down into the mantle at convergent plate boundaries. The Andes Mountains are a chain of coastal volcanic mountains. They are forming as the Nazca plate subducts beneath the South American plate (Figure 7.18). ,text,
L_0079,stress in earths crust,T_0802,"Mid-ocean ridges form at divergent plate boundaries. As the ocean floor separates an enormous line of volcanoes is created. When continental crust is pulled apart, it breaks into blocks. These blocks of crust are separated by normal faults. The blocks slide up or down. The result is alternating mountain ranges and valleys. This topography is known as basin-and-range (Figure 7.19). The area near Death Valley, California is the center of a classic basin-and-range province (Figure 7.20). ",text,
L_0079,stress in earths crust,T_0802,"Mid-ocean ridges form at divergent plate boundaries. As the ocean floor separates an enormous line of volcanoes is created. When continental crust is pulled apart, it breaks into blocks. These blocks of crust are separated by normal faults. The blocks slide up or down. The result is alternating mountain ranges and valleys. This topography is known as basin-and-range (Figure 7.19). The area near Death Valley, California is the center of a classic basin-and-range province (Figure 7.20). ",text,
L_0079,stress in earths crust,T_0802,"Mid-ocean ridges form at divergent plate boundaries. As the ocean floor separates an enormous line of volcanoes is created. When continental crust is pulled apart, it breaks into blocks. These blocks of crust are separated by normal faults. The blocks slide up or down. The result is alternating mountain ranges and valleys. This topography is known as basin-and-range (Figure 7.19). The area near Death Valley, California is the center of a classic basin-and-range province (Figure 7.20). ",text,
L_0086,igneous landforms and geothermal activ,T_0863,Extrusive igneous rocks cool at the surface. Volcanoes are one type of feature that forms from extrusive rocks. Several other interesting landforms are also extrusive features. Intrusive igneous rocks cool below the surface. These rocks do not always remain hidden. Rocks that formed in the crust are exposed when the rock and sediment that covers them is eroded away. ,text,
L_0086,igneous landforms and geothermal activ,T_0864,"When lava is thick, it flows slowly. If thick lava makes it to the surface, it cannot flow far from the vent. It often stays right in the middle of a crater at the top of a volcano. Here the lava creates a large, round lava dome (Figure ",text,
L_0086,igneous landforms and geothermal activ,T_0865,"A lava plateau is made of a large amount of fluid lava. The lava flows over a large area and cools. This creates a large, flat surface of igneous rock. Lava plateaus may be huge. The Columbia Plateau covers over 161,000 square kilometers (63,000 square miles). It makes up parts of the states of Washington, Oregon, and Idaho. Thin, fluid lava created the rock that makes up the entire ocean floor. This is from multiple eruptions from vents at the mid-ocean ridge. While not exactly a lava plateau, its interesting to think about so much lava! ",text,
L_0086,igneous landforms and geothermal activ,T_0866,New land is created in volcanic eruptions. The Hawaiian Islands are shield volcanoes. These volcanoes formed from fluid lava (Figure 8.21). The island grows as lava is added on the coast. New land may also emerge from lava that erupts from beneath the water. This is one way that new land is created. ,text,
L_0086,igneous landforms and geothermal activ,T_0867,Magma that cools underground forms intrusions (Figure 8.22). Intrusions become land formations if they are exposed at the surface by erosion. ,text,
L_0086,igneous landforms and geothermal activ,T_0868,"Water works its way through porous rocks or soil. Sometimes this water is heated by nearby magma. If the water makes its way to the surface, it forms a hot spring or a geyser. ",text,
L_0086,igneous landforms and geothermal activ,T_0869,"When hot water gently rises to the surface, it creates a hot spring. A hot spring forms where a crack in the Earth allows water to reach the surface after being heated underground. Many hot springs are used by people as natural hot tubs. Some people believe that hot springs can cure illnesses. Hot springs are found all over the world, even in Antarctica! ",text,
L_0086,igneous landforms and geothermal activ,T_0870,"Geysers are also created by water that is heated beneath the Earths surface. The water may become superheated by magma. It becomes trapped in a narrow passageway. The heat and pressure build as more water is added. When the pressure is too much, the superheated water bursts out onto the surface. This is a geyser. There are only a few areas in the world where the conditions are right for the formation of geysers. Only about 1,000 geysers exist worldwide. About half of them are in the United States. The most famous geyser is Old Faithful at Yellowstone National Park (Figure 8.23). It is rare for a geyser to erupt so regularly, which is why Old Faithful is famous. ",text,
L_0087,weathering,T_0871,"Weathering changes solid rock into sediments. Sediments are different sizes of rock particles. Boulders are sedi- ments; so is gravel. At the other end, silt and clay are also sediments. Weathering causes rocks at the Earths surface to change form. The new minerals that form are stable at the Earths surface. It takes a long time for a rock or mountain to weather. But a road can do so much more quickly. If you live in a part of the world that has cold winters, you may only have to wait one year to see a new road start to weather (Figure ",text,
L_0087,weathering,T_0872,"Mechanical weathering breaks rock into smaller pieces. These smaller pieces are just like the bigger rock; they are just smaller! The rock has broken without changing its composition. The smaller pieces have the same minerals in the same proportions. You could use the expression a chip off the old block to describe mechanical weathering! The main agents of mechanical weathering are water, ice, and wind. ",text,
L_0087,weathering,T_0873,"Rocks can break apart into smaller pieces in many ways. Ice wedging is common where water goes above and below its freezing point (Figure 9.2). This can happen in winter in the mid-latitudes or in colder climates in summer. Ice wedging is common in mountainous regions. This is how ice wedging works. When liquid water changes into solid ice, it increases in volume. You see this when you fill an ice cube tray with water and put it in the freezer. The ice cubes go to a higher level in the tray than the water. You also may have seen this if you put a can of soda into the freezer so that it cools down quickly. If you leave the can in the freezer too long, the liquid expands so much that it bends or pops the can. (For the record, water is very unusual. Most substances get smaller when they change from a liquid to a solid.) ",text,
L_0087,weathering,T_0874,"Abrasion is another type of mechanical weathering. With abrasion, one rock bumps against another rock. Gravity causes abrasion as a rock tumbles down a slope. Moving water causes abrasion it moves rocks so that they bump against one another (Figure 9.3). Strong winds cause abrasion by blasting sand against rock surfaces. Finally, the ice in glaciers cause abrasion. Pieces of rock embedded in ice at the bottom of a glacier scrape against the rock below. If you have ever collected beach glass or pebbles from a stream, you have witnessed the work of abrasion. ",text,
L_0087,weathering,T_0875,"Sometimes biological elements cause mechanical weathering. This can happen slowly. A plants roots grow into a crack in rock. As the roots grow larger, they wedge open the crack. Burrowing animals can also cause weathering. By digging for food or creating a hole to live in the animal may break apart rock. Today, human beings do a lot of mechanical weathering whenever we dig or blast into rock. This is common when we build homes, roads, and subways, or quarry stone for construction or other uses. ",text,
L_0087,weathering,T_0876,"Mechanical weathering increases the rate of chemical weathering. As rock breaks into smaller pieces, the surface area of the pieces increases. With more surfaces exposed, there are more places for chemical weathering to occur. Lets say you wanted to make some hot chocolate on a cold day. It would be hard to get a big chunk of chocolate to dissolve in your milk or hot water. Maybe you could make hot chocolate from some smaller pieces like chocolate chips, but it is much easier to add a powder to your milk. This is because the smaller the pieces are, the more surface area they have. Smaller pieces dissolve more easily. ",text,
L_0087,weathering,T_0877,"Chemical weathering is different than mechanical weathering. The minerals in the rock change. The rock changes composition and becomes a different type of rock. Most minerals form at high pressure or high temperatures deep within Earth. But at Earths surface, temperatures and pressures are much lower. Minerals that were stable deeper in the crust are not stable at the surface. Thats why chemical weathering happens. Minerals that formed at higher temperature and pressure change into minerals that are stable at the surface. Chemical weathering is important. It starts the process of changing solid rock into soil. We need soil to grow food and create other materials we need. Chemical weathering works through chemical reactions that change the rock. There are many agents of chemical weathering. Remember that water was a main agent of mechanical weathering. Well, water is also an agent of chemical weathering. That makes it a double agent! Carbon dioxide and oxygen are also agents of chemical weathering. Each of these is discussed below. ",text,
L_0087,weathering,T_0878,"Water is an amazing molecule. It has a very simple chemical formula, H2 O. It is made of just two hydrogen atoms bonded to one oxygen atom. Water is remarkable in terms of all the things it can do. Lots of things dissolve easily in water. Some types of rock can even completely dissolve in water! Other minerals change by adding water into their structure. ",text,
L_0087,weathering,T_0879,"Carbon dioxide (CO2 ) combines with water as raindrops fall through the air. This makes a weak acid, called carbonic acid. This happens so often that carbonic acid is a common, weak acid found in nature. This acid works to dissolve rock. It eats away at sculptures and monuments. While this is normal, more acids are made when we add pollutants to the air. Any time we burn any fossil fuel, it adds nitrous oxide to the air. When we burn coal rich in sulfur, it adds sulfur dioxide to the air. As nitrous oxide and sulfur dioxide react with water, they form nitric acid and sulfuric acid. These are the two main components of acid rain. Acid rain accelerates chemical weathering. ",text,
L_0087,weathering,T_0880,"Oxygen strongly reacts with elements at the Earths surface. You are probably most familiar with the rust that forms when iron reacts with oxygen (Figure 9.4). Many minerals are rich in iron. They break down as the iron changes into iron oxide. This makes the red color in soils. Plants and animals also cause chemical weathering. As plant roots take in nutrients, elements are exchanged. ",text,
L_0087,weathering,T_0881,"Each type of rock weathers in its own way. Certain types of rock are very resistant to weathering. Igneous rocks tend to weather slowly because they are hard. Water cannot easily penetrate them. Granite is a very stable igneous rock. Other types of rock are easily weathered because they dissolve easily in weak acids. Limestone is a sedimentary rock that dissolves easily. When softer rocks wear away, the more resistant rocks form ridges or hills. Devils Tower in Wyoming shows how different types of rock weather at different rates (Figure 9.5). The softer materials of the surrounding rocks were worn away. The resistant center of the volcano remains behind. Minerals also weather differently. Some minerals completely dissolve in water. As less resistant minerals dissolve away, a rocks surface becomes pitted and rough. When a less resistant mineral dissolves, more resistant mineral grains are released from the rock. ",text,
L_0087,weathering,T_0881,"Each type of rock weathers in its own way. Certain types of rock are very resistant to weathering. Igneous rocks tend to weather slowly because they are hard. Water cannot easily penetrate them. Granite is a very stable igneous rock. Other types of rock are easily weathered because they dissolve easily in weak acids. Limestone is a sedimentary rock that dissolves easily. When softer rocks wear away, the more resistant rocks form ridges or hills. Devils Tower in Wyoming shows how different types of rock weather at different rates (Figure 9.5). The softer materials of the surrounding rocks were worn away. The resistant center of the volcano remains behind. Minerals also weather differently. Some minerals completely dissolve in water. As less resistant minerals dissolve away, a rocks surface becomes pitted and rough. When a less resistant mineral dissolves, more resistant mineral grains are released from the rock. ",text,
L_0089,acid rain,T_0900,"Acid rain is caused by sulfur and nitrogen oxides emanating from power plants or metal refineries. The smokestacks have been built tall so that pollutants dont sit over cities (Figure 1.1). As they move, these pollutants combine with water vapor to form sulfuric and nitric acids. The acid droplets form acid fog, rain, snow, or they may be deposited dry. Most typical is acid rain (Figure 1.2). ",text,
L_0089,acid rain,T_0901,"Acid rain water is more acidic than normal rain water. Acidity is measured on the pH scale. Lower numbers are more acidic and higher numbers are less acidic (also called more alkaline) (Figure 1.3). Natural rain is somewhat acidic, with a pH of 5.6; acid rain must have a pH of less than 5.0. A small change in pH represents a large change in acidity: rain with a pH of 4.6 is 10 times more acidic than normal rain (with a pH of 5.6). Rain with a pH of 3.6 is 100 times more acidic. Regions with a lot of coal-burning power plants have the most acidic rain. The acidity of average rainwater in the northeastern United States has fallen to between 4.0 and 4.6. Acid fog has even lower pH with an average of around 3.4. One fog in Southern California in 1986 had a pH of 1.7, equal to toilet-bowl cleaner. In arid climates, such as in Southern California, acids deposit on the ground dry. Acid precipitation ends up on the land surface and in water bodies. Some forest soils in the northeast are five to ten times more acidic than they were two or three decades ago. Acid droplets move down through acidic soils to lower the pH of streams and lakes even more. Acids strip soil of metals and nutrients, which collect in streams and lakes. As a result, stripped soils may no longer provide the nutrients that native plants need. A pH scale goes from 1 to 14; numbers are shown with the pH of some common substances. A value of 7 is neutral. The strongest acids are at the low end of the scale and the strongest bases are at the high end. ",text,
L_0089,acid rain,T_0901,"Acid rain water is more acidic than normal rain water. Acidity is measured on the pH scale. Lower numbers are more acidic and higher numbers are less acidic (also called more alkaline) (Figure 1.3). Natural rain is somewhat acidic, with a pH of 5.6; acid rain must have a pH of less than 5.0. A small change in pH represents a large change in acidity: rain with a pH of 4.6 is 10 times more acidic than normal rain (with a pH of 5.6). Rain with a pH of 3.6 is 100 times more acidic. Regions with a lot of coal-burning power plants have the most acidic rain. The acidity of average rainwater in the northeastern United States has fallen to between 4.0 and 4.6. Acid fog has even lower pH with an average of around 3.4. One fog in Southern California in 1986 had a pH of 1.7, equal to toilet-bowl cleaner. In arid climates, such as in Southern California, acids deposit on the ground dry. Acid precipitation ends up on the land surface and in water bodies. Some forest soils in the northeast are five to ten times more acidic than they were two or three decades ago. Acid droplets move down through acidic soils to lower the pH of streams and lakes even more. Acids strip soil of metals and nutrients, which collect in streams and lakes. As a result, stripped soils may no longer provide the nutrients that native plants need. A pH scale goes from 1 to 14; numbers are shown with the pH of some common substances. A value of 7 is neutral. The strongest acids are at the low end of the scale and the strongest bases are at the high end. ",text,
L_0089,acid rain,T_0901,"Acid rain water is more acidic than normal rain water. Acidity is measured on the pH scale. Lower numbers are more acidic and higher numbers are less acidic (also called more alkaline) (Figure 1.3). Natural rain is somewhat acidic, with a pH of 5.6; acid rain must have a pH of less than 5.0. A small change in pH represents a large change in acidity: rain with a pH of 4.6 is 10 times more acidic than normal rain (with a pH of 5.6). Rain with a pH of 3.6 is 100 times more acidic. Regions with a lot of coal-burning power plants have the most acidic rain. The acidity of average rainwater in the northeastern United States has fallen to between 4.0 and 4.6. Acid fog has even lower pH with an average of around 3.4. One fog in Southern California in 1986 had a pH of 1.7, equal to toilet-bowl cleaner. In arid climates, such as in Southern California, acids deposit on the ground dry. Acid precipitation ends up on the land surface and in water bodies. Some forest soils in the northeast are five to ten times more acidic than they were two or three decades ago. Acid droplets move down through acidic soils to lower the pH of streams and lakes even more. Acids strip soil of metals and nutrients, which collect in streams and lakes. As a result, stripped soils may no longer provide the nutrients that native plants need. A pH scale goes from 1 to 14; numbers are shown with the pH of some common substances. A value of 7 is neutral. The strongest acids are at the low end of the scale and the strongest bases are at the high end. ",text,
L_0089,acid rain,T_0902,"Acid rain takes a toll on ecosystems (Figure 1.4). Plants that are exposed to acids become weak and are more likely to be damaged by bad weather, insect pests, or disease. Snails die in acid soils, so songbirds do not have as much food to eat. Young birds and mammals do not build bones as well and may not be as strong. Eggshells may also be weak and break more easily. As lakes become acidic, organisms die off. No fish can live if the pH drops below 4.5. Organic material cannot decay, and mosses take over the lake. Wildlife that depend on the lake for drinking water suffer population declines. Crops are damaged by acid rain. This is most noticeable in poor nations where people cant afford to fix the problems with fertilizers or other technology. Acid rain has killed trees in this forest in the Czech Republic. Acid rain damages cultural monuments like buildings and statues. These include the U.S. Capitol and many buildings in Europe, such as Westminster Abbey. Carbonate rocks neutralize acids and so some regions do not suffer the effects of acid rain nearly as much. Limestone in the midwestern United States protects the area. One reason that the northeastern United States is so vulnerable to acid rain damage is that the rocks are not carbonates. Because pollutants can travel so far, much of the acid rain that falls hurts states or nations other than ones where the pollutants were released. All the rain that falls in Sweden is acidic and fish in lakes all over the country are dying. The pollutants come from the United Kingdom and Western Europe, which are now working to decrease their emissions. Canada also suffers from acid rain that originates in the United States, a problem that is also improving. Southeast Asia is experiencing more acid rain between nations as the region industrializes. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0090,adaptation and evolution of populations,T_0903,"The characteristics of an organism that help it to survive in a given environment are called adaptations. Adaptations are traits that an organism inherits from its parents. Within a population of organisms are genes coding for a certain number of traits. For example, a human population may have genes for eyes that are blue, green, hazel, or brown, but as far as we know, not purple or lime green. Adaptations develop when certain variations or differences in a population help some members survive better than others (Figure 1.1). The variation may already exist within the population, but often the variation comes from a mutation, or a random change in an organisms genes. Some mutations are harmful and the organism dies; in that case, the variation will not remain in the population. Many mutations are neutral and remain in the population. If the environment changes, the mutation may be beneficial and it may help the organism adapt to the environment. The organisms that survive pass this favorable trait on to their offspring. ",text,
L_0090,adaptation and evolution of populations,T_0904,"Many changes in the genetic makeup of a species may accumulate over time, especially if the environment is changing. Eventually the descendants will be very different from their ancestors and may become a whole new species. Changes in the genetic makeup of a species over time are known as biological evolution. ",text,
L_0090,adaptation and evolution of populations,T_0905,"The mechanism for evolution is natural selection. Traits become more or less common in a population depending on whether they are beneficial or harmful. An example of evolution by natural selection can be found in the deer mouse, species Peromyscus maniculatus. In Nebraska this mouse is typically brown, but after glaciers carried lighter sand over the darker soil in the Sand Hills, predators could more easily spot the dark mice. Natural selection favored the light mice, and over time, the population became light colored. An explanation of how adaptations de- velop. Click image to the left or use the URL below. URL: ",text,
L_0091,age of earth,T_0906,"During the 18th and 19th centuries, geologists tried to estimate the age of Earth with indirect techniques. What methods can you think of for doing this? One example is that by measuring how much sediment a stream deposited in a year, a geologist might try to determine how long it took for a stream to deposit an ancient sediment layer. Not surprisingly, these methods resulted in wildly different estimates. A relatively good estimate was produced by the British geologist Charles Lyell, who thought that 240 million years had passed since the appearance of the first animals with shells. Today scientists know that this event occurred about 530 million years ago. In 1892, William Thomson (later known as Lord Kelvin) calculated that the Earth was 100 million years old, which he later lowered to 20 million years. He did this systematically assuming that the planet started off as a molten ball and calculating the time it would take for it to cool to its current temperature. This estimate was a blow to geologists and supporters of Charles Darwins theory of evolution, which required an older Earth to provide time for geological and evolutionary processes to take place. Kelvins calculations were soon shown to be flawed when radioactivity was discovered in 1896. What Kelvin didnt know is that radioactive decay of elements inside Earths interior provides a steady source of heat. He also didnt know that the mantle is able to flow and so convection moves heat from the interior to the surface of the planet. Thomson had grossly underestimated Earths age. ",text,
L_0091,age of earth,T_0907,"Radioactivity turned out to be useful for dating Earth materials and for coming up with a quantitative age for Earth. Scientists not only date ancient rocks from Earths crust, they also date meteorites that formed at the same time Earth and the rest of the solar system were forming. Moon rocks also have been radiometrically dated. Using a combination of radiometric dating, index fossils, and superposition, geologists have constructed a well- defined timeline of Earth history. With information gathered from all over the world, estimates of rock and fossil ages have become increasingly accurate. This is the modern geologic time scale with all of the ages. Click image to the left or use the URL below. URL: ",text,
L_0092,agriculture and human population growth,T_0908,"Every major advance in agriculture has allowed global population to increase. Early farmers could settle down to a steady food supply. Irrigation, the ability to clear large swaths of land for farming efficiently, and the development of farm machines powered by fossil fuels allowed people to grow more food and transport it to where it was needed. ",text,
L_0092,agriculture and human population growth,T_0909,"What is Earths carrying capacity for humans? Are humans now exceeding Earths carrying capacity for our species? Many anthropologists say that the carrying capacity of humans on the planet without agriculture is about 10 million (Figure 1.1). This population was reached about 10,000 years ago. At the time, people lived together in small bands of hunters and gatherers. Typically men hunted and fished; women gathered nuts and vegetables. Obviously, human populations have blown past this hypothetical carrying capacity. By using our brains, our erect posture, and our hands, we have been able to manipulate our environment in ways that no other species has ever done. What have been the important developments that have allowed population to grow? ",text,
L_0092,agriculture and human population growth,T_0910,"About 10,000 years ago, we developed the ability to grow our own food. Farming increased the yield of food plants and allowed people to have food available year round. Animals were domesticated to provide meat. With agriculture, people could settle down, so that they no longer needed to carry all their possessions (Figure 1.2). They could develop better farming practices and store food for when it was difficult to grow. Agriculture allowed people to settle in towns and cities. More advanced farming practices allowed a single farmer to grow food for many more people. When advanced farming practices allowed farmers to grow more food than they needed for their families (Figure ",text,
L_0092,agriculture and human population growth,T_0910,"About 10,000 years ago, we developed the ability to grow our own food. Farming increased the yield of food plants and allowed people to have food available year round. Animals were domesticated to provide meat. With agriculture, people could settle down, so that they no longer needed to carry all their possessions (Figure 1.2). They could develop better farming practices and store food for when it was difficult to grow. Agriculture allowed people to settle in towns and cities. More advanced farming practices allowed a single farmer to grow food for many more people. When advanced farming practices allowed farmers to grow more food than they needed for their families (Figure ",text,
L_0092,agriculture and human population growth,T_0911,"The next major stage in the growth of the human population was the Industrial Revolution, which started in the late 1700s (Figure 1.4). This major historical event marks when products were first mass-produced and when fossil fuels were first widely used for power. ",text,
L_0092,agriculture and human population growth,T_0912,"The Green Revolution has allowed the addition of billions of people to the population in the past few decades. The Green Revolution has improved agricultural productivity by: Improving crops by selecting for traits that promote productivity; recently, genetically engineered crops have been introduced. Increasing the use of artificial fertilizers and chemical pesticides. About 23 times more fertilizer and 50 times more pesticides are used around the world than were used just 50 years ago (Figure 1.5). Agricultural machinery: plowing, tilling, fertilizing, picking, and transporting are all done by machines. About 17% of the energy used each year in the United States is for agriculture. Increasing access to water. Many farming regions depend on groundwater, which is not a renewable resource. Some regions will eventually run out of this water source. Currently about 70% of the worlds fresh water is used for agriculture. Rows of a single crop and heavy ma- chinery are normal sights for modern day farms. The Green Revolution has increased the productivity of farms immensely. A century ago, a single farmer produced enough food for 2.5 people, but now a farmer can feed more than 130 people. The Green Revolution is credited for feeding 1 billion people that would not otherwise have been able to live. ",text,
L_0092,agriculture and human population growth,T_0913,"The flip side to this is that for the population to continue to grow, more advances in agriculture and an ever increasing supply of water will be needed. Weve increased the carrying capacity for humans by our genius: growing crops, trading for needed materials, and designing ways to exploit resources that are difficult to get at, such as groundwater. And most of these resources are limited. The question is, even though we have increased the carrying capacity of the planet, have we now exceeded it (Figure There is not yet an answer to that question, but there are many different opinions. In the eighteenth century, Thomas Malthus predicted that human population would continue to grow until we had exhausted our resources. At that point, humans would become victims of famine, disease, or war. This has not happened, at least not yet. Some scientists think that the carrying capacity of the planet is about 1 billion people, not the 7 billion people we have today. The limiting factors have changed as our intelligence has allowed us to expand our population. Can we continue to do this indefinitely into the future? ",text,
L_0094,air quality,T_0919,"Pollutants include materials that are naturally occurring but are added to the atmosphere so that they are there in larger quantities than normal. Pollutants may also be human-made compounds that have never before been found in the atmosphere. Pollutants dirty the air, change natural processes in the atmosphere, and harm living things. ",text,
L_0094,air quality,T_0920,Air pollution started to be a problem when early people burned wood for heat and cooking fires in enclosed spaces such as caves and small tents or houses. But the problems became more widespread as fossil fuels such as coal began to be burned during the Industrial Revolution. ,text,
L_0094,air quality,T_0921,Air pollution started to be a problem when early people burned wood for heat and cooking fires in enclosed spaces such as caves and small tents or houses. But the problems became more widespread as fossil fuels such as coal began to be burned during the Industrial Revolution (Figure 1.1). The 2012 Olympic Games in London opening ceremony contained a reen- actment of the Industrial Revolution - complete with pollution streaming from smokestacks. ,text,
L_0094,air quality,T_0922,"Photochemical smog, a different type of air pollution, first became a problem in Southern California after World War II. The abundance of cars and sunshine provided the perfect setting for a chemical reaction between some of the molecules in auto exhaust or oil refinery emissions and sunshine (Figure 1.2). Photochemical smog consists of more than 100 compounds, most importantly ozone. Smog over Los Angeles as viewed from the Hollywood Hills. ",text,
L_0094,air quality,T_0923,"Terrible air pollution events in Pennsylvania and London, in which many people died, plus the recognition of the hazards of photochemical smog, led to the passage of the Clean Air Act in 1970 in the United States. The act now regulates 189 pollutants. The six most important pollutants regulated by the Act are ozone, particulate matter, sulfur dioxide, nitrogen dioxide, carbon monoxide, and the heavy metal lead. Other important regulated pollutants include benzene, perchloroethylene, methylene chloride, dioxin, asbestos, toluene, and metals such as cadmium, mercury, chromium, and lead compounds. What is the result of the Clean Air Act? In short, the air in the United States is much cleaner. Visibility is better and people are no longer incapacitated by industrial smog. However, despite the Act, industry, power plants, and vehicles put 160 million tons of pollutants into the air each year. Some of this smog is invisible and some contributes to the orange or blue haze that affects many cities. ",text,
L_0094,air quality,T_0924,"Air quality in a region is not just affected by the amount of pollutants released into the atmosphere in that location but by other geographical and atmospheric factors. Winds can move pollutants into or out of a region and a mountain range can trap pollutants on its leeward side. Inversions commonly trap pollutants within a cool air mass. If the inversion lasts long enough, pollution can reach dangerous levels. Pollutants remain over a region until they are transported out of the area by wind, diluted by air blown in from another region, transformed into other compounds, or carried to the ground when mixed with rain or snow. Table 1.1 lists the smoggiest cities in 2013: 7 of the 10 are in California. Why do you think California cities are among those with the worst air pollution? The state has the right conditions for collecting pollutants including mountain ranges that trap smoggy air, arid and sometimes windless conditions, agriculture, industry, and lots and lots of cars. Rank 1 2 3 4 5 6 7 8 9 10 City, State Los Angeles area, California Visalia-Porterville, California Bakersfield-Delano, California Fresno-Madera, California Hanford-Corcoran, California Sacramento area, California Houston area, Texas Dallas-Fort Worth, Texas Washington D.C. area El Centro, California ",text,
L_0095,asteroids,T_0925,"Asteroids are very small, rocky bodies that orbit the Sun. ""Asteroid"" means ""star-like,"" and in a telescope, asteroids look like points of light, just like stars. Asteroids are irregularly shaped because they do not have enough gravity to become round. They are also too small to maintain an atmosphere, and without internal heat they are not geologically active (Figure 1.1). Collisions with other bodies may break up the asteroid or create craters on its surface. Asteroid impacts have had dramatic impacts on the shaping of the planets, including Earth. Early impacts caused the planets to grow as they cleared their portions of space. An impact with an asteroid about the size of Mars caused fragments of Earth to fly into space and ultimately create the Moon. Asteroid impacts are linked to mass extinctions throughout Earths history. ",text,
L_0095,asteroids,T_0926,"Hundreds of thousands of asteroids have been discovered in our solar system. They are still being discovered at a rate of about 5,000 new asteroids per month. The majority of the asteroids are found in between the orbits of Mars In 1991, Asteroid 951 Gaspra was the first asteroid photographed at close range. Gaspra is a medium-sized asteroid, mea- suring about 19 by 12 by 11 km (12 by 7.5 by 7 mi). and Jupiter, in a region called the asteroid belt, as shown in Figure 1.2. Although there are many thousands of asteroids in the asteroid belt, their total mass adds up to only about 4% of Earths Moon. The white dots in the figure are asteroids in the main asteroid belt. Other groups of asteroids closer to Jupiter are called the Hildas (orange), the Trojans (green), and the Greeks (also green). Scientists think that the bodies in the asteroid belt formed during the formation of the solar system. The asteroids might have come together to make a single planet, but they were pulled apart by the intense gravity of Jupiter. ",text,
L_0095,asteroids,T_0926,"Hundreds of thousands of asteroids have been discovered in our solar system. They are still being discovered at a rate of about 5,000 new asteroids per month. The majority of the asteroids are found in between the orbits of Mars In 1991, Asteroid 951 Gaspra was the first asteroid photographed at close range. Gaspra is a medium-sized asteroid, mea- suring about 19 by 12 by 11 km (12 by 7.5 by 7 mi). and Jupiter, in a region called the asteroid belt, as shown in Figure 1.2. Although there are many thousands of asteroids in the asteroid belt, their total mass adds up to only about 4% of Earths Moon. The white dots in the figure are asteroids in the main asteroid belt. Other groups of asteroids closer to Jupiter are called the Hildas (orange), the Trojans (green), and the Greeks (also green). Scientists think that the bodies in the asteroid belt formed during the formation of the solar system. The asteroids might have come together to make a single planet, but they were pulled apart by the intense gravity of Jupiter. ",text,
L_0095,asteroids,T_0927,"More than 4,500 asteroids cross Earths orbit; they are near-Earth asteroids. Between 500 and 1,000 of these are over 1 km in diameter. Any object whose orbit crosses Earths can collide with Earth, and many asteroids do. On average, each year a rock about 5-10 m in diameter hits Earth (Figure 1.3). Since past asteroid impacts have been implicated in mass extinctions, astronomers are always on the lookout for new asteroids, and follow the known near-Earth asteroids closely, so they can predict a possible collision as early as possible. A painting of what an asteroid a few kilometers across might look like as it strikes Earth. ",text,
L_0095,asteroids,T_0928,Scientists are interested in asteroids because they are representatives of the earliest solar system (Figure 1.4). Eventually asteroids could be mined for rare minerals or for construction projects in space. A few missions have studied asteroids directly. NASAs DAWN mission explored asteroid Vesta in 2011 and 2012 and will visit dwarf planet Ceres in 2015. Click image to the left or use the URL below. URL:  The NEAR Shoemaker probe took this photo as it was about to land on 433 Eros in 2001. ,text,
L_0095,asteroids,T_0929,"Thousands of objects, including comets and asteroids, are zooming around our solar system; some could be on a collision course with Earth. QUEST explores how these Near Earth Objects are being tracked and what scientists are saying should be done to prevent a deadly impact. Click image to the left or use the URL below. URL: ",text,
L_0096,availability of natural resources,T_0930,,text,
L_0096,availability of natural resources,T_0931,"From the table in the concept ""Materials Humans Use,"" you can see that many of the resources we depend on are non-renewable. Non-renewable resources vary in their availability; some are very abundant and others are rare. Materials, such as gravel or sand, are technically non-renewable, but they are so abundant that running out is no issue. Some resources are truly limited in quantity: when they are gone, they are gone, and something must be found that will replace them. There are even resources, such as diamonds and rubies, that are valuable in part because they are so rare. ",text,
L_0096,availability of natural resources,T_0932,"Besides abundance, a resources value is determined by how easy it is to locate and extract. If a resource is difficult to use, it will not be used until the price for that resource becomes so great that it is worth paying for. For example, the oceans are filled with an abundant supply of water, but desalination is costly, so it is used only where water is really limited (Figure 1.1). As the cost of desalination plants comes down, more will likely be built. Tampa Bay, Florida, has one of the few desalination plants in the United States. ",text,
L_0096,availability of natural resources,T_0933,"Politics is also part of determining resource availability and cost. Nations that have a desired resource in abundance will often export that resource to other countries, while countries that need that resource must import it from one of the countries that produces it. This situation is a potential source of economic and political trouble. Of course the greatest example of this is oil. Twelve countries have approximately 80% of all of the worlds oil (Figure 1.2). However, the biggest users of oil, the United States, China, and Japan, are all located outside this oil-rich region. This leads to a situation in which the availability and price of the oil is determined largely by one set of countries that have their own interests to look out for. The result has sometimes been war, which may have been attributed to all sorts of reasons, but at the bottom, the reason is oil. ",text,
L_0096,availability of natural resources,T_0934,"The topic of overconsumption was touched on in the chapter Life on Earth. Many people in developed countries, such as the United States and most of Europe, use many more natural resources than people in many other countries. We have many luxury and recreational items, and it is often cheaper for us to throw something away than to fix it or just hang on to it for a while longer. This consumerism leads to greater resource use, but it also leads to more waste. Pollution from discarded materials degrades the land, air, and water (Figure 1.3). Natural resource use is generally lower in developing countries because people cannot afford many products. Some of these nations export natural resources to the developed world since their deposits may be richer and the cost of labor lower. Environmental regulations are often more lax, further lowering the cost of resource extraction. Click image to the left or use the URL below. URL:  The nations in blue are the 12 biggest producers of oil; they are Algeria, Angola, Ecuador, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela. Pollution from discarded materials de- grades the environment and reduces the availability of natural resources. ",text,
L_0096,availability of natural resources,T_0934,"The topic of overconsumption was touched on in the chapter Life on Earth. Many people in developed countries, such as the United States and most of Europe, use many more natural resources than people in many other countries. We have many luxury and recreational items, and it is often cheaper for us to throw something away than to fix it or just hang on to it for a while longer. This consumerism leads to greater resource use, but it also leads to more waste. Pollution from discarded materials degrades the land, air, and water (Figure 1.3). Natural resource use is generally lower in developing countries because people cannot afford many products. Some of these nations export natural resources to the developed world since their deposits may be richer and the cost of labor lower. Environmental regulations are often more lax, further lowering the cost of resource extraction. Click image to the left or use the URL below. URL:  The nations in blue are the 12 biggest producers of oil; they are Algeria, Angola, Ecuador, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela. Pollution from discarded materials de- grades the environment and reduces the availability of natural resources. ",text,
L_0098,bathymetric evidence for seafloor spreading,T_0939,"Well go out on the research vessel (R/V in ship-speak) Atlantis, owned by the US Navy and operated by the Woods Hole Oceanographic Institution for the oceanographic community. The Atlantis has six science labs and storage spaces, precise navigation systems, seafloor-mapping sonar and satellite communications. Most importantly, the ship has all of the heavy equipment necessary to deploy and operate Alvin, the manned research submersible. The ship has 24 bunks available for scientists, including two for the chief scientists. The majority of these bunks are below waterline, which makes for good sleeping in the daytime. Ship time is really expensive research, so vessels operate all night and so do the scientists. Your watch, as your time on duty is called, may be 12-4, 4-8 or 8-12 - thats AM and PM. Alternately, if youre on the team doing a lot of diving in Alvin, you may just be up during the day. If youre mostly doing operations that dont involve Alvin, you may just be up at night. For safety reasons, Alvin is deployed and recovered only in daylight. Alvin is deployed from the stern of the R/V Atlantis. Scientists come from all over to meet a research ship in a port. An oceanographer these days doesnt need to be near the ocean, he or she just needs to have access to an airport! Lets begin this cruise in Woods Hole, Massachusetts, Atlantis home port. Our first voyage will be out to the Mid- Atlantic Ridge. Transit time to the research site can take days. By doing this virtually, we dont have to spend days in transit to our research site, and we dont have to get seasick! As we head to the site, we will run the echo sounder. Lets see what we can find! ",text,
L_0098,bathymetric evidence for seafloor spreading,T_0940,"The people who first mapped the seafloor were aboard military vessels during World War II. As stated in the Earth as a Planet chapter, echo sounders used sound waves to search for submarines, but also produced a map of seafloor depths. Depth sounding continued in earnest after the war. Scientists pieced together the ocean depths to produce bathymetric maps of the seafloor. During WWII and in the decade or so later, echo sounders had only one beam, so they just returned a line showing the depth beneath the ship. Later echo sounders sent out multiple beams and could create a bathymetric map of the seafloor below. We will run a multi-beam echo sounder as we go from Woods Hole out to the Mid-Atlantic Ridge. ",text,
L_0098,bathymetric evidence for seafloor spreading,T_0941,"Although they expected an expanse of flat, featureless plains, scientists were shocked to find tremendous features like mountain ranges, rifts, and trenches. This work continues on oceanographic research vessels as they sail across the seas today. The map in the Figure 1.2 is a modern map with data from several decades. The major features of the ocean basins and their colors on the map in Figure 1.2 include: mid-ocean ridges: these features rise up high above the deep seafloor as a long chain of mountains, e.g. the light blue gash in middle of Atlantic Ocean. rift zones: in the middle of the mid-ocean ridges is a rift zone that is lower in elevation than the mountains surrounding it. deep sea trenches: these features are found at the edges of continents or in the sea near chains of active volcanoes, e.g. the very deepest blue, off of western South America. abyssal plains: these features are flat areas, although many are dotted with volcanic mountains, e.g. consistent blue off of southeastern South America. See if you can identify each of these features in Figure 1.2. A modern map of the southeastern Pacific and Atlantic Oceans. When they first observed these bathymetric maps, scientists wondered what had formed these features. It turns out that they were crucial for fitting together ideas about seafloor spreading. ",text,
L_0098,bathymetric evidence for seafloor spreading,T_0942,"As we have seen, the ocean floor is not flat: mid-ocean ridges, deep sea trenches, and other features all rise sharply above or plunge deeply below the abyssal plains. In fact, Earths tallest mountain is Mauna Kea volcano, which rises 10,203 m (33,476 ft.)meters) from the Pacific Ocean floor to become one of the volcanic mountains of Hawaii. The deepest canyon is also on the ocean floor, the Challenger Deep in the Marianas Trench, 10,916 m (35,814 ft). The continental margin is the transition from the land to the deep sea or, geologically speaking, from continental crust to oceanic crust. More than one-quarter of the ocean basin is continental margin. (Figure 1.3). Click image to the left or use the URL below. URL: ",text,
L_0099,big bang,T_0943,"Timeline of the Big Bang and the expan- sion of the Universe. The Big Bang theory is the most widely accepted cosmological explanation of how the universe formed. If we start at the present and go back into the past, the universe is contracting  getting smaller and smaller. What is the end result of a contracting universe? According to the Big Bang theory, the universe began about 13.7 billion years ago. Everything that is now in the universe was squeezed into a very small volume. Imagine all of the known universe in a single, hot, chaotic mass. An enormous explosion  a big bang  caused the universe to start expanding rapidly. All the matter and energy in the universe, and even space itself, came out of this explosion. What came before the Big Bang? There is no way for scientists to know since there is no remaining evidence. ",text,
L_0099,big bang,T_0944,"In the first few moments after the Big Bang, the universe was unimaginably hot and dense. As the universe expanded, it became less dense and began to cool. After only a few seconds, protons, neutrons, and electrons could form. After a few minutes, those subatomic particles came together to create hydrogen. Energy in the universe was great enough to initiate nuclear fusion, and hydrogen nuclei were fused into helium nuclei. The first neutral atoms that included electrons did not form until about 380,000 years later. The matter in the early universe was not smoothly distributed across space. Dense clumps of matter held close together by gravity were spread around. Eventually, these clumps formed countless trillions of stars, billions of galaxies, and other structures that now form most of the visible mass of the universe. If you look at an image of galaxies at the far edge of what we can see, you are looking at great distances. But you are also looking across a different type of distance. What do those far away galaxies represent? Because it takes so long for light from so far away to reach us, you are also looking back in time (Figure 1.2). ",text,
L_0099,big bang,T_0945,"After the origin of the Big Bang hypothesis, many astronomers still thought the universe was static. Nearly all came around when an important line of evidence for the Big Bang was discovered in 1964. In a static universe, the space between objects should have no heat at all; the temperature should measure 0 K (Kelvin is an absolute temperature scale). But two researchers at Bell Laboratories used a microwave receiver to learn that the background radiation in the universe is not 0 K, but 3 K (Figure 1.3). This tiny amount of heat is left over from the Big Bang. Since nearly Images from very far away show what the universe was like not too long after the Big Bang. all astronomers now accept the Big Bang hypothesis, what is it usually referred to as? Click image to the left or use the URL below. URL: ",text,
L_0103,carbon cycle and climate,T_0958,"Carbon is a very important element to living things. As the second most common element in the human body, we know that human life without carbon would not be possible. Protein, carbohydrates, and fats are all part of the body and all contain carbon. When your body breaks down food to produce energy, you break down protein, carbohydrates, and fat, and you breathe out carbon dioxide. Carbon occurs in many forms on Earth. The element moves through organisms and then returns to the environment. When all this happens in balance, the ecosystem remains in balance too. ",text,
L_0103,carbon cycle and climate,T_0959,The short term cycling of carbon begins with carbon dioxide (CO2 ) in the atmosphere. ,text,
L_0103,carbon cycle and climate,T_0960,"Through photosynthesis, the inorganic carbon in carbon dioxide plus water and energy from sunlight is transformed into organic carbon (food) with oxygen given off as a waste product. The chemical equation for photosynthesis is: ",text,
L_0103,carbon cycle and climate,T_0961,"Plants and animals engage in the reverse of photosynthesis, which is respiration. In respiration, animals use oxygen to convert the organic carbon in sugar into food energy they can use. Plants also go through respiration and consume some of the sugars they produce. The chemical reaction for respiration is: C6 H12 O6 + 6 O2  6 CO2 + 6 H2 O + useable energy Photosynthesis and respiration are a gas exchange process. In photosynthesis, CO2 is converted to O2 ; in respiration, O2 is converted to CO2 . Remember that plants do not create energy. They change the energy from sunlight into chemical energy that plants and animals can use as food (Figure 1.1). ",text,
L_0103,carbon cycle and climate,T_0962,,text,
L_0103,carbon cycle and climate,T_0963,"Places in the ecosystem that store carbon are reservoirs. Places that supply and remove carbon are carbon sources and carbon sinks, respectively. If more carbon is provided than stored, the place is a carbon source. If more carbon dioxide is absorbed than is emitted, the reservoir is a carbon sink. What are some examples of carbon sources and sinks? Carbon sinks are reservoirs where carbon is stored. Healthy living forests and the oceans act as carbon sinks. Carbon sources are reservoirs from which carbon can enter the environment. The mantle is a source of carbon from volcanic gases. A reservoir can change from a sink to a source and vice versa. A forest is a sink, but when the forest burns it becomes a source. The amount of time that carbon stays, on average, in a reservoir is the residence time of carbon in that reservoir. ",text,
L_0103,carbon cycle and climate,T_0964,"Remember that the amount of CO2 in the atmosphere is very low. This means that a small increase or decrease in the atmospheric CO2 can have a large effect. By measuring the composition of air bubbles trapped in glacial ice, scientists can learn the amount of atmospheric CO2 at times in the past. Of particular interest is the time just before the Industrial Revolution, when society began to use fossil fuels. That value is thought to be the natural content of CO2 for this time period; that number was 280 parts per million (ppm). By 1958, when scientists began to directly measure CO2 content from the atmosphere at Mauna Loa volcano in the Pacific Ocean, the amount was 316 ppm (Figure 1.2). In 2014, the atmospheric CO2 content had risen to around 400 ppm. The amount of CO2 in the atmosphere has been measured at Mauna Loa Obser- vatory since 1958. The blue line shows yearly averaged CO2 . The red line shows seasonal variations in CO2 . This is an increase in atmospheric CO2 of 40% since the before the Industrial Revolution. About 65% of that increase has occurred since the first CO2 measurements were made on Mauna Loa Volcano, Hawaii, in 1958. ",text,
L_0103,carbon cycle and climate,T_0965,"Humans have changed the natural balance of the carbon cycle because we use coal, oil, and natural gas to supply our energy demands. Fossil fuels are a sink for CO2 when they form, but they are a source for CO2 when they are burned. The equation for combustion of propane, which is a simple hydrocarbon looks like this: The equation shows that when propane burns, it uses oxygen and produces carbon dioxide and water. So when a car burns a tank of gas, the amount of CO2 in the atmosphere increases just a little. Added over millions of tanks of gas and coal burned for electricity in power plants and all of the other sources of CO2 , the result is the increase in atmospheric CO2 seen in the Figure 1.2. The second largest source of atmospheric CO2 is deforestation (Figure 1.3). Trees naturally absorb CO2 while they are alive. Trees that are cut down lose their ability to absorb CO2 . If the tree is burned or decomposes, it becomes a source of CO2 . A forest can go from being a carbon sink to being a carbon source. This forest in Mexico has been cut down and burned to clear forested land for agri- culture. ",text,
L_0103,carbon cycle and climate,T_0966,"Why is such a small amount of carbon dioxide in the atmosphere even important? Carbon dioxide is a greenhouse gas. Greenhouse gases trap heat energy that would otherwise radiate out into space, which warms Earth. These gases were discussed in the chapter Atmospheric Processes. ",text,
L_0104,causes of air pollution,T_0967,"Most air pollutants come from burning fossil fuels or plant material. Some are the result of evaporation from human- made materials. Nearly half (49%) of air pollution comes from transportation, 28% from factories and power plants, and the remaining pollution from a variety of other sources. ",text,
L_0104,causes of air pollution,T_0968,"Fossil fuels are burned in most motor vehicles and power plants. These non-renewable resources are the power for nearly all manufacturing and other industries. Pure coal and petroleum can burn cleanly and emit only carbon dioxide and water, but most of the time these fossil fuels do not burn completely and the incomplete chemical reactions produce pollutants. Few sources of these fossil fuels are pure, so other pollutants are usually released. These pollutants include carbon monoxide, nitrogen dioxide, sulfur dioxide, and hydrocarbons. In large car-dependent cities such as Los Angeles and Mexico City, 80% to 85% of air pollution is from motor vehicles (Figure 1.1). Ozone, carbon monoxide, and nitrous oxides come from vehicle exhaust. Auto exhaust like this means that the fuels is not burning efficiently. A few pollutants come primarily from power plants or industrial plants that burn coal or oil. Sulfur dioxide (SO2 ) is a major component of industrial air pollution that is released whenever coal and petroleum are burned. SO2 mixes with H2 O in the air to produce sulfuric acid (H2 SO4 ). Mercury is released when coal and some types of wastes are burned. Mercury is emitted as a gas, but as it cools, it becomes a droplet. Mercury droplets eventually fall to the ground. If they fall into sediments, bacteria convert them to the most dangerous form of mercury: methyl mercury. Highly toxic, methyl mercury is one of the metals organic forms. ",text,
L_0104,causes of air pollution,T_0969,"Fossil fuels are ancient plants and animals that have been converted into usable hydrocarbons. Burning plant and animal material directly also produces pollutants. Biomass is the total amount of living material found in an environment. The biomass of a rainforest is the amount of living material found in that rainforest. The primary way biomass is burned is for slash-and-burn agriculture (Figure 1.2). The rainforest is slashed down and then the waste is burned to clear the land for farming. Biomass from other biomes, such as the savannah, is also burned to clear farmland. The pollutants are much the same as from burning fossil fuels: CO2 , carbon monoxide, methane, particulates, nitrous oxide, hydrocarbons, and organic and elemental carbon. Burning forests increases greenhouse gases in the atmosphere by releasing the CO2 stored in the biomass and also by removing the forest so that it cannot store CO2 in the future. As with all forms of air pollution, the smoke from biomass burning often spreads far and pollutants can plague neighboring states or countries. Particulates result when anything is burned. About 40% of the particulates that enter the atmosphere above the United States are from industry and about 17% are from vehicles. Particulates also occur naturally from volcanic eruptions or windblown dust. Like other pollutants, they travel all around the world on atmospheric currents. ",text,
L_0104,causes of air pollution,T_0970,"Volatile organic compounds (VOCs) enter the atmosphere by evaporation. VOCs evaporate from human-made substances, such as paint thinners, dry cleaning solvents, petroleum, wood preservatives, and other liquids. Naturally occurring VOCs evaporate off of pine and citrus trees. The atmosphere contains tens of thousands of different VOCs, A forest that has been slash-and-burned to make new farmland. nearly 100 of which are monitored. The most common is methane, a greenhouse gas (Figure 1.3). Methane occurs naturally, but human agriculture is increasing the amount of methane in the atmosphere. Methane forms when organic material decomposes in an oxygen-poor environment. In the top image, surface methane production is shown. Stratospheric methane concentrations in the bottom image show that methane is carried up into the stratosphere by the upward flow of air in the tropics. ",text,
L_0104,causes of air pollution,T_0970,"Volatile organic compounds (VOCs) enter the atmosphere by evaporation. VOCs evaporate from human-made substances, such as paint thinners, dry cleaning solvents, petroleum, wood preservatives, and other liquids. Naturally occurring VOCs evaporate off of pine and citrus trees. The atmosphere contains tens of thousands of different VOCs, A forest that has been slash-and-burned to make new farmland. nearly 100 of which are monitored. The most common is methane, a greenhouse gas (Figure 1.3). Methane occurs naturally, but human agriculture is increasing the amount of methane in the atmosphere. Methane forms when organic material decomposes in an oxygen-poor environment. In the top image, surface methane production is shown. Stratospheric methane concentrations in the bottom image show that methane is carried up into the stratosphere by the upward flow of air in the tropics. ",text,
L_0106,characteristics and origins of life,T_0975,"No one knows how or when life first began on the turbulent early Earth. There is little hard evidence from so long ago. Scientists think that it is extremely likely that life began and was wiped out more than once; for example, by the impact that created the Moon. This issue of whats living and whats not becomes important when talking about the origin of life. If were going to know when a blob of organic material crossed over into being alive, we need to have a definition of life. ",text,
L_0106,characteristics and origins of life,T_0976,"To be considered alive a molecule must: be organic. The organic molecules needed are amino acids, the building blocks of life. have a metabolism. be capable of replication (be able to reproduce). ",text,
L_0106,characteristics and origins of life,T_0977,"To look for information regarding the origin of life, scientists: perform experiments to recreate the environmental conditions found at that time. study the living creatures that make their homes in the types of extreme environments that were typical in Earths early days. seek traces of life left by ancient microorganisms, also called microbes, such as microscopic features or isotopic ratios indicative of life. Any traces of life from this time period are so ancient it is difficult to be certain whether they originated by biological or non-biological means. Click image to the left or use the URL below. URL: ",text,
L_0106,characteristics and origins of life,T_0978,"Amino acids are the building blocks of life because they create proteins. To form proteins, the amino acids are linked together by covalent bonds to form polymers called polypeptide chains (Figure 1.1). These chains are arranged in a specific order to form each different type of protein. Proteins are the most abundant class of biological molecules. An important question facing scientists is where the first amino acids came from: did they originate on Earth or did they fly in from outer space? No matter where they originated, the creation of amino acids requires the right starting materials and some energy. ",text,
L_0106,characteristics and origins of life,T_0979,"To see if amino acids could originate in the environment thought to be present in the first years of Earths existence, Stanley Miller and Harold Urey performed a famous experiment in 1953. To simulate the early atmosphere they Amino acids form polypeptide chains. The setup of the Miller-Urey experiment. placed hydrogen, methane, and ammonia in a flask of heated water that created water vapor, which they called the primordial soup. Sparks simulated lightning, which the scientists thought could have been the energy that drove the chemical reactions that created the amino acids. It worked! The gases combined to form water-soluble organic compounds including amino acids. Amino acids might also have originated at hydrothermal vents or deep in the crust where Earths internal heat is the energy source. Meteorites containing amino acids currently enter the Earth system and so meteorites could have delivered amino acids to the planet from elsewhere in the solar system (where they would have formed by processes similar to those outlined here). ",text,
L_0106,characteristics and origins of life,T_0979,"To see if amino acids could originate in the environment thought to be present in the first years of Earths existence, Stanley Miller and Harold Urey performed a famous experiment in 1953. To simulate the early atmosphere they Amino acids form polypeptide chains. The setup of the Miller-Urey experiment. placed hydrogen, methane, and ammonia in a flask of heated water that created water vapor, which they called the primordial soup. Sparks simulated lightning, which the scientists thought could have been the energy that drove the chemical reactions that created the amino acids. It worked! The gases combined to form water-soluble organic compounds including amino acids. Amino acids might also have originated at hydrothermal vents or deep in the crust where Earths internal heat is the energy source. Meteorites containing amino acids currently enter the Earth system and so meteorites could have delivered amino acids to the planet from elsewhere in the solar system (where they would have formed by processes similar to those outlined here). ",text,
L_0107,chemical bonding,T_0980,"Ions come together to create a molecule so that electrical charges are balanced; the positive charges balance the negative charges and the molecule has no electrical charge. To balance electrical charge, an atom may share its electron with another atom, give it away, or receive an electron from another atom. The joining of ions to make molecules is called chemical bonding. There are three main types of chemical bonds that are important in our discussion of minerals and rocks: Ionic bond: Electrons are transferred between atoms. An ion will give one or more electrons to another ion. Table salt, sodium chloride (NaCl), is a common example of an ionic compound. Note that sodium is on the left side of the periodic table and that chlorine is on the right side of the periodic table. In the Figure 1.2, an atom of lithium donates an electron to an atom of fluorine to form an ionic compound. The transfer of the electron gives the lithium ion a net charge of +1, and the fluorine ion a net charge of -1. These ions bond because they experience an attractive force due to the difference in sign of their charges. Covalent bond : In a covalent bond, an atom shares one or more electrons with another atom. Periodic Table of the Elements. Lithium (left) and fluorine (right) form an ionic compound called lithium fluoride. In the picture of methane (CH4 ) below (Figure 1.3), the carbon ion (with a net charge of +4) shares a single electron from each of the the four hydrogens. Covalent bonding is prevalent in organic compounds. In fact, your body is held together by electrons shared by carbons and hydrogens! Covalent bonds are also very strong, meaning it takes a lot of energy to break them apart. Hydrogen bond: These weak, intermolecular bonds are formed when the positive side of one polar molecule is attracted to the negative side of another polar molecule. Water is a classic example of a polar molecule because it has a slightly positive side, and a slightly negative side. In fact, this property is why water is so good at dissolving things. The positive side of the molecule is attracted to Methane is formed when four hydrogens and one carbon covalently bond. negative ions and the negative side is attracted to positive ions. ",text,
L_0107,chemical bonding,T_0980,"Ions come together to create a molecule so that electrical charges are balanced; the positive charges balance the negative charges and the molecule has no electrical charge. To balance electrical charge, an atom may share its electron with another atom, give it away, or receive an electron from another atom. The joining of ions to make molecules is called chemical bonding. There are three main types of chemical bonds that are important in our discussion of minerals and rocks: Ionic bond: Electrons are transferred between atoms. An ion will give one or more electrons to another ion. Table salt, sodium chloride (NaCl), is a common example of an ionic compound. Note that sodium is on the left side of the periodic table and that chlorine is on the right side of the periodic table. In the Figure 1.2, an atom of lithium donates an electron to an atom of fluorine to form an ionic compound. The transfer of the electron gives the lithium ion a net charge of +1, and the fluorine ion a net charge of -1. These ions bond because they experience an attractive force due to the difference in sign of their charges. Covalent bond : In a covalent bond, an atom shares one or more electrons with another atom. Periodic Table of the Elements. Lithium (left) and fluorine (right) form an ionic compound called lithium fluoride. In the picture of methane (CH4 ) below (Figure 1.3), the carbon ion (with a net charge of +4) shares a single electron from each of the the four hydrogens. Covalent bonding is prevalent in organic compounds. In fact, your body is held together by electrons shared by carbons and hydrogens! Covalent bonds are also very strong, meaning it takes a lot of energy to break them apart. Hydrogen bond: These weak, intermolecular bonds are formed when the positive side of one polar molecule is attracted to the negative side of another polar molecule. Water is a classic example of a polar molecule because it has a slightly positive side, and a slightly negative side. In fact, this property is why water is so good at dissolving things. The positive side of the molecule is attracted to Methane is formed when four hydrogens and one carbon covalently bond. negative ions and the negative side is attracted to positive ions. ",text,
L_0107,chemical bonding,T_0980,"Ions come together to create a molecule so that electrical charges are balanced; the positive charges balance the negative charges and the molecule has no electrical charge. To balance electrical charge, an atom may share its electron with another atom, give it away, or receive an electron from another atom. The joining of ions to make molecules is called chemical bonding. There are three main types of chemical bonds that are important in our discussion of minerals and rocks: Ionic bond: Electrons are transferred between atoms. An ion will give one or more electrons to another ion. Table salt, sodium chloride (NaCl), is a common example of an ionic compound. Note that sodium is on the left side of the periodic table and that chlorine is on the right side of the periodic table. In the Figure 1.2, an atom of lithium donates an electron to an atom of fluorine to form an ionic compound. The transfer of the electron gives the lithium ion a net charge of +1, and the fluorine ion a net charge of -1. These ions bond because they experience an attractive force due to the difference in sign of their charges. Covalent bond : In a covalent bond, an atom shares one or more electrons with another atom. Periodic Table of the Elements. Lithium (left) and fluorine (right) form an ionic compound called lithium fluoride. In the picture of methane (CH4 ) below (Figure 1.3), the carbon ion (with a net charge of +4) shares a single electron from each of the the four hydrogens. Covalent bonding is prevalent in organic compounds. In fact, your body is held together by electrons shared by carbons and hydrogens! Covalent bonds are also very strong, meaning it takes a lot of energy to break them apart. Hydrogen bond: These weak, intermolecular bonds are formed when the positive side of one polar molecule is attracted to the negative side of another polar molecule. Water is a classic example of a polar molecule because it has a slightly positive side, and a slightly negative side. In fact, this property is why water is so good at dissolving things. The positive side of the molecule is attracted to Methane is formed when four hydrogens and one carbon covalently bond. negative ions and the negative side is attracted to positive ions. ",text,
L_0107,chemical bonding,T_0980,"Ions come together to create a molecule so that electrical charges are balanced; the positive charges balance the negative charges and the molecule has no electrical charge. To balance electrical charge, an atom may share its electron with another atom, give it away, or receive an electron from another atom. The joining of ions to make molecules is called chemical bonding. There are three main types of chemical bonds that are important in our discussion of minerals and rocks: Ionic bond: Electrons are transferred between atoms. An ion will give one or more electrons to another ion. Table salt, sodium chloride (NaCl), is a common example of an ionic compound. Note that sodium is on the left side of the periodic table and that chlorine is on the right side of the periodic table. In the Figure 1.2, an atom of lithium donates an electron to an atom of fluorine to form an ionic compound. The transfer of the electron gives the lithium ion a net charge of +1, and the fluorine ion a net charge of -1. These ions bond because they experience an attractive force due to the difference in sign of their charges. Covalent bond : In a covalent bond, an atom shares one or more electrons with another atom. Periodic Table of the Elements. Lithium (left) and fluorine (right) form an ionic compound called lithium fluoride. In the picture of methane (CH4 ) below (Figure 1.3), the carbon ion (with a net charge of +4) shares a single electron from each of the the four hydrogens. Covalent bonding is prevalent in organic compounds. In fact, your body is held together by electrons shared by carbons and hydrogens! Covalent bonds are also very strong, meaning it takes a lot of energy to break them apart. Hydrogen bond: These weak, intermolecular bonds are formed when the positive side of one polar molecule is attracted to the negative side of another polar molecule. Water is a classic example of a polar molecule because it has a slightly positive side, and a slightly negative side. In fact, this property is why water is so good at dissolving things. The positive side of the molecule is attracted to Methane is formed when four hydrogens and one carbon covalently bond. negative ions and the negative side is attracted to positive ions. ",text,
L_0109,cleaning up groundwater,T_0989,"Preventing groundwater contamination is much easier and cheaper than cleaning it. To clean groundwater, the water, as well as the rock and soil through which it travels, must be cleansed. Thoroughly cleaning an aquifer would require cleansing each pore within the soil or rock unit. For this reason, cleaning polluted groundwater is very costly, takes years, and is sometimes not technically feasible. If the toxic materials can be removed from the aquifer, disposing of them is another challenge. ",text,
L_0109,cleaning up groundwater,T_0990,,text,
L_0109,cleaning up groundwater,T_0991,"If the source is an underground tank, the tank will be pumped dry and then dug out from the ground. If the source is a factory that is releasing toxic chemicals that are ending up in the groundwater, the factory may be required to stop the discharge. ",text,
L_0109,cleaning up groundwater,T_0992,"Hydrologists must determine how far, in what direction, and how rapidly the plume is moving. They must determine the concentration of the contaminant to determine how much it is being diluted. The scientists will use existing wells and may drill test wells to check for concentrations and monitor the movement of the plume. ",text,
L_0109,cleaning up groundwater,T_0993,"Using the well data, the hydrologist uses a computer program with information on the permeability of the aquifer and the direction and rate of groundwater flow, then models the plume to predict the dispersal of the contaminant through the aquifer. Drilling test wells to monitor pollution is expensive. ",text,
L_0109,cleaning up groundwater,T_0994,"First, an underground barrier is constructed to isolate the contaminated groundwater from the rest of the aquifer. Next, the contaminated groundwater may be treated in place. Bioremediation is relatively inexpensive. Bioengineered microorganisms are injected into the contaminant plume and allowed to consume the pollutant. Air may be pumped into the polluted region to encourage the growth and reproduction of the microbes. With chemical remediation, a chemical is pumped into the aquifer so the contaminant is destroyed. Acids or bases can neutralize contaminants or cause pollutants to precipitate from the water. The most difficult and expensive option is for reclamation teams to pump the water to the surface, cleanse it using chemical or biological methods, then re-inject it into the aquifer. The contaminated portions of the aquifer must be dug up and the pollutant destroyed by incinerating or chemically processing the soil, which is then returned to the ground. This technique is often prohibitively expensive and is done only in extreme cases. Click image to the left or use the URL below. URL: ",text,
L_0110,climate change in earth history,T_0995,"Climate has changed throughout Earth history. Much of the time Earths climate was hotter and more humid than it is today, but climate has also been colder, as when glaciers covered much more of the planet. The most recent ice ages were in the Pleistocene Epoch, between 1.8 million and 10,000 years ago (Figure 1.1). Glaciers advanced and retreated in cycles, known as glacial and interglacial periods. With so much of the worlds water bound into the ice, sea level was about 125 meters (395 feet) lower than it is today. Many scientists think that we are now in a warm, interglacial period that has lasted about 10,000 years. For the past 1500 years, climate has been relatively mild and stable when compared with much of Earths history. Why has climate stability been beneficial for human civilization? Stability has allowed the expansion of agriculture and the development of towns and cities. Fairly small temperature changes can have major effects on global climate. The average global temperature during glacial periods was only about 5.5o C (10o F) less than Earths current average temperature. Temperatures during the interglacial periods were about 1.1o C (2.0o F) higher than today (Figure 1.2). The maximum extent of Northern Hemi- sphere glaciers during the Pleistocene epoch. Since the end of the Pleistocene, the global average temperature has risen about 4o C (7o F). Glaciers are retreating and sea level is rising. While climate is getting steadily warmer, there have been a few more extreme warm and cool times in the last 10,000 years. Changes in climate have had effects on human civilization. The Medieval Warm Period from 900 to 1300 A.D. allowed Vikings to colonize Greenland and Great Britain to grow wine grapes. The Little Ice Age, from the 14th to 19th centuries, the Vikings were forced out of Greenland and humans had to plant crops further south. The graph is a compilation of 5 recon- structions (the green line is the mean of the five records) of mean temperature changes. This illustrates the high tem- peratures of the Medieval Warm Period, the lows of the Little Ice Age, and the very high (and climbing) temperature of this decade. Click image to the left or use the URL below. URL: ",text,
L_0110,climate change in earth history,T_0995,"Climate has changed throughout Earth history. Much of the time Earths climate was hotter and more humid than it is today, but climate has also been colder, as when glaciers covered much more of the planet. The most recent ice ages were in the Pleistocene Epoch, between 1.8 million and 10,000 years ago (Figure 1.1). Glaciers advanced and retreated in cycles, known as glacial and interglacial periods. With so much of the worlds water bound into the ice, sea level was about 125 meters (395 feet) lower than it is today. Many scientists think that we are now in a warm, interglacial period that has lasted about 10,000 years. For the past 1500 years, climate has been relatively mild and stable when compared with much of Earths history. Why has climate stability been beneficial for human civilization? Stability has allowed the expansion of agriculture and the development of towns and cities. Fairly small temperature changes can have major effects on global climate. The average global temperature during glacial periods was only about 5.5o C (10o F) less than Earths current average temperature. Temperatures during the interglacial periods were about 1.1o C (2.0o F) higher than today (Figure 1.2). The maximum extent of Northern Hemi- sphere glaciers during the Pleistocene epoch. Since the end of the Pleistocene, the global average temperature has risen about 4o C (7o F). Glaciers are retreating and sea level is rising. While climate is getting steadily warmer, there have been a few more extreme warm and cool times in the last 10,000 years. Changes in climate have had effects on human civilization. The Medieval Warm Period from 900 to 1300 A.D. allowed Vikings to colonize Greenland and Great Britain to grow wine grapes. The Little Ice Age, from the 14th to 19th centuries, the Vikings were forced out of Greenland and humans had to plant crops further south. The graph is a compilation of 5 recon- structions (the green line is the mean of the five records) of mean temperature changes. This illustrates the high tem- peratures of the Medieval Warm Period, the lows of the Little Ice Age, and the very high (and climbing) temperature of this decade. Click image to the left or use the URL below. URL: ",text,
L_0111,climate zones and biomes,T_0996,"The major factors that influence climate determine the different climate zones. In general, the same type of climate zone will be found at similar latitudes and in similar positions on nearly all continents, both in the Northern and Southern Hemispheres. The exceptions to this pattern are the climate zones called the continental climates, which are not found at higher latitudes in the Southern Hemisphere. This is because the Southern Hemisphere land masses are not wide enough to produce a continental climate. ",text,
L_0111,climate zones and biomes,T_0997,"Climate zones are classified by the Kppen classification system. This system is based on the temperature, the amount of precipitation, and the times of year when precipitation occurs. Since climate determines the type of vegetation that grows in an area, vegetation is used as an indicator of climate type. ",text,
L_0111,climate zones and biomes,T_0998,"A climate type and its plants and animals make up a biome. The organisms of a biome share certain characteristics around the world, because their environment has similar advantages and challenges. The organisms have adapted to that environment in similar ways over time. For example, different species of cactus live on different continents, but they have adapted to the harsh desert in similar ways. Click image to the left or use the URL below. URL: ",text,
L_0111,climate zones and biomes,T_0999,"The Kppen classification system recognizes five major climate groups. Each group is divided into subcategories. Some of these subcategories are forest, monsoon, and wet/dry types, based on the amount of precipitation and season when that precipitation occurs (Figure 1.1). This world map of the Kppen classification system indicates where the climate zones and major biomes are located. ",text,
L_0111,climate zones and biomes,T_1000,"Tropical moist climates are found in a band about 15o to 25o N and S of the Equator (Figure 1.1). Temperature: Intense sunshine. Each month has an average temperature of at least 18o C (64o F). Rainfall: Abundant, at least 150 cm (59 inches) per year. The main vegetation for this climate is the tropical rainforest. ",text,
L_0111,climate zones and biomes,T_1001,Dry climates have less precipitation than evaporation. Temperature: Abundant sunshine. Summer temperatures are high; winters are cooler and longer than in tropical moist climates. Rainfall: Irregular; several years of drought are often followed by a single year of abundant rainfall. Dry climates cover about 26% of the worlds land area. Low latitude deserts are found at the Ferrell cell high pressure zone. Higher latitude deserts occur within continents or in rainshadows. Vegetation is sparse but well adapted to the dry conditions. ,text,
L_0111,climate zones and biomes,T_1002,"Moist subtropical mid-latitude climates are found along the coastal areas in the United States. Temperature: The coldest month ranges from just below freezing to almost balmy, between -3o C and 18o C (27o to 64o F). Summers are mild, with average temperatures above 10o C (50o F). Seasons are distinct. Rainfall: There is plentiful annual rainfall. ",text,
L_0111,climate zones and biomes,T_1003,"Continental climates are found in most of the North American interior from about 40 N to 70 N. Temperature: The average temperature of the warmest month is higher than 10 C (50 F) and the coldest month is below -3 C (27 F). Precipitation: Winters are cold and stormy (look at the latitude of this zone and see if you can figure out why). Snowfall is common and snow stays on the ground for long periods of time. Trees grow in continental climates, even though winters are extremely cold, because the average annual temperature is fairly mild. Continental climates are not found in the Southern Hemisphere because of the absence of a continent large enough to generate this effect. ",text,
L_0111,climate zones and biomes,T_1004,"Polar climates are found across the continents that border the Arctic Ocean, Greenland, and Antarctica. Temperature: Winters are entirely dark and bitterly cold. Summer days are long, but the Sun is low on the horizon so summers are cool. The average temperature of the warmest month is less than 10o C (50o F). The annual temperature range is large. Precipitation: The region is dry, with less than 25 cm (10 inches) of precipitation annually; most precipitation occurs during the summer. ",text,
L_0111,climate zones and biomes,T_1005,"When climate conditions in a small area are different from those of the surroundings, the climate of the small area is called a microclimate. The microclimate of a valley may be cool relative to its surroundings since cold air sinks. The ground surface may be hotter or colder than the air a few feet above it, because rock and soil gain and lose heat readily. Different sides of a mountain will have different microclimates. In the Northern Hemisphere, a south-facing slope receives more solar energy than a north-facing slope, so each side supports different amounts and types of vegetation. Altitude mimics latitude in climate zones. Climates and biomes typical of higher latitudes may be found in other areas of the world at high altitudes. Click image to the left or use the URL below. URL: ",text,
L_0113,coal power,T_1012,"Coal, a solid fossil fuel formed from the partially decomposed remains of ancient forests, is burned primarily to produce electricity. Coal use is undergoing enormous growth as the availability of oil and natural gas decreases and cost increases. This increase in coal use is happening particularly in developing nations, such as China, where coal is cheap and plentiful. Coal is black or brownish-black. The most common form of coal is bituminous, a sedimentary rock that contains impurities such as sulfur (Figure 1.1). Anthracite coal has been metamorphosed and is nearly all carbon. For this reason, anthracite coal burns more cleanly than bituminous coal. ",text,
L_0113,coal power,T_1013,"Coal forms from dead plants that settled at the bottom of ancient swamps. Lush coal swamps were common in the tropics during the Carboniferous period, which took place more than 300 million years ago (Figure 1.2). The climate was warmer then. Mud and other dead plants buried the organic material in the swamp, and burial kept oxygen away. When plants are buried without oxygen, the organic material can be preserved or fossilized. Sand and clay settling on top of the decaying plants squeezed out the water and other substances. Millions of years later, what remains is a carbon- containing rock that we know as coal. ",text,
L_0113,coal power,T_1014,"Around the world, coal is the largest source of energy for electricity. The United States is rich in coal (Figure 1.3). California once had a number of small coal mines, but the state no longer produces coal. To turn coal into electricity, the rock is crushed into powder, which is then burned in a furnace that has a boiler. Like other fuels, coal releases its energy as heat when it burns. Heat from the burning coal boils the water in the boiler to make steam. The steam spins turbines, which turn generators to create electricity. In this way, the energy stored in the coal is converted to useful energy like electricity. ",text,
L_0113,coal power,T_1015,"For coal to be used as an energy source, it must first be mined. Coal mining occurs at the surface or underground by methods that are described in the the chapter Materials of Earths Crust (Figure 1.4). Mining, especially underground The location of the continents during the Carboniferous period. Notice that quite a lot of land area is in the region of the tropics. mining, can be dangerous. In April 2010, 29 miners were killed at a West Virginia coal mine when gas that had accumulated in the mine tunnels exploded and started a fire. Coal mining exposes minerals and rocks from underground to air and water at the surface. Many of these minerals contain the element sulfur, which mixes with air and water to make sulfuric acid, a highly corrosive chemical. If the sulfuric acid gets into streams, it can kill fish, plants, and animals that live in or near the water. Click image to the left or use the URL below. URL: ",text,
L_0114,coastal pollution,T_1016,"Most ocean pollution comes as runoff from land and originates as agricultural, industrial, and municipal wastes (Figure 1.1). The remaining 20% of water pollution enters the ocean directly from oil spills and people dumping wastes directly into the water. Ships at sea empty their wastes directly into the ocean, for example. Coastal pollution can make coastal water unsafe for humans and wildlife. After rainfall, there can be enough runoff pollution that beaches must be closed to prevent the spread of disease from pollutants. A surprising number of beaches are closed because of possible health hazards each year. A large proportion of the fish we rely on for food live in the coastal wetlands or lay their eggs there. Coastal runoff from farm waste often carries water-borne organisms that cause lesions that kill fish. Humans who come in In some areas of the world, ocean pollution is all too obvious. contact with polluted waters and affected fish can also experience harmful symptoms. More than one-third of the shellfish-growing waters of the United States are adversely affected by coastal pollution. ",text,
L_0114,coastal pollution,T_1017,"Fertilizers that run off of lawns and farm fields are extremely harmful to the environment. Nutrients, such as nitrates, in the fertilizer promote algae growth in the water they flow into. With the excess nutrients, lakes, rivers, and bays become clogged with algae and aquatic plants. Eventually these organisms die and decompose. Decomposition uses up all the dissolved oxygen in the water. Without oxygen, large numbers of plants, fish, and bottom-dwelling animals die. Every year dead zones appear in lakes and nearshore waters. A dead zone is an area of hundreds of kilometers of ocean without fish or plant life. The Mississippi is not the only river that carries the nutrients necessary to cause a dead zone. Rivers that drain regions where human population density is high and where crops are grown create dead zones all over the world (Figure 1.2). ",text,
L_0116,comets,T_1025,"Comets are small, icy objects that have very elliptical orbits around the Sun. Their orbits carry them from the outer solar system to the inner solar system, close to the Sun. Early in Earths history, comets may have brought water and other substances to Earth during collisions. Comet tails form the outer layers of ice melt and evaporate as the comet flies close to the Sun. The ice from the comet vaporizes and forms a glowing coma, which reflects light from the Sun. Radiation and particles streaming from the Sun push this gas and dust into a long tail that always points away from the Sun (Figure 1.1). Comets appear for only a short time when they are near the Sun, then seem to disappear again as they move back to the outer solar system. Comet Hale-Bopp, also called the Great Comet of 1997, shone brightly for several months in 1997. The comet has two visible tails: a bright, curved dust tail and a fainter, straight tail of ions (charged atoms) pointing directly away from the Sun. The time between one appearance of a comet and the next is called the comets period. Halleys comet, with a period of 75 years, will next be seen in 2061. The first mention of the comet in historical records may go back as much as two millennia. ",text,
L_0116,comets,T_1026,"Short-period comets, with periods of about 200 years or less, come from a region beyond the orbit of Neptune called the Kuiper belt (pronounced KI-per). It contains not only comets, but also asteroids and at least two dwarf planets. Comets with periods as long as thousands or even millions of years come from a very distant region of the solar system called the Oort cloud, about 50,000  100,000 AU from the Sun (50,000 - 100,000 times the distance from the Sun to Earth). Click image to the left or use the URL below. URL: ",text,
L_0118,conserving water,T_1032,"Water consumption per person has been going down for the past few decades. There are many ways that water conservation can be encouraged. Charging more for water gives a financial incentive for careful water use. Water use may be restricted by time of day, season, or activity. Good behavior can be encouraged; for example, people can be given an incentive to replace grass with desert plants in arid regions. ",text,
L_0118,conserving water,T_1033,"As human population growth continues, water conservation will become increasingly important globally, especially in developed countries where people use an enormous amount of water. What are some of the ways you can conserve water in and around your home? Avoid polluting water so that less is needed. Convert to more efficient irrigation methods on farms and in gardens. Reduce household demand by installing water-saving devices such as low-flow shower heads and toilets. Reduce personal demand by turning off the tap when water is not being used and taking shorter showers. Engage in water-saving practices: for instance, water lawns less and sweep rather than hose down sidewalks. At Earth Summit 2002, many governments approved a Plan of Action to address the scarcity of water and safe drinking water in developing countries. One goal of this plan was to cut in half the number of people without access to safe drinking water by 2015. Although this is a very important goal, it will not be met. Goals like these are made more difficult as population continues to grow. This colorful adobe house in Tucson, Arizona is surrounded by native cactus, which needs little water to thrive. Click image to the left or use the URL below. URL: ",text,
L_0119,continental drift,T_1034,"Alfred Wegener, born in 1880, was a meteorologist and explorer. In 1911, Wegener found a scientific paper that listed identical plant and animal fossils on opposite sides of the Atlantic Ocean. Intrigued, he then searched for and found other cases of identical fossils on opposite sides of oceans. The explanation put out by the scientists of the day was that land bridges had once stretched between these continents. Instead, Wegener pondered the way Africa and South America appeared to fit together like puzzle pieces. Other scientists had suggested that Africa and South America had once been joined, but Wegener was the ideas most dogged supporter. Wegener amassed a tremendous amount of evidence to support his hypothesis that the continents had once been joined. Imagine that youre Wegeners colleague. What sort of evidence would you look for to see if the continents had actually been joined and had moved apart? ",text,
L_0119,continental drift,T_1035,"Here is the main evidence that Wegener and his supporters collected for the continental drift hypothesis: The continents appear to fit together. Ancient fossils of the same species of extinct plants and animals are found in rocks of the same age but are on continents that are now widely separated (Figure 1.1). Wegener proposed that the organisms had lived side by side, but that the lands had moved apart after they were dead and fossilized. His critics suggested that the organisms moved over long-gone land bridges, but Wegener thought that the organisms could not have been able to travel across the oceans. Fossils of the seed fern Glossopteris were too heavy to be carried so far by wind. Mesosaurus was a swimming reptile, but could only swim in fresh water. Cynognathus and Lystrosaurus were land reptiles and were unable to swim. Wegener used fossil evidence to support his continental drift hypothesis. The fos- sils of these organisms are found on lands that are now far apart. Identical rocks, of the same type and age, are found on both sides of the Atlantic Ocean. Wegener said the rocks had formed side by side and that the land had since moved apart. Mountain ranges with the same rock types, structures, and ages are now on opposite sides of the Atlantic Ocean. The Appalachians of the eastern United States and Canada, for example, are just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway (Figure 1.2). Wegener concluded that they formed as a single mountain range that was separated as the continents drifted. Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the Equator. This would indicate that the glaciers either formed in the middle of the ocean and/or covered most of the Earth. Today, glaciers only form on land and nearer the poles. Wegener thought that the glaciers were centered over the southern land mass close to the South Pole and the continents moved to their present positions later on. The similarities between the Appalachian and the eastern Greenland mountain ranges are evidences for the continental drift hypothesis. Coral reefs and coal-forming swamps are found in tropical and subtropical environments, but ancient coal seams and coral reefs are found in locations where it is much too cold today. Wegener suggested that these creatures were alive in warm climate zones and that the fossils and coal later drifted to new locations on the continents. Wegener thought that mountains formed as continents ran into each other. This got around the problem of the leading hypothesis of the day, which was that Earth had been a molten ball that bulked up in spots as it cooled (the problem with this idea was that the mountains should all be the same age and they were known not to be). Click image to the left or use the URL below. URL: ",text,
L_0119,continental drift,T_1035,"Here is the main evidence that Wegener and his supporters collected for the continental drift hypothesis: The continents appear to fit together. Ancient fossils of the same species of extinct plants and animals are found in rocks of the same age but are on continents that are now widely separated (Figure 1.1). Wegener proposed that the organisms had lived side by side, but that the lands had moved apart after they were dead and fossilized. His critics suggested that the organisms moved over long-gone land bridges, but Wegener thought that the organisms could not have been able to travel across the oceans. Fossils of the seed fern Glossopteris were too heavy to be carried so far by wind. Mesosaurus was a swimming reptile, but could only swim in fresh water. Cynognathus and Lystrosaurus were land reptiles and were unable to swim. Wegener used fossil evidence to support his continental drift hypothesis. The fos- sils of these organisms are found on lands that are now far apart. Identical rocks, of the same type and age, are found on both sides of the Atlantic Ocean. Wegener said the rocks had formed side by side and that the land had since moved apart. Mountain ranges with the same rock types, structures, and ages are now on opposite sides of the Atlantic Ocean. The Appalachians of the eastern United States and Canada, for example, are just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway (Figure 1.2). Wegener concluded that they formed as a single mountain range that was separated as the continents drifted. Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the Equator. This would indicate that the glaciers either formed in the middle of the ocean and/or covered most of the Earth. Today, glaciers only form on land and nearer the poles. Wegener thought that the glaciers were centered over the southern land mass close to the South Pole and the continents moved to their present positions later on. The similarities between the Appalachian and the eastern Greenland mountain ranges are evidences for the continental drift hypothesis. Coral reefs and coal-forming swamps are found in tropical and subtropical environments, but ancient coal seams and coral reefs are found in locations where it is much too cold today. Wegener suggested that these creatures were alive in warm climate zones and that the fossils and coal later drifted to new locations on the continents. Wegener thought that mountains formed as continents ran into each other. This got around the problem of the leading hypothesis of the day, which was that Earth had been a molten ball that bulked up in spots as it cooled (the problem with this idea was that the mountains should all be the same age and they were known not to be). Click image to the left or use the URL below. URL: ",text,
L_0120,coriolis effect,T_1036,"The Coriolis effect describes how Earths rotation steers winds and surface ocean currents (Figure 1.1). Coriolis causes freely moving objects to appear to move to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The objects themselves are actually moving straight, but the Earth is rotating beneath them, so they seem to bend or curve. Thats why it is incorrect to call Coriolis a force. It is not forcing anything to happen! An example might make the Coriolis effect easier to visualize. If an airplane flies 500 miles due north, it will not arrive at the city that was due north of it when it began its journey. Over the time it takes for the airplane to fly 500 miles, that city moved, along with the Earth it sits on. The airplane will therefore arrive at a city to the west of the original city (in the Northern Hemisphere), unless the pilot has compensated for the change. So to reach his intended destination, the pilot must also veer right while flying north. As wind or an ocean current moves, the Earth spins underneath it. As a result, an object moving north or south along the Earth will appear to move in a curve instead of in a straight line. Wind or water that travels toward the poles from the Equator is deflected to the east, while wind or water that travels toward the Equator from the poles gets bent to the west. The Coriolis effect bends the direction of surface currents to the right in the Northern Hemisphere and left in the Southern Hemisphere. The Coriolis effect causes winds and cur- rents to form circular patterns. The di- rection that they spin depends on the hemisphere that they are in. Coriolis effect is demonstrated using a metal ball and a rotating plate in this video. The ball moves in a circular path just like a freely moving particle of gas or liquid moves on the rotating Earth (5b). Click image to the left or use the URL below. URL: ",text,
L_0121,correlation using relative ages,T_1037,Superposition and cross-cutting are helpful when rocks are touching one another and lateral continuity helps match up rock layers that are nearby. To match up rocks that are further apart we need the process of correlation. How do geologists correlate rock layers that are separated by greater distances? There are three kinds of clues: ,text,
L_0121,correlation using relative ages,T_1038,1. Distinctive rock formations may be recognizable across large regions (Figure 1.1). ,text,
L_0121,correlation using relative ages,T_1039,"2. Two separated rock units with the same index fossil are of very similar age. What traits do you think an index fossil should have? To become an index fossil the organism must have (1) been widespread so that it is useful for identifying rock layers over large areas and (2) existed for a relatively brief period of time so that the approximate age of the rock layer is immediately known. Many fossils may qualify as index fossils (Figure below). Ammonites, trilobites, and graptolites are often used as index fossils. Microfossils, which are fossils of microscopic organisms, are also useful index fossils. Fossils of animals that drifted in the upper layers of the ocean are particularly useful as index fossils, since they may be distributed over very large areas. A biostratigraphic unit, or biozone, is a geological rock layer that is defined by a single index fossil or a fossil assemblage. A biozone can also be used to identify rock layers across distances. The famous White Cliffs of Dover in southwest England can be matched to similar white cliffs in Denmark and Germany. ",text,
L_0121,correlation using relative ages,T_1040,"3. A key bed can be used like an index fossil since a key bed is a distinctive layer of rock that can be recognized across a large area. A volcanic ash unit could be a good key bed. One famous key bed is the clay layer at the boundary between the Cretaceous Period and the Tertiary Period, the time that the dinosaurs went extinct (Figure in asteroids. In 1980, the father-son team of Luis and Walter Alvarez proposed that a huge asteroid struck Earth 66 million years ago and caused the mass extinction. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0123,deep ocean currents,T_1044,"Thermohaline circulation drives deep ocean circulation. Thermo means heat and haline refers to salinity. Dif- ferences in temperature and in salinity change the density of seawater. So thermohaline circulation is the result of density differences in water masses because of their different temperature and salinity. What is the temperature and salinity of very dense water? Lower temperature and higher salinity yield the densest water. When a volume of water is cooled, the molecules move less vigorously, so same number of molecules takes up less space and the water is denser. If salt is added to a volume of water, there are more molecules in the same volume, so the water is denser. ",text,
L_0123,deep ocean currents,T_1045,"Changes in temperature and salinity of seawater take place at the surface. Water becomes dense near the poles. Cold polar air cools the water and lowers its temperature, increasing its salinity. Fresh water freezes out of seawater to become sea ice, which also increases the salinity of the remaining water. This very cold, very saline water is very dense and sinks. This sinking is called downwelling. This video lecture discusses the vertical distribution of life in the oceans. Seawater density creates currents, which provide different habitats for different creatures: Click image to the left or use the URL below. URL:  Two things then happen. The dense water pushes deeper water out of its way and that water moves along the bottom of the ocean. This deep water mixes with less dense water as it flows. Surface currents move water into the space vacated at the surface where the dense water sank (Figure 1.1). Water also sinks into the deep ocean off of Antarctica. Cold water (blue lines) sinks in the North Atlantic, flows along the bottom of the ocean and upwells in the Pacific or Indian. The water then travels in surface currents (red lines) back to the North Atlantic. Deep water also forms off of Antarctica. ",text,
L_0123,deep ocean currents,T_1046,"Since unlimited amounts of water cannot sink to the bottom of the ocean, water must rise from the deep ocean to the surface somewhere. This process is called upwelling (Figure 1.2). Upwelling forces denser water from below to take the place of less dense water at the surface that is pushed away by the wind. Generally, upwelling occurs along the coast when wind blows water strongly away from the shore. This leaves a void that is filled by deep water that rises to the surface. Upwelling is extremely important where it occurs. During its time on the bottom, the cold deep water has collected nutrients that have fallen down through the water column. Upwelling brings those nutrients to the surface. Those nutrients support the growth of plankton and form the base of a rich ecosystem. California, South America, South Africa, and the Arabian Sea all benefit from offshore upwelling. Upwelling also takes place along the Equator between the North and South Equatorial Currents. Winds blow the surface water north and south of the Equator, so deep water undergoes upwelling. The nutrients rise to the surface and support a great deal of life in the equatorial oceans. Click image to the left or use the URL below. URL: ",text,
L_0124,determining relative ages,T_1047,"Stenos and Smiths principles are essential for determining the relative ages of rocks and rock layers. In the process of relative dating, scientists do not determine the exact age of a fossil or rock but look at a sequence of rocks to try to decipher the times that an event occurred relative to the other events represented in that sequence. The relative age of a rock then is its age in comparison with other rocks. If you know the relative ages of two rock layers, (1) Do you know which is older and which is younger? (2) Do you know how old the layers are in years? In some cases, it is very tricky to determine the sequence of events that leads to a certain formation. Can you figure out what happened in what order in (Figure 1.1)? Write it down and then check the following paragraphs. The principle of cross-cutting relationships states that a fault or intrusion is younger than the rocks that it cuts through. The fault cuts through all three sedimentary rock layers (A, B, and C) and also the intrusion (D). So the fault must be the youngest feature. The intrusion (D) cuts through the three sedimentary rock layers, so it must be younger than those layers. By the law of superposition, C is the oldest sedimentary rock, B is younger and A is still younger. The full sequence of events is: 1. Layer C formed. 2. Layer B formed. A geologic cross section: Sedimentary rocks (A-C), igneous intrusion (D), fault (E). 3. Layer A formed. 4. After layers A-B-C were present, intrusion D cut across all three. 5. Fault E formed, shifting rocks A through C and intrusion D. 6. Weathering and erosion created a layer of soil on top of layer A. Click image to the left or use the URL below. URL: ",text,
L_0125,development of hypotheses,T_1048,"Before we develop some hypotheses, lets find a new question that we want to answer. What we just learned that atmospheric CO2 has been increasing at least since 1958. This leads us to ask this question: Why is atmospheric CO2 increasing? ",text,
L_0125,development of hypotheses,T_1049,"We do some background research to find the possible sources of carbon dioxide into the atmosphere. We discover two things: Carbon dioxide is released into the atmosphere by volcanoes when they erupt. Carbon dioxide is released when fossil fuels are burned. A hypothesis is a reasonable explanation to explain a small range of phenomena. A hypothesis is limited in scope, explaining a single event or a fact. A hypothesis must be testable and falsifiable. We must be able to test it and it must be possible to show that it is wrong. From these two facts we can create two hypotheses. We will have multiple working hypotheses. We can test each of these hypotheses. ",text,
L_0125,development of hypotheses,T_1050,"Atmospheric CO2 has increased over the past five decades, because the amount of CO2 gas released by volcanoes has increased. ",text,
L_0125,development of hypotheses,T_1051,"The increase in atmospheric CO2 is due to the increase in the amount of fossil fuels that are being burned. Usually, testing a hypothesis requires making observations or performing experiments. In this case, we will look into the scientific literature to see if we can support or refute either or both of these hypotheses. Click image to the left or use the URL below. URL: ",text,
L_0127,distance between stars,T_1054,"Distances to stars that are relatively close to us can be measured using parallax. Parallax is an apparent shift in position that takes place when the position of the observer changes. To see an example of parallax, try holding your finger about 1 foot (30 cm) in front of your eyes. Now, while focusing on your finger, close one eye and then the other. Alternate back and forth between eyes, and pay attention to how your finger appears to move. The shift in position of your finger is an example of parallax. Now try moving your finger closer to your eyes, and repeat the experiment. Do you notice any difference? The closer your finger is to your eyes, the greater the position changes because of parallax. As Figure 1.1 shows, astronomers use this same principle to measure the distance to stars. Instead of a finger, they focus on a star, and instead of switching back and forth between eyes, they switch between the biggest possible differences in observing position. To do this, an astronomer first looks at the star from one position and notes where the star is relative to more distant stars. Now where will the astronomer go to make an observation the greatest possible distance from the first observation? In six months, after Earth moves from one side of its orbit around the Sun to the other side, the astronomer looks at the star again. This time parallax causes the star to appear in a different position relative to more distant stars. From the size of this shift, astronomers can calculate the distance to the star. ",text,
L_0127,distance between stars,T_1055,"Even with the most precise instruments available, parallax is too small to measure the distance to stars that are more than a few hundred light years away. For these more distant stars, astronomers must use more indirect methods of determining distance. Most of these methods involve determining how bright the star they are looking at really is. For example, if the star has properties similar to the Sun, then it should be about as bright as the Sun. The astronomer compares the observed brightness to the expected brightness. ",text,
L_0128,distribution of water on earth,T_1056,"Earths oceans contain 97% of the planets water. That leaves just 3% as fresh water, water with low concentrations of salts (Figure 1.1). Most fresh water is trapped as ice in the vast glaciers and ice sheets of Greenland and Antarctica. How is the 3% of fresh water divided into different reservoirs? How much of that water is useful for living creatures? How much for people? A storage location for water such as an ocean, glacier, pond, or even the atmosphere is known as a reservoir. A water molecule may pass through a reservoir very quickly or may remain for much longer. The amount of time a molecule stays in a reservoir is known as its residence time. The distribution of Earths water. Click image to the left or use the URL below. URL: ",text,
L_0131,dwarf planets,T_1062,"In 2006, the International Astronomical Union decided that there were too many questions surrounding what could be called a planet, and so refined the definition of a planet. According to the new definition, a planet must: Orbit a star. Be big enough that its own gravity causes it to be shaped as a sphere. Be small enough that it isnt a star itself. Have cleared the area of its orbit of smaller objects. ",text,
L_0131,dwarf planets,T_1063,"The dwarf planets of our solar system are exciting proof of how much we are learning about our solar system. With the discovery of many new objects in our solar system, astronomers refined the definition of a dwarf planet in 2006. According to the IAU, a dwarf planet must: Orbit a star. Have enough mass to be nearly spherical. Not have cleared the area around its orbit of smaller objects. Not be a moon. ",text,
L_0131,dwarf planets,T_1064,"The reclassification of Pluto to the new category dwarf planet stirred up a great deal of controversy. How the classification of Pluto has evolved is an interesting story in science. From the time it was discovered in 1930 until the early 2000s, Pluto was considered the ninth planet. When astronomers first located Pluto, the telescopes were not as good, so Pluto and its moon, Charon, were seen as one much larger object (Figure 1.1). With better telescopes, astronomers realized that Pluto was much smaller than they had thought. Pluto and its moon, Charon, are actually two objects. Better technology also allowed astronomers to discover many smaller objects like Pluto that orbit the Sun. One of them, Eris, discovered in 2005, is even larger than Pluto. Even when it was considered a planet, Pluto was an oddball. Unlike the other outer planets in the solar system, which are all gas giants, it is small, icy, and rocky. With a diameter of about 2,400 km, it is only about one-fifth the mass of Earths Moon. Plutos orbit is tilted relative to the other planets and is shaped like a long, narrow ellipse. Plutos orbit sometimes even passes inside Neptunes orbit. From what youve read above, do you think Pluto should be called a planet? Why are people hesitant to take away Plutos planetary status? Is Pluto a dwarf planet? Pluto has three moons of its own. The largest, Charon, is big enough that the Pluto-Charon system is sometimes considered to be a double dwarf planet (Figure 1.1). Two smaller moons, Nix and Hydra, were discovered in 2005. But having moons is not enough to make an object a planet. Pluto and the other dwarf planets, besides Ceres, are found orbiting out beyond Neptune. Click image to the left or use the URL below. URL: ",text,
L_0131,dwarf planets,T_1065,"Ceres is by far the closest dwarf planet to the Sun; it resides between Mars and Jupiter. Ceres is the largest object in the asteroid belt (Figure 1.2). Before 2006, Ceres was considered the largest of the asteroids, with only about 1.3% of the mass of the Earths Moon. But unlike the asteroids, Ceres has enough mass that its gravity causes it to be shaped like a sphere. Like Pluto, Ceres is rocky. Is Ceres a planet? How does it match the criteria above? Ceres orbits the Sun, is round, and is not a moon. As part of the asteroid belt, its orbit is full of other smaller bodies, so Ceres fails the fourth criterion for being a planet. ",text,
L_0131,dwarf planets,T_1066,"Makemake is the third largest and second brightest dwarf planet we have discovered so far (Figure 1.3). With a diameter estimated to be between 1,300 and 1,900 km, it is about three-quarters the size of Pluto. Makemake orbits the Sun in 310 years at a distance between 38.5 to 53 AU. It is thought to be made of methane, ethane, and nitrogen ices. Largest Known Trans-Neptunian Objects. Makemake is named after the deity that created humanity in the mythology of the people of Easter Island. ",text,
L_0131,dwarf planets,T_1067,"Eris is the largest known dwarf planet in the solar system  it has about 27% more mass than Pluto (Figure 1.3). The object was not discovered until 2003 because it is about three times farther from the Sun than Pluto, and almost 100 times farther from the Sun than Earth is. For a short time Eris was considered the tenth planet in the solar system, but its discovery helped to prompt astronomers to better define planets and dwarf planets in 2006. Eris also has a small moon, Dysnomia, that orbits it once about every 16 days. Astronomers know there may be other dwarf planets in the outer reaches of the solar system. Haumea was made a dwarf planet in 2008, so the total number of dwarf planets is now five. Quaoar, Varuna, and Orcus may be added to the list of dwarf planets in the future. We still have a lot to discover and explore. Click image to the left or use the URL below. URL: ",text,
L_0132,early atmosphere and oceans,T_1068,"Earths first atmosphere was made of hydrogen and helium, the gases that were common in this region of the solar system as it was forming. Most of these gases were drawn into the center of the solar nebula to form the Sun. When Earth was new and very small, the solar wind blew off atmospheric gases that collected. If gases did collect, they were vaporized by impacts, especially from the impact that brought about the formation of the Moon. Eventually things started to settle down and gases began to collect. High heat in Earths early days meant that there were constant volcanic eruptions, which released gases from the mantle into the atmosphere (see opening image). Just as today, volcanic outgassing was a source of water vapor, carbon dioxide, small amounts of nitrogen, and other gases. Scientists have calculated that the amount of gas that collected to form the early atmosphere could not have come entirely from volcanic eruptions. Frequent impacts by asteroids and comets brought in gases and ices, including water, carbon dioxide, methane, ammonia, nitrogen, and other volatiles from elsewhere in the solar system (Figure Calculations also show that asteroids and comets cannot be responsible for all of the gases of the early atmosphere, so both impacts and outgassing were needed. ",text,
L_0132,early atmosphere and oceans,T_1069,"The second atmosphere, which was the first to stay with the planet, formed from volcanic outgassing and comet ices. This atmosphere had lots of water vapor, carbon dioxide, nitrogen, and methane but almost no oxygen. Why was there so little oxygen? Plants produce oxygen when they photosynthesize but life had not yet begun or had not yet developed photosynthesis. In the early atmosphere, oxygen only appeared when sunlight split water molecules into hydrogen and oxygen and the oxygen accumulated in the atmosphere. Without oxygen, life was restricted to tiny simple organisms. Why is oxygen essential for most life on Earth? 1. Oxygen is needed to make ozone, a molecule made of three oxygen ions, O3 . Ozone collects in the atmospheric ozone layer and blocks harmful ultraviolet radiation from the Sun. Without an ozone layer, life in the early Earth was almost impossible. 2. Animals need oxygen to breathe. No animals would have been able to breathe in Earths early atmosphere. ",text,
L_0132,early atmosphere and oceans,T_1070,"The early atmosphere was rich in water vapor from volcanic eruptions and comets. When Earth was cool enough, water vapor condensed and rain began to fall. The water cycle began. Over millions of years enough precipitation collected that the first oceans could have formed as early as 4.2 to 4.4 billion years ago. Dissolved minerals carried by stream runoff made the early oceans salty. What geological evidence could there be for the presence of an early ocean? Marine sedimentary rocks can be dated back about 4 billion years. By the Archean, the planet was covered with oceans and the atmosphere was full of water vapor, carbon dioxide, nitrogen, and smaller amounts of other gases. Click image to the left or use the URL below. URL: ",text,
L_0132,early atmosphere and oceans,T_1071,"When photosynthesis evolved and spread around the planet, oxygen was released in abundance. The addition of oxygen is what created Earths third atmosphere. This event, which occurred about 2.5 billion years ago, is sometimes called the oxygen catastrophe because so many organisms died. Although entire species died out and went extinct, this event is also called the Great Oxygenation Event because it was a great opportunity. The organisms that survived developed a use for oxygen through cellular respiration, the process by which cells can obtain energy from organic molecules. This opened up many opportunities for organisms to evolve to fill different niches and many new types of organisms first appeared on Earth. ",text,
L_0132,early atmosphere and oceans,T_1072,"What evidence do scientists have that large quantities of oxygen entered the atmosphere? The iron contained in the rocks combined with the oxygen to form reddish iron oxides. By the beginning of the Proterozoic, banded-iron formations (BIFs) were forming. Banded-iron formations display alternating bands of iron oxide and iron-poor chert that probably represent a seasonal cycle of an aerobic and an anaerobic environment. The oldest BIFs are 3.7 billion years old, but they are very common during the Great Oxygenation Event 2.4 billion years ago (Figure 1.2). By 1.8 billion years ago, the amount of BIF declined. In recent times, the iron in these formations has been mined, and that explains the location of the auto industry in the upper Midwest. ",text,
L_0132,early atmosphere and oceans,T_1073,"With more oxygen in the atmosphere, ultraviolet radiation could create ozone. With the formation of an ozone layer to protect the surface of the Earth from UV radiation, more complex life forms could evolve. Banded-iron formation. Click image to the left or use the URL below. URL: ",text,
L_0133,earth history and clues from fossils,T_1074,"Fossils are our best form of evidence about Earth history, including the history of life. Along with other geological evidence from rocks and structures, fossils even give us clues about past climates, the motions of plates, and other major geological events. Since the present is the key to the past, what we know about a type of organism that lives today can be applied to past environments. ",text,
L_0133,earth history and clues from fossils,T_1075,"That life on Earth has changed over time is well illustrated by the fossil record. Fossils in relatively young rocks resemble animals and plants that are living today. In general, fossils in older rocks are less similar to modern organisms. We would know very little about the organisms that came before us if there were no fossils. Modern technology has allowed scientists to reconstruct images and learn about the biology of extinct animals like dinosaurs! ",text,
L_0133,earth history and clues from fossils,T_1076,"By knowing something about the type of organism the fossil was, geologists can determine whether the region was terrestrial (on land) or marine (underwater) or even if the water was shallow or deep. The rock may give clues to whether the rate of sedimentation was slow or rapid. The amount of wear and fragmentation of a fossil allows scientists to learn about what happened to the region after the organism died; for example, whether it was exposed to wave action. ",text,
L_0133,earth history and clues from fossils,T_1077,The presence of marine organisms in a rock indicates that the region where the rock was deposited was once marine. Sometimes fossils of marine organisms are found on tall mountains indicating that rocks that formed on the seabed were uplifted. ,text,
L_0133,earth history and clues from fossils,T_1078,"By knowing something about the climate a type of organism lives in now, geologists can use fossils to decipher the climate at the time the fossil was deposited. For example, coal beds form in tropical environments but ancient coal beds are found in Antarctica. Geologists know that at that time the climate on the Antarctic continent was much warmer. Recall from the chapter Plate Tectonics that Wegener used the presence of coal beds in Antarctica as one of the lines of evidence for continental drift. ",text,
L_0133,earth history and clues from fossils,T_1079,"An index fossil can be used to identify a specific period of time. Organisms that make good index fossils are distinctive, widespread, and lived briefly. Their presence in a rock layer can be used to identify rocks that were deposited at that period of time over a large area. The fossil of a juvenile mammoth found near downtown San Jose California reveals an enormous amount about these majestic creatures: what they looked like, how they lived, and what the environment of the Bay Area was like so long ago. ",text,
L_0140,earths core,T_1099,"At the planets center lies a dense metallic core. Scientists know that the core is metal because: 1. The density of Earths surface layers is much less than the overall density of the planet, as calculated from the planets rotation. If the surface layers are less dense than average, then the interior must be denser than average. Calculations indicate that the core is about 85% iron metal with nickel metal making up much of the remaining 15%. 2. Metallic meteorites are thought to be representative of the core. The 85% iron/15% nickel calculation above is also seen in metallic meteorites (Figure 1.1). If Earths core were not metal, the planet would not have a magnetic field. Metals such as iron are magnetic, but rock, which makes up the mantle and crust, is not. Scientists know that the outer core is liquid and the inner core is solid because: 1. S-waves do not go through the outer core. 2. The strong magnetic field is caused by convection in the liquid outer core. Convection currents in the outer core are due to heat from the even hotter inner core. The heat that keeps the outer core from solidifying is produced by the breakdown of radioactive elements in the inner core. Click image to the left or use the URL below. URL: ",text,
L_0142,earths interior material,T_1103,"It wasnt always known that fossils were parts of living organisms. In 1666, a young doctor named Nicholas Steno dissected the head of an enormous great white shark that had been caught by fisherman near Florence, Italy. Steno was struck by the resemblance of the sharks teeth to fossils found in inland mountains and hills (Figure ??). Most people at the time did not believe that fossils were once part of living creatures. Authors in that day thought that the fossils of marine animals found in tall mountains, miles from any ocean could be explained in one of two ways: The shells were washed up during the Biblical flood. (This explanation could not account for the fact that fossils were not only found on mountains, but also within mountains, in rocks that had been quarried from deep below Earths surface.) The fossils formed within the rocks as a result of mysterious forces. But for Steno, the close resemblance between fossils and modern organisms was impossible to ignore. Instead of invoking supernatural forces, Steno concluded that fossils were once parts of living creatures. ",text,
L_0142,earths interior material,T_1104,"A fossil is any remains or traces of an ancient organism. Fossils include body fossils, left behind when the soft parts have decayed away, and trace fossils, such as burrows, tracks, or fossilized coprolites (feces) as seen above. Collections of fossils are known as fossil assemblages. ",text,
L_0142,earths interior material,T_1105,"Becoming a fossil isnt easy. Only a tiny percentage of the organisms that have ever lived become fossils. Why do you think only a tiny percentage of living organisms become fossils after death? Think about an antelope that dies on the African plain (Figure ??). Most of its body is eaten by hyenas and other scavengers and the remaining flesh is devoured by insects and bacteria. Only bones are left behind. As the years go by, the bones are scattered and fragmented into small pieces, eventually turning into dust. The remaining nutrients return to the soil. This antelope will not be preserved as a fossil. Is it more likely that a marine organism will become a fossil? When clams, oysters, and other shellfish die, the soft parts quickly decay, and the shells are scattered. In shallow water, wave action grinds them into sand-sized pieces. The shells are also attacked by worms, sponges, and other animals (Figure ??). How about a soft bodied organism? Will a creature without hard shells or bones become a fossil? There is virtually no fossil record of soft bodied organisms such as jellyfish, worms, or slugs. Insects, which are by far the most common land animals, are only rarely found as fossils (Figure ??). ",text,
L_0142,earths interior material,T_1106,"Despite these problems, there is a rich fossil record. How does an organism become fossilized? ",text,
L_0142,earths interior material,T_1107,"Usually its only the hard parts that are fossilized. The fossil record consists almost entirely of the shells, bones, or other hard parts of animals. Mammal teeth are much more resistant than other bones, so a large portion of the mammal fossil record consists of teeth. The shells of marine creatures are common also. ",text,
L_0142,earths interior material,T_1108,"Quick burial is essential because most decay and fragmentation occurs at the surface. Marine animals that die near a river delta may be rapidly buried by river sediments. A storm at sea may shift sediment on the ocean floor, covering a body and helping to preserve its skeletal remains (Figure ??). Quick burial is rare on land, so fossils of land animals and plants are less common than marine fossils. Land organisms can be buried by mudslides, volcanic ash, or covered by sand in a sandstorm (Figure ??). Skeletons can be covered by mud in lakes, swamps, or bogs. ",text,
L_0142,earths interior material,T_1109,"Unusual circumstances may lead to the preservation of a variety of fossils, as at the La Brea Tar Pits in Los Angeles, California. Although the animals trapped in the La Brea Tar Pits probably suffered a slow, miserable death, their bones were preserved perfectly by the sticky tar. (Figure ??). In spite of the difficulties of preservation, billions of fossils have been discovered, examined, and identified by thousands of scientists. The fossil record is our best clue to the history of life on Earth, and an important indicator of past climates and geological conditions as well. ",text,
L_0142,earths interior material,T_1110,Some rock beds contain exceptional fossils or fossil assemblages. Two of the most famous examples of soft organism preservation are from the 505 million-year-old Burgess Shale in Canada (Figure ??). The 145 million-year-old Solnhofen Limestone in Germany has fossils of soft body parts that are not normally preserved (Figure ??). ,text,
L_0142,earths interior material,T_1111,Use this resource to answer the questions that follow. Click image to the left for more content. 1. What are fossils? 2. What type of rocks are fossils found in? 3. What are sediments? 4. Explain how a fossil is created. 5. What factors have exposed sedimentary rock? ,text,
L_0144,earths magnetic field,T_1114,Earth is surrounded by a magnetic field (Figure 1.1) that behaves as if the planet had a gigantic bar magnet inside of it. Earths magnetic field also has a north and south pole. The magnetic field arises from the convection of molten iron and nickel metals in Earths liquid outer core. ,text,
L_0144,earths magnetic field,T_1115,"Many times during Earth history, even relatively recent Earth history, the planets magnetic field has flipped. That is, the north pole becomes the south pole and the south pole becomes the north pole. Scientists are not sure why this happens. One hypothesis is that the convection that drives the magnetic field becomes chaotic and then reverses itself. Another hypothesis is that an external event, such as an asteroid impact, disrupts motions in the core and causes the reversal. The first hypothesis is supported by computer models, but the second does not seem to be supported by much data. There is little correlation between impact events and magnetic reversals. Click image to the left or use the URL below. URL:  Earths magnetic field is like a bar magnet resides in the center of the planet. ",text,
L_0146,earths shape,T_1119,"Earth is a sphere or, more correctly, an oblate spheroid, which is a sphere that is a bit squished down at the poles and bulges a bit at the Equator. To be more technical, the minor axis (the diameter through the poles) is smaller than the major axis (the diameter through the Equator). Half of the sphere is a hemisphere. North of the Equator is the northern hemisphere and south of the Equator is the southern hemisphere. Eastern and western hemispheres are also designated. What evidence is there that Earth is spherical? What evidence was there before spaceships and satellites? Try to design an experiment involving a ship and the ocean to show Earth is round. If you are standing on the shore and a ship is going out to sea, the ship gets smaller as it moves further away from you. The ships bottom also starts to disappear as the vessel goes around the arc of the planet (Figure 1.1). There are many other ways that early scientists and mariners knew that Earth was not flat. The Sun and the other planets of the solar system are also spherical. Larger satellites, those that have enough mass for their gravitational attraction to have made them round, are spherical as well. Earths actual shape is not spherical but an oblate spheroid. The planet bulges around the equator due to mass collecting in the middle due to rotational momentum. ",text,
L_0148,eclipses,T_1123,"A solar eclipse occurs when the new Moon passes directly between the Earth and the Sun (Figure 1.1). This casts a shadow on the Earth and blocks Earths view of the Sun. A total solar eclipse occurs when the Moons shadow completely blocks the Sun (Figure 1.2). When only a portion of the Sun is out of view, it is called a partial solar eclipse. Solar eclipses are rare and usually only last a few minutes because the Moon casts only a small shadow (Figure 1.3). As the Sun is covered by the Moons shadow, it will actually get cooler outside. Birds may begin to sing, and stars will become visible in the sky. During a solar eclipse, the corona and solar prominences can be seen. A solar eclipse occurs when the Moon passes between Earth and the Sun in such a way that the Sun is either partially or totally hidden from view. Some people, including some scientists, chase eclipses all over the world to learn or just observe this amazing phenomenon. A solar eclipse shown as a series of pho- tos. Click image to the left or use the URL below. URL: ",text,
L_0148,eclipses,T_1123,"A solar eclipse occurs when the new Moon passes directly between the Earth and the Sun (Figure 1.1). This casts a shadow on the Earth and blocks Earths view of the Sun. A total solar eclipse occurs when the Moons shadow completely blocks the Sun (Figure 1.2). When only a portion of the Sun is out of view, it is called a partial solar eclipse. Solar eclipses are rare and usually only last a few minutes because the Moon casts only a small shadow (Figure 1.3). As the Sun is covered by the Moons shadow, it will actually get cooler outside. Birds may begin to sing, and stars will become visible in the sky. During a solar eclipse, the corona and solar prominences can be seen. A solar eclipse occurs when the Moon passes between Earth and the Sun in such a way that the Sun is either partially or totally hidden from view. Some people, including some scientists, chase eclipses all over the world to learn or just observe this amazing phenomenon. A solar eclipse shown as a series of pho- tos. Click image to the left or use the URL below. URL: ",text,
L_0148,eclipses,T_1124,"A lunar eclipse occurs when the full moon moves through Earths shadow, which only happens when Earth is between the Moon and the Sun and all three are lined up in the same plane, called the ecliptic (Figure 1.4). In an eclipse, Earths shadow has two distinct parts: the umbra and the penumbra. The umbra is the inner, cone-shaped part of the shadow, in which all of the light has been blocked. The penumbra is the outer part of Earths shadow where only part of the light is blocked. In the penumbra, the light is dimmed but not totally absent. A total lunar eclipse occurs when the Moon travels completely in Earths umbra. During a partial lunar eclipse, only a portion of the Moon enters Earths umbra. Earths shadow is large enough that a lunar eclipse lasts for hours and can be seen by any part of Earth with a view of the Moon at the time of the eclipse (Figure 1.5). A lunar eclipse does not occur every month because Moons orbit is inclined 5-degrees to Earths orbit, so the two bodies are not in the same plane every month. ",text,
L_0148,eclipses,T_1124,"A lunar eclipse occurs when the full moon moves through Earths shadow, which only happens when Earth is between the Moon and the Sun and all three are lined up in the same plane, called the ecliptic (Figure 1.4). In an eclipse, Earths shadow has two distinct parts: the umbra and the penumbra. The umbra is the inner, cone-shaped part of the shadow, in which all of the light has been blocked. The penumbra is the outer part of Earths shadow where only part of the light is blocked. In the penumbra, the light is dimmed but not totally absent. A total lunar eclipse occurs when the Moon travels completely in Earths umbra. During a partial lunar eclipse, only a portion of the Moon enters Earths umbra. Earths shadow is large enough that a lunar eclipse lasts for hours and can be seen by any part of Earth with a view of the Moon at the time of the eclipse (Figure 1.5). A lunar eclipse does not occur every month because Moons orbit is inclined 5-degrees to Earths orbit, so the two bodies are not in the same plane every month. ",text,
L_0150,effect of latitude on climate,T_1127,"Many factors influence the climate of a region. The most important factor is latitude because different latitudes receive different amounts of solar radiation. The Equator receives the most solar radiation. Days are equally long year-round and the Sun is just about directly overhead at midday. The polar regions receive the least solar radiation. The night lasts six months during the winter. Even in summer, the Sun never rises very high in the sky. Sunlight filters through a thick wedge of atmosphere, making the sunlight much less intense. The high albedo, because of ice and snow, reflects a good portion of the Suns light. ",text,
L_0150,effect of latitude on climate,T_1128,"Its easy to see the difference in temperature at different latitudes in the Figure 1.1. But temperature is not completely correlated with latitude. There are many exceptions. For example, notice that the western portion of South America The maximum annual temperature of the Earth, showing a roughly gradual temperature gradient from the low to the high latitudes. has relatively low temperatures due to the Andes Mountains. The Rocky Mountains in the United States also have lower temperatures due to high altitudes. Western Europe is warmer than it should be due to the Gulf Stream. Click image to the left or use the URL below. URL: ",text,
L_0151,effects of air pollution on human health,T_1129,Human health suffers in locations with high levels of air pollution. ,text,
L_0151,effects of air pollution on human health,T_1130,"Different pollutants have different health effects: Lead is the most common toxic material and is responsible for lead poisoning. Carbon monoxide can kill people in poorly ventilated spaces, such as tunnels. Nitrogen and sulfur-oxides cause lung disease and increased rates of asthma, emphysema, and viral infections such as the flu. Ozone damages the human respiratory system, causing lung disease. High ozone levels are also associated with increased heart disease and cancer. Particulates enter the lungs and cause heart or lung disease. When particulate levels are high, asthma attacks are more common. By some estimates, 30,000 deaths a year in the United States are caused by fine particle pollution. ",text,
L_0151,effects of air pollution on human health,T_1131,"Many but not all cases of asthma can be linked to air pollution. During the 1996 Olympic Games, Atlanta, Georgia, closed off their downtown to private vehicles. This action decreased ozone levels by 28%. At the same time, there were 40% fewer hospital visits for asthma. Can scientists conclude without a shadow of a doubt that the reduction in ozone caused the reduction in hospital visits? What could they do to make that determination? Lung cancer among people who have never smoked is around 15% and is increasing. One study showed that the risk of being afflicted with lung cancer increases directly with a persons exposure to air pollution (Figure 1.1). The study concluded that no level of air pollution should be considered safe. Exposure to smog also increased the risk of dying from any cause, including heart disease. One study found that in the United States, children develop asthma at more than twice the rate of two decades ago and at four times the rate of children in Canada. Adults also suffer from air pollution-related illnesses that include lung disease, heart disease, lung cancer, and weakened immune systems. The asthma rate worldwide is rising 20% to 50% every decade. ",text,
L_0154,electromagnetic energy in the atmosphere,T_1139,"Energy travels through space or material. This is obvious when you stand near a fire and feel its warmth or when you pick up the handle of a metal pot even though the handle is not sitting directly on the hot stove. Invisible energy waves can travel through air, glass, and even the vacuum of outer space. These waves have electrical and magnetic properties, so they are called electromagnetic waves. The transfer of energy from one object to another through electromagnetic waves is known as radiation. Different wavelengths of energy create different types of electromagnetic waves (Figure 1.1). The wavelengths humans can see are known as visible light. When viewed together, all of the wavelengths of visible light appear white. But a prism or water droplets can break the white light into different wavelengths so that separate colors appear (Figure 1.2). What objects can you think of that radiate visible light? Two include the Sun and a light bulb. The longest wavelengths of visible light appear red. Infrared wavelengths are longer than visible red. Snakes can see infrared energy. We feel infrared energy as heat. Wavelengths that are shorter than violet are called ultraviolet. Can you think of some objects that appear to radiate visible light, but actually do not? The Moon and the planets do not emit light of their own; they reflect the light of the Sun. Reflection is when light (or another wave) bounces back from a surface. Albedo is a measure of how well a surface reflects light. A surface with high albedo reflects a large percentage of light. A snow field has high albedo. One important fact to remember is that energy cannot be created or destroyed  it can only be changed from one form to another. This is such a fundamental fact of nature that it is a law: the law of conservation of energy. In photosynthesis, for example, plants convert solar energy into chemical energy that they can use. They do not create new energy. When energy is transformed, some nearly always becomes heat. Heat transfers between materials easily, from warmer objects to cooler ones. If no more heat is added, eventually all of a material will reach the same temperature. ",text,
L_0154,electromagnetic energy in the atmosphere,T_1139,"Energy travels through space or material. This is obvious when you stand near a fire and feel its warmth or when you pick up the handle of a metal pot even though the handle is not sitting directly on the hot stove. Invisible energy waves can travel through air, glass, and even the vacuum of outer space. These waves have electrical and magnetic properties, so they are called electromagnetic waves. The transfer of energy from one object to another through electromagnetic waves is known as radiation. Different wavelengths of energy create different types of electromagnetic waves (Figure 1.1). The wavelengths humans can see are known as visible light. When viewed together, all of the wavelengths of visible light appear white. But a prism or water droplets can break the white light into different wavelengths so that separate colors appear (Figure 1.2). What objects can you think of that radiate visible light? Two include the Sun and a light bulb. The longest wavelengths of visible light appear red. Infrared wavelengths are longer than visible red. Snakes can see infrared energy. We feel infrared energy as heat. Wavelengths that are shorter than violet are called ultraviolet. Can you think of some objects that appear to radiate visible light, but actually do not? The Moon and the planets do not emit light of their own; they reflect the light of the Sun. Reflection is when light (or another wave) bounces back from a surface. Albedo is a measure of how well a surface reflects light. A surface with high albedo reflects a large percentage of light. A snow field has high albedo. One important fact to remember is that energy cannot be created or destroyed  it can only be changed from one form to another. This is such a fundamental fact of nature that it is a law: the law of conservation of energy. In photosynthesis, for example, plants convert solar energy into chemical energy that they can use. They do not create new energy. When energy is transformed, some nearly always becomes heat. Heat transfers between materials easily, from warmer objects to cooler ones. If no more heat is added, eventually all of a material will reach the same temperature. ",text,
L_0155,energy conservation,T_1140,"Everyone can reduce their use of energy resources and the pollution the resources cause by conserving energy. Conservation means saving resources by using them more efficiently, using less of them, or not using them at all. You can read below about some of the ways you can conserve energy on the road and in the home. ",text,
L_0155,energy conservation,T_1141,"Much of the energy used in the U.S. is used for transportation. You can conserve transportation energy in several ways. For example, you can: plan ahead to avoid unnecessary trips. take public transit such as subways (see Figure 1.1) instead of driving. drive an energy-efficient vehicle when driving is the only way to get there. Q: What are some other ways you could save energy in transportation? A: You could carpool to save transportation energy. Even if you carpool with just one other person, thats one less vehicle on the road. For short trips, you could ride a bike or walk to you destination. The extra exercise is another benefit of using your own muscle power to get where you need to go. ",text,
L_0155,energy conservation,T_1142,"Many people waste energy at home, so a lot of energy can be saved there as well. What can you do to conserve energy? You can: turn off lights and unplug appliances and other electrical devices when not in use. use energy-efficient light bulbs and appliances. turn the thermostat down in winter and up in summer. Q: How can you tell which light bulbs and appliances use less energy? ",text,
L_0155,energy conservation,T_1142,"Many people waste energy at home, so a lot of energy can be saved there as well. What can you do to conserve energy? You can: turn off lights and unplug appliances and other electrical devices when not in use. use energy-efficient light bulbs and appliances. turn the thermostat down in winter and up in summer. Q: How can you tell which light bulbs and appliances use less energy? ",text,
L_0156,energy from biomass,T_1143,"Biomass is the material that comes from plants and animals that were recently living. Biomass can be burned directly, such as setting fire to wood. For as long as humans have had fire, people have used biomass for heating and cooking. People can also process biomass to make fuel, called biofuel. Biofuel can be created from crops, such as corn or Biofuels, such as ethanol, are added to gasoline to cut down the amount of fossil fuels that are used. algae, and processed for use in a car (Figure 1.1). The advantage to biofuels is that they burn more cleanly than fossil fuels. As a result, they create less pollution and less carbon dioxide. Organic material, like almond shells, can be made into electricity. Biomass power is a great use of wastes and is more reliable than other renewable energy sources, but harvesting biomass energy uses energy and biomass plants produce pollutants including greenhouse gases. Cow manure can have a second life as a source of methane gas, which can be converted to electricity. Not only that food scraps can also be converted into green energy. Food that is tossed out produces methane, a potent greenhouse gas. But that methane from leftovers can be harnessed and used as fuel. Sounds like a win-win situation. ",text,
L_0156,energy from biomass,T_1144,"In many instances, the amount of energy, fertilizer, and land needed to produce the crops used make biofuels mean that they often produce very little more energy than they consume. The fertilizers and pesticides used to grow the crops run off and become damaging pollutants in nearby water bodies or in the oceans. To generate biomass energy, break down the cell walls of plants to release the sugars and then ferment those sugars to create fuel. Corn is a very inefficient source; scientists are looking for much better sources of biomass energy. ",text,
L_0156,energy from biomass,T_1145,"Research is being done into alternative crops for biofuels. A very promising alternative is algae. Growing algae requires much less land and energy than crops. Algae can be grown in locations that are not used for other things, like in desert areas where other crops are not often grown. Algae can be fed agricultural and other waste so valuable resources are not used. Much research is being done to bring these alternative fuels to market. Many groups are researching the use of algae for fuel. Many people think that the best source of biomass energy for the future is algae. Compared to corn, algae is not a food crop, it can grow in many places, its much easier to convert to a usable fuel, and its carbon neutral. ",text,
L_0157,energy use,T_1146,"Look at the circle graph in the Figure 1.1. It shows that oil is the single most commonly used energy resource in the U.S., followed by natural gas, and then by coal. All of these energy resources are nonrenewable. Nonrenewable resources are resources that are limited in supply and cannot be replaced as quickly as they are used up. Renewable resources, in contrast, provide only 8 percent of all energy used in the U.S. Renewable resources are natural resources that can be replaced in a relatively short period of time or are virtually limitless in supply. They include solar energy from sunlight, geothermal energy from under Earths surface, wind, biomass (from once-living things or their wastes), and hydropower (from running water). ",text,
L_0157,energy use,T_1147,"People in the U.S. use far more energyespecially energy from oilthan people in any other nation. The bar graph in the Figure 1.2 compares the amount of oil used by the top ten oil-using nations. The U.S. uses more oil than several other top-ten countries combined. If you also consider the population size in these countries, the differences are even more stunning. The average person in the U.S. uses a whopping 23 barrels of oil a year! In comparison, the average person in India or China uses just 1 or 2 barrels of oil a year. Q: How does the use of oil and other fossil fuels relate to pollution? A: Greater use of oil and other fossil fuels causes more pollution. ",text,
L_0157,energy use,T_1147,"People in the U.S. use far more energyespecially energy from oilthan people in any other nation. The bar graph in the Figure 1.2 compares the amount of oil used by the top ten oil-using nations. The U.S. uses more oil than several other top-ten countries combined. If you also consider the population size in these countries, the differences are even more stunning. The average person in the U.S. uses a whopping 23 barrels of oil a year! In comparison, the average person in India or China uses just 1 or 2 barrels of oil a year. Q: How does the use of oil and other fossil fuels relate to pollution? A: Greater use of oil and other fossil fuels causes more pollution. ",text,
L_0158,environmental impacts of mining,T_1148,"Although mining provides people with many needed resources, the environmental costs can be high. Surface mining clears the landscape of trees and soil, and nearby streams and lakes are inundated with sediment. Pollutants from the mined rock, such as heavy metals, enter the sediment and water system. Acids flow from some mine sites, changing the composition of nearby waterways (Figure 1.1). U.S. law has changed in recent decades so that a mine region must be restored to its natural state, a process called reclamation. This is not true of older mines. Pits may be refilled or reshaped and vegetation planted. Pits may be allowed to fill with water and become lakes or may be turned into landfills. Underground mines may be sealed off or left open as homes for bats. Click image to the left or use the URL below. URL:  Acid drainage from a surface coal mine in Missouri. ",text,
L_0161,exoplanets,T_1158,"Since the early 1990s, astronomers have discovered other solar systems, with planets orbiting stars other than our own Sun. These are called ""extrasolar planets"" or simply exoplanets (see Figure 1.1). Exoplanets are not in our solar system, but are found in other solar systems. Some extrasolar planets have been directly imaged, but most have been discovered by indirect methods. One technique involves detecting the very slight motion of a star periodically moving toward and away from us along our line-of-sight (also known as a stars ""radial velocity""). This periodic motion can be attributed to the gravitational pull of a planet or, sometimes, another star orbiting the star. A planet may also be identified by measuring a stars brightness over time. A temporary, periodic decrease in light emitted from a star can occur when a planet crosses in front of, or ""transits,"" the star it is orbiting, momentarily blocking out some of the starlight. More than 1800 extrasolar planets have been identified and confirmed and the rate of discovery is increasing rapidly. Click image to the left or use the URL below. URL: ",text,
L_0162,expansion of the universe,T_1159,"After discovering that there are galaxies beyond the Milky Way, Edwin Hubble went on to measure the distance to hundreds of other galaxies. His data would eventually show how the universe is changing, and would even yield clues as to how the universe formed. ",text,
L_0162,expansion of the universe,T_1160,"If you look at a star through a prism, you will see a spectrum, or a range of colors through the rainbow. The spectrum will have specific dark bands where elements in the star absorb light of certain energies. By examining the arrangement of these dark absorption lines, astronomers can determine the composition of elements that make up a distant star. In fact, the element helium was first discovered in our Sun  not on Earth  by analyzing the absorption lines in the spectrum of the Sun. While studying the spectrum of light from distant galaxies, astronomers noticed something strange. The dark lines in the spectrum were in the patterns they expected, but they were shifted toward the red end of the spectrum, as shown in Figure 1.1. This shift of absorption bands toward the red end of the spectrum is known as redshift. Redshift is a shift in absorption bands toward the red end of the spectrum. What could make the absorption bands of a star shift toward the red? Redshift occurs when the light source is moving away from the observer or when the space between the observer and the source is stretched. What does it mean that stars and galaxies are redshifted? When astronomers see redshift in the light from a galaxy, they know that the galaxy is moving away from Earth. If galaxies were moving randomly, would some be redshifted but others be blueshifted? Of course. Since almost every galaxy in the universe has a redshift, almost every galaxy is moving away from Earth. Click image to the left or use the URL below. URL: ",text,
L_0162,expansion of the universe,T_1161,"Edwin Hubble combined his measurements of the distances to galaxies with other astronomers measurements of redshift. From this data, he noticed a relationship, which is now called Hubbles Law: the farther away a galaxy is, the faster it is moving away from us. What could this mean about the universe? It means that the universe is expanding. Figure 1.2 shows a simplified diagram of the expansion of the universe. One way to picture this is to imagine a balloon covered with tiny dots to represent the galaxies. When you inflate the balloon, the dots slowly move away from each other because the rubber stretches in the space between them. If you were standing on one of the dots, you would see the other dots moving away from you. Also, the dots farther away from you on the balloon would move away faster than dots nearby. In this diagram of the expansion of the universe over time, the distance between galaxies gets bigger over time, although the size of each galaxy stays the same. An inflating balloon is only a rough analogy to the expanding universe for several reasons. One important reason is that the surface of a balloon has only two dimensions, while space has three dimensions. But space itself is stretching out between galaxies, just as the rubber stretches when a balloon is inflated. This stretching of space, which increases the distance between galaxies, is what causes the expansion of the universe. One other difference between the universe and a balloon involves the actual size of the galaxies. On a balloon, the dots will become larger in size as you inflate it. In the universe, the galaxies stay the same size; only the space between the galaxies increases. ",text,
L_0165,faults,T_1169,A rock under enough stress will fracture. There may or may not be movement along the fracture. ,text,
L_0165,faults,T_1170,"If there is no movement on either side of a fracture, the fracture is called a joint. The rocks below show horizontal and vertical jointing. These joints formed when the confining stress was removed from the rocks as shown in (Figure ",text,
L_0165,faults,T_1171,"If the blocks of rock on one or both sides of a fracture move, the fracture is called a fault (Figure 1.2). Stresses along faults cause rocks to break and move suddenly. The energy released is an earthquake. How do you know theres a fault in this rock? Try to line up the same type of rock on either side of the lines that cut across them. One side moved relative to the other side, so you know the lines are a fault. Slip is the distance rocks move along a fault. Slip can be up or down the fault plane. Slip is relative, because there is usually no way to know whether both sides moved or only one. Faults lie at an angle to the horizontal surface of the Earth. That angle is called the faults dip. The dip defines which of two basic types a fault is. If the faults dip is inclined relative to the horizontal, the fault is a dip-slip fault (Figure 1.3). ",text,
L_0165,faults,T_1172,"There are two types of dip-slip faults. In a normal fault, the hanging wall drops down relative to the footwall. In a reverse fault, the footwall drops down relative to the hanging wall. This diagram illustrates the two types of dip-slip faults: normal faults and reverse faults. Imagine miners extracting a re- source along a fault. The hanging wall is where miners would have hung their lanterns. The footwall is where they would have walked. A thrust fault is a type of reverse fault in which the fault plane angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 1.4). At Chief Mountain in Montana, the upper rocks at the Lewis Overthrust are more than 1 billion years older than the lower rocks. How could this happen? Normal faults can be huge. They are responsible for uplifting mountain ranges in regions experiencing tensional stress. ",text,
L_0165,faults,T_1172,"There are two types of dip-slip faults. In a normal fault, the hanging wall drops down relative to the footwall. In a reverse fault, the footwall drops down relative to the hanging wall. This diagram illustrates the two types of dip-slip faults: normal faults and reverse faults. Imagine miners extracting a re- source along a fault. The hanging wall is where miners would have hung their lanterns. The footwall is where they would have walked. A thrust fault is a type of reverse fault in which the fault plane angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 1.4). At Chief Mountain in Montana, the upper rocks at the Lewis Overthrust are more than 1 billion years older than the lower rocks. How could this happen? Normal faults can be huge. They are responsible for uplifting mountain ranges in regions experiencing tensional stress. ",text,
L_0165,faults,T_1173,"A strike-slip fault is a dip-slip fault in which the dip of the fault plane is vertical. Strike-slip faults result from shear stresses. Imagine placing one foot on either side of a strike-slip fault. One block moves toward you. If that block moves toward your right foot, the fault is a right-lateral strike-slip fault; if that block moves toward your left foot, the fault is a left-lateral strike-slip fault (Figure 1.5). Californias San Andreas Fault is the worlds most famous strike-slip fault. It is a right-lateral strike slip fault (See opening image). People sometimes say that California will fall into the ocean someday, which is not true. Strike-slip faults. Click image to the left or use the URL below. URL: ",text,
L_0167,flooding,T_1179,"Floods usually occur when precipitation falls more quickly than water can be absorbed into the ground or carried away by rivers or streams. Waters may build up gradually over a period of weeks, when a long period of rainfall or snowmelt fills the ground with water and raises stream levels. Extremely heavy rains across the Midwestern U.S. in April 2011 led to flooding of the rivers in the Mississippi River basin in May 2011 (Figures 1.1 and 1.2). Click image to the left or use the URL below. URL:  This map shows the accumulated rainfall across the U.S. in the days from April 22 to April 29, 2011. Record flow in the Ohio and Mississippi Rivers has to go somewhere. Normal spring river levels are shown in 2010. The flooded region in the image from May 3, 2011 is the New Madrid Floodway, where overflow water is meant to go. 2011 is the first time since 1927 that this floodway was used. ",text,
L_0167,flooding,T_1179,"Floods usually occur when precipitation falls more quickly than water can be absorbed into the ground or carried away by rivers or streams. Waters may build up gradually over a period of weeks, when a long period of rainfall or snowmelt fills the ground with water and raises stream levels. Extremely heavy rains across the Midwestern U.S. in April 2011 led to flooding of the rivers in the Mississippi River basin in May 2011 (Figures 1.1 and 1.2). Click image to the left or use the URL below. URL:  This map shows the accumulated rainfall across the U.S. in the days from April 22 to April 29, 2011. Record flow in the Ohio and Mississippi Rivers has to go somewhere. Normal spring river levels are shown in 2010. The flooded region in the image from May 3, 2011 is the New Madrid Floodway, where overflow water is meant to go. 2011 is the first time since 1927 that this floodway was used. ",text,
L_0167,flooding,T_1180,"Flash floods are sudden and unexpected, taking place when very intense rains fall over a very brief period (Figure streambed. A 2004 flash flood in England devastated two villages when 3-1/2 inches of rain fell in 60 minutes. Pictured here is some of the damage from the flash flood. Click image to the left or use the URL below. URL: ",text,
L_0167,flooding,T_1181,"Heavily vegetated lands are less likely to experience flooding. Plants slow down water as it runs over the land, giving it time to enter the ground. Even if the ground is too wet to absorb more water, plants still slow the waters passage and increase the time between rainfall and the waters arrival in a stream; this could keep all the water falling over a region from hitting the stream at once. Wetlands act as a buffer between land and high water levels and play a key role in minimizing the impacts of floods. Flooding is often more severe in areas that have been recently logged. ",text,
L_0167,flooding,T_1182,"People try to protect areas that might flood with dams, and dams are usually very effective. But high water levels sometimes cause a dam to break and then flooding can be catastrophic. People may also line a river bank with levees, high walls that keep the stream within its banks during floods. A levee in one location may just force the high water up or downstream and cause flooding there. The New Madrid Overflow in the Figure 1.2 was created with the recognition that the Mississippi River sometimes simply cannot be contained by levees and must be allowed to flood. ",text,
L_0167,flooding,T_1183,"Within the floodplain of the Nile, soils are fertile enough for productive agriculture. Beyond this, infertile desert soils prevent viable farming. Not all the consequences of flooding are negative. Rivers deposit new nutrient-rich sediments when they flood, so floodplains have traditionally been good for farming. Flooding as a source of nutrients was important to Egyptians along the Nile River until the Aswan Dam was built in the 1960s. Although the dam protects crops and settlements from the annual floods, farmers must now use fertilizers to feed their cops. Floods are also responsible for moving large amounts of sediments about within streams. These sediments provide habitats for animals, and the periodic movement of sediment is crucial to the lives of several types of organisms. Plants and fish along the Colorado River, for example, depend on seasonal flooding to rearrange sand bars. ",text,
L_0169,folds,T_1186,"Rocks deforming plastically under compressive stresses crumple into folds. They do not return to their original shape. If the rocks experience more stress, they may undergo more folding or even fracture. You can see three types of folds. ",text,
L_0169,folds,T_1187,"A monocline is a simple bend in the rock layers so that they are no longer horizontal (see Figure 1.1 for an example). At Utahs Cockscomb, the rocks plunge downward in a monocline. What you see in the image appears to be a monocline. Are you certain it is a monocline? What else might it be? What would you have to do to figure it out? ",text,
L_0169,folds,T_1188,"Anticline: An anticline is a fold that arches upward. The rocks dip away from the center of the fold (Figure 1.2). The oldest rocks are at the center of an anticline and the youngest are draped over them. When rocks arch upward to form a circular structure, that structure is called a dome. If the top of the dome is sliced off, where are the oldest rocks located? ",text,
L_0169,folds,T_1189,"A syncline is a fold that bends downward. The youngest rocks are at the center and the oldest are at the outside (Figure 1.3). When rocks bend downward in a circular structure, that structure is called a basin (Figure 1.4). If the rocks are exposed at the surface, where are the oldest rocks located? Click image to the left or use the URL below. URL:  Anticlines are formations that have folded rocks upward. (a) Schematic of a syncline. (b) This syncline is in Rainbow Basin, California. Some folding can be fairly complicated. What do you see in the photo above? ",text,
L_0169,folds,T_1189,"A syncline is a fold that bends downward. The youngest rocks are at the center and the oldest are at the outside (Figure 1.3). When rocks bend downward in a circular structure, that structure is called a basin (Figure 1.4). If the rocks are exposed at the surface, where are the oldest rocks located? Click image to the left or use the URL below. URL:  Anticlines are formations that have folded rocks upward. (a) Schematic of a syncline. (b) This syncline is in Rainbow Basin, California. Some folding can be fairly complicated. What do you see in the photo above? ",text,
L_0169,folds,T_1189,"A syncline is a fold that bends downward. The youngest rocks are at the center and the oldest are at the outside (Figure 1.3). When rocks bend downward in a circular structure, that structure is called a basin (Figure 1.4). If the rocks are exposed at the surface, where are the oldest rocks located? Click image to the left or use the URL below. URL:  Anticlines are formations that have folded rocks upward. (a) Schematic of a syncline. (b) This syncline is in Rainbow Basin, California. Some folding can be fairly complicated. What do you see in the photo above? ",text,
L_0169,folds,T_1189,"A syncline is a fold that bends downward. The youngest rocks are at the center and the oldest are at the outside (Figure 1.3). When rocks bend downward in a circular structure, that structure is called a basin (Figure 1.4). If the rocks are exposed at the surface, where are the oldest rocks located? Click image to the left or use the URL below. URL:  Anticlines are formations that have folded rocks upward. (a) Schematic of a syncline. (b) This syncline is in Rainbow Basin, California. Some folding can be fairly complicated. What do you see in the photo above? ",text,
L_0170,formation of earth,T_1190,Earth formed at the same time as the other planets. The history of Earth is part of the history of the Solar System. ,text,
L_0170,formation of earth,T_1191,"Earth came together (accreted) from the cloud of dust and gas known as the solar nebula nearly 4.6 billion years ago, the same time the Sun and the rest of the solar system formed. Gravity caused small bodies of rock and metal orbiting the proto-Sun to smash together to create larger bodies. Over time, the planetoids got larger and larger until they became planets. ",text,
L_0170,formation of earth,T_1192,"When Earth first came together it was really hot, hot enough to melt the metal elements that it contained. Earth was so hot for three reasons: Gravitational contraction: As small bodies of rock and metal accreted, the planet grew larger and more massive. Gravity within such an enormous body squeezes the material in its interior so hard that the pressure swells. As Earths internal pressure grew, its temperature also rose. Radioactive decay: Radioactive decay releases heat, and early in the planets history there were many ra- dioactive elements with short half lives. These elements long ago decayed into stable materials, but they were responsible for the release of enormous amounts of heat in the beginning. Bombardment: Ancient impact craters found on the Moon and inner planets indicate that asteroid impacts were common in the early solar system. Earth was struck so much in its first 500 million years that the heat was intense. Very few large objects have struck the planet in the past many hundreds of millions of year. ",text,
L_0170,formation of earth,T_1193,"When Earth was entirely molten, gravity drew denser elements to the center and lighter elements rose to the surface. The separation of Earth into layers based on density is known as differentiation. The densest material moved to the center to create the planets dense metallic core. Materials that are intermediate in density became part of the mantle (Figure 1.1). ",text,
L_0170,formation of earth,T_1194,"Lighter materials accumulated at the surface of the mantle to become the earliest crust. The first crust was probably basaltic, like the oceanic crust is today. Intense heat from the early core drove rapid and vigorous mantle convection so that crust quickly recycled into the mantle. The recycling of basaltic crust was so effective that no remnants of it are found today. ",text,
L_0170,formation of earth,T_1195,"There is not much material to let us know about the earliest days of our planet Earth. What there is comes from three sources: (1) zircon crystals, the oldest materials found on Earth, which show that the age of the earliest crust formed at least 4.4 billion years ago; (2) meteorites that date from the beginning of the solar system, to nearly 4.6 billion years ago (Figure 1.2); and (3) lunar rocks, which represent the early days of the Earth-Moon system as far back as 4.5 billion years ago. ",text,
L_0171,formation of the moon,T_1196,"One of the most unique features of planet Earth is its large Moon. Unlike the only other natural satellites orbiting an inner planet, those of Mars, the Moon is not a captured asteroid. Understanding the Moons birth and early history reveals a great deal about Earths early days. ",text,
L_0171,formation of the moon,T_1197,"To determine how the Moon formed, scientists had to account for several lines of evidence: The Moon is large; not much smaller than the smallest planet, Mercury. Earth and Moon are very similar in composition. Moons surface is 4.5 billion years old, about the same as the age of the solar system. For a body its size and distance from the Sun, the Moon has very little core; Earth has a fairly large core. The oxygen isotope ratios of Earth and Moon indicate that they originated in the same part of the solar system. Earth has a faster spin than it should have for a planet of its size and distance from the Sun. Can you devise a birth story for the Moon that takes all of these bits of data into account? ",text,
L_0171,formation of the moon,T_1198,"Astronomers have carried out computer simulations that are consistent with these facts and have detailed a birth story for the Moon. A little more than 4.5 billion years ago, roughly 70 million years after Earth formed, planetary bodies were being pummeled by asteroids and planetoids of all kinds. Earth was struck by a Mars-sized asteroid (Figure 1.1). An artists depiction of the impact that produced the Moon. The tremendous energy from the impact melted both bodies. The molten material mixed up. The dense metals remained on Earth but some of the molten, rocky material was flung into an orbit around Earth. It eventually accreted into a single body, the Moon. Since both planetary bodies were molten, material could differentiate out of the magma ocean into core, mantle, and crust as they cooled. Earths fast spin is from energy imparted to it by the impact. ",text,
L_0171,formation of the moon,T_1199,"Lunar rocks reveal an enormous amount about Earths early days. The Genesis Rock, with a date of 4.5 billion years, is only about 100 million years younger than the solar system (see opening image). The rock is a piece of the Moons anorthosite crust, which was the original crust. Why do you think Moon rocks contain information that is not available from Earths own materials? Can you find how all of the evidence presented in the bullet points above is present in the Moons birth story? ",text,
L_0172,formation of the sun and planets,T_1200,"The most widely accepted explanation of how the solar system formed is called the nebular hypothesis. According to this hypothesis, the Sun and the planets of our solar system formed about 4.6 billion years ago from the collapse of a giant cloud of gas and dust, called a nebula. The nebula was drawn together by gravity, which released gravitational potential energy. As small particles of dust and gas smashed together to create larger ones, they released kinetic energy. As the nebula collapsed, the gravity at the center increased and the cloud started to spin because of its angular momentum. As it collapsed further, the spinning got faster, much as an ice skater spins faster when he pulls his arms to his sides during a spin. Much of the clouds mass migrated to its center but the rest of the material flattened out in an enormous disk. The disk contained hydrogen and helium, along with heavier elements and even simple organic molecules. ",text,
L_0172,formation of the sun and planets,T_1201,"As gravity pulled matter into the center of the disk, the density and pressure at the center became intense. When the pressure in the center of the disk was high enough, nuclear fusion began. A star was bornthe Sun. The burning star stopped the disk from collapsing further. Meanwhile, the outer parts of the disk were cooling off. Matter condensed from the cloud and small pieces of dust started clumping together. These clumps collided and combined with other clumps. Larger clumps, called An artists painting of a protoplanetary disk. planetesimals, attracted smaller clumps with their gravity. Gravity at the center of the disk attracted heavier particles, such as rock and metal and lighter particles remained further out in the disk. Eventually, the planetesimals formed protoplanets, which grew to become the planets and moons that we find in our solar system today. Because of the gravitational sorting of material, the inner planets  Mercury, Venus, Earth, and Mars  formed from dense rock and metal. The outer planets  Jupiter, Saturn, Uranus and Neptune  condensed farther from the Sun from lighter materials such as hydrogen, helium, water, ammonia, and methane. Out by Jupiter and beyond, where its very cold, these materials form solid particles. The nebular hypothesis was designed to explain some of the basic features of the solar system: The orbits of the planets lie in nearly the same plane with the Sun at the center The planets revolve in the same direction The planets mostly rotate in the same direction The axes of rotation of the planets are mostly nearly perpendicular to the orbital plane The oldest moon rocks are 4.5 billion years Click image to the left or use the URL below. URL: ",text,
L_0173,fossil fuel formation,T_1202,"Can you name some fossils? How about dinosaur bones or dinosaur footprints? Animal skeletons, teeth, shells, coprolites (otherwise known as feces), or any other remains or traces from a living creature that becomes rock is a fossil. The same processes that formed these fossils also created some of our most important energy resources, fossil fuels. Coal, oil, and natural gas are fossil fuels. Fossil fuels come from living matter starting about 500 million years ago. Millions of years ago, plants used energy from the Sun to form sugars, carbohydrates, and other energy-rich carbon compounds. As plants and animals died, their remains settled on the ground on land and in swamps, lakes, and seas (Figure 1.1). Over time, layer upon layer of these remains accumulated. Eventually, the layers were buried so deeply that they were crushed by an enormous mass of earth. The weight of this earth pressing down on these plant and animal remains created intense heat and pressure. After millions of years of heat and pressure, the material in these layers turned into chemicals called hydrocarbons (Figure 1.2). Hydrocarbons are made of carbon and hydrogen atoms. This molecule with one carbon and four hydrogen atoms is methane. Hydrocarbons can be solid, liquid, or gaseous. The solid form is what we know as coal. The liquid form is petroleum, or crude oil. Natural gas is the gaseous form. The solar energy stored in fossil fuels is a rich source of energy. Although fossil fuels provide very high quality energy, they are non-renewable. Click image to the left or use the URL below. URL: ",text,
L_0173,fossil fuel formation,T_1202,"Can you name some fossils? How about dinosaur bones or dinosaur footprints? Animal skeletons, teeth, shells, coprolites (otherwise known as feces), or any other remains or traces from a living creature that becomes rock is a fossil. The same processes that formed these fossils also created some of our most important energy resources, fossil fuels. Coal, oil, and natural gas are fossil fuels. Fossil fuels come from living matter starting about 500 million years ago. Millions of years ago, plants used energy from the Sun to form sugars, carbohydrates, and other energy-rich carbon compounds. As plants and animals died, their remains settled on the ground on land and in swamps, lakes, and seas (Figure 1.1). Over time, layer upon layer of these remains accumulated. Eventually, the layers were buried so deeply that they were crushed by an enormous mass of earth. The weight of this earth pressing down on these plant and animal remains created intense heat and pressure. After millions of years of heat and pressure, the material in these layers turned into chemicals called hydrocarbons (Figure 1.2). Hydrocarbons are made of carbon and hydrogen atoms. This molecule with one carbon and four hydrogen atoms is methane. Hydrocarbons can be solid, liquid, or gaseous. The solid form is what we know as coal. The liquid form is petroleum, or crude oil. Natural gas is the gaseous form. The solar energy stored in fossil fuels is a rich source of energy. Although fossil fuels provide very high quality energy, they are non-renewable. Click image to the left or use the URL below. URL: ",text,
L_0174,fossil fuel reserves,T_1203,"Fossil fuels provide about 85% of the worlds energy at this time. Worldwide fossil fuel usage has increased many times over in the past half century (coal - 2.6x, oil - 8x, natural gas - 14x) because of population increases, because of increases in the number of cars, televisions, and other fuel-consuming uses in the developed world, and because of lifestyle improvements in the developing world. The amount of fossil fuels that remain untapped is unknown, but can likely be measured in decades for oil and natural gas and in a few centuries for coal (Figure 1.1). ",text,
L_0174,fossil fuel reserves,T_1204,"As the easy-to-reach fossil fuel sources are depleted, alternative sources of fossil fuels are increasingly being exploited (Figure 1.2). These include oil shale and tar sands. Oil shale is rock that contains dispersed oil that has not collected in reservoirs. To extract the oil from the shale requires enormous amounts of hot water. Tar sands are rocky materials mixed with very thick oil. The tar is too thick to pump and so tar sands are strip-mined. Hot water and caustic soda are used to separate the oil from the rock. The environmental consequences of mining these fuels, and of fossil fuel use in general, along with the fact that these fuels do not have a limitless supply, are prompting the development of alternative energy sources in some regions. Click image to the left or use the URL below. URL:  A satellite image of an oil-sands mine in Canada. Click image to the left or use the URL below. URL: ",text,
L_0174,fossil fuel reserves,T_1204,"As the easy-to-reach fossil fuel sources are depleted, alternative sources of fossil fuels are increasingly being exploited (Figure 1.2). These include oil shale and tar sands. Oil shale is rock that contains dispersed oil that has not collected in reservoirs. To extract the oil from the shale requires enormous amounts of hot water. Tar sands are rocky materials mixed with very thick oil. The tar is too thick to pump and so tar sands are strip-mined. Hot water and caustic soda are used to separate the oil from the rock. The environmental consequences of mining these fuels, and of fossil fuel use in general, along with the fact that these fuels do not have a limitless supply, are prompting the development of alternative energy sources in some regions. Click image to the left or use the URL below. URL:  A satellite image of an oil-sands mine in Canada. Click image to the left or use the URL below. URL: ",text,
L_0175,fresh water ecosystems,T_1205,"Organisms that live in lakes, ponds, streams, springs or wetlands are part of freshwater ecosystems. These ecosys- tems vary by temperature, pressure (in lakes), the amount of light that penetrates and the type of vegetation that lives there. ",text,
L_0175,fresh water ecosystems,T_1206,"Limnology is the study of bodies of fresh water and the organisms that live there. A lake has zones just like the ocean. The ecosystem of a lake is divided into three distinct zones (Figure 1.1): 1. The surface (littoral) zone is the sloped area closest to the edge of the water. 2. The open-water zone (also called the photic or limnetic zone) has abundant sunlight. 3. The deep-water zone (also called the aphotic or profundal zone) has little or no sunlight. There are several life zones found within a lake: In the littoral zone, sunlight promotes plant growth, which provides food and shelter to animals such as snails, insects, and fish. In the open-water zone, other plants and fish, such as bass and trout, live. The deep-water zone does not have photosynthesis since there is no sunlight. Most deep-water organisms are scavengers, such as crabs and catfish that feed on dead organisms that fall to the bottom of the lake. Fungi and bacteria aid in the decomposition in the deep zone. Though different creatures live in the oceans, ocean waters also have these same divisions based on sunlight with similar types of creatures that live in each of the zones. The three primary zones of a lake are the littoral, open-water, and deep-water zones. ",text,
L_0175,fresh water ecosystems,T_1207,Wetlands are lands that are wet for significant periods of time. They are common where water and land meet. Wetlands can be large flat areas or relatively small and steep areas. Wetlands are rich and unique ecosystems with many species that rely on both the land and the water for survival. Only specialized plants are able to grow in these conditions. Wetlands tend have a great deal of biological diversity. Wetland ecosystems can also be fragile systems that are sensitive to the amount and quality of water present within them. Click image to the left or use the URL below. URL: ,text,
L_0175,fresh water ecosystems,T_1208,"Marshes are shallow wetlands around lakes, streams, or the ocean where grasses and reeds are common, but trees are not (Figure 1.2). Frogs, turtles, muskrats, and many varieties of birds are at home in marshes. A salt marsh on Cape Cod in Mas- sachusetts. ",text,
L_0175,fresh water ecosystems,T_1209,"A swamp is a wetland with lush trees and vines found in low-lying areas beside slow-moving rivers (Figure 1.3). Like marshes, they are frequently or always inundated with water. Since the water in a swamp moves slowly, oxygen in the water is often scarce. Swamp plants and animals must be adapted for these low-oxygen conditions. Like marshes, swamps can be fresh water, salt water, or a mixture of both. ",text,
L_0175,fresh water ecosystems,T_1210,"As mentioned above, wetlands are home to many different species of organisms. Although they make up only 5% of the area of the United States, wetlands contain more than 30% of the plant types. Many endangered species live in wetlands, so wetlands are protected from human use. Wetlands also play a key biological role by removing pollutants from water. For example, they can trap and use fertilizer that has washed off a farmers field, and therefore they prevent that fertilizer from contaminating another body of water. Since wetlands naturally purify water, preserving wetlands also helps to maintain clean supplies of water. ",text,
L_0176,galaxies,T_1211,"Galaxies are the biggest groups of stars and can contain anywhere from a few million stars to many billions of stars. Every star that is visible in the night sky is part of the Milky Way Galaxy. To the naked eye, the closest major galaxy the Andromeda Galaxy, shown in Figure 1.1  looks like only a dim, fuzzy spot. But that fuzzy spot contains one trillion  1,000,000,000,000  stars! Galaxies are divided into three types according to shape: spiral galaxies, elliptical galaxies, and irregular galaxies. ",text,
L_0176,galaxies,T_1212,"Spiral galaxies spin, so they appear as a rotating disk of stars and dust, with a bulge in the middle, like the Sombrero Galaxy shown in Figure 1.2. Several arms spiral outward in the Pinwheel Galaxy (seen in Figure 1.2) and are appropriately called spiral arms. Spiral galaxies have lots of gas and dust and lots of young stars. The Andromeda Galaxy is a large spiral galaxy similar to the Milky Way. (a) The Sombrero Galaxy is a spiral galaxy that we see from the side so the disk and central bulge are visible. (b) The Pinwheel Galaxy is a spiral galaxy that we see face-on so we can see the spiral arms. Because they contain lots of young stars, spiral arms tend to be blue. ",text,
L_0176,galaxies,T_1212,"Spiral galaxies spin, so they appear as a rotating disk of stars and dust, with a bulge in the middle, like the Sombrero Galaxy shown in Figure 1.2. Several arms spiral outward in the Pinwheel Galaxy (seen in Figure 1.2) and are appropriately called spiral arms. Spiral galaxies have lots of gas and dust and lots of young stars. The Andromeda Galaxy is a large spiral galaxy similar to the Milky Way. (a) The Sombrero Galaxy is a spiral galaxy that we see from the side so the disk and central bulge are visible. (b) The Pinwheel Galaxy is a spiral galaxy that we see face-on so we can see the spiral arms. Because they contain lots of young stars, spiral arms tend to be blue. ",text,
L_0176,galaxies,T_1213,"Figure 1.3 shows a typical egg-shaped elliptical galaxy. The smallest elliptical galaxies are as small as some globular clusters. Giant elliptical galaxies, on the other hand, can contain over a trillion stars. Elliptical galaxies are reddish to yellowish in color because they contain mostly old stars. Most elliptical galaxies contain very little gas and dust because the gas and dust have already formed into stars. However, some elliptical galaxies, such as the one shown in Figure 1.4, contain lots of dust. Why might some elliptical galaxies contain dust? ",text,
L_0176,galaxies,T_1213,"Figure 1.3 shows a typical egg-shaped elliptical galaxy. The smallest elliptical galaxies are as small as some globular clusters. Giant elliptical galaxies, on the other hand, can contain over a trillion stars. Elliptical galaxies are reddish to yellowish in color because they contain mostly old stars. Most elliptical galaxies contain very little gas and dust because the gas and dust have already formed into stars. However, some elliptical galaxies, such as the one shown in Figure 1.4, contain lots of dust. Why might some elliptical galaxies contain dust? ",text,
L_0176,galaxies,T_1214,"Is the galaxy in Figure 1.5 a spiral galaxy or an elliptical galaxy? It is neither one! Galaxies that are not clearly elliptical galaxies or spiral galaxies are irregular galaxies. How might an irregular galaxy form? Most irregular galaxies were once spiral or elliptical galaxies that were then deformed either by gravitational attraction to a larger galaxy or by a collision with another galaxy. This galaxy, called NGC 1427A, has nei- ther a spiral nor an elliptical shape. ",text,
L_0176,galaxies,T_1215,"Dwarf galaxies are small galaxies containing only a few million to a few billion stars. Dwarf galaxies are the most common type in the universe. However, because they are relatively small and dim, we dont see as many dwarf galaxies from Earth. Most dwarf galaxies are irregular in shape. However, there are also dwarf elliptical galaxies and dwarf spiral galaxies. Look back at the picture of the elliptical galaxy. In the figure, you can see two dwarf elliptical galaxies that are companions to the Andromeda Galaxy. One is a bright sphere to the left of center, and the other is a long ellipse below and to the right of center. Dwarf galaxies are often found near larger galaxies. They sometimes collide with and merge into their larger neighbors. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0177,geologic time scale,T_1216,"To be able to discuss Earth history, scientists needed some way to refer to the time periods in which events happened and organisms lived. With the information they collected from fossil evidence and using Stenos principles, they created a listing of rock layers from oldest to youngest. Then they divided Earths history into blocks of time with each block separated by important events, such as the disappearance of a species of fossil from the rock record. Since many of the scientists who first assigned names to times in Earths history were from Europe, they named the blocks of time from towns or other local places where the rock layers that represented that time were found. From these blocks of time the scientists created the geologic time scale (Figure 1.1). In the geologic time scale the youngest ages are on the top and the oldest on the bottom. Why do you think that the more recent time periods are divided more finely? Do you think the divisions in the scale below are proportional to the amount of time each time period represented in Earth history? In what eon, era, period and epoch do we now live? We live in the Holocene (sometimes called Recent) epoch, Quaternary period, Cenozoic era, and Phanerozoic eon. ",text,
L_0177,geologic time scale,T_1217,"Its always fun to think about geologic time in a framework that we can more readily understand. Here are when some major events in Earth history would have occurred if all of earth history was condensed down to one calendar year. January 1 12 am: Earth forms from the planetary nebula - 4600 million years ago February 25, 12:30 pm: The origin of life; the first cells - 3900 million years ago March 4, 3:39 pm: Oldest dated rocks - 3800 million years ago March 20, 1:33 pm: First stromatolite fossils - 3600 million years ago July 17, 9:54 pm: first fossil evidence of cells with nuclei - 2100 million years ago November 18, 5:11 pm: Cambrian Explosion - 544 million years ago December 1, 8:49 am: first insects - 385 million years ago December 2, 3:54 am: first land animals, amphibians - 375 million years ago December 5, 5:50 pm: first reptiles - 330 million years ago December 12, 12:09 pm: Permo-Triassic Extinction - 245 million years ago December 13, 8:37 pm: first dinosaurs - 228 million years ago December 14, 9:59 am: first mammals  220 million years ago December 22, 8:24 pm: first flowering plants - 115 million years ago December 26, 7:52 pm: Cretaceous-Tertiary Extinction - 66 million years ago December 26, 9:47 pm: first ancestors of dogs - 64 million years ago December 27, 5:25 am: widespread grasses - 60 million years ago December 27, 11:09 am: first ancestors of pigs and deer - 57 million years ago December 28, 9:31 pm: first monkeys - 39 million years ago December 31, 5:18 pm: oldest hominid - 4 million years ago December 31, 11:02 pm: oldest direct human ancestor - 1 million years ago December 31, 11:48 pm: first modern human - 200,000 years ago December 31, 11:59 pm: Revolutionary War - 235 years ago ",text,
L_0178,geological stresses,T_1218,"Stress is the force applied to an object. In geology, stress is the force per unit area that is placed on a rock. Four types of stresses act on materials. A deeply buried rock is pushed down by the weight of all the material above it. Since the rock cannot move, it cannot deform. This is called confining stress. Compression squeezes rocks together, causing rocks to fold or fracture (break) (Figure 1.1). Compression is the most common stress at convergent plate boundaries. Stress caused these rocks to fracture. Rocks that are pulled apart are under tension. Rocks under tension lengthen or break apart. Tension is the major type of stress at divergent plate boundaries. When forces are parallel but moving in opposite directions, the stress is called shear (Figure 1.2). Shear stress is the most common stress at transform plate boundaries. Shearing in rocks. The white quartz vein has been elongated by shear. When stress causes a material to change shape, it has undergone strain or deformation. Deformed rocks are common in geologically active areas. A rocks response to stress depends on the rock type, the surrounding temperature, the pressure conditions the rock is under, the length of time the rock is under stress, and the type of stress. ",text,
L_0178,geological stresses,T_1218,"Stress is the force applied to an object. In geology, stress is the force per unit area that is placed on a rock. Four types of stresses act on materials. A deeply buried rock is pushed down by the weight of all the material above it. Since the rock cannot move, it cannot deform. This is called confining stress. Compression squeezes rocks together, causing rocks to fold or fracture (break) (Figure 1.1). Compression is the most common stress at convergent plate boundaries. Stress caused these rocks to fracture. Rocks that are pulled apart are under tension. Rocks under tension lengthen or break apart. Tension is the major type of stress at divergent plate boundaries. When forces are parallel but moving in opposite directions, the stress is called shear (Figure 1.2). Shear stress is the most common stress at transform plate boundaries. Shearing in rocks. The white quartz vein has been elongated by shear. When stress causes a material to change shape, it has undergone strain or deformation. Deformed rocks are common in geologically active areas. A rocks response to stress depends on the rock type, the surrounding temperature, the pressure conditions the rock is under, the length of time the rock is under stress, and the type of stress. ",text,
L_0178,geological stresses,T_1219,"Rocks have three possible responses to increasing stress (illustrated in Figure 1.3): elastic deformation: the rock returns to its original shape when the stress is removed. plastic deformation: the rock does not return to its original shape when the stress is removed. fracture: the rock breaks. Under what conditions do you think a rock is more likely to fracture? Is it more likely to break deep within Earths crust or at the surface? What if the stress applied is sharp rather than gradual? At the Earths surface, rocks usually break quite quickly, but deeper in the crust, where temperatures and pressures are higher, rocks are more likely to deform plastically. Sudden stress, such as a hit with a hammer, is more likely to make a rock break. Stress applied over time often leads to plastic deformation. Click image to the left or use the URL below. URL: ",text,
L_0179,geothermal power,T_1220,"The heat that is used for geothermal power may come to the surface naturally as hot springs or geysers, like The Geysers in northern California. Where water does not naturally come to the surface, engineers may pump cool water into the ground. The water is heated by the hot rock and then pumped back to the surface for use. The hot water or steam from a geothermal well spins a turbine to make electricity. Geothermal energy is clean and safe. The energy source is renewable since hot rock is found everywhere in the Earth, although in many parts of the world the hot rock is not close enough to the surface for building geothermal power plants. In some areas, geothermal power is common (Figure 1.1). In the United States, California is a leader in producing geothermal energy. The largest geothermal power plant in the state is in the Geysers Geothermal Resource Area in Napa and Sonoma Counties. The source of heat is thought to be a large magma chamber lying beneath the area. Where Earths internal heat gets close to the surface, geothermal power is a clean source of energy. In California, The Geysers supplies energy for many nearby homes and businesses. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0180,glaciers,T_1221,"Nearly all glacial ice, 99%, is contained in ice sheets in the polar regions, particularly Antarctica and Greenland. Glaciers often form in the mountains because higher altitudes are colder and more likely to have snow that falls and collects. Every continent, except Australia, hosts at least some glaciers in the high mountains. ",text,
L_0180,glaciers,T_1222,"The types of glaciers are: Continental glaciers are large ice sheets that cover relatively flat ground. These glaciers flow outward from where the greatest amounts of snow and ice accumulate. Alpine (valley) glaciers flow downhill from where the snow and ice accumulates through mountains along existing valleys. Ice caps are large glaciers that cover a larger area than just a valley, possibly an entire mountain range or region. Glaciers come off of ice caps into valleys. The Greenland ice cap covers the entire landmass. ",text,
L_0180,glaciers,T_1223,,text,
L_0180,glaciers,T_1224,"Glaciers grow when more snow falls near the top of the glacier, in the zone of accumulation, than is melted from lower down in the glacier, in the zone of ablation. These two zones are separated by the equilibrium line. Snow falls and over time converts to granular ice known as firn. Eventually, as more snow and ice collect, the firn becomes denser and converts to glacial ice. Water is too warm for a glacier to form, so they form only on land. A glacier may run out from land into water, but it usually breaks up into icebergs that eventually melt into the water. ",text,
L_0180,glaciers,T_1225,"Whether an ice field moves or not depends on the amount of ice in the field, the steepness of the slope and the roughness of the ground surface. Ice moves where the pressure is so great that it undergoes plastic flow. Ice also slides at the bottom, often lubricated by water that has melted and travels between the ground and the ice. The speed of a glacier ranges from extremely fast, where conditions are favorable, to nearly zero. Because the ice is moving, glaciers have crevasses, where cracks form in the ice as a result of movement. The large crevasse at the top of an alpine glacier where ice that is moving is separated from ice that is stuck to the mountain above is called a bergshrund. Crevasses in a glacier are the result of movement. ",text,
L_0180,glaciers,T_1226,"Glaciers are melting back in many locations around the world. When a glacier no longer moves, it is called an ice sheet. This usually happens when it is less than 0.1 km2 in area and 50 m thick. ",text,
L_0180,glaciers,T_1227,"Many of the glaciers in Glacier National Park have shrunk and are no longer active. Summer temperatures have risen rapidly in this part of the country and so the rate of melting has picked up. Whereas Glacier National Park had 150 glaciers in 1850, there are only about 25 today. Recent estimates are that the park will have no active glaciers as early as 2020. This satellite image shows Grinnell Glacier, Swiftcurrent Glacier, and Gem Glacier in 2003 with an outline of the extent of the glaciers as they were in 1950. Although it continues to be classified as a glacier, Gem Glacier is only 0.020 km2 (5 acres) in area, only one-fifth the size of the smallest active glaciers. ",text,
L_0180,glaciers,T_1228,"In regions where summers are long and dry, melting glaciers in mountain regions provide an important source of water for organisms and often for nearby human populations. Click image to the left or use the URL below. URL: ",text,
L_0181,global warming,T_1229,"With more greenhouse gases trapping heat, average annual global temperatures are rising. This is known as global warming. ",text,
L_0181,global warming,T_1230,"While temperatures have risen since the end of the Pleistocene, 10,000 years ago, this rate of increase has been more rapid in the past century, and has risen even faster since 1990. The 10 warmest years in the 134-year record have all occurred since in the 21st century, and only one year during the 20th century (1998) was warmer than 2013, the 4th warmest year on record (through 2013) (Figure 1.1). The 2000s were the warmest decade yet. Annual variations aside, the average global temperature increased about 0.8o C (1.5o F) between 1880 and 2010, according to the Goddard Institute for Space Studies, NOAA. This number doesnt seem very large. Why is it important? ",text,
L_0181,global warming,T_1231,"The United States has long been the largest emitter of greenhouse gases, with about 20% of total emissions in 2004. As a result of Chinas rapid economic growth, its emissions surpassed those of the United States in 2008. However, its also important to keep in mind that the United States has only about one-fifth the population of China. Whats the significance of this? The average United States citizen produces far more greenhouse gas emissions than the average Chinese person. ",text,
L_0181,global warming,T_1232,"The following images show changes in the Earth and organisms as a result of global warming: Figure 1.2, Figure (a) Breakup of the Larsen Ice Shelf in Antarctica in 2002 was related to climate warming in the region. (b) The Boulder Glacier has melted back tremendously since 1985. Other mountain glaciers around the world are also melting. The timing of events for species is changing. Mating and migrations take place earlier in the spring months. Species that can are moving their ranges uphill. Some regions that were already marginal for agriculture are no longer arable because they have become too warm or dry. What are the two major effects being seen in this animation? Glaciers are melting and vegetation zones are moving uphill. If fossil fuel use exploded in the 1950s, why do these changes begin early in the animation? Does this mean that the climate change we are seeing is caused by natural processes and not by fossil fuel use? Permafrost is melting and its extent de- creasing. There are now fewer summer lakes in Siberia. (a) Melting ice caps add water to the oceans, so sea level is rising. Remember that water slightly expands as it warms this expansion is also causing sea level to rise. (b) Weather is becoming more variable with more severe storms and droughts. Snow blanketed the west- ern United States in December 2009. (c) As surface seas warm, phytoplankton productivity has decreased. (d) Coral reefs are dying worldwide; corals that are stressed by high temperatures turn white. (e) Pine beetle infestations have killed trees in western North America The insects have expanded their ranges into areas that were once too cold. Warming temperatures are bringing changes to much of the planet, including California. Sea level is rising, snow pack is changing, and the ecology of the state is responding to these changes. Click image to the left or use the URL below. URL: ",text,
L_0181,global warming,T_1232,"The following images show changes in the Earth and organisms as a result of global warming: Figure 1.2, Figure (a) Breakup of the Larsen Ice Shelf in Antarctica in 2002 was related to climate warming in the region. (b) The Boulder Glacier has melted back tremendously since 1985. Other mountain glaciers around the world are also melting. The timing of events for species is changing. Mating and migrations take place earlier in the spring months. Species that can are moving their ranges uphill. Some regions that were already marginal for agriculture are no longer arable because they have become too warm or dry. What are the two major effects being seen in this animation? Glaciers are melting and vegetation zones are moving uphill. If fossil fuel use exploded in the 1950s, why do these changes begin early in the animation? Does this mean that the climate change we are seeing is caused by natural processes and not by fossil fuel use? Permafrost is melting and its extent de- creasing. There are now fewer summer lakes in Siberia. (a) Melting ice caps add water to the oceans, so sea level is rising. Remember that water slightly expands as it warms this expansion is also causing sea level to rise. (b) Weather is becoming more variable with more severe storms and droughts. Snow blanketed the west- ern United States in December 2009. (c) As surface seas warm, phytoplankton productivity has decreased. (d) Coral reefs are dying worldwide; corals that are stressed by high temperatures turn white. (e) Pine beetle infestations have killed trees in western North America The insects have expanded their ranges into areas that were once too cold. Warming temperatures are bringing changes to much of the planet, including California. Sea level is rising, snow pack is changing, and the ecology of the state is responding to these changes. Click image to the left or use the URL below. URL: ",text,
L_0181,global warming,T_1232,"The following images show changes in the Earth and organisms as a result of global warming: Figure 1.2, Figure (a) Breakup of the Larsen Ice Shelf in Antarctica in 2002 was related to climate warming in the region. (b) The Boulder Glacier has melted back tremendously since 1985. Other mountain glaciers around the world are also melting. The timing of events for species is changing. Mating and migrations take place earlier in the spring months. Species that can are moving their ranges uphill. Some regions that were already marginal for agriculture are no longer arable because they have become too warm or dry. What are the two major effects being seen in this animation? Glaciers are melting and vegetation zones are moving uphill. If fossil fuel use exploded in the 1950s, why do these changes begin early in the animation? Does this mean that the climate change we are seeing is caused by natural processes and not by fossil fuel use? Permafrost is melting and its extent de- creasing. There are now fewer summer lakes in Siberia. (a) Melting ice caps add water to the oceans, so sea level is rising. Remember that water slightly expands as it warms this expansion is also causing sea level to rise. (b) Weather is becoming more variable with more severe storms and droughts. Snow blanketed the west- ern United States in December 2009. (c) As surface seas warm, phytoplankton productivity has decreased. (d) Coral reefs are dying worldwide; corals that are stressed by high temperatures turn white. (e) Pine beetle infestations have killed trees in western North America The insects have expanded their ranges into areas that were once too cold. Warming temperatures are bringing changes to much of the planet, including California. Sea level is rising, snow pack is changing, and the ecology of the state is responding to these changes. Click image to the left or use the URL below. URL: ",text,
L_0183,gravity in the solar system,T_1238,"Isaac Newton first described gravity as the force that causes objects to fall to the ground and also the force that keeps the Moon circling Earth instead of flying off into space in a straight line. Newton defined the Universal Law of Gravitation, which states that a force of attraction, called gravity, exists between all objects in the universe (Figure from each other. The greater the objects mass, the greater the force of attraction; in addition, the greater the distance between objects, the smaller the force of attraction. The distance between the Sun and each of its planets is very large, but the Sun and each of the planets are also very large. Gravity keeps each planet orbiting the Sun because the star and its planets are very large objects. The force of gravity also holds moons in orbit around planets. The force of gravity exists between all objects in the universe; the strength of the force depends on the mass of the objects and the distance between them. Click image to the left or use the URL below. URL: ",text,
L_0184,greenhouse effect,T_1239,"The exception to Earths temperature being in balance is caused by greenhouse gases. But first the role of greenhouse gases in the atmosphere must be explained. Greenhouse gases warm the atmosphere by trapping heat. Some of the heat that radiates out from the ground is trapped by greenhouse gases in the troposphere. Like a blanket on a sleeping person, greenhouse gases act as insulation for the planet. The warming of the atmosphere because of insulation by greenhouse gases is called the greenhouse effect (Figure 1.1). Greenhouse gases are the component of the atmosphere that moderate Earths temperatures. ",text,
L_0184,greenhouse effect,T_1240,"Greenhouse gases include CO2 , H2 O, methane, O3 , nitrous oxides (NO and NO2 ), and chlorofluorocarbons (CFCs). All are a normal part of the atmosphere except CFCs. Table 1.1 shows how each greenhouse gas naturally enters the atmosphere. Greenhouse Gas Carbon dioxide Methane Nitrous oxide Ozone Chlorofluorocarbons Where It Comes From Respiration, volcanic eruptions, decomposition of plant material; burning of fossil fuels Decomposition of plant material under some condi- tions, biochemical reactions in stomachs Produced by bacteria Atmospheric processes Not naturally occurring; made by humans Different greenhouse gases have different abilities to trap heat. For example, one methane molecule traps 23 times as much heat as one CO2 molecule. One CFC-12 molecule (a type of CFC) traps 10,600 times as much heat as one CO2 . Still, CO2 is a very important greenhouse gas because it is much more abundant in the atmosphere. ",text,
L_0184,greenhouse effect,T_1241,Human activity has significantly raised the levels of many of greenhouse gases in the atmosphere. Methane levels are about 2 1/2 times higher as a result of human activity. Carbon dioxide has increased more than 35%. CFCs have only recently existed. What do you think happens as atmospheric greenhouse gas levels increase? More greenhouse gases trap more heat and warm the atmosphere. The increase or decrease of greenhouse gases in the atmosphere affect climate and weather the world over. Click image to the left or use the URL below. URL: ,text,
L_0185,groundwater aquifers,T_1242,"To be a good aquifer, the rock in the aquifer must have good: porosity: small spaces between grains permeability: connections between pores To reach an aquifer, surface water infiltrates downward into the ground through tiny spaces or pores in the rock. The water travels down through the permeable rock until it reaches a layer that does not have pores; this rock is impermeable (Figure 1.1). This impermeable rock layer forms the base of the aquifer. The upper surface where the groundwater reaches is the water table. Groundwater is found beneath the solid surface. Notice that the water table roughly mirrors the slope of the lands surface. A well penetrates the water table. ",text,
L_0185,groundwater aquifers,T_1243,"For a groundwater aquifer to contain the same amount of water, the amount of recharge must equal the amount of discharge. What are the likely sources of recharge? What are the likely sources of discharge? What happens to the water table when there is a lot of rainfall? What happens when there is a drought? Although groundwater levels do not rise and fall as rapidly as at the surface, over time the water table will rise during wet periods and fall during droughts. In wet regions, streams are fed by groundwater; the surface of the stream is the top of the water table (Figure 1.2). In dry regions, water seeps down from the stream into the aquifer. These streams are often dry much of the year. Water leaves a groundwater reservoir in streams or springs. People take water from aquifers, too. ",text,
L_0185,groundwater aquifers,T_1244,"Groundwater meets the surface in a stream (Figure 1.2) or a spring (Figure 1.3). A spring may be constant, or may only flow at certain times of year. Towns in many locations depend on water from springs. Springs can be an extremely important source of water in locations where surface water is scarce. ",text,
L_0185,groundwater aquifers,T_1245,"A well is created by digging or drilling to reach groundwater. It is important for anyone who intends to dig a well to know how deep beneath the surface the water table is. When the water table is close to the surface, wells are a convenient method for extracting water. When the water table is far below the surface, specialized equipment must The top of the stream is the top of the water table. The stream feeds the aquifer. A spring in Croatia bubbles to the surface and feeds the river Cetina. be used to dig a well. Most wells use motorized pumps to bring water to the surface, but some still require people to use a bucket to draw water up (Figure 1.4). An old-fashioned well that uses a bucket drawn up by hand. ",text,
L_0185,groundwater aquifers,T_1245,"A well is created by digging or drilling to reach groundwater. It is important for anyone who intends to dig a well to know how deep beneath the surface the water table is. When the water table is close to the surface, wells are a convenient method for extracting water. When the water table is far below the surface, specialized equipment must The top of the stream is the top of the water table. The stream feeds the aquifer. A spring in Croatia bubbles to the surface and feeds the river Cetina. be used to dig a well. Most wells use motorized pumps to bring water to the surface, but some still require people to use a bucket to draw water up (Figure 1.4). An old-fashioned well that uses a bucket drawn up by hand. ",text,
L_0185,groundwater aquifers,T_1245,"A well is created by digging or drilling to reach groundwater. It is important for anyone who intends to dig a well to know how deep beneath the surface the water table is. When the water table is close to the surface, wells are a convenient method for extracting water. When the water table is far below the surface, specialized equipment must The top of the stream is the top of the water table. The stream feeds the aquifer. A spring in Croatia bubbles to the surface and feeds the river Cetina. be used to dig a well. Most wells use motorized pumps to bring water to the surface, but some still require people to use a bucket to draw water up (Figure 1.4). An old-fashioned well that uses a bucket drawn up by hand. ",text,
L_0186,groundwater depletion,T_1246,"Some aquifers are overused; people pump out more water than is replaced. As the water is pumped out, the water table slowly falls, requiring wells to be dug deeper, which takes more money and energy. Wells may go completely dry if they are not deep enough to reach into the lowered water table. Other problems may stem from groundwater overuse. Subsidence and saltwater intrusion are two of them. ",text,
L_0186,groundwater depletion,T_1247,"The Ogallala Aquifer supplies about one-third of the irrigation water in the United States. The Ogallala Aquifer is widely used by people for municipal and agricultural needs. (Figure 1.2). The aquifer is found from 30 to 100 meters deep over an area of about 440,000 square kilometers! The water in the aquifer is mostly from the last ice age. About eight times more water is taken from the Ogallala Aquifer each year than is replenished. Much of the water is used for irrigation (Figure 1.3). Click image to the left or use the URL below. URL:  Intense drought has reduced groundwater levels in the southern U.S., particularly in Texas and New Mexico. ",text,
L_0186,groundwater depletion,T_1248,Lowering the water table may cause the ground surface to sink. Subsidence may occur beneath houses and other structures (Figure 1.4). ,text,
L_0186,groundwater depletion,T_1249,"When coastal aquifers are overused, salt water from the ocean may enter the aquifer, contaminating the aquifer and making it less useful for drinking and irrigation. Salt water incursion is a problem in developed coastal regions, such as on Hawaii. ",text,
L_0187,groundwater pollution,T_1250,"Groundwater pollutants are the same as surface water pollutants: municipal, agricultural, and industrial. Ground- water is more susceptible to some sources of pollution. For example, irrigation water infiltrates into the ground, bringing with it the pesticides, fertilizers, and herbicides that were sprayed on the fields. Water that seeps through landfills also carries toxins into the ground. Toxic substances and things like gasoline are kept in underground storage tanks; more than 100,000 of the tanks are currently leaking and many more may develop leaks. ",text,
L_0187,groundwater pollution,T_1251,"Groundwater is a bit safer from pollution than surface water from some types of pollution because some pollutants are filtered out by the rock and soil that water travels through as it travels through the ground or once it is in the aquifer. But rock and soil cant get out everything, depending on the type of rock and soil and on the types of pollutants. As it is, about 25% of the usable groundwater and 45% of the municipal groundwater supplies in the United States are polluted. ",text,
L_0187,groundwater pollution,T_1252,"When the pollutant enters the aquifer, contamination spreads in the water outward from the source and travels in the direction that the water is moving. This pollutant plume may travel very slowly, only a few inches a day, but over time can contaminate a large portion of the aquifer. Many wells that are currently in use are contaminated. In Florida, for example, more than 90% of wells have detectible contaminants and thousands have been closed. ",text,
L_0188,growth of human populations,T_1253,"Human population growth over the past 10,000 years has been tremendous (Figure 1.1). The entire human popula- tion was estimated to be 5 million in 8000 B.C. 300 million in A.D. 1 1 billion in 1802 3 billion in 1961 7 billion in 2011 As the human population continues to grow, different factors limit population in different parts of the world. What might be a limiting factor for human population in a particular location? Space, clean air, clean water, and food to feed everyone are limiting in some locations. ",text,
L_0188,growth of human populations,T_1254,"Not only has the population increased, but the rate of population growth has increased (Figure 1.2). The population was estimated to reach 7 billion in 2012, but it did so in 2011, just 12 years after reaching 6 billion. Human population from 10,000 BC through 2000 AD, showing the exponential increase in human population that has occurred in the last few centuries. The amount of time between the addition of each one billion people to the planets population, including speculation about the future. Although population continues to grow rapidly, the rate that the growth rate is increasing has declined. Still, a recent estimate by the United Nations estimates that 10.1 billion people will be sharing this planet by the end of the century. The total added will be about 3 billion people, which is more than were even in existence as recently as 1960. ",text,
L_0188,growth of human populations,T_1254,"Not only has the population increased, but the rate of population growth has increased (Figure 1.2). The population was estimated to reach 7 billion in 2012, but it did so in 2011, just 12 years after reaching 6 billion. Human population from 10,000 BC through 2000 AD, showing the exponential increase in human population that has occurred in the last few centuries. The amount of time between the addition of each one billion people to the planets population, including speculation about the future. Although population continues to grow rapidly, the rate that the growth rate is increasing has declined. Still, a recent estimate by the United Nations estimates that 10.1 billion people will be sharing this planet by the end of the century. The total added will be about 3 billion people, which is more than were even in existence as recently as 1960. ",text,
L_0189,hazardous waste,T_1255,"Hazardous waste is any waste material that is dangerous to human health or that degrades the environment. Haz- ardous waste includes substances that are: 1. 2. 3. 4. Toxic: causes serious harm or death, or is poisonous. Chemically active: causes dangerous or unwanted chemical reactions, such as explosions. Corrosive: destroys other things by chemical reactions. Flammable: easily catches fire and may send dangerous smoke into the air. All sorts of materials are hazardous wastes and there are many sources. Many people have substances that could become hazardous wastes in their homes. Several cleaning and gardening chemicals are hazardous if not used properly. These include chemicals like drain cleaners and pesticides that are toxic to humans and many other creatures. While these chemicals are fine if they are stored and used properly, if they are used or disposed of improperly, they may become hazardous wastes. Others sources of hazardous waste are shown in Table 1.1. Type of Hazardous Waste Chemicals from the automobile in- dustry Example Gasoline, used motor oil, battery acid, brake fluid Batteries Car batteries, household batteries Medical wastes Dry cleaning chemicals Surgical gloves, wastes contami- nated with body fluids such as blood, x-ray equipment Paints, paint thinners, paint strip- pers, wood stains Many various chemicals Agricultural chemicals Pesticides, herbicides, fertilizers Paints Why it is Hazardous Toxic to humans and other organ- isms; often chemically active; often flammable. Contain toxic chemicals; are often corrosive. Toxic to humans and other organ- isms; may be chemically active. Toxic; flammable. Toxic; many cause cancer in hu- mans. Toxic to humans; can harm other organism; pollute soils and water. Click image to the left or use the URL below. URL: ",text,
L_0190,heat budget of planet earth,T_1256,"About half of the solar radiation that strikes the top of the atmosphere is filtered out before it reaches the ground. This energy can be absorbed by atmospheric gases, reflected by clouds, or scattered. Scattering occurs when a light wave strikes a particle and bounces off in some other direction. About 3% of the energy that strikes the ground is reflected back into the atmosphere. The rest is absorbed by rocks, soil, and water and then radiated back into the air as heat. These infrared wavelengths can only be seen by infrared sensors. Click image to the left or use the URL below. URL: ",text,
L_0190,heat budget of planet earth,T_1257,"Because solar energy continually enters Earths atmosphere and ground surface, is the planet getting hotter? The answer is no (although the next section contains an exception), because energy from Earth escapes into space through the top of the atmosphere. If the amount that exits is equal to the amount that comes in, then average global temperature stays the same. This means that the planets heat budget is in balance. What happens if more energy comes in than goes out? If more energy goes out than comes in? To say that the Earths heat budget is balanced ignores an important point. The amount of incoming solar energy is different at different latitudes. Where do you think the most solar energy ends up and why? Where does the least solar energy end up and why? See the Table 1.1. Equatorial Region Polar Regions Day Length Nearly the same all year Night 6 months Sun Angle High Solar Radiation High Albedo Low Low Low High Note: Colder temperatures mean more ice and snow cover the ground, making albedo relatively high. The difference in solar energy received at different latitudes drives atmospheric circulation. ",text,
L_0191,heat transfer in the atmosphere,T_1258,"Heat moves in the atmosphere the same way it moves through the solid Earth or another medium. What follows is a review of the way heat flows, but applied to the atmosphere. Radiation is the transfer of energy between two objects by electromagnetic waves. Heat radiates from the ground into the lower atmosphere. In conduction, heat moves from areas of more heat to areas of less heat by direct contact. Warmer molecules vibrate rapidly and collide with other nearby molecules, transferring their energy. In the atmosphere, conduction is more effective at lower altitudes, where air density is higher. This transfers heat upward to where the molecules are spread further apart or transfers heat laterally from a warmer to a cooler spot, where the molecules are moving less vigorously. Heat transfer by movement of heated materials is called convection. Heat that radiates from the ground initiates convection cells in the atmosphere (Figure 1.1). Click image to the left or use the URL below. URL: ",text,
L_0191,heat transfer in the atmosphere,T_1259,Different parts of the Earth receive different amounts of solar radiation. Which part of the planet receives the most solar radiation? The Suns rays strike the surface most directly at the Equator. The difference in solar energy received at different latitudes drives atmospheric circulation. ,text,
L_0192,heat waves and droughts,T_1260,"A heat wave is different depending on its location. According to the World Meteorological Organization, a region is in a heat wave if it has more than five consecutive days of temperatures that are more than 9 F (5 C) above average. Heat waves have increased in frequency and duration in recent years. The summer 2011 North American heat wave brought record temperatures across the Midwestern and Eastern United States. Many states and localities broke records for temperatures and for most days above 100 F. ",text,
L_0192,heat waves and droughts,T_1261,A high pressure cell sitting over a region with no movement is the likely cause of a heat wave. What do you think caused the heat wave in the image below (Figure 1.1)? A high pressure zone kept the jet stream further north than normal for August. A heat wave over the United States as in- dicated by heat radiated from the ground. The bright yellow areas are the hottest and the blue and white are coolest. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ,text,
L_0192,heat waves and droughts,T_1262,"Droughts also depend on what is normal for a region. When a region gets significantly less precipitation than normal for an extended period of time, it is in drought. The Southern United States is experiencing an ongoing and prolonged drought. Drought has many consequences. When soil loses moisture it may blow away, as happened during the Dust Bowl in the United States in the 1930s. Forests may be lost, dust storms may become common, and wildlife are disturbed. Wildfires become much more common during times of drought. ",text,
L_0196,hot springs and geysers,T_1277,Water sometimes comes into contact with hot rock. The water may emerge at the surface as either a hot spring or a geyser. ,text,
L_0196,hot springs and geysers,T_1278,"Water heated below ground that rises through a crack to the surface creates a hot spring. The water in hot springs may reach temperatures in the hundreds of degrees Celsius beneath the surface, although most hot springs are much cooler. Click image to the left or use the URL below. URL: ",text,
L_0196,hot springs and geysers,T_1279,"Geysers are also created by water that is heated beneath the Earths surface, but geysers do not bubble to the surface they erupt. When water is both superheated by magma and flows through a narrow passageway underground, the environment is ideal for a geyser. The passageway traps the heated water underground, so that heat and pressure can build. Eventually, the pressure grows so great that the superheated water bursts out onto the surface to create a geyser. Figure 1.2. Conditions are right for the formation of geysers in only a few places on Earth. Of the roughly 1,000 geysers worldwide, about half are found in the United States. Yellowstone isnt the only place in the continental U.S. with hot springs and geysers. Hot Creek in California deserves its name; Like Yellowstone, it is above a supervolcano. Click image to the left or use the URL below. URL:  Castle Geyser is one of the many gey- sers at Yellowstone National Park. Castle erupts regularly, but not as frequently or predictably as Old Faithful. ",text,
L_0197,how fossilization creates fossils,T_1280,"It wasnt always known that fossils were parts of living organisms. In 1666, a young doctor named Nicholas Steno dissected the head of an enormous great white shark that had been caught by fisherman near Florence, Italy. Steno was struck by the resemblance of the sharks teeth to fossils found in inland mountains and hills (Figure 1.1). Most people at the time did not believe that fossils were once part of living creatures. Authors in that day thought that the fossils of marine animals found in tall mountains, miles from any ocean could be explained in one of two ways: The shells were washed up during the Biblical flood. (This explanation could not account for the fact that fossils were not only found on mountains, but also within mountains, in rocks that had been quarried from deep below Earths surface.) The fossils formed within the rocks as a result of mysterious forces. But for Steno, the close resemblance between fossils and modern organisms was impossible to ignore. Instead of invoking supernatural forces, Steno concluded that fossils were once parts of living creatures. Fossil Shark Tooth (left) and Modern Shark Tooth (right). ",text,
L_0197,how fossilization creates fossils,T_1281,"A fossil is any remains or traces of an ancient organism. Fossils include body fossils, left behind when the soft parts have decayed away, and trace fossils, such as burrows, tracks, or fossilized coprolites (feces). Collections of fossils are known as fossil assemblages. Click image to the left or use the URL below. URL: ",text,
L_0197,how fossilization creates fossils,T_1282,"Becoming a fossil isnt easy. Only a tiny percentage of the organisms that have ever lived become fossils. Why do you think only a tiny percentage of living organisms become fossils after death? Think about an antelope that dies on the African plain (Figure 1.2). Most of its body is eaten by hyenas and other scavengers and the remaining flesh is devoured by insects and bacteria. Only bones are left behind. As the years go by, the bones are scattered and fragmented into small pieces, eventually turning into dust. The remaining nutrients return to the soil. This antelope will not be preserved as a fossil. Is it more likely that a marine organism will become a fossil? When clams, oysters, and other shellfish die, the soft parts quickly decay, and the shells are scattered. In shallow water, wave action grinds them into sand-sized pieces. The shells are also attacked by worms, sponges, and other animals (Figure 1.3). How about a soft bodied organism? Will a creature without hard shells or bones become a fossil? There is virtually no fossil record of soft bodied organisms such as jellyfish, worms, or slugs. Insects, which are by far the most common land animals, are only rarely found as fossils (Figure 1.4). ",text,
L_0197,how fossilization creates fossils,T_1282,"Becoming a fossil isnt easy. Only a tiny percentage of the organisms that have ever lived become fossils. Why do you think only a tiny percentage of living organisms become fossils after death? Think about an antelope that dies on the African plain (Figure 1.2). Most of its body is eaten by hyenas and other scavengers and the remaining flesh is devoured by insects and bacteria. Only bones are left behind. As the years go by, the bones are scattered and fragmented into small pieces, eventually turning into dust. The remaining nutrients return to the soil. This antelope will not be preserved as a fossil. Is it more likely that a marine organism will become a fossil? When clams, oysters, and other shellfish die, the soft parts quickly decay, and the shells are scattered. In shallow water, wave action grinds them into sand-sized pieces. The shells are also attacked by worms, sponges, and other animals (Figure 1.3). How about a soft bodied organism? Will a creature without hard shells or bones become a fossil? There is virtually no fossil record of soft bodied organisms such as jellyfish, worms, or slugs. Insects, which are by far the most common land animals, are only rarely found as fossils (Figure 1.4). ",text,
L_0197,how fossilization creates fossils,T_1283,"Despite these problems, there is a rich fossil record. How does an organism become fossilized? A rare insect fossil. ",text,
L_0197,how fossilization creates fossils,T_1284,"Usually its only the hard parts that are fossilized. The fossil record consists almost entirely of the shells, bones, or other hard parts of animals. Mammal teeth are much more resistant than other bones, so a large portion of the mammal fossil record consists of teeth. The shells of marine creatures are common also. ",text,
L_0197,how fossilization creates fossils,T_1285,"Quick burial is essential because most decay and fragmentation occurs at the surface. Marine animals that die near a river delta may be rapidly buried by river sediments. A storm at sea may shift sediment on the ocean floor, covering a body and helping to preserve its skeletal remains (Figure 1.5). This fish was quickly buried in sediment to become a fossil. Quick burial is rare on land, so fossils of land animals and plants are less common than marine fossils. Land People buried by the extremely hot eruption of ash and gases at Mt. Vesuvius in 79 AD. ",text,
L_0197,how fossilization creates fossils,T_1285,"Quick burial is essential because most decay and fragmentation occurs at the surface. Marine animals that die near a river delta may be rapidly buried by river sediments. A storm at sea may shift sediment on the ocean floor, covering a body and helping to preserve its skeletal remains (Figure 1.5). This fish was quickly buried in sediment to become a fossil. Quick burial is rare on land, so fossils of land animals and plants are less common than marine fossils. Land People buried by the extremely hot eruption of ash and gases at Mt. Vesuvius in 79 AD. ",text,
L_0197,how fossilization creates fossils,T_1286,"Unusual circumstances may lead to the preservation of a variety of fossils, as at the La Brea Tar Pits in Los Angeles, California. Although the animals trapped in the La Brea Tar Pits probably suffered a slow, miserable death, their bones were preserved perfectly by the sticky tar. (Figure 1.7). Artists concept of animals surrounding the La Brea Tar Pits. In spite of the difficulties of preservation, billions of fossils have been discovered, examined, and identified by thousands of scientists. The fossil record is our best clue to the history of life on Earth, and an important indicator ",text,
L_0197,how fossilization creates fossils,T_1287,"Some rock beds contain exceptional fossils or fossil assemblages. Two of the most famous examples of soft organism preservation are from the 505 million-year-old Burgess Shale in Canada (Figure 1.8). The 145 million-year-old Solnhofen Limestone in Germany has fossils of soft body parts that are not normally preserved (Figure 1.8). (a) The Burgess shale contains soft-bodied fossils. (b) Anomalocaris, meaning abnormal shrimp is now extinct. The image is of a fossil. (c) The famous Archeopteryx fossil from the Solnhofen Limestone has distinct feathers and was one of the earliest birds. Click image to the left or use the URL below. URL: ",text,
L_0198,how ocean currents moderate climate,T_1288,"Surface currents play an enormous role in Earths climate. Even though the Equator and poles have very different climates, these regions would have more extremely different climates if ocean currents did not transfer heat from the equatorial regions to the higher latitudes. The Gulf Stream is a river of warm water in the Atlantic Ocean, about 160 kilometers wide and about a kilometer deep. Water that enters the Gulf Stream is heated as it travels along the Equator. The warm water then flows up the east coast of North America and across the Atlantic Ocean to Europe (see opening image). The energy the Gulf Stream transfers is enormous: more than 100 times the worlds energy demand. The Gulf Streams warm waters raise temperatures in the North Sea, which raises the air temperatures over land between 3 to 6 C (5 to 11 F). London, U.K., for example, is at about six degrees further south than Quebec, Canada. However, Londons average January temperature is 3.8 C (38 F), while Quebecs is only -12 C (10 F). Because air traveling over the warm water in the Gulf Stream picks up a lot of water, London gets a lot of rain. In contrast, Quebec is much drier and receives its precipitation as snow. Quebec City, Quebec in winter. Click image to the left or use the URL below. URL: ",text,
L_0198,how ocean currents moderate climate,T_1288,"Surface currents play an enormous role in Earths climate. Even though the Equator and poles have very different climates, these regions would have more extremely different climates if ocean currents did not transfer heat from the equatorial regions to the higher latitudes. The Gulf Stream is a river of warm water in the Atlantic Ocean, about 160 kilometers wide and about a kilometer deep. Water that enters the Gulf Stream is heated as it travels along the Equator. The warm water then flows up the east coast of North America and across the Atlantic Ocean to Europe (see opening image). The energy the Gulf Stream transfers is enormous: more than 100 times the worlds energy demand. The Gulf Streams warm waters raise temperatures in the North Sea, which raises the air temperatures over land between 3 to 6 C (5 to 11 F). London, U.K., for example, is at about six degrees further south than Quebec, Canada. However, Londons average January temperature is 3.8 C (38 F), while Quebecs is only -12 C (10 F). Because air traveling over the warm water in the Gulf Stream picks up a lot of water, London gets a lot of rain. In contrast, Quebec is much drier and receives its precipitation as snow. Quebec City, Quebec in winter. Click image to the left or use the URL below. URL: ",text,
L_0199,human evolution,T_1289,"Humans evolved during the later Cenozoic. New fossil discoveries alter the details of what we know about the evolution of modern humans, but the major evolutionary path is well understood. ",text,
L_0199,human evolution,T_1290,"Humans evolved from primates, and apes and humans have a primate common ancestor. About 7 million years ago, chimpanzees (our closest living relatives) and humans shared their last common ancestor. ",text,
L_0199,human evolution,T_1291,"Animals of the genus Ardipithecus, living roughly 4 to 6 million years ago, had brains roughly the size of a female chimp. Although they lived in trees, they were bipedal. Standing on two feet allows an organism to see and also to use its hands and arms for hunting. By the time of Australopithecus afarensis, between 3.9 and 2.9 million years ago, these human ancestors were completely bipedal and their brains were growing rapidly (Figure 1.1). Australopithecus afarensis is a human ancestor that lived about 3 million years ago. The genus Homo appeared about 2.5 million years ago. Humans developed the first stone tools. Homo erectus evolved in Africa about 1.8 million years ago. Fossils of these animals show a much more human-like body structure, which allowed them to travel long distances to hunt. Cultures begin and evolve. Homo sapiens, our species, originated about 200,000 years ago in Africa. Evidence of a spiritual life appears about 32,000 years ago with stone figurines that probably have religious significance (Figure 1.2). The ice ages allowed humans to migrate. During the ice ages, water was frozen in glaciers and so land bridges such as the Bering Strait allowed humans to walk from the old world to the new world. DNA evidence suggests that the humans who migrated out of Africa interbred with Neanderthal since these people contain some Neanderthal DNA. Click image to the left or use the URL below. URL:  Stone figurines likely indicate a spiritual life. ",text,
L_0199,human evolution,T_1291,"Animals of the genus Ardipithecus, living roughly 4 to 6 million years ago, had brains roughly the size of a female chimp. Although they lived in trees, they were bipedal. Standing on two feet allows an organism to see and also to use its hands and arms for hunting. By the time of Australopithecus afarensis, between 3.9 and 2.9 million years ago, these human ancestors were completely bipedal and their brains were growing rapidly (Figure 1.1). Australopithecus afarensis is a human ancestor that lived about 3 million years ago. The genus Homo appeared about 2.5 million years ago. Humans developed the first stone tools. Homo erectus evolved in Africa about 1.8 million years ago. Fossils of these animals show a much more human-like body structure, which allowed them to travel long distances to hunt. Cultures begin and evolve. Homo sapiens, our species, originated about 200,000 years ago in Africa. Evidence of a spiritual life appears about 32,000 years ago with stone figurines that probably have religious significance (Figure 1.2). The ice ages allowed humans to migrate. During the ice ages, water was frozen in glaciers and so land bridges such as the Bering Strait allowed humans to walk from the old world to the new world. DNA evidence suggests that the humans who migrated out of Africa interbred with Neanderthal since these people contain some Neanderthal DNA. Click image to the left or use the URL below. URL:  Stone figurines likely indicate a spiritual life. ",text,
L_0201,igneous rocks,T_1298,Different factors play into the composition of a magma and the rock it produces. ,text,
L_0201,igneous rocks,T_1299,The rock beneath the Earths surface is sometimes heated to high enough temperatures that it melts to create magma. Different magmas have different composition and contain whatever elements were in the rock or rocks that melted. Magmas also contain gases. The main elements are the same as the elements found in the crust. Table 1.1 lists the abundance of elements found in the Earths crust and in magma. The remaining 1.5% is made up of many other elements that are present in tiny quantities. Element Symbol Percent Element Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium Total Symbol O Si Al Fe Ca Na K Mg Percent 46.6% 27.7% 8.1% 5.0% 3.6% 2.8% 2.6% 2.1% 98.5% ,text,
L_0201,igneous rocks,T_1300,"Whether rock melts to create magma depends on: Temperature: Temperature increases with depth, so melting is more likely to occur at greater depths. Pressure: Pressure increases with depth, but increased pressure raises the melting temperature, so melting is less likely to occur at higher pressures. Water: The addition of water changes the melting point of rock. As the amount of water increases, the melting point decreases. Rock composition: Minerals melt at different temperatures, so the temperature must be high enough to melt at least some minerals in the rock. The first mineral to melt from a rock will be quartz (if present) and the last will be olivine (if present). The different geologic settings that produce varying conditions under which rocks melt will be discussed in the chapter Plate Tectonics. ",text,
L_0201,igneous rocks,T_1301,"As a rock heats up, the minerals that melt at the lowest temperatures melt first. Partial melting occurs when the temperature on a rock is high enough to melt only some of the minerals in the rock. The minerals that will melt will be those that melt at lower temperatures. Fractional crystallization is the opposite of partial melting. This process describes the crystallization of different minerals as magma cools. Bowens Reaction Series indicates the temperatures at which minerals melt or crystallize (Figure 1.1). An under- standing of the way atoms join together to form minerals leads to an understanding of how different igneous rocks form. Bowens Reaction Series also explains why some minerals are always found together and some are never found together. If the liquid separates from the solids at any time in partial melting or fractional crystallization, the chemical composition of the liquid and solid will be different. When that liquid crystallizes, the resulting igneous rock will have a different composition from the parent rock. Bowens Reaction Series. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0202,impact of continued global warming,T_1302,"The amount CO2 levels will rise in the next decades is unknown. What will this number depend on in the developed nations? What will it depend on in the developing nations? In the developed nations it will depend on technological advances or lifestyle changes that decrease emissions. In the developing nations, it will depend on how much their lifestyles improve and how these improvements are made. If nothing is done to decrease the rate of CO2 emissions, by 2030, CO2 emissions are projected to be 63% greater than they were in 2002. ",text,
L_0202,impact of continued global warming,T_1303,"Computer models are used to predict the effects of greenhouse gas increases on climate for the planet as a whole and also for specific regions. If nothing is done to control greenhouse gas emissions and they continue to increase at current rates, the surface temperature of the Earth can be expected to increase between 0.5o C and 2.0o C (0.9o F and 3.6o F) by 2050 and between 2o and 4.5o C (3.5o and 8o F) by 2100, with CO2 levels over 800 parts per million (ppm). Global CO2 emissions are rising rapidly. The industrial revolution began about 1850 and industrialization has been ac- celerating. On the other hand, if severe limits on CO2 emissions begin soon, temperatures could rise less than 1.1o C (2o F) by 2100. Click image to the left or use the URL below. URL:  Whatever the temperature increase, it will not be uniform around the globe. A rise of 2.8o C (5o F) would result in 0.6o to 1.2o C (1o to 2o F) at the Equator, but up to 6.7o C (12o F) at the poles. So far, global warming has affected the North Pole more than the South Pole, but temperatures are still increasing at Antarctica (Figure 1.2). ",text,
L_0202,impact of continued global warming,T_1304,"As greenhouse gases increase, changes will be more extreme. Oceans will become more acidic, making it more difficult for creatures with carbonate shells to grow, and that includes coral reefs. A study monitoring ocean acidity in the Pacific Northwest found ocean acidity increasing ten times faster than expected and 10% to 20% of shellfish (mussels) being replaced by acid-tolerant algae. Plant and animal species seeking cooler temperatures will need to move poleward 100 to 150 km (60 to 90 miles) or upward 150 m (500 feet) for each 1.0o C (8o F) rise in global temperature. There will be a tremendous loss of biodiversity because forest species cant migrate that rapidly. Biologists have already documented the extinction of high-altitude species that have nowhere higher to go. Decreased snow packs, shrinking glaciers, and the earlier arrival of spring will all lessen the amount of water available in some regions of the world, including the western United States and much of Asia. Ice will continue to melt and sea level is predicted to rise 18 to 97 cm (7 to 38 inches) by 2100 (Figure 1.3). An increase this large will gradually flood coastal regions, where about one-third of the worlds population lives, forcing billions of people to move inland. Sea ice thickness around the North Pole has been decreasing in recent decades and will continue to decrease in the com- ing decades. Weather will become more extreme, with more frequent and more intense heat waves and droughts. Some modelers predict that the midwestern United States will become too dry to support agriculture and that Canada will become the new breadbasket. In all, about 10% to 50% of current cropland worldwide may become unusable if CO2 doubles. You may notice that the numerical predictions above contain wide ranges. Sea level, for example, is expected to rise somewhere between 18 and 97 cm  quite a wide range. What is the reason for this uncertainty? It is partly because scientists cannot predict exactly how the Earth will respond to increased levels of greenhouses gases. How quickly greenhouse gases continue to build up in the atmosphere depends in part on the choices we make. An important question people ask is this: Are the increases in global temperature natural? In other words, can natural variations in temperature account for the increase in temperature that we see? The answer is no. Changes in the Suns irradiance, El Nio and La Nia cycles, natural changes in greenhouse gas, and other atmospheric gases cannot account for the increase in temperature that has already happened in the past decades. Along with the rest of the worlds oceans, San Francisco Bay is rising. Changes are happening slowly in the coastal arena of the San Francisco Bay Area and even the most optimistic estimates about how high and how quickly this rise will occur indicate potentially huge problems for the region. Click image to the left or use the URL below. URL: ",text,
L_0202,impact of continued global warming,T_1304,"As greenhouse gases increase, changes will be more extreme. Oceans will become more acidic, making it more difficult for creatures with carbonate shells to grow, and that includes coral reefs. A study monitoring ocean acidity in the Pacific Northwest found ocean acidity increasing ten times faster than expected and 10% to 20% of shellfish (mussels) being replaced by acid-tolerant algae. Plant and animal species seeking cooler temperatures will need to move poleward 100 to 150 km (60 to 90 miles) or upward 150 m (500 feet) for each 1.0o C (8o F) rise in global temperature. There will be a tremendous loss of biodiversity because forest species cant migrate that rapidly. Biologists have already documented the extinction of high-altitude species that have nowhere higher to go. Decreased snow packs, shrinking glaciers, and the earlier arrival of spring will all lessen the amount of water available in some regions of the world, including the western United States and much of Asia. Ice will continue to melt and sea level is predicted to rise 18 to 97 cm (7 to 38 inches) by 2100 (Figure 1.3). An increase this large will gradually flood coastal regions, where about one-third of the worlds population lives, forcing billions of people to move inland. Sea ice thickness around the North Pole has been decreasing in recent decades and will continue to decrease in the com- ing decades. Weather will become more extreme, with more frequent and more intense heat waves and droughts. Some modelers predict that the midwestern United States will become too dry to support agriculture and that Canada will become the new breadbasket. In all, about 10% to 50% of current cropland worldwide may become unusable if CO2 doubles. You may notice that the numerical predictions above contain wide ranges. Sea level, for example, is expected to rise somewhere between 18 and 97 cm  quite a wide range. What is the reason for this uncertainty? It is partly because scientists cannot predict exactly how the Earth will respond to increased levels of greenhouses gases. How quickly greenhouse gases continue to build up in the atmosphere depends in part on the choices we make. An important question people ask is this: Are the increases in global temperature natural? In other words, can natural variations in temperature account for the increase in temperature that we see? The answer is no. Changes in the Suns irradiance, El Nio and La Nia cycles, natural changes in greenhouse gas, and other atmospheric gases cannot account for the increase in temperature that has already happened in the past decades. Along with the rest of the worlds oceans, San Francisco Bay is rising. Changes are happening slowly in the coastal arena of the San Francisco Bay Area and even the most optimistic estimates about how high and how quickly this rise will occur indicate potentially huge problems for the region. Click image to the left or use the URL below. URL: ",text,
L_0203,impacts of hazardous waste,T_1305,"The story of Love Canal, New York, begins in the 1950s, when a local chemical company placed hazardous wastes in 55-gallon steel drums and buried them. Love Canal was an abandoned waterway near Niagara Falls and was thought to be a safe site for hazardous waste disposal because the ground was fairly impermeable (Figure 1.1). After burial, the company covered the containers with soil and sold the land to the local school system for $1. The company warned the school district that the site had been used for toxic waste disposal. Steel drums were used to contain 21,000 tons of hazardous chemicals at Love Canal. Soon a school, a playground, and 100 homes were built on the site. The impermeable ground was breached when sewer systems were dug into the rock layer. Over time, the steel drums rusted and the chemicals were released into the ground. In the 1960s people began to notice bad odors. Children developed burns after playing in the soil, and they were often sick. In 1977 a swamp created by heavy rains was found to contain 82 toxic chemicals, including 11 suspected cancer-causing chemicals. A Love Canal resident, Lois Gibbs, organized a group of citizens called the Love Canal Homeowners Association to try to find out what was causing the problems (See opening image). When they discovered that toxic chemicals were buried beneath their homes and school, they demanded that the government take action to clean up the area and remove the chemicals. ",text,
L_0203,impacts of hazardous waste,T_1306,"In 1978, people were relocated to safe areas. The problem of Love Canal was instrumental in the passage of the the Superfund Act in 1980. This law requires companies to be responsible for hazardous chemicals that they put into the environment and to pay to clean up polluted sites, which can often cost hundreds of millions of dollars. Love Canal became a Superfund site in 1983 and as a result, several measures were taken to secure the toxic wastes. The land was capped so that water could not reach the waste, debris was cleaned from the nearby area, and contaminated soils were removed. ",text,
L_0203,impacts of hazardous waste,T_1307,"The pollution at Love Canal was not initially visible, but it became visible. The health effects from the waste were also not initially visible, but they became clearly visible. The effects of the contamination that were seen in human health included sickness in children and a higher than normal number of miscarriages in pregnant women. Toxic chemicals may cause cancer and birth defects. Why do you think children and fetuses are more susceptible? Because young organisms grow more rapidly, they take in more of the toxic chemicals and are more affected. ",text,
L_0203,impacts of hazardous waste,T_1308,"Sometimes the chemicals are not so easily seen as they were at Love Canal. But the impacts can be seen statistically. For example, contaminated drinking water may cause an increase in some types of cancer in a community. Why is one person with cancer not enough to suspect contamination by toxic waste? One is not a statistically valid number. A certain number of people get cancer all the time. To identify contamination, a number of cancers above the normal rate, called a cancer cluster, must be discovered. A case that was made into a book and movie called A Civil Action involved the community of Woburn, Massachusetts. Groundwater contamination was initially suspected because of an increase in childhood leukemia and other illnesses. As a result of concern by parents, the well water was analyzed and shown to have high levels of TCE (trichloroethylene). ",text,
L_0203,impacts of hazardous waste,T_1309,"Lead and mercury are two chemicals that are especially toxic to humans. Lead was once a common ingredient in gasoline and paint, but it was shown to damage human brains and nervous systems. Since young children are growing rapidly, lead is especially harmful in children under the age of six (Figure 1.2). In the 1970s and 1980s, the United States government passed laws completely banning lead in gasoline and paint. Homes built before the 1970s may contain lead paint. Paint so old is likely to be peeling and poses a great threat to human health. About 200 children die every year from lead poisoning. (a) Leaded gasoline. (b) Leaded paint. Mercury is a pollutant that can easily spread around the world. Sources of mercury include volcanic eruptions, coal burning, and wastes such as batteries, electronic switches, and electronic appliances such as television sets. Like lead, mercury damages the brain and impairs nervous system function. More about the hazards of mercury pollution can be found later in this concept. ",text,
L_0204,importance of the atmosphere,T_1310,"Earths atmosphere is a thin blanket of gases and tiny particles  together called air. We are most aware of air when it moves and creates wind. Earths atmosphere, along with the abundant liquid water at Earths surface, are the keys to our planets unique place in the solar system. Much of what makes Earth exceptional depends on the atmosphere. For example, all living things need some of the gases in air for life support. Without an atmosphere, Earth would likely be just another lifeless rock. Lets consider some of the reasons we are lucky to have an atmosphere. ",text,
L_0204,importance of the atmosphere,T_1311,"Without the atmosphere, Earth would look a lot more like the Moon. Atmospheric gases, especially carbon dioxide (CO2 ) and oxygen (O2 ), are extremely important for living organisms. How does the atmosphere make life possible? How does life alter the atmosphere? The composition of Earths atmosphere. ",text,
L_0204,importance of the atmosphere,T_1312,"In photosynthesis, plants use CO2 and create O2 . Photosynthesis is responsible for nearly all of the oxygen currently found in the atmosphere. The chemical reaction for photosynthesis is: 6CO2 + 6H2 O + solar energy  C6 H12 O6 (sugar) + 6O2 ",text,
L_0204,importance of the atmosphere,T_1313,"By creating oxygen and food, plants have made an environment that is favorable for animals. In respiration, animals use oxygen to convert sugar into food energy they can use. Plants also go through respiration and consume some of the sugars they produce. The chemical reaction for respiration is: C6 H12 O6 + 6O2  6CO2 + 6H2 O + useable energy How is respiration similar to and different from photosynthesis? They are approximately the reverse of each other. In photosynthesis, CO2 is converted to O2 and in respiration, O2 is converted to CO2 (Figure 1.2). ",text,
L_0204,importance of the atmosphere,T_1314,"As part of the hydrologic cycle, water spends a lot of time in the atmosphere, mostly as water vapor. The atmosphere is an important reservoir for water. Chlorophyll indicates the presence of photosynthesizing plants as does the veg- etation index. ",text,
L_0204,importance of the atmosphere,T_1315,"Ozone is a molecule composed of three oxygen atoms, (O3 ). Ozone in the upper atmosphere absorbs high-energy ultraviolet (UV) radiation coming from the Sun. This protects living things on Earths surface from the Suns most harmful rays. Without ozone for protection, only the simplest life forms would be able to live on Earth. The highest concentration of ozone is in the ozone layer in the lower stratosphere. ",text,
L_0204,importance of the atmosphere,T_1316,"Along with the oceans, the atmosphere keeps Earths temperatures within an acceptable range. Without an atmo- sphere, Earths temperatures would be frigid at night and scorching during the day. If the 12-year-old in the scenario above asked why, she would find out. Greenhouse gases trap heat in the atmosphere. Important greenhouse gases include carbon dioxide, methane, water vapor, and ozone. ",text,
L_0204,importance of the atmosphere,T_1317,"The atmosphere is made of gases that take up space and transmit energy. Sound waves are among the types of energy that travel though the atmosphere. Without an atmosphere, we could not hear a single sound. Earth would be as silent as outer space (explosions in movies about space should be silent). Of course, no insect, bird, or airplane would be able to fly, because there would be no atmosphere to hold it up. Click image to the left or use the URL below. URL: ",text,
L_0205,importance of the oceans,T_1318,"The oceans, along with the atmosphere, keep temperatures fairly constant worldwide. While some places on Earth get as cold as -70o C and others as hot as 55o C, the range is only 125o C. On Mercury temperatures go from -180o C to 430o C, a range of 610o C. The oceans, along with the atmosphere, distribute heat around the planet. The oceans absorb heat near the Equator and then move that solar energy to more polar regions. The oceans also moderate climate within a region. At the same latitude, the temperature range is smaller in lands nearer the oceans than away from the oceans. Summer temperatures are not as hot, and winter temperatures are not as cold, because water takes a long time to heat up or cool down. ",text,
L_0205,importance of the oceans,T_1319,"The oceans are an essential part of Earths water cycle. Since they cover so much of the planet, most evaporation comes from oceans and most precipitation falls on oceans. ",text,
L_0205,importance of the oceans,T_1320,"The oceans are home to an enormous amount of life. That is, they have tremendous biodiversity (Figure 1.1). Tiny ocean plants, called phytoplankton, create the base of a food web that supports all sorts of life forms. Marine life makes up the majority of all biomass on Earth. (Biomass is the total mass of living organisms in a given area.) These organisms supply us with food and even the oxygen created by marine plants. Polar bears are well adapted to frigid Arc- tic waters. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0206,influences on weathering,T_1321,"Different rock types weather at different rates. Certain types of rock are very resistant to weathering. Igneous rocks, especially intrusive igneous rocks such as granite, weather slowly because it is hard for water to penetrate them. Other types of rock, such as limestone, are easily weathered because they dissolve in weak acids. Rocks that resist weathering remain at the surface and form ridges or hills. Shiprock in New Mexico is the throat of a volcano thats left after the rest of the volcano eroded away. The rock thats left behind is magma that cooled relatively slowly and is harder than the rock that had surrounded it. Different minerals also weather at different rates. Some minerals in a rock might completely dissolve in water, but the more resistant minerals remain. In this case, the rocks surface becomes pitted and rough. When a less resistant mineral dissolves, more resistant mineral grains are released from the rock. A beautiful example of this effect is the ""Stone Forest"" in China, see the video below: The Shiprock formation in northwest New Mexico is the central plug of resistant lava from which the surrounding rock weath- ered and eroded away. Click image to the left or use the URL below. URL: ",text,
L_0206,influences on weathering,T_1322,"A regions climate strongly influences weathering. Climate is determined by the temperature of a region plus the amount of precipitation it receives. Climate is weather averaged over a long period of time. Chemical weathering increases as: Temperature increases: Chemical reactions proceed more rapidly at higher temperatures. For each 10o C increase in average temperature, the rate of chemical reactions doubles. Precipitation increases: More water allows more chemical reactions. Since water participates in both mechan- ical and chemical weathering, more water strongly increases weathering. So how do different climates influence weathering? A cold, dry climate will produce the lowest rate of weathering. A warm, wet climate will produce the highest rate of weathering. The warmer a climate is, the more types of vegetation it will have and the greater the rate of biological weathering (Figure 1.2). This happens because plants and bacteria grow and multiply faster in warmer temperatures. ",text,
L_0206,influences on weathering,T_1323,"Some resources are concentrated by weathering processes. In tropical climates, intense chemical weathering carries away all soluble minerals, leaving behind just the least soluble components. The aluminum oxide, bauxite, forms this way and is our main source of aluminum ore. ",text,
L_0207,inner vs. outer planets,T_1324,"The inner planets, or terrestrial planets, are the four planets closest to the Sun: Mercury, Venus, Earth, and Mars. Figure 1.1 shows the relative sizes of these four inner planets. Unlike the outer planets, which have many satellites, Mercury and Venus do not have moons, Earth has one, and Mars has two. Of course, the inner planets have shorter orbits around the Sun, and they all spin more slowly. Geologically, the inner planets are all made of cooled igneous rock with iron cores, and all have been geologically active, at least early in their history. None of the inner planets has rings. Click image to the left or use the URL below. URL:  This composite shows the relative sizes of the four inner planets. From left to right, they are Mercury, Venus, Earth, and Mars. ",text,
L_0207,inner vs. outer planets,T_1325,"The four planets farthest from the Sun are the outer planets. Figure 1.2 shows the relative sizes of the outer planets and the Sun. These planets are much larger than the inner planets and are made primarily of gases and liquids, so they are also called gas giants. The gas giants are made up primarily of hydrogen and helium, the same elements that make up most of the Sun. Astronomers think that hydrogen and helium gases comprised much of the solar system when it first formed. Since the inner planets didnt have enough mass to hold on to these light gases, their hydrogen and helium floated away into space. The Sun and the massive outer planets had enough gravity to keep hydrogen and helium from drifting away. All of the outer planets have numerous moons. They all also have planetary rings, composed of dust and other small particles that encircle the planet in a thin plane. Click image to the left or use the URL below. URL:  This image shows the four outer planets and the Sun, with sizes to scale. From left to right, the outer planets are Jupiter, Saturn, Uranus, and Neptune. ",text,
L_0208,interior of the sun,T_1326,"Fossils are our best form of evidence about Earth history, including the history of life. Along with other geological evidence from rocks and structures, fossils even give us clues about past climates, the motions of plates, and other major geological events. Since the present is the key to the past, what we know about a type of organism that lives today can be applied to past environments. ",text,
L_0208,interior of the sun,T_1327,"That life on Earth has changed over time is well illustrated by the fossil record. Fossils in relatively young rocks resemble animals and plants that are living today. In general, fossils in older rocks are less similar to modern organisms. We would know very little about the organisms that came before us if there were no fossils. Modern technology has allowed scientists to reconstruct images and learn about the biology of extinct animals like dinosaurs! Click image to the left for more content. ",text,
L_0208,interior of the sun,T_1328,"By knowing something about the type of organism the fossil was, geologists can determine whether the region was terrestrial (on land) or marine (underwater) or even if the water was shallow or deep. The rock may give clues to whether the rate of sedimentation was slow or rapid. The amount of wear and fragmentation of a fossil allows scientists to learn about what happened to the region after the organism died; for example, whether it was exposed to wave action. ",text,
L_0208,interior of the sun,T_1329,The presence of marine organisms in a rock indicates that the region where the rock was deposited was once marine. Sometimes fossils of marine organisms are found on tall mountains indicating that rocks that formed on the seabed were uplifted. ,text,
L_0208,interior of the sun,T_1330,"By knowing something about the climate a type of organism lives in now, geologists can use fossils to decipher the climate at the time the fossil was deposited. For example, coal beds form in tropical environments but ancient coal beds are found in Antarctica. Geologists know that at that time the climate on the Antarctic continent was much warmer. Recall from Concept Plate Tectonics that Wegener used the presence of coal beds in Antarctica as one of the lines of evidence for continental drift. ",text,
L_0208,interior of the sun,T_1331,"An index fossil can be used to identify a specific period of time. Organisms that make good index fossils are distinctive, widespread, and lived briefly. Their presence in a rock layer can be used to identify rocks that were deposited at that period of time over a large area. ",text,
L_0208,interior of the sun,T_1332,Use this resource to answer the questions that follow. Clues to the End - Permian Extinction Click image to the left for more content. 1. Why is the paleocologists collecting samples? 2. What does he want to create from the fossil evidence? 3. How is this similar to forensic science? 4. Why is it important to understand insect feeding? 5. What has been discovered from these fossils? ,text,
L_0211,introduction to groundwater,T_1339,"Groundwater resides in aquifers, porous rock and sediment with water in between. Water is attracted to the soil particles, and capillary action, which describes how water moves through porous media, moves water from wet soil to dry areas. Aquifers are found at different depths. Some are just below the surface and some are found much deeper below the land surface. A region may have more than one aquifer beneath it and even most deserts are above aquifers. The source region for an aquifer beneath a desert is likely to be far away, perhaps in a mountainous area. ",text,
L_0211,introduction to groundwater,T_1340,"The amount of water that is available to enter groundwater in a region, called recharge, is influenced by the local climate, the slope of the land, the type of rock found at the surface, the vegetation cover, land use in the area, and water retention, which is the amount of water that remains in the ground. More water goes into the ground where there is a lot of rain, flat land, porous rock, exposed soil, and where water is not already filling the soil and rock. ",text,
L_0211,introduction to groundwater,T_1341,"The residence time of water in a groundwater aquifer can be from minutes to thousands of years. Groundwater is often called fossil water because it has remained in the ground for so long, often since the end of the ice ages. A diagram of groundwater flow through aquifers showing residence times. Deeper aquifers typically contain older ""fossil water."" Click image to the left or use the URL below. URL: ",text,
L_0212,intrusive and extrusive igneous rocks,T_1342,The rate at which magma cools determines whether an igneous rock is intrusive or extrusive. The cooling rate is reflected in the rocks texture. ,text,
L_0212,intrusive and extrusive igneous rocks,T_1343,"Igneous rocks are called intrusive when they cool and solidify beneath the surface. Intrusive rocks form plutons and so are also called plutonic. A pluton is an igneous intrusive rock body that has cooled in the crust. When magma cools within the Earth, the cooling proceeds slowly. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have visible crystals. Granite is the most common intrusive igneous rock (see Figure 1.1 for an example). Igneous rocks make up most of the rocks on Earth. Most igneous rocks are buried below the surface and covered with sedimentary rock, or are buried beneath the ocean water. In some places, geological processes have brought Granite is made of four minerals, all visible to the naked eye: feldspar (white), quartz (translucent), hornblende (black), and bi- otite (black, platy). igneous rocks to the surface. Figure 1.2 shows a landscape in Californias Sierra Nevada Mountains made of granite that has been raised to create mountains. Californias Sierra Nevada Mountains are intrusive igneous rock exposed at Earths surface. ",text,
L_0212,intrusive and extrusive igneous rocks,T_1343,"Igneous rocks are called intrusive when they cool and solidify beneath the surface. Intrusive rocks form plutons and so are also called plutonic. A pluton is an igneous intrusive rock body that has cooled in the crust. When magma cools within the Earth, the cooling proceeds slowly. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have visible crystals. Granite is the most common intrusive igneous rock (see Figure 1.1 for an example). Igneous rocks make up most of the rocks on Earth. Most igneous rocks are buried below the surface and covered with sedimentary rock, or are buried beneath the ocean water. In some places, geological processes have brought Granite is made of four minerals, all visible to the naked eye: feldspar (white), quartz (translucent), hornblende (black), and bi- otite (black, platy). igneous rocks to the surface. Figure 1.2 shows a landscape in Californias Sierra Nevada Mountains made of granite that has been raised to create mountains. Californias Sierra Nevada Mountains are intrusive igneous rock exposed at Earths surface. ",text,
L_0212,intrusive and extrusive igneous rocks,T_1344,"Igneous rocks are called extrusive when they cool and solidify above the surface. These rocks usually form from a volcano, so they are also called volcanic rocks (Figure 1.3). Extrusive igneous rocks cool much more rapidly than intrusive rocks. There is little time for crystals to form, so extrusive igneous rocks have tiny crystals (Figure 1.4). Some volcanic rocks have a different texture. The rock has large crystals set within a matrix of tiny crystals. In this Extrusive igneous rocks form after lava cools above the surface. Cooled lava forms basalt with no visible crystals. Why are there no visible crys- tals? Cooling rate and gas content create other textures (see Figure 1.5 for examples of different textures). Lavas that cool extremely rapidly may have a glassy texture. Those with many holes from gas bubbles have a vesicular texture. Different cooling rate and gas content resulted in these different textures. Click image to the left or use the URL below. URL: ",text,
L_0212,intrusive and extrusive igneous rocks,T_1344,"Igneous rocks are called extrusive when they cool and solidify above the surface. These rocks usually form from a volcano, so they are also called volcanic rocks (Figure 1.3). Extrusive igneous rocks cool much more rapidly than intrusive rocks. There is little time for crystals to form, so extrusive igneous rocks have tiny crystals (Figure 1.4). Some volcanic rocks have a different texture. The rock has large crystals set within a matrix of tiny crystals. In this Extrusive igneous rocks form after lava cools above the surface. Cooled lava forms basalt with no visible crystals. Why are there no visible crys- tals? Cooling rate and gas content create other textures (see Figure 1.5 for examples of different textures). Lavas that cool extremely rapidly may have a glassy texture. Those with many holes from gas bubbles have a vesicular texture. Different cooling rate and gas content resulted in these different textures. Click image to the left or use the URL below. URL: ",text,
L_0212,intrusive and extrusive igneous rocks,T_1344,"Igneous rocks are called extrusive when they cool and solidify above the surface. These rocks usually form from a volcano, so they are also called volcanic rocks (Figure 1.3). Extrusive igneous rocks cool much more rapidly than intrusive rocks. There is little time for crystals to form, so extrusive igneous rocks have tiny crystals (Figure 1.4). Some volcanic rocks have a different texture. The rock has large crystals set within a matrix of tiny crystals. In this Extrusive igneous rocks form after lava cools above the surface. Cooled lava forms basalt with no visible crystals. Why are there no visible crys- tals? Cooling rate and gas content create other textures (see Figure 1.5 for examples of different textures). Lavas that cool extremely rapidly may have a glassy texture. Those with many holes from gas bubbles have a vesicular texture. Different cooling rate and gas content resulted in these different textures. Click image to the left or use the URL below. URL: ",text,
L_0213,jupiter,T_1345,"Jupiter is enormous, the largest object in the solar system besides the Sun. Although Jupiter is over 1,300 times Earths volume, it has only 318 times the mass of Earth. Like the other gas giants, it is much less dense than Earth. Because Jupiter is so large, it reflects a lot of sunlight. Jupiter is extremely bright in the night sky; only the Moon and Venus are brighter (Figure 1.1). This brightness is all the more impressive because Jupiter is quite far from the Earth  5.20 AUs away. It takes Jupiter about 12 Earth years to orbit once around the Sun. ",text,
L_0213,jupiter,T_1346,"Astronauts trying to land a spaceship on the surface of Jupiter would find that there is no solid surface at all! Jupiter is made mostly of hydrogen, with some helium, and small amounts of other elements (Figure 1.2). Jupiters atmosphere is composed of hydrogen and helium. Deeper within the planet, pressure compresses the gases into a liquid. Some evidence suggests that Jupiter may have a small rocky core of heavier elements at its center. This image of Jupiter was taken by Voy- ager 2 in 1979. The colors were later enhanced to bring out more details. ",text,
L_0213,jupiter,T_1346,"Astronauts trying to land a spaceship on the surface of Jupiter would find that there is no solid surface at all! Jupiter is made mostly of hydrogen, with some helium, and small amounts of other elements (Figure 1.2). Jupiters atmosphere is composed of hydrogen and helium. Deeper within the planet, pressure compresses the gases into a liquid. Some evidence suggests that Jupiter may have a small rocky core of heavier elements at its center. This image of Jupiter was taken by Voy- ager 2 in 1979. The colors were later enhanced to bring out more details. ",text,
L_0213,jupiter,T_1347,"The upper layer of Jupiters atmosphere contains clouds of ammonia (NH3 ) in bands of different colors. These bands rotate around the planet, but also swirl around in turbulent storms. The Great Red Spot (Figure 1.3) is an enormous, oval-shaped storm found south of Jupiters equator. This storm is more than three times as wide as the entire Earth. Clouds in the storm rotate in a counterclockwise direction, making one complete turn every six days or so. The Great Red Spot has been on Jupiter for at least 300 years, since astronomers could first see the storm through telescopes. Do you think the Great Red Spot is a permanent feature on Jupiter? How could you know? This image of Jupiters Great Red Spot (upper right of image) was taken by the Voyager 1 spacecraft. The white storm just below the Great Red Spot is about the same diameter as Earth. ",text,
L_0213,jupiter,T_1348,"Jupiter has a very large number of moons  63 have been discovered so far. Four are big enough and bright enough to be seen from Earth, using no more than a pair of binoculars. These moons  Io, Europa, Ganymede, and Callisto were first discovered by Galileo in 1610, so they are sometimes referred to as the Galilean moons (Figure 1.4). The Galilean moons are larger than the dwarf planets Pluto, Ceres, and Eris. Ganymede is not only the biggest moon in the solar system; it is even larger than the planet Mercury! Scientists are particularly interested in Europa because it may be a place to find extraterrestrial life. What features might make a satellite so far from the Sun a candidate for life? Although the surface of Europa is a smooth layer of ice, there is evidence that there is an ocean of liquid water underneath (Figure 1.5). Europa also has a continual source of energy  it is heated as it is stretched and squashed by tidal forces from Jupiter. Numerous missions have been planned to explore Europa, including plans to drill through the ice and send a probe into the ocean. However, no such mission has yet been attempted. In 1979, two spacecraft  Voyager 1 and Voyager 2  visited Jupiter and its moons. Photos from the Voyager missions showed that Jupiter has a ring system. This ring system is very faint, so it is difficult to observe from Earth. This composite image shows the four Galilean moons and their sizes relative to the Great Red Spot. From top to bottom, the moons are Io, Europa, Ganymede, and Callisto. Jupiters Great Red Spot is in the background. Sizes are to scale. Click image to the left or use the URL below. URL: ",text,
L_0215,landforms from glacial erosion and deposition,T_1360,"Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL:  Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. ",text,
L_0215,landforms from glacial erosion and deposition,T_1360,"Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL:  Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. ",text,
L_0215,landforms from glacial erosion and deposition,T_1360,"Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL:  Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. ",text,
L_0215,landforms from glacial erosion and deposition,T_1360,"Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL:  Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. ",text,
L_0215,landforms from glacial erosion and deposition,T_1360,"Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL:  Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. ",text,
L_0215,landforms from glacial erosion and deposition,T_1361,"As glaciers flow, mechanical weathering loosens rock on the valley walls, which falls as debris on the glacier. Glaciers can carry rock of any size, from giant boulders to silt (Figure 1.6). These rocks can be carried for many kilometers for many years. ",text,
L_0215,landforms from glacial erosion and deposition,T_1362,Rocks carried by a glacier are eventually dropped. These glacial erratics are noticeable because they are a different rock type from the surrounding bedrock. ,text,
L_0215,landforms from glacial erosion and deposition,T_1363,Melting glaciers deposit all the big and small bits of rocky material they are carrying in a pile. These unsorted deposits of rock are called glacial till. Glacial till is found in different types of deposits. Linear rock deposits are called moraines. Geologists study moraines to figure out how far glaciers extended and how long it took them to melt away. Moraines are named by their location relative to the glacier: Lateral moraines form at the edges of the glacier as material drops onto the glacier from erosion of the valley walls. Medial moraines form where the lateral moraines of two tributary glaciers join together in the middle of a larger glacier (Figure 1.7). Ground moraines forms from sediments that were beneath the glacier and left behind after the glacier melts. Ground moraine sediments contribute to the fertile transported soils in many regions. Terminal moraines are long ridges of till left at the furthest point the glacier reached. End moraines are deposited where the glacier stopped for a long enough period to create a rocky ridge as it retreated. Long Island in New York is formed by two end moraines. ,text,
L_0215,landforms from glacial erosion and deposition,T_1364,"Several types of stratified deposits form in glacial regions but are not formed directly by the ice. Varves form where lakes are covered by ice in the winter. Dark, fine-grained clays sink to the bottom in winter, but melting ice in spring brings running water that deposits lighter colored sands. Each alternating dark/light layer represents one year of deposits. (a) An esker is a winding ridge of sand and gravel deposited under a glacier by a stream of meltwater. (b) A drumlin is an asymmetrical hill made of sediments that points in the direction the ice moved. Usually drumlins are found in groups called drumlin fields. Click image to the left or use the URL below. URL: ",text,
L_0216,landforms from groundwater erosion and deposition,T_1365,"Rainwater absorbs carbon dioxide (CO2 ) as it falls. The CO2 combines with water to form carbonic acid. The slightly acidic water sinks into the ground and moves through pore spaces in soil and cracks and fractures in rock. The flow of water underground is groundwater. Groundwater is described further in the chapter Water on Earth. Groundwater is a strong erosional force, as it works to dissolve away solid rock (Figure 1.1). Carbonic acid is especially good at dissolving the rock limestone. ",text,
L_0216,landforms from groundwater erosion and deposition,T_1366,"Working slowly over many years, groundwater travels along small cracks. The water dissolves and carries away the solid rock, gradually enlarging the cracks. Eventually, a cave may form (Figure 1.2). ",text,
L_0216,landforms from groundwater erosion and deposition,T_1367,"If the roof of a cave collapses, a sinkhole could form. Some sinkholes are large enough to swallow up a home or several homes in a neighborhood (Figure 1.3). Water flows through Russell Cave Na- tional Monument in Alabama. ",text,
L_0216,landforms from groundwater erosion and deposition,T_1367,"If the roof of a cave collapses, a sinkhole could form. Some sinkholes are large enough to swallow up a home or several homes in a neighborhood (Figure 1.3). Water flows through Russell Cave Na- tional Monument in Alabama. ",text,
L_0216,landforms from groundwater erosion and deposition,T_1368,"Groundwater carries dissolved minerals in solution. The minerals may then be deposited, for example, as stalag- mites or stalactites (Figure 1.4). Stalactites form as calcium carbonate drips from the ceiling of a cave, forming beautiful icicle-like formations. The word stalactite has a c, and it forms from the ceiling. Stalagmites form as calcium carbonate drips from the ceiling to the floor of a cave and then grow upwards. The g in stalagmite means it forms on the ground. If a stalactite and stalagmite join together, they form a column. One of the wonders of visiting a cave is to witness the beauty of these amazing and strangely captivating structures. Some of the largest, and most beautiful, natural crystals can be found in the Naica mine, in Mexico. These gypsum crystals were formed over thousands of years as groundwater, rich in calcium and sulfur flowed through an underground cave. Check it out: A relatively small sinkhole in a Georgia parking lot. Stalactites hang from the ceiling and stalagmites rise from the floor of Carlsbad Caverns in New Mexico. The large stalagmite on the right is almost tall enough to reach the ceiling (or a stalactite) and form a column. Click image to the left or use the URL below. URL: ",text,
L_0216,landforms from groundwater erosion and deposition,T_1368,"Groundwater carries dissolved minerals in solution. The minerals may then be deposited, for example, as stalag- mites or stalactites (Figure 1.4). Stalactites form as calcium carbonate drips from the ceiling of a cave, forming beautiful icicle-like formations. The word stalactite has a c, and it forms from the ceiling. Stalagmites form as calcium carbonate drips from the ceiling to the floor of a cave and then grow upwards. The g in stalagmite means it forms on the ground. If a stalactite and stalagmite join together, they form a column. One of the wonders of visiting a cave is to witness the beauty of these amazing and strangely captivating structures. Some of the largest, and most beautiful, natural crystals can be found in the Naica mine, in Mexico. These gypsum crystals were formed over thousands of years as groundwater, rich in calcium and sulfur flowed through an underground cave. Check it out: A relatively small sinkhole in a Georgia parking lot. Stalactites hang from the ceiling and stalagmites rise from the floor of Carlsbad Caverns in New Mexico. The large stalagmite on the right is almost tall enough to reach the ceiling (or a stalactite) and form a column. Click image to the left or use the URL below. URL: ",text,
L_0217,lithification of sedimentary rocks,T_1369,"Accumulated sediments harden into rock by lithification, as illustrated in the Figure 1.1. Two important steps are needed for sediments to lithify. 1. Sediments are squeezed together by the weight of overlying sediments on top of them. This is called com- paction. Cemented, non-organic sediments become clastic rocks. If organic material is included, they are bioclastic rocks. 2. Fluids fill in the spaces between the loose particles of sediment and crystallize to create a rock by cementation. The sediment size in clastic sedimentary rocks varies greatly (see Table in Sedimentary Rocks Classification). This cliff is made of sandstone. Sands were deposited and then lithified. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0221,location and direction,T_1381,How would you find Old Faithful? One way is by using latitude and longitude. Any location on Earths surface or on a map  can be described using these coordinates. Latitude and longitude are expressed as degrees that are divided into 60 minutes. Each minute is divided into 60 seconds. ,text,
L_0221,location and direction,T_1382,"A look on a reliable website shows us that Old Faithful Geyser is located at N44o 27 43. What does this mean? Latitude tells the distance north or south of the Equator. Latitude lines start at the Equator and circle around the planet. The North Pole is 90o N, with 90 degree lines in the Northern Hemisphere. Old Faithful is at 44 degrees, 27 minutes and 43 seconds north of the Equator. Thats just about exactly half way between the Equator and the North Pole! ",text,
L_0221,location and direction,T_1383,"The latitude mentioned above does not locate Old Faithful exactly, since a circle could be drawn that latitude north of the Equator. To locate Old Faithful we need another point - longitude. At Old Faithful the longitude is W110o 4957. Longitude lines are circles that go around the Earth from north to south, like the sections of an orange. Longitude is measured perpendicular to the Equator. The Prime Meridian is 0o longitude and passes through Greenwich, England. The International Date Line is the 180o meridian. Old Faithful is in the Western Hemisphere, between the Prime Meridian in the east and the International Date Line in the west. ",text,
L_0221,location and direction,T_1384,"An accurate location must take into account the third dimension. Elevation is the height above or below sea level. Sea level is the average height of the oceans surface or the midpoint between high and low tide. Sea level is the same all around Earth. Old Faithful is higher above sea level than most locations at 7,349 ft (2240 m). Of course, the highest point on Earth, Mount Everest, is much higher at 29,029 ft (8848 m). ",text,
L_0221,location and direction,T_1385,Satellites continually orbit Earth and can be used to indicate location. A global positioning system receiver detects radio signals from at least four nearby GPS satellites. The receiver measures the time it takes for radio signals to travel from a satellite and then calculates its distance from the satellite using the speed of radio signals. By calculating distances from each of the four satellites the receiver can triangulate to determine its location. You can use a GPS meter to tell you how to get to Old Faithful. ,text,
L_0221,location and direction,T_1386,"Direction is important if you want to go between two places. Directions are expressed as north (N), east (E), south (S), and west (W), with gradations in between. The most common way to describe direction in relation to the Earths surface is with a compass, a device with a floating needle that is actually a small magnet. The compass needle aligns itself with the Earths magnetic north pole. Since the magnetic north pole is 11.5 degrees offset from its geographic north pole on the axis of rotation, you must correct for this discrepancy. Map of the Visitor Center at Old Faithful, Yellowstone National Park, Wyoming. Without using a compass, we can say that to get to Old Faithful, you enter Yellowstone National Park at the South Entrance, drive north-northeast to West Thumb, and then drive west-northwest to Old Faithful. Click image to the left or use the URL below. URL: ",text,
L_0222,long term climate change,T_1387,"Many processes can cause climate to change. These include changes: In the amount of energy the Sun produces over years. In the positions of the continents over millions of years. In the tilt of Earths axis and orbit over thousands of years. That are sudden and dramatic because of random catastrophic events, such as a large asteroid impact. In greenhouse gases in the atmosphere, caused naturally or by human activities. ",text,
L_0222,long term climate change,T_1388,"The amount of energy the Sun radiates is variable. Sunspots are magnetic storms on the Suns surface that increase and decrease over an 11-year cycle (Figure 1.1). When the number of sunspots is high, solar radiation is also relatively high. But the entire variation in solar radiation is tiny relative to the total amount of solar radiation that there is, and there is no known 11-year cycle in climate variability. The Little Ice Age corresponded to a time when there were no sunspots on the Sun. Sunspots on the face of the Sun. ",text,
L_0222,long term climate change,T_1389,"Plate tectonic movements can alter climate. Over millions of years as seas open and close, ocean currents may distribute heat differently. For example, when all the continents are joined into one supercontinent (such as Pangaea), nearly all locations experience a continental climate. When the continents separate, heat is more evenly distributed. Plate tectonic movements may help start an ice age. When continents are located near the poles, ice can accumulate, which may increase albedo and lower global temperature. Low enough temperatures may start a global ice age. Plate motions trigger volcanic eruptions, which release dust and CO2 into the atmosphere. Ordinary eruptions, even large ones, have only a short-term effect on weather (Figure 1.2). Massive eruptions of the fluid lavas that create lava plateaus release much more gas and dust, and can change climate for many years. This type of eruption is exceedingly rare; none has occurred since humans have lived on Earth. ",text,
L_0222,long term climate change,T_1390,"The most extreme climate of recent Earth history was the Pleistocene. Scientists attribute a series of ice ages to variation in the Earths position relative to the Sun, known as Milankovitch cycles. The Earth goes through regular variations in its position relative to the Sun: 1. The shape of the Earths orbit changes slightly as it goes around the Sun. The orbit varies from more circular to more elliptical in a cycle lasting between 90,000 and 100,000 years. When the orbit is more elliptical, there is a greater difference in solar radiation between winter and summer. 2. The planet wobbles on its axis of rotation. At one extreme of this 27,000 year cycle, the Northern Hemisphere points toward the Sun when the Earth is closest to the Sun. Summers are much warmer and winters are much colder than now. At the opposite extreme, the Northern Hemisphere points toward the Sun when it is farthest from the Sun. An eruption like Sarychev Volcano (Kuril Islands, northeast of Japan) in 2009 would have very little impact on weather. This results in chilly summers and warmer winters. 3. The planets tilt on its axis varies between 22.1o and 24.5o . Seasons are caused by the tilt of Earths axis of rotation, which is at a 23.5o angle now. When the tilt angle is smaller, summers and winters differ less in temperature. This cycle lasts 41,000 years. When these three variations are charted out, a climate pattern of about 100,000 years emerges. Ice ages correspond closely with Milankovitch cycles. Since glaciers can form only over land, ice ages only occur when landmasses cover the polar regions. Therefore, Milankovitch cycles are also connected to plate tectonics. ",text,
L_0222,long term climate change,T_1391,"Since greenhouse gases trap the heat that radiates off the planets surfaces, what would happen to global temperatures if atmospheric greenhouse gas levels decreased? What if greenhouse gases increased? A decrease in greenhouse gas levels decreases global temperature and an increase raises global temperature. Greenhouse gas levels have varied throughout Earth history. For example, CO2 has been present at concentrations less than 200 parts per million (ppm) and more than 5,000 ppm. But for at least 650,000 years, CO2 has never risen above 300 ppm, during either glacial or interglacial periods (Figure 1.3). Natural processes add and remove CO2 from the atmosphere. Processes that add CO2 : volcanic eruptions decay or burning of organic matter. Processes that remove CO2 : absorption by plant and animal tissue. When plants are turned into fossil fuels, the CO2 in their tissue is stored with them. So CO2 is removed from the atmosphere. What does this do to Earths average temperature? What happens to atmospheric CO2 when the fossil fuels are burned? What happens to global temperatures? CO2 levels during glacial (blue) and inter- glacial (yellow) periods. Are CO2 levels relatively high or relatively low during in- terglacial periods? Current carbon diox- ide levels are at around 400 ppm, the highest level for the last 650,000 years. BP means years before present. ",text,
L_0224,magnetic evidence for seafloor spreading,T_1393,"On our transit to the Mid-Atlantic ridge, we tow a magnetometer behind the ship. Shipboard magnetometers reveal the magnetic polarity of the rock beneath them. The practice of towing a magnetometer began during WWII when navy ships towed magnetometers to search for enemy submarines. When scientists plotted the points of normal and reversed polarity on a seafloor map they made an astonishing discovery: the normal and reversed magnetic polarity of seafloor basalts creates a pattern. Stripes of normal polarity and reversed polarity alternate across the ocean bottom. Stripes form mirror images on either side of the mid-ocean ridges (Figure 1.1). Stripes end abruptly at the edges of continents, sometimes at a deep sea trench (Figure 1.2). The magnetic stripes are what created the Figure 1.1. Research cruises today tow magnetometers to add detail to existing magnetic polarity data. ",text,
L_0224,magnetic evidence for seafloor spreading,T_1394,"By combining magnetic polarity data from rocks on land and on the seafloor with radiometric age dating and fossil ages, scientists came up with a time scale for the magnetic reversals. The first four magnetic periods are: Brunhes normal - present to 730,000 years ago. Matuyama reverse - 730,000 years ago to 2.48 million years ago. Gauss normal - 2.48 to 3.4 million years ago. Gilbert reverse - 3.4 to 5.3 million years ago. The scientists noticed that the rocks got older with distance from the mid-ocean ridges. The youngest rocks were located at the ridge crest and the oldest rocks were located the farthest away, abutting continents. Scientists also noticed that the characteristics of the rocks and sediments changed with distance from the ridge axis as seen in the Table 1.1. Rock ages At ridge axis With distance from axis youngest becomes older Sediment thickness none becomes thicker Crust thickness Heat flow thinnest becomes thicker hottest becomes cooler Away from the ridge crest, sediment becomes older and thicker, and the seafloor becomes thicker. Heat flow, which indicates the warmth of a region, is highest at the ridge crest. The oldest seafloor is near the edges of continents or deep sea trenches and is less than 180 million years old (Figure something was happening to the older seafloor. Seafloor is youngest at the mid-ocean ridges and becomes progressively older with distance from the ridge. How can you explain the observations that scientists have made in the oceans? Why is rock younger at the ridge and oldest at the farthest points from the ridge? The scientists suggested that seafloor was being created at the ridge. Since the planet is not getting larger, they suggested that it is destroyed in a relatively short amount of geologic time. Click image to the left or use the URL below. URL: ",text,
L_0225,magnetic polarity evidence for continental drift,T_1395,"The next breakthrough in the development of the theory of plate tectonics came two decades after Wegeners death. Magnetite crystals are shaped like a tiny bar magnet. As basalt lava cools, the magnetite crystals line up in the magnetic field like tiny magnets. When the lava is completely cooled, the crystals point in the direction of magnetic north pole at the time they form. How do you expect this would help scientists see whether continents had moved or not? As a Wegener supporter, (and someone who is omniscient), you have just learned of a new tool that may help you. A magnetometer is a device capable of measuring the magnetic field intensity. This allows you to look at the magnetic properties of rocks in many locations. First, youre going to look at rocks on land. Which rocks should you seek out for study? ",text,
L_0225,magnetic polarity evidence for continental drift,T_1396,"Geologists noted important things about the magnetic polarity of different aged rocks on the same continent: Magnetite crystals in fresh volcanic rocks point to the current magnetic north pole (Figure 1.2) no matter what continent or where on the continent the rocks are located. Older rocks that are the same age and are located on the same continent point to the same location, but that location is not the current north magnetic pole. Older rocks that are of different ages do not point to the same locations or to the current magnetic north pole. In other words, although the magnetite crystals were pointing to the magnetic north pole, the location of the pole seemed to wander. Scientists were amazed to find that the north magnetic pole changed location over time (Figure Can you figure out the three possible explanations for this? They are: The location of the north magnetic north pole 80 million years before present (mybp), then 60, 40, 20, and now. 1. The continents remained fixed and the north magnetic pole moved. 2. The north magnetic pole stood still and the continents moved. 3. Both the continents and the north pole moved. ",text,
L_0225,magnetic polarity evidence for continental drift,T_1396,"Geologists noted important things about the magnetic polarity of different aged rocks on the same continent: Magnetite crystals in fresh volcanic rocks point to the current magnetic north pole (Figure 1.2) no matter what continent or where on the continent the rocks are located. Older rocks that are the same age and are located on the same continent point to the same location, but that location is not the current north magnetic pole. Older rocks that are of different ages do not point to the same locations or to the current magnetic north pole. In other words, although the magnetite crystals were pointing to the magnetic north pole, the location of the pole seemed to wander. Scientists were amazed to find that the north magnetic pole changed location over time (Figure Can you figure out the three possible explanations for this? They are: The location of the north magnetic north pole 80 million years before present (mybp), then 60, 40, 20, and now. 1. The continents remained fixed and the north magnetic pole moved. 2. The north magnetic pole stood still and the continents moved. 3. Both the continents and the north pole moved. ",text,
L_0225,magnetic polarity evidence for continental drift,T_1397,"How do you figure out which of those three possibilities is correct? You decide to look at magnetic rocks on different continents. Geologists noted that for rocks of the same age but on different continents, the little magnets pointed to different magnetic north poles. 400 million-year-old magnetite in Europe pointed to a different north magnetic pole than magnetite of the same age in North America. 250 million years ago, the north poles were also different for the two continents. Now look again at the three possible explanations. Only one can be correct. If the continents had remained fixed while the north magnetic pole moved, there must have been two separate north poles. Since there is only one north pole today, what is the best explanation? The only reasonable explanation is that the magnetic north pole has remained fixed but that the continents have moved. ",text,
L_0225,magnetic polarity evidence for continental drift,T_1398,"How does this help you to provide evidence for continental drift? To test the idea that the pole remained fixed but the continents moved, geologists fitted the continents together as Wegener had done. It worked! There has only been one magnetic north pole and the continents have drifted (Figure 1.4). They named the phenomenon of the magnetic pole that seemed to move but actually did not apparent polar wander. On the left: The apparent north pole for Europe and North America if the continents were always in their current locations. The two paths merge into one if the continents are allowed to drift. This evidence for continental drift gave geologists renewed interest in understanding how continents could move about on the planets surface. ",text,
L_0226,maps,T_1399,"Topographic maps represent the locations of geographical features, such as hills and valleys. Topographic maps use contour lines to show different elevations. A contour line is a line of equal elevation. If you walk along a contour line you will not go uphill or downhill. Topographic maps are also called contour maps. The rules of topographic maps are: Each line connects all points of a specific elevation. Contour lines never cross since a single point can only have one elevation. Every fifth contour line is bolded and labeled. Adjacent contour lines are separated by a constant difference in elevation (such as 20 ft or 100 ft). The difference in elevation is the contour interval, which is indicated in the map legend. Scales indicate horizontal distance and are also found on the map legend. Old Faithful erupting, Yellowstone Na- tional Park. While the Figure 1.1 isnt exactly the same view as the map at the top of this concept, it is easy to see the main features. Hills, forests, development, and trees are all seen around Old Faithful. ",text,
L_0226,maps,T_1400,"A bathymetric map is like a topographic map with the contour lines representing depth below sea level, rather than height above. Numbers are low near sea level and become higher with depth. Kilauea is the youngest volcano found above sea level in Hawaii. On the flank of Kilauea is an even younger volcano called Loihi. The bathymetric map pictured in the Figure 1.2 shows the form of Loihi. Loihi volcano growing on the flank of Kilauea volcano in Hawaii. Black lines in the inset show the land surface above sea level and blue lines show the topography below sea level. A geologic map of the region around Old Faithful, Yellowstone National Park. ",text,
L_0226,maps,T_1400,"A bathymetric map is like a topographic map with the contour lines representing depth below sea level, rather than height above. Numbers are low near sea level and become higher with depth. Kilauea is the youngest volcano found above sea level in Hawaii. On the flank of Kilauea is an even younger volcano called Loihi. The bathymetric map pictured in the Figure 1.2 shows the form of Loihi. Loihi volcano growing on the flank of Kilauea volcano in Hawaii. Black lines in the inset show the land surface above sea level and blue lines show the topography below sea level. A geologic map of the region around Old Faithful, Yellowstone National Park. ",text,
L_0226,maps,T_1401,A geologic map shows the geological features of a region (see Figure 1.3 for an example). Rock units are color- coded and identified in a key. Faults and folds are also shown on geologic maps. The geology is superimposed on a topographic map to give a more complete view of the geology of the region. Click image to the left or use the URL below. URL: ,text,
L_0227,mars,T_1402,"Mars is the fourth planet from the Sun, and the first planet beyond Earths orbit (Figure 1.1). Mars is a quite different from Earth and yet more similar than any other planet. Mars is smaller, colder, drier, and appears to have no life, but volcanoes are common to both planets and Mars has many. Mars is easy to observe, so Mars has been studied more thoroughly than any other extraterrestrial planet. Space probes, rovers, and orbiting satellites have all yielded information to planetary geologists. Although no humans have ever set foot on Mars, both NASA and the European Space Agency have set goals of sending people to Mars sometime between 2030 and 2040. This image of Mars, taken by the Hubble Space Telescope in October, 2005, shows the planets red color, a small ice cap on the south pole, and a dust storm. ",text,
L_0227,mars,T_1403,"Viewed from Earth, Mars is reddish in color. The ancient Greeks and Romans named the planet after the god of war. The surface is not red from blood but from large amounts of iron oxide in the soil. The Martian atmosphere is very thin relative to Earths and has much lower atmospheric pressure. Although the atmosphere is made up mostly of carbon dioxide, the planet has only a weak greenhouse effect, so temperatures are only slightly higher than if the planet had no atmosphere. ",text,
L_0227,mars,T_1404,"Mars has mountains, canyons, and other features similar to Earth. Some of these surface features are amazing for their size! Olympus Mons is a shield volcano, similar to the volcanoes that make up the Hawaiian Islands. But Olympus Mons is also the largest mountain in the solar system (Figure 1.2). Mars also has the largest canyon in the solar system, Valles Marineris (Figure 1.3). ",text,
L_0227,mars,T_1405,"It was previously believed that water cannot stay in liquid form on Mars because the atmospheric pressure is too low. However, there is a lot of water in the form of ice and even prominent ice caps (Figure 1.4). Scientists also think Olympus Mons is about 27 km (16.7 miles/88,580 ft) above the Martian sur- face, more than three times taller than Mount Everest. The volcanos base is about the size of the state of Arizona. Valles Marineris is 4,000 km (2,500 mi) long, as long as Europe is wide, and one-fifth the circumference of Mars. The canyon is 7 km (4.3 mi) deep. By comparison, the Grand Canyon on Earth is only 446 km (277 mi) long and about 2 km (1.2 mi) deep. that there is a lot of ice present just under the Martian surface. This ice can melt when volcanoes erupt, and water can flow across the surface. In late 2015, NASA confirmed the presence of water on Mars. Scientists think that water once flowed over the Martian surface because there are surface features that look like water-eroded canyons. The presence of water on Mars suggests that it might have been possible for life to exist on Mars in the past. ",text,
L_0227,mars,T_1405,"It was previously believed that water cannot stay in liquid form on Mars because the atmospheric pressure is too low. However, there is a lot of water in the form of ice and even prominent ice caps (Figure 1.4). Scientists also think Olympus Mons is about 27 km (16.7 miles/88,580 ft) above the Martian sur- face, more than three times taller than Mount Everest. The volcanos base is about the size of the state of Arizona. Valles Marineris is 4,000 km (2,500 mi) long, as long as Europe is wide, and one-fifth the circumference of Mars. The canyon is 7 km (4.3 mi) deep. By comparison, the Grand Canyon on Earth is only 446 km (277 mi) long and about 2 km (1.2 mi) deep. that there is a lot of ice present just under the Martian surface. This ice can melt when volcanoes erupt, and water can flow across the surface. In late 2015, NASA confirmed the presence of water on Mars. Scientists think that water once flowed over the Martian surface because there are surface features that look like water-eroded canyons. The presence of water on Mars suggests that it might have been possible for life to exist on Mars in the past. ",text,
L_0227,mars,T_1405,"It was previously believed that water cannot stay in liquid form on Mars because the atmospheric pressure is too low. However, there is a lot of water in the form of ice and even prominent ice caps (Figure 1.4). Scientists also think Olympus Mons is about 27 km (16.7 miles/88,580 ft) above the Martian sur- face, more than three times taller than Mount Everest. The volcanos base is about the size of the state of Arizona. Valles Marineris is 4,000 km (2,500 mi) long, as long as Europe is wide, and one-fifth the circumference of Mars. The canyon is 7 km (4.3 mi) deep. By comparison, the Grand Canyon on Earth is only 446 km (277 mi) long and about 2 km (1.2 mi) deep. that there is a lot of ice present just under the Martian surface. This ice can melt when volcanoes erupt, and water can flow across the surface. In late 2015, NASA confirmed the presence of water on Mars. Scientists think that water once flowed over the Martian surface because there are surface features that look like water-eroded canyons. The presence of water on Mars suggests that it might have been possible for life to exist on Mars in the past. ",text,
L_0227,mars,T_1406,"Mars has two very small moons that are irregular rocky bodies (Figure 1.5). Phobos and Deimos are named after characters in Greek mythology  the two sons of Ares, who followed their father into war. Ares is equivalent to the Roman god Mars. Mars has two small moons, Phobos (left) and Deimos (right). Both were discovered in 1877 and are thought to be captured asteroids. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0229,measuring earthquake magnitude,T_1408,"A seismograph produces a graph-like representation of the seismic waves it receives and records them onto a seismogram (Figure 1.1). Seismograms contain information that can be used to determine how strong an earthquake was, how long it lasted, and how far away it was. Modern seismometers record ground motions using electronic motion detectors. The data are then kept digitally on a computer. If a seismogram records P-waves and surface waves but not S-waves, the seismograph was on the other side of the Earth from the earthquake. The amplitude of the waves can be used to determine the magnitude of the earthquake, which will be discussed in a later section. ",text,
L_0229,measuring earthquake magnitude,T_1409,The seismogram in the introduction shows: foreshocks. the arrival of the P-waves. the arrival of the S-waves. the arrival of the surface waves (very hard to pick out). aftershocks. the times when all of these things occur. These seismograms show the arrival of P- waves and S-waves. The surface waves arrive just after the S-waves and are diffi- cult to distinguish. Time is indicated on the horizontal portion (or x-axis) of the graph. Click image to the left or use the URL below. URL: ,text,
L_0230,mechanical weathering,T_1410,"Mechanical weathering (also called physical weathering) breaks rock into smaller pieces. These smaller pieces are just like the bigger rock, but smaller. That means the rock has changed physically without changing its composition. The smaller pieces have the same minerals, in just the same proportions as the original rock. ",text,
L_0230,mechanical weathering,T_1411,"There are many ways that rocks can be broken apart into smaller pieces. Ice wedging is the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point (Figure 1.1). Ice wedging works quickly, breaking apart rocks in areas with temperatures that cycle above and below freezing in the day and night, and also that cycle above and below freezing with the seasons. Ice wedging breaks apart so much rock that large piles of broken rock are seen at the base of a hillside, as rock fragments separate and tumble down. Ice wedging is common in Earths polar regions and mid latitudes, and also at higher elevations, such as in the mountains. ",text,
L_0230,mechanical weathering,T_1412,"Abrasion is another form of mechanical weathering. In abrasion, one rock bumps against another rock. Gravity causes abrasion as a rock tumbles down a mountainside or cliff. Moving water causes abrasion as particles in the water collide and bump against one another. Strong winds carrying pieces of sand can sandblast surfaces. Ice in glaciers carries many bits and pieces of rock. Rocks embedded at the bottom of the glacier scrape against the rocks below. Abrasion makes rocks with sharp or jagged edges smooth and round. If you have ever collected beach glass or cobbles from a stream, you have witnessed the work of abrasion (Figure 1.2). ",text,
L_0230,mechanical weathering,T_1413,"Now that you know what mechanical weathering is, can you think of other ways it could happen? Plants and animals can do the work of mechanical weathering (Figure 1.3). This could happen slowly as a plants roots grow into a crack or fracture in rock and gradually grow larger, wedging open the crack. Burrowing animals can also break apart rock as they dig for food or to make living spaces for themselves. ",text,
L_0230,mechanical weathering,T_1414,"Human activities are responsible for enormous amounts of mechanical weathering, by digging or blasting into rock to build homes, roads, and subways, or to quarry stone. (a) Humans are tremendous agents of mechanical weathering. (b) Salt weathering of building stone on the island of Gozo, Malta. ",text,
L_0231,mercury,T_1415,"The smallest planet, Mercury, is the planet closest to the Sun. Because Mercury is so close to the Sun, it is difficult to observe from Earth, even with a telescope. However, the Mariner 10 spacecraft, shown in Figure 1.1, visited Mercury from 1974 to 1975. The MESSENGER spacecraft has been studying Mercury in detail since 2005. The craft is currently in orbit around the planet, where it is creating detailed maps. MESSENGER stands for Mercury Surface, Space Environment, Geochemistry and Ranging. (a) Mariner 10 made three flybys of Mercury in 1974 and 1975. (b) A 2008 image of compiled from a flyby by MESSENGER. As Figure 1.2 shows, the surface of Mercury is covered with craters, like Earths Moon. Ancient impact craters means that for billions of years Mercury hasnt changed much geologically. Also, with very little atmosphere, the processes of weathering and erosion do not wear down structures on the planet. ",text,
L_0231,mercury,T_1416,"Mercury is named for the Roman messenger god, who could run extremely quickly, just as the planet moves very quickly in its orbit around the Sun. A year on Mercury  the length of time it takes to orbit the Sun  is just 88 Earth days. Despite its very short years, Mercury has very long days. A day is defined as the time it takes a planet to turn on its axis. Mercury rotates slowly on its axis, turning exactly three times for every two times it orbits the Sun. Therefore, each day on Mercury is 57 Earth days long. In other words, on Mercury, a year is only a Mercury day and a half long! ",text,
L_0231,mercury,T_1417,"Mercury is close to the Sun, so it can get very hot. However, Mercury has virtually no atmosphere, no water to insulate the surface, and it rotates very slowly. For these reasons, temperatures on the surface of Mercury vary widely. In direct sunlight, the surface can be as hot as 427 C (801 F). On the dark side, or in the shadows inside craters, the surface can be as cold as -183 C (-297 F)! Although most of Mercury is extremely dry, scientists think Mercury is covered with craters, like Earths Moon. MESSENGER has taken extremely detailed pictures of the planets surface. there may be a small amount of water in the form of ice at the poles of Mercury, in areas that never receive direct sunlight. ",text,
L_0231,mercury,T_1418,"Figure 1.3 shows a diagram of Mercurys interior. Mercury is one of the densest planets. Its relatively large, liquid core, made mostly of melted iron, takes up about 42% of the planets volume. ",text,
L_0232,mercury pollution,T_1419,"Mercury is released into the atmosphere when coal is burned (Figure 1.1). But breathing the mercury is not harmful. In the atmosphere, the mercury forms small droplets that are deposited in water or sediments. ",text,
L_0232,mercury pollution,T_1420,"Do you know why you are supposed to eat large predatory fish like tuna infrequently? It is because of the bioaccu- mulation of mercury in those species. Some pollutants remain in an organism throughout its life, a phenomenon called bioaccumulation. In this process, an organism accumulates the entire amount of a toxic compound that it consumes over its lifetime. Not all substances bioaccumulate. Can you name one that does not? Aspirin does not bioaccumulate; if it did, a person would quickly accumulate a toxic amount in her body. Compounds that bioaccumulate are usually stored in the organisms fat. In the sediments, bacteria convert the droplets to the hazardous compound methyl mercury. Bacteria and plankton store all of the mercury from all of the seawater they ingest (Figure 1.2). A small fish that eats bacteria and plankton accumulates all of the mercury from all of the tiny creatures it eats over its lifetime. A big fish accumulates all of the mercury from all of the small fish it eats over its lifetime. For a tuna at the top of the food chain, thats a lot of mercury. Historic increases of mercury in the atmo- sphere: blue is volcanic eruptions; brown, purple, and pink are human-caused. The red region shows the effect of industrial- ization on atmospheric mercury. So tuna pose a health hazard to anything that eats them because their bodies are so high in mercury. This is why the government recommends limits on the amount of tuna that people eat. Limiting intake of large predatory fish is especially important for children and pregnant women. If the mercury just stayed in a persons fat, it would not be harmful, but that fat is used when a woman is pregnant or nursing a baby. A person will also get the mercury into her system when she (or he) burns the fat while losing weight. ",text,
L_0232,mercury pollution,T_1421,"Methyl mercury poisoning can cause nervous system or brain damage, especially in infants and children. Children may experience brain damage or developmental delays. The phrase mad as a hatter was common when Lewis Carroll wrote his Alice in Wonderland stories. It was based on symptoms suffered by hatters who were exposed to mercury and experienced mercury poisoning while using the metal to make hats (Figure 1.3). Like mercury, other metals and VOCS can bioaccumulate, causing harm to animals and people high on the food chain. Mercury, a potent neurotoxin, has been flowing into the San Francisco Bay since the Gold Rush Era. It has settled in the bays mud and made its way up the food chain, endangering wildlife and making many fish unsafe to eat. Now a multi-billion-dollar plan aims to clean it up. Click image to the left or use the URL below. URL: ",text,
L_0233,mesosphere,T_1422,"Above the stratosphere is the mesosphere. Temperatures in the mesosphere decrease with altitude. Because there are few gas molecules in the mesosphere to absorb the Suns radiation, the heat source is the stratosphere below. The mesosphere is extremely cold, especially at its top, about -90o C (-130o F). ",text,
L_0233,mesosphere,T_1423,"The air in the mesosphere has extremely low density: 99.9% of the mass of the atmosphere is below the mesosphere. As a result, air pressure is very low (Figure 1.1). A person traveling through the mesosphere would experience severe burns from ultraviolet light since the ozone layer, which provides UV protection, is in the stratosphere below. There would be almost no oxygen for breathing. And, of course, your blood would boil at normal body temperature. Click image to the left or use the URL below. URL: ",text,
L_0236,metamorphic rock classification,T_1430,"Table 1.1 shows some common metamorphic rocks and their original parent rock. Picture Rock Name Slate Type of Rock Foliated Metamorphic Comments Phyllite Foliated Metamorphism of slate, but under greater heat and pressure than slate Schist Foliated Often derived from meta- morphism of claystone or shale; metamorphosed under more heat and pres- sure than phyllite Gneiss Foliated Metamorphism of various different rocks, under ex- treme conditions of heat and pressure Hornfels Non-foliated Contact metamorphism of various different rock types Metamorphism of shale Picture Rock Name Comments Quartzite Type of Metamorphic Rock Non-foliated Marble Non-foliated Metamorphism of lime- stone Metaconglomerate Non-foliated Metamorphism of con- glomerate Metamorphism of quartz sandstone Click image to the left or use the URL below. URL: ",text,
L_0237,metamorphic rocks,T_1431,"Any type of rock - igneous, sedimentary, or metamorphic  can become a metamorphic rock. All that is needed is enough heat and/or pressure to alter the existing rocks physical or chemical makeup without melting the rock entirely. Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. The need for stability may cause the structure of minerals to rearrange and form new minerals. Ions may move between minerals to create minerals of different chemical composition. Hornfels, with its alternating bands of dark and light crystals, is a good example of how minerals rearrange themselves during metamorphism. Hornfels is shown in the table for the ""Metamorphic Rock Classification"" concept. ",text,
L_0237,metamorphic rocks,T_1432,"Extreme pressure may also lead to foliation, the flat layers that form in rocks as the rocks are squeezed by pressure (Figure 1.1). Foliation normally forms when pressure is exerted in only one direction. Metamorphic rocks may also be non-foliated. Quartzite and marble, shown in the concept ""Metamorphic Rock Classification,"" are non-foliated. A foliated metamorphic rock. ",text,
L_0237,metamorphic rocks,T_1433,The two main types of metamorphism are both related to heat within Earth: 1. Regional metamorphism: Changes in enormous quantities of rock over a wide area caused by the extreme pressure from overlying rock or from compression caused by geologic processes. Deep burial exposes the rock to high temperatures. 2. Contact metamorphism: Changes in a rock that is in contact with magma. The changes occur because of the magmas extreme heat. Click image to the left or use the URL below. URL: ,text,
L_0238,meteors,T_1434,"A meteor, such as in Figure 1.1, is a streak of light across the sky. People call them shooting stars but they are actually small pieces of matter burning up as they enter Earths atmosphere from space. Meteors are called meteoroids before they reach Earths atmosphere. Meteoroids are smaller than asteroids and range from the size of boulders down to the size of tiny sand grains. Still smaller objects are called interplanetary dust. When Earth passes through a cluster of meteoroids, there is a meteor shower. These clusters are often remnants left behind by comet tails. ",text,
L_0238,meteors,T_1435,"Although most meteors burn up in the atmosphere, larger meteoroids may strike the Earths surface to create a meteorite. Meteorites are valuable to scientists because they provide clues about our solar system. Many meteorites are from asteroids that formed when the solar system formed (Figure 1.2). A few meteorites are made of rocky material that is thought to have come from Mars when an asteroid impact shot material off the Martian surface and into space. Click image to the left or use the URL below. URL: ",text,
L_0238,meteors,T_1435,"Although most meteors burn up in the atmosphere, larger meteoroids may strike the Earths surface to create a meteorite. Meteorites are valuable to scientists because they provide clues about our solar system. Many meteorites are from asteroids that formed when the solar system formed (Figure 1.2). A few meteorites are made of rocky material that is thought to have come from Mars when an asteroid impact shot material off the Martian surface and into space. Click image to the left or use the URL below. URL: ",text,
L_0240,milky way,T_1438,"The Milky Way Galaxy, which is our galaxy. The Milky Way is made of millions of stars along with a lot of gas and dust. It looks different from other galaxies because we are looking at the main disk from within the galaxy. Astronomers estimate that the Milky Way contains 200 to 400 billion stars. ",text,
L_0240,milky way,T_1439,"Although it is difficult to know what the shape of the Milky Way Galaxy is because we are inside of it, astronomers have identified it as a typical spiral galaxy containing about 200 billion to 400 billion stars (Figure 1.1). An artists rendition of what astronomers think the Milky Way Galaxy would look like seen from above. The Sun is located approximately where the arrow points. Like other spiral galaxies, our galaxy has a disk, a central bulge, and spiral arms. The disk is about 100,000 light- years across and 3,000 light-years thick. Most of the Galaxys gas, dust, young stars, and open clusters are in the disk. What evidence do astronomers find that lets them know that the Milky Way is a spiral galaxy? 1. The shape of the galaxy as we see it (Figure 1.2). 2. The velocities of stars and gas in the galaxy show a rotational motion. 3. The gases, color, and dust are typical of spiral galaxies. The central bulge is about 12,000 to 16,000 light-years wide and 6,000 to 10,000 light-years thick. The central bulge contains mostly older stars and globular clusters. Some recent evidence suggests the bulge might not be spherical, but is instead shaped like a bar. The bar might be as long as 27,000 light-years long. The disk and bulge are surrounded by a faint, spherical halo, which also contains old stars and globular clusters. Astronomers have discovered that there is a gigantic black hole at the center of the galaxy. The Milky Way Galaxy is a big place. If our solar system were the size of your fist, the Galaxys disk would still be An infrared image of the Milky Way shows the long thin line of stars and the central bulge typical of spiral galaxies. wider than the entire United States! ",text,
L_0240,milky way,T_1439,"Although it is difficult to know what the shape of the Milky Way Galaxy is because we are inside of it, astronomers have identified it as a typical spiral galaxy containing about 200 billion to 400 billion stars (Figure 1.1). An artists rendition of what astronomers think the Milky Way Galaxy would look like seen from above. The Sun is located approximately where the arrow points. Like other spiral galaxies, our galaxy has a disk, a central bulge, and spiral arms. The disk is about 100,000 light- years across and 3,000 light-years thick. Most of the Galaxys gas, dust, young stars, and open clusters are in the disk. What evidence do astronomers find that lets them know that the Milky Way is a spiral galaxy? 1. The shape of the galaxy as we see it (Figure 1.2). 2. The velocities of stars and gas in the galaxy show a rotational motion. 3. The gases, color, and dust are typical of spiral galaxies. The central bulge is about 12,000 to 16,000 light-years wide and 6,000 to 10,000 light-years thick. The central bulge contains mostly older stars and globular clusters. Some recent evidence suggests the bulge might not be spherical, but is instead shaped like a bar. The bar might be as long as 27,000 light-years long. The disk and bulge are surrounded by a faint, spherical halo, which also contains old stars and globular clusters. Astronomers have discovered that there is a gigantic black hole at the center of the galaxy. The Milky Way Galaxy is a big place. If our solar system were the size of your fist, the Galaxys disk would still be An infrared image of the Milky Way shows the long thin line of stars and the central bulge typical of spiral galaxies. wider than the entire United States! ",text,
L_0240,milky way,T_1440,"Our solar system, including the Sun, Earth, and all the other planets, is within one of the spiral arms in the disk of the Milky Way Galaxy. Most of the stars we see in the sky are relatively nearby stars that are also in this spiral arm. We are about 26,000 light-years from the center of the galaxy, a little more than halfway out from the center of the galaxy to the edge. Just as Earth orbits the Sun, the Sun and solar system orbit the center of the Galaxy. One orbit of the solar system takes about 225 to 250 million years. The solar system has orbited 20 to 25 times since it formed 4.6 billion years ago. Astronomers have recently discovered that at the center of the Milky Way, and most other galaxies, is a supermassive black hole, although a black hole cannot be seen. This video describes the solar system in which we live. It is located in an outer edge of the Milky Way galaxy, which spans 100,000 light years. Click image to the left or use the URL below. URL:  The Universe contains many billions of stars and there are many billions of galaxies. Our home, the Milky Way galaxy, is only one. Click image to the left or use the URL below. URL: ",text,
L_0246,moon,T_1473,"The Moon is Earths only natural satellite, a body that moves around a larger body in space. The Moon orbits Earth for the same reason Earth orbits the Sun  gravity. The Moon is 3,476 km in diameter, about one-fourth the size of Earth. The satellite is also not as dense as the Earth; gravity on the Moon is only one-sixth as strong as it is on Earth. An astronaut can jump six times as high on the Moon as on Earth! The Moon makes one complete orbit around the Earth every 27.3 days. The Moon also rotates on its axis once every 27.3 days. Do you know what this means? The same side of the Moon always faces Earth, so that side of the Moon is what we always see in the night sky (Figure 1.1). The Moon makes no light of its own, but instead only reflects light from the Sun. (a) The near side of the Moon faces Earth continually. It has a thinner crust with many more maria (flat areas of basaltic rock). (b) The far side of the Moon has only been seen by spacecraft. It has a thicker crust and far fewer maria (flat areas of basaltic rock). ",text,
L_0246,moon,T_1474,"The Moon has no atmosphere. Since an atmosphere moderates temperature, the Moons average surface temperature during the day is approximately 225 F, but drops to -243 F at night. The coldest temperatures, around -397 F, occur in craters in the permanently shaded south polar basin. These are among the coldest temperatures recorded in the entire solar system. Earths landscape is extremely varied, with mountains, valleys, plains and hills. This landscape is always changing as plate tectonics builds new features and weathering and erosion destroys them. The landscape of the Moon is very different. With no plate tectonics, features are not built. With no atmosphere, features are not destroyed. Still, the Moon has a unique surface. Lunar surface features include the bowl-shaped craters that are caused by meteorite impacts (Figure 1.2). If Earth did not have plate tectonics or erosion, its surface would also be covered with meteorite craters. Even from Earth, the Moon has visible dark areas and light areas. The dark areas are called maria, which means seas because thats what the ancients thought they were. In fact, the maria are not water but solid, flat areas of basaltic lava. From about 3.0 to 3.5 billion years ago the Moon was continually bombarded by meteorites. Some of these meteorites were so large that they broke through the Moons newly formed surface. Then, magma flowed out and filled the craters. Scientists estimate this meteorite-caused volcanic activity on the Moon ceased about 1.2 billion years ago, but most occurred long before that. The lighter parts of the Moon are called terrae or highlands (Figure 1.3). The terrae are higher than the maria and A crater on the surface of the Moon. include several high mountain ranges. The terrae are the light silicate minerals that precipitated out of the ancient magma ocean and formed the early lunar crust. There are no lakes, rivers, or even small puddles anywhere to be found on the Moons surface, but water in the form of ice has been found in the extremely cold craters and bound up in the lunar soil. Despite the possible presence of water, the lack of an atmosphere and the extreme temperatures make it no surprise to scientists that the Moon has absolutely no evidence of life. Life from Earth has visited the Moon and there are footprints of astronauts on the lunar surface. With no wind, rain, or living thing to disturb them, these footprints will remain as long as the Moon exists. Only an impact with a meteorite could destroy them. ",text,
L_0246,moon,T_1475,"Like Earth, the Moon has a distinct crust, mantle, and core. What is known about the Moons interior was determined from the analysis of rock samples gathered by astronauts and from unmanned spacecraft sent to the Moon (Figure The Moons small core, 600 to 800 kilometers in diameter, is mostly iron with some sulfur and nickel. The mantle is composed of the minerals olivine and orthopyroxene. Analysis of Moon rocks indicates that there may also be high levels of iron and titanium in the lunar mantle. A close-up of the Moon, showing maria (the dark areas) and terrae (the light areas); maria covers around 16% of the Moons surface, mostly on the side of the Moon we see. LCROSS crashed into the Moon in May 2009. This QUEST video describes the mission. After watching, look up the mission to see what they found! Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0246,moon,T_1475,"Like Earth, the Moon has a distinct crust, mantle, and core. What is known about the Moons interior was determined from the analysis of rock samples gathered by astronauts and from unmanned spacecraft sent to the Moon (Figure The Moons small core, 600 to 800 kilometers in diameter, is mostly iron with some sulfur and nickel. The mantle is composed of the minerals olivine and orthopyroxene. Analysis of Moon rocks indicates that there may also be high levels of iron and titanium in the lunar mantle. A close-up of the Moon, showing maria (the dark areas) and terrae (the light areas); maria covers around 16% of the Moons surface, mostly on the side of the Moon we see. LCROSS crashed into the Moon in May 2009. This QUEST video describes the mission. After watching, look up the mission to see what they found! Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0248,natural gas power,T_1480,"Natural gas, often known simply as gas, is composed mostly of the hydrocarbon methane. The amount of natural gas being extracted and used in the Untied States is increasing rapidly. ",text,
L_0248,natural gas power,T_1481,"Natural gas forms under the same conditions that create oil. Organic material buried in the sediments harden to become a shale formation that is the source of the gas. Although natural gas forms at higher temperatures than crude oil, the two are often found together. The largest natural gas reserves in the United States are in the Appalachian Basin, North Dakota and Montana, Texas, and the Gulf of Mexico region (Figure 1.1). California also has natural gas, found mostly in the Central Valley. In the northern Sacramento Valley and the Sacramento Delta, a sediment-filled trough formed along a location where crust was pushed together (an ancient convergent margin). Gas production in the lower 48 United States. ",text,
L_0248,natural gas power,T_1482,"Like crude oil, natural gas must be processed before it can be used as a fuel. Some of the chemicals in unprocessed natural gas are poisonous to humans. Other chemicals, such as water, make the gas less useful as a fuel. Processing natural gas removes almost everything except the methane. Once the gas is processed, it is ready to be delivered and used. Natural gas is delivered to homes for uses such as cooking and heating. Like coal and oil, natural gas is also burned to generate heat for powering turbines. The spinning turbines turn generators, and the generators create electricity. Click image to the left or use the URL below. URL: ",text,
L_0248,natural gas power,T_1483,"Natural gas burns much cleaner than other fossil fuels, meaning that it causes less air pollution. Natural gas also produces less carbon dioxide than other fossil fuels do for the same amount of energy, so its global warming effects are less (Figure 1.2). Unfortunately, drilling for natural gas can be environmentally destructive. One technique used is hydraulic fractur- ing, also called fracking, which increases the rate of recovery of natural gas. Fluids are pumped through a borehole to create fractures in the reservoir rock that contains the natural gas. Material is added to the fluid to prevent the fractures from closing. The damage comes primarily from chemicals in the fracturing fluids. Chemicals that have been found in the fluids may be carcinogens (cancer-causing), radioactive materials, or endocrine disruptors, which interrupt hormones in the bodies of humans and animals. The fluids may get into groundwater or may runoff into streams and other surface waters. As noted above, fracking may cause earthquakes. Click image to the left or use the URL below. URL: ",text,
L_0249,natural resource conservation,T_1484,"So that people in developed nations maintain a good lifestyle and people in developing nations have the ability to improve their lifestyles, natural resources must be conserved and protected (Figure 1.1). People are researching ways to find renewable alternatives to non-renewable resources. Here is a checklist of ways to conserve resources: Buy less stuff (use items as long as you can, and ask yourself if you really need something new). Reduce excess packaging (drink tap water instead of water from plastic bottles). Recycle materials such as metal cans, old cell phones, and plastic bottles. Purchase products made from recycled materials. Reduce pollution so that resources are maintained. Prevent soil erosion. Plant new trees to replace those that are cut down. Drive cars less, take public transportation, bicycle, or walk. Conserve energy at home (turn out lights when they are not needed). Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0250,neptune,T_1485,"Neptune, shown in Figure 1.1, is the only major planet that cant be seen from Earth without a telescope. Scientists predicted the existence of Neptune before it was discovered because Uranus did not always appear exactly where it should appear. They knew that the gravitational pull of another planet beyond Uranus must be affecting Uranus orbit. Neptune was discovered in 1846, in the position that had been predicted, and it was named Neptune for the Roman god of the sea because of its bluish color. This image of Neptune was taken by Voy- ager 2 in 1989. The Great Dark Spot seen on the left center in the picture has since disappeared, but a similar dark spot has appeared on another part of the planet. In many respects, Neptune is similar to Uranus (Figure 1.2). Neptune has slightly more mass than Uranus, but it is slightly smaller in size. Neptune is much farther from the Sun, at nearly 4.5 billion km (2.8 billion mi). The planets slow orbit means that it takes 165 Earth years to go once around the Sun. ",text,
L_0250,neptune,T_1486,"Neptunes blue color is mostly because of frozen methane (CH4 ). When Voyager 2 visited Neptune in 1986, there was a large dark-blue spot, which scientists named the Great Dark Spot, south of the equator. When the Hubble Space Telescope took pictures of Neptune in 1994, the Great Dark Spot had disappeared, but another dark spot had appeared north of the equator. Astronomers think that both of these spots represent gaps in the methane clouds on Neptune. The changing appearance of Neptune is caused by its turbulent atmosphere. The winds on Neptune are stronger than on any other planet in the solar system, reaching speeds of 1,100 km/h (700 mi/h), close to the speed of sound. This extreme weather surprised astronomers, since the planet receives little energy from the Sun to power weather systems. Neptunes core is 7000 C (12,632 C) which means that it produces more energy than it receives from the Sun. Neptune is also one of the coldest places in the solar system. Temperatures at the top of the clouds are about -218 C (-360 F). Neptunes composition is that of a gas giant: (1) upper atmosphere, (2) atmo- sphere composed of hydrogen, helium and methane gas, (3) mantle of water, ammonia and methane ice, (4) core of rock and ice. ",text,
L_0250,neptune,T_1487,"Neptune has faint rings of ice and dust that may change or disappear in fairly short time frames. Neptune has 13 known moons. Triton, shown in Figure 1.3, is the only one of them that has enough mass to be spherical in shape. Triton orbits in the direction opposite to the orbit of Neptune. Scientists think Triton did not form around Neptune, but instead was captured by Neptunes gravity as it passed by. This image of Triton, Neptunes largest moon, was taken by Voyager 2 in 1989. ",text,
L_0251,nitrogen cycle in ecosystems,T_1488,"Nitrogen (N2 ) is vital for life on Earth as an essential component of organic materials, such as amino acids, chloro- phyll, and nucleic acids such as DNA and RNA (Figure 1.1). Chlorophyll molecules, essential for photosynthesis, contain nitrogen. ",text,
L_0251,nitrogen cycle in ecosystems,T_1489,"Although nitrogen is the most abundant gas in the atmosphere, it is not in a form that plants can use. To be useful, nitrogen must be fixed, or converted into a more useful form. Although some nitrogen is fixed by lightning or blue-green algae, much is modified by bacteria in the soil. These bacteria combine the nitrogen with oxygen or hydrogen to create nitrates or ammonia (Figure 1.2). (a) Nucleic acids contain nitrogen (b) Chlorophyll molecules contain nitrogen ",text,
L_0251,nitrogen cycle in ecosystems,T_1489,"Although nitrogen is the most abundant gas in the atmosphere, it is not in a form that plants can use. To be useful, nitrogen must be fixed, or converted into a more useful form. Although some nitrogen is fixed by lightning or blue-green algae, much is modified by bacteria in the soil. These bacteria combine the nitrogen with oxygen or hydrogen to create nitrates or ammonia (Figure 1.2). (a) Nucleic acids contain nitrogen (b) Chlorophyll molecules contain nitrogen ",text,
L_0251,nitrogen cycle in ecosystems,T_1490,"Animals eat plant tissue and create animal tissue. After a plant or animal dies or an animal excretes waste, bacteria and some fungi in the soil fix the organic nitrogen and return it to the soil as ammonia. Nitrifying bacteria oxidize the ammonia to nitrites, while other bacteria oxidize the nitrites to nitrates, which can be used by the next generation of plants. In this way, nitrogen does not need to return to a gas. Under conditions when there is no oxygen, some bacteria can reduce nitrates to molecular nitrogen. Click image to the left or use the URL below. URL: ",text,
L_0252,non renewable energy resources,T_1491,Nonrenewable resources are natural resources that are limited in supply and cannot be replaced as quickly as they are used up. A natural resource is anything people can use that comes from nature. Energy resources are some of the most important natural resources because everything we do requires energy. Nonrenewable energy resources include fossil fuels such as oil and the radioactive element uranium. ,text,
L_0252,non renewable energy resources,T_1492,"Oil, or petroleum, is one of several fossil fuels. Fossil fuels are mixtures of hydrocarbons (compounds containing only hydrogen and carbon) that formed over millions of years from the remains of dead organisms. In addition to oil, they include coal and natural gas. Fossil fuels provide most of the energy used in the world today. They are burned in power plants to produce electrical energy, and they also fuel cars, heat homes, and supply energy for many other purposes. You can see some ways they are used in the Figure 1.1. Q: Why do fossil fuels have energy? A: Fossil fuels contain stored chemical energy that came originally from the sun. ",text,
L_0252,non renewable energy resources,T_1493,"When ancient plants underwent photosynthesis, they changed energy in sunlight to stored chemical energy in food. The plants used the food and so did the organisms that ate the plants. After the plants and other organisms died, their remains gradually changed to fossil fuels as they were covered and compressed by layers of sediments. Petroleum and natural gas formed from ocean organisms and are found together. Coal formed from giant tree ferns and other swamp plants. ",text,
L_0252,non renewable energy resources,T_1494,"When fossil fuels burn, they release thermal energy, water vapor, and carbon dioxide. The thermal energy can be used to generate electricity or do other work. The carbon dioxide is released into the atmosphere and is a major cause of global climate change. The burning of fossil fuels also releases many pollutants into the air. Pollutants such as sulfur dioxide form acid rain, which kills living things and damages metals, stonework, and other materials. Pollutants such as nitrogen oxides cause smog, which is harmful to human health. Tiny particles, or particulates, released when fossil fuels burn also harm human health. The Figure 1.2 shows the amounts of pollutants released by different fossil fuels. Natural gas releases the least pollution; coal releases the most. Petroleum has the additional risk of oil spills, which may seriously damage ecosystems. Q: Some newer models of cars and other motor vehicles can run on natural gas. Why would a natural gas vehicle be better for the environment than a vehicle that burns gasoline, which is made from oil? A: Natural gas produces much less pollution and carbon dioxide when it burns than gasoline does. So a natural gas vehicle would contribute less to global climate change, acid rain, and air pollution that harms health. Besides being better for the environment, burning natural gas instead of gasoline results in less engine wear and provides more energy for a given amount of fuel. ",text,
L_0252,non renewable energy resources,T_1495,"Like fossil fuels, the radioactive element uranium can be used to generate electrical energy in power plants. This source of energy is known as nuclear energy. In a nuclear power plant, the nuclei of uranium atoms are split apart into smaller nuclei in the process of nuclear fission. This process releases a tremendous amount of energy from just a small amount of uranium. The total supply of uranium in the world is quite limited, however, and cannot be replaced once it is used up. Thats why nuclear energy is a nonrenewable resource. The use of nuclear energy also produces dangerous radioactive wastes. In addition, accidents at nuclear power plants have the potential to release large amounts of harmful radiation into the environment. Q: Why is nuclear energy often considered to be greener than energy from fossil fuels? A: Unlike energy from fossil fuels, nuclear energy doesnt produce air pollution or carbon dioxide that contributes to global climate change. ",text,
L_0253,nuclear power,T_1496,"When the nucleus of an atom is split, it releases a huge amount of energy called nuclear energy. For nuclear energy to be used as a power source, scientists and engineers have learned to split nuclei and to control the release of energy (Figure 1.1). ",text,
L_0253,nuclear power,T_1497,"Nuclear power plants, such as the one seen in Figure 1.2, use uranium, which is mined, processed, and then concentrated into fuel rods. When the uranium atoms in the fuel rods are hit by other extremely tiny particles, they split apart. The number of tiny particles allowed to hit the fuel rods needs to be controlled, or they would cause a dangerous explosion. The energy from a nuclear power plant heats water, which creates steam and causes a turbine to spin. The spinning turbine turns a generator, which in turn produces electricity. Many countries around the world use nuclear energy as a source of electricity. In the United States, a little less than 20% of electricity comes from nuclear energy. ",text,
L_0253,nuclear power,T_1497,"Nuclear power plants, such as the one seen in Figure 1.2, use uranium, which is mined, processed, and then concentrated into fuel rods. When the uranium atoms in the fuel rods are hit by other extremely tiny particles, they split apart. The number of tiny particles allowed to hit the fuel rods needs to be controlled, or they would cause a dangerous explosion. The energy from a nuclear power plant heats water, which creates steam and causes a turbine to spin. The spinning turbine turns a generator, which in turn produces electricity. Many countries around the world use nuclear energy as a source of electricity. In the United States, a little less than 20% of electricity comes from nuclear energy. ",text,
L_0253,nuclear power,T_1498,"Nuclear power is clean. It does not pollute the air. However, the use of nuclear energy does create other environ- mental problems. Uranium must be mined (Figure 1.3). The process of splitting atoms creates radioactive waste, which remains dangerous for thousands or hundreds of thousands of years. As yet, there is no long-term solution for storing this waste. The development of nuclear power plants has been on hold for three decades. Accidents at Three Mile Island and Chernobyl, Ukraine verified peoples worst fears about the dangers of harnessing nuclear power (Figure 1.4). Recently, nuclear power appeared to be making a comeback as society looked for alternatives to fossil fuels. After all, nuclear power emits no pollutants, including no greenhouse gases. But the 2011 disaster at the Fukushima Daiichi Nuclear Power Plant in Japan may have resulted in a new fear of nuclear power. The cause of the disaster was a 9.0 magnitude earthquake and subsequent tsunami, which compromised the plant. Although a total meltdown was averted, the plant experienced multiple partial meltdowns, core breaches, radiation releases, and cooling failures. The plant is scheduled for a complete cold shutdown before the end of 2011. Damaged building near the site of the Chernobyl disaster. Nuclear power is a controversial subject in California and most other places. Nuclear power has no pollutants including carbon emissions, but power plants are not always safe and the long-term disposal of wastes is a problem that has not yet been solved. The future of nuclear power is murky. ",text,
L_0253,nuclear power,T_1498,"Nuclear power is clean. It does not pollute the air. However, the use of nuclear energy does create other environ- mental problems. Uranium must be mined (Figure 1.3). The process of splitting atoms creates radioactive waste, which remains dangerous for thousands or hundreds of thousands of years. As yet, there is no long-term solution for storing this waste. The development of nuclear power plants has been on hold for three decades. Accidents at Three Mile Island and Chernobyl, Ukraine verified peoples worst fears about the dangers of harnessing nuclear power (Figure 1.4). Recently, nuclear power appeared to be making a comeback as society looked for alternatives to fossil fuels. After all, nuclear power emits no pollutants, including no greenhouse gases. But the 2011 disaster at the Fukushima Daiichi Nuclear Power Plant in Japan may have resulted in a new fear of nuclear power. The cause of the disaster was a 9.0 magnitude earthquake and subsequent tsunami, which compromised the plant. Although a total meltdown was averted, the plant experienced multiple partial meltdowns, core breaches, radiation releases, and cooling failures. The plant is scheduled for a complete cold shutdown before the end of 2011. Damaged building near the site of the Chernobyl disaster. Nuclear power is a controversial subject in California and most other places. Nuclear power has no pollutants including carbon emissions, but power plants are not always safe and the long-term disposal of wastes is a problem that has not yet been solved. The future of nuclear power is murky. ",text,
L_0255,obtaining energy resources,T_1503,"Net energy is the amount of useable energy available from a resource after subtracting the amount of energy needed to make the energy from that resource available. For example, every 5 barrels of oil that are made available for use require 1 barrel for extracting and refining the petroleum. What is the net energy from this process? About 4 barrels (5 barrels minus 1 barrel). What happens if the energy needed to extract and refine oil increases? Why might that happen? The energy cost of an energy resource increases when the easy deposits of that resource have already been consumed. For example, if all the nearshore petroleum in a region has been extracted, more costly drilling must take place further offshore (Figure 1.1). If the energy cost of obtaining energy increases, the resource will be used even faster. Offshore drilling is taking place in deeper water than before. It takes a lot of energy to build a deep drilling platform and to run it. ",text,
L_0255,obtaining energy resources,T_1504,"The net-energy ratio demonstrates the difference between the amount of energy available in a resource and the amount of energy used to get it. If it takes 8 units of energy to make available 10 units of energy, then the net-energy ratio is 10/8 or 1.25. What does a net-energy ratio larger than 1 mean? What if the net-energy ratio is less than 1? A net-energy ratio larger than 1 means that there is a net gain in usable energy; a net-energy ratio smaller than one means there is an overall energy loss. Table 1.1 shows the net-energy ratios for some common energy sources. Energy Source Solar Energy Natural Gas Petroleum Coal-fired Electricity Net-energy Ratio 5.8 4.9 4.5 2.5-5.1 Notice from the table that solar energy yields much more net energy than other sources. This is because it takes very little energy to get usable solar energy. Sunshine is abundant and does not need to be found, extracted, or transported very far. The range for coal-fired electricity is because of the differing costs of transporting the coal. What does this suggest about using coal to generate electricity? The efficiency is greater in areas where the coal is locally mined and does not have to be transported great distances (Figure 1.2). Obtaining coal for energy takes a lot of energy. The coal must be located, extracted, refined, and transported. Because so much of the energy we use is from fossil fuels, we need to be especially concerned about using them efficiently. Sometimes our choices affect energy efficiency. For example, transportation by cars and airplanes is less energy-efficient than transportation by boats and trains. ",text,
L_0256,ocean ecosystems,T_1505,"Conditions in the intertidal zone change rapidly as water covers and uncovers the region and waves pound on the rocks. A great abundance of life is found in the intertidal zone (Figure 1.1). High energy waves hit the organisms that live in this zone, so they must be adapted to pounding waves and exposure to air during low tides. Hard shells protect from waves and also protect against drying out when the animal is above water. Strong attachments keep the animals anchored to the rock. In a tide pool, as in the photo, what organisms are found where and what specific adaptations do they have to that zone? The mussels on the top left have hard shells for protection and to prevent drying because they are often not covered by water. The sea anemones in the lower right are more often submerged and have strong attachments but can close during low tides. Many young organisms get their start in estuaries and so they must be adapted to rapid shifts in salinity. Organisms in a tide pool include sea stars and sea urchins. Click image to the left or use the URL below. URL: ",text,
L_0256,ocean ecosystems,T_1506,"Corals and other animals deposit calcium carbonate to create rock reefs near the shore. Coral reefs are the rain- forests of the oceans, with a tremendous amount of species diversity (Figure 1.2). Reefs can form interesting shapes in the oceans. Remember that hot spots create volcanoes on the seafloor. If these volcanoes rise above sea level to become islands, and if they occur in tropical waters, coral reefs will form on them. Since the volcanoes are cones, the reef forms in a circle around the volcano. As the volcano comes off the hot spot, the crust cools. The volcano subsides and then begins to erode away (Figure 1.3). Eventually, all that is left is a reef island called an atoll. A lagoon is found inside the reef. ",text,
L_0256,ocean ecosystems,T_1507,"The open ocean is a vast area. Food either washes down from the land or is created by photosynthesizing plankton. Zooplankton and larger animals feed on the phytoplankton and on each other. Larger animals such as whales and giant groupers may live their entire lives in the open water. How do fish survive in the deepest ocean? The few species that live in the greatest depths are very specialized (Figure 1.4). Since its rare to find a meal, the fish use very little energy; they move very little, breathe slowly, have minimal bone structure and a slow metabolism. These fish are very small. To maximize the chance of getting a meal, some species may have jaws that unhinge to accept a larger fish or backward-folding teeth to keep prey from escaping. Coral reefs are among the most densely inhabited and diverse areas on the globe. In this image of Maupiti Island in the South Pacific, the remnants of the volcano are surrounded by the circular reef. An 1896 drawing of a deep sea angler fish with a bioluminescent lure to attract prey. ",text,
L_0256,ocean ecosystems,T_1507,"The open ocean is a vast area. Food either washes down from the land or is created by photosynthesizing plankton. Zooplankton and larger animals feed on the phytoplankton and on each other. Larger animals such as whales and giant groupers may live their entire lives in the open water. How do fish survive in the deepest ocean? The few species that live in the greatest depths are very specialized (Figure 1.4). Since its rare to find a meal, the fish use very little energy; they move very little, breathe slowly, have minimal bone structure and a slow metabolism. These fish are very small. To maximize the chance of getting a meal, some species may have jaws that unhinge to accept a larger fish or backward-folding teeth to keep prey from escaping. Coral reefs are among the most densely inhabited and diverse areas on the globe. In this image of Maupiti Island in the South Pacific, the remnants of the volcano are surrounded by the circular reef. An 1896 drawing of a deep sea angler fish with a bioluminescent lure to attract prey. ",text,
L_0256,ocean ecosystems,T_1507,"The open ocean is a vast area. Food either washes down from the land or is created by photosynthesizing plankton. Zooplankton and larger animals feed on the phytoplankton and on each other. Larger animals such as whales and giant groupers may live their entire lives in the open water. How do fish survive in the deepest ocean? The few species that live in the greatest depths are very specialized (Figure 1.4). Since its rare to find a meal, the fish use very little energy; they move very little, breathe slowly, have minimal bone structure and a slow metabolism. These fish are very small. To maximize the chance of getting a meal, some species may have jaws that unhinge to accept a larger fish or backward-folding teeth to keep prey from escaping. Coral reefs are among the most densely inhabited and diverse areas on the globe. In this image of Maupiti Island in the South Pacific, the remnants of the volcano are surrounded by the circular reef. An 1896 drawing of a deep sea angler fish with a bioluminescent lure to attract prey. ",text,
L_0256,ocean ecosystems,T_1508,"Hydrothermal vents are among the most unusual ecosystems on Earth since they are dependent on chemosynthetic organisms at the base of the food web. At mid-ocean ridges at hydrothermal vents, bacteria that use chemosyn- thesis for food energy are the base of a unique ecosystem (Figure 1.5). This ecosystem is entirely separate from the photosynthesis at the surface. Shrimp, clams, fish, and giant tube worms have been found in these extreme places. Giant tube worms found at hydrothermal vents get food from the chemosynthetic bacteria that live within them. The bacte- ria provide food; the worms provide shel- ter. A video explaining hydrothermal vents with good footage is seen here: ",text,
L_0257,ocean garbage patch,T_1509,"Trash from land may end up as trash in the ocean, sometimes extremely far from land. Some of it will eventually wash ashore, possibly far from where it originated (Figure 1.1). ",text,
L_0257,ocean garbage patch,T_1510,"Although people had once thought that the trash found everywhere at sea was from ships, it turns out that 80% is from land. Some of that is from runoff, some is blown from nearshore landfills, and some is dumped directly into the sea. The 20% that comes from ships at sea includes trash thrown overboard by large cruise ships and many other vessels. It also includes lines and nets from fishing vessels. Ghost nets, nets abandoned by fishermen intentionally or not, float the seas and entangle animals so that they cannot escape. Containers sometimes go overboard in storms. Some noteworthy events, like a container of rubber ducks that entered the sea in 1992, are used to better understand ocean currents. The ducks went everywhere! ",text,
L_0257,ocean garbage patch,T_1511,"About 80% of the trash that ends up in the oceans is plastic. This is because a large amount of the trash produced since World War II is plastic. Also many types of plastic do not biodegrade, so they simply accumulate. While many types of plastic photodegrade  that is, they break up in sunlight  this process only works when the plastics are dry. Plastic trash in the water does break down into smaller pieces, eventually becoming molecule-sized polymers. Other trash in the oceans includes chemical sludge and materials that do biodegrade, like wood. ",text,
L_0257,ocean garbage patch,T_1512,"Some plastics contain toxic chemicals, such as bisphenol A. Plastics can also absorb organic pollutants that may be floating in the water, such as the pesticide DDT (which is banned in the U.S. but not in other nations) and some endocrine disruptors. ",text,
L_0257,ocean garbage patch,T_1513,"Trash from the lands all around the North Pacific is caught up in currents. The currents bring the trash into the center of the North Pacific Gyre. Scientists estimate that it takes about six years for trash to move from west coast of North America to the center of the gyre. The concentration of trash increases toward the center of the gyre. While recognizable pieces of garbage are visible, much of the trash is tiny plastic polymers that are invisible but can be detected in water samples. The particles are at or just below the surface within the gyre. Plastic confetti-like pieces are visible beneath the surface at the gyres center. This albatross likely died from the plastic it had ingested. The size of the garbage patch is unknown, since it cant be seen from above. Some people estimate that its twice the size of continental U.S, with a mass of 100 million tons. ",text,
L_0257,ocean garbage patch,T_1513,"Trash from the lands all around the North Pacific is caught up in currents. The currents bring the trash into the center of the North Pacific Gyre. Scientists estimate that it takes about six years for trash to move from west coast of North America to the center of the gyre. The concentration of trash increases toward the center of the gyre. While recognizable pieces of garbage are visible, much of the trash is tiny plastic polymers that are invisible but can be detected in water samples. The particles are at or just below the surface within the gyre. Plastic confetti-like pieces are visible beneath the surface at the gyres center. This albatross likely died from the plastic it had ingested. The size of the garbage patch is unknown, since it cant be seen from above. Some people estimate that its twice the size of continental U.S, with a mass of 100 million tons. ",text,
L_0257,ocean garbage patch,T_1514,"Marine birds, such as albatross, or animals like sea turtles, live most of their lives at sea and just come ashore to mate. These organisms cant break down the plastic and they may eventually die (Figure 1.2). Boats may be affected. Plastic waste is estimated to kill 100,000 sea turtles and marine mammals annually, but exact numbers are unknown. Plastic shopping bags are extremely abundant in the oceans. If an organism accidentally ingests one, it may clog digestion and cause starvation by stopping food from moving through or making the animal not feel hungry. In some areas, plastics have seven times the concentration of zooplankton. This means that filter feeders are ingesting a lot of plastics. This may kill the organisms or the plastics may remain in their bodies. They are then eaten by larger organisms that store the plastics and may eventually die. Fish may eat organisms that have eaten plastic and then be eaten by people. This also exposes humans to toxic chemicals that the fish may have ingested with the plastic. There are similar patches of trash in the gyres of the North Atlantic and Indian oceans. The Southern Hemisphere has less trash buildup because less of the region is continent. ",text,
L_0258,ocean zones,T_1515,Oceanographers divide the ocean into zones both vertically and horizontally. ,text,
L_0258,ocean zones,T_1516,"To better understand regions of the ocean, scientists define the water column by depth. They divide the entire ocean into two zones vertically, based on light level. Large lakes are divided into similar regions. Sunlight only penetrates the sea surface to a depth of about 200 m, creating the photic zone (""photic"" means light). Organisms that photosynthesize depend on sunlight for food and so are restricted to the photic zone. Since tiny photosynthetic organisms, known as phytoplankton, supply nearly all of the energy and nutrients to the rest of the marine food web, most other marine organisms live in or at least visit the photic zone. In the aphotic zone there is not enough light for photosynthesis. The aphotic zone makes up the majority of the ocean, but has a relatively small amount of its life, both in diversity of type and in numbers. The aphotic zone is subdivided based on depth (Figure 1.1). The average depth of the ocean is 3,790 m, a lot more shallow than the deep trenches but still an incredible depth for sea creatures to live in. What makes it so hard to live at the bottom of the ocean? The three major factors that make the deep ocean hard to inhabit are the absence of light, low temperature, and extremely high pressure. ",text,
L_0258,ocean zones,T_1517,"The seabed is divided into the zones described above, but ocean itself is also divided horizontally by distance from the shore. Nearest to the shore lies the intertidal zone (also called the littoral zone), the region between the high and low tidal marks. The hallmark of the intertidal is change: water is in constant motion in the form of waves, tides, and currents. The land is sometimes under water and sometimes exposed. The neritic zone is from low tide mark and slopes gradually downward to the edge of the seaward side of the continental shelf. Some sunlight penetrates to the seabed here. The oceanic zone is the entire rest of the ocean from the bottom edge of the neritic zone, where sunlight does not reach the bottom. The sea bed and water column are subdivided further, as seen in the Figure 1.1. Click image to the left or use the URL below. URL: ",text,
L_0259,oil spills,T_1518,"Large oil spills, like the Exxon Valdez in Alaska in 1989, get a lot of attention, as they should. Besides these large spills, though, much more oil enters the oceans from small leaks that are only a problem locally. In this concept, well take a look at a large recent oil spill in the Gulf of Mexico. ",text,
L_0259,oil spills,T_1519,"New drilling techniques have allowed oil companies to drill in deeper waters than ever before. This allows us to access oil deposits that were never before accessible, but only with great technological difficulty. The risks from deepwater drilling and the consequences when something goes wrong are greater than those associated with shallower wells. ",text,
L_0259,oil spills,T_1520,"Working on oil platforms is dangerous. Workers are exposed to harsh ocean conditions and gas explosions. The danger was never more obvious than on April 20, 2010, when 11 workers were killed and 17 injured in an explosion on a deepwater oil rig in the Gulf of Mexico (Figure 1.1). The drilling rig, operated by BP, was 77 km (48 miles) offshore and the depth to the well was more than 5,000 feet. The U.S. Coast Guard tries to put out the fire and search for missing workers after the explosion on the Deepwater Horizon drilling rig. Eleven workers were killed. ",text,
L_0259,oil spills,T_1521,"Two days after the explosion, the drill rig sank. The 5,000-foot pipe that connected the wellhead to the drilling platform bent. Oil was free to gush into the Gulf of Mexico from nearly a mile deep (Figure 1.2). Initial efforts to cap or contain the spill at or near its source all failed to stop the vast oil spill. It was not until July 15, nearly three months after the accident, that the well was successfully capped. Estimating the flow of oil into the Gulf from the well was extremely difficult because the leak was so far below the surface. The U.S. government estimates that about 4.9 million barrels entered the Gulf at a rate of 35,000 to 60,000 barrels a day. The largest previous oil spill in the United States was of 300,000 barrels by the Exxon Valdez in 1989 in Prince William Sound, Alaska. ",text,
L_0259,oil spills,T_1522,"Once the oil is in the water, there are three types of methods for dealing with it: 1. Removal: Oil is corralled and then burned; natural gas is flared off (Figure 1.3). Machines that can separate oil from the water are placed aboard ships stationed in the area. These ships cleaned tens of thousands of barrels of contaminated seawater each day. 2. Containment: Floating containment booms are placed on the surface offshore of the most sensitive coastal areas in an attempt to attempt to trap the oil. But the seas must be calm for the booms to be effective, and so were not very useful in the Gulf (Figure 1.4). Sand berms have been constructed off of the Louisiana coast to keep the oil from reaching shore. (a) On May 17, 2010, oil had been leaking into the Gulf for nearly one month. On that date government estimates put the maximum total oil leak at 1,600,000 barrels, according to the New York Times. (b) The BP oil spill on June 19, 2010. The government estimates for total oil leaked by this date was 3,200,000 barrels. 3. Dispersal: Oil disperses naturally over time because it mixes with the water. However, such large amounts of oil will take decades to disperse. To speed the process up, BP has sprayed unprecedented amounts of chemical dispersants on the spill. That action did not receive support from the scientific community since no one knows the risks to people and the environment from such a large amount of these harmful chemicals. Some workers may have become ill from exposure to the chemicals. ",text,
L_0259,oil spills,T_1522,"Once the oil is in the water, there are three types of methods for dealing with it: 1. Removal: Oil is corralled and then burned; natural gas is flared off (Figure 1.3). Machines that can separate oil from the water are placed aboard ships stationed in the area. These ships cleaned tens of thousands of barrels of contaminated seawater each day. 2. Containment: Floating containment booms are placed on the surface offshore of the most sensitive coastal areas in an attempt to attempt to trap the oil. But the seas must be calm for the booms to be effective, and so were not very useful in the Gulf (Figure 1.4). Sand berms have been constructed off of the Louisiana coast to keep the oil from reaching shore. (a) On May 17, 2010, oil had been leaking into the Gulf for nearly one month. On that date government estimates put the maximum total oil leak at 1,600,000 barrels, according to the New York Times. (b) The BP oil spill on June 19, 2010. The government estimates for total oil leaked by this date was 3,200,000 barrels. 3. Dispersal: Oil disperses naturally over time because it mixes with the water. However, such large amounts of oil will take decades to disperse. To speed the process up, BP has sprayed unprecedented amounts of chemical dispersants on the spill. That action did not receive support from the scientific community since no one knows the risks to people and the environment from such a large amount of these harmful chemicals. Some workers may have become ill from exposure to the chemicals. ",text,
L_0259,oil spills,T_1522,"Once the oil is in the water, there are three types of methods for dealing with it: 1. Removal: Oil is corralled and then burned; natural gas is flared off (Figure 1.3). Machines that can separate oil from the water are placed aboard ships stationed in the area. These ships cleaned tens of thousands of barrels of contaminated seawater each day. 2. Containment: Floating containment booms are placed on the surface offshore of the most sensitive coastal areas in an attempt to attempt to trap the oil. But the seas must be calm for the booms to be effective, and so were not very useful in the Gulf (Figure 1.4). Sand berms have been constructed off of the Louisiana coast to keep the oil from reaching shore. (a) On May 17, 2010, oil had been leaking into the Gulf for nearly one month. On that date government estimates put the maximum total oil leak at 1,600,000 barrels, according to the New York Times. (b) The BP oil spill on June 19, 2010. The government estimates for total oil leaked by this date was 3,200,000 barrels. 3. Dispersal: Oil disperses naturally over time because it mixes with the water. However, such large amounts of oil will take decades to disperse. To speed the process up, BP has sprayed unprecedented amounts of chemical dispersants on the spill. That action did not receive support from the scientific community since no one knows the risks to people and the environment from such a large amount of these harmful chemicals. Some workers may have become ill from exposure to the chemicals. ",text,
L_0259,oil spills,T_1523,"BP drilled two relief wells into the original well. When the relief wells entered the original borehole, specialized liquids were pumped into the original well to stop the flow. Operation of the relief wells began in August 2010. The original well was declared effectively dead on September 19, 2010. ",text,
L_0259,oil spills,T_1524,"The economic and environmental impact of this spill will be felt for many years. Many people rely on the Gulf for their livelihoods or for recreation. Commercial fishing, tourism, and oil-related jobs are the economic engines of the region. Fearing contamination, NOAA imposed a fishing ban on approximately one-third of the Gulf (Figure 1.5). Tourism is down in the region as beach goers find other ways to spend their time. Real estate prices along the Gulf have declined precipitously. This was the extent of the banned area on June 21, 2010. The Gulf of Mexico is one of only two places in the world where bluefin tuna spawn and they are also already endangered. Marine mammals in the Gulf may come up into the slick as they come to the surface to breathe. Eight national parks and seashores are found along the Gulf shores. Other locations may be ecologically sensitive habitats such as mangroves or marshlands. ",text,
L_0259,oil spills,T_1525,There is still oil on beaches and in sediment on the seafloor in the region. Chemicals from the oil dispersants are still in the water. In October 2011 a report was issued that showed that whales and dolphins are dying in the Gulf at twice their normal rate. The long-term effects will be with us for a long time. Click image to the left or use the URL below. URL: ,text,
L_0260,overpopulation and over consumption,T_1526,The Green Revolution has brought enormous impacts to the planet. ,text,
L_0260,overpopulation and over consumption,T_1527,"Natural landscapes have been altered to create farmland and cities. Already, half of the ice-free lands have been converted to human uses. Estimates are that by 2030, that number will be more than 70%. Forests and other landscapes have been cleared for farming or urban areas. Rivers have been dammed and the water is transported by canals for irrigation and domestic uses. Ecologically sensitive areas have been altered: wetlands are now drained and coastlines are developed. ",text,
L_0260,overpopulation and over consumption,T_1528,"Modern agricultural practices produce a lot of pollution (Figure 1.1). Some pesticides are toxic. Dead zones grow as fertilizers drain off farmland and introduce nutrients into lakes and coastal areas. Farm machines and vehicles used to transport crops produce air pollutants. Pollutants enter the air, water, or are spilled onto the land. Moreover, many types of pollution easily move between air, water, and land. As a result, no location or organism  not even polar bears in the remote Arctic  is free from pollution. ",text,
L_0260,overpopulation and over consumption,T_1529,"The increased numbers of people have other impacts on the planet. Humans do not just need food. They also need clean water, secure shelter, and a safe place for their wastes. These needs are met to different degrees in different nations and among different socioeconomic classes of people. For example, about 1.2 billion of the worlds people do not have enough clean water for drinking and washing each day (Figure 1.2). ",text,
L_0260,overpopulation and over consumption,T_1530,"The addition of more people has not just resulted in more poor people. A large percentage of people expect much more than to have their basic needs met. For about one-quarter of people there is an abundance of food, plenty of water, and a secure home. Comfortable temperatures are made possible by heating and cooling systems, rapid trans- portation is available by motor vehicles or a well-developed public transportation system, instant communication takes place by phones and email, and many other luxuries are available that were not even dreamed of only a few The percentage of people in the world that live in abject poverty is decreasing some- what globally, but increasing in some re- gions, such as Sub-Saharan Africa. decades ago. All of these require resources in order to be produced, and fossil fuels in order to be powered (Figure Many people refer to the abundance of luxury items in these peoples lives as over-consumption. People in developed nations use 32 times more resources than people in the developing countries of the world. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0261,ozone depletion,T_1531,"At this point you might be asking yourself, Is ozone bad or is ozone good? There is no simple answer to that question: It depends on where the ozone is located (Figure 1.1). In the troposphere, ozone is a pollutant. In the ozone layer in the stratosphere, ozone screens out high energy ultraviolet radiation and makes Earth habitable. ",text,
L_0261,ozone depletion,T_1532,"Human-made chemicals are breaking ozone molecules in the ozone layer. Chlorofluorocarbons (CFCs) are the most common, but there are others, including halons, methyl bromide, carbon tetrachloride, and methyl chloroform. CFCs were once widely used because they are cheap, nontoxic, nonflammable, and non-reactive. They were used as spray-can propellants, refrigerants, and in many other products. Once they are released into the air, CFCs float up to the stratosphere. Air currents move them toward the poles. In the winter, they freeze onto nitric acid molecules in polar stratospheric clouds (PSC) (Figure 1.2). In the spring, (1) Solar energy breaks apart oxygen molecules into two oxygen atoms. (2) Ozone forms when oxygen atoms bond together as O3 . UV rays break apart the ozone molecules into one oxygen molecule (O2 ) and one oxygen atom (O). These processes convert UV radiation into heat, which is how the Sun heats the stratosphere. (3) Under natural cir- cumstances, the amount of ozone cre- ated equals the amount destroyed. When O3 interacts with chlorine or some other gases the O3 breaks down into O2 and O and so the ozone layer loses its ability to filter out UV. the Suns warmth starts the air moving, and ultraviolet light breaks the CFCs apart. The chlorine atom floats away and attaches to one of the oxygen atoms on an ozone molecule. The chlorine pulls the oxygen atom away, leaving behind an O2 molecule, which provides no UV protection. The chlorine then releases the oxygen atom and moves on to destroy another ozone molecule. One CFC molecule can destroy as many as 100,000 ozone molecules. PSCs form only where the stratosphere is coldest, and are most common above Antarctica in the wintertime. PSCs are needed for stratospheric ozone to be de- stroyed. ",text,
L_0261,ozone depletion,T_1532,"Human-made chemicals are breaking ozone molecules in the ozone layer. Chlorofluorocarbons (CFCs) are the most common, but there are others, including halons, methyl bromide, carbon tetrachloride, and methyl chloroform. CFCs were once widely used because they are cheap, nontoxic, nonflammable, and non-reactive. They were used as spray-can propellants, refrigerants, and in many other products. Once they are released into the air, CFCs float up to the stratosphere. Air currents move them toward the poles. In the winter, they freeze onto nitric acid molecules in polar stratospheric clouds (PSC) (Figure 1.2). In the spring, (1) Solar energy breaks apart oxygen molecules into two oxygen atoms. (2) Ozone forms when oxygen atoms bond together as O3 . UV rays break apart the ozone molecules into one oxygen molecule (O2 ) and one oxygen atom (O). These processes convert UV radiation into heat, which is how the Sun heats the stratosphere. (3) Under natural cir- cumstances, the amount of ozone cre- ated equals the amount destroyed. When O3 interacts with chlorine or some other gases the O3 breaks down into O2 and O and so the ozone layer loses its ability to filter out UV. the Suns warmth starts the air moving, and ultraviolet light breaks the CFCs apart. The chlorine atom floats away and attaches to one of the oxygen atoms on an ozone molecule. The chlorine pulls the oxygen atom away, leaving behind an O2 molecule, which provides no UV protection. The chlorine then releases the oxygen atom and moves on to destroy another ozone molecule. One CFC molecule can destroy as many as 100,000 ozone molecules. PSCs form only where the stratosphere is coldest, and are most common above Antarctica in the wintertime. PSCs are needed for stratospheric ozone to be de- stroyed. ",text,
L_0261,ozone depletion,T_1533,"Ozone destruction creates the ozone hole where the layer is dangerously thin (Figure 1.3). As air circulates over Antarctica in the spring, the ozone hole expands northward over the southern continents, including Australia, New Zealand, southern South America, and southern Africa. UV levels may rise as much as 20% beneath the ozone hole. The hole was first measured in 1981 when it was 2 million square km (900,000 square miles). The 2006 hole was the largest ever observed at 28 million square km (11.4 million square miles). The size of the ozone hole each year depends on many factors, including whether conditions are right for the formation of PSCs. The September 2006 ozone hole, the largest observed (through 2013). Blue and purple colors show particularly low levels of ozone. ",text,
L_0261,ozone depletion,T_1534,"Ozone loss also occurs over the North Polar Region, but it is not enough for scientists to call it a hole. Why do you think there is less ozone loss over the North Pole area? The region of low ozone levels is small because the atmosphere is not as cold and PSCs do not form as readily. Still, springtime ozone levels are relatively low. This low moves south over some of the worlds most populated areas in Europe, North America, and Asia. At 40o N, the latitude of New York City, UV-B has increased about 4% per decade since 1978. At 55o N, the approximate latitude of Moscow and Copenhagen, the increase has been 6.8% per decade since 1978. Click image to the left or use the URL below. URL: ",text,
L_0261,ozone depletion,T_1535,"Ozone losses on human health and environment include: Increases in sunburns, cataracts (clouding of the lens of the eye), and skin cancers. A loss of ozone of only 1% is estimated to increase skin cancer cases by 5% to 6%. Decreases in the human immune systems ability to fight off infectious diseases. Reduction in crop yields because many plants are sensitive to ultraviolet light. Decreases in phytoplankton productivity. A decrease of 6% to 12% has been measured around Antarctica, which may be at least partly related to the ozone hole. The effects of excess UV on other organisms is not known. Whales in the Gulf of California have been found to have sunburned cells in their lowest skin layers, indicating very severe sunburns. The problem is greatest with light colored species or species that spend more time near the sea surface. When the problem with ozone depletion was recognized, world leaders took action. CFCs were banned in spray cans in some nations in 1978. The greatest production of CFCs was in 1986, but it has declined since then. This will be discussed more in the next concept. ",text,
L_0262,paleozoic and mesozoic seas,T_1536,"Some of the most important events of the Paleozoic and Mesozoic were the rising and falling of sea level over the continents. Sea level rises over the land during a marine transgression. During a marine regression, sea level retreats. During the Paleozoic there were four complete cycles of marine transgressions and regressions. There were two additional cycles during the Mesozoic (Figure 1.1). One of two things must happen for sea level to change in a marine transgression: either the land must sink or the water level must rise. What could cause sea level to rise? When little or no fresh water is tied up in glaciers and ice caps, sea level is high. Sea level also appears to rise if land is down dropped. Sea level rises if an increase in seafloor spreading rate buoys up the ocean crust, causing the ocean basin to become smaller. What could cause sea level to fall in a marine regression? Six marine transgressions and regres- sions have occurred during the Phanero- zoic. Geologists think that the Paleozoic marine transgressions and regressions were the result of the decrease and increase in the size of glaciers covering the lands. Click image to the left or use the URL below. URL: ",text,
L_0262,paleozoic and mesozoic seas,T_1537,"Geologists know about marine transgressions and regressions from the sedimentary rock record. These events leave characteristic rock layers known as sedimentary facies. On a shoreline, sand and other coarse grained rock fragments are commonly found on the beach where the wave energy is high. Away from the shore in lower energy environments, fine-grained silt that later creates shale is deposited. In deeper, low-energy waters, carbonate mud that later hardens into limestone is deposited. ",text,
L_0262,paleozoic and mesozoic seas,T_1538,"The Paleozoic sedimentary rocks of the Grand Canyon contain evidence of marine transgressions and regressions, but even there the rock record is not complete. Look at the sequence in the Figure 1.2 and see if you can determine whether the sea was transgressing or regressing. At the bottom, the Tonto Group represents a marine transgression: sandstone (11), shale (10), and limestone (9) laid down during 30 million years of the Cambrian Period. The Ordovician and Silurian are unknown because of an unconformity. Above that is freshwater limestone (8), which is overlain by limestone (7) and then shale (6), indicating that the sea was regressing. After another unconformity, the rocks of the Supai Group (5) include limestone, siltstone, and sandstone indicative of a regressing sea. Above those rocks are shale (4), sandstone (3), a limestone and sandstone mix (2) showing that the sea regressed and transgressed and finally limestone (1) indicating that the sea had come back in. ",text,
L_0263,paleozoic plate tectonics,T_1539,"The Paleozoic is the furthest back era of the Phanerozoic and it lasted the longest. But the Paleozoic was relatively recent, beginning only 570 million years ago. Compared with the long expanse of the Precambrian, the Phanerozoic is recent history. Much more geological evidence is available for scientists to study so the Phanerozoic is much better known. The Paleozoic begins and ends with a supercontinent. At the beginning of the Paleozoic, the supercontinent Rodinia began to split up. At the end, Pangaea came together. ",text,
L_0263,paleozoic plate tectonics,T_1540,"A mountain-building event is called an orogeny. Orogenies take place over tens or hundreds of millions of years. As continents smash into microcontinents and island arcs collided, mountains rise. Geologists find evidence for the orogenies that took place while Pangaea was forming in many locations. For example, Laurentia collided with the Taconic Island Arc during the Taconic Orogeny (Figure 1.1). The remnants of this mountain range make up the Taconic Mountains in New York. The Taconic Orogeny is an example of a collision between a continent and a volcanic island arc. Laurentia experienced other orogenies as it merged with the northern continents. The southern continents came together to form Gondwana. When Laurentia and Gondwana collided to create Pangaea, the Appalachians rose. Geologists think they may once have been higher than the Himalayas are now. ",text,
L_0263,paleozoic plate tectonics,T_1541,"Pangaea was the last supercontinent on Earth. Evidence for the existence of Pangaea was what Alfred Wegener used to create his continental drift hypothesis, which was described in the chapter Plate Tectonics. As the continents move and the land masses change shape, the shape of the oceans changes too. During the time of Pangaea, about 250 million years ago, most of Earths water was collected in a huge ocean called Panthalassa (Figure 1.2). Click image to the left or use the URL below. URL: ",text,
L_0264,petroleum power,T_1542,Oil is a liquid fossil fuel that is extremely useful because it can be transported easily and can be used in cars and other vehicles. Oil is currently the single largest source of energy in the world. ,text,
L_0264,petroleum power,T_1543,"Oil from the ground is called crude oil, which is a mixture of many different hydrocarbons. Crude oil is a thick dark brown or black liquid hydrocarbon. Oil also forms from buried dead organisms, but these are tiny organisms that live on the sea surface and then sink to the seafloor when they die. The dead organisms are kept away from oxygen by layers of other dead creatures and sediments. As the layers pile up, heat and pressure increase. Over millions of years, the dead organisms turn into liquid oil. ",text,
L_0264,petroleum power,T_1544,"In order to be collected, the oil must be located between a porous rock layer and an impermeable layer (Figure 1.1). Trapped above the porous rock layer and beneath the impermeable layer, the oil will remain between these layers until it is extracted from the rock. Oil (red) is found in the porous rock layer (yellow) and trapped by the impermeable layer (brown). The folded structure has allowed the oil to pool so a well can be drilled into the reservoir. To separate the different types of hydrocarbons in crude oil for different uses, the crude oil must be refined in refineries like the one shown in Figure 1.2. Refining is possible because each hydrocarbon in crude oil boils at a different temperature. When the oil is boiled in the refinery, separate equipment collects the different compounds. ",text,
L_0264,petroleum power,T_1545,"Most of the compounds that come out of the refining process are fuels, such as gasoline, diesel, and heating oil. Because these fuels are rich sources of energy and can be easily transported, oil provides about 90% of the energy used for transportation around the world. The rest of the compounds from crude oil are used for waxes, plastics, fertilizers, and other products. Gasoline is in a convenient form for use in cars and other transportation vehicles. In a car engine, the burned gasoline mostly turns into carbon dioxide and water vapor. The fuel releases most of its energy as heat, which causes the gases to expand. This creates enough force to move the pistons inside the engine and to power the car. Refineries like this one separate crude oil into many useful fuels and other chemi- cals. Click image to the left or use the URL below. URL: ",text,
L_0264,petroleum power,T_1546,"The United States does produce oil, but the amount produced is only about one-quarter as much as the nation uses. The United States has only about 1.5% of the worlds proven oil reserves, so most of the oil used by Americans must be imported from other nations. The main oil-producing regions in the United States are the Gulf of Mexico, Texas, Alaska, and California (Figure As in every type of mining, mining for oil has environmental consequences. Oil rigs are unsightly (Figure 1.4), and spills are too common (Figure 1.5). Click image to the left or use the URL below. URL:  Offshore well locations in the Gulf of Mex- ico. Note that some wells are located in very deep water. Drill rigs at the San Ardo Oil Field in Monterey, California. ",text,
L_0264,petroleum power,T_1546,"The United States does produce oil, but the amount produced is only about one-quarter as much as the nation uses. The United States has only about 1.5% of the worlds proven oil reserves, so most of the oil used by Americans must be imported from other nations. The main oil-producing regions in the United States are the Gulf of Mexico, Texas, Alaska, and California (Figure As in every type of mining, mining for oil has environmental consequences. Oil rigs are unsightly (Figure 1.4), and spills are too common (Figure 1.5). Click image to the left or use the URL below. URL:  Offshore well locations in the Gulf of Mex- ico. Note that some wells are located in very deep water. Drill rigs at the San Ardo Oil Field in Monterey, California. ",text,
L_0265,planet orbits in the solar system,T_1547,"Figure 1.1 shows the relative sizes of the orbits of the planets, asteroid belt, and Kuiper belt. In general, the farther away from the Sun, the greater the distance from one planets orbit to the next. The orbits of the planets are not circular but slightly elliptical, with the Sun located at one of the foci (see opening image). While studying the solar system, Johannes Kepler discovered the relationship between the time it takes a planet to make one complete orbit around the Sun, its ""orbital period,"" and the distance from the Sun to the planet. If the orbital period of a planet is known, then it is possible to determine the planets distance from the Sun. This is how astronomers without modern telescopes could determine the distances to other planets within the solar system. How old are you on Earth? How old would you be if you lived on Jupiter? How many days is it until your birthday on Earth? How many days until your birthday if you lived on Saturn? Click image to the left or use the URL below. URL:  The relative sizes of the orbits of planets in the solar system. The inner solar sys- tem and asteroid belt is on the upper left. The upper right shows the outer planets and the Kuiper belt. ",text,
L_0266,planets of the solar system,T_1548,"Since the time of Copernicus, Kepler, and Galileo, we have learned a lot more about our solar system. Astronomers have discovered two more planets (Uranus and Neptune), five dwarf planets (Ceres, Pluto, Makemake, Haumea, and Eris), more than 150 moons, and many, many asteroids and other small objects. Although the Sun is just an average star compared to other stars, it is by far the largest object in the solar system. The Sun is more than 500 times the mass of everything else in the solar system combined! Table 1.1 gives data on the sizes of the Sun and planets relative to Earth. Object Mass (Relative to Earth) Sun Mercury Venus Earth 333,000 Earths mass 0.06 Earths mass 0.82 Earths mass 1.00 Earths mass Diameter of Planet (Relative to Earth) 109.2 Earths diameter 0.39 Earths diameter 0.95 Earths diameter 1.00 Earths diameter Object Mass (Relative to Earth) Mars Jupiter Saturn Uranus Neptune 0.11 Earths mass 317.8 Earths mass 95.2 Earths mass 14.6 Earths mass 17.2 Earths mass Diameter of Planet (Relative to Earth) 0.53 Earths diameter 11.21 Earths diameter 9.41 Earths diameter 3.98 Earths diameter 3.81 Earths diameter ",text,
L_0266,planets of the solar system,T_1549,"Distances in the solar system are often measured in astronomical units (AU). One astronomical unit is defined as the distance from Earth to the Sun. 1 AU equals about 150 million km, or 93 million miles. Table 1.2 shows the distances to the planets (the average radius of orbits) in AU. The table also shows how long it takes each planet to spin on its axis (the length of a day) and how long it takes each planet to complete an orbit (the length of a year); in particular, notice how slowly Venus rotates relative to Earth. Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Average Distance from Sun (AU) 0.39 AU 0.72 1.00 1.52 5.20 9.54 19.22 30.06 Length of Day (In Earth Days) 56.84 days 243.02 1.00 1.03 0.41 0.43 0.72 0.67 Length of Year (In Earth Years) 0.24 years 0.62 1.00 1.88 11.86 29.46 84.01 164.8 Click image to the left or use the URL below. URL: ",text,
L_0268,ponds and lakes,T_1552,"Ponds are small bodies of fresh water that usually have no outlet; ponds are often are fed by underground springs. Like lakes, ponds are bordered by hills or low rises so the water is blocked from flowing directly downhill. ",text,
L_0268,ponds and lakes,T_1553,"Lakes are larger bodies of water. Lakes are usually fresh water, although the Great Salt Lake in Utah is just one exception. Water usually drains out of a lake through a river or a stream and all lakes lose water to evaporation. Lakes form in a variety of different ways: in depressions carved by glaciers, in calderas (Figure 1.1), and along tectonic faults, to name a few. Subglacial lakes are even found below a frozen ice cap. As a result of geologic history and the arrangement of land masses, most lakes are in the Northern Hemisphere. In fact, more than 60% of all the worlds lakes are in Canada  most of these lakes were formed by the glaciers that covered most of Canada in the last Ice Age (Figure 1.2). Lakes are not permanent features of a landscape. Some come and go with the seasons, as water levels rise and fall. Over a longer time, lakes disappear when they fill with sediments, if the springs or streams that fill them diminish, (a) Crater Lake in Oregon is in a volcanic caldera. Lakes can also form in volcanic craters and impact craters. (b) The Great Lakes fill depressions eroded as glaciers scraped rock out from the landscape. (c) Lake Baikal, ice coated in winter in this image, formed as water filled up a tectonic faults. Lakes near Yellowknife were carved by glaciers during the last Ice Age. or if their outlets grow because of erosion. When the climate of an area changes, lakes can either expand or shrink (Figure 1.3). Lakes may disappear if precipitation significantly diminishes. Large lakes have tidal systems and currents, and can even affect weather patterns. The Great Lakes in the United States contain 22% of the worlds fresh surface water (Figure 1.1). The largest them, Lake Superior, has a tide that rises and falls several centimeters each day. The Great Lakes are large enough to alter the weather system in Northeastern United States by the lake effect, which is an increase in snow downwind of the relatively warm lakes. The Great Lakes are home to countless species of fish and wildlife. Many lakes are not natural, but are human-made. People dam a stream in a suitable spot and then let the water back up behind it, creating a lake. These lakes are called ""reservoirs."" Click image to the left or use the URL below. URL: ",text,
L_0268,ponds and lakes,T_1553,"Lakes are larger bodies of water. Lakes are usually fresh water, although the Great Salt Lake in Utah is just one exception. Water usually drains out of a lake through a river or a stream and all lakes lose water to evaporation. Lakes form in a variety of different ways: in depressions carved by glaciers, in calderas (Figure 1.1), and along tectonic faults, to name a few. Subglacial lakes are even found below a frozen ice cap. As a result of geologic history and the arrangement of land masses, most lakes are in the Northern Hemisphere. In fact, more than 60% of all the worlds lakes are in Canada  most of these lakes were formed by the glaciers that covered most of Canada in the last Ice Age (Figure 1.2). Lakes are not permanent features of a landscape. Some come and go with the seasons, as water levels rise and fall. Over a longer time, lakes disappear when they fill with sediments, if the springs or streams that fill them diminish, (a) Crater Lake in Oregon is in a volcanic caldera. Lakes can also form in volcanic craters and impact craters. (b) The Great Lakes fill depressions eroded as glaciers scraped rock out from the landscape. (c) Lake Baikal, ice coated in winter in this image, formed as water filled up a tectonic faults. Lakes near Yellowknife were carved by glaciers during the last Ice Age. or if their outlets grow because of erosion. When the climate of an area changes, lakes can either expand or shrink (Figure 1.3). Lakes may disappear if precipitation significantly diminishes. Large lakes have tidal systems and currents, and can even affect weather patterns. The Great Lakes in the United States contain 22% of the worlds fresh surface water (Figure 1.1). The largest them, Lake Superior, has a tide that rises and falls several centimeters each day. The Great Lakes are large enough to alter the weather system in Northeastern United States by the lake effect, which is an increase in snow downwind of the relatively warm lakes. The Great Lakes are home to countless species of fish and wildlife. Many lakes are not natural, but are human-made. People dam a stream in a suitable spot and then let the water back up behind it, creating a lake. These lakes are called ""reservoirs."" Click image to the left or use the URL below. URL: ",text,
L_0268,ponds and lakes,T_1553,"Lakes are larger bodies of water. Lakes are usually fresh water, although the Great Salt Lake in Utah is just one exception. Water usually drains out of a lake through a river or a stream and all lakes lose water to evaporation. Lakes form in a variety of different ways: in depressions carved by glaciers, in calderas (Figure 1.1), and along tectonic faults, to name a few. Subglacial lakes are even found below a frozen ice cap. As a result of geologic history and the arrangement of land masses, most lakes are in the Northern Hemisphere. In fact, more than 60% of all the worlds lakes are in Canada  most of these lakes were formed by the glaciers that covered most of Canada in the last Ice Age (Figure 1.2). Lakes are not permanent features of a landscape. Some come and go with the seasons, as water levels rise and fall. Over a longer time, lakes disappear when they fill with sediments, if the springs or streams that fill them diminish, (a) Crater Lake in Oregon is in a volcanic caldera. Lakes can also form in volcanic craters and impact craters. (b) The Great Lakes fill depressions eroded as glaciers scraped rock out from the landscape. (c) Lake Baikal, ice coated in winter in this image, formed as water filled up a tectonic faults. Lakes near Yellowknife were carved by glaciers during the last Ice Age. or if their outlets grow because of erosion. When the climate of an area changes, lakes can either expand or shrink (Figure 1.3). Lakes may disappear if precipitation significantly diminishes. Large lakes have tidal systems and currents, and can even affect weather patterns. The Great Lakes in the United States contain 22% of the worlds fresh surface water (Figure 1.1). The largest them, Lake Superior, has a tide that rises and falls several centimeters each day. The Great Lakes are large enough to alter the weather system in Northeastern United States by the lake effect, which is an increase in snow downwind of the relatively warm lakes. The Great Lakes are home to countless species of fish and wildlife. Many lakes are not natural, but are human-made. People dam a stream in a suitable spot and then let the water back up behind it, creating a lake. These lakes are called ""reservoirs."" Click image to the left or use the URL below. URL: ",text,
L_0269,population size,T_1554,"Biotic and abiotic factors determine the population size of a species in an ecosystem. What are some important biotic factors? Biotic factors include the amount of food that is available to that species and the number of organisms that also use that food source. What are some important abiotic factors? Space, water, and climate all help determine a species population. When does a population grow? A population grows when the number of births is greater than the number of deaths. When does a population shrink? When deaths exceed births. What causes a population to grow? For a population to grow there must be ample resources and no major problems. What causes a population to shrink? A population can shrink either because of biotic or abiotic limits. An increase in predators, the emergence of a new disease, or the loss of habitat are just three possible problems that will decrease a population. A population may also shrink if it grows too large for the resources required to support it. ",text,
L_0269,population size,T_1555,"When the number of births equals the number of deaths, the population is at its carrying capacity for that habitat. In a population at its carrying capacity, there are as many organisms of that species as the habitat can support. The carrying capacity depends on biotic and abiotic factors. If these factors improve, the carrying capacity increases. If the factors become less plentiful, the carrying capacity drops. If resources are being used faster than they are being replenished, then the species has exceeded its carrying capacity. If this occurs, the population will then decrease in size. ",text,
L_0269,population size,T_1556,"Every stable population has one or more factors that limit its growth. A limiting factor determines the carrying capacity for a species. A limiting factor can be any biotic or abiotic factor: nutrient, space, and water availability are examples (Figure 1.1). The size of a population is tied to its limiting factor. What happens if a limiting factor increases a lot? Is it still a limiting factor? If a limiting factor increases a lot, another factor will most likely become the new limiting factor. This may be a bit confusing, so lets look at an example of limiting factors. Say you want to make as many chocolate chip cookies as you can with the ingredients you have on hand. It turns out that you have plenty of flour and other ingredients, but only two eggs. You can make only one batch of cookies, because eggs are the limiting factor. But then your neighbor comes over with a dozen eggs. Now you have enough eggs for seven batches of cookies, but only two pounds of butter. You can make four batches of cookies, with butter as the limiting factor. If you get more butter, some other ingredient will be limiting. Species ordinarily produce more offspring than their habitat can support (Figure 1.2). If conditions improve, more young survive and the population grows. If conditions worsen, or if too many young are born, there is competition between individuals. As in any competition, there are some winners and some losers. Those individuals that survive to fill the available spots in the niche are those that are the most fit for their habitat. Click image to the left or use the URL below. URL:  A frog in frog spawn. An animal produces many more offspring than will survive. ",text,
L_0269,population size,T_1556,"Every stable population has one or more factors that limit its growth. A limiting factor determines the carrying capacity for a species. A limiting factor can be any biotic or abiotic factor: nutrient, space, and water availability are examples (Figure 1.1). The size of a population is tied to its limiting factor. What happens if a limiting factor increases a lot? Is it still a limiting factor? If a limiting factor increases a lot, another factor will most likely become the new limiting factor. This may be a bit confusing, so lets look at an example of limiting factors. Say you want to make as many chocolate chip cookies as you can with the ingredients you have on hand. It turns out that you have plenty of flour and other ingredients, but only two eggs. You can make only one batch of cookies, because eggs are the limiting factor. But then your neighbor comes over with a dozen eggs. Now you have enough eggs for seven batches of cookies, but only two pounds of butter. You can make four batches of cookies, with butter as the limiting factor. If you get more butter, some other ingredient will be limiting. Species ordinarily produce more offspring than their habitat can support (Figure 1.2). If conditions improve, more young survive and the population grows. If conditions worsen, or if too many young are born, there is competition between individuals. As in any competition, there are some winners and some losers. Those individuals that survive to fill the available spots in the niche are those that are the most fit for their habitat. Click image to the left or use the URL below. URL:  A frog in frog spawn. An animal produces many more offspring than will survive. ",text,
L_0270,precambrian continents,T_1557,"The first crust was made of basaltic rock, like the current ocean crust. Partial melting of the lower portion of the basaltic crust began more than 4 billion years ago. This created the silica-rich crust that became the felsic continents. ",text,
L_0270,precambrian continents,T_1558,"The earliest felsic continental crust is now found in the ancient cores of continents, called the cratons. Rapid plate motions meant that cratons experienced many continental collisions. Little is known about the paleogeography, or the ancient geography, of the early planet, although smaller continents could have come together and broken up. Geologists can learn many things about the Pre-Archean by studying the rocks of the cratons. Cratons also contain felsic igneous rocks, which are remnants of the first continents. Cratonic rocks contain rounded sedimentary grains. Of what importance is this fact? Rounded grains indicate that the minerals eroded from an earlier rock type and that rivers or seas also existed. One common rock type in the cratons is greenstone, a metamorphosed volcanic rock (Figure 1.1). Since greenstones are found today in oceanic trenches, what does the presence of greenstones mean? These ancient greenstones indicate the presence of subduction zones. Ice age glaciers scraped the Canadian Shield down to the 4.28 billion year old greenstone in Northwestern Quebec. ",text,
L_0270,precambrian continents,T_1559,"Places the craton crops out at the surface is known as a shield. Cratons date from the Precambrian and are called Precambrian shields. Many Precambrian shields are about 570 million years old (Figure 1.2). The Canadian Shield is the ancient flat part of Canada that lies around Hudson Bay, the northern parts of Minnesota, Wisconsin and Michigan and much of Greenland. ",text,
L_0270,precambrian continents,T_1560,"In most places the cratons were covered by younger rocks, which together are called a platform. Sometimes the younger rocks eroded away to expose the Precambrian craton (Figure 1.3). ",text,
L_0270,precambrian continents,T_1561,"During the Pre-Archean and Archean, Earths interior was warmer than today. Mantle convection was faster and plate tectonics processes were more vigorous. Since subduction zones were more common, the early crustal plates were relatively small. Since the time that it was completely molten, Earth has been cooling. Still, about half the internal heat that was generated when Earth formed remains in the planet and is the source of the heat in the core and mantle today. ",text,
L_0271,precambrian plate tectonics,T_1562,"By the end of the Archean, about 2.5 billion years ago, plate tectonics processes were completely recognizable. Small Proterozoic continents known as microcontinents collided to create supercontinents, which resulted in the uplift of massive mountain ranges. The history of the North American craton is an example of what generally happened to the cratons during the Precambrian. As the craton drifted, it collided with microcontinents and oceanic island arcs, which were added to the continents. Convergence was especially active between 1.5 and 1.0 billion years ago. These lands came together to create the continent of Laurentia. About 1.1 billion years ago, Laurentia became part of the supercontinent Rodinia (Figure 1.1). Rodinia probably contained all of the landmass at the time, which was about 75% of the continental landmass present today. Rodinia broke up about 750 million years ago. The geological evidence for this breakup includes large lava flows that are found where continental rifting took place. Seafloor spreading eventually started and created the oceans between the continents. The breakup of Rodinia may have triggered Snowball Earth around 700 million years ago. ",text,
L_0277,preventing hazardous waste problems,T_1581,"Nations that have more industry produce more hazardous waste. Currently, the United States is the worlds largest producer of hazardous wastes, but China, which produces so many products for the developed world, may soon take over the number-one spot. Countries with more industry produce more hazardous wastes than those with little industry. Problems with haz- ardous wastes and their disposal became obvious sooner in the developed world than in the developing world. As a result, many developed nations, including the United States, have laws to help control hazardous waste disposal and to clean toxic sites. As mentioned in the ""Impacts of Hazardous Waste"" concept, the Superfund Act requires companies to clean up contaminated sites that are designated as Superfund sites (Figure 1.1). If a responsible party cannot be identified, because the company has gone out of business or its culpability cannot be proven, the federal government pays for the cleanup out of a trust fund with money put aside by the petroleum and chemical industries. As a result of the Superfund Act, companies today are more careful about how they deal with hazardous substances. Superfund sites are located all over the nation and many are waiting to be cleaned up. The Resource Conservation and Recovery Act of 1976 requires that companies keep track of any hazardous materials they produce. These materials must be disposed of using government guidelines and records must be kept to show the government that the wastes were disposed of safely. Workers must be protected from the hazardous materials. To some extent, individuals can control the production and disposal of hazardous wastes. We can choose to use materials that are not hazardous, such as using vinegar as a cleanser. At home, people can control the amount of pesticides that they use (or they can use organic methods of pest control). It is also necessary to dispose of hazardous materials properly by not pouring them over the land, down the drain or toilet, or into a sewer or trashcan. Click image to the left or use the URL below. URL: ",text,
L_0278,principle of horizontality,T_1582,"Sedimentary rocks follow certain rules. 1. Sedimentary rocks are formed with the oldest layers on the bottom and the youngest on top. 2. Sediments are deposited horizontally, so sedimentary rock layers are originally horizontal, as are some vol- canic rocks, such as ash falls. 3. Sedimentary rock layers that are not horizontal are deformed. Since sedimentary rocks follow these rules, they are useful for seeing the effects of stress on rocks. Sedimentary rocks that are not horizontal must have been deformed. You can trace the deformation a rock has experienced by seeing how it differs from its original horizontal, oldest- on-bottom position. This deformation produces geologic structures such as folds, joints, and faults that are caused by stresses. ",text,
L_0278,principle of horizontality,T_1583,"Youre standing in the Grand Canyon and you see rocks like those in the Figure 1.1. Using the rules listed above, try to figure out the geologic history of the geologic column. The Grand Canyon is full mostly of sedimentary rocks, which are important for deciphering the geologic history of a region. In the Grand Canyon, the rock layers are exposed like a layer cake. Each layer is made of sediments that were deposited in a particular environment - perhaps a lake bed, shallow offshore region, or a sand dune. (a) The rocks of the Grand Canyon are like a layer cake. (b) A geologic column showing the rocks of the Grand Canyon. In this geologic column of the Grand Canyon, the sedimentary rocks of groups 3 through 6 are still horizontal. Group 2 rocks have been tilted. Group 1 rocks are not sedimentary. The oldest layers are on the bottom and youngest are on the top. The ways geologists figure out the geological history of an area will be explored more in the chapter Earth History. Click image to the left or use the URL below. URL: ",text,
L_0279,principle of uniformitarianism,T_1584,"The outcrop in the Figure 1.1 is at Checkerboard Mesa in Zion National Park, Utah. It has a very interesting pattern on it. As a geology student you may ask: how did this rock form? If you poke at the rock and analyze its chemistry you will see that its made of sand. In fact, the rock formation is called the Navajo sandstone. But knowing that the rock is sandstone doesnt tell you how it formed. It would be hard to design an experiment to show how this rock formed. But we can make observations now and apply them to this rock that formed long ago. ",text,
L_0279,principle of uniformitarianism,T_1585,"James Hutton came up with this idea in the late 1700s. The present is the key to the past. He called this the principle of uniformitarianism. It is that if we can understand a geological process now and we find evidence of that same Checkerboard Mesa in Zion National Park, Utah. process in the past, then we can assume that the process operated the same way in the past. Hutton speculated that it has taken millions of years to shape the planet, and it is continuing to be changed. He said that there are slow, natural processes that changed, and continue to change, the planets landscape. For example, given enough time, a stream could erode a valley, or sediment could accumulate and form a new landform. Lets go back to that outcrop. What would cause sandstone to have layers that cross each other, a feature called cross-bedding? ",text,
L_0279,principle of uniformitarianism,T_1586,"In the photo of the Mesquite sand dune in Death Valley National Park, California (Figure 1.2), we see that wind can cause cross-bedding in sand. Cross-bedding is due to changes in wind direction. There are also ripples caused by the wind waving over the surface of the dune. Since we can observe wind forming sand dunes with these patterns now, we have a good explanation for how the Navajo sandstone formed. The Navajo sandstone is a rock formed from ancient sand dunes in which wind direction changed from time to time. This is just one example of how geologists use observations they make today to unravel what happened in Earths past. Rocks formed from volcanoes, oceans, rivers, and many other features are deciphered by looking at the geological work those features do today. Click image to the left or use the URL below. URL: ",text,
L_0280,principles of relative dating,T_1587,"Early geologists had no way to determine the absolute age of a geological material. If they didnt see it form, they couldnt know if a rock was one hundred years or 100 million years old. What they could do was determine the ages of materials relative to each other. Using sensible principles they could say whether one rock was older than another and when a process occurred relative to those rocks. ",text,
L_0280,principles of relative dating,T_1588,"Remember Nicholas Steno, who determined that fossils represented parts of once-living organisms? Steno also noticed that fossil seashells could be found in rocks and mountains far from any ocean. He wanted to explain how that could occur. Steno proposed that if a rock contained the fossils of marine animals, the rock formed from sediments that were deposited on the seafloor. These rocks were then uplifted to become mountains. This scenario led him to develop the principles that are discussed below. They are known as Stenos laws. Stenos laws are illustrated in Figure 1.1. Original horizontality: Sediments are deposited in fairly flat, horizontal layers. If a sedimentary rock is found tilted, the layer was tilted after it was formed. Lateral continuity: Sediments are deposited in continuous sheets that span the body of water that they are deposited in. When a valley cuts through sedimentary layers, it is assumed that the rocks on either side of the valley were originally continuous. Superposition: Sedimentary rocks are deposited one on top of another. The youngest layers are found at the top of the sequence, and the oldest layers are found at the bottom. (a) Original horizontality. (b) Lateral continuity. (c) Superposition. ",text,
L_0280,principles of relative dating,T_1589,"Other scientists observed rock layers and formulated other principles. Geologist William Smith (1769-1839) identified the principle of faunal succession, which recognizes that: Some fossil types are never found with certain other fossil types (e.g. human ancestors are never found with dinosaurs) meaning that fossils in a rock layer represent what lived during the period the rock was deposited. Older features are replaced by more modern features in fossil organisms as species change through time; e.g. feathered dinosaurs precede birds in the fossil record. Fossil species with features that change distinctly and quickly can be used to determine the age of rock layers quite precisely. Scottish geologist, James Hutton (1726-1797) recognized the principle of cross-cutting relationships. This helps geologists to determine the older and younger of two rock units (Figure 1.2). If an igneous dike (B) cuts a series of metamorphic rocks (A), which is older and which is younger? In this image, A must have existed first for B to cut across it. ",text,
L_0280,principles of relative dating,T_1590,"The Grand Canyon provides an excellent illustration of the principles above. The many horizontal layers of sedi- mentary rock illustrate the principle of original horizontality (Figure 1.3). The youngest rock layers are at the top and the oldest are at the bottom, which is described by the law of superposition. Distinctive rock layers, such as the Kaibab Limestone, are matched across the broad expanse of the canyon. These rock layers were once connected, as stated by the rule of lateral continuity. The Colorado River cuts through all the layers of rock to form the canyon. Based on the principle of cross- cutting relationships, the river must be younger than all of the rock layers that it cuts through. ",text,
L_0281,processes of the water cycle,T_1591,"The movement of water around Earths surface is the hydrological (water) cycle (Figure 1.1). Water inhabits reservoirs within the cycle, such as ponds, oceans, or the atmosphere. The molecules move between these reservoirs by certain processes, including condensation and precipitation. There are only so many water molecules and these molecules cycle around. If climate cools and glaciers and ice caps grow, there is less water for the oceans and sea level will fall. The reverse can also happen. The following section looks at the reservoirs and the processes that move water between them. ",text,
L_0281,processes of the water cycle,T_1592,"The Sun, many millions of kilometers away, provides the energy that drives the water cycle. Our nearest star directly impacts the water cycle by supplying the energy needed for evaporation. ",text,
L_0281,processes of the water cycle,T_1593,"Most of Earths water is stored in the oceans, where it can remain for hundreds or thousands of years. ",text,
L_0281,processes of the water cycle,T_1594,"Water changes from a liquid to a gas by evaporation to become water vapor. The Suns energy can evaporate water from the ocean surface or from lakes, streams, or puddles on land. Only the water molecules evaporate; the salts remain in the ocean or a fresh water reservoir. The water vapor remains in the atmosphere until it undergoes condensation to become tiny droplets of liquid. The droplets gather in clouds, which are blown about the globe by wind. As the water droplets in the clouds collide and grow, they fall from the sky as precipitation. Precipitation can be rain, sleet, hail, or snow. Sometimes precipitation falls back into the ocean and sometimes it falls onto the land surface. ",text,
L_0281,processes of the water cycle,T_1595,"When water falls from the sky as rain it may enter streams and rivers that flow downward to oceans and lakes. Water that falls as snow may sit on a mountain for several months. Snow may become part of the ice in a glacier, where it may remain for hundreds or thousands of years. Snow and ice may go directly back into the air by sublimation, the process in which a solid changes directly into a gas without first becoming a liquid. Although you probably have not seen water vapor undergoing sublimation from a glacier, you may have seen dry ice sublimate in air. Snow and ice slowly melt over time to become liquid water, which provides a steady flow of fresh water to streams, rivers, and lakes below. A water droplet falling as rain could also become part of a stream or a lake. At the surface, the water may eventually evaporate and reenter the atmosphere. ",text,
L_0281,processes of the water cycle,T_1596,A significant amount of water infiltrates into the ground. Soil moisture is an important reservoir for water (Figure The moisture content of soil in the United States varies greatly. ,text,
L_0281,processes of the water cycle,T_1597,"Water may seep through dirt and rock below the soil and then through pores infiltrating the ground to go into Earths groundwater system. Groundwater enters aquifers that may store fresh water for centuries. Alternatively, the water may come to the surface through springs or find its way back to the oceans. ",text,
L_0281,processes of the water cycle,T_1598,"Plants and animals depend on water to live. They also play a role in the water cycle. Plants take up water from the soil and release large amounts of water vapor into the air through their leaves (Figure 1.3), a process known as transpiration. ",text,
L_0281,processes of the water cycle,T_1599,"People also depend on water as a natural resource. Not content to get water directly from streams or ponds, humans create canals, aqueducts, dams, and wells to collect water and direct it to where they want it (Figure 1.4). Clouds form above the Amazon Rainfor- est even in the dry season because of moisture from plant transpiration. Pont du Gard in France is an ancient aqueduct and bridge that was part of of a well-developed system that supplied wa- ter around the Roman empire. Click image to the left or use the URL below. URL: ",text,
L_0281,processes of the water cycle,T_1599,"People also depend on water as a natural resource. Not content to get water directly from streams or ponds, humans create canals, aqueducts, dams, and wells to collect water and direct it to where they want it (Figure 1.4). Clouds form above the Amazon Rainfor- est even in the dry season because of moisture from plant transpiration. Pont du Gard in France is an ancient aqueduct and bridge that was part of of a well-developed system that supplied wa- ter around the Roman empire. Click image to the left or use the URL below. URL: ",text,
L_0282,protecting water from pollution,T_1600,Water pollution can be reduced in two ways: Keep the water from becoming polluted. Clean water that is already polluted. ,text,
L_0282,protecting water from pollution,T_1601,"Keeping water from becoming polluted often requires laws to be sure that people and companies behave responsibly. In the United States, the Clean Water Act gives the Environmental Protection Agency (EPA) the authority to set standards for water quality for industry, agriculture, and domestic uses. The law gives the EPA the authority to reduce the discharge of pollution into waterways, finance wastewater treatment plants, and manage runoff. Since its passage in 1972, more wastewater treatment plants have been constructed and the release of industrial waste into the water supply is better controlled. Scientists control water pollution by sam- pling the water and studying the pollutants that are in the water. The United Nations and other international groups are working to improve global water quality standards by pro- viding the technology for treating water. These organizations also educate people in how to protect and improve the quality of the water they use (Figure 1.1). Click image to the left or use the URL below. URL: ",text,
L_0282,protecting water from pollution,T_1602,"The goal of water treatment is to make water suitable for such uses as drinking, medicine, agriculture, and industrial processes. People living in developed countries suffer from few waterborne diseases and illness, because they have extensive water treatment systems to collect, treat, and redeliver clean water. Many underdeveloped nations have few or no water treatment facilities. Wastewater contains hundreds of contaminants, such as suspended solids, oxygen-demanding materials, dissolved inorganic compounds, and harmful bacteria. In a wastewater treatment plant, multiple processes must be used to produce usable water: Sewage treatment removes contaminants, such as solids and particles, from sewage. Water purification produces drinking water by removing bacteria, algae, viruses, fungi, unpleasant elements such as iron and sulfur, and man-made chemical pollutants. The treatment method used depends on the kind of wastewater being treated and the desired end result. Wastewater is treated using a series of steps, each of which produces water with fewer contaminants. ",text,
L_0282,protecting water from pollution,T_1603,"What can individuals do to protect water quality? Find approved recycling or disposal facilities for motor oil and household chemicals. Use lawn, garden, and farm chemicals sparingly and wisely. Repair automobile or boat engine leaks immediately. Keep litter, pet waste, leaves, and grass clippings out of street gutters and storm drains. Click image to the left or use the URL below. URL: ",text,
L_0283,radioactive decay as a measure of age,T_1604,"Radioactivity is the tendency of certain atoms to decay into lighter atoms, a process that emits energy. Radioactivity also provides a way to find the absolute age of a rock. First, we need to know about radioactive decay. ",text,
L_0283,radioactive decay as a measure of age,T_1605,"Some isotopes are radioactive; radioactive isotopes are unstable and spontaneously change by gaining or losing particles. Two types of radioactive decay are relevant to dating Earth materials (Table 1.1): Particle Alpha Composition 2 protons, 2 neutrons Beta 1 electron Effect on Nucleus The nucleus contains two fewer protons and two fewer neutrons. One neutron decays to form a pro- ton and an electron. The electron is emitted. The radioactive decay of a parent isotope (the original element) leads to the formation of stable daughter product, also known as daughter isotope. As time passes, the number of parent isotopes decreases and the number of daughter isotopes increases (Figure 1.1). ",text,
L_0283,radioactive decay as a measure of age,T_1606,"Radioactive materials decay at known rates, measured as a unit called half-life. The half-life of a radioactive substance is the amount of time it takes for half of the parent atoms to decay. This is how the material decays over time (see Table 1.2). No. of half lives passed 0 1 2 3 4 5 6 7 8 Percent parent remaining 100 50 25 12.5 6.25 3.125 1.563 0.781 0.391 Percent daughter produced 0 50 75 87.5 93.75 96.875 98.437 99.219 99.609 Pretend you find a rock with 3.125% parent atoms and 96.875% daughter atoms. How many half lives have passed? If the half-life of the parent isotope is 1 year, then how old is the rock? The decay of radioactive materials can be shown with a graph (Figure 1.2). Notice how it doesnt take too many half lives before there is very little parent remaining and most of the isotopes are daughter isotopes. This limits how many half lives can pass before a radioactive element is no longer useful for Decay of an imaginary radioactive sub- stance with a half-life of one year. dating materials. Fortunately, different isotopes have very different half lives. Click image to the left or use the URL below. URL: ",text,
L_0284,radiometric dating,T_1607,Radiometric dating is the process of using the concentrations of radioactive substances and daughter products to estimate the age of a material. Different isotopes are used to date materials of different ages. Using more than one isotope helps scientists to check the accuracy of the ages that they calculate. ,text,
L_0284,radiometric dating,T_1608,"Radiocarbon dating is used to find the age of once-living materials between 100 and 50,000 years old. This range is especially useful for determining ages of human fossils and habitation sites (Figure 1.1). The atmosphere contains three isotopes of carbon: carbon-12, carbon-13 and carbon-14. Only carbon-14 is radioac- tive; it has a half-life of 5,730 years. The amount of carbon-14 in the atmosphere is tiny and has been relatively stable through time. Plants remove all three isotopes of carbon from the atmosphere during photosynthesis. Animals consume this carbon when they eat plants or other animals that have eaten plants. After the organisms death, the carbon-14 decays to stable nitrogen-14 by releasing a beta particle. The nitrogen atoms are lost to the atmosphere, but the amount of carbon-14 that has decayed can be estimated by measuring the proportion of radioactive carbon-14 to stable carbon- 12. As time passes, the amount of carbon-14 decreases relative to the amount of carbon-12. Carbon isotopes from the black material in these cave paintings places their cre- ating at about 26,000 to 27,000 years BP (before present). ",text,
L_0284,radiometric dating,T_1609,"Potassium-40 decays to argon-40 with a half-life of 1.26 billion years. Argon is a gas so it can escape from molten magma, meaning that any argon that is found in an igneous crystal probably formed as a result of the decay of potassium-40. Measuring the ratio of potassium-40 to argon-40 yields a good estimate of the age of that crystal. Potassium is common in many minerals, such as feldspar, mica, and amphibole. With its half-life, the technique is used to date rocks from 100,000 years to over a billion years old. The technique has been useful for dating fairly young geological materials and deposits containing the bones of human ancestors. ",text,
L_0284,radiometric dating,T_1610,"Two uranium isotopes are used for radiometric dating. Uranium-238 decays to lead-206 with a half-life of 4.47 billion years. Uranium-235 decays to form lead-207 with a half-life of 704 million years. Uranium-lead dating is usually performed on zircon crystals (Figure 1.2). When zircon forms in an igneous rock, the crystals readily accept atoms of uranium but reject atoms of lead. If any lead is found in a zircon crystal, it can be assumed that it was produced from the decay of uranium. Uranium-lead dating is useful for dating igneous rocks from 1 million years to around 4.6 billion years old. Zircon crystals from Australia are 4.4 billion years old, among the oldest rocks on the planet. ",text,
L_0284,radiometric dating,T_1611,"Radiometric dating is a very useful tool for dating geological materials but it does have limits: 1. The material being dated must have measurable amounts of the parent and/or the daughter isotopes. Ideally, different radiometric techniques are used to date the same sample; if the calculated ages agree, they are thought to be accurate. 2. Radiometric dating is not very useful for determining the age of sedimentary rocks. To estimate the age of a sedimentary rock, geologists find nearby igneous rocks that can be dated and use relative dating to constrain the age of the sedimentary rock. ",text,
L_0284,radiometric dating,T_1612,"As youve learned, radiometric dating can only be done on certain materials. But these important numbers can still be used to get the ages of other materials! How would you do this? One way is to constrain a material that cannot be dated by one or more that can. For example, if sedimentary rock A is below volcanic rock B and the age of volcanic rock B is 2.0 million years, then you know that sedimentary rock A is older than 2.0 million years. If sedimentary rock A is above volcanic rock C and its age is 2.5 million years then you know that sedimentary rock A is between 2.0 and 2.5 million years. In this way, geologists can figure out the approximate ages of many different rock formations. ",text,
L_0285,reducing air pollution,T_1613,"The Clean Air Act of 1970 and the amendments since then have done a great job in requiring people to clean up the air over the United States. Emissions of the six major pollutants regulated by the Clean Air Act  carbon monoxide, lead, nitrous oxides, ozone, sulfur dioxide, and particulates  have decreased by more than 50%. Cars, power plants, and factories individually release less pollution than they did in the mid-20th century. But there are many more cars, power plants, and factories. Many pollutants are still being released and some substances have been found to be pollutants that were not known to be pollutants in the past. There is still much work to be done to continue to clean up the air. ",text,
L_0285,reducing air pollution,T_1614,"Reducing air pollution from vehicles can be done in a number of ways. Breaking down pollutants before they are released into the atmosphere. Motor vehicles emit less pollution than they once did because of catalytic converters (Figure 1.1). Catalytic converters contain a catalyst that speeds up chemical reactions and breaks down nitrous oxides, carbon monoxide, and VOCs. Catalytic converters only work when they are hot, so a lot of exhaust escapes as the car is warming up. Catalytic converters are placed on mod- ern cars in the United States. Making a vehicle more fuel efficient. Lighter, more streamlined vehicles need less energy. Hybrid vehicles have an electric motor and a rechargeable battery. The energy that would be lost during braking is funneled into charging the battery, which then can power the car. The internal combustion engine only takes over when power in the battery has run out. Hybrids can reduce auto emissions by 90% or more, but many models do not maximize the possible fuel efficiency of the vehicle. A plug-in hybrid is plugged into an electricity source when it is not in use, perhaps in a garage, to make sure that the battery is charged. Plug-in hybrids run for a longer time on electricity and so are less polluting than regular hybrids. Plug-in hybrids began to become available in 2010. Developing new technologies that do not use fossil fuels. Fueling a car with something other than a liquid organic-based fuel is difficult. A fuel cell converts chemical energy into electrical energy. Hydrogen fuel cells harness the energy released when hydrogen and oxygen come together to create water (Figure 1.2). Fuel cells are extremely efficient and they produce no pollutants. But developing fuel-cell technology has had many problems and no one knows when or if they will become practical. ",text,
L_0285,reducing air pollution,T_1615,"Pollutants are removed from the exhaust streams of power plants and industrial plants before they enter the atmo- sphere. Particulates can be filtered out, and sulfur and nitric oxides can be broken down by catalysts. Removing these oxides reduces the pollutants that cause acid rain. Particles are relatively easy to remove from emissions by using motion or electricity to separate particles from the gases. Scrubbers remove particles and waste gases from exhaust using liquids or neutralizing materials (Figure 1.3). Gases, such as nitrogen oxides, can be broken down at very high temperatures. A hydrogen fuel-cell car looks like a gasoline-powered car. Scrubbers remove particles and waste gases from exhaust. ",text,
L_0285,reducing air pollution,T_1615,"Pollutants are removed from the exhaust streams of power plants and industrial plants before they enter the atmo- sphere. Particulates can be filtered out, and sulfur and nitric oxides can be broken down by catalysts. Removing these oxides reduces the pollutants that cause acid rain. Particles are relatively easy to remove from emissions by using motion or electricity to separate particles from the gases. Scrubbers remove particles and waste gases from exhaust using liquids or neutralizing materials (Figure 1.3). Gases, such as nitrogen oxides, can be broken down at very high temperatures. A hydrogen fuel-cell car looks like a gasoline-powered car. Scrubbers remove particles and waste gases from exhaust. ",text,
L_0285,reducing air pollution,T_1616,"Gasification is a developing technology. In gasification, coal (rarely is another organic material used) is heated to extremely high temperatures to create syngas, which is then filtered. The energy goes on to drive a generator. Syngas releases about 80% less pollution than regular coal plants, and greenhouse gases are also lower. Clean coal plants do not need scrubbers or other pollution control devices. Although the technology is ready, clean coal plants are more expensive to construct and operate. Also, heating the coal to high enough temperatures uses a great deal of energy, so the technology is not energy efficient. In addition, large amounts of the greenhouse gas CO2 are still released with clean coal technology. Nonetheless, a few of these plants are operating in the United States and around the world. ",text,
L_0285,reducing air pollution,T_1617,"How can air pollution be reduced? Using less fossil fuel is one way to lessen pollution. Some examples of ways to conserve fossil fuels are: Riding a bike or walking instead of driving. Taking a bus or carpooling. Buying a car that has greater fuel efficiency. Turning off lights and appliances when they are not in use. Using energy efficient light bulbs and appliances. Buying fewer things that are manufactured using fossil fuels. All these actions reduce the amount of energy that power plants need to produce. Click image to the left or use the URL below. URL:  Developing alternative energy sources is important. What are some of the problems facing wider adoption of alternative energy sources? The technologies for several sources of alternative energy, including solar and wind, are still being developed. Solar and wind are still expensive relative to using fossil fuels. The technology needs to advance so that the price falls. Some areas get low amounts of sunlight and are not suited for solar. Others do not have much wind. It is important that regions develop what best suits them. While the desert Southwest will need to develop solar, the Great Plains can use wind energy as its energy source. Perhaps some locations will rely on nuclear power plants, although current nuclear power plants have major problems with safety and waste disposal. Sometimes technological approaches are what is needed. Click image to the left or use the URL below. URL: ",text,
L_0286,reducing ozone destruction,T_1618,"One success story in reducing pollutants that harm the atmosphere concerns ozone-destroying chemicals. In 1973, scientists calculated that CFCs could reach the stratosphere and break apart. This would release chlorine atoms, which would then destroy ozone. Based only on their calculations, the United States and most Scandinavian countries banned CFCs in spray cans in 1978. More confirmation that CFCs break down ozone was needed before more was done to reduce production of ozone- destroying chemicals. In 1985, members of the British Antarctic Survey reported that a 50% reduction in the ozone layer had been found over Antarctica in the previous three springs. ",text,
L_0286,reducing ozone destruction,T_1619,"Two years after the British Antarctic Survey report, the ""Montreal Protocol on Substances that Deplete the Ozone Layer"" was ratified by nations all over the world. The Montreal Protocol controls the production and consumption of 96 chemicals that damage the ozone layer (Figure 1.1). Hazardous substances are phased out first by developed nations and one decade later by developing nations. More hazardous substances are phased out more quickly. CFCs have been mostly phased out since 1995, although were used in developing nations until 2010. Some of the less hazardous substances will not be phased out until 2030. The Protocol also requires that wealthier nations donate money to develop technologies that will replace these chemicals. Ozone levels over North America decreased between 1974 and 2009. Models of the future predict what ozone levels would have been if CFCs were not being phased out. Warmer colors indicate more ozone. Since CFCs take many years to reach the stratosphere and can survive there a long time before they break down, the ozone hole will probably continue to grow for some time before it begins to shrink. The ozone layer will reach the same levels it had before 1980 around 2068 and 1950 levels in one or two centuries. ",text,
L_0287,revolutions of earth,T_1620,"Certainly no one today doubts that Earth orbits a star, the Sun. Photos taken from space, observations made by astronauts, and the fact that there has been so much successful space exploration that depends on understanding the structure of the solar system all confirm it. But in the early 17th century saying that Earth orbited the Sun rather than the reverse could get you tried for heresy, as it did Galileo. Lets explore the evolution of the idea that Earth orbits the Sun. ",text,
L_0287,revolutions of earth,T_1621,"To an observer, Earth appears to be the center of the universe. That is what the ancient Greeks believed. This view is called the geocentric model, or ""Earth-centered"" model, of the universe. In the geocentric model, the sky, or heavens, are a set of spheres layered on top of one another. Each object in the sky is attached to a sphere and moves around Earth as that sphere rotates. From Earth outward, these spheres contain the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn. An outer sphere holds all the stars. Since the planets appear to move much faster than the stars, the Greeks placed them closer to Earth. The geocentric model explained why all the stars appear to rotate around Earth once per day. The model also explained why the planets move differently from the stars and from each other. One problem with the geocentric model is that some planets seem to move backwards (in retrograde) instead of in their usual forward motion around Earth. Around 150 A.D. the astronomer Ptolemy resolved this problem by using a system of circles to describe the motion of planets (Figure 1.1). In Ptolemys system, a planet moves in a small circle, called an epicycle. This circle moves around Earth in a larger circle, called a deferent. Ptolemys version of the geocentric model worked so well that it remained the accepted model of the universe for more than a thousand years. ",text,
L_0287,revolutions of earth,T_1622,"Ptolemys geocentric model worked, but it was complicated and occasionally made errors in predicting the movement of planets. At the beginning of the 16th century A.D., Nicolaus Copernicus proposed that Earth and all the other planets orbit the Sun. With the Sun at the center, this model is called the heliocentric model, or ""sun-centered"" model. Although Copernicus model was simpler - it didnt need epicycles and deferents - it still did not perfectly describe the motion of the planets. Johannes Kepler solved the problem a short time later when he determined that the planets moved around the Sun in ellipses (ovals), not circles (Figure 1.2). Keplers model matched observations perfectly. The heliocentric model did not catch on right away. When Galileo Galilei first turned a telescope to the heavens in 1610, he made several striking discoveries. Galileo discovered that the planet Jupiter has moons orbiting around it. This provided the first evidence that objects could orbit something besides Earth. Galileo also discovered that Venus has phases like the Moon (Figure 1.3), which provides direct evidence that Venus orbits the Sun. Galileos discoveries caused many more people to accept the heliocentric model of the universe, although Galileo himself was found guilty of heresy. The shift from an Earth-centered view to a Sun-centered view of the universe is referred to as the Copernican Revolution. In their elliptical orbits, each planet is sometimes farther away from the Sun than at other times. This movement is called revolution. At the same time, Earth spins on its axis. Earths axis is an imaginary line passing through the Keplers model showed the planets moving around the Sun in ellipses. The phases of Venus. planets center that goes through both the North Pole and the South Pole. This spinning movement is called Earths rotation. ",text,
L_0287,revolutions of earth,T_1622,"Ptolemys geocentric model worked, but it was complicated and occasionally made errors in predicting the movement of planets. At the beginning of the 16th century A.D., Nicolaus Copernicus proposed that Earth and all the other planets orbit the Sun. With the Sun at the center, this model is called the heliocentric model, or ""sun-centered"" model. Although Copernicus model was simpler - it didnt need epicycles and deferents - it still did not perfectly describe the motion of the planets. Johannes Kepler solved the problem a short time later when he determined that the planets moved around the Sun in ellipses (ovals), not circles (Figure 1.2). Keplers model matched observations perfectly. The heliocentric model did not catch on right away. When Galileo Galilei first turned a telescope to the heavens in 1610, he made several striking discoveries. Galileo discovered that the planet Jupiter has moons orbiting around it. This provided the first evidence that objects could orbit something besides Earth. Galileo also discovered that Venus has phases like the Moon (Figure 1.3), which provides direct evidence that Venus orbits the Sun. Galileos discoveries caused many more people to accept the heliocentric model of the universe, although Galileo himself was found guilty of heresy. The shift from an Earth-centered view to a Sun-centered view of the universe is referred to as the Copernican Revolution. In their elliptical orbits, each planet is sometimes farther away from the Sun than at other times. This movement is called revolution. At the same time, Earth spins on its axis. Earths axis is an imaginary line passing through the Keplers model showed the planets moving around the Sun in ellipses. The phases of Venus. planets center that goes through both the North Pole and the South Pole. This spinning movement is called Earths rotation. ",text,
L_0287,revolutions of earth,T_1623,"Copernicus, Galileo, and Kepler were all right: Earth and the other planets travel in an elliptical orbit around the Sun. The gravitational pull of the Sun keeps the planets in orbit. This ellipse is barely elliptical; its very close to being a circle. The closest Earth gets to the Sun each year is at perihelion (147 million km) on about January 3rd, and the furthest is at aphelion (152 million km) on July 4th. The shape of Earths orbit has nothing to do with Earths seasons. Earth and the other planets in the solar system make elliptical orbits around the Sun. For Earth to make one complete revolution around the Sun takes 365.24 days. This amount of time is the definition of one year. Earth has one large moon, which orbits Earth once every 29.5 days, a period known as a month. Click image to the left or use the URL below. URL: ",text,
L_0288,rocks,T_1624,"A rock is a naturally formed, non-living Earth material. Rocks are made of collections of mineral grains that are held together in a firm, solid mass (Figure 1.1). How is a rock different from a mineral? Rocks are made of minerals. The mineral grains in a rock may be so tiny that you can only see them with a microscope, or they may be as big as your fingernail or even your finger (Figure Rocks are identified primarily by the minerals they contain and by their texture. Each type of rock has a distinctive set of minerals. A rock may be made of grains of all one mineral type, such as quartzite. Much more commonly, rocks are made of a mixture of different minerals. Texture is a description of the size, shape, and arrangement of mineral grains. Are the two samples in Figure 1.3 the same rock type? Do they have the same minerals? The same texture? The different colors and textures seen in this rock are caused by the presence of different minerals. A pegmatite from South Dakota with crystals of lepidolite, tourmaline, and quartz (1 cm scale on the upper left). Sample 2 Crystals are tiny or microscopic Magma erupted and cooled quickly Andesite As seen in Table 1.1, these two rocks have the same chemical composition and contain mostly the same minerals, but they do not have the same texture. Sample 1 has visible mineral grains, but Sample 2 has very tiny or invisible grains. The two different textures indicate different histories. Sample 1 is a diorite, a rock that cooled slowly from magma (molten rock) underground. Sample 2 is an andesite, a rock that cooled rapidly from a very similar magma that erupted onto Earths surface. A few rocks are not made of minerals because the material they are made of does not fit the definition of a mineral. Coal, for example, is made of organic material, which is not a mineral. Can you think of other rocks that are not made of minerals? Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0288,rocks,T_1624,"A rock is a naturally formed, non-living Earth material. Rocks are made of collections of mineral grains that are held together in a firm, solid mass (Figure 1.1). How is a rock different from a mineral? Rocks are made of minerals. The mineral grains in a rock may be so tiny that you can only see them with a microscope, or they may be as big as your fingernail or even your finger (Figure Rocks are identified primarily by the minerals they contain and by their texture. Each type of rock has a distinctive set of minerals. A rock may be made of grains of all one mineral type, such as quartzite. Much more commonly, rocks are made of a mixture of different minerals. Texture is a description of the size, shape, and arrangement of mineral grains. Are the two samples in Figure 1.3 the same rock type? Do they have the same minerals? The same texture? The different colors and textures seen in this rock are caused by the presence of different minerals. A pegmatite from South Dakota with crystals of lepidolite, tourmaline, and quartz (1 cm scale on the upper left). Sample 2 Crystals are tiny or microscopic Magma erupted and cooled quickly Andesite As seen in Table 1.1, these two rocks have the same chemical composition and contain mostly the same minerals, but they do not have the same texture. Sample 1 has visible mineral grains, but Sample 2 has very tiny or invisible grains. The two different textures indicate different histories. Sample 1 is a diorite, a rock that cooled slowly from magma (molten rock) underground. Sample 2 is an andesite, a rock that cooled rapidly from a very similar magma that erupted onto Earths surface. A few rocks are not made of minerals because the material they are made of does not fit the definition of a mineral. Coal, for example, is made of organic material, which is not a mineral. Can you think of other rocks that are not made of minerals? Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0288,rocks,T_1624,"A rock is a naturally formed, non-living Earth material. Rocks are made of collections of mineral grains that are held together in a firm, solid mass (Figure 1.1). How is a rock different from a mineral? Rocks are made of minerals. The mineral grains in a rock may be so tiny that you can only see them with a microscope, or they may be as big as your fingernail or even your finger (Figure Rocks are identified primarily by the minerals they contain and by their texture. Each type of rock has a distinctive set of minerals. A rock may be made of grains of all one mineral type, such as quartzite. Much more commonly, rocks are made of a mixture of different minerals. Texture is a description of the size, shape, and arrangement of mineral grains. Are the two samples in Figure 1.3 the same rock type? Do they have the same minerals? The same texture? The different colors and textures seen in this rock are caused by the presence of different minerals. A pegmatite from South Dakota with crystals of lepidolite, tourmaline, and quartz (1 cm scale on the upper left). Sample 2 Crystals are tiny or microscopic Magma erupted and cooled quickly Andesite As seen in Table 1.1, these two rocks have the same chemical composition and contain mostly the same minerals, but they do not have the same texture. Sample 1 has visible mineral grains, but Sample 2 has very tiny or invisible grains. The two different textures indicate different histories. Sample 1 is a diorite, a rock that cooled slowly from magma (molten rock) underground. Sample 2 is an andesite, a rock that cooled rapidly from a very similar magma that erupted onto Earths surface. A few rocks are not made of minerals because the material they are made of does not fit the definition of a mineral. Coal, for example, is made of organic material, which is not a mineral. Can you think of other rocks that are not made of minerals? Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0289,rocks and processes of the rock cycle,T_1625,"The rock cycle, illustrated in Figure 1.1, depicts how the three major rock types - igneous, sedimentary, and meta- morphic - convert from one to another. Arrows connecting the rock types represent the processes that accomplish these changes. Rocks change as a result of natural processes that are taking place all the time. Most changes happen very slowly. Rocks deep within the Earth are right now becoming other types of rocks. Rocks at the surface are lying in place before they are next exposed to a process that will change them. Even at the surface, we may not notice the changes. The rock cycle has no beginning or end. ",text,
L_0289,rocks and processes of the rock cycle,T_1626,"Rocks are classified into three major groups according to how they form. These three types are described in more detail in other concepts in this chapter, but here is a summary. The Rock Cycle. Igneous rocks form from the cooling and hardening of molten magma in many different environments. The chemical composition of the magma and the rate at which it cools determine what rock forms. Igneous rocks can cool slowly beneath the surface or rapidly at the surface. These rocks are identified by their composition and texture. More than 700 different types of igneous rocks are known. Sedimentary rocks form by the compaction and cementing together of sediments, broken pieces of rock-like gravel, sand, silt, or clay. Those sediments can be formed from the weathering and erosion of preexisting rocks. Sedimentary rocks also include chemical precipitates, the solid materials left behind after a liquid evaporates. Metamorphic rocks form when the minerals in an existing rock are changed by heat or pressure below the surface. Click image to the left or use the URL below. URL: ",text,
L_0289,rocks and processes of the rock cycle,T_1627,"Several processes can turn one type of rock into another type of rock. The key processes of the rock cycle are crystallization, erosion and sedimentation, and metamorphism. ",text,
L_0289,rocks and processes of the rock cycle,T_1628,"Magma cools either underground or on the surface and hardens into an igneous rock. As the magma cools, different crystals form at different temperatures, undergoing crystallization. For example, the mineral olivine crystallizes out of magma at much higher temperatures than quartz. The rate of cooling determines how much time the crystals will have to form. Slow cooling produces larger crystals. ",text,
L_0289,rocks and processes of the rock cycle,T_1629,"Weathering wears rocks at the Earths surface down into smaller pieces. The small fragments are called sediments. Running water, ice, and gravity all transport these sediments from one place to another by erosion. During sedimen- tation, the sediments are laid down or deposited. In order to form a sedimentary rock, the accumulated sediment must become compacted and cemented together. ",text,
L_0289,rocks and processes of the rock cycle,T_1630,"When a rock is exposed to extreme heat and pressure within the Earth but does not melt, the rock becomes meta- morphosed. Metamorphism may change the mineral composition and the texture of the rock. For that reason, a metamorphic rock may have a new mineral composition and/or texture. ",text,
L_0291,rotation of earth,T_1635,"In 1851, a French scientist named Lon Foucault took an iron sphere and hung it from a wire. He pulled the sphere to one side and then released it, as a pendulum. Although a pendulum set in motion should not change its motion, Foucault observed that his pendulum did seem to change direction relative to the circle below. Foucault concluded that Earth was moving underneath the pendulum. People at that time already knew that Earth rotated on its axis, but Foucaults experiment was nice confirmation. ",text,
L_0291,rotation of earth,T_1636,"Imagine a line passing through the center of Earth that goes through both the North Pole and the South Pole. This imaginary line is called an axis. Earth spins around its axis, just as a top spins around its spindle. This spinning movement is called Earths rotation. An observer in space will see that Earth requires 23 hours, 59 minutes, and 4 seconds to make one complete rotation on its axis. But because Earth moves around the Sun at the same time that it is rotating, the planet must turn just a little bit more to reach the same place relative to the Sun. Hence the length of a day on Earth is actually 24 hours. At the Equator, the Earth rotates at a speed of about 1,700 km per hour, but at the poles the movement speed is nearly nothing. ",text,
L_0291,rotation of earth,T_1637,"Earth rotates once on its axis about every 24 hours. To an observer looking down at the North Pole, the rotation appears counterclockwise. From nearly all points on Earth, the Sun appears to move across the sky from east to west each day. Of course, the Sun is not moving from east to west at all; Earth is rotating. The Moon and stars also seem to rise in the east and set in the west. Earths rotation means that there is a cycle of daylight and darkness approximately every 24 hours, the length of a day. Different places experience sunset and sunrise at different times and the amount of daylight and darkness also differs by location. Shadows are areas where an object obstructs a light source so that darkness takes on the form of the object. On Earth, a shadow can be cast by the Sun, Moon, or (rarely) Mercury or Venus. Click image to the left or use the URL below. URL: ",text,
L_0292,safety of water,T_1638,The water that comes out of our faucets is safe because it has gone through a series of treatment and purification processes to remove contaminants. Those of us who are fortunate enough to always be able to get clean water from a tap in our home may have trouble imagining life in a country that cannot afford the technology to treat and purify water. ,text,
L_0292,safety of water,T_1639,"Many people in the world have no choice but to drink from the same polluted river where sewage is dumped. One- fifth of all people in the world, more than 1.1 billion people, do not have access to safe water for drinking, personal cleanliness, and domestic use. Unsafe drinking water carries many pathogens, or disease-causing biological agents such as infectious bacteria and parasites. Toxic chemicals and radiological hazards in water can also cause diseases. ",text,
L_0292,safety of water,T_1640,"Waterborne disease caused by unsafe drinking water is the leading cause of death for children under the age of five in many nations and a cause of death and illness for many adults. About 88% of all diseases are caused by drinking unsafe water (Figure 1.1). Throughout the world, more than 14,000 people die every day from waterborne diseases, such as cholera, and many of the worlds hospital beds are occupied by patients suffering from a waterborne disease. Guinea worm is a serious problem in parts of Africa that is being eradicated. Learn what is being done to decrease the number of people suffering from this parasite at the video below. Click image to the left or use the URL below. URL: ",text,
L_0293,satellites shuttles and space stations,T_1641,"A rocket is propelled into space by particles flying out of one end at high speed (see Figure 1.1). A rocket in space moves like a skater holding the fire extinguisher. Fuel is ignited in a chamber, which causes an explosion of gases. The explosion creates pressure that forces the gases out of the rocket. As these gases rush out the end, the rocket moves in the opposite direction, as predicted by Newtons Third Law of Motion. The reaction force of the gases on the rocket pushes the rocket forward. The force pushing the rocket is called thrust. Nothing would get into space without being thrust upward by a rocket. ",text,
L_0293,satellites shuttles and space stations,T_1642,"One of the first uses of rockets in space was to launch satellites. A satellite is an object that orbits a larger object. An orbit is a circular or elliptical path around an object. The Moon was Earths first satellite, but now many human- made ""artificial satellites"" orbit the planet. Thousands of artificial satellites have been put into orbit around Earth (Figure 1.2). We have even put satellites into orbit around the Moon, the Sun, Venus, Mars, Jupiter, and Saturn. There are four main types of satellites. Imaging satellites take pictures of Earths surface for military or scientific purposes. Imaging satellites study the Moon and other planets. Communications satellites receive and send signals for telephone, television, or other types of communica- tions. Navigational satellites are used for navigation systems, such as the Global Positioning System (GPS). The International Space Station, the largest artificial satellite, is designed for humans to live in space while conducting scientific research. ",text,
L_0293,satellites shuttles and space stations,T_1643,"Humans have a presence in space at the International Space Station (ISS) (pictured in Figure 1.3). Modern space stations are constructed piece by piece to create a modular system. The primary purpose of the ISS is scientific research, especially in medicine, biology, and physics. ",text,
L_0293,satellites shuttles and space stations,T_1644,"Craft designed for human spaceflight, like the Apollo missions, were very successful, but were also very expensive, could not carry much cargo, and could be used only once. To outfit the ISS, NASA needed a space vehicle that was reusable and able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The resulting spacecraft was a space shuttle, shown in (Figure 1.4). Satellites operate with solar panels for energy. A photograph of the International Space Station was taken from the space shuttle Atlantis in June 2007. Construction of the station was completed in 2011, but new pieces and experiments continue to be added. A space shuttle has three main parts. The part you are probably most familiar with is the orbiter, with wings like an airplane. When a space shuttle launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large ""booster rockets."" All of this is needed to get the orbiter out of Earths atmosphere. Once in space, the orbiter can be used to release equipment (such as a satellite or supplies for the International Space Station), to repair existing equipment such as the Hubble Space Telescope, or to do experiments directly on board the orbiter. When the mission is complete, the orbiter re-enters Earths atmosphere and flies back to Earth more like a glider than an airplane. The Space Shuttle program did 135 missions between 1981 and 2011, when the remaining shuttles were retired. The ISS is now serviced by Russian Soyuz spacecraft. Atlantis on the launch pad in 2006. Since 1981, the space shuttle has been the United States primary vehicle for carrying people and large equipment into space. ",text,
L_0293,satellites shuttles and space stations,T_1644,"Craft designed for human spaceflight, like the Apollo missions, were very successful, but were also very expensive, could not carry much cargo, and could be used only once. To outfit the ISS, NASA needed a space vehicle that was reusable and able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The resulting spacecraft was a space shuttle, shown in (Figure 1.4). Satellites operate with solar panels for energy. A photograph of the International Space Station was taken from the space shuttle Atlantis in June 2007. Construction of the station was completed in 2011, but new pieces and experiments continue to be added. A space shuttle has three main parts. The part you are probably most familiar with is the orbiter, with wings like an airplane. When a space shuttle launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large ""booster rockets."" All of this is needed to get the orbiter out of Earths atmosphere. Once in space, the orbiter can be used to release equipment (such as a satellite or supplies for the International Space Station), to repair existing equipment such as the Hubble Space Telescope, or to do experiments directly on board the orbiter. When the mission is complete, the orbiter re-enters Earths atmosphere and flies back to Earth more like a glider than an airplane. The Space Shuttle program did 135 missions between 1981 and 2011, when the remaining shuttles were retired. The ISS is now serviced by Russian Soyuz spacecraft. Atlantis on the launch pad in 2006. Since 1981, the space shuttle has been the United States primary vehicle for carrying people and large equipment into space. ",text,
L_0293,satellites shuttles and space stations,T_1644,"Craft designed for human spaceflight, like the Apollo missions, were very successful, but were also very expensive, could not carry much cargo, and could be used only once. To outfit the ISS, NASA needed a space vehicle that was reusable and able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The resulting spacecraft was a space shuttle, shown in (Figure 1.4). Satellites operate with solar panels for energy. A photograph of the International Space Station was taken from the space shuttle Atlantis in June 2007. Construction of the station was completed in 2011, but new pieces and experiments continue to be added. A space shuttle has three main parts. The part you are probably most familiar with is the orbiter, with wings like an airplane. When a space shuttle launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large ""booster rockets."" All of this is needed to get the orbiter out of Earths atmosphere. Once in space, the orbiter can be used to release equipment (such as a satellite or supplies for the International Space Station), to repair existing equipment such as the Hubble Space Telescope, or to do experiments directly on board the orbiter. When the mission is complete, the orbiter re-enters Earths atmosphere and flies back to Earth more like a glider than an airplane. The Space Shuttle program did 135 missions between 1981 and 2011, when the remaining shuttles were retired. The ISS is now serviced by Russian Soyuz spacecraft. Atlantis on the launch pad in 2006. Since 1981, the space shuttle has been the United States primary vehicle for carrying people and large equipment into space. ",text,
L_0293,satellites shuttles and space stations,T_1644,"Craft designed for human spaceflight, like the Apollo missions, were very successful, but were also very expensive, could not carry much cargo, and could be used only once. To outfit the ISS, NASA needed a space vehicle that was reusable and able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The resulting spacecraft was a space shuttle, shown in (Figure 1.4). Satellites operate with solar panels for energy. A photograph of the International Space Station was taken from the space shuttle Atlantis in June 2007. Construction of the station was completed in 2011, but new pieces and experiments continue to be added. A space shuttle has three main parts. The part you are probably most familiar with is the orbiter, with wings like an airplane. When a space shuttle launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large ""booster rockets."" All of this is needed to get the orbiter out of Earths atmosphere. Once in space, the orbiter can be used to release equipment (such as a satellite or supplies for the International Space Station), to repair existing equipment such as the Hubble Space Telescope, or to do experiments directly on board the orbiter. When the mission is complete, the orbiter re-enters Earths atmosphere and flies back to Earth more like a glider than an airplane. The Space Shuttle program did 135 missions between 1981 and 2011, when the remaining shuttles were retired. The ISS is now serviced by Russian Soyuz spacecraft. Atlantis on the launch pad in 2006. Since 1981, the space shuttle has been the United States primary vehicle for carrying people and large equipment into space. ",text,
L_0294,saturn,T_1645,"Saturn, shown in Figure 1.1, is famous for its beautiful rings. Although all the gas giants have rings, only Saturns can be easily seen from Earth. In Roman mythology, Saturn was the father of Jupiter. Saturns mass is about 95 times the mass of Earth, and its volume is 755 times Earths volume, making it the second largest planet in the solar system. Saturn is also the least dense planet in the solar system. It is less dense than water. What would happen if you had a large enough bathtub to put Saturn in? Saturn would float! Saturn orbits the Sun once about every 30 Earth years. Like Jupiter, Saturn is made mostly of hydrogen and helium gases in the outer layers and liquids at greater depths. The upper atmosphere has clouds in bands of different colors. These rotate rapidly around the planet, but there seems to be less turbulence and fewer storms on Saturn than on Jupiter. One interesting phenomenon that has been observed in the storms on Saturn is the presence of thunder and lightning (see video, below). The planet likely has a small rocky and metallic core. This image of Saturn and its rings is a composite of pictures taken by the Cassini orbiter in 2008 ",text,
L_0294,saturn,T_1646,"In 1610, Galileo first observed Saturns rings with his telescope, but he thought they might be two large moons, one on either side of the planet. In 1659, the Dutch astronomer Christian Huygens realized that the features were rings (Figure 1.2). Saturns rings circle the planets equator and appear tilted because Saturn itself is tilted about 27 degrees. The rings do not touch the planet. The Voyager 1 and 2 spacecraft in 1980 and 1981 sent back detailed pictures of Saturn, its rings, and some of its moons. Saturns rings are made of particles of water and ice, with some dust and rocks (Figure 1.3). There are several gaps in the rings that scientists think have originated because the material was cleared out by the gravitational pull within the rings, or by the gravitational forces of Saturn and of moons outside the rings. The rings were likely formed by the breakup of one of Saturns moons or from material that never accreted into the planet when Saturn originally formed. ",text,
L_0294,saturn,T_1647,"Most of Saturns moons are very small, and only seven are large enough for gravity to have made them spherical. Only Titan is larger than Earths Moon at about 1.5 times its size. Titan is even larger than the planet Mercury. Scientists are interested in Titan because its atmosphere is similar to what Earths was like before life developed. Nitrogen is dominant and methane is the second most abundant gas. Titan may have a layer of liquid water and ammonia under a layer of surface ice. Lakes of liquid methane (CH4 ) and ethane (C2 H6 ) are found on Titans surface. Although conditions are similar enough to those of early Earth for scientists to speculate that extremely A color-exaggerated mosaic of Saturn and its rings taken by Cassini as Saturn eclipses the Sun. A close-up of Saturns outer C ring show- ing areas with higher particle concentra- tion and gaps. This composite image compares Saturns largest moon, Titan (right) to Earth (left). Click image to the left or use the URL below. URL: ",text,
L_0294,saturn,T_1647,"Most of Saturns moons are very small, and only seven are large enough for gravity to have made them spherical. Only Titan is larger than Earths Moon at about 1.5 times its size. Titan is even larger than the planet Mercury. Scientists are interested in Titan because its atmosphere is similar to what Earths was like before life developed. Nitrogen is dominant and methane is the second most abundant gas. Titan may have a layer of liquid water and ammonia under a layer of surface ice. Lakes of liquid methane (CH4 ) and ethane (C2 H6 ) are found on Titans surface. Although conditions are similar enough to those of early Earth for scientists to speculate that extremely A color-exaggerated mosaic of Saturn and its rings taken by Cassini as Saturn eclipses the Sun. A close-up of Saturns outer C ring show- ing areas with higher particle concentra- tion and gaps. This composite image compares Saturns largest moon, Titan (right) to Earth (left). Click image to the left or use the URL below. URL: ",text,
L_0294,saturn,T_1647,"Most of Saturns moons are very small, and only seven are large enough for gravity to have made them spherical. Only Titan is larger than Earths Moon at about 1.5 times its size. Titan is even larger than the planet Mercury. Scientists are interested in Titan because its atmosphere is similar to what Earths was like before life developed. Nitrogen is dominant and methane is the second most abundant gas. Titan may have a layer of liquid water and ammonia under a layer of surface ice. Lakes of liquid methane (CH4 ) and ethane (C2 H6 ) are found on Titans surface. Although conditions are similar enough to those of early Earth for scientists to speculate that extremely A color-exaggerated mosaic of Saturn and its rings taken by Cassini as Saturn eclipses the Sun. A close-up of Saturns outer C ring show- ing areas with higher particle concentra- tion and gaps. This composite image compares Saturns largest moon, Titan (right) to Earth (left). Click image to the left or use the URL below. URL: ",text,
L_0299,scientific models,T_1662,"Scientific models are useful tools in science. Earths climate is extremely complex, with many factors that are dependent on one another. Such a system is impossible for scientists to work with as a whole. To deal with such complexity, scientists may create models to represent the system that they are interested in studying. Scientists must validate their ideas by testing. A model can be manipulated and adjusted far more easily than a real system. Models help scientists understand, analyze, and make predictions about systems that would be impossible to study as a whole. If a scientist wants to understand how rising CO2 levels will affect climate, it will be easier to model a smaller portion of that system. For example, he may model how higher levels of CO2 affect plant growth and the effect that will have on climate. ",text,
L_0299,scientific models,T_1663,"How can scientists know if a model designed to predict the future is likely to be accurate, since it may not be possible to wait long enough to see if the prediction comes true? One way is to run the model using a time in the past as the starting point see if the model can accurately predict the present. A model that can successfully predict the present is more likely to be accurate when predicting the future. Many models are created on computers because only computers can handle and manipulate such enormous amounts of data. For example, climate models are very useful for trying to determine what types of changes we can expect as the composition of the atmosphere changes. A reasonably accurate climate model would be impossible on anything other than the most powerful computers. ",text,
L_0299,scientific models,T_1664,"Since models are simpler than real objects or systems, they have limitations. A model deals with only a portion of a system. It may not predict the behavior of the real system very accurately. But the more computing power that goes into the model and the care with which the scientists construct the model can increase the chances that a model will be accurate. ",text,
L_0299,scientific models,T_1665,Physical models are smaller and simpler representations of the thing being studied. A globe or a map is a physical model of a portion or all of Earth. Conceptual models tie together many ideas to explain a phenomenon or event. Mathematical models are sets of equations that take into account many factors to represent a phenomenon. Mathematical models are usually done on computers. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ,text,
L_0300,seafloor spreading hypothesis,T_1666,"Harry Hess was a geology professor and a naval officer who commanded an attack transport ship during WWII. Like other ships, Hesss ship had echo sounders that mapped the seafloor. Hess discovered hundreds of flat-topped mountains in the Pacific that he gave the name guyot. He puzzled at what could have formed mountains that appeared to be eroded at the top but were more than a mile beneath the sea surface. Hess also noticed trenches that were as much as 7 miles deep. Meanwhile, other scientists like Bruce Heezen discovered the underwater mountain range they called the Great Global Rift. Although the rift was mostly in the deep sea, it occasionally came close to land. These scientists thought the rift was a set of breaks in Earths crust. The final piece that was needed was the work of Vine and Matthews, who had discovered the bands of alternating magnetic polarity in the seafloor symmetrically about the rift. ",text,
L_0300,seafloor spreading hypothesis,T_1667,"The features of the seafloor and the patterns of magnetic polarity symmetrically about the mid-ocean ridges were the pieces that Hess needed. He resurrected Wegeners continental drift hypothesis and also the mantle convection idea of Holmes. Hess wrote that hot magma rose up into the rift valley at the mid-ocean ridges. The lava oozed up and forced the existing seafloor away from the rift in opposite directions. Since magnetite crystals point in the direction of the magnetic north pole as the lava cools, the different stripes of magnetic polarity revealed the different ages of the seafloor. The seafloor at the ridge is from the Brunhes normal; beyond that is basalt from the Matuyama reverse; and beyond that from the Gauss normal. Hess called this idea seafloor spreading. As oceanic crust forms and spreads, moving away from the ridge crest, it pushes the continent away from the ridge axis. If the oceanic crust reaches a deep sea trench, it sinks into the trench and is lost into the mantle. The oldest crust is coldest and lies deepest in the ocean because it is less buoyant than the hot new crust. Hess could also use seafloor spreading to explain the flat topped guyots. He suggested that they were once active volcanoes that were exposed to erosion above sea level. As the seafloor they sat on moved away from the ridge, the crust on which they sat become less buoyant and the guyots moved deeper beneath sea level. ",text,
L_0300,seafloor spreading hypothesis,T_1668,"Seafloor spreading is the mechanism for Wegeners drifting continents. Convection currents within the mantle take the continents on a conveyor-belt ride of oceanic crust that, over millions of years, takes them around the planets surface. The spreading plate takes along any continent that rides on it. Click image to the left or use the URL below. URL: ",text,
L_0301,seasons,T_1669,"A common misconception is that the Sun is closer to Earth in the summer and farther away from it during the winter. Instead, the seasons are caused by the 23.5o tilt of Earths axis of rotation relative to its plane of orbit around the Sun (Figure 1.1). Solstice refers to the position of the Sun when it is closest to one of the poles. At summer solstice, June 21 or 22, Earths axis points toward the Sun and so the Sun is directly overhead at its furthest north point of the year, the Tropic of Cancer (23.5o N). During the summer, areas north of the Equator experience longer days and shorter nights. In the Southern Hemi- sphere, the Sun is as far away as it will be and so it is their winter. Locations will have longer nights and shorter days. The opposite occurs on winter solstice, which begins on December 21. More about seasons can be found in the Atmospheric Processes chapter. ",text,
L_0301,seasons,T_1670,"Different parts of the Earth receive different amounts of solar radiation. Which part of the planet receives the most solar radiation? The Suns rays strike the surface most directly at the Equator. Different areas also receive different amounts of sunlight in different seasons. What causes the seasons? The seasons are caused by the direction Earths axis is pointing relative to the Sun. The Earth revolves around the Sun once each year and spins on its axis of rotation once each day. This axis of rotation is tilted 23.5o relative to its plane of orbit around the Sun. The axis of rotation is pointed toward Polaris, the North Star. As the Earth orbits the Sun, the tilt of Earths axis stays lined up with the North Star. ",text,
L_0301,seasons,T_1671,"The North Pole is tilted towards the Sun and the Suns rays strike the Northern Hemisphere more directly in summer (Figure 1.2). At the summer solstice, June 21 or 22, the Suns rays hit the Earth most directly along the Tropic of Cancer (23.5o N); that is, the angle of incidence of the Suns rays there is zero (the angle of incidence is the deviation in the angle of an incoming ray from straight on). When it is summer solstice in the Northern Hemisphere, it is winter solstice in the Southern Hemisphere. ",text,
L_0301,seasons,T_1672,"Winter solstice for the Northern Hemisphere happens on December 21 or 22. The tilt of Earths axis points away from the Sun (Figure 1.3). Light from the Sun is spread out over a larger area, so that area isnt heated as much. With fewer daylight hours in winter, there is also less time for the Sun to warm the area. When it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere. ",text,
L_0301,seasons,T_1673,"Halfway between the two solstices, the Suns rays shine most directly at the Equator, called an equinox (Figure 1.4). The daylight and nighttime hours are exactly equal on an equinox. The autumnal equinox happens on September 22 or 23 and the vernal, or spring, equinox happens March 21 or 22 in the Northern Hemisphere. Summer solstice in the Northern Hemisphere. Click image to the left or use the URL below. URL: ",text,
L_0302,seawater chemistry,T_1674,"Remember that H2 O is a polar molecule, so it can dissolve many substances (Figure 1.1). Salts, sugars, acids, bases, and organic molecules can all dissolve in water. ",text,
L_0302,seawater chemistry,T_1675,"Where does the salt in seawater come from? As water moves through rock and soil on land it picks up ions. This is the flip side of weathering. Salts comprise about 3.5% of the mass of ocean water, but the salt content, or salinity, is different in different locations. What would the salinity be like in an estuary? Where seawater mixes with fresh water, salinity is lower than average. What would the salinity be like where there is lots of evaporation? Where there is lots of evaporation but little circulation of water, salinity can be much higher. The Dead Sea has 30% salinity  nearly nine times the average salinity of ocean water (Figure 1.2). Why do you think this water body is called the Dead Sea? In some areas, dense saltwater and less dense freshwater mix, and they form an immiscible layer, just like oil and water. One such place is a ""cenote"", or underground cave, very common in certain parts of Central America. Ocean water is composed of many sub- stances, many of them salts such as sodium, magnesium, and calcium chlo- ride. Because of the increased salinity, the wa- ter in the Dead Sea is very dense, it has such high salinity that people can easily float in it! ",text,
L_0302,seawater chemistry,T_1675,"Where does the salt in seawater come from? As water moves through rock and soil on land it picks up ions. This is the flip side of weathering. Salts comprise about 3.5% of the mass of ocean water, but the salt content, or salinity, is different in different locations. What would the salinity be like in an estuary? Where seawater mixes with fresh water, salinity is lower than average. What would the salinity be like where there is lots of evaporation? Where there is lots of evaporation but little circulation of water, salinity can be much higher. The Dead Sea has 30% salinity  nearly nine times the average salinity of ocean water (Figure 1.2). Why do you think this water body is called the Dead Sea? In some areas, dense saltwater and less dense freshwater mix, and they form an immiscible layer, just like oil and water. One such place is a ""cenote"", or underground cave, very common in certain parts of Central America. Ocean water is composed of many sub- stances, many of them salts such as sodium, magnesium, and calcium chlo- ride. Because of the increased salinity, the wa- ter in the Dead Sea is very dense, it has such high salinity that people can easily float in it! ",text,
L_0302,seawater chemistry,T_1676,"With so many dissolved substances mixed in seawater, what is the density (mass per volume) of seawater relative to fresh water? Water density increases as: salinity increases temperature decreases pressure increases Differences in water density are responsible for deep ocean currents, as will be discussed in the ""Deep Ocean Currents"" concept. Click image to the left or use the URL below. URL: ",text,
L_0303,sedimentary rock classification,T_1677,"Rock Conglomerate Breccia Sandstone Siltstone Shale Sediment Size Large Large Sand-sized Silt-sized, smaller than sand Clay-sized, smallest Other Features Rounded Angular When sediments settle out of calmer water, they form horizontal layers. One layer is deposited first, and another layer is deposited on top of it. So each layer is younger than the layer beneath it. When the sediments harden, the layers are preserved. Sedimentary rocks formed by the crystallization of chemical precipitates are called chemical sedimentary rocks. As discussed in the concepts on minerals, dissolved ions in fluids precipitate out of the fluid and settle out, just like the halite in Figure 1.1. The evaporite, halite, on a cobble from the Dead Sea, Israel. Biochemical sedimentary rocks form in the ocean or a salt lake. Living creatures remove ions, such as calcium, magnesium, and potassium, from the water to make shells or soft tissue. When the organism dies, it sinks to the ocean floor to become a biochemical sediment, which may then become compacted and cemented into solid rock (Figure 1.2). Table 1.2 shows some common types of sedimentary rocks. Breccia Clastic Sandstone Clastic Siltstone Clastic Shale Clastic Rock Salt Chemical precipitate Dolostone Chemical precipitate Limestone Bioclastic (sediments from organic materials, or plant or animal re- mains) Coal Organic Click image to the left or use the URL below. URL: ",text,
L_0303,sedimentary rock classification,T_1677,"Rock Conglomerate Breccia Sandstone Siltstone Shale Sediment Size Large Large Sand-sized Silt-sized, smaller than sand Clay-sized, smallest Other Features Rounded Angular When sediments settle out of calmer water, they form horizontal layers. One layer is deposited first, and another layer is deposited on top of it. So each layer is younger than the layer beneath it. When the sediments harden, the layers are preserved. Sedimentary rocks formed by the crystallization of chemical precipitates are called chemical sedimentary rocks. As discussed in the concepts on minerals, dissolved ions in fluids precipitate out of the fluid and settle out, just like the halite in Figure 1.1. The evaporite, halite, on a cobble from the Dead Sea, Israel. Biochemical sedimentary rocks form in the ocean or a salt lake. Living creatures remove ions, such as calcium, magnesium, and potassium, from the water to make shells or soft tissue. When the organism dies, it sinks to the ocean floor to become a biochemical sediment, which may then become compacted and cemented into solid rock (Figure 1.2). Table 1.2 shows some common types of sedimentary rocks. Breccia Clastic Sandstone Clastic Siltstone Clastic Shale Clastic Rock Salt Chemical precipitate Dolostone Chemical precipitate Limestone Bioclastic (sediments from organic materials, or plant or animal re- mains) Coal Organic Click image to the left or use the URL below. URL: ",text,
L_0304,sedimentary rocks,T_1678,"Sandstone is one of the common types of sedimentary rocks that form from sediments. There are many other types. Sediments may include: fragments of other rocks that often have been worn down into small pieces, such as sand, silt, or clay. organic materials, or the remains of once-living organisms. chemical precipitates, which are materials that get left behind after the water evaporates from a solution. Rocks at the surface undergo mechanical and chemical weathering. These physical and chemical processes break rock into smaller pieces. Mechanical weathering simply breaks the rocks apart. Chemical weathering dissolves the less stable minerals. These original elements of the minerals end up in solution and new minerals may form. Sediments are removed and transported by water, wind, ice, or gravity in a process called erosion (Figure 1.1). Much more information about weathering and erosion can be found in the chapter Surface Processes and Landforms. Streams carry huge amounts of sediment (Figure 1.2). The more energy the water has, the larger the particle it can carry. A rushing river on a steep slope might be able to carry boulders. As this stream slows down, it no longer has the energy to carry large sediments and will drop them. A slower moving stream will only carry smaller particles. Water erodes the land surface in Alaskas Valley of Ten Thousand Smokes. Sediments are deposited on beaches and deserts, at the bottom of oceans, and in lakes, ponds, rivers, marshes, and swamps. Landslides drop large piles of sediment. Glaciers leave large piles of sediments, too. Wind can only transport sand and smaller particles. The type of sediment that is deposited will determine the type of sedimentary rock that can form. Different colors of sedimentary rock are determined by the environment where they are deposited. Red rocks form where oxygen is present. Darker sediments form when the environment is oxygen poor. Click image to the left or use the URL below. URL: ",text,
L_0304,sedimentary rocks,T_1678,"Sandstone is one of the common types of sedimentary rocks that form from sediments. There are many other types. Sediments may include: fragments of other rocks that often have been worn down into small pieces, such as sand, silt, or clay. organic materials, or the remains of once-living organisms. chemical precipitates, which are materials that get left behind after the water evaporates from a solution. Rocks at the surface undergo mechanical and chemical weathering. These physical and chemical processes break rock into smaller pieces. Mechanical weathering simply breaks the rocks apart. Chemical weathering dissolves the less stable minerals. These original elements of the minerals end up in solution and new minerals may form. Sediments are removed and transported by water, wind, ice, or gravity in a process called erosion (Figure 1.1). Much more information about weathering and erosion can be found in the chapter Surface Processes and Landforms. Streams carry huge amounts of sediment (Figure 1.2). The more energy the water has, the larger the particle it can carry. A rushing river on a steep slope might be able to carry boulders. As this stream slows down, it no longer has the energy to carry large sediments and will drop them. A slower moving stream will only carry smaller particles. Water erodes the land surface in Alaskas Valley of Ten Thousand Smokes. Sediments are deposited on beaches and deserts, at the bottom of oceans, and in lakes, ponds, rivers, marshes, and swamps. Landslides drop large piles of sediment. Glaciers leave large piles of sediments, too. Wind can only transport sand and smaller particles. The type of sediment that is deposited will determine the type of sedimentary rock that can form. Different colors of sedimentary rock are determined by the environment where they are deposited. Red rocks form where oxygen is present. Darker sediments form when the environment is oxygen poor. Click image to the left or use the URL below. URL: ",text,
L_0305,seismic waves,T_1679,Energy is transmitted in waves. Every wave has a high point called a crest and a low point called a trough. The height of a wave from the center line to its crest is its amplitude. The distance between waves from crest to crest (or trough to trough) is its wavelength. The parts of a wave are illustrated in Figure 1.1. ,text,
L_0305,seismic waves,T_1680,The energy from earthquakes travels in waves. The study of seismic waves is known as seismology. Seismologists use seismic waves to learn about earthquakes and also to learn about the Earths interior. One ingenious way scientists learn about Earths interior is by looking at earthquake waves. Seismic waves travel outward in all directions from where the ground breaks and are picked up by seismographs around the world. Two types of seismic waves are most useful for learning about Earths interior. ,text,
L_0305,seismic waves,T_1681,"P-waves and S-waves are known as body waves because they move through the solid body of the Earth. P-waves travel through solids, liquids, and gases. S-waves only move through solids (Figure 1.2). Surface waves only travel along Earths surface. In an earthquake, body waves produce sharp jolts. They do not do as much damage as surface waves. P-waves (primary waves) are fastest, traveling at about 6 to 7 kilometers (about 4 miles) per second, so they arrive first at the seismometer. P-waves move in a compression/expansion type motion, squeezing and S-waves (secondary waves) are about half as fast as P-waves, traveling at about 3.5 km (2 miles) per second, and arrive second at seismographs. S-waves move in an up and down motion perpendicular to the direction of wave travel. This produces a change in shape for the Earth materials they move through. Only solids resist a change in shape, so S-waves are only able to propagate through solids. S-waves cannot travel through liquid. ",text,
L_0305,seismic waves,T_1681,"P-waves and S-waves are known as body waves because they move through the solid body of the Earth. P-waves travel through solids, liquids, and gases. S-waves only move through solids (Figure 1.2). Surface waves only travel along Earths surface. In an earthquake, body waves produce sharp jolts. They do not do as much damage as surface waves. P-waves (primary waves) are fastest, traveling at about 6 to 7 kilometers (about 4 miles) per second, so they arrive first at the seismometer. P-waves move in a compression/expansion type motion, squeezing and S-waves (secondary waves) are about half as fast as P-waves, traveling at about 3.5 km (2 miles) per second, and arrive second at seismographs. S-waves move in an up and down motion perpendicular to the direction of wave travel. This produces a change in shape for the Earth materials they move through. Only solids resist a change in shape, so S-waves are only able to propagate through solids. S-waves cannot travel through liquid. ",text,
L_0305,seismic waves,T_1682,"By tracking seismic waves, scientists have learned what makes up the planets interior (Figure 1.4). P-waves slow down at the mantle core boundary, so we know the outer core is less rigid than the mantle. S-waves disappear at the mantle core boundary, so we know the outer core is liquid. ",text,
L_0305,seismic waves,T_1683,"Surface waves travel along the ground, outward from an earthquakes epicenter. Surface waves are the slowest of all seismic waves, traveling at 2.5 km (1.5 miles) per second. There are two types of surface waves. The rolling motions of surface waves do most of the damage in an earthquake. ",text,
L_0306,short term climate change,T_1684,Short-term changes in climate are common and they have many causes (Figure 1.1). The largest and most important of these is the oscillation between El Nio and La Nia conditions. This cycle is called the ENSO (El Nio Southern Oscillation). The ENSO drives changes in climate that are felt around the world about every two to seven years. ,text,
L_0306,short term climate change,T_1685,"In a normal year, the trade winds blow across the Pacific Ocean near the Equator from east to west (toward Asia). A low pressure cell rises above the western equatorial Pacific. Warm water in the western Pacific Ocean raises sea levels by half a meter. Along the western coast of South America, the Peru Current carries cold water northward, and then westward along the Equator with the trade winds. Upwelling brings cold, nutrient-rich waters from the deep sea. ",text,
L_0306,short term climate change,T_1686,"In an El Nio year, when water temperature reaches around 28o C (82o F), the trade winds weaken or reverse direction and blow east (toward South America) (Figure 1.2). Warm water is dragged back across the Pacific Ocean and piles up off the west coast of South America. With warm, low-density water at the surface, upwelling stops. Without upwelling, nutrients are scarce and plankton populations decline. Since plankton form the base of the food web, fish cannot find food, and fish numbers decrease as well. All the animals that eat fish, including birds and humans, are affected by the decline in fish. By altering atmospheric and oceanic circulation, El Nio events change global climate patterns. Some regions receive more than average rainfall, including the west coast of North and South America, the southern United States, and Western Europe. Drought occurs in other parts of South America, the western Pacific, southern and northern Africa, and southern Europe. An El Nio cycle lasts one to two years. Often, normal circulation patterns resume. Sometimes circulation patterns bounce back quickly and extremely (Figure 1.3). This is a La Nia. ",text,
L_0306,short term climate change,T_1686,"In an El Nio year, when water temperature reaches around 28o C (82o F), the trade winds weaken or reverse direction and blow east (toward South America) (Figure 1.2). Warm water is dragged back across the Pacific Ocean and piles up off the west coast of South America. With warm, low-density water at the surface, upwelling stops. Without upwelling, nutrients are scarce and plankton populations decline. Since plankton form the base of the food web, fish cannot find food, and fish numbers decrease as well. All the animals that eat fish, including birds and humans, are affected by the decline in fish. By altering atmospheric and oceanic circulation, El Nio events change global climate patterns. Some regions receive more than average rainfall, including the west coast of North and South America, the southern United States, and Western Europe. Drought occurs in other parts of South America, the western Pacific, southern and northern Africa, and southern Europe. An El Nio cycle lasts one to two years. Often, normal circulation patterns resume. Sometimes circulation patterns bounce back quickly and extremely (Figure 1.3). This is a La Nia. ",text,
L_0306,short term climate change,T_1687,"In a La Nia year, as in a normal year, trade winds moves from east to west and warm water piles up in the western Pacific Ocean. Ocean temperatures along coastal South America are colder than normal (instead of warmer, as in El Nio). Cold water reaches farther into the western Pacific than normal. Other important oscillations are smaller and have a local, rather than global, effect. The North Atlantic Oscillation mostly alters climate in Europe. The Mediterranean also goes through cycles, varying between being dry at some times and warm and wet at others. Click image to the left or use the URL below. URL: ",text,
L_0311,solar energy on earth,T_1708,"Most of the energy that reaches the Earths surface comes from the Sun (Figure 1.1). About 44% of solar radiation is in the visible light wavelengths, but the Sun also emits infrared, ultraviolet, and other wavelengths. ",text,
L_0311,solar energy on earth,T_1709,"Of the solar energy that reaches the outer atmosphere, ultraviolet (UV) wavelengths have the greatest energy. Only about 7% of solar radiation is in the UV wavelengths. The three types are: UVC: the highest energy ultraviolet, does not reach the planets surface at all. UVB: the second highest energy, is also mostly stopped in the atmosphere. UVA: the lowest energy, travels through the atmosphere to the ground. ",text,
L_0311,solar energy on earth,T_1710,"The remaining solar radiation is the longest wavelength, infrared. Most objects radiate infrared energy, which we feel as heat. Some of the wavelengths of solar radiation traveling through the atmosphere may be lost because they are absorbed by various gases (Figure 1.2). Ozone completely removes UVC, most UVB, and some UVA from incoming sunlight. O2 , CO2 , and H2 O also filter out some wavelengths. An image of the Sun taken by the SOHO spacecraft. The sensor is picking up only the 17.1 nm wavelength, in the ultraviolet wavelengths. Atmospheric gases filter some wave- lengths of incoming solar energy. Yel- low shows the energy that reaches the top of the atmosphere. Red shows the wavelengths that reach sea level. Ozone filters out the shortest wavelength UV and oxygen filters out most infrared. Click image to the left or use the URL below. URL: ",text,
L_0311,solar energy on earth,T_1710,"The remaining solar radiation is the longest wavelength, infrared. Most objects radiate infrared energy, which we feel as heat. Some of the wavelengths of solar radiation traveling through the atmosphere may be lost because they are absorbed by various gases (Figure 1.2). Ozone completely removes UVC, most UVB, and some UVA from incoming sunlight. O2 , CO2 , and H2 O also filter out some wavelengths. An image of the Sun taken by the SOHO spacecraft. The sensor is picking up only the 17.1 nm wavelength, in the ultraviolet wavelengths. Atmospheric gases filter some wave- lengths of incoming solar energy. Yel- low shows the energy that reaches the top of the atmosphere. Red shows the wavelengths that reach sea level. Ozone filters out the shortest wavelength UV and oxygen filters out most infrared. Click image to the left or use the URL below. URL: ",text,
L_0312,solar power,T_1711,"Energy from the Sun comes from the lightest element, hydrogen, fusing together to create the second lightest element, helium. Nuclear fusion on the Sun releases tremendous amounts of solar energy. The energy travels to the Earth, mostly as visible light. The light carries the energy through the empty space between the Sun and the Earth as radiation. ",text,
L_0312,solar power,T_1712,"Solar energy has been used for power on a small scale for hundreds of years, and plants have used it for billions of years. Unlike energy from fossil fuels, which almost always come from a central power plant or refinery, solar power can be harnessed locally (Figure 1.1). A set of solar panels on a homes rooftop can be used to heat water for a swimming pool or can provide electricity to the house. Societys use of solar power on a larger scale is just starting to increase. Scientists and engineers have very active, ongoing research into new ways to harness energy from the Sun more efficiently. Because of the tremendous amount of incoming sunlight, solar power is being developed in the United States in southeastern California, Nevada, and Arizona. Solar panels supply power to the Interna- tional Space Station. Solar power plants turn sunlight into electricity using a large group of mirrors to focus sunlight on one place, called a receiver (Figure 1.2). A liquid, such as oil or water, flows through this receiver and is heated to a high temperature by the focused sunlight. The heated liquid transfers its heat to a nearby object that is at a lower temperature through a process called conduction. The energy conducted by the heated liquid is used to make electricity. This solar power plant uses mirrors to focus sunlight on the tower in the center. The sunlight heats a liquid inside the tower to a very high temperature, producing energy to make electricity. ",text,
L_0312,solar power,T_1712,"Solar energy has been used for power on a small scale for hundreds of years, and plants have used it for billions of years. Unlike energy from fossil fuels, which almost always come from a central power plant or refinery, solar power can be harnessed locally (Figure 1.1). A set of solar panels on a homes rooftop can be used to heat water for a swimming pool or can provide electricity to the house. Societys use of solar power on a larger scale is just starting to increase. Scientists and engineers have very active, ongoing research into new ways to harness energy from the Sun more efficiently. Because of the tremendous amount of incoming sunlight, solar power is being developed in the United States in southeastern California, Nevada, and Arizona. Solar panels supply power to the Interna- tional Space Station. Solar power plants turn sunlight into electricity using a large group of mirrors to focus sunlight on one place, called a receiver (Figure 1.2). A liquid, such as oil or water, flows through this receiver and is heated to a high temperature by the focused sunlight. The heated liquid transfers its heat to a nearby object that is at a lower temperature through a process called conduction. The energy conducted by the heated liquid is used to make electricity. This solar power plant uses mirrors to focus sunlight on the tower in the center. The sunlight heats a liquid inside the tower to a very high temperature, producing energy to make electricity. ",text,
L_0312,solar power,T_1713,"Solar energy has many benefits. It is extremely abundant, widespread, and will never run out. But there are problems with the widespread use of solar power. Sunlight must be present. Solar power is not useful in locations that are often cloudy or dark. However, storage technology is being developed. The technology needed for solar power is still expensive. An increase in interested customers will provide incentive for companies to research and develop new technologies and to figure out how to mass-produce existing technologies (Figure 1.3). Solar panels require a lot of space. Fortunately, solar panels can be placed on any rooftop to supply at least some of the power required for a home or business. This experimental car is one example of the many uses that engineers have found for solar energy. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0313,star classification,T_1714,"Think about how the color of a piece of metal changes with temperature. A coil of an electric stove will start out black, but with added heat will start to glow a dull red. With more heat, the coil turns a brighter red, then orange. At extremely high temperatures the coil will turn yellow-white, or even blue-white (its hard to imagine a stove coil getting that hot). A stars color is also determined by the temperature of the stars surface. Relatively cool stars are red, warmer stars are orange or yellow, and extremely hot stars are blue or blue-white (Figure 1.1). ",text,
L_0313,star classification,T_1715,"Color is the most common way to classify stars. Table 1.1 shows the classification system. The class of a star is given by a letter. Each letter corresponds to a color, and also to a range of temperatures. Note that these letters dont match the color names; they are left over from an older system that is no longer used. Class O B A F G K M Color Blue Blue-white White Yellowish-white Yellow Orange Red Temperature Range 30,000 K or more 10,000-30,000 K 7,500-10,000 K 6,000-7,500 K 5,500-6,000 K 3,500-5,000 K 2,000-3,500 K Sample Star Zeta Ophiuchi Rigel Altair Procyon A Sun Epsilon Indi Betelgeuse, Proxima Cen- tauri For most stars, surface temperature is also related to size. Bigger stars produce more energy, so their surfaces are hotter. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0314,star constellations,T_1716,"When you look at the sky on a clear night, you can see dozens, perhaps even hundreds, of tiny points of light. Almost every one of these points of light is a star, a giant ball of glowing gas at a very, very high temperature. Stars differ in size, temperature, and age, but they all appear to be made up of the same elements and to behave according to the same principles. ",text,
L_0314,star constellations,T_1717,"People of many different cultures, including the Greeks, identified patterns of stars in the sky. We call these patterns constellations. Figure 1.1 shows one of the most easily recognized constellations. Why do the patterns in constellations and in groups or clusters of stars, called asterisms, stay the same night after night? Although the stars move across the sky, they stay in the same patterns. This is because the apparent nightly motion of the stars is actually caused by the rotation of Earth on its axis. The patterns also shift in the sky with the seasons as Earth revolves around the Sun. As a result, people in a particular location can see different constellations in the winter than in the summer. For example, in the Northern Hemisphere Orion is a prominent constellation in the winter sky, but not in the summer sky. This is the annual traverse of the constellations. ",text,
L_0314,star constellations,T_1718,"Although the stars in a constellation appear close together as we see them in our night sky, they are not at all close together out in space. In the constellation Orion, the stars visible to the naked eye are at distances ranging from just 26 light-years (which is relatively close to Earth) to several thousand light-years away. Click image to the left or use the URL below. URL: ",text,
L_0314,star constellations,T_1719,"There is no reason to think that the alignment of the stars has anything to do with events that happen on Earth. The constellations were defined by people who noticed that patterns could be made from stars, but the patterns do not reflect any characteristics of the stars themselves. When scientific tests are done to provide evidence in support of astrological ideas, the tests fail. When a scientific idea fails, it is abandoned or modified. Astrologers do not change or abandon their ideas. Click image to the left or use the URL below. URL: ",text,
L_0315,star power,T_1720,"The Sun is Earths major source of energy, yet the planet only receives a small portion of its energy. The Sun is just an ordinary star. Many stars produce much more energy than the Sun. The energy source for all stars is nuclear fusion. ",text,
L_0315,star power,T_1721,"Stars are made mostly of hydrogen and helium, which are packed so densely in a star that in the stars center the pressure is great enough to initiate nuclear fusion reactions. In a nuclear fusion reaction, the nuclei of two atoms combine to create a new atom. Most commonly, in the core of a star, two hydrogen atoms fuse to become a helium atom. Although nuclear fusion reactions require a lot of energy to get started, once they are going they produce enormous amounts of energy (Figure 1.1). In a star, the energy from fusion reactions in the core pushes outward to balance the inward pull of gravity. This energy moves outward through the layers of the star until it finally reaches the stars outer surface. The outer layer of the star glows brightly, sending the energy out into space as electromagnetic radiation, including visible light, heat, ultraviolet light, and radio waves (Figure 1.2). ",text,
L_0315,star power,T_1722,"In particle accelerators, subatomic particles are propelled until they have attained almost the same amount of energy as found in the core of a star (Figure 1.3). When these particles collide head-on, new particles are created. This process simulates the nuclear fusion that takes place in the cores of stars. The process also simulates the conditions A diagram of a star like the Sun. that allowed for the first helium atom to be produced from the collision of two hydrogen atoms in the first few minutes of the universe. The SLAC National Accelerator Lab in California can propel particles a straight 2 mi (3.2 km). The CERN Particle Accelerator presented in this video is the worlds largest and most powerful particle accelerator. The accelerator can boost subatomic particles to energy levels that simulate conditions in the stars and in the early history of the universe before stars formed. Click image to the left or use the URL below. URL: ",text,
L_0315,star power,T_1722,"In particle accelerators, subatomic particles are propelled until they have attained almost the same amount of energy as found in the core of a star (Figure 1.3). When these particles collide head-on, new particles are created. This process simulates the nuclear fusion that takes place in the cores of stars. The process also simulates the conditions A diagram of a star like the Sun. that allowed for the first helium atom to be produced from the collision of two hydrogen atoms in the first few minutes of the universe. The SLAC National Accelerator Lab in California can propel particles a straight 2 mi (3.2 km). The CERN Particle Accelerator presented in this video is the worlds largest and most powerful particle accelerator. The accelerator can boost subatomic particles to energy levels that simulate conditions in the stars and in the early history of the universe before stars formed. Click image to the left or use the URL below. URL: ",text,
L_0316,states of water,T_1723,"Water is simply two atoms of hydrogen and one atom of oxygen bonded together (Figure 1.1). The hydrogen ions are on one side of the oxygen ion, making water a polar molecule. This means that one side, the side with the hydrogen ions, has a slightly positive electrical charge. The other side, the side without the hydrogen ions, has a slightly negative charge. Despite its simplicity, water has remarkable properties. Water expands when it freezes, has high surface tension (because of the polar nature of the molecules, they tend to stick together), and others. Without water, life might not be able to exist on Earth and it certainly would not have the tremendous complexity and diversity that we see. ",text,
L_0316,states of water,T_1724,"Water is the only substance on Earth that is present in all three states of matter - as a solid, liquid or gas. (And Earth is the only planet where water is abundantly present in all three states.) Because of the ranges in temperature in specific locations around the planet, all three phases may be present in a single location or in a region. The three phases are solid (ice or snow), liquid (water), and gas (water vapor). See ice, water, and clouds (Figure 1.2). (a) Ice floating in the sea. Can you find all three phases of water in this image? (b) Liquid water. (c) Water vapor is invisible, but clouds that form when water vapor condenses are not. Click image to the left or use the URL below. URL: ",text,
L_0316,states of water,T_1724,"Water is the only substance on Earth that is present in all three states of matter - as a solid, liquid or gas. (And Earth is the only planet where water is abundantly present in all three states.) Because of the ranges in temperature in specific locations around the planet, all three phases may be present in a single location or in a region. The three phases are solid (ice or snow), liquid (water), and gas (water vapor). See ice, water, and clouds (Figure 1.2). (a) Ice floating in the sea. Can you find all three phases of water in this image? (b) Liquid water. (c) Water vapor is invisible, but clouds that form when water vapor condenses are not. Click image to the left or use the URL below. URL: ",text,
L_0318,stratosphere,T_1729,"There is little mixing between the stratosphere, the layer above the troposphere, and the troposphere below it. The two layers are quite separate. Sometimes ash and gas from a large volcanic eruption may burst into the stratosphere. Once in the stratosphere, it remains suspended there for many years because there is so little mixing between the two layers. ",text,
L_0318,stratosphere,T_1730,"In the stratosphere, temperature increases with altitude. What is the heat source for the stratosphere? The direct heat source for the stratosphere is the Sun. The ozone layer in the stratosphere absorbs high energy ultraviolet radiation, which breaks the ozone molecule (3-oxygens) apart into an oxygen molecule (2-oxygens) and an oxygen atom (1- oxygen). In the mid-stratosphere there is less UV light and so the oxygen atom and molecule recombine to from ozone. The creation of the ozone molecule releases heat. Because warmer, less dense air sits over cooler, denser air, air in the stratosphere is stable. As a result, there is little mixing of air within the layer. There is also little interaction between the troposphere and stratosphere for this reason. ",text,
L_0318,stratosphere,T_1731,"The ozone layer is found within the stratosphere between 15 to 30 km (9 to 19 miles) altitude. The ozone layer has a low concentration of ozone; its just higher than the concentration elsewhere. The thickness of the ozone layer varies by the season and also by latitude. Ozone is created in the stratosphere by solar energy. Ultraviolet radiation splits an oxygen molecule into two oxygen atoms. One oxygen atom combines with another oxygen molecule to create an ozone molecule, O3 . The ozone is unstable and is later split into an oxygen molecule and an oxygen atom. This is a natural cycle that leaves some ozone in the stratosphere. The ozone layer is extremely important because ozone gas in the stratosphere absorbs most of the Suns harmful ultraviolet (UV) radiation. Because of this, the ozone layer protects life on Earth. High-energy UV light penetrates cells and damages DNA, leading to cell death (which we know as a bad sunburn). Organisms on Earth are not adapted to heavy UV exposure, which kills or damages them. Without the ozone layer to absorb UVC and UVB radiation, most complex life on Earth would not survive long. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0319,streams and rivers,T_1732,"Streams are bodies of water that have a current; they are in constant motion. Geologists recognize many categories of streams depending on their size, depth, speed, and location. Creeks, brooks, tributaries, bayous, and rivers are all streams. In streams, water always flows downhill, but the form that downhill movement takes varies with rock type, topography, and many other factors. Stream erosion and deposition are extremely important creators and destroyers of landforms. Rivers are the largest streams. People have used rivers since the beginning of civilization as a source of water, food, transportation, defense, power, recreation, and waste disposal. With its high mountains, valleys and Pacific coastline, the western United States exhibits nearly all of the features common to rivers and streams. The photos below are from the western states of Montana, California and Colorado. ",text,
L_0319,streams and rivers,T_1733,"A stream originates at its source. A source is likely to be in the high mountains where snows collect in winter and melt in summer, or a source might be a spring. A stream may have more than one source. Two streams come together at a confluence. The smaller of the two streams is a tributary of the larger stream (Figure 1.1). The confluence between the Yellowstone River and one of its tributaries, the Gar- diner River, in Montana. The point at which a stream comes into a large body of water, like an ocean or a lake, is called the mouth. Where the stream meets the ocean or lake is an estuary (Figure 1.2). The mouth of the Klamath River creates an estuary where it flows into the Pacific Ocean in California. The mix of fresh and salt water where a river runs into the ocean creates a diversity of environments where many different types of organisms create unique ecosystems. ",text,
L_0319,streams and rivers,T_1733,"A stream originates at its source. A source is likely to be in the high mountains where snows collect in winter and melt in summer, or a source might be a spring. A stream may have more than one source. Two streams come together at a confluence. The smaller of the two streams is a tributary of the larger stream (Figure 1.1). The confluence between the Yellowstone River and one of its tributaries, the Gar- diner River, in Montana. The point at which a stream comes into a large body of water, like an ocean or a lake, is called the mouth. Where the stream meets the ocean or lake is an estuary (Figure 1.2). The mouth of the Klamath River creates an estuary where it flows into the Pacific Ocean in California. The mix of fresh and salt water where a river runs into the ocean creates a diversity of environments where many different types of organisms create unique ecosystems. ",text,
L_0319,streams and rivers,T_1734,"As a stream flows from higher elevations, like in the mountains, towards lower elevations, like the ocean, the work of the stream changes. At a streams headwaters, often high in the mountains, gradients are steep (Figure 1.3). The stream moves fast and does lots of work eroding the stream bed. Headwaters of the Roaring Fork River in Colorado. As a stream moves into lower areas, the gradient is not as steep. Now the stream does more work eroding the edges of its banks. Many streams develop curves in their channels called meanders (Figure 1.4). As the river moves onto flatter ground, the stream erodes the outer edges of its banks to carve a floodplain, which is a flat, level area surrounding the stream channel (Figure 1.5). Base level is where a stream meets a large body of standing water, usually the ocean, but sometimes a lake or pond. Streams work to down cut in their stream beds until they reach base level. The higher the elevation, the farther the stream is from where it will reach base level and the more cutting it has to do. The ultimate base level is sea level. ",text,
L_0319,streams and rivers,T_1734,"As a stream flows from higher elevations, like in the mountains, towards lower elevations, like the ocean, the work of the stream changes. At a streams headwaters, often high in the mountains, gradients are steep (Figure 1.3). The stream moves fast and does lots of work eroding the stream bed. Headwaters of the Roaring Fork River in Colorado. As a stream moves into lower areas, the gradient is not as steep. Now the stream does more work eroding the edges of its banks. Many streams develop curves in their channels called meanders (Figure 1.4). As the river moves onto flatter ground, the stream erodes the outer edges of its banks to carve a floodplain, which is a flat, level area surrounding the stream channel (Figure 1.5). Base level is where a stream meets a large body of standing water, usually the ocean, but sometimes a lake or pond. Streams work to down cut in their stream beds until they reach base level. The higher the elevation, the farther the stream is from where it will reach base level and the more cutting it has to do. The ultimate base level is sea level. ",text,
L_0319,streams and rivers,T_1735,"A divide is a topographically high area that separates a landscape into different water basins (Figure 1.6). Rain that falls on the north side of a ridge flows into the northern drainage basin and rain that falls on the south side flows into the southern drainage basin. On a much grander scale, entire continents have divides, known as continental divides. A green floodplain surrounds the Red Rock River as it flows through Montana. (a) The divides of North America. In the Rocky Mountains in Colorado, where does a raindrop falling on the western slope end up? How about on the eastern slope? (b) At Triple Divide Peak in Montana water may flow to the Pacific, the Atlantic, or Hudson Bay depending on where it falls. Can you locate where in the map of North America this peak sits? ",text,
L_0319,streams and rivers,T_1735,"A divide is a topographically high area that separates a landscape into different water basins (Figure 1.6). Rain that falls on the north side of a ridge flows into the northern drainage basin and rain that falls on the south side flows into the southern drainage basin. On a much grander scale, entire continents have divides, known as continental divides. A green floodplain surrounds the Red Rock River as it flows through Montana. (a) The divides of North America. In the Rocky Mountains in Colorado, where does a raindrop falling on the western slope end up? How about on the eastern slope? (b) At Triple Divide Peak in Montana water may flow to the Pacific, the Atlantic, or Hudson Bay depending on where it falls. Can you locate where in the map of North America this peak sits? ",text,
L_0320,supervolcanoes,T_1736,"Supervolcano eruptions are extremely rare in Earths history. Its a good thing because they are unimaginably large. A supervolcano must erupt more than 1,000 cubic km (240 cubic miles) of material, compared with 1.2 km3 for Mount St. Helens or 25 km3 for Mount Pinatubo, a large eruption in the Philippines in 1991. Not surprisingly, supervolcanoes are the most dangerous type of volcano. ",text,
L_0320,supervolcanoes,T_1737,"The exact cause of supervolcano eruptions is still debated. However, scientists think that a very large magma chamber erupts entirely in one catastrophic explosion. This creates a huge hole or caldera into which the surface collapses (Figure 1.1). The caldera at Santorini in Greece is so large that it can only be seen by satellite. ",text,
L_0320,supervolcanoes,T_1738,"The largest supervolcano in North America is beneath Yellowstone National Park in Wyoming. Yellowstone sits above a hotspot that has erupted catastrophically three times: 2.1 million, 1.3 million, and 640,000 years ago. Yellowstone has produced many smaller (but still enormous) eruptions more recently (Figure 1.2). Fortunately, current activity at Yellowstone is limited to the regions famous geysers. Click image to the left or use the URL below. URL:  The Yellowstone hotspot has produced enormous felsic eruptions. The Yellowstone caldera collapsed in the most recent super eruption. ",text,
L_0320,supervolcanoes,T_1739,"A supervolcano could change life on Earth as we know it. Ash could block sunlight so much that photosynthesis would be reduced and global temperatures would plummet. Volcanic eruptions could have contributed to some of the mass extinctions in our planets history. No one knows when the next super eruption will be. Interesting volcano videos are seen on National Geographic Videos, Environment Video, Natural Disasters, Earth- quakes: One interesting one is Mammoth Mountain, which explores Hot Creek and the volcanic area it is a part of in California. Click image to the left or use the URL below. URL: ",text,
L_0321,surface features of the sun,T_1740,"The Suns surface features are quite visible, but only with special equipment. For example, sunspots are only visible with special light-filtering lenses. ",text,
L_0321,surface features of the sun,T_1741,"The most noticeable surface features of the Sun are cooler, darker areas known as sunspots (Figure 1.1). Sunspots are located where loops of the Suns magnetic field break through the surface and disrupt the smooth transfer of heat from lower layers of the Sun, making them cooler, darker, and marked by intense magnetic activity. Sunspots usually occur in pairs. When a loop of the Suns magnetic field breaks through the surface, a sunspot is created where the loop comes out and where it goes back in again. Sunspots usually occur in 11-year cycles, increasing from a minimum number to a maximum number and then gradually decreasing to a minimum number again. ",text,
L_0321,surface features of the sun,T_1742,"There are other types of interruptions of the Suns magnetic energy. If a loop of the Suns magnetic field snaps and breaks, it creates solar flares, which are violent explosions that release huge amounts of energy (Figure 1.2). A strong solar flare can turn into a coronal mass ejection. A solar flare or coronal mass ejection releases streams of highly energetic particles that make up the solar wind. The solar wind can be dangerous to spacecraft and astronauts because it sends out large amounts of radiation that can harm the human body. Solar flares have knocked out entire power grids and disturbed radio, satellite, and cell phone communications. (a) Sunspots. (b) A close-up of a sunspot taken in ultraviolet light. ",text,
L_0321,surface features of the sun,T_1742,"There are other types of interruptions of the Suns magnetic energy. If a loop of the Suns magnetic field snaps and breaks, it creates solar flares, which are violent explosions that release huge amounts of energy (Figure 1.2). A strong solar flare can turn into a coronal mass ejection. A solar flare or coronal mass ejection releases streams of highly energetic particles that make up the solar wind. The solar wind can be dangerous to spacecraft and astronauts because it sends out large amounts of radiation that can harm the human body. Solar flares have knocked out entire power grids and disturbed radio, satellite, and cell phone communications. (a) Sunspots. (b) A close-up of a sunspot taken in ultraviolet light. ",text,
L_0321,surface features of the sun,T_1743,"Another highly visible feature on the Sun are solar prominences. If plasma flows along a loop of the Suns magnetic field from sunspot to sunspot, it forms a glowing arch that reaches thousands of kilometers into the Suns atmosphere. Prominences can last lengths of time ranging from a day to several months. Prominences are also visible during a total solar eclipse. Most of the imagery comes from SDOs AIA instrument; different colors represent different temperatures, a common technique for observing solar features. SDO sees the entire disk of the Sun in extremely high spatial and temporal resolution, allowing scientists to zoom in on notable events such as flares, waves, and sunspots. ",text,
L_0321,surface features of the sun,T_1744,"The video above was taken from the SDO, the most advanced spacecraft ever designed to study the Sun. During its five-year mission, SDO will examine the Suns magnetic field and also provide a better understanding of the role the Sun plays in Earths atmospheric chemistry and climate. Since just after its launch on February 11, 2010, SDO is providing images with clarity 10 times better than high-definition television and will return more comprehensive science data faster than any other solar-observing spacecraft. The Solar Dynamics Observatory is a NASA spacecraft launched in early 2010 is obtaining IMAX-like images of the Sun every second of the day, generating more data than any NASA mission in history. The data will allow researchers to learn about solar storms and other phenomena that can cause blackouts and harm astronauts. Click image to the left or use the URL below. URL: ",text,
L_0323,sustainable development,T_1750,"Can society change and get on a sustain- able path? A topic generating a great deal of discussion these days is sustainable development. The goals of sustainable development are to: help people out of poverty. protect the environment. use resources no faster than the rate at which they are regenerated. Science can be an important part of sustainable development. When scientists understand how Earths natural systems work, they can recognize how people are impacting them. Scientists can work to develop technologies that can be used to solve problems wisely. An example of a practice that can aid sustainable development is fish farming, as long as it is done in environmentally sound ways. Engineers can develop cleaner energy sources to reduce pollution and greenhouse gas emissions. Citizens can change their behavior to reduce the impact they have on the planet by demanding products that are produced sustainably. When forests are logged, new trees should be planted. Mining should be done so that the landscape is not destroyed. People can consume less and think more about the impacts of what they do consume. And what of the waste products of society? Will producing all that we need to keep the population growing result in a planet so polluted that the quality of life will be greatly diminished? Will warming temperatures cause problems for human populations? The only answer to all of these questions is, time will tell. Click image to the left or use the URL below. URL: ",text,
L_0326,testing hypotheses,T_1757,"How do you test a hypothesis? In this example, we will look into the scientific literature to find data in studies that were done using scientific method. To test Hypothesis 1 from the concept ""Development of Hypotheses,"" we need to see if the amount of CO2 gas released by volcanoes over the past several decades has increased. There are two ways volcanoes could account for the increase in CO2 : There has been an increase in volcanic eruptions in that time. The CO2 content of volcanic gases has increased over time globally. To test the first hypothesis, we look at the scientific literature. We see that the number of volcanic eruptions is about constant. We also learn from the scientific literature that volcanic gas compositions have not changed over time. Different types of volcanoes have different gas compositions, but overall the gases are the same. Another journal article states that major volcanic eruptions for the past 30 years have caused short-term cooling, not warming! Hypothesis 1 is wrong! Volcanic activity is not able to account for the rise in atmospheric CO2 . Remember that science is falsifiable. We can discard Hypothesis 1. ",text,
L_0326,testing hypotheses,T_1758,"Hypothesis 2 states that the increase in atmospheric CO2 is due to the increase in the amount of fossil fuels that are being burned. We look into the scientific literature and find this graph in the Figure 1.1. Global carbon dioxide emissions from fos- sil fuel consumption and cement produc- tion. The black line represents all emis- sion types combined, and colored lines show emissions from individual fossil fu- els. Fossil fuels have added an increasing amount of carbon dioxide to the atmosphere since the beginning of the Industrial Revolution in the mid 19th century. Hypothesis 2 is true! Click image to the left or use the URL below. URL: ",text,
L_0327,the hertzsprung russell diagra,T_1759,"The Hertzsprung-Russell diagram (often referred to as the H-R diagram) is a scatter graph that shows various classes of stars in the context of properties such as their luminosity, absolute magnitude, color, and effective temperature. Created around 1910 by Ejnar Hertzsprung and Henry Norris Russell, the diagram provided a great help in understanding stellar evolution. There are several forms of the Hertzsprung-Russell diagram, and the nomenclature is not very well defined. The original diagram displayed the spectral type of stars on the horizontal axis and the absolute magnitude on the vertical axis. The form below shows Kelvin temperature along the horizontal axis going from high temperature on the left to low temperature on the right and luminosity on the vertical axis. We can think of the luminosity as brightness in multiples of the Sun. A luminosity of 100 on the axis would mean 100 times as bright as the Sun. Most of the stars occupy a region in the diagram along a line called the Main Sequence. During that stage, stars are fusing hydrogen into helium in their cores. The position of the Sun in the main sequence is shown in the diagram. You should note that the axial scales for this diagram are not linear. The vertical scale is logarithmic, each line is 100 times greater than the previous line. On the horizontal axis, as we move to the right, the temperature reduces by between 1,000 and 10,000 degrees K between each line. If all other factors were the same, the highest temperature stars would also be the most luminous (the brightest). In the main sequence of stars, we see that as the temperature increases to the left, the luminosity also increases, demonstrating that the hottest stars in this grouping are also the brightest. There are stars, however, that are less bright than their temperature would predict. This group of stars is called white dwarfs. These stars are less bright than expected because of their very small size. These dwarf stars are only one one-thousandth the size of stars in the main sequence. There are also stars that are much brighter than their temperature would predict. This group of stars are called red giants. They are brighter than their temperature would predict because they are much larger than stars in the main sequence. These stars have expanded to several thousand times the size of stars in the main sequence. Stars that are reddish in color are cooler than other stars while stars that are bluish in color are hotter than other stars. A white dwarf is a stellar remnant that is very dense. A white dwarfs mass is comparable to the Sun and its volume is comparable to that of Earth. The very low brightness of a white dwarf comes from the emission of stored heat energy. White dwarfs are thought to be the final evolutionary state of any star whose mass is not great enough to become a neutron star. Approximately 97% of the stars in our galaxy will become neutron stars. After the hydrogen-fusing lifetime of a main-sequence star of low or medium mass ends, it will expand to a red giant which fuses helium to carbon and oxygen in its core. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon, around 1 billion K, an inert mass of carbon and oxygen will build up at its center. After blowing off its outer layers to form a planetary nebula, the core will be left behind to form the remnant white dwarf. White dwarfs are composed of carbon and oxygen. A white dwarf is very hot when it is formed, but since it has no source of energy (no further fusion reactions), it will gradually radiate away its energy and cool down. Over a very long time, a white dwarf will cool to temperatures at which it will no longer emit significant light, and it will become a cold black dwarf. A red giant star is a star with a mass like the Sun that is in the last phase of its life, when Hydrogen fusion reactions in the core decrease due to the lack of fuel. With the gravitational collapse of the core, the fusion reactions now occur in a shell surrounding the core. The outer layer of the star expands enormously up to 1000 times the size of the Sun. When the Sun becomes a red giant, its volume will include the orbit of Mercury and Venus and maybe even Earth. The increased size increases the luminosity even though the outer layer cools to only 3000 K or so. The cooler outer layer causes it to be a red star. After a few more million years, the star evolves into a white dwarf-planetary nebula system. ",text,
L_0328,the history of astronom,T_1760,,text,
L_0328,the history of astronom,T_1761,"The Astronomy of the ancient Greeks was linked to mathematics, and Greek astronomers sought to create geomet- rical models that could imitate the appearance of celestial motions. This tradition originated around the 6th century BCE, with the followers of the mathematician Pythagoras (~580 - 500 BCE). Pythagoras believed that everything was related to mathematics and that through mathematics everything could be predicted and measured in rhythmic patterns or cycles. He placed astronomy as one of the four mathematical arts, the others being arithmetic, geometry and music. While best known for the Pythagorean Theorem, Pythagoras did have some input into astronomy. By the time of Pythagoras, the five planets visible to the naked eye - Mercury, Venus, Mars, Jupiter and Saturn - had long been identified. The names of these planets were initially derived from Greek mythology before being given the equivalent Roman mythological names, which are the ones we still use today. The word planet is a Greek term meaning wanderer, as these bodies move across the sky at different speeds from the stars, which appear fixed in the same positions relative to each other. For part of the year Venus appears in the eastern sky as an early morning object before disappearing and reappearing a few weeks later in the evening western sky. Early Greek astronomers thought this was two different bodies and assigned the names Phosphorus and Hesperus to the morning and evening apparitions respectively. Pythagoras is given credit for being the first to realize that these two bodies were in fact the same planet, a notion he arrived at through observation and geometrical calculations. Pythagoras was also one of the first to think that the Earth was round, a theory that was finally proved around 330 BCE by Aristotle. (Although, as you are probably aware, many people in 1642 CE still believed the earth to be flat.) Aristotle (384 BCE - 322 BCE) demonstrates in his writings that he knew we see the moon by the light of the sun, how the phases of the moon occur, and understood how eclipses work. He also knew that the earth was a sphere. Philosophically, he argued that each part of the earth is trying to be pulled to the center of the earth, and so the earth would naturally take on a spherical shape. He then pointed out observations that support the idea of a spherical earth. First, the shadow of the earth on the moon during a lunar eclipse is always circular. The only shape that always casts a circular shadow is a sphere. Second, as one traveles more north or south, the positions of the stars in the sky change. There are constellations visible in the north that one cannot see in the south and vice versa. He related this to the curvature of the earth. Aristotle talked about the work of earlier Greeks, who had developed an earth centered model of the planets. In these models, the center of the earth is the center of all the other motions. While it is not sure if the earlier Greeks actually thought the planets moved in circles, it is clear that Aristotle did. Aristotle rejected a moving earth for two reasons. Most importantly he didnt understand inertia. To Aristotle, the natural state for an object was to be at rest. He believed that it takes a force in order for an object to move. Using Aristotles ideas, if the earth were moving through space, if you tripped, you would not be in contact with the earth, and so would get left behind in space. Since this obviously does not happen, the earth must not move. This misunderstanding of inertia confused scientists until the time of Galileo. A second, but not as important, reason Aristotle rejected a moving earth is that he recognized that if the earth moved and rotated around the sun, there would be an observable parallax of the stars. One cannot see stellar parallax with the naked-eye, so Aristotle concluded that the earth must be at rest. (The stars are so far away, that one needs a good telescope to measure stellar parallax, which was first measured in 1838.) Aristotle believed that the objects in the heavens are perfect and unchanging. Since he believed that the only eternal motion is circular with a constant speed, the motions of the planets must be circular. This came to be called The Principal of Uniform Circular Motion. Aristotle and his ideas became very important because they became incorporated into the Catholic Churchs theology in the twelfth century by Thomas Aquinas. In the early 16th century, the Church banned new interpretations of scripture and this included a ban on ideas of a moving earth. Claudius Ptolemy (90 - 168 CE) was a citizen of Egypt which was under Roman rule during Ptolemys lifetime. During his lifetime he was a mathematician, astronomer, and geographer. His theories dominated the worlds understanding of astronomy for over a thousand years. While it is known that many astronomers published works during this time, only Ptolemys work The Almagest survived. In it, he outlined his geometrical reasoning for a geocentric view of the Universe. As outlined in the Almagest, the Universe according to Ptolemy was based on five main points: 1) the celestial realm is spherical, 2) the celestial realm moves in a circle, 3) the earth is a sphere, 4) the celestial realm orbit is a circle centered on the earth, and 5) earth does not move. Ptolemy also identified eight circular orbits surrounding earth where the other planets existed. In order, they were the moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn, and the sphere of fixed stars. A serious problem with the earth-centered system was the fact that at certain times in their orbits, some of the planets appeared to move in the opposite direction of their normal movement. This reverse direction movement is referred to as retrograde motion. If the earth was to remain motionless at the center of the system, some very intricate designs were necessary to explain the movement of the retrograde planets. In the Ptolemaic system, each retrograde planet moved by two spheres. The Ptolemaic system had circles within circles that produced epicycles. In the sketch above on the left, the red ball moved clockwise in its little circle while the entire orbit also orbited clockwise around the big circle. This process produced a path like that shown in the sketch above on the right. As the red ball moved around its path, at some times it would be moving clockwise and then for a short period, it would move counterclockwise. This motion was able to explain the retrograde motion noted for some planets. ",text,
L_0328,the history of astronom,T_1762,"It was not until 1543, when Copernicus (1473 - 1543) introduced a sun-centered design (heliocentric), that Ptolemys astronomy was seriously questioned and eventually overthrown. Copernicus studied at the University of Bologna, where he lived in the same house as the principal astronomer there. Copernicus assisted the astronomer in some of his observations and in the production of the annual astrological forecasts for the city. It is at Bologna that he probably first encountered a translation of Ptolemys Almagest that would later make it possible for Copernicus to successfully refute the ancient astronomer. Later, at the University of Padua, Copernicus studied medicine, which was closely associated with astrology at that time due to the belief that the stars influenced the dispositions of the body. Returning to Poland, Copernicus secured a teaching post at Wroclaw, where he primarily worked as a medical doctor and manager of Church affairs. In his spare time, he studied the stars and the planets (decades before the telescope was invented), and applied his mathematical understanding to the mysteries of the night sky. In so doing, he developed his theory of a system in which the Earth, like all the planets, revolved around the sun, and which simply and elegantly explained the curious retrograde movements of the planets. Copernicus wrote his theory in De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Orbs). The book was completed in 1530 or so, but it wasnt published until the year he died, 1543. It has been suggested that Copernicus knew the publication would incur the wrath of the Catholic church and he didnt want to deal with problems so he didnt publish his theory until he was on his death bed. Legend has it that a copy of the printers proof was placed in his hands as he lay in a coma, and he woke long enough to recognize what he was holding before he died. Tycho Brahe (1546 - 1601) was born in a part of southern Sweden that was part of Denmark at the time. While attending the university to study law and philosophy, he became interested in astronomy and spent most evenings observing the stars. One of Tycho Brahes first contributions to astronomy was the detection and correction of several serious errors in the standard astronomical tables. Then, in 1572, he discovered a supernova located in the constellation of Cassiopeia. Tycho built his own instruments and made the most complete and accurate observations available without the use of a telescope. Eventually, his fame led to an offer from King Frederick II of Denmark & Norway to fund the construction of an astronomical observatory. The island of Van was chosen and in 1576, construction began. Tycho Brahe spent twenty years there, making observations on celestial bodies. During his life, Tycho Brahe did not accept Copernicus model of the universe. He attempted to combine it with the Ptolemaic model. As a theoretician, Tycho was a failure but his observations and the data he collected was far superior to any others made prior to the invention of the telescope. After Tycho Brahes death, his assistant, Johannes Kepler used Tycho Brahes observations to calculate his own three laws of planetary motion. In 1600, Johannes Kepler (1571 - 1630) began working as Tychos assistant. They recognized that neither the Ptolemaic (geocentric) or Copernican (heliocentric) models could predict positions of Mars as accurately as they could measure them. Tycho died in 1601 and after that Kepler had full access to Tychos data. He analyzed the data for 8 years and tried to calculate an orbit that would fit the data, but was unable to do so. Kepler later determined that the orbits were not circular but elliptical. ",text,
L_0328,the history of astronom,T_1763,"1. The orbits of the planets are elliptical. 2. An imaginary line connecting a planet and the sun sweeps out equal areas during equal time intervals. (Therefore, the earths orbital speed varies at different times of the year. The earth moves fastest in its orbit when closest to the sun and slowest when farthest away.) Keplers Second Law of Planetary Motion was calculated for Earth, then the hypothesis was tested using data for Mars, and it worked! 3. Keplers Third Law of Planetary Motion showed the relationship between the size of a planets orbit radius, R ( 12 the major axis), and its orbital period, T . R2 = T 3 This law is true for all planets if you use astronomical units (that is, distance in multiples of earths orbital radium and time in multiples of earth years). Keplers three laws replaced the cumbersome epicycles to explain planetary motion with three mathematical laws that allowed the positions of the planets to be predicted with accuracies ten times better than Ptolemaic or Copernican models. ",text,
L_0328,the history of astronom,T_1764,"Galileo Galilei (1564-1642) was a very important person in the development of modern astronomy, both because of his contributions directly to astronomy, and because of his work in physics. He provided the crucial observations that proved the Copernican hypothesis, and also laid the foundations for a correct understanding of how objects moved on the surface of the earth and of gravity. One could, with considerable justification, view Galileo as the father both of modern astronomy and of modern physics. Galileo did not invent the telescope, but he was the first to turn his telescope toward the sky to study the heavens systematically. His telescope was poorer than even a cheap modern amateur telescope, but what he observed in the heavens showed errors in Aristotles opinion of the universe and the worldview that it supported. Observations through Galileos telescope made it clear that the earth-centered and earth doesnt move solar system of Aristotle was incorrect. Since church officials had made some of Aristotles opinions a part of the religious views of the church, proving Aristotles views to be incorrect also pointed out flaws in the church. Galileo observed four points of light that changed their positions around the planet Jupiter and he concluded that these were moons in orbit around Jupiter. These observations showed that there were new things in the heavens that Aristotle and Ptolemy had known nothing about. Furthermore, they demonstrated that a planet could have moons circling it that would not be left behind as the planet moved around its orbit. One of the arguments against the Copernican system had been that if the moon were in orbit around the Earth and the Earth in orbit around the Sun, the Earth would leave the Moon behind as it moved around its orbit. Galileo used his telescope to show that Venus, like the moon, went through a complete set of phases. This observation was extremely important because it was the first observation that was consistent with the Copernican system but not the Ptolemaic system. In the Ptolemaic system, Venus should always be in crescent phase as viewed from the Earth because the sun is beyond Venus, but in the Copernican system Venus should exhibit a complete set of phases over time as viewed from the Earth because it is illuminated from the center of its orbit. It is important to note that this was the first empirical evidence (coming almost a century after Copernicus) that allowed a definitive test of the two models. Until that point, both the Ptolemaic and Copernican models described the available data. The primary attraction of the Copernican system was that it described the data in a simpler fashion, but here finally was conclusive evidence that not only was the Ptolemaic universe more complicated, it also was incorrect. As each new observation was brought to light, increasing doubt was cast on the old views of the heavens. It also raised the credibility issue: could the authority of Aristotle and Ptolemy be trusted concerning the nature of the Universe if there were so many things in the Universe about which they had been unaware and/or incorrect? Galileos challenge of the Churchs authority through his refutation of the Aristotelian concept of the Universe eventually got him into deep trouble. Late in his life he was forced, under threat of torture, to publicly recant his Copernican views and spent his last years under house arrest. Galileos life is a sad example of the conflict between the scientific method and unquestioned authority. Sir Isaac Newton (1642-1727), who was born the same year that Galileo died, would build on Galileos ideas to demonstrate that the laws of motion in the heavens and the laws of motion on the earth were the same. Thus Galileo began, and Newton completed, a synthesis of astronomy and physics in which astronomy was recognized as but a part of physics, and that the opinions of Aristotle were almost completely eliminated from both. Many scientists consider Newton to be a peer of Einstein in scientific thinking. Newtons accomplishments had even greater scope than those of Einstein. The poet Alexander Pope wrote of Newton: Nature and Natures laws lay hid in night; God said, Let Newton be! and all was light. In terms of astronomy, Newton gave reasons for and corrections to Keplers Laws. Kepler had proposed three Laws of Planetary motion based on Tycho Brahes data. These Laws were supposed to apply only to the motions of the planets. Further, they were purely empirical, that is, they worked, but no one knew why they worked. Newton changed all of that. First, he demonstrated that the motion of objects on the Earth could be described by three new Laws of motion, and then he went on to show that Keplers three Laws of Planetary Motion were but special cases of Newtons three Laws when his gravitational force was postulated to exist between all masses in the Universe. In fact, Newton showed that Keplers Laws of planetary motion were only approximately correct, and supplied the quantitative corrections that with careful observations proved to be valid. ",text,
L_0328,the history of astronom,T_1765,"The Big Bang Theory is the dominant and highly supported theory of the origin of the universe. It states that the universe began from an initial point which has expanded over billions of years to form the universe as we now know it. In 1922, Alexander Friedman found that the solutions to Einsteins general relativity equations resulted in an expanding universe. Einstein, at that time, believed in a static, eternal universe so he added a constant to his equations to eliminate the expansion. Einstein would later call this the biggest blunder of his life. In 1924, Edwin Hubble was able to measure the distance to observed celestial objects that were thought to be nebula and discovered that they were so far away they were not actually part of the Milky Way (the galaxy containing our sun). He discovered that the Milky Way was only one of many galaxies. In 1927, Georges Lemaitre, a physicist, suggested that the universe must be expanding. Lemaitres theory was supported by Hubble in 1929 when he found that the galaxies most distant from us also had the greatest red shift (were moving away from us with the greatest speed). The idea that the most distance galaxies were moving away from us at the greatest speed was exactly what was predicted by Lemaitre. In 1931, Lemaitre went further with his predictions and by extrapolating backwards, found that the matter of the universe would reach an infinite density and temperature at a finite time in the past (around 15 billion years). This meant that the universe must have begun as a small, extremely dense point of matter. At the time, the only other theory that competed with Lemaitres theory was the Steady State Theory of Fred Hoyle. The steady state theory predicted that new matter was created which made it appear that the universe was expanding but that the universe was constant. It was Hoyle who coined the term Big Bang Theory which he used as a derisive name for Lemaitres theory. George Gamow (1904 - 1968) was the major advocate of the Big Bang theory. He predicted that cosmic microwave background radiation should exist throughout the universe as a remnant of the Big Bang. As atoms formed from sub-atomic particles shortly after the Big Bang, electromagnetic radiation would be emitted and this radiation would still be observable today. Gamow predicted that the expansion of the universe would cool the original radiation so that now the radiation would be in the microwave range. The debate continued until 1965 when two Bell Telephone scientists stumbled upon the microwave radiation with their radio telescope. ",text,
L_0329,thermosphere and beyond,T_1766,"The density of molecules is so low in the thermosphere that one gas molecule can go about 1 km before it collides with another molecule. Since so little energy is transferred, the air feels very cold (See opening image). ",text,
L_0329,thermosphere and beyond,T_1767,"Within the thermosphere is the ionosphere. The ionosphere gets its name from the solar radiation that ionizes gas molecules to create a positively charged ion and one or more negatively charged electrons. The freed electrons travel within the ionosphere as electric currents. Because of the free ions, the ionosphere has many interesting characteristics. At night, radio waves bounce off the ionosphere and back to Earth. This is why you can often pick up an AM radio station far from its source at night. ",text,
L_0329,thermosphere and beyond,T_1768,"The Van Allen radiation belts are two doughnut-shaped zones of highly charged particles that are located very high the atmosphere in the magnetosphere. The particles originate in solar flares and fly to Earth on the solar wind. Once trapped by Earths magnetic field, they follow along the fields magnetic lines of force. These lines extend from above the Equator to the North Pole and also to the South Pole, then return to the Equator. ",text,
L_0329,thermosphere and beyond,T_1769,"When massive solar storms cause the Van Allen belts to become overloaded with particles, the result is the most spectacular feature of the ionosphere  the nighttime aurora (Figure 1.1). The particles spiral along magnetic field lines toward the poles. The charged particles energize oxygen and nitrogen gas molecules, causing them to light up. Each gas emits a particular color of light. (a) Spectacular light displays are visible as the aurora borealis or northern lights in the Northern Hemisphere. (b) The aurora australis or southern lights encircles Antarctica. What would Earths magnetic field look like if it were painted in colors? It would look like the aurora! This QUEST video looks at the aurora, which provides clues about the solar wind, Earths magnetic field and Earths atmosphere. Click image to the left or use the URL below. URL: ",text,
L_0329,thermosphere and beyond,T_1770,"There is no real outer limit to the exosphere, the outermost layer of the atmosphere; the gas molecules finally become so scarce that at some point there are no more. Beyond the atmosphere is the solar wind. The solar wind is made of high-speed particles, mostly protons and electrons, traveling rapidly outward from the Sun. ",text,
L_0331,tides,T_1779,"Tides are the daily rise and fall of sea level at any given place. The pull of the Moons gravity on Earth is the primary cause of tides and the pull of the Suns gravity on Earth is the secondary cause (Figure 1.1). The Moon has a greater effect because, although it is much smaller than the Sun, it is much closer. The Moons pull is about twice that of the Suns. To understand the tides it is easiest to start with the effect of the Moon on Earth. As the Moon revolves around our planet, its gravity pulls Earth toward it. The lithosphere is unable to move much, but the water is pulled by the gravity and a bulge is created. This bulge is the high tide beneath the Moon. On the other side of the Earth, a high tide is produced where the Moons pull is weakest. These two water bulges on opposite sides of the Earth aligned with the Moon are the high tides. The places directly in between the high tides are low tides. As the Earth rotates beneath the Moon, a single spot will experience two high tides and two low tides approximately every day. High tides occur about every 12 hours and 25 minutes. The reason is that the Moon takes 24 hours and 50 minutes to rotate once around the Earth, so the Moon is over the same location every 24 hours and 50 minutes. Since high tides occur twice a day, one arrives each 12 hours and 25 minutes. What is the time between a high tide and the next low tide? The gravity of the Sun also pulls Earths water towards it and causes its own tides. Because the Sun is so far away, its pull is smaller than the Moons. Some coastal areas do not follow this pattern at all. These coastal areas may have one high and one low tide per day or a different amount of time between two high tides. These differences are often because of local conditions, such as the shape of the coastline that the tide is entering. The gravitational attraction of the Moon to ocean water creates the high and low tides. ",text,
L_0331,tides,T_1780,"The tidal range is the difference between the ocean level at high tide and the ocean level at low tide (Figure 1.2). The tidal range in a location depends on a number of factors, including the slope of the seafloor. Water appears to move a greater distance on a gentle slope than on a steep slope. ",text,
L_0331,tides,T_1781,"If you look at the diagram of high and low tides on a circular Earth above, youll see that tides are waves. So when the Sun and Moon are aligned, what do you expect the tides to look like? Waves are additive, so when the gravitational pull of both bodies is in the same direction, the high tides are higher and the low tides lower than at other times through the month (Figure 1.3). These more extreme tides, with a greater tidal range, are called spring tides. Spring tides dont just occur in the spring; they occur whenever the Moon is in a new-moon or full-moon phase, about every 14 days. Neap tides are tides that have the smallest tidal range, and they occur when the Earth, the Moon, and the Sun form a 90o angle (Figure 1.4). They occur exactly halfway between the spring tides, when the Moon is at first or last quarter. How do the tides add up to create neap tides? The Moons high tide occurs in the same place as the Suns low tide and the Moons low tide in the same place as the Suns high tide. At neap tides, the tidal range is relatively small. The tidal range is the difference between the ocean level at high tide and low tide. Studying ocean tides rhythmic movements helps scientists understand the ocean and the Sun/Moon/Earth system. This QUEST video explains how tides work, and visits the oldest continually operating tidal gauge in the Western Hemisphere. Click image to the left or use the URL below. URL: ",text,
L_0331,tides,T_1781,"If you look at the diagram of high and low tides on a circular Earth above, youll see that tides are waves. So when the Sun and Moon are aligned, what do you expect the tides to look like? Waves are additive, so when the gravitational pull of both bodies is in the same direction, the high tides are higher and the low tides lower than at other times through the month (Figure 1.3). These more extreme tides, with a greater tidal range, are called spring tides. Spring tides dont just occur in the spring; they occur whenever the Moon is in a new-moon or full-moon phase, about every 14 days. Neap tides are tides that have the smallest tidal range, and they occur when the Earth, the Moon, and the Sun form a 90o angle (Figure 1.4). They occur exactly halfway between the spring tides, when the Moon is at first or last quarter. How do the tides add up to create neap tides? The Moons high tide occurs in the same place as the Suns low tide and the Moons low tide in the same place as the Suns high tide. At neap tides, the tidal range is relatively small. The tidal range is the difference between the ocean level at high tide and low tide. Studying ocean tides rhythmic movements helps scientists understand the ocean and the Sun/Moon/Earth system. This QUEST video explains how tides work, and visits the oldest continually operating tidal gauge in the Western Hemisphere. Click image to the left or use the URL below. URL: ",text,
L_0331,tides,T_1781,"If you look at the diagram of high and low tides on a circular Earth above, youll see that tides are waves. So when the Sun and Moon are aligned, what do you expect the tides to look like? Waves are additive, so when the gravitational pull of both bodies is in the same direction, the high tides are higher and the low tides lower than at other times through the month (Figure 1.3). These more extreme tides, with a greater tidal range, are called spring tides. Spring tides dont just occur in the spring; they occur whenever the Moon is in a new-moon or full-moon phase, about every 14 days. Neap tides are tides that have the smallest tidal range, and they occur when the Earth, the Moon, and the Sun form a 90o angle (Figure 1.4). They occur exactly halfway between the spring tides, when the Moon is at first or last quarter. How do the tides add up to create neap tides? The Moons high tide occurs in the same place as the Suns low tide and the Moons low tide in the same place as the Suns high tide. At neap tides, the tidal range is relatively small. The tidal range is the difference between the ocean level at high tide and low tide. Studying ocean tides rhythmic movements helps scientists understand the ocean and the Sun/Moon/Earth system. This QUEST video explains how tides work, and visits the oldest continually operating tidal gauge in the Western Hemisphere. Click image to the left or use the URL below. URL: ",text,
L_0334,tree rings ice cores and varves,T_1789,"In locations where summers are warm and winters are cool, trees have a distinctive growth pattern. Tree trunks display alternating bands of light-colored, low density summer growth and dark, high density winter growth. Each light-dark band represents one year. By counting tree rings it is possible to find the number of years the tree lived (Figure 1.1). The width of these growth rings varies with the conditions present that year. A summer drought may make the tree grow more slowly than normal and so its light band will be relatively small. These tree-ring variations appear in all trees in a region. The same distinctive pattern can be found in all the trees in an area for the same time period. Scientists have created continuous records of tree rings going back over the past 2,000 years. Wood fragments from old buildings and ancient ruins can be age dated by matching up the pattern of tree rings in the wood fragment in Cross-section showing growth rings. question and the scale created by scientists. The outermost ring indicates when the tree stopped growing; that is, when it died. The tree-ring record is extremely useful for finding the age of ancient structures. ",text,
L_0334,tree rings ice cores and varves,T_1790,"Besides tree rings, other processes create distinct yearly layers that can be used for dating. On a glacier, snow falls in winter but in summer dust accumulates. This leads to a snow-dust annual pattern that goes down into the ice (Figure gather allows them to determine how the environment has changed as the glacier has stayed in its position. Analyses of the ice tell how concentrations of atmospheric gases changed, which can yield clues about climate. The longest cores allow scientists to create a record of polar climate stretching back hundreds of thousands of years. ",text,
L_0334,tree rings ice cores and varves,T_1791,"Lake sediments, especially in lakes that are located at the end of glaciers, also have an annual pattern. In the summer, the glacier melts rapidly, producing a thick deposit of sediment. These alternate with thin, clay-rich layers deposited in the winter. The resulting layers, called varves, give scientists clues about past climate conditions (Figure 1.3). A warm summer might result in a very thick sediment layer while a cooler summer might yield a thinner layer. ",text,
L_0335,troposphere,T_1792,"The temperature of the troposphere is highest near the surface of the Earth and decreases with altitude. On average, the temperature gradient of the troposphere is 6.5o C per 1,000 m (3.6o F per 1,000 ft) of altitude. Earths surface is the source of heat for the troposphere. Rock, soil, and water on Earth absorb the Suns light and radiate it back into the atmosphere as heat, so there is more heat near the surface. The temperature is also higher near the surface because gravity pulls in more gases. The greater density of gases causes the temperature to rise. Notice that in the troposphere warmer air is beneath cooler air. This condition is unstable since warm air is less dense than cool air. The warm air near the surface rises and cool air higher in the troposphere sinks, so air in the troposphere does a lot of mixing. This mixing causes the temperature gradient to vary with time and place. The rising and sinking of air in the troposphere means that all of the planets weather takes place in the troposphere. ",text,
L_0335,troposphere,T_1793,"Sometimes there is a temperature inversion, in which air temperature in the troposphere increases with altitude and warm air sits over cold air. Inversions are very stable and may last for several days or even weeks. Inversions form: Over land at night or in winter when the ground is cold. The cold ground cools the air that sits above it, making this low layer of air denser than the air above it. Near the coast, where cold seawater cools the air above it. When that denser air moves inland, it slides beneath the warmer air over the land. Since temperature inversions are stable, they often trap pollutants and produce unhealthy air conditions in cities (Figure 1.1). Smoke makes a temperature inversion visible. The smoke is trapped in cold dense air that lies beneath a cap of warmer air. At the top of the troposphere is a thin layer in which the temperature does not change with height. This means that the cooler, denser air of the troposphere is trapped beneath the warmer, less dense air of the stratosphere. Air from the troposphere and stratosphere rarely mix. Click image to the left or use the URL below. URL: ",text,
L_0336,tsunami,T_1794,"Tsunami are deadly ocean waves from the sharp jolt of an undersea earthquake. Less frequently, these waves can be generated by other shocks to the sea, like a meteorite impact. Fortunately, few undersea earthquakes, and even fewer meteorite impacts, generate tsunami. ",text,
L_0336,tsunami,T_1795,"Tsunami waves have small wave heights relative to their long wavelengths, so they are usually unnoticed at sea. When traveling up a slope onto a shoreline, the wave is pushed upward. As with wind waves, the speed of the bottom of the wave is slowed by friction. This causes the wavelength to decrease and the wave to become unstable. These factors can create an enormous and deadly wave. Landslides, meteorite impacts, or any other jolt to ocean water may form a tsunami. Tsunami can travel at speeds of 800 kilometers per hour (500 miles per hour). ",text,
L_0336,tsunami,T_1796,"Since tsunami are long-wavelength waves, a long time can pass between crests or troughs. Any part of the wave can make landfall first. In 1755 in Lisbon, Portugal, a tsunami trough hit land first. A large offshore earthquake did a great deal of damage on land. People rushed out to the open space of the shore. Once there, they discovered that the water was flowing seaward fast and some of them went out to observe. What do you think happened next? The people on the open beach drowned when the crest of the wave came up the beach. Large tsunami in the Indian Ocean and more recently Japan have killed hundreds of thousands of people in recent years. The west coast is vulnerable to tsunami since it sits on the Pacific Ring of Fire. Scientists are trying to learn everything they can about predicting tsunamis before a massive one strikes a little closer to home. Although most places around the Indian Ocean did not have warning systems in 2005, there is a tsunami warning system in that region now. Tsunami warning systems have been placed in most locations where tsunami are possible. Click image to the left or use the URL below. URL: ",text,
L_0337,types of air pollution,T_1797,"The two types of air pollutants are primary pollutants, which enter the atmosphere directly, and secondary pollutants, which form from a chemical reaction. ",text,
L_0337,types of air pollution,T_1798,"Some primary pollutants are natural, such as volcanic ash. Dust is natural but exacerbated by human activities; for example, when the ground is torn up for agriculture or development. Most primary pollutants are the result of human activities, the direct emissions from vehicles and smokestacks. Primary pollutants include: Carbon oxides include carbon monoxide (CO) and carbon dioxide (CO2 ) (Figure 1.1). Both are colorless, odorless gases. CO is toxic to both plants and animals. CO and CO2 are both greenhouse gases. Nitrogen oxides are produced when nitrogen and oxygen from the atmosphere come together at high temper- atures. This occurs in hot exhaust gas from vehicles, power plants, or factories. Nitrogen oxide (NO) and nitrogen dioxide (NO2 ) are greenhouse gases. Nitrogen oxides contribute to acid rain. Sulfur oxides include sulfur dioxide (SO2 ) and sulfur trioxide (SO3 ). These form when sulfur from burning coal reaches the air. Sulfur oxides are components of acid rain. Particulates are solid particles, such as ash, dust, and fecal matter (Figure 1.2). They are commonly formed from combustion of fossil fuels, and can produce smog. Particulates can contribute to asthma, heart disease, and some types of cancers. Lead was once widely used in automobile fuels, paint, and pipes. This heavy metal can cause brain damage or blood poisoning. High CO2 levels are found in major metropolitan areas and along the major interstate highways. Particulates from a brush fire give the sky a strange glow in Arizona. ",text,
L_0337,types of air pollution,T_1798,"Some primary pollutants are natural, such as volcanic ash. Dust is natural but exacerbated by human activities; for example, when the ground is torn up for agriculture or development. Most primary pollutants are the result of human activities, the direct emissions from vehicles and smokestacks. Primary pollutants include: Carbon oxides include carbon monoxide (CO) and carbon dioxide (CO2 ) (Figure 1.1). Both are colorless, odorless gases. CO is toxic to both plants and animals. CO and CO2 are both greenhouse gases. Nitrogen oxides are produced when nitrogen and oxygen from the atmosphere come together at high temper- atures. This occurs in hot exhaust gas from vehicles, power plants, or factories. Nitrogen oxide (NO) and nitrogen dioxide (NO2 ) are greenhouse gases. Nitrogen oxides contribute to acid rain. Sulfur oxides include sulfur dioxide (SO2 ) and sulfur trioxide (SO3 ). These form when sulfur from burning coal reaches the air. Sulfur oxides are components of acid rain. Particulates are solid particles, such as ash, dust, and fecal matter (Figure 1.2). They are commonly formed from combustion of fossil fuels, and can produce smog. Particulates can contribute to asthma, heart disease, and some types of cancers. Lead was once widely used in automobile fuels, paint, and pipes. This heavy metal can cause brain damage or blood poisoning. High CO2 levels are found in major metropolitan areas and along the major interstate highways. Particulates from a brush fire give the sky a strange glow in Arizona. ",text,
L_0337,types of air pollution,T_1799,"Any city can have photochemical smog, but it is most common in sunny, dry locations. A rise in the number of vehicles in cities worldwide has increased photochemical smog. Nitrogen oxides, ozone, and several other compounds are some of the components of this type of air pollution. Photochemical smog forms when car exhaust is exposed to sunlight. Nitrogen oxide is created by gas combustion in cars and then into the air (Figure 1.3). In the presence of sunshine, the NO2 splits and releases an oxygen ion (O). The O then combines with an oxygen molecule (O2 ) to form ozone (O3 ). This reaction can also go in reverse: Nitric oxide (NO) removes an oxygen atom from ozone to make it O2 . The direction the reaction goes depends on how much NO2 and NO there is. If NO2 is three times more abundant than NO, ozone will be produced. If nitric oxide levels are high, ozone will not be created. The brown color of the air behind the Golden Gate Bridge is typical of California cities, because of nitrogen oxides. Ozone is one of the major secondary pollutants. It is created by a chemical reaction that takes place in exhaust and in the presence of sunlight. The gas is acrid-smelling and whitish. Warm, dry cities surrounded by mountains, such as Los Angeles, Phoenix, and Denver, are especially prone to photochemical smog. Photochemical smog peaks at midday on the hottest days of summer. Ozone is also a greenhouse gas. ",text,
L_0338,types of fossilization,T_1800,Most fossils are preserved by one of five processes outlined below (Figure 1.1): ,text,
L_0338,types of fossilization,T_1801,"Most uncommon is the preservation of soft-tissue original material. Insects have been preserved perfectly in amber, which is ancient tree sap. Mammoths and a Neanderthal hunter were frozen in glaciers, allowing scientists the rare opportunity to examine their skin, hair, and organs. Scientists collect DNA from these remains and compare the DNA sequences to those of modern counterparts. ",text,
L_0338,types of fossilization,T_1802,"The most common method of fossilization is permineralization. After a bone, wood fragment, or shell is buried in sediment, mineral-rich water moves through the sediment. This water deposits minerals into empty spaces and Five types of fossils: (a) insect preserved in amber, (b) petrified wood (permineralization), (c) cast and mold of a clam shell, (d) pyritized ammonite, and (e) compression fossil of a fern. produces a fossil. Fossil dinosaur bones, petrified wood, and many marine fossils were formed by permineralization. ",text,
L_0338,types of fossilization,T_1802,"The most common method of fossilization is permineralization. After a bone, wood fragment, or shell is buried in sediment, mineral-rich water moves through the sediment. This water deposits minerals into empty spaces and Five types of fossils: (a) insect preserved in amber, (b) petrified wood (permineralization), (c) cast and mold of a clam shell, (d) pyritized ammonite, and (e) compression fossil of a fern. produces a fossil. Fossil dinosaur bones, petrified wood, and many marine fossils were formed by permineralization. ",text,
L_0338,types of fossilization,T_1803,"When the original bone or shell dissolves and leaves behind an empty space in the shape of the material, the depression is called a mold. The space is later filled with other sediments to form a matching cast within the mold that is the shape of the original organism or part. Many mollusks (clams, snails, octopi, and squid) are found as molds and casts because their shells dissolve easily. ",text,
L_0338,types of fossilization,T_1804,"The original shell or bone dissolves and is replaced by a different mineral. For example, calcite shells may be replaced by dolomite, quartz, or pyrite. If a fossil that has been replace by quartz is surrounded by a calcite matrix, mildly acidic water may dissolve the calcite and leave behind an exquisitely preserved quartz fossil. ",text,
L_0338,types of fossilization,T_1805,"Some fossils form when their remains are compressed by high pressure, leaving behind a dark imprint. Compression is most common for fossils of leaves and ferns, but can occur with other organisms. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0342,universe,T_1825,"The study of the universe is called cosmology. Cosmologists study the structure and changes in the present universe. The universe contains all of the star systems, galaxies, gas, and dust, plus all the matter and energy that exists now, that existed in the past, and that will exist in the future. The universe includes all of space and time. ",text,
L_0342,universe,T_1826,"What did the ancient Greeks recognize as the universe? In their model, the universe contained Earth at the center, the Sun, the Moon, five planets, and a sphere to which all the stars were attached. This idea held for many centuries until Galileos telescope helped people recognize that Earth is not the center of the universe. They also found out that there are many more stars than were visible to the naked eye. All of those stars were in the Milky Way Galaxy. In the early 20th century, an astronomer named Edwin Hubble (Figure 1.1) discovered that what scientists called the Andromeda Nebula was actually over 2 million light years away  many times farther than the farthest distances that had ever been measured. Hubble realized that many of the objects that astronomers called nebulas were not actually clouds of gas, but were collections of millions or billions of stars  what we now call galaxies. Hubble showed that the universe was much larger than our own galaxy. Today, we know that the universe contains about a hundred billion galaxies  about the same number of galaxies as there are stars in the Milky Way Galaxy. (a) Edwin Hubble used the 100-inch reflecting telescope at the Mount Wilson Observatory in California to show that some distant specks of light were galaxies. (b) Hubbles namesake space telescope spotted this six galaxy group. Edwin Hubble demonstrated the existence of galaxies. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0343,uranus,T_1827,"Uranus (YOOR-uh-nuhs) is named for the Greek god of the sky. From Earth, Uranus is so faint that it was unnoticed by ancient observers. William Herschel first discovered the planet in 1781. Although Uranus is very large, it is extremely far away, about 2.8 billion km (1.8 billion mi) from the Sun. Light from the Sun takes about 2 hours and 40 minutes to reach Uranus. Uranus orbits the Sun once about every 84 Earth years. Uranus has a mass about 14 times the mass of Earth, but it is much less dense than Earth. Gravity at the surface of Uranus is weaker than on Earths surface, so if you were at the top of the clouds on Uranus, you would weigh about 10% less than what you weigh on Earth. ",text,
L_0343,uranus,T_1828,"Like Jupiter and Saturn, Uranus is composed mainly of hydrogen and helium, with an outer gas layer that gives way to liquid on the inside. Uranus has a higher percentage of icy materials, such as water, ammonia (NH3 ), and methane (CH4 ), than Jupiter and Saturn. When sunlight reflects off Uranus, clouds of methane filter out red light, giving the planet a blue-green color. There are bands of clouds in the atmosphere of Uranus, but they are hard to see in normal light, so the planet looks like a plain blue ball. ",text,
L_0343,uranus,T_1829,"Most of the planets in the solar system rotate on their axes in the same direction that they move around the Sun. Uranus, though, is tilted on its side, so its axis is almost parallel to its orbit. In other words, it rotates like a top that was turned so that it was spinning parallel to the floor. Scientists think that Uranus was probably knocked over by a collision with another planet-sized object billions of years ago. ",text,
L_0343,uranus,T_1830,"Uranus has a faint system of rings (Figure 1.1). The rings circle the planets equator, but because Uranus is tilted on its side, the rings are almost perpendicular to the planets orbit. This image from the Hubble Space Tele- scope shows the faint rings of Uranus. The planet is tilted on its side, so the rings are nearly vertical. Uranus has 27 known moons and all but a few of them are named for characters from the plays of William Shakespeare. The five biggest moons of Uranus  Miranda, Ariel, Umbriel, Titania, and Oberon  are shown in Figure 1.2. These Voyager 2 photos have been resized to show the relative sizes of the five main moons of Uranus. Click image to the left or use the URL below. URL: ",text,
L_0343,uranus,T_1830,"Uranus has a faint system of rings (Figure 1.1). The rings circle the planets equator, but because Uranus is tilted on its side, the rings are almost perpendicular to the planets orbit. This image from the Hubble Space Tele- scope shows the faint rings of Uranus. The planet is tilted on its side, so the rings are nearly vertical. Uranus has 27 known moons and all but a few of them are named for characters from the plays of William Shakespeare. The five biggest moons of Uranus  Miranda, Ariel, Umbriel, Titania, and Oberon  are shown in Figure 1.2. These Voyager 2 photos have been resized to show the relative sizes of the five main moons of Uranus. Click image to the left or use the URL below. URL: ",text,
L_0344,uses of water,T_1831,Humans use six times as much water today as they did 100 years ago. People living in developed countries use a far greater proportion of the worlds water than people in less developed countries. What do people use all of that water for? ,text,
L_0344,uses of water,T_1832,"Besides drinking and washing, people need water for agriculture, industry, household uses, and recreation (Figure Water use can be consumptive or non-consumptive, depending on whether the water is lost to the ecosystem. Non-consumptive water use includes water that can be recycled and reused. For example, the water that goes down the drain and enters the sewer system is purified and then redistributed for reuse. By recycling water, the overall water consumption is reduced. Consumptive water use takes the water out of the ecosystem. Can you name some examples of consumptive water use? ",text,
L_0344,uses of water,T_1833,"Some of the worlds farmers still farm without irrigation by choosing crops that match the amount of rain that falls in their area. But some years are wet and others are dry. For farmers to avoid years in which they produce little or no food, many of the worlds crops are produced using irrigation. Water used for home, industrial, and agricultural purposes in different regions. Globally more than two-thirds of water is for agriculture. ",text,
L_0344,uses of water,T_1834,Three popular irrigation methods are: Overhead sprinklers. Trench irrigation: canals carry water from a water source to the fields. Flood irrigation: fields are flooded with water. All of these methods waste water. Between 15% and 36% percent of the water never reaches the crops because it evaporates or leaves the fields as runoff. Water that runs off a field often takes valuable soil with it. ,text,
L_0344,uses of water,T_1835,"A much more efficient way to water crops is drip irrigation (Figure 1.2). With drip irrigation, pipes and tubes deliver small amounts of water directly to the soil at the roots of each plant or tree. The water is not sprayed into the air or over the ground, so nearly all of it goes directly into the soil and plant roots. ",text,
L_0344,uses of water,T_1836,"Why do farmers use wasteful irrigation methods when water-efficient methods are available? Many farmers and farming corporations have not switched to more efficient irrigation methods for two reasons: 1. Drip irrigation and other more efficient irrigation methods are more expensive than sprinklers, trenches, and flooding. 2. In the United States and some other countries, the government pays for much of the cost of the water that is used for agriculture. Because farmers do not pay the full cost of their water use, they do not have any financial incentive to use less water. What ideas can you come up with to encourage farmers to use more efficient irrigation systems? ",text,
L_0344,uses of water,T_1837,"Aquaculture is a different type of agriculture. Aquaculture is farming to raise fish, shellfish, algae, or aquatic plants (Figure 1.3). As the supplies of fish from lakes, rivers, and the oceans dwindle, people are getting more fish from aquaculture. Raising fish increases our food resources and is especially valuable where protein sources are limited. Farmed fish are becoming increasingly common in grocery stores all over the world. Workers at a fish farm harvest fish they will sell to stores. Growing fish in a large scale requires that the fish stocks are healthy and protected from predators. The species raised must be hearty, inexpensive to feed, and able to reproduce in captivity. Wastes must be flushed out to keep animals healthy. Raising shellfish at farms can also be successful. ",text,
L_0344,uses of water,T_1838,"For some species, aquaculture is very successful and environmental harm is minimal. But for other species, aqua- culture can cause problems. Natural landscapes, such as mangroves, which are rich ecosystems and also protect coastlines from storm damage, may be lost to fish farms (Figure 1.4). For fish farmers, keeping costs down may be a problem since coastal land may be expensive and labor costs may be high. Large predatory fish at the 4th or 5th trophic level must eat a lot, so feeding large numbers of these fish is expensive and environmentally costly. Farmed fish are genetically different from wild stocks, and if they escape into the wild they may cause problems for native fish. Because the organisms live so close together, parasites are common and may also escape into the wild. Shrimp farms on the coast of Ecuador are shown as blue rectangles. Mangrove forests, salt flats, and salt marshes have been converted to shrimp farms. ",text,
L_0344,uses of water,T_1839,"Industrial water use accounts for an estimated 15% of worldwide water use, with a much greater percentage in developed nations. Industrial uses of water include power plants that use water to cool their equipment and oil refineries that use water for chemical processes. Manufacturing is also water intensive. ",text,
L_0344,uses of water,T_1840,"Think about all the ways you use water in a day. You need to count the water you drink, cook with, bathe in, garden with, let run down the drain, or flush down the toilet. In developed countries, people use a lot of water, while in less developed countries people use much less. Globally, household or personal water use is estimated to account for 15% of world-wide water use. Some household water uses are non-consumptive, because water is recaptured in sewer systems, treated, and returned to surface water supplies for reuse. Many things can be done to lower water consumption at home. Convert lawns and gardens to drip-irrigation systems. Install low-flow shower heads and low-flow toilets. In what other ways can you use less water at home? ",text,
L_0344,uses of water,T_1841,"People love water for swimming, fishing, boating, river rafting, and other activates. Even activities such as golf, where there may not be any standing water, require plenty of water to make the grass on the course green. Despite its value, the amount of water that most recreational activities use is low: less than 1% of all the water we use. Many recreational water uses are non-consumptive including swimming, fishing, and boating. Golf courses are the biggest recreational water consumer since they require large amounts for irrigation, especially because many courses are located in warm, sunny, desert regions where water is scarce and evaporation is high. ",text,
L_0344,uses of water,T_1842,Environmental use of water includes creating wildlife habitat. Lakes are built to create places for fish and water birds (Figure 1.5). Most environmental uses are non-consumptive and account for an even smaller percentage of water use than recreational uses. A shortage of this water is a leading cause of global biodiversity loss. Click image to the left or use the URL below. URL: ,text,
L_0345,venus,T_1843,"Venus thick clouds reflect sunlight well, so Venus is very bright. When it is visible, Venus is the brightest object in the sky besides the Sun and the Moon. Because the orbit of Venus is inside Earths orbit, Venus always appears close to the Sun. When Venus rises just before the Sun rises, the bright object is called the morning star. When it sets just after the Sun sets, it is the evening star. Of the planets, Venus is most similar to Earth in size and density. Venus is also our nearest neighbor. The planets interior structure is similar to Earths, with a large iron core and a silicate mantle (Figure 1.1). But the resemblance between the two inner planets ends there. ",text,
L_0345,venus,T_1844,"Venus rotates in a direction opposite the other planets and opposite to the direction it orbits the Sun. This rotation is extremely slow, only one turn every 243 Earth days. This is longer than a year on Venus  it takes Venus only 224 days to orbit the Sun. Diagram of Venuss interior, which is simi- lar to Earths. ",text,
L_0345,venus,T_1845,"Venus is covered by a thick layer of clouds, as shown in pictures of Venus taken at ultraviolet wavelengths (Figure This ultraviolet image from the Pioneer Venus Orbiter shows thick layers of clouds in the atmosphere of Venus. Venus clouds are not made of water vapor like Earths clouds. Clouds on Venus are made mostly of carbon dioxide Click image to the left or use the URL below. URL:  The atmosphere of Venus is so thick that the atmospheric pressure on the planets surface is 90 times greater than the atmospheric pressure on Earths surface. The dense atmosphere totally obscures the surface of Venus, even from spacecraft orbiting the planet. ",text,
L_0345,venus,T_1846,"Since spacecraft cannot see through the thick atmosphere, radar is used to map Venus surface. Many features found on the surface are similar to Earth and yet are very different. Figure 1.3 shows a topographical map of Venus produced by the Magellan probe using radar. This false color image of Venus was made from radar data collected by the Magellan probe between 1990 and 1994. What features can you identify? Most of the volcanoes are no longer active, but scientists have found evidence that there is some active volcanism (Figure 1.4). Think about what you know about the geology of Earth and what produces volcanoes. What does the presence of volcanoes suggest about the geology of Venus? What evidence would you look for to find the causes of volcanism on Venus? This image of the Maat Mons volcano with lava beds in the foreground was gen- erated by a computer from radar data. The reddish-orange color is close to what scientists think the color of sunlight would look like on the surface of Venus. Venus also has very few impact craters compared with Mercury and the Moon. What is the significance of this? Earth has fewer impact craters than Mercury and the Moon, too. Is this for the same reason that Venus has fewer impact craters? Its difficult for scientists to figure out the geological history of Venus. The environment is too harsh for a rover to go there. It is even more difficult for students to figure out the geological history of a distant planet based on the information given here. Still, we can piece together a few things. On Earth, volcanism is generated because the planets interior is hot. Much of the volcanic activity is caused by plate tectonic activity. But on Venus, there is no evidence of plate boundaries and volcanic features do not line up the way they do at plate boundaries. Because the density of impact craters can be used to determine how old a planets surface is, the small number of impact craters means that Venus surface is young. Scientists think that there is frequent, planet-wide resurfacing of Venus with volcanism taking place in many locations. The cause is heat that builds up below the surface, which has no escape until finally it destroys the crust and results in volcanoes. Click image to the left or use the URL below. URL: ",text,
L_0345,venus,T_1846,"Since spacecraft cannot see through the thick atmosphere, radar is used to map Venus surface. Many features found on the surface are similar to Earth and yet are very different. Figure 1.3 shows a topographical map of Venus produced by the Magellan probe using radar. This false color image of Venus was made from radar data collected by the Magellan probe between 1990 and 1994. What features can you identify? Most of the volcanoes are no longer active, but scientists have found evidence that there is some active volcanism (Figure 1.4). Think about what you know about the geology of Earth and what produces volcanoes. What does the presence of volcanoes suggest about the geology of Venus? What evidence would you look for to find the causes of volcanism on Venus? This image of the Maat Mons volcano with lava beds in the foreground was gen- erated by a computer from radar data. The reddish-orange color is close to what scientists think the color of sunlight would look like on the surface of Venus. Venus also has very few impact craters compared with Mercury and the Moon. What is the significance of this? Earth has fewer impact craters than Mercury and the Moon, too. Is this for the same reason that Venus has fewer impact craters? Its difficult for scientists to figure out the geological history of Venus. The environment is too harsh for a rover to go there. It is even more difficult for students to figure out the geological history of a distant planet based on the information given here. Still, we can piece together a few things. On Earth, volcanism is generated because the planets interior is hot. Much of the volcanic activity is caused by plate tectonic activity. But on Venus, there is no evidence of plate boundaries and volcanic features do not line up the way they do at plate boundaries. Because the density of impact craters can be used to determine how old a planets surface is, the small number of impact craters means that Venus surface is young. Scientists think that there is frequent, planet-wide resurfacing of Venus with volcanism taking place in many locations. The cause is heat that builds up below the surface, which has no escape until finally it destroys the crust and results in volcanoes. Click image to the left or use the URL below. URL: ",text,
L_0350,water distribution,T_1867,"Water is unevenly distributed around the world. Large portions of the world, such as much of northern Africa, receive very little water relative to their population (Figure 1.1). The map shows the number of months in which there is little rainfall in each region. In developed nations, water is stored, but in underdeveloped nations, water storage may be minimal. Over time, as population grows, rainfall totals will change, resulting in less water per person in some regions. In 2025, many nations, even developed nations, are projected to have less water per person than now ",text,
L_0350,water distribution,T_1868,"Water scarcity is a problem now and will become an even larger problem in the future as water sources are reduced or polluted and population grows. In 1995, about 40% of the worlds population faced water scarcity. Scientists estimate that by the year 2025, nearly half of the worlds people wont have enough water to meet their daily needs. Nearly one-quarter of the worlds people will have less than 500 m3 of water to use in an entire year. That amount is less water in a year than some people in the United States use in one day. Some regions have very little rainfall per month. ",text,
L_0350,water distribution,T_1869,"Droughts occur when a region experiences unusually low precipitation for months or years (Figure 1.2). Periods of drought may create or worsen water shortages. Human activities can contribute to the frequency and duration of droughts. For example, deforestation keeps trees from returning water to the atmosphere by transpiration; part of the water cycle becomes broken. Because it is difficult to predict when droughts will happen, it is difficult for countries to predict how serious water shortages will be each year. Extended periods with lower than normal rainfall cause droughts. ",text,
L_0350,water distribution,T_1870,"Global warming will change patterns of rainfall and water distribution. As the Earth warms, regions that currently receive an adequate supply of rain may shift. Regions that rely on snowmelt may find that there is less snow and the melt comes earlier and faster in the spring, causing the water to run off and not be available through the dry summers. A change in temperature and precipitation would completely change the types of plants and animals that can live successfully in that region. ",text,
L_0350,water distribution,T_1871,"Water scarcity can have dire consequences for the people, the economy, and the environment. Without adequate water, crops and livestock dwindle and people go hungry. Industry, construction, and economic development is halted, causing a nation to sink further into poverty. The risk of regional conflicts over scarce water resources rises. People die from diseases, thirst, or even in war over scarce resources. Californias population is growing by hundreds of thousands of people a year, but much of the state receives as much annual rainfall as Morocco. With fish populations crashing, global warming, and the demands of the countrys largest agricultural industry, the pressures on our water supply are increasing. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0350,water distribution,T_1872,"As water supplies become scarce, conflicts will arise between the individuals or nations that have enough clean water and those that do not (Figure 1.3). Some of todays greatest tensions are happening in places where water is scarce. Water disputes may add to tensions between countries where differing national interests and withdrawal rights have been in conflict. Just as with energy resources today, wars may erupt over water. Water disputes are happening along 260 different river systems that cross national boundaries. Some of these disputes are potentially very serious. International water laws, such as the Helsinki Rules, help interpret water rights among countries. Many regions already experience water scarcity. This map shows the number of months in which the amount of water that is used exceeds the availability of water that can be used sustainably. This is projected to get worse as demand increases. ",text,
L_0351,water pollution,T_1873,"Water pollution contributes to water shortages by making some water sources unavailable for use. In underdeveloped countries, raw sewage is dumped into the same water that people drink and bathe in. Even in developed countries, water pollution affects human and environmental health. Water pollution includes any contaminant that gets into lakes, streams, and oceans. The most widespread source of water contamination in developing countries is raw sewage. In developed countries, the three main sources of water pollution are described below. ",text,
L_0351,water pollution,T_1874,"Wastewater from cities and towns contains many different contaminants from many different homes, businesses, and industries (Figure 1.1). Contaminants come from: Sewage disposal (some sewage is inadequately treated or untreated). Storm drains. Septic tanks (sewage from homes). Boats that dump sewage. Yard runoff (fertilizer and herbicide waste). Large numbers of sewage spills into San Francisco Bay are forcing cities, water agencies and the public to take a closer look at wastewater and its impacts on the health of the bay. QUEST investigates the causes of the spills and whats being done to prevent them. Click image to the left or use the URL below. URL: ",text,
L_0351,water pollution,T_1875,"Factories and hospitals spew pollutants into the air and waterways (Figure 1.2). Some of the most hazardous industrial pollutants include: Radioactive substances from nuclear power plants and medical and scientific sources. Heavy metals, organic toxins, oils, and solids in industrial waste. Chemicals, such as sulfur, from burning fossil fuels. Oil and other petroleum products from supertanker spills and offshore drilling accidents. Heated water from industrial processes, such as power stations. ",text,
L_0351,water pollution,T_1876,"Runoff from crops, livestock, and poultry farming carries contaminants such as fertilizers, pesticides, and animal waste into nearby waterways (Figure 1.3). Soil and silt also run off farms. Animal wastes may carry harmful diseases, particularly in the developing world. The high density of animals in a factory farm means that runoff from the area is full of pollutants. Fertilizers that run off of lawns and farm fields are extremely harmful to the environment. Nutrients, such as nitrates, in the fertilizer promote algae growth in the water they flow into. With the excess nutrients, lakes, rivers, and bays become clogged with algae and aquatic plants. Eventually these organisms die and decompose. Decomposition uses up all the dissolved oxygen in the water. Without oxygen, large numbers of plants, fish, and bottom-dwelling animals die. ",text,
L_0351,water pollution,T_1876,"Runoff from crops, livestock, and poultry farming carries contaminants such as fertilizers, pesticides, and animal waste into nearby waterways (Figure 1.3). Soil and silt also run off farms. Animal wastes may carry harmful diseases, particularly in the developing world. The high density of animals in a factory farm means that runoff from the area is full of pollutants. Fertilizers that run off of lawns and farm fields are extremely harmful to the environment. Nutrients, such as nitrates, in the fertilizer promote algae growth in the water they flow into. With the excess nutrients, lakes, rivers, and bays become clogged with algae and aquatic plants. Eventually these organisms die and decompose. Decomposition uses up all the dissolved oxygen in the water. Without oxygen, large numbers of plants, fish, and bottom-dwelling animals die. ",text,
L_0355,weathering and erosion,T_1885,"Weathering is the process that changes solid rock into sediments. Sediments were described in the chapter ""Ma- terials of Earths Crust."" With weathering, rock is disintegrated. It breaks into pieces. Once these sediments are separated from the rocks, erosion is the process that moves the sediments. While plate tectonics forces work to build huge mountains and other landscapes, the forces of weathering gradually wear those rocks and landscapes away. Together with erosion, tall mountains turn into hills and even plains. The Appalachian Mountains along the east coast of North America were once as tall as the Himalayas. ",text,
L_0355,weathering and erosion,T_1886,"No human being can watch for millions of years as mountains are built, nor can anyone watch as those same mountains gradually are worn away. But imagine a new sidewalk or road. The new road is smooth and even. Over hundreds of years, it will completely disappear, but what happens over one year? What changes would you see? (Figure 1.1). What forces of weathering wear down that road, or rocks or mountains over time? A once smooth road surface has cracks and fractures, plus a large pothole. Click image to the left or use the URL below. URL: ",text,
L_0356,wegener and the continental drift hypothesis,T_1887,"Wegener put his idea and his evidence together in his book The Origin of Continents and Oceans, first published in 1915. New editions with additional evidence were published later in the decade. In his book he said that around 300 million years ago the continents had all been joined into a single landmass he called Pangaea, meaning all earth in ancient Greek. The supercontinent later broke apart and the continents having been moving into their current positions ever since. He called his hypothesis continental drift. ",text,
L_0356,wegener and the continental drift hypothesis,T_1888,"Wegeners idea seemed so outlandish at the time that he was ridiculed by other scientists. What do you think the problem was? To his colleagues, his greatest problem was that he had no plausible mechanism for how the continents could move through the oceans. Based on his polar experiences, Wegener suggested that the continents were like icebreaking ships plowing through ice sheets. The continents moved by centrifugal and tidal forces. As Wegeners colleague, how would you go about showing whether these forces could move continents? What observations would you expect to see on these continents? Alfred Wegener suggested that continen- tal drift occurred as continents cut through the ocean floor, in the same way as this icebreaker plows through sea ice. Early hypotheses proposed that centrifu- gal forces moved continents. This is the same force that moves the swings out- ward on a spinning carnival ride. Scientists at the time calculated that centrifugal and tidal forces were too weak to move continents. When one scientist did calculations that assumed that these forces were strong enough to move continents, his result was that if Earth had such strong forces the planet would stop rotating in less than one year. In addition, scientists also thought that the continents that had been plowing through the ocean basins should be much more deformed than they are. Wegener answered his question of whether Africa and South America had once been joined. But a hypothesis is rarely accepted without a mechanism to drive it. Are you going to support Wegener? A very few scientists did, since his hypothesis elegantly explained the similar fossils and rocks on opposite sides of the ocean, but most did not. ",text,
L_0356,wegener and the continental drift hypothesis,T_1888,"Wegeners idea seemed so outlandish at the time that he was ridiculed by other scientists. What do you think the problem was? To his colleagues, his greatest problem was that he had no plausible mechanism for how the continents could move through the oceans. Based on his polar experiences, Wegener suggested that the continents were like icebreaking ships plowing through ice sheets. The continents moved by centrifugal and tidal forces. As Wegeners colleague, how would you go about showing whether these forces could move continents? What observations would you expect to see on these continents? Alfred Wegener suggested that continen- tal drift occurred as continents cut through the ocean floor, in the same way as this icebreaker plows through sea ice. Early hypotheses proposed that centrifu- gal forces moved continents. This is the same force that moves the swings out- ward on a spinning carnival ride. Scientists at the time calculated that centrifugal and tidal forces were too weak to move continents. When one scientist did calculations that assumed that these forces were strong enough to move continents, his result was that if Earth had such strong forces the planet would stop rotating in less than one year. In addition, scientists also thought that the continents that had been plowing through the ocean basins should be much more deformed than they are. Wegener answered his question of whether Africa and South America had once been joined. But a hypothesis is rarely accepted without a mechanism to drive it. Are you going to support Wegener? A very few scientists did, since his hypothesis elegantly explained the similar fossils and rocks on opposite sides of the ocean, but most did not. ",text,
L_0356,wegener and the continental drift hypothesis,T_1889,"Wegener had many thoughts regarding what could be the driving force behind continental drift. Another of We- geners colleagues, Arthur Holmes, elaborated on Wegeners idea that there is thermal convection in the mantle. In a convection cell, material deep beneath the surface is heated so that its density is lowered and it rises. Near the surface it becomes cooler and denser, so it sinks. Holmes thought this could be like a conveyor belt. Where two adjacent convection cells rise to the surface, a continent could break apart with pieces moving in opposite directions. Although this sounds like a great idea, there was no real evidence for it, either. Alfred Wegener died in 1930 on an expedition on the Greenland icecap. For the most part the continental drift idea was put to rest for a few decades, until technological advances presented even more evidence that the continents moved and gave scientists the tools to develop a mechanism for Wegeners drifting continents. Since youre on a virtual field trip, you get to go along with them as well. Click image to the left or use the URL below. URL: ",text,
L_0358,wind waves,T_1893,"Waves have been discussed in previous concepts in several contexts: seismic waves traveling through the planet, sound waves traveling through seawater, and ocean waves eroding beaches. Waves transfer energy, and the size of a wave and the distance it travels depends on the amount of energy that it carries. This concept studies the most familiar waves, those on the oceans surface. ",text,
L_0358,wind waves,T_1894,"Ocean waves originate from wind blowing - steady winds or high storm winds - over the water. Sometimes these winds are far from where the ocean waves are seen. What factors create the largest ocean waves? The largest wind waves form when the wind is very strong blows steadily for a long time blows over a long distance The wind could be strong, but if it gusts for just a short time, large waves wont form. Wind blowing across the water transfers energy to that water. The energy first creates tiny ripples, which make an uneven surface for the wind to catch so that it may create larger waves. These waves travel across the ocean out of the area where the wind is blowing. Remember that a wave is a transfer of energy. Do you think the same molecules of water that start out in a wave in the middle of the ocean later arrive at the shore? The molecules are not the same, but the energy is transferred across the ocean. ",text,
L_0358,wind waves,T_1895,"Water molecules in waves make circles or ellipses (Figure 1.1). Energy transfers between molecules, but the molecules themselves mostly bob up and down in place. The circles show the motion of a water molecule in a wind wave. Wave energy is greatest at the surface and decreases with depth. ""A"" shows that a water molecule travels in a circular motion in deep water. ""B"" shows that molecules in shallow water travel in an elliptical path because of the ocean bottom. ",text,
L_0358,wind waves,T_1896,"When does a wave break? Do waves only break when they reach shore? Waves break when they become too tall to be supported by their base. This can happen at sea but happens predictably as a wave moves up a shore. The energy at the bottom of the wave is lost by friction with the ground, so that the bottom of the wave slows down but the top of the wave continues at the same speed. The crest falls over and crashes down. ",text,
L_0358,wind waves,T_1897,"Some of the damage done by storms is from storm surge. Water piles up at a shoreline as storm winds push waves into the coast. Storm surge may raise sea level as much as 7.5 m (25 ft), which can be devastating in a shallow land area when winds, waves, and rain are intense. Maverick waves are massive. Learning how they are generated can tell scientists a great deal about how the ocean creates waves and especially large waves. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0362,the microscope,T_1911,"Many life science discoveries would not have been possible without the microscope. For example: Cells are the tiny building blocks of living things. They couldnt be discovered until the microscope was invented. The discovery of cells led to the cell theory. This is one of the most important theories in life science. Bacteria are among the most numerous living things on the planet. They also cause many diseases. However, no one knew bacteria even existed until they could be seen with a microscope. The invention of the microscope allowed scientists to see cells, bacteria, and many other structures that are too small to be seen with the unaided eye. It gave them a direct view into the unseen world of the extremely tiny. You can get a glimpse of that world in Figure 1.10. ",text,
L_0362,the microscope,T_1912,"The microscope was invented more than four centuries ago. In the late 1500s, two Dutch eyeglass makers, Zacharias Jansen and his father Hans, built the first microscope. They put several magnifying lenses in a tube. They discovered that using more than one lens magnified objects more than a single lens. Their simple microscope could make small objects appear nine times bigger than they really were. ",text,
L_0362,the microscope,T_1913,"In the mid-1600s, the English scientist Robert Hooke was one of the first scientists to observe living things with a microscope. He published the first book of microscopic studies, called Micrographia. It includes wonderful drawings of microscopic organisms and other objects. One of Hookes most important discoveries came when he viewed thin slices of cork under a microscope. Cork is made from the bark of a tree. When Hooke viewed it under a microscope, he saw many tiny compartments that he called cells. He made the drawing in Figure 1.11 to show what he observed. Hooke was the first person to observe the cells from a once-living organism. ",text,
L_0362,the microscope,T_1914,"In the late 1600s, Anton van Leeuwenhoek, a Dutch lens maker and scientist, started making much stronger microscopes. His microscopes could magnify objects as much as 270 times their actual size. Van Leeuwenhoek made many scientific discoveries using his microscopes. He was the first to see and describe bacteria. He observed them in a sample of plaque that he had scraped off his own teeth. He also saw yeast cells, human sperm cells, and the microscopic life teeming in a drop of pond water. He even saw blood cells circulating in tiny blood vessels called capillaries. The drawings in Figure 1.12 show some of tiny organisms and living cells that van Leeuwenhoek viewed with his microscopes. He called them animalcules. ",text,
L_0362,the microscope,T_1915,"These early microscopes used lenses to refract light and create magnified images. This type of microscope is called a light microscope. Light microscopes continued to improve and are still used today. The microscope you might use in science class is a light microscope. The most powerful light microscopes now available can make objects look up to 2000 times their actual size. You can learn how to use a light microscope by watching this short video: http MEDIA Click image to the left or use the URL below. URL:  To see what you might observe with a light microscope, watch the following video. It shows some amazing creatures in a drop of stagnant water from an old boat. What do you think the creatures might be? Do they look like any of van Leeuwenhoeks animalcules in Figure 1.12? MEDIA Click image to the left or use the URL below. URL:  For an object to be visible with a light microscope, it cant be smaller than the wavelength of visible light (about 550 nanometers). To view smaller objects, a different type of microscope, such as an electron microscope, must be used. Electron microscopes pass beams of electrons through or across an object. They can make a very clear image that is up to 2 million times bigger than the actual object. An electron microscope was used to make the image of the ant head in Figure 1.10. ",text,
L_0370,flatworms and roundworms,T_1993,"Flatworms are invertebrates that belong to Phylum Platyhelminthes. There are more than 25,000 species in the flatworm phylum. Not all flatworms are as long as tapeworms. Some are only about a millimeter in length. ",text,
L_0370,flatworms and roundworms,T_1994,"Flatworms have a flat body because they lack a fluid-filled body cavity. They also have an incomplete digestive system with a single opening. However, flatworms represent several evolutionary advances in invertebrates. They have the following adaptations: Flatworms have three embryonic cell layers. They have a mesoderm layer in addition to ectoderm and endoderm layers. The mesoderm layer allows flatworms to develop muscle tissues so they can move easily over solid surfaces. Flatworms have a concentration of nerve tissue in the head end. This was a major step in the evolution of a brain. It was also needed for bilateral symmetry. Flatworms have bilateral symmetry. This gives them a better sense of direction than radial symmetry would. Watch this amazing flatworm video to learn about some of the other firsts these simple animals achieved, including being the first hunters: http://shapeoflife.org/video/flatworms-first-hunter MEDIA Click image to the left or use the URL below. URL: ",text,
L_0370,flatworms and roundworms,T_1995,"Flatworms reproduce sexually. In most species, the same individuals produce both eggs and sperm. After fertilization occurs, the fertilized eggs pass out of the adults body and hatch into larvae. There may be several different larval stages. The final larval stage develops into the adult form. Then the life cycle repeats. ",text,
L_0370,flatworms and roundworms,T_1996,"Some flatworms live in water or moist soil. They eat invertebrates and decaying animals. Other flatworms, such as tapeworms, are parasites that live inside vertebrate hosts. Usually, more than one type of host is needed to complete the parasites life cycle, as shown in Figure 12.12. ",text,
L_0370,flatworms and roundworms,T_1997,"Roundworms are invertebrates in Phylum Nematoda. This is a very diverse phylum. It has more than 80,000 known species. Roundworms range in length from less than 1 millimeter to over 7 meters in length. You can see an example of a roundworm in Figure 12.13. ",text,
L_0370,flatworms and roundworms,T_1997,"Roundworms are invertebrates in Phylum Nematoda. This is a very diverse phylum. It has more than 80,000 known species. Roundworms range in length from less than 1 millimeter to over 7 meters in length. You can see an example of a roundworm in Figure 12.13. ",text,
L_0370,flatworms and roundworms,T_1998,"Roundworms have a round body because they have a partial fluid-filled body cavity (pseudocoelom). This is one way that roundworms differ from flatworms. Another way is their complete digestive system. It allows them to eat, digest food, and eliminate wastes all at the same time. Roundworms have a tough covering of cuticle on the surface of their body. It prevents their body from expanding. This allows the buildup of fluid pressure in their partial body cavity. The fluid pressure adds stiffness to the body. This provides a counterforce for the contraction of muscles, allowing roundworms to move easily over surfaces. ",text,
L_0370,flatworms and roundworms,T_1999,"Roundworms reproduce sexually. Sperm and eggs are produced by separate male and female adults. Fertilization takes place inside the female organism. Females lay huge numbers of eggs, sometimes as many as 100,000 per day! The eggs hatch into larvae, which develop into adults. Then the life cycle repeats. ",text,
L_0370,flatworms and roundworms,T_2000,"Roundworms may be free-living or parasitic organisms. Free-living worms are found mainly in freshwater habitats. Some live in moist soil. They generally feed on bacteria, fungi, protozoa, or decaying organic matter. By breaking down organic matter, they play an important role in the carbon cycle. Parasitic roundworms may have plant, invertebrate, or vertebrate hosts. Several roundworm species infect humans. Besides ascaris, they include hookworms. Hookworms are named for the hooks they use to grab onto the hosts intestines. You can see the hooks in Figure 12.14. Hookworm larvae enter the host through the skin. They migrate to the intestine, where they mature into adults. Female adults lay large quantities of eggs. Eggs pass out of the host in feces. Eggs hatch into larvae in the feces or soil. Then the cycle repeats. You can learn more about parasitic roundworms in humans by watching this short video:  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0371,mollusks and annelids,T_2001,"Have you ever been to the ocean or eaten seafood? If you have, then youve probably encountered members of Phylum Mollusca. In addition to snails, mollusks include squids, slugs, scallops, and clams. You can see a clam in Figure 12.15. There are more than 100,000 known species of mollusks. Some mollusks are nearly microscopic. The largest mollusk, the colossal squid, may be as long as a school bus and weigh over half a ton! Watch this short video to see an amazing diversity of mollusks:  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0371,mollusks and annelids,T_2002,"Mollusks have a true coelom and complete digestive system. They also have circulatory and excretory systems. They have a heart that pumps blood, and organs that filter out wastes from the blood. You can see some other traits of mollusks in the garden snail in Figure 12.16. Like the snail, many other mollusks have a hard outer shell. It is secreted by special tissue called mantle on the outer surface of the body. The shell covers the top of the body and encloses the internal organs. Most mollusks have a distinct head region. The head may have tentacles for sensing the environment and grasping food. Mollusks generally have a muscular foot, which may be used for walking or other purposes. A unique feature of mollusks is the radula. This is a feeding organ with teeth made of chitin. It is located in front of the mouth in the head region. It can be used to scrape algae off rocks or drill holes in the shells of prey. You can see the radula of the sea slug in Figure 12.17. ",text,
L_0371,mollusks and annelids,T_2002,"Mollusks have a true coelom and complete digestive system. They also have circulatory and excretory systems. They have a heart that pumps blood, and organs that filter out wastes from the blood. You can see some other traits of mollusks in the garden snail in Figure 12.16. Like the snail, many other mollusks have a hard outer shell. It is secreted by special tissue called mantle on the outer surface of the body. The shell covers the top of the body and encloses the internal organs. Most mollusks have a distinct head region. The head may have tentacles for sensing the environment and grasping food. Mollusks generally have a muscular foot, which may be used for walking or other purposes. A unique feature of mollusks is the radula. This is a feeding organ with teeth made of chitin. It is located in front of the mouth in the head region. It can be used to scrape algae off rocks or drill holes in the shells of prey. You can see the radula of the sea slug in Figure 12.17. ",text,
L_0371,mollusks and annelids,T_2002,"Mollusks have a true coelom and complete digestive system. They also have circulatory and excretory systems. They have a heart that pumps blood, and organs that filter out wastes from the blood. You can see some other traits of mollusks in the garden snail in Figure 12.16. Like the snail, many other mollusks have a hard outer shell. It is secreted by special tissue called mantle on the outer surface of the body. The shell covers the top of the body and encloses the internal organs. Most mollusks have a distinct head region. The head may have tentacles for sensing the environment and grasping food. Mollusks generally have a muscular foot, which may be used for walking or other purposes. A unique feature of mollusks is the radula. This is a feeding organ with teeth made of chitin. It is located in front of the mouth in the head region. It can be used to scrape algae off rocks or drill holes in the shells of prey. You can see the radula of the sea slug in Figure 12.17. ",text,
L_0371,mollusks and annelids,T_2003,"Mollusks reproduce sexually. Most species have separate male and female sexes. Fertilization may be internal or external, depending on the species. Fertilized eggs develop into larvae. There may be one or more larval stages. Each one is different from the adult stage. ",text,
L_0371,mollusks and annelids,T_2004,"Mollusks live in most terrestrial, freshwater, and marine habitats. However, the majority of species live in the ocean. They can be found in both shallow and deep water and from tropical to polar latitudes. They have a variety of ways of getting food. Some are free-living heterotrophs. Others are internal parasites. Mollusks are also eaten by many other organisms, including humans. ",text,
L_0371,mollusks and annelids,T_2005,"Annelids are segmented worms in Phylum Annelida. There are about 15,000 species of annelids. They range in length from less than a millimeter to more than 3 meters. To learn more about the amazing diversity and adaptations of annelids, watch this excellent video: http://shapeoflife.org/video/annelids-powerful-and-capable-worms MEDIA Click image to the left or use the URL below. URL: ",text,
L_0371,mollusks and annelids,T_2006,"Annelids are divided into many repeating segments. The earthworm in Figure 12.18 is an annelid. You can clearly see its many segments. Segmentation of annelids is highly adaptive. Each segment has its own nerve and muscle tissues. This allows the animal to move very efficiently. Some segments can also be specialized to carry out particular functions. They may have special structures on them. For example, they might have tentacles for sensing or feeding, paddles for swimming, or suckers for clinging to surfaces. ",text,
L_0371,mollusks and annelids,T_2007,"Annelids have a large coelom. They also have several organ systems. These include a: circulatory system; excretory system; complete digestive system; and nervous system, with a brain and sensory organs. ",text,
L_0371,mollusks and annelids,T_2008,Most annelids can reproduce both asexually and sexually. Asexual reproduction may occur by budding or fission. Sexual reproduction varies by species. Some species go through a larval stage before developing into adults. Other species grow to adult size without going through a larval stage. ,text,
L_0371,mollusks and annelids,T_2009,"Annelids live in a diversity of freshwater, salt-water, and terrestrial habitats. They vary in what they eat and how they get their food. Some annelids, such as earthworms, eat soil and extract organic material from it. Annelids called leeches are either predators or parasites. Some leeches capture and eat other invertebrates. Others feed off the blood of vertebrate hosts. Annelids called polychaete worms live on the ocean floor. They may be filter feeders, predators, or scavengers. The amazing feather duster worm in Figure 12.19 is a polychaete that has a fan-like crown of tentacles for filter feeding. ",text,
L_0374,introduction to vertebrates,T_2028,"Like all chordates, vertebrates are animals with four defining traits, at least during the embryonic stage. The four traits are: a notochord; a dorsal hollow nerve cord; a post-anal tail; and pharyngeal slits. Some invertebrates also have these traits and are classified as chordates. What traits do vertebrates have that set them apart from invertebrate chordates? ",text,
L_0374,introduction to vertebrates,T_2029,"The main trait that sets vertebrates apart from invertebrate chordates is their vertebral column, or backbone. It develops from the notochord after the embryonic stage. As you can see in Figure 13.2 the vertebral column runs from head to tail along the dorsal (top) side of the body. The vertebral column is made up of repeating units of bone called vertebrae (vertebra, singular). The vertebral column helps the vertebrate body hold its shape. It also protects the spinal (nerve) cord that runs through it. ",text,
L_0374,introduction to vertebrates,T_2030,"The vertebral column is the core of the vertebrate endoskeleton, or internal skeleton. You can see a human skeleton as an example of the vertebrate endoskeleton in Figure 13.3. In addition to the vertebral column, the vertebrate endoskeleton includes: a cranium, or bony skull, that encloses and protects the brain; two pairs of limbs (in humans, arms and legs); limb girdles that connect the limbs to the rest of the endoskeleton (in humans, shoulders and hips). ",text,
L_0374,introduction to vertebrates,T_2031,"The vertebrate endoskeleton is made of bone and cartilage. Cartilage is a tough, flexible tissue that contains a protein called collagen. Bone is a hard tissue consisting of a collagen framework that is filled in with minerals such as calcium. Bone is less flexible than cartilage but stronger. A bony endoskeleton allows an animal to grow larger and heavier than a cartilage endoskeleton would. Bone also provides more protection for soft tissues and internal organs. ",text,
L_0374,introduction to vertebrates,T_2032,"Most vertebrates share several other traits. The majority of vertebrates have: scales, feathers, fur, or hair covering their skin; muscles attached to the endoskeleton to allow movement; a circulatory system with a heart that pumps blood through a closed network of blood vessels; an excretory system that includes a pair of kidneys for filtering wastes out of the blood; a central nervous system with a brain, spinal cord, and nerve fibers throughout the body; an adaptive immune system that learns to recognize specific pathogens and launch tailor-made attacks against them; and an endocrine system with glands that secrete chemical messenger molecules called hormones. ",text,
L_0374,introduction to vertebrates,T_2033,"Vertebrates reproduce sexually. Most have separate male and female sexes. Vertebrates have one of three reproduc- tive strategies: ovipary, ovovivipary, or vivipary. Ovipary refers to the development of an embryo within an egg outside the mothers body. This occurs in most fish, amphibians, and reptiles. It also occurs in all birds. Ovovivipary refers to the development of an embryo inside an egg within the mothers body. The egg remains inside the mothers body until it hatches, but the mother provides no nourishment to the developing embryo inside the egg. This occurs in some species of fish and reptiles. Vivipary refers to the development and nourishment of an embryo within the mothers body but not inside an egg. Birth may be followed by a period of parental care of the offspring. This reproductive strategy occurs in almost all mammals including humans. ",text,
L_0374,introduction to vertebrates,T_2034,"There are about 50,000 living species of vertebrates. They are placed in nine different classes. Table 13.1 lists these vertebrate classes and some of their traits. Five of the classes are fish. The other four classes are amphibians, reptiles, birds, and mammals. Class Hagfish Distinguishing Traits They have a cranium but no back- bone; they do not have jaws; their endoskeleton is made of cartilage; they are ectothermic. Example hagfish Class Lampreys Distinguishing Traits They have a partial backbone; they do not have jaws; their endoskele- ton is made of cartilage; they are ectothermic. Example lamprey Cartilaginous Fish They have a complete backbone; they have jaws; their endoskeleton is made of cartilage; they are ec- tothermic. shark Ray-Finned Fish They have a backbone and jaws; their endoskeleton is made of bones; they have thin, bony fins; they are ectothermic. perch Lobe-Finned Fish They have a backbone and jaws; their endoskeleton is made of bones; they have thick, fleshy fins; they are ectothermic. coelacanth Amphibians They have a bony endoskeleton with a backbone and jaws; they have gills as larvae and lungs as adults; they have four limbs; they are ectothermic frog Reptiles They have a bony endoskeleton with a backbone and jaws; they breathe only with lungs; they have four limbs; their skin is covered with scales; they have amniotic eggs; they are ectothermic. alligator Class Birds Distinguishing Traits They have a bony endoskeleton with a backbone but no jaws; they breathe only with lungs; they have four limbs, with the two front limbs modified as wings; their skin is cov- ered with feathers; they have amni- otic eggs; they are endothermic. Example bird Mammals They have a bony endoskeleton with a backbone and jaws; they breathe only with lungs; they have four limbs; their skin is covered with hair or fur; they have am- niotic eggs; they have mammary (milk-producing) glands; they are endothermic. bear ",text,
L_0374,introduction to vertebrates,T_2035,The earliest vertebrates were jawless fish. They evolved about 550 million years ago. They were probably similar to modern hagfish (see Table 13.1). The tree diagram in Figure 13.4 summarizes how vertebrates evolved from that time forward. ,text,
L_0374,introduction to vertebrates,T_2036,"The earliest fish had an endoskeleton made of cartilage rather than bone. They also lacked a complete vertebral column. The first fish with a complete vertebral column evolved about 450 million years ago. These fish had jaws. They may have been similar to living sharks. About 400 million years ago, the first fish with a bony endoskeleton evolved. A bony skeleton could support a bigger body. Early bony fish evolved into modern ray-finned fish and lobe-finned fish. ",text,
L_0374,introduction to vertebrates,T_2037,"The earliest amphibians evolved from a lobe-finned fish ancestor. This occurred about 365 million years ago. Amphibians were the first terrestrial vertebrates. They lived on land as adults, but they had to return to the water to reproduce. The earliest reptiles evolved from an amphibian ancestor. This occurred at least 300 million years ago. Reptiles were the first vertebrates that did not need water to reproduce. Thats because they laid waterproof amniotic eggs. These eggs allowed the embryo inside to breathe without drying out. Mammals and birds both evolved from reptile-like ancestors. The first mammals appeared about 200 million years ago. The earliest birds evolved about 150 million years ago. ",text,
L_0374,introduction to vertebrates,T_2038,"Early vertebrates were ectothermic. Ectothermy means controlling body temperature to just a limited extent from the outside by changing behavior. For example, an ectotherm might stay in the shade to keep cool on a hot, sunny day. On a cold day, an ectotherm might bask in the sun to warm up, like the snake in Figure 13.5. Almost all living fish, amphibians, and reptiles are ectothermic. They can raise or lower their body temperature by their behavior but not by very much. In cold weather, an ectotherm cools down. As its body temperature drops, its metabolism slows down and it becomes inactive. Both mammals and birds evolved endothermy. Endothermy means controlling body temperature within a narrow range from the inside through biochemical or physical means. For example, on a cold day, an endotherm may produce more body heat by increasing its rate of metabolism. On a hot day, it may give off more heat by increasing blood flow to the surface of the body. That way, some of the heat can radiate into the air from the bodys surface. Endothermy requires more energy (and food) than ectothermy. However, it allows the animal to stay active regardless of the temperature outside. You can learn more about how vertebrates regulate their temperature by watching this video:  . ",text,
L_0375,fish,T_2039,Fish are aquatic vertebrates. They make up more than half of all living vertebrate species. Most fish are ectothermic. They share several adaptations that suit them for life in the water. ,text,
L_0375,fish,T_2040,"You can see some of the aquatic adaptations of fish in Figure 13.7. For a video introduction to aquatic adaptations of fish, go to this link:  . MEDIA Click image to the left or use the URL below. URL:  Fish are covered with scales. Scales are overlapping tissues, like shingles on a roof. They reduce friction with the water. They also provide a flexible covering that lets fish move their body to swim. Fish have gills. Gills are organs behind the head that absorb oxygen from water. Water enters through the mouth, passes over the gills, and then exits the body. Fish typically have a stream-lined body. This reduces water resistance. Most fish have fins. Fins function like paddles or rudders. They help fish swim and navigate in the water. Most fish have a swim bladder. This is a balloon-like organ containing gas. By inflating or deflating their swim bladder, fish can rise or sink in the water. ",text,
L_0375,fish,T_2041,"Fish have a circulatory system with a heart. They also have a complete digestive system. It includes several organs and other structures. Fish with jaws use their jaws and teeth to chew food before swallowing it. This allows them to eat larger prey animals. Fish have a nervous system with a brain. Fish brains are small compared with the brains of other vertebrates. However, they are large and complex compared with the brains of invertebrates. Fish also have highly developed sense organs. They include organs to see, hear, feel, smell, and taste. ",text,
L_0375,fish,T_2042,"Almost all fish have sexual reproduction, generally with separate sexes. Each fish typically produces large numbers of sperm or eggs. Fertilization takes place in the water outside the body in the majority of fish. Most fish are oviparous. The embryo develops in an egg outside the mothers body. ",text,
L_0375,fish,T_2043,"Many species of fish reproduce by spawning. Spawning occurs when many adult fish group together and release their sperm or eggs into the water at the same time. You can see fish spawning in Figure 13.8. Spawning increases the changes that fertilization will take place. It typically results in a large number of embryos forming at once. This makes it more likely that at least some of the embryos will avoid being eaten by predators. You can watch trout spawning in Yellowstone Park in this interesting video: http://video.nationalgeographic.com/video/trout_spawning MEDIA Click image to the left or use the URL below. URL:  With spawning, fish parents cant identify their own offspring. Therefore, in most species, there is no parental care of offspring. However, there are exceptions. Some species of fish carry their fertilized eggs in their mouth until they ",text,
L_0375,fish,T_2044,Fish eggs hatch into larvae. Each larva swims around attached to a yolk sac from the egg (see Figure 13.9). The yolk sac provides it with food. Fish larvae look different from adult fish of the same species. They must go through metamorphosis to change into the adult form. ,text,
L_0375,fish,T_2045,"There are about 28,000 living species of fish. They are placed in five different classes. The classes are commonly called hagfish, lampreys, cartilaginous fish, ray-finned fish, and lobe-finned fish. Table 13.2 shows pictures of fish in each class. It also provides additional information about the classes. Class Hagfish Lampreys Cartilaginous Fish Distinguishing Traits Hagfish are very primitive fish. They lack scales and fins. They even lack a backbone, but they do have a cranium. They secrete large amounts of thick, slimy mucus. This makes them slippery, so they can slip out of the jaws of predators. Lampreys lack scales but have fins and a partial backbone. Their mouth is surrounded by a large round sucker with teeth. They use the sucker to suck the blood of other fish. Example hagfish Cartilaginous fish include sharks, rays, and ratfish. Their endoskele- ton is made of cartilage instead of bone. They also lack a swim blad- der. However, they have a complete vertebral column and jaws. They also have a relatively big brain. shark lampreys Class Ray-Finned Fish Lobe-Finned Fish Distinguishing Traits Ray-finned fish make up the ma- jority of living fish species. They are a type of bony fish, with an en- doskeleton made of bone instead of cartilage. Their fins consist of webs of skin over flexible bony spines, called rays. They have a swim blad- der. Lobe-finned fish include only coelacanths and lungfish. They are bony fish with an endoskeleton made of bone. Their fleshy fins contain bone and muscle. Lungfish are named for a lung-like organ that they can use for breathing air. It evolved from the swim bladder. It allows them to survive for long periods of time out of water. Example puffer lungfish ",text,
L_0375,fish,T_2046,"Fish vary in the types of places they live and what they eat. Many fish live in the salt water of the ocean. Other fish live in freshwater lakes, ponds, rivers, or streams. Most fish are predators, but they may differ in their prey and how they get it. Hagfish are deep-ocean bottom dwellers. They feed on other fish, either living or dead. They enter the body of their prey through the mouth or anus. Then they literally eat their prey from the inside out. Lampreys generally live in shallow water, either salty or fresh. They eat small invertebrates or suck the blood of larger fish. Cartilaginous fish, such as sharks, mainly live in the ocean. They prey on other fish and aquatic mammals, or else they eat plankton. Their jaws and teeth allow them to eat large prey. Bony fish, such as ray-finned or lobe-finned fish, may live in salt water or fresh water. They may eat algae, smaller fish like the butterfly fish in Figure 13.10, or dead organisms. To see how one species of predatory bony fish catches its prey, watch this amazing video: http://video.nationalgeographic.com/video/stonefish- MEDIA Click image to the left or use the URL below. URL: ",text,
L_0383,introduction to the human body,T_2121,"The basic building blocks of the human body are cells. Human cells are organized into tissues, tissues are organized into organs, and organs are organized into organ systems. ",text,
L_0383,introduction to the human body,T_2122,"The average human adult consists of an incredible 100 trillion cells! Cells are the basic units of structure and function in the human body, as they are in all living things. Each cell must carry out basic life processes in order to survive and help keep the body alive. Most human cells also have characteristics for carrying out other, special functions. For example, muscle cells have extra mitochondria to provide the energy needed to move the body. You can see examples of these and some other specialized human cells in Figure 16.1. To learn more about specialized human cells and what they do, watch this video:  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0383,introduction to the human body,T_2123,"Specialized cells are organized into tissues. A tissue is a group of specialized cells of the same kind that perform the same function. There are four basic types of human tissues: connective, epithelial, muscle, and nervous tissues. The four types are shown in Figure 16.2. Connective tissue consists of cells that form the bodys structure. Examples include bone and cartilage, which protect and support the body. Blood is also a connective tissue. It circulates and connects cells throughout the body. Epithelial tissue consists of cells that cover inner and outer body surfaces. Examples include skin and the linings of internal organs. Epithelial tissue protects the body and its internal organs. It also secretes substances such as hormones and absorbs substances such as nutrients. Muscle tissue consists of cells that can contract, or shorten. Examples include skeletal muscle, which is attached to bones and makes them move. Other types of muscle include cardiac muscle, which makes the heart beat, and smooth muscle, which is found in other internal organs. Nervous tissue consists of nerve cells, or neurons, which can send and receive electrical messages. Nervous tissue makes up the brain, spinal cord, and other nerves that run throughout the body. ",text,
L_0383,introduction to the human body,T_2124,"The four types of tissues make up all the organs of the human body. An organ is a structure composed of two or more types of tissues that work together to perform the same function. Examples of human organs include the skin, brain, lungs, kidneys, and heart. Consider the heart as an example. Figure 16.3 shows how all four tissue types work together to make the heart pump blood. ",text,
L_0383,introduction to the human body,T_2124,"The four types of tissues make up all the organs of the human body. An organ is a structure composed of two or more types of tissues that work together to perform the same function. Examples of human organs include the skin, brain, lungs, kidneys, and heart. Consider the heart as an example. Figure 16.3 shows how all four tissue types work together to make the heart pump blood. ",text,
L_0383,introduction to the human body,T_2125,"Human organs are organized into organ systems. An organ system is a group of organs that work together to carry out a complex function. Each organ of the system does part of the overall job. For example, the heart is an organ in the circulatory system. The circulatory system also includes the blood vessels and blood. There are many different human organ systems. Figure 16.4 shows six of them and gives their functions. ",text,
L_0383,introduction to the human body,T_2126,"The organ systems of the body work together to carry out life processes and maintain homeostasis. The body is in homeostasis when its internal environment is kept more-or-less constant. For example, levels of sugar, carbon dioxide, and water in the blood must be kept within narrow ranges. This requires continuous adjustments. For example: After you eat and digest a sugary snack, the level of sugar in your blood quickly rises. In response, the endocrine system secretes the hormone insulin. Insulin helps cells absorb sugar from the blood. This causes the level of sugar in the blood to fall back to its normal level. When you work out on a hot day, you lose a lot of water through your skin in sweat. The level of water in the blood may fall too low. In response, the excretory system excretes less water in urine. Instead, the water is returned to the blood to keep water levels from falling lower. What happens if homeostasis is not maintained? Cells may not get everything they need, or toxic wastes may build up in the body. If homeostasis is not restored, it may cause illness or even death. ",text,
L_0384,the integumentary system,T_2127,"From the outside, the skin looks plain and simple, as you can see in Figure 16.5. But at a cellular level, theres nothing plain or simple about it. A single square inch of skin contains about 20 blood vessels, hundreds of sweat glands, and more than a thousand nerve endings. It also contains tens of thousands of pigment-producing cells. Clearly, there is much more to skin than meets the eye! For a dramatic introduction to the skin, watch this video: MEDIA Click image to the left or use the URL below. URL:  The skin is only about 2 mm thick, or about as thick as the cover of a book. Although it is very thin, it consists of two distinct layers, called the epidermis and the dermis. You can see both layers and some of their structures in Figure 16.6. Refer to the figure as you read about the epidermis and dermis below. ",text,
L_0384,the integumentary system,T_2127,"From the outside, the skin looks plain and simple, as you can see in Figure 16.5. But at a cellular level, theres nothing plain or simple about it. A single square inch of skin contains about 20 blood vessels, hundreds of sweat glands, and more than a thousand nerve endings. It also contains tens of thousands of pigment-producing cells. Clearly, there is much more to skin than meets the eye! For a dramatic introduction to the skin, watch this video: MEDIA Click image to the left or use the URL below. URL:  The skin is only about 2 mm thick, or about as thick as the cover of a book. Although it is very thin, it consists of two distinct layers, called the epidermis and the dermis. You can see both layers and some of their structures in Figure 16.6. Refer to the figure as you read about the epidermis and dermis below. ",text,
L_0384,the integumentary system,T_2128,"The epidermis is the outer layer of skin. It consists almost entirely of epithelial cells. There are no blood vessels, nerve endings, or glands in this skin layer. Nonetheless, this layer of skin is very active. It is constantly being renewed. How does this happen? 1. The cells at the bottom of the epidermis are always dividing by mitosis to form new cells. 2. The new cells gradually move up through the epidermis toward the surface of the body. As they move, they produce the tough, fibrous protein called keratin. 3. By the time the cells reach the surface, they have filled with keratin and died. On the surface, the dead cells form a protective, waterproof layer. 4. Dead cells are gradually shed from the surface of the epidermis. As they are shed, they are replaced by other dead cells that move up from below. The epidermis also contains cells called melanocytes. You can see a melanocyte in Figure 16.7. Melanocytes produce melanin. Melanin is a brown pigment that gives skin much of its color. Everyones skin has about the same number of melanocytes per square inch. However, the melanocytes of people with darker skin produce more melanin. The amount of melanin that is produced depends partly on your genes and partly on how much ultraviolet light strikes your skin. The more light you get, the more melanin your melanocytes produce. This explains why skin tans when its exposed to sunlight. ",text,
L_0384,the integumentary system,T_2129,"The dermis is the inner layer of skin. It is made of tough connective tissue. The dermis is attached to the epidermis by fibers made of the protein collagen. The dermis is where most skin structures are located. Look again at Figure pain, pressure, and temperature. If you cut your skin and it bleeds, the cut has penetrated the dermis and damaged a blood vessel. The cut probably hurts as well because of the nerve endings in this skin layer. The dermis also contains hair follicles and two types of glands. You can see some of these structures in Figure 16.8. Hair follicles are structures where hairs originate. Each hair grows out of a follicle, passes up through the epidermis, and extends above the skin surface. Sebaceous glands are commonly called oil glands. They produce an oily substance called sebum. Sebum is secreted into hair follicles. Then it makes its way along the hair shaft to the surface of the skin. Sebum waterproofs the hair and skin and helps prevent them from drying out. Sweat glands produce the salty fluid known as sweat. Sweat contains excess water, salts, and other waste products. Each sweat gland has a duct that passes through the epidermis. Sweat travels from the gland through the duct and out through a pore on the surface of the skin. ",text,
L_0384,the integumentary system,T_2130,"You couldnt survive without your skin. It has many important functions. In several ways, it helps maintain homeostasis. The main function of the skin is controlling what enters and leaves the body. It prevents the loss of too much water from the body. It also prevents bacteria and other microorganisms from entering the body. Melanin in the epidermis absorbs ultraviolet light. This prevents the light from reaching and damaging the dermis. The skin helps maintain a constant body temperature. It keeps the body cool in two ways. Sweat from sweat glands in the skin evaporates to cool the body. Blood vessels in the skin dilate, or widen, increasing blood flow to the body surface. This allows more heat to reach the surface and radiate into the environment. The opposite happens to retain body heat. Blood vessels in the skin constrict, or narrow, decreasing blood flow to the body surface. This reduces the amount of heat that reaches the surface so less heat is lost to the environment. ",text,
L_0384,the integumentary system,T_2131,"What can you do to keep your skin healthy? The most important step you can take is to protect your skin from sun exposure. On sunny days, wear long sleeves and pants and a hat with a brim. Also apply sunscreen to exposed areas of skin. Protecting your skin in these ways will reduce damage to your skin by ultraviolet light. This is important because skin that has been damaged by ultraviolet light is at greater risk of developing skin cancer. This is true whether the damage is due to sunlight or the light in tanning beds. About 85 percent of teens develop acne, like the boy in Figure 16.9. Acne is a condition in which pimples form on the skin. It is caused by a bacterial infection. It happens when the sebaceous glands secrete too much sebum. The excess oil provides a good place for bacteria to grow. Keeping the skin clean helps prevent acne. Over-the-counter products or prescription drugs may be needed if the problem is serious or doesnt clear up on its own. ",text,
L_0384,the integumentary system,T_2132,"You may spend a lot of time and money on your hair and nails. You may think of them as accessories, like clothes or jewelry. However, like the skin, the hair and nails also play important roles in helping the body maintain homeostasis. ",text,
L_0384,the integumentary system,T_2133,"Only mammals have hair. Hair is a fiber made mainly of the tough protein keratin. The cells of each hair are filled with keratin and no longer alive. The dead cells overlap each other, almost like shingles on a roof. They work like shingles as well, by helping shed water from hair. Head hair helps protect the scalp from sun exposure. It also helps insulate the body. It traps air so heat cant escape from the head. Hair in eyelashes and eyebrows helps keep water and dust out of the eyes. Hairs inside the nostrils of the nose trap dust and germs in the air so they cant reach the lungs. ",text,
L_0384,the integumentary system,T_2134,Fingernails and toenails are made of specialized cells that grow out of the epidermis. They too are filled with keratin. The keratin makes them tough and hard. Their job is to protect the ends of the fingers and toes. They also make it easier to feel things with the sensitive fingertips by acting as a counterforce when things are handled. ,text,
L_0385,the skeletal system,T_2135,"Bones are the main organs of the skeletal system. In adults, the skeleton consists of a whopping 206 bones, many of them in the hands and feet. You can see many of the bones of the human skeleton in Figure 16.10. The skeletal system also includes cartilage and ligaments. Cartilage is a tough, flexible connective tissue that contains the protein collagen. It covers the ends of bones where they meet. The gray tissue in Figure 16.10 is cartilage. A ligament is a band of fibrous connective tissue. Ligaments connect bones of the skeleton and hold them together. ",text,
L_0385,the skeletal system,T_2136,"Your skeletal system supports your body and gives it shape. What else does it do? The skeletal system makes blood cells. Most blood cells are produced inside certain types of bones. The skeletal system stores calcium and helps maintain normal levels of calcium in the blood. Bones take up and store calcium when blood levels of calcium are high. They release some of the stored calcium when blood levels of calcium are low. The skeletal system works with muscles to move the body. Try to walk without bending your knees and youll see how important the skeletal system is for movement. The skeletal system protects the soft organs of the body. For example, the skull surrounds and protects the brain. The ribs protect the heart and lungs. ",text,
L_0385,the skeletal system,T_2137,"Some people think bones are like chalk: dead, dry, and brittle. In reality, bones are very much alive. They consist of living tissues and are supplied with blood and nerves. ",text,
L_0385,the skeletal system,T_2138,"Bones are organs. Like other organs, they are made up of more than one kind of tissue. There are four different kinds of tissues in bones, as shown in Figure 16.11. From the outside of the bone to the center, the tissues are periosteum, compact bone, spongy bone, and bone marrow. Periosteum is a tough, fibrous membrane that covers and protects the outer surfaces of bone. Compact bone lies below periosteum. It is very dense and hard. Compact bone gives bones their strength. Spongy bone lies below compact bone. It is less dense than compact bone. Spongy bone contains many tiny holes, or pores, which provide spaces for blood vessels and bone marrow. Bone marrow is a soft connective tissue inside pores and cavities in spongy bone. Bone marrow makes blood cells. ",text,
L_0385,the skeletal system,T_2139,"Early in the development of a human fetus, the skeleton is made entirely of cartilage. The relatively soft cartilage gradually changes to hard bone through ossification. This is a process in which mineral deposits replace cartilage in bone. At birth, several areas of cartilage remain, including the ends of the long bones in the arms and legs. This allows these bones to keep growing in length during childhood. By the late teens or early twenties, all of the cartilage has been replaced by bone. Bones cannot grow in length after this point has been reached. However, bones can continue to grow in width. They are stimulated to grow thicker when they are put under stress by muscles. Weight-bearing activities such as weight lifting can increase growth in bone width. ",text,
L_0385,the skeletal system,T_2140,"A joint is a place where two or more bones of the skeleton meet. There are three different types of joints based on the degree to which they allow movement of the bones: immovable, partly movable, and movable joints. Immovable joints do not allow the bones to move at all. In these joints, the bones are fused together by very tough collagen. Examples of immovable joints include the joints between bones of the skull. You can see them in Figure 16.12. Partly movable joints allow very limited movement. In these joints, the bones are held together by cartilage, which is more flexible than collagen. Examples of partly moveable joints include the bones of the rib cage. Movable joints allow the greatest movement and are the most common. In these joints, the bones are connected by ligaments. The surfaces of the bones at the joints are covered with a smooth layer of cartilage. It reduces friction between the bones when they move. The space between the bones is also filled with a liquid called synovial fluid. It helps to cushion the bones. There are several different types of movable joints. You can see three of them in Figure 16.13. Move these three joints in your own skeleton to experience the range of motion each allows. ",text,
L_0385,the skeletal system,T_2140,"A joint is a place where two or more bones of the skeleton meet. There are three different types of joints based on the degree to which they allow movement of the bones: immovable, partly movable, and movable joints. Immovable joints do not allow the bones to move at all. In these joints, the bones are fused together by very tough collagen. Examples of immovable joints include the joints between bones of the skull. You can see them in Figure 16.12. Partly movable joints allow very limited movement. In these joints, the bones are held together by cartilage, which is more flexible than collagen. Examples of partly moveable joints include the bones of the rib cage. Movable joints allow the greatest movement and are the most common. In these joints, the bones are connected by ligaments. The surfaces of the bones at the joints are covered with a smooth layer of cartilage. It reduces friction between the bones when they move. The space between the bones is also filled with a liquid called synovial fluid. It helps to cushion the bones. There are several different types of movable joints. You can see three of them in Figure 16.13. Move these three joints in your own skeleton to experience the range of motion each allows. ",text,
L_0385,the skeletal system,T_2141,"What you eat as a teen can affect how healthy your skeletal system is not only now but also in the future. Eating a diet with plenty of calcium and vitamin D can help keep your bones strong. If you dont get enough calcium and vitamin D in your diet as a teen, you will be more likely to develop osteoporosis when you are older. ",text,
L_0385,the skeletal system,T_2142,"Osteoporosis is a disease in which the bones become porous and weak because they do not contain enough calcium. The graph in Figure 16.14 shows how the mass of calcium in bone peaks around age 30 and declines after that, especially in women. Maximizing the calcium in your bones while youre young will reduce your risk of developing osteoporosis later in of life. ",text,
L_0385,the skeletal system,T_2143,"People with osteoporosis have an increased risk of bone fractures. A bone fracture is a crack or break in bone. Even if you have healthy bones, you may fracture a bone if too much stress is placed on it. This could happen in a car crash or while playing a sport. Wearing a seatbelt when you ride in a motor vehicle and wearing safety gear when you play sports may help prevent bone fractures. Bone fractures heal naturally as new bone tissue forms at the site of the fracture. However, the bone may have to be placed in a cast or have rods or screws inserted into it to keep it correctly aligned until it heals. The healing process usually takes several weeks or even months. ",text,
L_0385,the skeletal system,T_2144,"Another type of skeletal system injury is a sprain. A sprain is a strain or tear in a ligament that has been twisted or stretched too far. Ankle sprains are a common type of sprain. Athletes often strain a ligament in the knee called the ACL. Warming up adequately and stretching before playing sports may reduce the risk of a sprain. Ligament injuries can take a long time to heal. Rest, ice, compression, and elevation of the sprained area may help the healing process. ",text,
L_0386,the muscular system,T_2145,"Muscles are the main organs of the muscular system. Muscles are composed primarily of cells called muscle fibers. A muscle fiber is a very long, thin cell, as you can see in Figure 16.16. It contains multiple nuclei and many mitochondria, which produce ATP for energy. It also contains many organelles called myofibrils. Myofibrils allow muscles to contract, or shorten. Muscle contractions are responsible for virtually all the movements of the body, both inside and out. ",text,
L_0386,the muscular system,T_2145,"Muscles are the main organs of the muscular system. Muscles are composed primarily of cells called muscle fibers. A muscle fiber is a very long, thin cell, as you can see in Figure 16.16. It contains multiple nuclei and many mitochondria, which produce ATP for energy. It also contains many organelles called myofibrils. Myofibrils allow muscles to contract, or shorten. Muscle contractions are responsible for virtually all the movements of the body, both inside and out. ",text,
L_0386,the muscular system,T_2146,"To understand how a muscle contracts, you need to dive deeper into the structure of muscle fibers. You can see in Figure 16.16 that a muscle fiber is full of myofibrils. Each myofibril is made up of two types of proteins, called actin and myosin. These proteins form thread-like filaments. The myosin filaments use energy from ATP to pull on the actin filaments. This causes the actin filaments to slide over the myosin filaments and shorten a section of the myofibril. You can see a simple animation of the process at this link: http://commons.wikimedia.org/wiki/File:Actin_Myosin.gif The sliding-and-shortening process occurs all along many myofibrils and in many muscle fibers. It causes the muscle fibers to shorten and the muscle to contract. ",text,
L_0386,the muscular system,T_2147,"There are three different types of muscle tissue in the human body: cardiac, smooth, and skeletal muscle tissues. All three types consist mainly of muscle fibers, but the fibers have different arrangements. You can see how each type of muscle tissue looks in Figure 16.17. Cardiac muscle is found only in the walls of the heart. It is striated, or striped, because its muscle fibers are arranged in bundles. Contractions of cardiac muscle are involuntary. This means that they are not under conscious control. When cardiac muscle contracts, the heart beats and pumps blood. Smooth muscle is found in the walls of other internal organs such as the stomach. It isnt striated because its muscle fibers are arranged in sheets rather than bundles. Contractions of smooth muscle are involuntary. When smooth muscles in the stomach contract, they squeeze food inside the stomach. This helps break the food into smaller pieces. Skeletal muscle is attached to the bones of the skeleton. It is striated like cardiac muscle because its muscle fibers are arranged in bundles. Contractions of skeletal muscle are voluntary. This means that they are under conscious control. Whether you are doing pushups or pushing a pencil, you are using skeletal muscles. Skeletal muscles are the most common type of muscles in the body. You can read more about them below. ",text,
L_0386,the muscular system,T_2148,The human body has more than 600 skeletal muscles. You can see some of them in Figure 16.18. A few of the larger muscles are labeled in the figure. ,text,
L_0386,the muscular system,T_2149,"You can see the bundles of muscle fibers that make up a skeletal muscle in Figure 16.19. You can also see in the figure how the muscle is attached to a bone by a tendon. Tendons are tough connective tissues that anchor skeletal muscles to bones throughout the body. Many skeletal muscles are attached to the ends of bones where they meet at a joint. The muscles span the joint and connect the bones. When the muscles contract, they pull on the bones, causing them to move. ",text,
L_0386,the muscular system,T_2149,"You can see the bundles of muscle fibers that make up a skeletal muscle in Figure 16.19. You can also see in the figure how the muscle is attached to a bone by a tendon. Tendons are tough connective tissues that anchor skeletal muscles to bones throughout the body. Many skeletal muscles are attached to the ends of bones where they meet at a joint. The muscles span the joint and connect the bones. When the muscles contract, they pull on the bones, causing them to move. ",text,
L_0386,the muscular system,T_2150,"Muscles can only contract. They cant actively lengthen. Therefore, to move bones back and forth at a joint, skeletal muscles must work in pairs. For example, the bicep and triceps muscles of the upper arm work as a pair. You can see how this pair of muscles works in Figure 16.20. When the bicep muscle contracts, it bends the arm at the elbow. When the triceps muscle contracts, it straightens the arm. ",text,
L_0386,the muscular system,T_2151,"Did you ever hear the saying, Use it or lose it? Thats certainly true when it comes to muscles. If you dont exercise your muscles, they will actually shrink in size. They will also become weaker and more prone to injury. ",text,
L_0386,the muscular system,T_2152,"Exercising muscles increases their size, and bigger muscles have greater strength. What type of exercises should you do? For all-round muscular health, you should do two basic types of exercise. To increase the size and strength of skeletal muscles, you need to make these muscles contract against a resisting force. For example, you can do sit-ups or pushups, where the resisting force is your own body weight. You can see another way to do it in Figure 16.21. To exercise cardiac muscle and increase muscle endurance, you need to do aerobic exercise. Aerobic exercise increases the size and strength of muscles in the heart and helps all your muscles develop greater endurance. This means they can work longer without getting tired. Aerobic exercise is any exercise such as running, biking, or swimming that causes an increase in your heart rate. You can see another example of aerobic exercise in Figure 16.22. Lifting weights is one way to pit skeletal muscles against a resisting force. Snowshoeing is a fun way to get aerobic exercise. ",text,
L_0386,the muscular system,T_2153,You are less likely to have a muscle injury if you exercise regularly and have strong muscles. Stretching also helps prevent muscle injuries. Stretching improves the range of motion of muscles and tendons at joints. You should always warm up before stretching or doing any type of exercise. Warmed-up muscles and tendons are less likely to be injured. One way to warm up is to jog slowly for a few minutes. ,text,
L_0386,the muscular system,T_2153,You are less likely to have a muscle injury if you exercise regularly and have strong muscles. Stretching also helps prevent muscle injuries. Stretching improves the range of motion of muscles and tendons at joints. You should always warm up before stretching or doing any type of exercise. Warmed-up muscles and tendons are less likely to be injured. One way to warm up is to jog slowly for a few minutes. ,text,
L_0387,food and nutrients,T_2154,Your body needs food for three purposes: 1. Food gives the body energy. You need energy for everything you do. The energy in food is measured in a unit called the Calorie. 2. Food provides building materials for the body. The body needs building materials for growth and repair. 3. Food contains substances that help control body processes. Body processes must be kept in balance for good health. ,text,
L_0387,food and nutrients,T_2155,"There are a variety of substances in foods that the body needs. Any substance in food that the body needs is called a nutrient. There are six major types of nutrients: carbohydrates, proteins, lipids, water, minerals, and vitamins. Carbohydrates, proteins, and lipids can be used for energy. Proteins also provide building materials. Proteins, minerals, and vitamins help control body processes. Water is needed by all cells just to stay alive. The six types of nutrients can be divided into two major categories based on how much of them the body needs. The categories are macronutrients and micronutrients. ",text,
L_0387,food and nutrients,T_2156,"Macronutrients are nutrients the body needs in relatively large amounts. They include carbohydrates, proteins, lipids, and water. ",text,
L_0387,food and nutrients,T_2157,"Carbohydrates include sugars, starches, and fiber. Sugars and starches are used by the body for energy. One gram of sugar or starch provides 4 Calories of energy. Fiber doesnt provide energy, but it is needed for other uses. At age 13 years, you need about 130 grams of carbohydrates a day. Figure 17.2 shows good food sources of each type. Sugars are small, simple carbohydrates. They are found in foods such as milk and fruit. Sugars in foods such as these are broken down by your digestive system to glucose, the simplest of all sugars. Glucose is taken up by cells for energy. Starches are larger, complex carbohydrates. They are found in foods such as grains and vegetables. Starches are broken down by your digestive system to glucose, which is used for energy. Fiber is a complex carbohydrate that consists mainly of cellulose and comes only from plants. High-fiber foods include whole grains and legumes such as beans. Fiber cant be broken down by the digestive system, but it plays important roles in the body. It helps keep sugar and lipids at normal levels in the blood. It also helps keep food waste moist so it can pass easily out of the body. ",text,
L_0387,food and nutrients,T_2158,"Proteins are nutrients made up of smaller molecules called amino acids. The digestive system breaks down proteins in food to amino acids, which are used for protein synthesis. Proteins synthesized from the amino acids in food serve many vital functions. They make up muscles, control body processes, fight infections, and carry substances in the blood. If you eat more protein than you need for these functions, the extra protein is used for energy. One gram of protein provides 4 Calories of energy, the same as carbohydrates. A 13-year-old needs to eat about 34 grams of protein a day. Figure 17.3 shows good food sources of protein. ",text,
L_0387,food and nutrients,T_2159,"Lipids are nutrients such as fats. They are used for energy and other important purposes. One gram of lipids provides the body with 9 Calories of energy, more than twice as much as carbohydrates or proteins. Lipids also make up cell membranes, protect nerves, control blood pressure, and help blood clot. You must consume some lipids for these purposes. Good food sources of lipids are shown in Figure 17.4. Any extra lipids you consume are stored as fat. A certain amount of stored fat is needed to cushion and protect internal organs and insulate the body. However, too much stored fat can lead to obesity and cause significant health problems. A type of lipid called trans fat is found in many processed foods. Trans fat is rare in nature but is manufactured and added to foods to preserve freshness. Eating foods that contain trans fat increases the risk of heart disease. Trans fat may be found in such foods as cookies, doughnuts, crackers, fried foods, ground beef, and margarine. ",text,
L_0387,food and nutrients,T_2159,"Lipids are nutrients such as fats. They are used for energy and other important purposes. One gram of lipids provides the body with 9 Calories of energy, more than twice as much as carbohydrates or proteins. Lipids also make up cell membranes, protect nerves, control blood pressure, and help blood clot. You must consume some lipids for these purposes. Good food sources of lipids are shown in Figure 17.4. Any extra lipids you consume are stored as fat. A certain amount of stored fat is needed to cushion and protect internal organs and insulate the body. However, too much stored fat can lead to obesity and cause significant health problems. A type of lipid called trans fat is found in many processed foods. Trans fat is rare in nature but is manufactured and added to foods to preserve freshness. Eating foods that contain trans fat increases the risk of heart disease. Trans fat may be found in such foods as cookies, doughnuts, crackers, fried foods, ground beef, and margarine. ",text,
L_0387,food and nutrients,T_2160,"Water is essential to life because chemical reactions within cells take place in water. Most people can survive only a few days without consuming water to replace their water losses. How do you lose water? You lose water in your breath each time you exhale. You lose water in urine. You lose water in sweat, especially if you are active in warm weather. The boy in Figure 17.5 is taking a water break while playing outside on a hot day. If he doesnt take in enough water to replace the water lost in sweat, he may become dehydrated. Symptoms of dehydration include dry mouth, headache, and dizziness. Dehydration can be very serious. It can even cause death. ",text,
L_0387,food and nutrients,T_2161,"Micronutrients are nutrients the body needs in relatively small amounts. They include minerals and vitamins. These nutrients dont provide the body with energy, but they are still essential for good health. ",text,
L_0387,food and nutrients,T_2162,"Minerals are chemical elements that dont come from living things or include the element carbon. Many minerals are needed in the diet for normal functioning of the body. Several minerals that are needed in relatively large amounts are listed in Table 17.1. As you can see from these examples, minerals have a diversity of important functions. Your body cant produce any of the minerals it needs, so you must get them from the food you eat. The table shows good food sources of the minerals. Mineral Calcium Chloride Magnesium Phosphorus Potassium Sodium Function strong bones and teeth salt-water balance strong bones strong bones and teeth muscle and nerve functions muscle and nerve functions Good Food Sources milk, green leafy vegetables table salt, most packaged foods whole grains, nuts poultry, whole grains meat, bananas table salt, most packaged foods Not getting enough minerals can cause health problems. For example, not getting enough calcium may cause osteoporosis. This is a disease in which the bones become porous so they break easily. Getting too much of some minerals can also cause health problems. Many people get too much sodium. Sodium is added to most packaged foods. People often add more sodium to their food by using table salt. Too much sodium has been linked to high blood pressure in some people. ",text,
L_0387,food and nutrients,T_2163,"The vitamins to watch out for are A, D, E, and K. These vitamins are stored by the body, so they can build up to high levels. ",text,
L_0389,the digestive system,T_2171,"The digestive system is the body system that breaks down food and absorbs nutrients. It also eliminates solid food wastes that remain after food is digested. The major organs of the digestive system are shown in Figure 17.10. For an entertaining overview of the digestive system and how it works, watch this video:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0389,the digestive system,T_2172,"The organs in Figure 17.10 make up the gastrointestinal (GI) tract. This is essentially a long tube that connects the mouth to the anus. Food enters the mouth and then passes through the rest of the GI tract. Food waste leaves the body through the anus. In adults, the GI tract is more than 9 meters (30 feet) long! Organs of the GI tract are covered by muscles that contract to keep food moving along. A series of involuntary muscle contractions moves rapidly along the tract, like a wave travelling through a spring toy. The muscle contractions are called peristalsis. The diagram in Figure 17.11 shows how peristalsis works. ",text,
L_0389,the digestive system,T_2173,"As food is pushed through the GI tract by peristalsis, it undergoes digestion. Digestion is the process of breaking down food into nutrients. There are two types of digestion: mechanical digestion and chemical digestion. Mechanical digestion occurs when large chunks of food are broken down into smaller pieces. This is a physical process that happens mainly in the mouth and stomach. Chemical digestion occurs when large food molecules are broken down into smaller nutrient molecules. This is a chemical process that begins in the mouth and stomach but occurs mainly in the small intestine. ",text,
L_0389,the digestive system,T_2174,"After food is broken down into nutrient molecules, the molecules are absorbed by the blood. Absorption is the process in which nutrients or other molecules are taken up by the blood. Once absorbed by the blood, nutrients can travel in the bloodstream to cells throughout the body. ",text,
L_0389,the digestive system,T_2175,Some substances in food cant be broken down into nutrients. They remain behind in the digestive system after the nutrients have been absorbed. Any substances in food that cant be digested pass out of the body as solid waste. This process is called elimination. ,text,
L_0389,the digestive system,T_2176,"Chemical digestion could not take place without the help of digestive enzymes and other substances secreted into the GI tract. An enzyme is a protein that speeds up a biochemical reaction. Digestive enzymes speed up the reactions of chemical digestion. Table 17.3 lists a few digestive enzymes, the organs that produce them, and their functions in digestion. Enzyme Amylase Pepsin Organ that Produces It mouth stomach Substance It Helps Digest starch protein Enzyme Lipase Ribonuclease Organ that Produces It pancreas pancreas Substance It Helps Digest fat RNA Most digestive enzymes are secreted into the GI tract by organs of the GI tract or from a nearby gland named the pancreas. Figure 17.12 shows where the pancreas is located. The figure also shows the locations of the liver and gall bladder. These organs produce or store other digestive secretions. The liver secretes bile acids. Bile acids help digest fat. Some liver bile is secreted directly into the small intestine. Some liver bile goes to the gall bladder. This sac-like organ stores and concentrates the liver bile before releasing it into the small intestine. ",text,
L_0389,the digestive system,T_2177,"Does the sight or smell of your favorite food make your mouth water? When this happens, you are getting ready for digestion. ",text,
L_0389,the digestive system,T_2178,"The mouth is the first digestive organ that food enters. The sight, smell, or taste of food stimulates the release of saliva and digestive enzymes by salivary glands inside the mouth. Saliva wets the food, which makes it easier to break up and swallow. The enzyme amylase in saliva begins the chemical digestion of starches to sugars. Your teeth help to mechanically digest food. Look at the different types of human teeth in Figure 17.13. Sharp teeth in the front of the mouth cut or tear food when you bite into it. Broad teeth in the back of the mouth grind food when you chew. Your tongue helps mix the food with saliva and enzymes and also helps you swallow. When you swallow, a lump of chewed food passes from the mouth into a tube in your throat called the pharynx. From the pharynx, the food passes into the esophagus. ",text,
L_0389,the digestive system,T_2179,"The esophagus is a long, narrow tube that carries food from the pharynx to the stomach. It has no other purpose. Food moves through the esophagus because of peristalsis. At the lower end of the esophagus, a circular muscle, called a sphincter, controls the opening to the stomach. The sphincter relaxes to let food pass into the stomach. Then the sphincter contracts to prevent food from passing back into the esophagus. ",text,
L_0389,the digestive system,T_2180,"The stomach is a sac-like organ at the end of the esophagus. It has thick muscular walls that contract and relax to squeeze and mix food. This helps break the food into smaller pieces. It also helps mix the food with enzymes and other secretions in the stomach. For example, the stomach secretes the enzyme pepsin, which helps digest proteins. Water, salt, and simple sugars can be absorbed into the blood from the lining of the stomach. However, most substances must undergo further digestion in the small intestine before they can be absorbed. The stomach stores the partly digested food until the small intestine is empty. Then a sphincter between the stomach and small intestine relaxes, allowing food to enter the small intestine. ",text,
L_0389,the digestive system,T_2181,"The small intestine is a narrow tube that starts at the stomach and ends at the large intestine. In adults, its about 7 meters (23 feet) long. Most chemical digestion and almost all nutrient absorption take place in the small intestine. The small intestine is made up of three parts: 1. The duodenum is the first part of the small intestine. It is also the shortest part. This is where most chemical digestion takes place. Many enzymes and other substances involved in digestion are secreted into the duodenum 2. The jejunum is the second part of the small intestine. This is where most nutrients are absorbed into the blood. The inside surface of the jejunum is covered with tiny projections called villi (villus, singular). The villi make the inner surface of the small intestine 1000 times greater than it would be without them. You can read in Figure 17.14 how villi are involved in absorption. 3. The ileum is the last part of the small intestine. It is covered with villi like the jejunum. A few remaining nutrients are absorbed in the ileum. From the ileum, any remaining food waste passes into the large intestine. ",text,
L_0389,the digestive system,T_2182,"The large intestine is a wide tube that connects the small intestine with the anus. In adults, the large intestine is about 1.5 meters (5 feet) long. It is larger in width but shorter in length than the small intestine. ",text,
L_0389,the digestive system,T_2183,"Food waste enters the large intestine from the small intestine in a liquid state. As the waste moves through the large intestine, excess water is absorbed from it. The remaining solid waste is called feces. After a certain amount of feces have collected, a sphincter relaxes to let the feces pass out of the body through the anus. This is elimination. ",text,
L_0389,the digestive system,T_2184,"Trillions of bacteria normally live in the large intestine. Dont worrymost of them are helpful. They have several important roles. For example, intestinal bacteria: produce vitamins B12 and K. control the growth of harmful bacteria. break down toxins in the large intestine. break down fiber and some other substances in food that cant be digested. ",text,
L_0389,the digestive system,T_2185,"Much of the time, you probably arent aware of your digestive system. It works well without causing any problems. But most people have problems with their digestive system at least once in a while. Did you ever eat something that didnt agree with you? Maybe you had a stomachache or felt sick to your stomach. Perhaps you had diarrhea. These can be symptoms of food poisoning. ",text,
L_0389,the digestive system,T_2186,"Food poisoning is the common term for foodborne illness. This type of illness occurs when harmful bacteria enter your digestive system in food and make you sick. The bacteriaor toxins they producemay cause cramping, vomiting, or other GI tract symptoms. Following these healthy practices may decrease your risk of foodborne illness: Wash your hands after handling raw foods such as meats, poultry, fish, or eggs. These foods often contain bacteria that your hands could transfer to your mouth. Cook meats, poultry, fish, or eggs thoroughly before eating them. The heat of cooking kills any bacteria the foods may contain so they cant make you sick. Keep hot foods hot and cold foods cold. This is especially important when food is packed for lunch or a picnic (see Figure 17.15). Maintaining the proper temperature slows the growth of bacteria in the food. ",text,
L_0389,the digestive system,T_2187,"Food allergies occur when the immune system reacts to harmless substances in food as though they were harmful germs. Food allergies are relatively common. Almost 10 percent of children have them. Some of the foods most likely to cause allergies include milk, shellfish, nuts, grains, and eggs. If you eat foods to which you are allergic, you may experience vomiting, diarrhea, or a rash. In some people, eating even tiny amounts of certain foods causes them to have serious symptoms, such as difficulty breathing. They need immediate medical attention. The best way to prevent food allergy symptoms is to avoid eating the offending food. This may require careful reading of food labels. ",text,
L_0390,overview of the cardiovascular system,T_2188,The organs that make up the cardiovascular system are the heart and a network of blood vessels that run throughout the body. The blood in the cardiovascular system is a liquid connective tissue. Figure 18.1 shows the heart and major vessels through which blood flows in the system. The heart is basically a pump that keeps blood moving through the blood vessels. ,text,
L_0390,overview of the cardiovascular system,T_2189,"The main function of the cardiovascular system is transporting substances around the body. Figure 18.1 shows some of the substances that are transported in the blood. They include hormones, oxygen, nutrients from digested food, and cellular wastes. Transport of all these materials is necessary to maintain homeostasis of the body and life itself. The cardiovascular system also helps regulate body temperature by controlling where blood moves around the body. Blood is warm, so when more blood flows to the surface of the body, it warms the surface. This allows the body to lose excess heat from the surface. When less blood flows to the surface, it cools the surface. This allows the body to conserve heat and stay warm. You can see the role of blood vessels in the regulation of body temperature in this video:  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0390,overview of the cardiovascular system,T_2190,"The heart and blood vessels form a closed system through which blood keeps circulating. However, blood actually circulates in two different loops within this closed system. The two loops are called pulmonary circulation and systemic circulation. In both loops, blood passes through the heart. You can see a simple model of each circulation loop in Figure 18.2. As blood circulates through the body, it travels first through one loop and then the other loop, over and over again. ",text,
L_0390,overview of the cardiovascular system,T_2191,"Pulmonary circulation is the shorter loop of the cardiovascular system. It carries blood between the heart and lungs. Oxygen-poor blood flows from the heart to the lungs. In the lungs, the blood absorbs oxygen and releases carbon dioxide. Then the oxygen-rich blood returns to the heart. ",text,
L_0390,overview of the cardiovascular system,T_2192,"Systemic circulation is the longer loop of the cardiovascular system. It carries blood between the heart and the rest of the body. Oxygen-rich blood flows from the heart to cells throughout the body. As it passes cells, the blood releases oxygen and absorbs carbon dioxide. Then the oxygen-poor blood returns to the heart. ",text,
L_0391,heart and blood vessels,T_2193,"The heart is a muscular organ in the chest. It consists mainly of cardiac muscle tissue. It pumps blood by repeated, rhythmic contractions. This produces the familiar lub-dub sound of each heartbeat. For a good video introduction to the heart and how it works, watch this entertaining Bill Nye video:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0391,heart and blood vessels,T_2194,"The heart has four chambers, or rooms, which you can see in Figure 18.3. Each chamber is an empty space with muscular walls through which blood can flow. The top two chambers of the heart are called the left and right atria (atrium, singular). The atria of the heart receive blood from the body or lungs and pump it into the bottom chambers of the heart. The bottom two chambers of the heart are called the left and right ventricles. The ventricles receive blood from the atria and pump it out of the heart, either to the lungs or to the rest of the body. Flaps of tissue called valves separate the hearts chambers. Valves keep blood flowing in just one direction through the heart. For example, a valve at the bottom of the right atrium opens to let blood flow from the right atrium to the right ventricle. Then the valve closes so the blood cant flow back into the right atrium. ",text,
L_0391,heart and blood vessels,T_2195,Blood flows through the heart in two paths. Trace these two paths in Figure 18.4 as you read about them below. You can also learn about how blood flows through the heart with this rap:  MEDIA Click image to the left or use the URL below. URL:  1. One path of blood in the heart is through the right atrium and right ventricle. The right atrium receives oxygen- poor blood from the body. It pumps the blood into the right ventricle. Then the right ventricle pumps the blood out of the heart to the lungs. This path through the heart is part of the pulmonary circulation. 2. The other path of blood in the heart is through the left atrium and left ventricle. The left atrium receives oxygen-rich blood from the lungs. It pumps the blood into the left ventricle. Then the left ventricle pumps the blood out of the heart to the rest of the body. This path through the heart is part of the systemic circulation. ,text,
L_0391,heart and blood vessels,T_2196,"To move blood through the heart, cardiac muscles must contract in a certain sequence. First the atria must contract, followed quickly by the ventricles contracting. This series of contractions keeps blood moving continuously through the heart. Contractions of cardiac muscles arent under voluntary control. They are controlled by a cluster of special cells within the heart, commonly called the pacemaker. These cells send electrical signals to cardiac muscles so they contract in the correct sequence and with just the right timing. ",text,
L_0391,heart and blood vessels,T_2197,"Blood vessels are long, tube-like organs that consist mainly of muscle, connective, and epithelial tissues. They branch to form a complex network of vessels that run throughout the body. This network transports blood to all the bodys cells. ",text,
L_0391,heart and blood vessels,T_2198,"There are three major types of blood vessels: arteries, veins, and capillaries. You can see each type in Figure 18.5. You can watch a good video introduction to the three types at this link:  MEDIA Click image to the left or use the URL below. URL:  Arteries are muscular blood vessels that carry blood away from the heart. They have thick walls that can withstand the pressure of blood pumped by the heart. Arteries generally carry oxygen-rich blood. The largest artery is the aorta, which receives blood directly from the heart. It branches to form smaller and smaller arteries throughout the body. The smallest arteries are called arterioles. Veins are blood vessels that carry blood toward the heart. This blood is no longer under pressure, so veins have thinner walls. To keep the blood moving, many veins have valves that prevent the backflow of blood. Veins generally carry oxygen-poor blood. The smallest veins are called venules. They merge to form larger and larger veins. The largest vein is the inferior vena cava, which carries blood from the lower body directly to the heart. Capillaries are the smallest type of blood vessels. They connect the smallest arteries (arterioles) and veins (venules). Exchange of substances between cells and the blood takes place across the walls of capillaries, which may be only one cell thick. ",text,
L_0391,heart and blood vessels,T_2199,"Blood vessels help regulate body processes by either dilating (widening) or constricting (narrowing). This changes the amount of blood flowing to particular organs. For example, dilation of blood vessels in the skin allows more blood to flow to the surface of the body. This helps the body lose excess heat. Constriction of these blood vessels has the opposite effect and helps the body conserve heat. ",text,
L_0391,heart and blood vessels,T_2200,Diseases of the cardiovascular system are common and may be life threatening. A healthy lifestyle can reduce the risk of such diseases developing. ,text,
L_0391,heart and blood vessels,T_2201,"Diseases of the heart and blood vessels are called cardiovascular diseases. The leading cause of cardiovascular disease is atherosclerosis. Atherosclerosis is a condition in which a material called plaque builds up inside arteries. Plaque consists of cell debris, cholesterol, and other substances. As plaque builds up in an artery, the artery narrows, as shown in Figure If plaque blocks coronary arteries that supply blood to the heart, coronary heart disease results. Poor blood flow to the heart may cause chest pain or a heart attack. A heart attack occurs when the blood supply to part of the heart muscle is completely blocked so that cardiac muscle cells die. Coronary heart disease is the leading cause of death in U.S adults. ",text,
L_0391,heart and blood vessels,T_2202,"Many factors influence your risk of developing cardiovascular diseases. Some of these factors you cant control. Older age, male gender, and a family history of cardiovascular disease all increase the risk and cant be controlled. However, you can control many other factors. To reduce the risk of cardiovascular disease, you can: avoid smoking. get regular physical activity. maintain a healthy percent of body fat. eat a healthy, low-fat diet. get regular checkups to detect and manage problems such as high blood pressure and high blood cholesterol. ",text,
L_0392,blood,T_2203,Blood is a liquid connective tissue. It circulates throughout the body via blood vessels due to the pumping action of the heart. You couldnt survive without the approximately 4.5 to 5 liters of blood that are constantly being pumped through your blood vessels. ,text,
L_0392,blood,T_2204,"Blood consists of both liquid and cells. The liquid part of blood is called plasma. Plasma is a watery, golden-yellow fluid that contains many dissolved substances. Substances dissolved in plasma include glucose, proteins, and gases. Plasma also contains blood cells. There are three types of blood cells: red blood cells, white blood cells, and platelets. You can see all three types in Figure 18.8. 1. Red blood cells are shaped like flattened disks. There are trillions of red blood cells in your blood. Each red blood cell has millions of molecules of hemoglobin. Hemoglobin is a protein that contains iron. The iron in hemoglobin gives red blood cells their red color. It also explains how hemoglobin carries oxygen. The iron in hemoglobin binds with oxygen molecules so they can be carried by red blood cells. 2. White blood cells are larger than red blood cells, but there are far fewer of them. Their role is to defend the body in various ways. For example, white blood cells called phagocytes engulf and destroy microorganisms and debris in the blood. 3. Platelets are small, sticky cell fragments that help blood clot. A blood clot is a solid mass of cell fragments and other substances that plugs a leak in a damaged blood vessel. Platelets stick to tears in blood vessels and to each other, helping to form a clot at the site of injury. Platelets also release chemicals that are needed for clotting to occur. ",text,
L_0392,blood,T_2205,"The main function of blood is transport. Blood in arteries carries oxygen and nutrients to all the bodys cells. Blood in veins carries carbon dioxide and other wastes away from cells to be excreted. Blood also transports the chemical messengers called hormones to cells throughout the body where they are needed to regulate body functions. Blood has several other functions as well. For example, blood: defends the body against infections. repairs body tissues. controls the bodys pH. helps regulate body temperature. ",text,
L_0392,blood,T_2206,"Red blood cells carry proteins called antigens on their surface. People may vary in the exact antigens their red blood cells carry. The specific proteins are controlled by the genes they inherit from their parents. The particular antigens you inherit determine your blood type. Why does your blood type matter? Blood type is important for medical reasons. A patient cant safely receive a transfusion of blood containing antigens not found in the patients own blood. With foreign antigens, the transfused blood will be rejected by the persons immune system. This causes a reaction in the patients bloodstream, called agglutination. The transfused red blood cells clump together, as shown in Figure 18.9. The clumped cells block blood vessels and cause other life-threatening problems. There are many sets of antigens that determine different blood types. Two of the best known are the ABO and Rhesus antigens. Both are described below. You can also learn more about them by watching this video: ",text,
L_0392,blood,T_2207,"ABO blood type is determined by two common antigens, often called antigen A and antigen B. If your red blood cells carry only antigen A, you have blood type A. If your red blood cells carry only antigen B, you have blood type B. If your red blood cells carry both antigen A and antigen B, you have blood type AB. If your red blood cells carry neither antigen A nor antigen B, you have blood type O. ",text,
L_0392,blood,T_2208,"Another red blood cell antigen determines a persons Rhesus blood type. This blood type depends on a single common antigen, typically referred to as the Rhesus (Rh) antigen. If your red blood cells carry the Rhesus antigen, you have Rhesus-positive blood, or blood type Rh+. If your red blood cells lack the Rhesus antigen, you have Rhesus-negative blood, or blood type Rh-. ",text,
L_0392,blood,T_2209,"Some diseases affect mainly the blood or its components. They include anemia, leukemia, hemophilia, and sickle- cell disease. ",text,
L_0392,blood,T_2210,Anemia is a disease that occurs when there is not enough hemoglobin (or iron) in the blood so it cant carry adequate oxygen to the cells. There are many possible causes of anemia. One possible cause is excessive blood loss due to an injury or surgery. Not getting enough iron in the diet is another possible cause. ,text,
L_0392,blood,T_2211,"Leukemia is a type of cancer in which bone marrow produces abnormal white blood cells. The abnormal cells cant do their job of fighting infections. Like most cancers, leukemia is thought to be caused by a combination of genetic and environmental factors. It is the most common cancer in children. ",text,
L_0392,blood,T_2212,"Hemophilia is a genetic disorder in which blood fails to clot properly because a normal clotting factor in the blood is lacking. In people with hemophilia, even a minor injury can cause a life-threatening loss of blood. Most cases of hemophilia are caused by a recessive gene on the X chromosome. The disorder is expressed much more commonly in males because they have just one X chromosome. ",text,
L_0392,blood,T_2213,"Sickle-Cell Disease is another genetic disorder of the blood. It is more common in people with African origins because it helps protect against malaria. Sickle-cell disease occurs in people who inherit two copies of the recessive mutant gene for hemoglobin. The abnormal hemoglobin that results causes red blood cells to take on a characteristic sickle shape under certain conditions. You can compare sickle-shaped and normal red blood cells in Figure 18.10. The sickle-shaped cells get stuck in tiny capillaries and block blood flow. This causes serious, painful symptoms. Watch this video animation to learn more about the genetic basis of sickle-cell disease: ",text,
L_0393,the respiratory system,T_2214,"The bodys exchange of oxygen and carbon dioxide with the air is called respiration. Respiration actually consists of two stages. In one stage, air is taken into the body and carbon dioxide is released to the outside air. In the other stage, oxygen is delivered to all the cells of the body and carbon dioxide is carried away from the cells. Another kind of respiration takes place within body cells. This kind of respiration is called cellular respiration. Its the process in which cells obtain energy by burning glucose. Both types of respiration are connected. Cellular respiration uses oxygen and produces carbon dioxide. Respiration by the respiratory system supplies the oxygen needed for cellular respiration. It also removes the carbon dioxide produced by cellular respiration. ",text,
L_0393,the respiratory system,T_2215,"You can see the main structures of the respiratory system in Figure 19.1. They include the nose, trachea, lungs, and diaphragm. Use the figure to trace how air moves through the respiratory system when you read about it below. You can also use this interactive to explore the respiratory system and see how it functions: http://science.nationalgeogr ",text,
L_0393,the respiratory system,T_2216,"Take in a big breath of air through your nose. As you breathe in, you may feel the air pass down through your throat and notice your chest expand. Now breathe out and observe the opposite events occurring. Breathing in and out may seem like simple actions, but they are just part of the complex process of respiration. Respiration actually occurs in four steps: 1. 2. 3. 4. breathing (inhaling and exhaling) gas exchange between the air and blood gas transport by the blood gas exchange between the blood and cells ",text,
L_0393,the respiratory system,T_2217,"Breathing is the process of moving air into and out of the lungs. The process depends on a muscle called the diaphragm. This is a large, sheet-like muscle below the lungs. You can see it in Figure 19.2. Inhaling, or breathing in, occurs when the diaphragm contracts. This increases the size of the chest, which decreases air pressure inside the lungs. The difference in air pressure between the lungs and outside air causes air to rush into the lungs. Exhaling, or breathing out, occurs when the diaphragm relaxes. This decreases the size of the chest, which increases air pressure inside the lungs. The difference in air pressure between the lungs and outside air causes air to rush out of the lungs. When you inhale, air enters the respiratory system through your nose and ends up in your lungs, where gas exchange with the blood takes place. What happens to the air along the way? In the nose, mucus and hairs trap any dust or other particles in the air. The air is also warmed and moistened so it wont harm delicate tissues of the lungs. Next, air passes through the pharynx, a passageway that is shared with the digestive system. From the pharynx, the air passes next through the larynx, or voice box. After the larynx, air moves into the trachea, or wind pipe. This is a long tube that leads down to the lungs in the chest. In the chest, the trachea divides as it enters the lungs to form the right and left bronchi (bronchus, singular). These passages are covered with mucus and tiny hairs called cilia. The mucus traps any remaining particles in the air. The cilia move and sweep the particles and mucus toward the throat so they can be expelled from the body. Air passes from the bronchi into smaller passages called bronchioles. The bronchioles end in clusters of tiny air sacs called alveoli (alveolus, singular). ",text,
L_0393,the respiratory system,T_2218,"The alveoli in the lungs are where gas exchange between the air and blood takes place. Each alveolus is surrounded by a network of capillaries. When you inhale, air in the alveoli has a greater concentration of oxygen than does blood in the capillaries. The difference in oxygen concentration causes oxygen to diffuse from the air into the blood. You can see how this occurs in Figure 19.3. Unlike oxygen, carbon dioxide is more concentrated in the blood in the capillaries surrounding the alveoli than it is in the air inside the alveoli. Therefore, carbon dioxide diffuses in the opposite direction. It moves out of the blood and into the air. ",text,
L_0393,the respiratory system,T_2219,"After the blood in the capillaries in the lungs picks up oxygen, it leaves the lungs and travels to the heart. The heart pumps the oxygen-rich blood into arteries, which carry it throughout the body. The blood passes eventually into capillaries that supply body cells. ",text,
L_0393,the respiratory system,T_2220,"The cells of the body have a lower concentration of oxygen that does blood in the capillaries that supply body cells. Therefore, oxygen diffuses from the blood into the cells. Carbon dioxide, which cells produce in cellular respiration, is more concentrated in the cells. Therefore, carbon dioxide diffuses out of the cells and into the blood. The carbon dioxide travels in capillaries to veins and then to the heart. The heart pumps the blood to the lungs, where the carbon dioxide diffuses into the alveoli. It passes out of the body during exhalation. This brings the process of respiration full circle. ",text,
L_0393,the respiratory system,T_2221,"No doubt youve had the common cold. When you did, you probably had respiratory system symptoms. For example, you may have had a stuffy nose that made it hard to breathe. While you may feel miserable when you have a cold, it is generally a relatively mild disease. Many other respiratory system diseases are more serious. ",text,
L_0393,the respiratory system,T_2222,"Common diseases of the respiratory system include asthma, pneumonia, and emphysema. All of them are diseases of the lungs. You can see some of the changes in the lungs that occur in each of these diseases in Figure 19.4. Asthma is a disease in which bronchioles in the lungs periodically swell and fill with mucus. Symptoms of asthma may include difficulty breathing, wheezing, coughing, and chest tightness. An asthma attack may be triggered by allergies, strenuous exercise, stress, or another respiratory illness such as a cold. Pneumonia is a disease in which some of the alveoli of the lungs fill with fluid so they can no longer exchange gas. Symptoms of pneumonia typically include coughing, chest pain, difficulty breathing, and fatigue. Pneumonia may be caused by an infection or an injury to the lungs. Emphysema is a disease in which the walls of the alveoli break down so less gas can be exchanged by the lungs. The main symptom of emphysema is shortness of breath. The damage to the alveoli is usually caused by smoking and is permanent. ",text,
L_0393,the respiratory system,T_2223,"The main way to keep your respiratory system healthy is to avoid smoking or breathing in the smoke of others. Smoking causes, or makes you more susceptible to, many respiratory diseases, including asthma, bronchitis, em- physema, and lung cancer. Other steps you can take to keep your respiratory system healthy are listed below. Eat well, get enough sleep, and be active every day. These healthy lifestyle choices will help keep your immune system healthy so it can fight off respiratory infections and other diseases. Wash your hands often. This will reduce your risk of picking up viruses or bacteria that could make you sick with colds or other respiratory infections. Avoid contact with other people when they are sick and stay home when you are sick. These steps will help reduce the spread of infectious diseases. ",text,
L_0394,the excretory system,T_2224,"Excretion is any process in which excess water or wastes are removed from the body. Excretion is the job of the excretory system. Besides the kidneys, other organs of excretion include the large intestine, liver, skin and lungs. The large intestine eliminates food wastes that remain after digestion takes place. The liver removes excess amino acids and toxins from the blood. Sweat glands in the skin excrete excess water and salts in sweat. The lungs exhale carbon dioxide and also excess water as water vapor. Each of the above organs of excretion is also part of another body system. For example, the large intestine and liver are part of the digestive system, and the lungs are part of the respiratory system. The kidneys are the main organs of excretion. They are part of the urinary system. ",text,
L_0394,the excretory system,T_2225,"The urinary system is shown in Figure 19.6. It includes two kidneys, two ureters, the urinary bladder, and the urethra. The main function of the urinary system is to filter waste products and excess water from the blood and excrete them from the body as urine. For a visual presentation on the urinary system and how it works, watch this video:  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0394,the excretory system,T_2226,"The kidneys are a pair of bean-shaped organs at each side of the body just above the waist. You can see a diagram of a kidney in Figure 19.7. The function of the kidneys is to filter blood and form urine. Tiny structures in the kidneys, called nephrons, perform this function. Each kidney contains more than a million nephrons. ",text,
L_0394,the excretory system,T_2226,"The kidneys are a pair of bean-shaped organs at each side of the body just above the waist. You can see a diagram of a kidney in Figure 19.7. The function of the kidneys is to filter blood and form urine. Tiny structures in the kidneys, called nephrons, perform this function. Each kidney contains more than a million nephrons. ",text,
L_0394,the excretory system,T_2227,"Blood with wastes enters each kidney through an artery, which branches into many capillaries. After passing through capillaries and being filtered, the clean blood leaves the kidney through a vein. The part of each nephron called the glomerulus is where blood in the capillaries is filtered. Excess water and wastes are filtered out of the blood. The tubule of the nephron collects these substances. Some of the water is reabsorbed. The remaining fluid is urine. ",text,
L_0394,the excretory system,T_2228,"From the kidneys, urine enters the ureters. These are two muscular tubes that carry urine to the urinary bladder. Contractions of the muscles of the ureters move the urine along by peristalsis. The urinary bladder is a sac-like organ that stores urine. When the bladder is about half full, a sphincter relaxes to let urine flow out of the bladder and into the urethra. The urethra is a muscular tube that carries urine out of the body through another sphincter. The process of urine leaving the body is called urination. The second sphincter and the process of urination are normally under conscious control. ",text,
L_0394,the excretory system,T_2229,"The kidneys help the body maintain homeostasis in several ways. They filter all the blood in the body many times each day and produce urine. They control the amount of water and dissolved substances in the blood by excreting more or less of them in urine. The kidneys also secrete hormones that help maintain homeostasis. For example, they produce a hormone that stimulates bone marrow to produce red blood cells when more are needed. They also secrete a hormone that regulates blood pressure and keeps it in a normal range. ",text,
L_0394,the excretory system,T_2230,"You need only one kidney to live a normal, healthy life. A single kidney can do all the work of filtering the blood and maintaining homeostasis. However, at least one kidney must function properly to maintain life. Diseases that threaten the health and functioning of the kidneys include kidney stones, infections, and diabetes. You can learn more about kidney diseases in this video:  . MEDIA Click image to the left or use the URL below. URL:  Kidney stones are mineral crystals that form in urine inside a kidney, as shown in Figure 19.8. The stones may be extremely painful. If a kidney stone blocks a ureter, it must be removed so urine can leave the kidney and be excreted. Bacterial infections of urinary organs, especially the urinary bladder, are common. They are called urinary tract infections. Generally, they can be cured with antibiotic drugs. However, if they arent treated, they can lead to more serious infections and damage to the kidneys. Untreated diabetes may damage capillaries in the kidneys so the nephrons can no longer filter blood. This is called kidney failure. The only cure for kidney failure is to receive a healthy transplanted kidney from a donor. Until that happens, a patient with kidney failure can be kept alive by artificially filtering the blood through a machine. This is called hemodialysis. You can see how it works in Figure 19.9. ",text,
L_0396,chemistry of living things,T_2237,All known matter can be divided into a little more than 100 different substances called elements. ,text,
L_0396,chemistry of living things,T_2238,"An element is pure substance that cannot be broken down into other substances. Each element has a particular set of properties that, taken together, distinguish it from all other elements. Table 2.1 lists the major elements in the human body. As you can see, you consist mainly of the elements oxygen, carbon, and hydrogen. Element Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Potassium Sulfur Percent of Body Mass 65 18 10 3 1.5 1.0 0.35 0.25 In your body, most elements are combined with other elements to form chemical compounds. A compound is a unique type of matter in which two or more elements are combined chemically in a certain ratio. For example, much of the oxygen and hydrogen in your body are combined in the chemical compound water, or H2O. ",text,
L_0396,chemistry of living things,T_2239,"The smallest particle of an element that still has the properties of that element is an atom. Atoms are extremely tiny. They can be observed only with an electron microscope. They are commonly represented by models, like the one Figure 2.6. An atom has a central nucleus that is positive in charge. The nucleus is surrounded by negatively charged particles called electrons. The smallest particle of a compound that still has the properties of that compound is a molecule. A molecule consists of two or more atoms. For example, a molecule of water consists of two atoms of hydrogen and one atom of oxygen. Thats why the chemical formula for water is H2 O. You can see a simple model of a water molecule in Figure 2.7. ",text,
L_0396,chemistry of living things,T_2239,"The smallest particle of an element that still has the properties of that element is an atom. Atoms are extremely tiny. They can be observed only with an electron microscope. They are commonly represented by models, like the one Figure 2.6. An atom has a central nucleus that is positive in charge. The nucleus is surrounded by negatively charged particles called electrons. The smallest particle of a compound that still has the properties of that compound is a molecule. A molecule consists of two or more atoms. For example, a molecule of water consists of two atoms of hydrogen and one atom of oxygen. Thats why the chemical formula for water is H2 O. You can see a simple model of a water molecule in Figure 2.7. ",text,
L_0396,chemistry of living things,T_2240,"Besides water, most of the compounds in living things are biochemical compounds. A biochemical compound is a carbon-based compound that is found in living organisms. Carbon is an element that has a tremendous ability to form large compounds. Each atom of carbon can form four chemical bonds with other atoms. A chemical bond is the sharing of electrons between atoms. Bonds hold the atoms together in chemical compounds. A carbon atom can form bonds with other carbon atoms or with atoms of other elements. ",text,
L_0396,chemistry of living things,T_2241,"Biochemical compounds make up the cells and tissues of living things. They are also involved in all life processes. Given their diversity of functions, its not surprising that there are millions of different biochemical compounds. Even so, all biochemical compounds can be grouped into just four main classes: carbohydrates, proteins, lipids, and nucleic acids. The classes are summarized in Table 2.1. Class Elements Examples Functions Class Carbohydrates Elements carbon hydrogen oxygen Examples sugars starch glycogen cellulose Proteins carbon hydrogen oxygen nitrogen sulfur carbon hydrogen oxygen carbon hydrogen oxygen nitrogen phosphorus enzymes hormones Lipids Nucleic acids fats oils phospholipids DNA RNA Functions provide energy to cells stores energy in plants stores energy in animals makes up the cell walls of plants speed up biochemical re- actions regulate life processes store energy in animals store energy in plants make up cell membranes stores genetic information in cells helps cells make proteins ",text,
L_0396,chemistry of living things,T_2242,"You can see from Table 2.1 that all biochemical compounds contain hydrogen and oxygen as well as carbon. They may also contain nitrogen, phosphorus, and/or sulfur. Almost all biochemical compounds are polymers. Polymers are large molecules that consist of many smaller, repeating molecules, called monomers. Most biochemical molecules are macromolecules. The prefix macro- means large, and many biochemical molecules are very large indeed. They may contain thousands of monomer molecules. The largest known biochemical molecule contains more than 34,000 monomers! ",text,
L_0396,chemistry of living things,T_2243,"Carbohydrates are biochemical compounds that include sugar, starch, glycogen, and cellulose. Sugars are simple carbohydrates with relatively small molecules. Glucose is the smallest of all the sugar molecules with its chemical formula of C6 H12 O6 . This means that a molecule of glucose contains 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen. Plants and some other organisms make glucose in the process of photosynthesis. Living things that cannot make glucose can obtain it by consuming plants or organisms that consume plants. Starches are complex carbohydrates. They are polymers of glucose. Starches contain hundreds of glucose monomers. Plants make starches to store extra glucose. Consumers can get starches by eating plants. Common sources of starches in the human diet are pictured in the Figure 2.8. Our digestive system breaks down starches to sugar, which our cells use for energy. Like other animals, we store any extra glucose as the complex carbohydrate called glycogen. Glycogen is also a polymer of glucose. Cellulose is another complex carbohydrate found in plants that is a polymer of glucose. Cellulose molecules bundle together to form long, tough fibers. Cellulose is the most abundant biochemical compound. It makes up the cell walls of plants and gives support to stems and tree trunks. ",text,
L_0396,chemistry of living things,T_2244,"Proteins are biochemical compounds that consist of one or more chains of small molecules called amino acids. Amino acids are the monomers of proteins. There are only about 20 different amino acids. The sequence of amino acids in chains and the number of chains in a protein determine the proteins shape. Shapes may be very complex. You can learn more about the shapes of proteins at this link: MEDIA Click image to the left or use the URL below. URL:  The shape of a protein determines its function. Proteins have many different functions. For example, proteins: make up muscle tissues. speed up chemical reactions in cells. regulate life processes. help defend against infections. 2.2. Chemistry of Living Things transport materials around the body in the blood. blood How hemoglobin transports oxygen in the ",text,
L_0396,chemistry of living things,T_2245,"Lipids are biochemical compounds that living things use to store energy and make cell membranes. Types of lipids include fats, oils, and phospholipids. Fats are solid lipids that animals use to store energy. Examples of fats include butter and the fat in meat. Oils are liquid lipids that plants use to store energy. Examples of oils include olive oil and corn oil. Phospholipids contain the element phosphorus. They make up the cell membranes of living things. Lipids are made of long chains consisting almost solely of carbon and hydrogen. These long chains are called fatty acids. Fatty acids may be saturated or unsaturated. The Figure 2.10 shows an example of each type of fatty acid. ",text,
L_0396,chemistry of living things,T_2246,"Nucleic acids are biochemical compounds that include RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). Nucleic acids consist of chains of small molecules called nucleotides. Nucleotides are the monomers of nucleic 40 acids. A nucleotide is shown in Figure 2.11. Each nucleotide consists of: 1. a phosphate group, which contains phosphorus and oxygen. 2. a sugar, which is deoxyribose in DNA and ribose in RNA. 3. one of four nitrogen-containing bases. (A base is a compound that is not neither acidic nor neutral.) In DNA, the bases are adenine, thymine, guanine, and cytosine. RNA has the base uracil instead of thymine, but the other three bases are the same. RNA consists of just one chain of nucleotides. DNA consists of two chains. Nitrogen bases on the two chains of DNA form bonds with each other. The bonded bases are called base pairs. Bonds form only between adenine and thymine, and between guanine and cytosine. They hold together the two chains of DNA and give it its characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in Figure 2.12. Sugars and phosphate groups form the backbone of each chain of DNA. Determining the structure of DNA was a huge scientific breakthrough. You can read the interesting story of its discovery and why it was so important at this link: DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in DNAs nucleotide chains. RNA copies and interprets the genetic code in DNA. RNA is also involved in the synthesis of proteins based on the code. You can watch these events unfolding at this link: MEDIA Click image to the left or use the URL below. URL: ",text,
L_0396,chemistry of living things,T_2246,"Nucleic acids are biochemical compounds that include RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). Nucleic acids consist of chains of small molecules called nucleotides. Nucleotides are the monomers of nucleic 40 acids. A nucleotide is shown in Figure 2.11. Each nucleotide consists of: 1. a phosphate group, which contains phosphorus and oxygen. 2. a sugar, which is deoxyribose in DNA and ribose in RNA. 3. one of four nitrogen-containing bases. (A base is a compound that is not neither acidic nor neutral.) In DNA, the bases are adenine, thymine, guanine, and cytosine. RNA has the base uracil instead of thymine, but the other three bases are the same. RNA consists of just one chain of nucleotides. DNA consists of two chains. Nitrogen bases on the two chains of DNA form bonds with each other. The bonded bases are called base pairs. Bonds form only between adenine and thymine, and between guanine and cytosine. They hold together the two chains of DNA and give it its characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in Figure 2.12. Sugars and phosphate groups form the backbone of each chain of DNA. Determining the structure of DNA was a huge scientific breakthrough. You can read the interesting story of its discovery and why it was so important at this link: DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in DNAs nucleotide chains. RNA copies and interprets the genetic code in DNA. RNA is also involved in the synthesis of proteins based on the code. You can watch these events unfolding at this link: MEDIA Click image to the left or use the URL below. URL: ",text,
L_0396,chemistry of living things,T_2247,"The student athlete in Figure 2.13 is practically flying down the track! Running takes a lot of energy. But you dont have to run a race to use energy. All living things need energy all the time just to stay alive. The energy is produced in chemical reactions. A chemical reaction is a process in which some substances, called reactants, change chemically into different substances, called products. Reactants and products may be elements or compounds. Chemical reactions that take place inside living things are called biochemical reactions. Living things depend on biochemical reactions for more than just energy. Every function and structure of a living organism depends on thousands of biochemical reactions taking place in each cell. ",text,
L_0396,chemistry of living things,T_2248,"The sum of all of an organisms biochemical reactions is called metabolism. Biochemical reactions of metabolism can be divided into two general categories: catabolic reactions and anabolic reactions. You can watch an animation showing how the two categories of reactions are related at this link: Anabolic reactions involve forming bonds. Smaller molecules combine to form larger ones. These reactions require energy. For example, it takes energy to build starches from sugars. Catabolic reactions involve breaking bonds. Larger molecules break down to form smaller ones. These reactions release energy. For example, energy is released when starches break down to sugars. ",text,
L_0396,chemistry of living things,T_2249,"Each of the trillions of cells in your body is continuously performing thousands of anabolic and catabolic reactions. Thats an amazing number of biochemical reactionsfar more than the number of chemical reactions that might take place in a science lab or chemical plant. So many biochemical reactions can take place simultaneously in our cells because biochemical reactions occur very quickly. Thats because of enzymes. Enzymes are proteins that increase the rate of biochemical reactions. Enzymes arent changed or used up in the reactions, so they can be used to speed up the same reaction over and over again. Enzymes are highly specific for certain chemical reactions, so they are very effective. A reaction that would take years to occur without its enzyme might occur in a split second with the enzyme. ",text,
L_0396,chemistry of living things,T_2250,Some of the most important biochemical reactions are the reactions involved in photosynthesis and cellular respira- tion. Photosynthesis is the process in which producers capture light energy from the sun and use it to make glucose. This involves anabolic reactions. Cellular respiration is the process in which energy is released from glucose and stored in smaller amounts in other molecules that cells can use for energy. This involves catabolic reactions. Photosynthesis and cellular respiration together provide energy to almost all living cells. Figure 2.14 shows how photosynthesis and cellular respiration are related. You can read more about both processes in the chapter Cell Functions. ,text,
L_0398,the nervous system,T_2257,"Controlling muscles and maintaining balance are just two of the functions of the human nervous system. What else does the nervous system do? It senses the surrounding environment with sense organs that include the eyes and ears. It senses the bodys own internal environment, including its temperature. It controls internal body systems to make sure the body maintains homeostasis. It prepares the body to fight or flee in the case of an emergency. It allows thinking, learning, memory, and language. Remember Hakeem the skater from the first page of the chapter? When Hakeem started to fall off the railing, his nervous system sensed that he was losing his balance. It responded by sending messages to his muscles. Some muscles contracted while other relaxed. As a result, Hakeem gained his balance again. How did his nervous system accomplish all of this in just a split second? You need to know how the nervous system transmits messages to answer that question. ",text,
L_0398,the nervous system,T_2258,"The nervous system is made up of nerves. A nerve is a bundle of nerve cells. A nerve cell that carries messages is called a neuron. The messages carried by neurons are called nerve impulses. A nerve impulse can travel very quickly because it is an electrical signal. Think about flipping on a light switch when you enter a room. When you flip the switch, electricity flows to the light through wires inside the walls. The electricity may have to travel many meters to reach the light. Nonetheless, the light still comes on as soon as you flip the switch. Nerve impulses travel just as quickly through the network of nerves inside the body. ",text,
L_0398,the nervous system,T_2259,"The structure of a neuron suits it for its function of transmitting nerve impulses. You can see what a neuron looks like in Figure 20.2. It has a special shape that lets it pass electrical signals to and from other cells. A neuron has three main parts: cell body, dendrites, and axon. 1. The cell body contains the nucleus and other organelles. 2. Dendrites receive nerve impulses from other cells. A single neuron may have thousands of dendrites. 3. The axon passes on the nerve impulses to other cells. It branches at the end into multiple nerve endings so it can transmit impulses to many other cells. ",text,
L_0398,the nervous system,T_2260,"There are three basic types of neurons: sensory neurons, motor neurons, and interneurons. All three types must work together to receive and respond to information. 1. Sensory neurons transmit nerve impulses from sense organs and internal organs to the brain via the spinal cord. In other words, they carry information about the inside and outside environment to the brain. 2. Motor neurons transmit nerve impulses from the brain via the spinal cord to internal organs, glands, and muscles. In other words, they carry information from the brain to the body, telling the body how to respond. 3. Interneurons carry nerve impulses back and forth between sensory and motor neurons. ",text,
L_0398,the nervous system,T_2261,"The nerve endings of an axon dont actually touch the dendrites of other neurons. The messages must cross a tiny gap between the two neurons, called the synapse. Chemicals called neurotransmitters carry the message across this gap. When a nerve impulse arrives at the end of an axon, neurotransmitters are released. They travel across the synaptic gap to a dendrite of another neuron. The neurotransmitters bind to the membrane of the dendrite, triggering a nerve impulse in the next neuron. You can see how this works in Figure 20.3 and in this animation:  The transmission of nerve impulses between neurons is like the passing of a baton between runners in a relay race. After the first runner races, she passes the baton to the second runner. Then the second runner takes over. Instead of a baton, a neuron passes neurotransmitters to the next neuron. ",text,
L_0398,the nervous system,T_2262,"The nervous system has two main parts, called the central nervous system and the peripheral nervous system. The peripheral nervous system is described later in this lesson. The central nervous system is shown in Figure 20.4. It includes the brain and spinal cord. ",text,
L_0398,the nervous system,T_2263,"The human brain is an amazing organ. It is the most complex organ in the human body. By adulthood, the brain weighs about 3 pounds and consists of billions of neurons. All those cells need a lot of energy. In fact, the adult brain uses almost a quarter of the total energy used by the body! The brain serves as the control center of the nervous system and the body as a whole. It lets us understand what we see, hear, or sense in other ways. It allows us to learn, think, remember, and use language. It controls all the organs and muscles in our body. ",text,
L_0398,the nervous system,T_2264,"The brain consists of three major parts, called the cerebrum, cerebellum, and brain stem. You can see these three parts of the brain in Figure 20.5. You can use this interactive animation to explore these parts of the brain: http://s 1. The cerebrum is the largest part of the brain. It controls conscious functions, such as thinking, sensing, speaking, and voluntary muscle movements. Whether you are chatting with a friend or playing a video game, you are using your cerebrum. 2. The cerebellum is the next largest part of the brain. It controls body position, coordination, and balance. Hakeems cerebellum kicked in when he started to lose his balance on the railing in the opening photo. It allowed him to regain his balance. 3. The brain stem (also called the medulla) is the smallest part of the brain. It controls involuntary body functions such as breathing, heartbeat, and digestion. It also carries nerve impulses back and forth between the rest of the brain and the spinal cord. ",text,
L_0398,the nervous system,T_2265,"The cerebrum is divided down the middle from the front to the back of the head. The two halves of the cerebrum are called the right and left hemispheres. The two hemispheres are very similar but not identical. They are connected to each other by a thick bundle of axons deep within the brain. These axons allow the two hemispheres to communicate with each other. Did you know that the right hemisphere of the cerebrum controls the left side of the body, and vice versa? This can happen because of the connections between the two hemispheres. Each hemisphere is further divided into four parts, called lobes, as you can see in Figure 20.6. Each lobe has different functions. One function of each lobe is listed in the figure. ",text,
L_0398,the nervous system,T_2266,"The spinal cord is a long, tube-shaped bundle of neurons. It runs from the brain stem to the lower back. The main job of the spinal cord is to carry nerve impulses back and forth between the body and brain. The spinal cord is like a two-way road. Messages about the body, both inside and out, pass through the spinal cord to the brain. Messages from the brain pass in the other direction through the spinal cord to tell the body what to do. ",text,
L_0398,the nervous system,T_2267,"All the other nervous tissues in the body are part of the peripheral nervous system. If you look again at Figure 20.1, you can see the major nerves of the peripheral nervous system. They include nerves that run through virtually every part of the body, both inside and out, except for the brain and spinal cord. The peripheral nervous system has two main divisions: the sensory division and the motor division. The divisions carry messages in opposite directions. Figure 20.7 shows these divisions of the peripheral nervous system. ",text,
L_0398,the nervous system,T_2268,"The sensory division of the peripheral nervous system carries messages from sense organs and internal organs to the central nervous system. For example, it carries messages about images from the eyes to the brain. Once the messages reach the brain, the brain interprets the information. ",text,
L_0398,the nervous system,T_2269,"The motor division of the peripheral nervous system carries messages from the central nervous system to muscles, internal organs, and glands throughout the body. The brain sends commands to these tissues, telling them how to respond. As you can see in Figure 20.7, the motor division is divided into additional parts. The autonomic part of the motor division controls involuntary responses. It sends messages to organs and glands. These messages control the body both during emergencies (sympathetic division) and during none- mergencies (parasympathetic division). The somatic part of the motor division controls voluntary responses. It sends messages to the skeletal muscles for movements that are under conscious control. ",text,
L_0398,the nervous system,T_2270,Nervous system problems include diseases and injuries. Most nervous system diseases cant be prevented. But you can take steps to decrease your risk of nervous system injuries. ,text,
L_0398,the nervous system,T_2271,"Bacteria and viruses can infect the brain or spinal cord. An infection of the brain is called encephalitis. An infection of the membranes that cover the brain and spinal cord is called meningitis. A vaccine is available to prevent meningitis caused by viruses (see Figure 20.8). Encephalitis and meningitis arent very common, but they can be extremely serious. They may cause swelling of the brain, which can be fatal. Thats why its important to know the symptoms of these diseases. Both encephalitis and meningitis typically cause a severe headache and a fever. Meningitis also causes a stiff neck. Both require emergency medical treatment. ",text,
L_0398,the nervous system,T_2272,"Epilepsy is a disease in which seizures occur. A seizure is a period of lost consciousness that may include violent muscle contractions. It is caused by abnormal electrical activity in the brain. Epilepsy may result from an infection, injury, or tumor. In many cases, however, the cause cant be identified. There is no known cure for epilepsy, but the seizures often can be prevented with medicine. Sometimes children with epilepsy outgrow it by adulthood. ",text,
L_0398,the nervous system,T_2273,"A stroke occurs when a blood clot blocks blood flow to part of the brain. Brain cells die quickly when their oxygen supply is cut off. Therefore, a stroke may cause permanent loss of normal mental functions. Many stroke patients suffer some degree of paralysis, or loss of the ability to feel or move certain parts of the body. If medical treatment is given very soon after a stroke occurs, some of the damage may be reversed. Strokes occur mainly in older adults. ",text,
L_0398,the nervous system,T_2274,"Alzheimers disease is another disease that occurs mainly in older adults. In Alzheimers disease, a person gradually loses most normal mental functions. The patient typically suffers from increasing memory loss, confusion, and mood swings. The cause of Alzheimers isnt known for certain, but it appears to be associated with certain abnormal changes in the brain. There is no known cure for this devastating disease, but medicines may be able to slow its progression. ",text,
L_0398,the nervous system,T_2275,"The brain and spinal cord are protected within bones of the skeletal system, but injuries to these organs still occur. With mild injuries, there may be no lasting effects. With severe injuries, there may be permanent disability or even death. Brain and spinal cord injuries most commonly occur because of car crashes or athletic activities. Fortunately, many injuries can be prevented by wearing seat belts and safety helmets (see Figure 20.9). Avoiding unnecessary risks, such as doing stunts on a bike or diving into shallow water, can also reduce the chances of brain and spinal cord injuries. The most common type of brain injury is a concussion. This is a bruise on the surface of the brain. It may cause temporary symptoms such as headache and confusion. Most concussions heal on their own in a few days or weeks. However, repeated concussions can lead to permanent changes in the brain. More serious brain injuries also often cause permanent brain damage. Spinal cord injuries may cause paralysis. Some people recover from spinal cord injuries. However, many people remain paralyzed for life. This happens when the spinal cord can no longer transmit nerve impulses between the body and brain. ",text,
L_0398,the nervous system,T_2276,"A drug is any chemical substance that affects the body or brain. Some drugs are medicines. Although these drugs are helpful when used properly, they can be misused like any other drug. Drugs that arent medicines include both legal and illegal drugs. Both can do harm. ",text,
L_0398,the nervous system,T_2277,"Many drugs affect the brain and influence how a person feels, thinks, or acts. Such drugs are called psychoactive drugs. They include legal drugs such as caffeine and alcohol, as well as illegal drugs such as cocaine and heroin. They also include certain medicines, such as antidepressant drugs and medical marijuana. Some psychoactive drugs, such as caffeine, stimulate the central nervous system. They may make the user feel more alert. Some psychoactive drugs, such as alcohol, depress the central nervous system. They may make the user feel more relaxed. Still other psychoactive drugs, such as marijuana, are hallucinogenic drugs. They may make the user have altered sensations, perceptions, or thoughts. ",text,
L_0398,the nervous system,T_2278,"Psychoactive drugs may bring about changes in mood that users find desirable. These drugs may be abused. Drug abuse is use of a drug without the advice of a medical professional and for reasons not originally intended. Continued use of a psychoactive drug may lead to drug addiction. This occurs when a drug user is unable to stop using the drug. Over time, a drug user may need more of the drug to get the desired effect. This can lead to drug overdose and death. ",text,
L_0399,the senses,T_2279,"The ability to see is called vision. It depends on both the eyes and the brain. The eyes sense light and form images. The brain interprets the images formed by the eyes and tells us what we are seeing. For a fascinating account of how the brain helps us see, watch this short video:  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0399,the senses,T_2280,"Did you ever use 3-D glasses to watch a movie, like the teens in Figure 20.11? If you did, then you know that the glasses make images on the flat screen seem more realistic by giving them depth. The images seem to jump right out of the screen toward you. Unlike many other animals, human beings and other primates normally see the world around them in three dimen- sions. Thats because we have two eyes that face the same direction but are a few inches apart. Both eyes focus on the same object at the same time but from slightly different angles. The brain uses the different images from the two eyes to determine the distance to the object. Human beings and other primates also have the ability to see in color. We have special cells inside our eyes that can distinguish different wavelengths of visible light. Visible light is light in the range of wavelengths that the human eye can sense. The exact wavelength of visible light determines its color. ",text,
L_0399,the senses,T_2281,"The function of the eye is to focus light and form images. We see some objects, such as stars and light bulbs, because they give off their own light. However, we see most objects because they reflect light from another source such as the sun. We form images of the objects when some of the reflected light enters our eyes. Look at the parts of the eye in Figure 20.12. Follow the path of light through the eye as you read about it below. 1. Light from an object passes first through the cornea. This is a clear, protective covering on the outside of the eye. 2. Then light passes through the pupil, an opening in the center of the eye. The pupil, which looks black, is surrounded by the colored part of the eye, called the iris. 3. Light entering through the pupil next passes through the lens. The lens is a clear, curved structure, like the lens of a magnifying glass. Along with the cornea, the lens focuses the light on the back of the eye. 4. The back of the eye is covered by a thin layer called the retina. This is where the image of the object normally forms. The retina consists of special light-sensing cells called rods and cones. Rods sense dim light. Cones sense different colors of light. 5. Nerve impulses from rods and cones travel to the optic nerve. It carries the nerve impulses to the brain. ",text,
L_0399,the senses,T_2282,"You probably know people who need eyeglasses or contact lenses to see clearly. Maybe you need them yourself. Lenses are used to correct vision problems. Two of the most common vision problems in young people are myopia and hyperopia. You can compare myopia and hyperopia in Figure 20.13. To learn about astigmatism, another common vision problem, watch this very short video:  . MEDIA Click image to the left or use the URL below. URL:  Myopia is commonly called nearsightedness. People with myopia can see nearby objects clearly, but distant objects appear blurry. Myopia occurs when images focus in front of the retina because the eyeball is too long. This vision problem can be corrected with concave lenses, which curve inward. The lenses focus images correctly on the retina. Hyperopia is commonly called farsightedness. People with hyperopia can see distant objects clearly, but nearby objects appear blurry. Hyperopia occurs when images focus in back of the retina because the eyeball is too short. This vision problem can be corrected with convex lenses, which curve outward. The lenses focus images correctly on the retina. ",text,
L_0399,the senses,T_2283,"Vision is just one of several human senses. Other human senses include hearing, touch, taste, and smell. Imagine shopping at the fruit market in Figure 20.14. It would stimulate all of these senses. You would hear the noisy bustle of the market. You could feel the smooth skin of the fruit. If you tried a sample, you could smell the fruity aroma and taste its sweet flavor. ",text,
L_0399,the senses,T_2284,"What do listening to music and riding a bike have in common? Both activities depend on the ears. The ears are organs that sense sound. They also sense the position of the body and help maintain balance. Hearing is the ability to sense sound. Sound travels through the air in waves. Suppose a car horn blows in the distance. Sound waves spread through the air from the horn. Some of the sound waves enter your ears and cause vibrations. The vibrations trigger nerve impulses that travel to the brain through the auditory nerve. You can learn how this happens in Figure 20.15. The brain then interprets the impulses and tells you what you are hearing. To find out how the brain determines where a sound is coming from, watch this amusing video:  MEDIA Click image to the left or use the URL below. URL:  The parts of the ears involved in balance are the semicircular canals. These are the curved structures above the cochlea in the inner ear in Figure 20.15. Like the cochlea, the semicircular canals contain liquid and are lined with tiny hair cells. As the head changes position, the liquid moves. This causes the hair cells to bend. The bending of the hair cells triggers nerve impulses that travel to the cerebellum in the brain. The cerebellum uses the information to maintain balance. ",text,
L_0399,the senses,T_2285,"Touch is the ability to sense pain, pressure, or temperature. Nerve cells that sense touch are found mainly in the skin. The skin on the palms, soles, face, and lips has the most neurons. Neurons that sense pain are also found inside the body inside the body in the tongue, joints, muscles, and other organs. Suppose you wanted to test the temperature of bath water before getting into the tub. You might stick one toe in the water. Neurons in the skin on your toe would sense the temperature of the water and send a message about it to the brain through the spinal cord. The brain would process the information. It might decide that the water is too hot and send a message to your muscles to pull your toe out of the water. ",text,
L_0399,the senses,T_2286,"The sense of taste is controlled by sensory neurons on the tongue. They are grouped in bundles called taste buds. You can see taste buds on the tongue in Figure 20.16. Taste neurons sense chemicals in food. They can detect five different tastes: sweet, salty, sour, bitter, and umami, which is a meaty taste. When taste neurons sense chemicals, they send messages to the brain about them. The brain then decides what you are tasting. The sense of smell also involves sensory neurons that sense chemicals. These neurons are found in the nose, and they sense chemicals in the air. Unlike taste neurons, smell neurons can detect thousands of different odors. Your sense of smell plays a big role in your sense of taste. You can use your sense of taste alone to learn that a food is sweet. However, you have to use your sense of smell as well to learn that the food tastes like apple pie. ",text,
L_0400,the endocrine system,T_2287,"The endocrine system is a system of glands that release chemical messenger molecules into the blood stream. The messenger molecules are called hormones. Hormones act slowly compared with the rapid transmission of electrical impulses of the nervous system. Endocrine hormones must travel through the bloodstream to the cells they control, and this takes time. On the other hand, because endocrine hormones are released into the bloodstream, they travel to cells everywhere in the body. For a good visual introduction to the endocrine system, watch this short video: http MEDIA Click image to the left or use the URL below. URL: ",text,
L_0400,the endocrine system,T_2288,"An endocrine gland is a gland that secretes hormones into the bloodstream for transport around the body (instead of secreting hormones locally, like sweat glands in the skin). Major glands of the endocrine system are shown in Figure 20.17. The glands are the same in males and females except for the ovaries and testes. ",text,
L_0400,the endocrine system,T_2289,"The hypothalamus is actually part of the brain, but it also secretes hormones. Some of its hormones go directly to the pituitary gland in the endocrine system. These hypothalamus hormones tell the pituitary to either secrete or stop secreting its hormones. In this way, the hypothalamus provides a link between the nervous and endocrine systems. The hypothalamus also produces hormones that directly regulate body processes. For example, it produces antid- iuretic hormone. This hormone travels to the kidneys and stimulates them to conserve water by producing more concentrated urine. ",text,
L_0400,the endocrine system,T_2290,The pea-sized pituitary gland is just below the hypothalamus and attached directly to it. The pituitary receives hormones from the hypothalamus. It also secretes its own hormones. Most pituitary hormones control other endocrine glands. Thats why the pituitary gland is called the master gland of the endocrine system. Table Pituitary Hormone Adrenocorticotropic (ACTH) hormone Target Glands/Cells adrenal glands Thyroid-stimulating (TSH) Growth hormone (GH) hormone thyroid gland Follicle-stimulating (FSH) hormone body cells ovaries or testes Luteinizing hormone (LH) ovaries or testes Prolactin (PRL) mammary glands Effects(s) Stimulates the cortex (outer layer) of the adrenal glands to secrete their hormones Stimulates the thyroid gland to se- crete its hormones Stimulates body cells to make pro- teins and grow Stimulates the ovaries to develop mature eggs; stimulates the testes to produce sperm Stimulates the ovaries or testes to secrete sex hormones; stimulates the ovaries to release eggs Stimulates the mammary glands to produce milk ,text,
L_0400,the endocrine system,T_2291,"There are several other endocrine glands. Find them in Figure 20.17 as you read about them below. The thyroid gland is a relatively large gland in the neck. Hormones secreted by the thyroid gland include thyroxin. Thyroxin increases the rate of metabolism in cells throughout the body. The pancreas is a large gland located near the stomach. Hormones secreted by the pancreas include insulin. Insulin helps cells absorb glucose from the blood. It also stimulates the liver to take up and store excess glucose. The two adrenal glands are glands located just above the kidneys. Each adrenal gland has an outer layer (cortex) and inner layer (medulla) that secrete different hormones. The hormone adrenaline is secreted by the inner layer. It prepares the body to respond to emergencies. For example, it increases the amount of oxygen and glucose going to the muscles. The gonads are glands that secrete sex hormones. Male gonads are called testes. They secrete the male sex hormone testosterone. The female gonads are called ovaries. They secrete the female sex hormone estrogen. Sex hormones stimulate the changes of puberty. They also control the production of sperm or eggs by the gonads. ",text,
L_0400,the endocrine system,T_2292,"Endocrine hormones travel throughout the body in the blood. However, each endocrine hormone affects only certain cells, called target cells. ",text,
L_0400,the endocrine system,T_2293,"A target cell is the type of cell on which a given endocrine hormone has an effect. A target cell is affected by a given hormone because it has proteins on its surface to which the hormone can bind. When the hormone binds to target cell proteins, it causes changes inside the cell. For example, binding of the hormone might cause the release of enzymes inside the cell. The enzymes then influence cell processes. ",text,
L_0400,the endocrine system,T_2294,"Endocrine hormones control many cell activities, so they are very important for homeostasis. But what controls the hormones? Most endocrine hormones are controlled by feedback loops. In a feedback loop, the hormone produced by a gland feeds back to control its own production by the gland. A feedback loop can be negative or positive. Most endocrine hormones are controlled by negative feedback loops. .Negative feedback occurs when rising levels of a hormone feed back to decrease secretion of the hormone or when falling levels of the hormone feed back to increase its secretion. You can see an example of a negative feedback loop in Figure 20.18. It shows how levels of thyroid hormones regulate the thyroid gland. This loop involves the hypothalamus and pituitary gland as well as the thyroid gland. Low levels of thyroid hormones in the blood cause the release of hormones by the hypothalamus and pituitary gland. These hormones stimulate the thyroid gland to secrete more hormones. The opposite happens with high levels of thyroid hormones in the blood. The hypothalamus and pituitary gland stop releasing hormones that stimulate the thyroid. ",text,
L_0400,the endocrine system,T_2295,"Diseases of the endocrine system are fairly common. An endocrine disease usually involves the secretion of too much or not enough hormone by an endocrine gland. This may happen because the gland develops an abnormal lump of cells called a tumor. For example, a tumor of the pituitary gland can cause secretion of too much growth hormone. If this occurs in a child, it may result in very rapid growth and unusual tallness by adulthood. This is called gigantism. Type 1 diabetes is another endocrine system disease. In this disease, the bodys own immune system attacks insulin- secreting cells of the pancreas. As a result, not enough insulin is secreted to maintain normal levels of glucose in the blood. Patients with type 1 diabetes must regularly check the level of glucose in their blood. When it gets too high, they must give themselves an injection of insulin to bring it under control. You can learn more about glucose, insulin, and type 1 diabetes by watching this video:  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0401,infectious diseases,T_2296,An infectious disease is a disease that is caused by a pathogen. A pathogen is an organism or virus that causes disease in another living thing. Pathogens are commonly called germs. Watch this dramatic video for an historic perspective on infectious diseases and their causes:  . MEDIA Click image to the left or use the URL below. URL: ,text,
L_0401,infectious diseases,T_2297,"There are several types of pathogens that cause diseases in human beings. They include bacteria, viruses, fungi, and protozoa. The different types are described in Table 21.1. The table also lists several diseases caused by each type of pathogen. Many infectious diseases caused by these pathogens can be cured with medicines. For example, antibiotic drugs can cure most diseases caused by bacteria. ",text,
L_0401,infectious diseases,T_2298,"Different pathogens spread in different ways. Some are easy to catch. Others are much less contagious. Some pathogens spread through food or water. When harmful bacteria contaminate food, they cause foodborne illness, commonly called food poisoning. An example of a pathogen that spreads through water is the protozoan named Giardia lamblia, described in Table 21.1. It causes a disease called giardiasis. Some pathogens spread through sexual contact. In the U.S., the pathogen most commonly spread this way is HPV, or human papillomavirus. It may cause genital warts and certain types of cancer. A vaccine can prevent the spread of this pathogen. Many pathogens spread by droplets in the air. Droplets are released when a person coughs or sneezes, as you can see in Figure 21.2. The droplets may be loaded with pathogens. Other people may get sick if they breathe in the pathogens on the droplets. Viruses that cause colds and flu can spread this way. Other pathogens spread when they are deposited on objects or surfaces. The fungus that causes athletes food spreads this way. For example, you might pick up the fungus from the floor of a public shower. You can also pick up viruses for colds and flu from doorknobs and other commonly touched surfaces. Still other pathogens are spread by vectors. A vector is an organism that carries pathogens from one person or animal to another. Most vectors are insects such as ticks or mosquitoes. They pick up pathogens when they bite an infected animal and then transmit the pathogens to the next animal they bite. Ticks spread the bacteria that cause Lyme disease. Mosquitoes spread the protozoa that cause malaria. ",text,
L_0401,infectious diseases,T_2299,"What can you do to avoid infectious diseases? Eating well and getting plenty of sleep are a good start. These habits will help keep your immune system healthy. With a healthy immune system, you will be able to fight off many pathogens. Vaccines are available for some infectious diseases. For example, there are vaccines to prevent measles, mumps, whooping cough, and chicken pox. These vaccines are recommended for infants and young children. You can also take the following steps to avoid picking up pathogens or spreading them to others. Watch this video for additional information on preventing the spread of infectious diseases:  MEDIA Click image to the left or use the URL below. URL:  Wash your hands often with soap and water. Spend at least 20 seconds scrubbing with soap. See Figure 21.3 for effective hand washing tips. Avoid touching your eyes, nose, or mouth with unwashed hands. Avoid close contact with people who are sick. This includes kissing, hugging, shaking hands, and sharing cups or eating utensils. Cover your coughs and sneezes with a tissue or shirt sleeve, not your hands. Disinfect frequently touched surfaces, such as keyboards and doorknobs, especially if someone is sick. Stay home when you are sick. The best way to prevent diseases spread by vectors is to avoid contact with the vectors. For example, you can wear long sleeves and long pants to avoid tick and mosquito bites. Using insect repellent can also reduce your risk of insect bites. ",text,
L_0402,noninfectious diseases,T_2300,"Cancer is a disease in which cells divide out of control. Normally, the body has ways to prevent cells from dividing out of control. However, in the case of cancer, these ways fail. The rapidly dividing cells may form a mass of abnormal tissue called a tumor. This is illustrated in Figure 21.4. Watch this video for an animated introduction to cancer:  . MEDIA Click image to the left or use the URL below. URL:  As a tumor increases in size, it may harm normal tissues around it. Sometimes cancer cells break away from a tumor. If they enter the bloodstream, they are carried throughout the body. Then the cells may start growing in other tissues. This is usually how cancer spreads from one part of the body to another. Once this happens, cancer is very hard to stop. ",text,
L_0402,noninfectious diseases,T_2301,"Most cancers are caused by mutations. Mutations are random errors in genes. Mutations that lead to cancer usually occur in genes that control the cell cycle. Because of the mutations, abnormal cells are allowed to divide. Some mutations that lead to cancer may be inherited. However, most of the mutations are caused by environmental factors. Anything in the environment that can cause cancer is called a carcinogen. Common carcinogens include certain chemicals and some types of radiation. Many different chemicals can cause cancer. For example, tobacco contains dozens of chemicals, including nicotine, that have been shown to cause cancer. Figure 21.5 shows some of these chemicals. Smoking tobacco or using smokeless tobacco increases the risk of cancer of the lung, mouth, throat, and urinary bladder. Types of radiation that cause cancer include ultraviolet (UV) radiation and radon. UV radiation is part of sunlight. It is the leading cause of skin cancer. Radon is a naturally occurring radioactive gas that escapes from underground rocks. It may seep into the basements of buildings. It can cause lung cancer. ",text,
L_0402,noninfectious diseases,T_2302,"Cancer occurs most often in adults, especially adults over the age of 50. The most common types of cancer in adults differ between males and females. The most common type of cancer in adult males is cancer of the prostate gland. The prostate gland is part of the male reproductive system. About one third of all cancers in men are prostate cancers. The most common type of cancer in adult females is cancer of the breast. About one third of all cancers in women are breast cancers. In both men and women, the second most common type of cancer is lung cancer. Most cases of lung cancer develop in people who smoke. Childhood cancer is rare. The main type of cancer in children is leukemia. It makes up about one third of all childhood cancers. It occurs when the body makes abnormal white blood cells. ",text,
L_0402,noninfectious diseases,T_2303,"Many cases of cancer can be cured if the cancer is diagnosed and treated early. Treatment often involves removing a tumor with surgery. This may be followed by other types of treatments. These treatments may include drugs and radiation, both of which target and kill cancer cells. Its important to know the warning signs of cancer so it can be diagnosed as early as possible. Having warning signs doesnt mean that you have cancer, but you should check with a doctor to be sure. Warning signs of cancer include: a change in bowel or bladder habits. a sore that doesnt heal. unusual bleeding or discharge. a lump in the breast or elsewhere. frequent, long-term indigestion. difficulty swallowing. obvious changes in a wart or mole. persistent cough or hoarseness. ",text,
L_0402,noninfectious diseases,T_2304,"Making healthy lifestyle choices can help prevent some types of cancer. For example, you can reduce your risk of lung cancer by not smoking. You can reduce your risk of skin cancer by using sunscreen (see Figure 21.6). ",text,
L_0402,noninfectious diseases,T_2305,"Diabetes is another type of noninfectious disease. Diabetes occurs when the pancreas doesnt make enough insulin or else the bodys cells are resistant to the effects of insulin. Insulin is a hormone that helps cells absorb glucose from the blood. When there is too little insulin or cells do not respond to it, the blood contains too much glucose. High glucose levels in the blood can damage blood vessels and other cells in the body. The kidneys work harder to filter the extra glucose from the blood and excrete it in urine. This leads to frequent urination, which in turn causes excessive thirst. Watch this short video for an animated introduction to diabetes, its causes, and its consequences:  MEDIA Click image to the left or use the URL below. URL:  There are two main types of diabetes: type 1 diabetes and type 2 diabetes. The two types of diabetes have different causes. ",text,
L_0402,noninfectious diseases,T_2306,"Type 1 diabetes is caused by the immune system attacking and destroying normal cells of the pancreas. As a result, the cells can no longer produce insulin. Why the immune system acts this way is not known for certain. Its possible that a virus may trigger the attack. This type of diabetes usually develops in childhood or adolescence. At present, there is no known way to prevent the development of type 1 diabetes. However, it is a treatable disease. Treatment of type 1 diabetes includes: taking several insulin injections every day or using an insulin pump (see Figure 21.7). monitoring blood glucose levels several times a day. eating a healthy diet that spreads out carbohydrate intake throughout the day. regular physical activity, which helps the body use insulin more efficiently. regular medical checkups. ",text,
L_0402,noninfectious diseases,T_2307,"Type 2 diabetes is much more common than type 1 diabetes. Type 2 diabetes occurs when body cells no longer respond normally to insulin. The pancreas still makes insulin, but the cells of the body cant use it. Being overweight and having high blood pressure increase the chances of developing type 2 diabetes. This type of diabetes usually develops in adulthood. However, it is becoming more common in teens and children because more young people are overweight now than ever before. You can greatly reduce your risk of developing type 2 diabetes by maintaining a healthy body weight. Some cases of type 2 diabetes can be cured with weight loss. However, most people with the disease need to take medicine to control their blood glucose. Regular exercise and balanced eating also help. Like people with type 1 diabetes, people with type 2 diabetes must frequently check their blood glucose. ",text,
L_0402,noninfectious diseases,T_2308,"The immune system is the body system that normally fights infections and defends against other causes of disease. When the immune system is working well, it usually keeps you from getting sick. But like any other body system, the immune system can have problems and develop diseases. Two types of immune system diseases are autoimmune diseases and allergies. ",text,
L_0402,noninfectious diseases,T_2309,"An autoimmune disease is a disease in which the immune system attacks the bodys own cells. Why this happens is not known for certain, but a combination of genetic and environmental factors are likely to be responsible. Type 1 diabetes is an example of an autoimmune disease. In this case, the immune system attacks cells of the pancreas. Two other examples are multiple sclerosis and rheumatoid arthritis. In multiple sclerosis, the immune system attacks nerve cells. This causes weakness and pain that gradually get worse over time. In rheumatoid arthritis, the immune system attacks joints. This causes joint damage and pain. These diseases cant be prevented and have no known cure. However, they can be treated with medicines that weaken the immune systems attack on normal cells. ",text,
L_0402,noninfectious diseases,T_2310,"An allergy is a disorder in which the immune system responds to a harmless substance as though it was a pathogen. Any substance that causes an allergy is called an allergen. The most common allergens are pollen, dust mites, mold, animal dander, insect stings, latex, and certain foods and medications. To see in greater detail how allergies occur, watch this animated video:  . MEDIA Click image to the left or use the URL below. URL:  Did you ever hear of hay fever? Its not really a fever, and it may have nothing to do with hay. Its actually an allergy to plant pollens. People with this type of allergy generally have seasonal allergies that come back year after year. Symptoms commonly include watery eyes and nasal congestion. Ragweed, shown blooming in Figure 21.8, causes more pollen allergies than any other plant. Allergy symptoms can range from mild to severe. Mild symptoms might include itchy eyes, sneezing, and a runny nose. Severe symptoms can cause difficulty breathing, which may be life threatening. Keep in mind that it is the immune system and not the allergen that causes the allergy symptoms. Allergy symptoms can be treated with medications such as antihistamines. Severe allergic reactions may require an injection of the hormone epinephrine. These treatments lessen or counter the immune systems response. Often, allergy symptoms can be prevented. One way is to avoid exposure to the allergens that cause your symptoms. If you are allergic to pollen, for example, you can reduce your exposure by staying inside when pollen levels are highest. Some people receive allergy shots to help prevent allergic reactions. The shots contain tiny amounts of allergens. After many months or years of shots, the immune system gets used to the allergens and no longer reacts to them. ",text,
L_0405,male reproductive system,T_2327,"The male reproductive system has two main functions: producing sperm and releasing testosterone. Sperm are male gametes, or reproductive cells. Sperm form when certain cells in the male reproductive system divide by meiosis to form haploid cells. Being haploid means they have half the number of chromosomes of other cells in the body. An adult male may produce millions of sperm each day! Testosterone is the major sex hormone in males. Testosterone has two primary roles: 1. During adolescence, testosterone causes most of the changes associated with puberty. It causes the reproduc- tive organs to mature. It also causes other adult male traits to develop. For example, it causes the voice to deepen and facial hair to start growing. 2. During adulthood, testosterone is needed for the production of sperm. ",text,
L_0405,male reproductive system,T_2328,"The male reproductive organs include the penis, testes, epididymis, vas deferens, and prostate gland. These organs are shown in Figure 22.1. The figure also shows some other parts of the male reproductive system. Find each organ in the drawing as you read about it below. For a cartoon about the male reproductive system, watch this video: http MEDIA Click image to the left or use the URL below. URL:  The penis is an external, cylinder-shaped organ that contains the urethra. The urethra is the tube that carries urine out of the body. It also carries sperm out of the body. The two testes (testis, singular) are oval organs that produce sperm and secrete testosterone. They are located inside a sac called the scrotum that hangs down outside the body. The scrotum also contains the epididymis. ",text,
L_0405,male reproductive system,T_2329,"Sperm are tiny cells. In fact, they are the smallest of all human cells. They have a structure that suits them well to perform their function. ",text,
L_0405,male reproductive system,T_2330,"As you can see in Figure 22.2, a sperm has three main parts: the head, connecting piece (or midpiece), and tail. 1. The head of the sperm contains the nucleus. The nucleus holds the chromosomes. In humans, the nucleus of a sperm cell contains 23 chromosomes. The acrosome on the head contains enzymes that help the sperm penetrate an egg. 2. The connecting piece of the sperm is packed with mitochondria. Mitochondria are organelles in cells that produce energy. Sperm use the energy to move. 3. The tail of the sperm moves like a propeller. It spins around and around and pushes the sperm forward. Sperm can travel about 30 inches per hour. ",text,
L_0405,male reproductive system,T_2331,"It takes up to two months for mature sperm to form. The process occurs in several steps: 1. Special cells in the testes go through mitosis to make identical copies of themselves. 2. The copies of the original cells divide by meiosis. This results in haploid cells called spermatids. These cells lack tails and cannot yet swim. 3. Spermatids move from the testes to the epididymis, where they slowly mature. For example, they grow a tail and lose some of the cytoplasm from the head. 4. Once sperm are mature, they can swim. The mature sperm remain in the epididymis until it is time for them to leave the body. Sperm leave the epididymis through the vas deferens. As they travel through the vas deferens, they pass by the prostate and other glands. The sperm mix with secretions from these glands, forming semen. Semen travels through the urethra and leaves the body through the penis. A teaspoon of semen may contain as many as half a billion sperm! ",text,
L_0406,female reproductive system,T_2332,"Two functions of the female reproductive system are similar to the functions of the male reproductive system: producing gametes and secreting a major sex hormone. In the case of females, however, the gametes are eggs, and they are produced by the ovaries. The hormone is estrogen, which is the main sex hormone in females. Estrogen has two major roles: During adolescence, estrogen causes the changes of puberty. It causes the reproductive organs to mature. It also causes other female traits to develop. For example, it causes the breasts to grow and the hips to widen. During adulthood, estrogen is needed for a woman to release eggs from the ovaries. The female reproductive system has another important function, which is not found in males. It supports a baby as it develops before birth. It also gives birth to the baby at the end of pregnancy. ",text,
L_0406,female reproductive system,T_2333,"The female reproductive organs include the ovaries, fallopian tubes, uterus, and vagina. These organs are shown in Figure 22.3, along with some other structures of the female reproductive system. Find each organ in the drawing as you read about it below. For a cartoon about the female reproductive system, watch this video: http://education-por The two ovaries are small, oval organs on either side of the abdomen. Each ovary contains thousands of eggs. However, the eggs do not develop fully until a female has gone through puberty. Then, about once a month, an egg is released by one of the ovaries. The ovaries also secrete estrogen. The two fallopian tubes are thin tubes that are connected to the uterus and extend almost to the ovaries. The upper end of each fallopian tube has fingers (called fimbriae) that sweep an egg into the fallopian tube when it is released by the ovary. The egg then passes through the fallopian tube to the uterus. If an egg is fertilized, this occurs in the fallopian tube. The uterus is a hollow organ with muscular walls. The uterus is where a baby develops until birth. The walls of the uterus stretch to accommodate the growing fetus. The muscles in the walls contract to push the baby out during birth. The uterus is connected to the vagina by a small opening called the cervix. The vagina is a cylinder-shaped organ that opens to the outside of the body. The other end joins with the uterus. Sperm deposited in the vagina swim up through the cervix, into the uterus, and from there into a ",text,
L_0406,female reproductive system,T_2334,"When a baby girl is born, her ovaries contain all of the eggs they will ever produce. But these eggs are not fully developed. They develop only after the female reaches puberty at about age 12 or 13. Then, just one egg develops each month until she reaches her 40s or early 50s. ",text,
L_0406,female reproductive system,T_2335,"Human eggs are very large cells. In fact, they are the largest of all human cells. You can even see an egg without a microscope. Its almost as big as the period at the end of this sentence. Like a sperm cell, an egg cell is a haploid cell with half the number of chromosomes of other cells in the body. Unlike a sperm cell, the egg lacks a tail and contains a lot of cytoplasm. ",text,
L_0406,female reproductive system,T_2336,"Egg production takes place in the ovaries. It occurs in several steps: 1. Before birth, special cells in the ovaries go through mitosis to make identical daughter cells. 2. The daughter cells then start to divide by meiosis. However, they go though only the first of the two cell divisions of meiosis at this time. They remain in that stage until the girl goes through puberty. 3. After puberty, an egg develops in an ovary about once a month. As you can see in Figure 22.4, the egg rests in a nest of cells called a follicle. The follicle and egg grow larger and go through other changes. 4. After a couple of weeks, the egg bursts out of the follicle and through the wall of the ovary. This is called ovulation. After ovulation occurs, the moving fingers of the nearby fallopian tube sweep the egg into the tube. Fertilization may occur if sperm reach the egg while it is passing through the fallopian tube. If this happens, the egg finally completes meiosis. This results in two daughter cells that differ in size. The smaller cell is called a polar body. It soon breaks down and disappears. The larger cell is the fertilized egg, which will develop into a new human being. ",text,
L_0406,female reproductive system,T_2337,"Egg production in the ovary is part of the menstrual cycle. The menstrual cycle is a series of changes in the reproductive system of mature females that repeats every month on average. These changes include the development of an egg and follicle in the ovary. While the egg is developing, other changes are taking place in the uterus. It develops a thick lining that is full of tiny blood vessels. The lining prepares the uterus to receive a fertilized egg if fertilization actually takes place. If fertilization doesnt occur, the egg passes through the uterus and vagina and out of the body. The lining of the uterus also breaks down. Blood and other tissues from the lining pass through the vagina and leave the body. This is called menstruation. Menstruation is also called a menstrual period. It typically lasts about 4 days. When the menstrual period ends, the cycle begins repeats. ",text,
L_0407,reproduction and life stages,T_2338,"When a sperm penetrates the cell membrane of an egg, it triggers the egg to complete meiosis. The sperm also undergoes changes. Its tail falls off, and its nucleus fuses with the nucleus of the egg. The resulting cell, called a zygote, contains the diploid number of chromosomes. Half of the chromosomes come from the egg, and half come from the sperm. You can watch the process of fertilization and the development of a baby until birth in this amazing video:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0407,reproduction and life stages,T_2339,"The zygote spends the next few days traveling down the fallopian tube toward the uterus, where it will take up residence. As it travels, it divides many times by mitosis. It soon forms a tiny, fluid-filled ball of cells called a blastocyst. The blastocyst has an inner and outer layer of cells, as you can see in Figure 22.5. The inner layer, called the embryoblast, will develop into the new human being. The outer layer, called the trophoblast, will develop into other structures needed to support the new organism. ",text,
L_0407,reproduction and life stages,T_2340,"The blastocyst continues down the fallopian tube until it reaches the uterus, about 4 or 5 days after fertilization. When the outer cells of the blastocyst contact cells lining the uterus (the endometrium in Figure 22.5), the blastocyst embeds itself in the uterine lining. This process is called implantation. It generally occurs about a week after fertilization. ",text,
L_0407,reproduction and life stages,T_2341,"After implantation occurs, the blastocyst is called an embryo. The embryonic stage lasts from the end of the first week following fertilization through the end of the eighth week. During this time, the embryo grows in size and becomes more complex. It develops specialized cells and tissues. Most organs also start to form. You can see some of the specific changes that take place during weeks four to eight of the embryonic period in Figure 22.6. By the end of week eight, the embryo is about 30 millimeters (just over 1 inch) in length. It may also have begun to move. ",text,
L_0407,reproduction and life stages,T_2342,"From the eighth week following fertilization until birth, the developing human being is called a fetus. Birth typically occurs at about 38 weeks after fertilization, so the fetal period generally lasts about 30 weeks. During this time, the organs complete their development. The fetus also grows rapidly in length and weight. Some of the specific changes that occur during the fetal stage are listed in Figure 22.7. By the 38th week, the fetus is fully developed and ready to be born. A 38-week fetus normally ranges from about 36 to 51 centimeters (1420 inches) in length and weighs between 2.7 and 4.6 kilograms (about 610 pounds). ",text,
L_0407,reproduction and life stages,T_2343,"The fetus could not grow and develop without oxygen and nutrients from the mother. Wastes from the fetus also must be removed in order for it to survive. The exchange of these substances between the mother and fetus occurs through the placenta. The placenta is a temporary organ that starts to form shortly after implantation. It forms from the trophoblast layer of cells in the blastocyst and from maternal cells in the uterus. The placenta continues to develop and grow to meet the needs of the growing fetus. A fully developed placenta, like the one in Figure 22.8, is made up of a large mass of blood vessels from both mother and fetus. The maternal and fetal vessels are close together but separated by tiny spaces. This allows the mothers and fetuss blood to exchange substances across their capillary walls without the blood actually mixing. The fetus is connected to the placenta through the umbilical cord. This is a long tube that contains two arteries and a vein. Blood from the fetus enters the placenta through the umbilical arteries. It exchanges gases and other substances with the mothers blood. Then it travels back to the fetus through the umbilical vein. Another structure that supports the fetus is the amniotic sac. This is a membrane that surrounds and protects the fetus. It contains amniotic fluid, which consists of water and dissolved substances. The fluid allows the fetus to move freely until it grows to fill most of the available space. The fluid also cushions the fetus and helps protect it from injury. ",text,
L_0407,reproduction and life stages,T_2344,Pregnancy is the carrying of one or more offspring from the time of implantation until birth. It is the development of an embryo and fetus from the expectant mothers point of view. ,text,
L_0407,reproduction and life stages,T_2345,"The pregnant mother plays a critical role in the development of the embryo and fetus. She must avoid toxic substances such as alcohol, which can damage the developing offspring. She also must provide all the nutrients and other substances needed for normal growth and development. Most nutrients are needed in greater amounts by a pregnant woman because she is literally eating for two people. Thats why its important for a woman to eat plenty of nutritious foods during pregnancy. The pregnant woman in Figure 22.9 is eating a variety of fresh fruits, which provide energy, vitamins, and other nutrients. ",text,
L_0407,reproduction and life stages,T_2346,"Near the time of birth, the amniotic sac breaks in a gush of liquid. Labor usually begins within a day of this event. Labor involves contractions of the muscular walls of the uterus. With the mothers help, the contractions eventually push the fetus out of the uterus and through the vagina. Within seconds of birth, the umbilical cord is cut. Without this connection to the placenta, the baby cant exchange gases, so carbon dioxide quickly builds up in the babys blood. This stimulates the babys brain to trigger breathing, and the newborn takes her first breath. ",text,
L_0407,reproduction and life stages,T_2347,"For the first year after birth, a baby is referred to as an infant. Childhood begins at the age of two years and continues until puberty. Adolescence begins with puberty and lasts until adulthood. ",text,
L_0407,reproduction and life stages,T_2348,"The first year of life after birth is called infancy. During infancy, a baby grows very quickly. The babys length typically doubles and her weight triples by her first birthday. Many other important changes also occur during infancy: The baby starts smiling, usually by about 6 weeks of age (see Figure 22.10). The baby starts noticing people and grabbing toys and other objects The baby teeth start to come in, usually by 6 months of age. The baby begins making babbling sounds. By the end of the first year, the baby may be saying a few words, such as Mama and Dada. The baby learns to sit, crawl, and stand. By the end of the first year, the baby may be starting to walk. ",text,
L_0407,reproduction and life stages,T_2349,"Childhood begins after the babys first birthday and continues until puberty. Between 1 and 3 years of age, a child is called a toddler. During the toddler stage, growth is still very rapid, but not as rapid as it was during infancy. Toddlers learn many new words and starts putting them together in simple sentences. Motor skills also develop quickly during the toddler stage. By the age of 3 years, most children can run and climb steps. They can hold crayons and scribble with them. They can also feed themselves, and most can use the toilet. From age 3 until puberty, growth slows down. The body also changes shape. The arms and legs grow longer relative to the trunk. Children continue to develop new motor skills. For example, many young children learn how to ride a tricycle and then a bicycle. Most learn how to play games and sports. By the age of 6 years, children start losing their baby teeth. Permanent teeth come in to replace them. Most children have started school by this age. They typically start learning to read and write around age 6 or 7 (see Figure 22.11). During the later years of childhood, children also start to develop friendships and become less dependent on their parents. ",text,
L_0407,reproduction and life stages,T_2350,"Puberty is the stage of life when a child becomes sexually mature. Puberty lasts from about 10 to 16 years of age in girls and from about 12 to 18 years of age in boys. In both girls and boys, puberty begins when the pituitary gland signals the gonads (ovaries or testes) to start secreting sex hormones (estrogen in girls, testosterone in boys). Sex hormones, in turn, cause many other changes to take place. In girls, estrogen causes the following changes to occur: The uterus and ovaries grow. The ovaries start releasing eggs. The menstrual cycle begins. Pubic hair grows. The hips widen and the breasts develop. In boys, testosterone causes these changes to take place: The penis and testes grow. The testes start producing sperm. Pubic and facial hair grow. The shoulders broaden. The voice becomes deeper as the larynx in the throat grows larger (see Figure 22.12). Girls and boys of the same age are similar in height during childhood. In both girls and boys, growth in height and weight is very fast during puberty. But boys grow more quickly that girls do, and their period of rapid growth also lasts longer. In addition, boys generally start puberty later than girls, so they have a longer period of childhood growth. For all these reasons, by the end of puberty, the average height of boys is 10 centimeters (about 4 inches) greater than the average height of girls. ",text,
L_0407,reproduction and life stages,T_2351,"Adolescence is the stage of life between the start of puberty and the beginning of adulthood. Adolescence begins with the physical changes of puberty. It also includes many other changes, including mental, emotional, and social changes. During adolescence: Teens develop new thinking abilities. For example, they develop the ability to understand abstract ideas, such as honesty and freedom. Their ability to think logically also improves. They usually get better at problem solving as well. Teens try to establish a sense of identity. They typically become increasingly independent from their parents. Many teens have emotional ups and downs. This is at least partly due to their changing hormone levels. Teens usually start spending more time with their peers, like the girls in Figure 22.13. Adolescents usually spend much more time with their friends and classmates than they do with family members. ",text,
L_0407,reproduction and life stages,T_2351,"Adolescence is the stage of life between the start of puberty and the beginning of adulthood. Adolescence begins with the physical changes of puberty. It also includes many other changes, including mental, emotional, and social changes. During adolescence: Teens develop new thinking abilities. For example, they develop the ability to understand abstract ideas, such as honesty and freedom. Their ability to think logically also improves. They usually get better at problem solving as well. Teens try to establish a sense of identity. They typically become increasingly independent from their parents. Many teens have emotional ups and downs. This is at least partly due to their changing hormone levels. Teens usually start spending more time with their peers, like the girls in Figure 22.13. Adolescents usually spend much more time with their friends and classmates than they do with family members. ",text,
L_0407,reproduction and life stages,T_2352,"Adulthood doesnt have a definite starting point. Teens may become physically mature by the age 16 years, but they are not adults in a legal sense until they are older. For example, in the U.S., you must be 18 years old to vote or serve in the armed forces. You must be 21 years old before you can take on many legal and financial responsibilities. Once adulthood begins, it can be divided into three stages: early, middle, and late adulthood. ",text,
L_0407,reproduction and life stages,T_2353,"Early adulthood refers to the 20s and early 30s. During early adulthood, most people are at their physical peak, and they are usually in good health. Often, they are completing their education and getting established in the workforce. Many people become engaged or marry during this time. ",text,
L_0407,reproduction and life stages,T_2354,"Middle adulthood is the period from the mid-30s to the mid-60s. During this stage of life, people start showing signs of aging. Their hair may thin and slowly turn gray. Their skin develops wrinkles. The risk of serious health problems increases. For example, cardiovascular diseases, cancer, and type 2 diabetes become more common in people of middle age. This is also the stage when many people raise a family and strive to attain career goals. ",text,
L_0407,reproduction and life stages,T_2355,"Late adulthood begins in the mid-60s and continues until death. This is the stage of life when most people retire from work. This frees up their time for hobbies, grandchildren, or other interests. For example, the man in Figure During late adulthood, the risk of developing diseases such as cardiovascular diseases and cancer continues to rise. Most people also have a decline in strength and stamina. Their senses may start failing, and their reflex time typically increases. Their immune system also doesnt work as well as it used to. As a result, common diseases like the flu may become more serious and even lead to death. The majority of late adults develop arthritis, and as many as one in four develop Alzheimers disease. Despite problems such as these, many people remain healthy and active into their 80s and even 90s. Do you want ",text,
L_0408,reproductive system health,T_2356,"A sexually transmitted infection (STI) is a disease that spreads mainly through sexual contact. STIs are caused by pathogens that enter the body through the reproductive organs. Many STIs also spread through body fluids such as blood. For example, a shared tattoo needle is one way that some STIs can spread. Some STIs can also spread from a mother to her infant during birth. ",text,
L_0408,reproductive system health,T_2357,"STIs are more common in teens and young adults than in older people. One reason is that young people are more likely to engage in risky behaviors. They also may not know how STIs spread. Instead, they may believe myths about STIs, like those in Table 22.1. Knowing the facts is important to prevent the spread of STIs. Myth If you are sexually active with just one person, then you cant get STIs. If you dont have any symptoms, then you dont have an STI. Getting STIs is no big deal, because they can be cured with medicines. Fact The only sure way to avoid getting STIs is to practice abstinence from sexual activity. Many STIs do not cause symptoms, especially in fe- males. Only some STIs can be cured with medicines; others cannot be cured. ",text,
L_0408,reproductive system health,T_2358,"A number of STIs are caused by bacteria. Bacterial STIs can usually be cured with antibiotics. However, some people with bacterial STIs may not have symptoms so they fail to get treatment. Left untreated, these infections may damage reproductive organs and lead to an inability to have children. Three bacterial STIs are chlamydia, gonorrhea, and syphilis. Chlamydia is the most common bacterial STI in the U.S. Females are more likely to develop it than males. Symptoms may include burning during urination and a discharge from the vagina or penis. Gonorrhea is another common bacterial STI. Symptoms may include painful urination and a discharge from the vagina or penis. Syphilis is a very serious STI but somewhat less common than chlamydia or gonorrhea. It usually begins with a small sore on the genitals. This is followed a few months later by a rash and flu-like symptoms. If syphilis isnt treated, it can eventually damage the heart, brain, and other organs and even cause death. ",text,
L_0408,reproductive system health,T_2359,"Several STIs are caused by viruses. Viral STIs cant be cured with antibiotics. Other drugs may help control the symptoms of viral STIs, but the infections usually last for life. Three viral STIs are genital warts, genital herpes, and AIDS. Genital herpes is a common STI caused by a herpes virus. The virus causes painful blisters on the penis or near the vaginal opening. The blisters generally go away on their own, but they may return repeatedly throughout life. There is no cure for genital herpes, but medicines can help prevent or shorten outbreaks. Acquired Immunodeficiency Syndrome (AIDS) is caused by human immunodeficiency virus (HIV). HIV destroys lymphocytes that normally fight infections. AIDS develops if the number of lymphocytes drops to a very low level. People with AIDS come down with diseasessuch as certain rare cancersthat almost never occur in people with a healthy immune system. Medicines can delay the progression of an HIV infection and may prevent AIDS from developing. Genital warts is an STI caused by human papilloma virus (HPV), which is pictured in Figure 22.15. This is one of the most common STIs in U.S. teens. Genital warts cant be cured, but a vaccine can prevent most HPV infections. The vaccine is recommended for boys and girls starting at 11 or 12 years of age. Its important to prevent HPV infections because they may lead to cancer later in life. ",text,
L_0408,reproductive system health,T_2360,Other reproductive system disorders include injuries and noninfectious diseases. These are different in males and females. ,text,
L_0408,reproductive system health,T_2361,"Most common disorders of the male reproductive system involve the testes. They include injuries and cancer. Injuries to the testes are very common. In teens, such injuries occur most often while playing sports. Injuries to the testes are likely to be very painful and cause bruising and swelling. However, they generally subside fairly quickly. Cancer of the testes is most common in males aged 15 to 35. It occurs when cells in the testes grow out of control and form a tumor. If found early, cancer of the testes usually can be cured with surgery. ",text,
L_0408,reproductive system health,T_2362,"Disorders of the female reproductive system may involve the vagina, uterus, or ovaries. They may also affect the breasts. Vaginitis is a very common disorder. Symptoms include redness and itching of the vagina. It may be caused by soap or bubble bath. Another possible cause is a yeast infection. Yeast normally grow in the vagina. If they multiple too quickly, they may cause irritation. A yeast infection can be treated with medication. Cysts may develop in the ovaries. A cyst is a sac filled with fluid or other material. Ovarian cysts are usually harmless and often disappear on their own. However, some cysts may be painful and require surgery. Many females experience abdominal cramps during menstruation. This is usually normal and not a cause for concern. Exercise, heat, or medication may help relieve the pain. In severe cases, prescription medicine may be needed. Breast cancer is the most common type of cancer in females. It occurs when cells in the breast grow out of control and form a tumor. Breast cancer is rare in teens but becomes more common as females get older. Regular screening is recommended for most women starting around age 40. If found early, breast cancer usually can be cured with surgery. ",text,
L_0408,reproductive system health,T_2363,"Maintaining overall good health will help keep your reproductive system healthy. You should eat right, get regular exercise, and follow other healthy lifestyle behaviors. In addition, the following practices will help keep the reproductive system healthy: Keep the genitals clean. A daily shower or bath is all thats needed. Avoid harsh soaps or other personal hygiene products that may be irritating. Avoid risky behaviors. This includes contact with blood or dirty needles as well as sexual activity. If you are a girl and use tampons, be sure to change them every 4 to 6 hours. This will reduce your risk of toxic shock syndrome. This is a very dangerous condition that may occur if tampons are left in too long. If you are a boy, wear a protective cup if you play a contact sport. This will help protect the testes from injury. You should also learn how to check yourself for testicular cancer (see Figure 22.16). You can learn how by watching this video:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0409,what is ecology,T_2364,"Organisms are individual living things. They range from microscopic bacteria to gigantic blue whales (see Figure must be obtained from the environment. Biotic factors are all of the living or once-living aspects of the environment. They include all the organisms that live there as well as the remains of dead organisms. Abiotic factors are all of the aspects of the environment that have never been alive. They include factors such as sunlight, minerals in soil, temperature, and moisture. ",text,
L_0409,what is ecology,T_2365,"Ecologists study organisms and environments at several different levels, from the individual to the biosphere. The levels are depicted in Figure 23.2 and described below. For a video introduction to the levels of organization in ecology, click on this link:  . MEDIA Click image to the left or use the URL below. URL:  An individual is an organism, or single living thing. A population is a group of individuals of the same species that live in the same area. Members of the same population generally interact with each other. A community is made up of all the populations of all the species that live in the same area. Populations in a community also generally interact with each other. ",text,
L_0410,populations,T_2366,"Population size is the number of individuals in a population. Population size influences the chances of a species surviving or going extinct. If a species populations become very small, the species may be at risk of going extinct. ",text,
L_0410,populations,T_2367,"Another sign of a species state of health is the density of its populations. Population density is the average number of individuals in a population for a given area. Density is a measure of how crowded or spread out the individuals in a population are on average. For example, a population of 100 deer that live in an area of 10 square kilometers has a population density of 10 deer per square kilometer. Population density is an average measure. Often, individuals in a population are not spread out evenly. Instead, they may live in clumps or some other pattern. How individuals in a population are distributed, or spread throughout their area, is called population distribution. You can see different patterns of population distribution in Figure 23.3. Different patterns characterize different species and types of environments, as you can read in the figure. ",text,
L_0410,populations,T_2368,"Whether its populations are growing or shrinking in size may be another indicator of a species health. Individuals may be added to a population through births and the migration of individuals into the population. Individuals may be lost from a population through deaths and the migration of individuals out of the population. The population growth rate is how quickly a population changes in size over time. The rate of growth of a population may be positive or negative. A positive growth rate means that the population is increasing in size because more people are being added than lost. A negative growth rate means that the population is decreasing in size because more people are being lost than added. Populations may show different patterns of growth. The growth pattern depends partly on the conditions under which a population lives. Two common growth patterns are exponential growth and logistic growth. Both are represented in Figure 23.4. With exponential growth, the population starts out growing slowly. As population size increases, the growth rate also increases. The larger the population becomes, the more quickly it grows. This type of growth generally occurs only when a population is living under ideal conditions. However, it cant continue for very long. With logistic growth, the population starts out growing slowly, and then the rate of growth increasesbut only to a point. The rate of growth tapers off as the population size approaches its carrying capacity. Carrying capacity is the largest population size that can be supported in an area without harming the environment. This type of growth characterizes many populations. ",text,
L_0410,populations,T_2369,"Another way of describing a population is its age-sex structure. This refers to the numbers of individuals of each sex and age in the population. The age-sex structure of a population may influence the population growth rate. This is because only individuals of certain ages are able to reproduce, and because individuals of certain ages may be more likely to die. For example, if there are many individuals of reproductive age, there are likely to be many births, causing the population to grow rapidly. The age-sex structure of a population is often represented with a special bar graph called a population pyramid. You can see an example of a population pyramid in Figure 23.5. The graph in the figure actually has a pyramid shape because the bars become narrower from younger to older ages. However, this is not always the case. In some populations, for example, there may be more people at older than younger ages, resulting in a top-heavy population pyramid. Learn more about population pyramids and what you can learn from them, watch this TED video: http://w MEDIA Click image to the left or use the URL below. URL: ",text,
L_0410,populations,T_2370,"Human beings have been called the most successful weed species on Earth. Like garden weeds, populations of human beings grow quickly and disperse rapidly. Human beings have colonized almost every terrestrial part of the planet. Overall, the human population has had a pattern of exponential growth, as you can see in Figure 23.6. The early human population grew very slowly. However, as the population grew larger, it started to grow more rapidly. ",text,
L_0410,populations,T_2370,"Human beings have been called the most successful weed species on Earth. Like garden weeds, populations of human beings grow quickly and disperse rapidly. Human beings have colonized almost every terrestrial part of the planet. Overall, the human population has had a pattern of exponential growth, as you can see in Figure 23.6. The early human population grew very slowly. However, as the population grew larger, it started to grow more rapidly. ",text,
L_0410,populations,T_2371,"The earliest members of the human species evolved around 200,000 years ago in Africa. Early humans lived in small populations of nomadic hunters and gatherers. Human beings remained in Africa until about 40,000 years ago. After that, they spread throughout Europe, Asia, and Australia. By 10,000 years ago, the first human beings colonized the Americas. During this long period of time, the total number of human beings increased very slowly. Birth rates were fairly high but so were death rates, producing low rates of population growth. Human beings invented agriculture about 10,000 years ago. This provided a bigger, more dependable food supply. It also allowed people to settle down in villages and cities for the first time. Birth rates went up because there was more food and settled life had other advantages. Death rates also rose because of crowded living conditions and diseases that spread from domestic animals. Because the higher birth rates were matched by higher death rates, the human population continued to grow very slowly. ",text,
L_0410,populations,T_2372,"Major changes in the human population first began in the 1700s. These changes occurred mainly in Europe, North America, and a few other places that became industrialized. First death rates fell. Then, somewhat later, birth rates also fell. These changes in death and birth rates affected the rate of population growth and are referred to as the demographic transition. The graph in Figure 23.7 shows the stages in which the demographic transition occurred. You can learn more about the stages by watching this video: http://education-portal.com/academy/lesson/what-is-d In Stage 1, both birth and death rates were high so population growth was slow. In Stage 2, death rates fell while birth rates remained high. Why did death rates fall? There were several reasons, including new scientific knowledge of the causes of disease. Water supplies were cleaned up and sewage was disposed of more safely. Better farming techniques and machines increased the food supply and the distribution of food. For all these reasons, death rates fell, especially in children. Birth rates, on the other hand, remained high. This resulted in faster population growth. Before long, birth rates also started to fall. People started having fewer children because large families became too expensive. For example, with better farming machines, farm families no longer needed as many children to work in the fields. Laws were also passed that required children to go to school. They could no longer work and help support the family. Having many children became too costly. Eventually, birth rates fell to match death rates (Stage 4). As a result, population growth slowed down. ",text,
L_0410,populations,T_2373,"Just as they did in Europe and North America, death rates have fallen throughout the world. No country today remains in Stage 1 of the demographic transition. However, birth rates are still high in many of the poorest countries of the world. These populations seem to be stuck in Stage 2 or 3 of the demographic transition. They have high population growth rates because low death rates are not matched by equally low birth rates. Whether these populations will ever enter Stage 4 and attain very low rates of population growth is uncertain. ",text,
L_0410,populations,T_2374,"As of 2014, there were more than 7 billion human beings on planet Earth. That number is increasing rapidly. More than 200,000 people are added to the human population each day! At this rate, the human population will pass 9 billion by 2050. Many experts think that the human population has reached its carrying capacity. It has already harmed the environ- ment. An even larger human population may cause severe environmental problems. It could also lead to devastating outbreaks of disease, starvation, and war. To solve these problems, two approaches may be needed: Slow down human population growth so there are fewer people. Distribute Earths resources more fairly so that everyone has enough. Hopefully, we will act before its too late. Otherwise, the planet may be ruined for future generations of human beings and other species. ",text,
L_0413,biomes,T_2389,Terrestrial biomes are land-based biomes. They range from arctic tundra to tropical rainforests. Figure 23.18 shows the locations of the worlds major terrestrial biomes. ,text,
L_0413,biomes,T_2390,"Plants are the primary producers in terrestrial biomes. They make food for themselves and other organisms by photosynthesis. The major plants in a given biome, in turn, help determine the types of animals and other organisms that can live there. Which plants grow in a given biome depends mainly on climate. Climate is the average weather in a place over a long period of time. The major climatic factors affecting plant growth are temperature and moisture. ",text,
L_0413,biomes,T_2391,"You can read about three different terrestrial biomes in Figure 23.19: tropical rainforest, temperate grassland, and tundra. You can learn more about these and other terrestrial biomes by watching this video:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0413,biomes,T_2392,"Aquatic biomes are water-based biomes. They include both freshwater biomes, such as rivers and lakes, and marine biomes, which are salt-water biomes in the ocean. The primary producers in most aquatic biomes are phytoplankton. Phytoplankton consist of microscopic bacteria and tiny algae that make food by photosynthesis. Unlike terrestrial biomes, which are determined mainly by temperature and moisture, aquatic biomes are determined mainly by sunlight and dissolved substances in the water. These factors, in turn, depend mainly on depth of water and distance from shore. ",text,
L_0413,biomes,T_2393,"Only the top 200 meters or so of water receive enough sunlight for photosynthesis. This part of the water is called the photic zone. Below 200 meters, there is too little sunlight for photosynthesis to take place. This part of the water is called the aphotic zone. In this zone, food must come from other sources. It may be made by chemosynthesis, in which microorganisms use energy in chemicals instead of sunlight to make food. Or, food may drift down from the water above. ",text,
L_0413,biomes,T_2394,"In addition to sunlight, aquatic producers also need dissolved oxygen and nutrients. Water near the surface generally contains more dissolved oxygen than deeper water. Many nutrients enter the water from the land. Therefore, water nearer shore usually contains more dissolved nutrients than water farther from shore. ",text,
L_0413,biomes,T_2395,"A lake is an example of a freshwater biome. Water in a lake generally forms three different zones based on water depth and distance from shore. The shallow water near the shore is called the littoral zone. It has diverse community of organisms. There is adequate light for photosynthesis and plenty of dissolved oxygen and nutrients. Producers include algae and aquatic plants (see Figure 23.20). Animals in this zone may include insects, crustaceans, fish, and turtles. The top layer of water farther from shore is called the limnetic zone. There is enough light for photosynthesis and plenty of dissolved oxygen. However, dissolved nutrients tend not to be as plentiful as they are in the littoral zone. Producers here are mainly phytoplankton. A variety of zooplankton and fish also occupy this zone. The deeper water of a lake makes up the profundal zone. There isnt enough light for photosynthesis in this zone, so most organisms here eat dead organisms that drift down from the water above. Organisms in the profundal zone may include clams, snails, and some species of fish. ",text,
L_0413,biomes,T_2396,"Zones in the oceans include the intertidal, pelagic, and benthic zones. The types of organisms found in these ocean zones are also determined by such factors as depth of water and distance from shore, among other factors. One of the most familiar ocean zones is the intertidal zone. This is the narrow strip along a coastline that is covered by water at high tide and exposed to air at low tide. You can see an example of an intertidal zone in Figure 23.21. There are plenty of nutrients and sunlight in the intertidal zone. Producers here include phytoplankton and algae. Other organisms include barnacles, snails, crabs, and mussels. They must have adaptations for the constantly changing conditions in this zone. Other ocean zones are farther from shore in the open ocean. All the water in the open ocean is called the pelagic zone. It is further divided by depth: The top 200 meters of water is the photic zone. Producers here include seaweeds and phytoplankton. Other organisms are plentiful. They include zooplankton and animals such as fish, whales, and dolphins. ",text,
L_0413,biomes,T_2396,"Zones in the oceans include the intertidal, pelagic, and benthic zones. The types of organisms found in these ocean zones are also determined by such factors as depth of water and distance from shore, among other factors. One of the most familiar ocean zones is the intertidal zone. This is the narrow strip along a coastline that is covered by water at high tide and exposed to air at low tide. You can see an example of an intertidal zone in Figure 23.21. There are plenty of nutrients and sunlight in the intertidal zone. Producers here include phytoplankton and algae. Other organisms include barnacles, snails, crabs, and mussels. They must have adaptations for the constantly changing conditions in this zone. Other ocean zones are farther from shore in the open ocean. All the water in the open ocean is called the pelagic zone. It is further divided by depth: The top 200 meters of water is the photic zone. Producers here include seaweeds and phytoplankton. Other organisms are plentiful. They include zooplankton and animals such as fish, whales, and dolphins. ",text,
L_0415,cycles of matter,T_2407,"The chemical elements and water that are needed by living things keep recycling on Earth. They pass back and forth through biotic and abiotic components of ecosystems. Thats why their cycles are called biogeochemical cycles. For example, a chemical element or water might move from organisms (bio) to the atmosphere or ocean (geo) and back to organisms again. Elements or water may be held for various periods of time in different parts of a biogeochemical cycle. An exchange pool is part of a cycle that holds a substance for a short period of time. For example, the atmosphere is an exchange pool for water. It usually holds water (as water vapor) for just a few days. A reservoir is part of a cycle that holds a substance for a long period of time. For example, the ocean is a reservoir for water. It may hold water for thousands of years. The rest of this lesson describes three biogeochemical cycles: water cycle, carbon cycle, and nitrogen cycle. ",text,
L_0415,cycles of matter,T_2408,"Water is an extremely important aspect of every ecosystem. Life cant exist without water. Most organisms contain a large amount of water, and many live in water. Therefore, the water cycle is essential to life on Earth. Water on Earth is billions of years old. However, individual water molecules keep moving through the water cycle. The water cycle is a global cycle. It takes place on, above, and below Earths surface, as shown in Figure 24.7. During the water cycle, water occurs in three different states: gas (water vapor), liquid (water), and solid (ice). Many processes are involved as water changes state to move through the cycle. Watch this video for an excellent visual introduction to the water cycle:  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0415,cycles of matter,T_2409,"Water changes to a gas by three different processes called evaporation, sublimation, and transpiration. Evaporation takes place when water on Earths surface changes to water vapor. The sun heats the water and gives water molecules enough energy to escape into the atmosphere. Most evaporation occurs from the surface of the ocean. Sublimation takes place when snow and ice on Earths surface change directly to water vapor without first melting to form liquid water. This also happens because of heat from the sun. Transpiration takes place when plants release water vapor through pores in their leaves called stomata. ",text,
L_0415,cycles of matter,T_2410,"Rising air currents carry water vapor into the atmosphere. As the water vapor rises in the atmosphere, it cools and condenses. Condensation is the process in which water vapor changes to tiny droplets of liquid water. The water droplets may form clouds. If the droplets get big enough, they fall as precipitation. Precipitation is any form of water that falls from the atmosphere. It includes rain, snow, sleet, hail, and freezing rain. Most precipitation falls into the ocean. Eventually, this water evaporates again and repeats the water cycle. Some frozen precipitation becomes part of ice caps and glaciers. These masses of ice can store frozen water for hundreds of years or even longer. Condensation may also form fog or dew. Some living things, like the lizard in Figure 24.8, depend directly on these sources of liquid water. ",text,
L_0415,cycles of matter,T_2411,Precipitation that falls on land may flow over the surface of the ground. This water is called runoff. It may eventually flow into a body of water. Some precipitation that falls on land soaks into the ground. This water becomes groundwater. Groundwater may seep out of the ground at a spring or into a body of water such as the ocean. Some groundwater is taken up by plant roots. Some may flow deeper underground to an aquifer. An aquifer is an underground layer of rock that stores water. Water may be stored in an aquifer for thousands of years. ,text,
L_0415,cycles of matter,T_2412,"The element carbon is the basis of all life on Earth. Biochemical compounds consist of chains of carbon atoms and just a few other elements. Like water, carbon is constantly recycled through the biotic and abiotic factors of ecosystems. The carbon cycle includes carbon in sedimentary rocks and fossil fuels under the ground, the ocean, the atmosphere, and living things. The diagram in Figure 24.9 represents the carbon cycle. It shows some of the ways that carbon moves between the different parts of the cycle. You can see an animated carbon cycle at this link: http://commons.w ",text,
L_0415,cycles of matter,T_2413,"Major reservoirs of carbon include sedimentary rocks, fossil fuels, and the ocean. Sediments from dead organisms may form carbon-containing sedimentary rocks. Alternatively, the sediments may form carbon-rich fossil fuels, which include oil, natural gas, and coal. Carbon can be stored in these reservoirs for millions of years. However, if fossil fuels are extracted and burned, the stored carbon enters the atmosphere as carbon dioxide. Natural processes, such as volcanic eruptions, can also release underground carbon from rocks into the atmosphere. Water erosion by runoff, rivers, and streams dissolves carbon in rocks and carries it to the ocean. Ocean water near the surface dissolves carbon dioxide from the atmosphere. Dissolved carbon may be stored in the deep ocean for thousands of years. ",text,
L_0415,cycles of matter,T_2414,"Major exchange pools of carbon include organisms and the atmosphere. Carbon cycles more quickly between these components of the carbon cycle. Photosynthesis by plants and other producers removes carbon dioxide from the atmosphere to make organic compounds for living things. Cellular respiration by living things releases carbon into the atmosphere or ocean as carbon dioxide. Decomposition of dead organisms and organic wastes releases carbon back to the atmosphere, soil, or ocean. ",text,
L_0415,cycles of matter,T_2415,"Nitrogen is another common element found in living things. It is needed to form both proteins and nucleic acids such as DNA. Nitrogen gas makes up 78 percent of Earths atmosphere. In the nitrogen cycle, nitrogen flows back and forth between the atmosphere and living things. You can see how it happens in Figure 24.10. Several different types of bacteria play major roles in the cycle. Animals get nitrogen by eating plants or other organisms that eat plants. Where do plants get nitrogen? They cant use nitrogen gas in the air. The only form of nitrogen that plants can use is in chemical compounds called nitrates. Plants absorb nitrates through their roots. This is called assimilation. Most of the nitrates are produced by bacteria that live in soil or in the roots of plants called legumes. Nitrogen-fixing bacteria change nitrogen gas from the atmosphere to nitrates in soil. When organisms die and decompose, their nitrogen is returned to the soil as ammonium ions. Nitrifying bacteria change some of the ammonium ions into nitrates. The other ammonium ions are changed into nitrogen gas by denitrifying bacteria. ",text,
L_0417,air pollution,T_2421,"The major cause of outdoor air pollution is the burning of fossil fuels. Fossil fuels are burned in power plants, factories, motor vehicles, and home heating systems. Ranching and using chemicals such as fertilizers also cause outdoor air pollution. Erosion of soil in farm fields, mining activities, and construction sites adds dust particles to the air as well. Some specific outdoor air pollutants are described in Table 25.1. Air Pollutant Sulfur oxides Nitrogen oxides Carbon monoxide Carbon dioxide Particles (dust, smoke) Mercury Smog Ground-level ozone Source coal burning motor vehicle exhaust motor vehicle exhaust all fossil fuel burning wood and coal burning coal burning coal burning motor vehicle exhaust Problem acid rain acid rain poisoning global climate change respiratory problems nerve poisoning respiratory problems respiratory problems ",text,
L_0417,air pollution,T_2422,"Outdoor air pollution causes serious human health problems. For example, pollutants in the air are major contributors to respiratory and cardiovascular diseases. Air pollution may trigger asthma attacks and heart attacks in people with underlying health problems. In fact, more people die each year from air pollution than automobile accidents. ",text,
L_0417,air pollution,T_2423,"Air pollution may also cause acid rain. This is rain that is more acidic (has a lower pH) than normal rain. Acids form in the atmosphere when nitrogen and sulfur oxides mix with water in air. Nitrogen and sulfur oxides come mainly from motor vehicle exhaust and coal burning. If acid rain falls into lakes, it lowers the pH of the water and may kill aquatic organisms. If it falls on the ground, it may damage soil and soil organisms. If it falls on plants, it may make them sick or even kill them. Acid rain also damages stone buildings, bridges, and statues, like the one in Figure 25.1. ",text,
L_0417,air pollution,T_2424,"Another major problem caused by air pollution is global climate change. Gases such as carbon dioxide from the burning of fossil fuels increase the greenhouse effect and raise Earths temperature. The greenhouse effect is a natural feature of Earths atmosphere. It occurs when certain gases in the atmosphere, including carbon dioxide, radiate the suns heat back down to Earths surface. Figure 25.2 shows how this happens. Without greenhouse gases in the atmosphere, the heat would escape into space. The natural greenhouse effect of Earths atmosphere keeps the planets temperature within a range that can support life. The rise in greenhouse gases due to human actions is too much of a good thing. It increases the greenhouse effect and causes Earths average temperature to rise. Rising global temperatures, in turn, are melting polar ice caps and glaciers. Figure 25.3 shows how much smaller the Arctic ice cap was in 2012 than it was in 1984. With more liquid water on Earths surface, sea levels are rising. Adding more heat energy to Earths atmosphere also causes more extreme weather and changes in precipitation patterns. Global warming is already causing food and water shortages and species extinctions. These problems will only grow worse unless steps are taken to curb greenhouse gases and global climate change. ",text,
L_0417,air pollution,T_2424,"Another major problem caused by air pollution is global climate change. Gases such as carbon dioxide from the burning of fossil fuels increase the greenhouse effect and raise Earths temperature. The greenhouse effect is a natural feature of Earths atmosphere. It occurs when certain gases in the atmosphere, including carbon dioxide, radiate the suns heat back down to Earths surface. Figure 25.2 shows how this happens. Without greenhouse gases in the atmosphere, the heat would escape into space. The natural greenhouse effect of Earths atmosphere keeps the planets temperature within a range that can support life. The rise in greenhouse gases due to human actions is too much of a good thing. It increases the greenhouse effect and causes Earths average temperature to rise. Rising global temperatures, in turn, are melting polar ice caps and glaciers. Figure 25.3 shows how much smaller the Arctic ice cap was in 2012 than it was in 1984. With more liquid water on Earths surface, sea levels are rising. Adding more heat energy to Earths atmosphere also causes more extreme weather and changes in precipitation patterns. Global warming is already causing food and water shortages and species extinctions. These problems will only grow worse unless steps are taken to curb greenhouse gases and global climate change. ",text,
L_0417,air pollution,T_2425,"You may be able to avoid some of the health effects of outdoor air pollution by staying indoors on high-pollution days. However, some indoor air is just as polluted as outdoor air. ",text,
L_0417,air pollution,T_2426,"One source of indoor air pollution is radon gas. Radon is a radioactive gas that may seep into buildings from rocks underground. Exposure to radon gas may cause lung cancer. Another potential poison in indoor air is carbon monoxide. It may be released by faulty or poorly vented furnaces or other fuel-burning appliances. Indoor furniture, carpets, and paints may release toxic compounds into the air as well. Other possible sources of indoor air pollution include dust, mold, and pet dander. ",text,
L_0417,air pollution,T_2427,"Its easier to control the quality of indoor air than outdoor air. Steps home owners can take to improve indoor air quality include: keeping the home clean so it is as free as possible from dust, mold, and pet dander. choosing indoor furniture, flooring, and paints that are low in toxic compounds such as VOCs (volatile organic compounds). making sure that fuel-burning appliances are working correctly and venting properly. installing carbon monoxide alarms like the one in Figure 25.4 at every level of the home. ",text,
L_0418,water pollution,T_2428,"Water pollution has many causes. One of the biggest causes is fertilizer in runoff. Runoff dissolves fertilizer as it flows over farm fields, lawns, and golf courses. It carries the dissolved fertilizer into bodies of water. More dissolved fertilizer may enter a body of water at the mouth of a river, but there is generally no single point where this type of pollution enters the water. Thats why this type of water pollution is called nonpoint-source pollution. ",text,
L_0418,water pollution,T_2429,"When fertilizer ends up in bodies of water, the added nutrients cause excessive growth of algae. This is called an algal bloom. You can see one in Figure 25.5. The algae out-compete other water organisms. They may make the water unfit for human consumption or recreation. ",text,
L_0418,water pollution,T_2430,"Eventually, the algae in an algal bloom die and decompose. Their decomposition uses up oxygen in the water so that the water becomes hypoxic (without oxygen). This has occurred in many bodies of fresh water and large areas of the ocean, creating dead zones. Dead zones are areas where the hypoxic water cant support life. A very large dead zone exists in the Gulf of Mexico (see Figure 25.6). Nutrients carried into the Gulf by the Mississippi River caused this dead zone. Cutting down on the use of chemical fertilizers is one way to prevent dead zones in bodies of water. Preserving wetlands is also important. Wetlands are habitats such as swamps, marshes, and bogs where the ground is soggy or covered with water much of the year. Wetlands slow down and filter runoff before it reaches bodies of water. Wetlands also provide breeding grounds for many different species of organisms. ",text,
L_0418,water pollution,T_2431,"Unlike runoff, which enters bodies of water everywhere, some sources of pollution enter the water at a single point. This type of water pollution is called point-source pollution. ",text,
L_0418,water pollution,T_2432,"An example of point-source pollution is the release of pollution into a body of water through a pipe from a factory or sewage treatment plant. Waste water from a factory might contain dangerous chemicals such as strong acids, mercury, or lead. Water from a sewage treatment plant might contain untreated or partially treated sewage. Such pollution can make water dangerous for drinking or other uses. You can learn more about the problem of sewage contaminating the water in U.S. coastal communities by watching this video:  MEDIA Click image to the left or use the URL below. URL:  In poor nations, many people have no choice but to drink water from polluted sources. Drinking sewage-contaminated water causes waterborne diseases, due to pathogens such as protozoa, viruses, or bacteria. Most waterborne diseases cause diarrhea. ",text,
L_0418,water pollution,T_2433,"If heated water is released into a body of water, it may cause thermal pollution. Thermal pollution is a reduction in the quality of water because of an increase in water temperature. A common cause of thermal pollution is the use of water as a coolant by power plants and factories. This water is heated and then returned to the natural environment at a higher temperature. Warm water cant hold as much dissolved oxygen as cool water, so an increase in the temperature of water decreases the amount of oxygen it contains. Fish and other organisms adapted to a particular temperature range and oxygen concentration may be killed by the change in water temperature. ",text,
L_0418,water pollution,T_2434,The ocean is huge but even this body of water is becoming seriously polluted. Climate change also affects the quality of ocean water for living things. ,text,
L_0418,water pollution,T_2435,"One way that the ocean is becoming polluted is with trash, mainly plastics. The waste comes from shipping accidents, landfill erosion, and the dumping of trash. Plastics may take hundreds or even thousands of years to break down. In the meantime, the waste can be very dangerous to aquatic organisms. Some organisms may swallow plastic bags, for example, and others may be strangled by plastic six-pack rings. You can see some of the trash that routinely washes up on coastlines in Figure 25.7. There are five massive garbage patches floating on the Pacific Ocean. Watch this video to learn more about them:  . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0418,water pollution,T_2436,"Ocean water normally dissolves some of the carbon dioxide in the atmosphere. The burning of fossil fuels has increased the amount of carbon dioxide in the atmosphere. As a result, ocean water is also dissolving more carbon dioxide. When carbon dioxide dissolves in water, it forms a weak acid. With higher levels of dissolved carbon dioxide in ocean water, the water becomes more acidic. This process is called ocean acidification. Ocean acidification can kill some aquatic organisms, including corals and shellfish. It may make it more difficult for other aquatic organisms to reproduce. Both effects of acidification interfere with marine food webs, threatening the survival of many aquatic organisms. ",text,
L_0419,natural resources,T_2437,"From a human point of view, natural resources can be classified as either renewable or nonrenewable. ",text,
L_0419,natural resources,T_2438,"Renewable resources are natural resources that are remade by natural processes as quickly as people use them. Examples of renewable resources include sunlight and wind. They are in no danger of being used up. Metals and some other minerals are considered renewable as well because they are not destroyed when they are used. Instead, they can be recycled and used over and over again. Living things are also renewable resources. They can reproduce to replace themselves. However, living things can be over-used or misused to the point of extinction. For example, over-fishing has caused some of the best fishing spots in the ocean to be nearly depleted, threatening entire fish species with extinction. To be truly renewable, living things must be used wisely. They must be used in a way that meets the needs of the present generation but also preserves them for future generations. Using resources in this way is called sustainable use. ",text,
L_0419,natural resources,T_2439,"Nonrenewable resources are natural resources that cant be remade or else take too long to remake to keep up with human use. Examples of nonrenewable resources are coal, oil, and natural gas, all of which are fossil fuels. Fossil fuels form from the remains of plants and animals over hundreds of millions of years. We are using them up far faster than they can be replaced. At current rates of use, oil and natural gas will be used up in just a few decades, and coal will be used up in a couple of centuries. Uranium is another nonrenewable resource. It is used to produce nuclear power. Uranium is a naturally occurring chemical element that cant be remade. It will run out sooner or later if nuclear energy continues to be used. Soil is a very important natural resource. Plants need soil to grow, and plants are the basis of terrestrial ecosystems. Theoretically, soil can be remade. However, it takes millions of years for soil to form, so from a human point of view, it is a nonrenewable resource. Soil can be misused and eroded (see Figure 25.9). It must be used wisely to preserve it for the future. This means taking steps to avoid soil erosion and contamination of soil by toxins such as oil spills. ",text,
L_0419,natural resources,T_2440,"Some of the resources we depend on the most are energy resources. Whether its powering our lights and computers, heating our homes, or providing energy for cars and other vehicles, its hard to imagine what our lives would be like without a constant supply of energy. ",text,
L_0419,natural resources,T_2441,"Fossil fuels and nuclear energy are nonrenewable energy resources. People worldwide depend far more on these energy sources than any others. Figure 25.10 shows the worldwide consumption of energy sources by type in 2010. Nonrenewable energy sources accounted for 83 percent of the total energy used. Fossil fuels and the uranium needed for nuclear power will soon be used up if we continue to consume them at these rates. Using fossil fuels and nuclear energy creates other problems as well. The burning of fossil fuels releases carbon dioxide into the atmosphere. This is one of the major greenhouse gases causing global climate change. Nuclear power creates another set of problems, including the disposal of radioactive waste. ",text,
L_0419,natural resources,T_2442,"Switching to renewable energy sources solves many of the problems associated with nonrenewable energy. While it may be expensive to develop renewable energy sources, they are clearly the way of the future. Figure 25.11 represents three different renewable energy sources: solar, wind, and biomass energy. The three types are described below. You can watch Bill Nyes introduction to renewable energy resources in this video:  MEDIA Click image to the left or use the URL below. URL:  Solar energy is energy provided by sunlight. Solar cells can turn sunlight into electricity. The energy in sunlight is virtually limitless and free and creates no pollution to use. Wind energy is energy provided by the blowing wind. Wind turbines, like those in Figure 25.11, can turn wind energy into electricity. The wind blows because of differences in heating of Earths atmosphere by the sun. There will never be a shortage of wind. Biomass energy is energy provided by burning or decomposing organic matter. For example, when garbage decomposes in a landfill, it releases methane gas. This gas can be captured and burned to produce electricity. Crops such as corn can also be converted into a liquid fuel and added to gasoline. Although biomass is renewable, burning it produces carbon dioxide, similar to fossil fuels. ",text,
L_0419,natural resources,T_2443,"Especially when it comes to nonrenewable resources, conserving natural resources is important. Using less of them means that they will last longer. It also means they will impact the environment less. Everyone can help make a difference. There are three basic ways that all of us can conserve natural resources. They are referred to as the three Rs: reduce, reuse, and recycle. ",text,
L_0419,natural resources,T_2444,"Reducing the amount of natural resources you use is the best way to conserve resources. It takes energy to make new items, and even reusing or recycling items takes energy. You can reduce the amount of natural resources you use by not using the resources in the first place. Often, this involves just being less wasteful. Follow these tips to reduce your use of natural resources: Walk, bike, or use public transit instead of driving. If you must drive, a fuel-efficient vehicle will reduce energy use. Plan ahead to avoid making extra trips. Dont buy more than you need. For example, dont buy more fresh food than you can use without it going to waste. You will not only reduce your use of food. You will also reduce your use of energy resources. It takes a lot of energy to grow, process, and ship many of the foods we buy. When you shop, keep packaging in mind. ""Precycle"" by buying items with the least amount of wasted packaging. Use energy-efficient appliances and LED light bulbs. Also, turn off appliances and lights when you arent using them. Both steps will reduce the amount of energy resources you use. Keep the thermostat set low in the winter and high in the summer (see Figure 25.12). Instead of turning up the heat in cold weather, put on an extra layer of clothes to save energy resources. Open windows and use fans in hot weather rather than turning on the air conditioning. ",text,
L_0419,natural resources,T_2445,"Reusing means to use an item again rather than throwing it away and replacing it. Items can be reused for the same purpose or for a different purpose. Generally, it takes less energy to reuse an item than to recycle it, so choose this option over recycling when you can. Here are some specific tips for reusing natural resources: Consider mending or repairing worn or broken items rather than throwing them out and replacing them. Shop with reuse in mind. You can find great buys at flea markets and resale shops. You may be able to get free items online at free-cycle sites. Youll save money as well as natural resources. You can also sell (or give away) your own reusable items. Reuse cloth shopping bags. Instead of getting new plastic or paper bags for your purchases each time you shop, take your own reusable bag to the store each time. Even little steps can add up and help save natural resources. For example, unwrap gifts carefully and youll be able to reuse the gift wrap on a package for someone else. You can also reuse writing paper that has only been used on one side. Its great for notes and shopping lists. ",text,
L_0419,natural resources,T_2446,"If an item can no longer be used or reused, try to recycle it. Recycling means taking a used item, breaking it down, and reusing the components. It generally takes less energy to recycle materials than obtain new ones. Recycling also keeps waste out of landfills. Some of the items that can be recycled include: glass, paper, cardboard, plastic, aluminum, iron, steel, batteries, electronics, tires, and concrete. You can learn how some of these materials are recycled by watching this video:  . MEDIA Click image to the left or use the URL below. URL:  Even kitchen scraps and garden wastes can be recycled. They can be tossed into a compost bin, like the one in Figure 25.13. The recycled compost gradually breaks down to form rich humus that can be added to lawns and gardens to improve the soil. Encourage your family to recycle if they dont already. Even if you dont have curbside recycling where you live, there are likely to be recycling drop boxes or centers available for recycling many items. If you have recycling bins at school, be sure to use them. If not, raise the issue with your teacher or principal. You can also write a letter to the editor of your local newspaper encouraging everyone in your community to recycle. ",text,
L_0424,photosynthesis,T_2492,"Chemical energy that organisms need comes from food. The nearly universal food for life is the sugar glucose. Glucose is a simple carbohydrate with the chemical formula C6 H12 O6 . The glucose molecule stores chemical energy in a concentrated, stable form. In your body, glucose is the form of energy that is carried in your blood and taken up by each of your trillions of cells. ",text,
L_0424,photosynthesis,T_2493,"What is the source of glucose for living things? It is made by plants and certain other organisms. The process in which glucose is made using energy in light is photosynthesis. This process requires carbon dioxide and water. It produces oxygen in addition to glucose. Photosynthesis consists of many chemical reactions. Overall, the reactions of photosynthesis can be summed up by this chemical equation: 6CO2 + 6H2 O + light energy ! C6 H12 O6 + 6O2 In words, this means that six molecules of carbon dioxide (CO2 ) combine with six molecules of water (H2 O) in the presence of light energy. This produces one molecule of glucose (C6 H12 O6 ) and six molecules of oxygen (O2 ). Use this interactive animation to learn more about photosynthesis: Click on this link for a song about photosynthesis to reinforce the basic ideas:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0424,photosynthesis,T_2494,"Types of organisms that make glucose by photosynthesis are pictured in Figure 4.7. They include plants, plant-like protists such as algae, and some kinds of bacteria. Living things that make glucose are called autotrophs (""self feeders""). All other living things obtain glucose by eating autotrophs (or organisms that eat autotrophs). These living things are called heterotrophs (""other feeders""). ",text,
L_0424,photosynthesis,T_2495,"In plants and algae, photosynthesis takes place in chloroplasts. (Photosynthetic bacteria have other structures for this purpose.) A chloroplast is a type of plastid, or plant organelle. It contains the green pigment known as chlorophyll. The presence of chloroplasts in plant cells is one of the major ways they differ from animal cells. You can see chloroplasts in plant cells Figure 4.8. ",text,
L_0424,photosynthesis,T_2496,"The structure of a chloroplast is shown in Figure 4.9. The chloroplast is surrounded by two membranes. Inside the chloroplast are stacks of flattened sacs of membrane, called thylakoids. The thylakoids contain chlorophyll. Surrounding the thylakoids is a space called the stroma. The stroma is filled with watery (""aqueous"") fluid. ",text,
L_0424,photosynthesis,T_2497,"In plants, most chloroplasts are found in the leaves. Therefore, all the raw materials needed for photosynthesis must be present in the leaves. These materials include light, water, and carbon dioxide. The shape of the leaves gives them a lot of surface area to absorb light for photosynthesis. Roots take up water from the soil. Stems carry the water from the roots to the leaves. Carbon dioxide enters the leaves through tiny openings called stomata. (The oxygen released during photosynthesis also exits the leaves through the stomata.) ",text,
L_0424,photosynthesis,T_2498,"Photosynthesis occurs in two stages, called the light reactions and the Calvin cycle. Figure 4.10 sums up what happens in these two stages. Both stages are described below. ",text,
L_0424,photosynthesis,T_2499,"The light reactions occur in the first stage of photosynthesis. This stage takes place in the thylakoid membranes of the chloroplast. In the light reactions, energy from sunlight is absorbed by chlorophyll. This energy is temporarily transferred to two molecules: ATP and NADPH. These molecules are used to store the energy for the second stage of photosynthesis. The light reactions use water and produce oxygen. ",text,
L_0424,photosynthesis,T_2500,"The Calvin cycle occurs in the second stage of photosynthesis. This stage takes place in the stroma of the chloroplast. In the Calvin cycle, carbon dioxide is used to produce glucose (sugar) using the energy stored in ATP and NADPH. The energy is released from these molecules when ATP loses phosphate (Pi ) to become ADP and NADPH loses hydrogen (H) to become NADP+ . ",text,
L_0425,cellular respiration,T_2501,"Cellular respiration is the process in which cells break down glucose, release the stored energy, and use the energy to make ATP. For each glucose molecule that undergoes this process, up to 38 molecules of ATP are produced. Each ATP molecules forms when a phosphate is added to ADP, or adenosine diphosphate. This requires energy, which is stored in the ATP molecule. When cells need energy, a phosphate can be removed from ATP. This releases the energy and forms ADP again. ",text,
L_0425,cellular respiration,T_2502,"Cellular respiration involves many biochemical reactions. However, the overall process can be summed up in a single chemical equation: C6 H12 O6 + 6O2 ! 6CO2 + 6H2 O + energy (stored in ATP) Cellular respiration uses oxygen in addition to glucose. It releases carbon dioxide and water as waste products. Cellular respiration actually ""burns"" glucose for energy. However, it doesnt produce light or intense heat like burning a candle or log. Instead, it releases the energy slowly, in many small steps. The energy is used to form dozens of molecules of ATP. ",text,
L_0425,cellular respiration,T_2503,"Cellular respiration takes place in the cells of all organisms. It occurs in autotrophs such as plants as well as heterotrophs such as animals. Cellular respiration begins in the cytoplasm of cells. It is completed in mitochondria. The mitochondrion is a membrane-enclosed organelle in the cytoplasm. Its sometimes called the ""powerhouse"" of the cell because of its role in cellular respiration. Figure 4.12 shows the parts of the mitochondrion involved in cellular respiration. ",text,
L_0425,cellular respiration,T_2504,"Cellular respiration occurs in three stages. The flow chart in Figure dont purge me shows the order in which the stages occur and how much ATP forms in each stage. The names of the stages are glycolysis, the Krebs cycle, and electron transport. Each stage is described below. ",text,
L_0425,cellular respiration,T_2505,"Glycolysis is the first stage of cellular respiration. It takes place in the cytoplasm of the cell. The world glycolysis means ""glucose splitting"". Thats exactly what happens in this stage. Enzymes split a molecule of glucose into two smaller molecules called pyruvate. This results in a net gain of two molecules of ATP. Other energy-storing molecules are also produced. (Their energy will be used in stage 3 to make more ATP.) Glycolysis does not require oxygen. Anything that doesnt need oxygen is described as anaerobic. ",text,
L_0425,cellular respiration,T_2505,"Glycolysis is the first stage of cellular respiration. It takes place in the cytoplasm of the cell. The world glycolysis means ""glucose splitting"". Thats exactly what happens in this stage. Enzymes split a molecule of glucose into two smaller molecules called pyruvate. This results in a net gain of two molecules of ATP. Other energy-storing molecules are also produced. (Their energy will be used in stage 3 to make more ATP.) Glycolysis does not require oxygen. Anything that doesnt need oxygen is described as anaerobic. ",text,
L_0425,cellular respiration,T_2506,"The pyruvate molecules from glycolysis next enter the matrix of a mitochondrion. Thats where the second stage of cellular respiration takes place. This stage is called the Krebs cycle. During this stage, two more molecules of ATP are produced. Other energy-storing molecules are also produced (to be used to make more ATP in stage 3). The Krebs cycle requires oxygen. Anything that needs oxygen is described as aerobic. The oxygen combines with the carbon from the pyruvate molecules. This forms carbon dioxide, a waste product. ",text,
L_0425,cellular respiration,T_2507,"The third and final stage of cellular respiration is called electron transport. Remember the other energy-storing molecules from glycolysis and the Krebs cycle? Their energy is used in this stage to make many more molecules of ATP. In fact, during this stage, as many as 34 molecules of ATP are produced. Electron transport requires oxygen, so this stage is also aerobic. The oxygen combines with hydrogen from the energy-storing molecules. This forms water, another waste product. ",text,
L_0425,cellular respiration,T_2508,"Cellular respiration and photosynthesis are like two sides of the same coin. This is clear from the diagram in Figure needed for photosynthesis. Together, the two processes store and release energy in virtually all living things. ",text,
L_0425,cellular respiration,T_2509,"Some organisms can produce ATP from glucose anaerobically. One way this happens is called fermentation. Fermentation includes the glycolysis step of cellular respiration. However, it doesnt include the other, aerobic steps. There are two types of fermentation: lactic acid fermentation and alcoholic fermentation. ",text,
L_0425,cellular respiration,T_2510,"In lactic acid fermentation, glycolysis is followed by a step that produces lactic acid. This step forms additional molecules of ATP. Lactic acid fermentation occurs in some bacteria, including the bacteria in yogurt. The lactic acid gives unsweetened yogurt its sour taste. Your own muscle cells can also undertake lactic acid fermentation. This occurs when the cells are working very hard. They use fermentation because they cant get oxygen fast enough for aerobic respiration to supply them with all the energy they need. The muscle cells of the hurdlers in Figure 4.15 are using lactic acid fermentation by the time the athletes reach finish line. ",text,
L_0425,cellular respiration,T_2511,"In alcoholic fermentation, glycolysis is followed by a step that produces alcohol and carbon dioxide. This step also forms additional molecules of ATP. It occurs in yeast, such as the yeast in bread. Carbon dioxide from alcoholic fermentation creates gas bubbles in bread dough. The bubbles leave little holes in the bread after it bakes. You can see them in the bread in Figure 4.16. The holes make the bread light and fluffy. ",text,
L_0425,cellular respiration,T_2512,"Both aerobic and anaerobic respiration have certain advantages. Aerobic respiration releases far more energy than anaerobic respiration does. It results in the formation of many more molecules of ATP. Anaerobic respiration is much quicker than aerobic respiration. It also allows organisms to live in places where there is little or no oxygen, such as deep under water or soil. For an entertaining review of aerobic and anaerobic respiration, watch this creative music video:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0428,protein synthesis,T_2537,"DNA and RNA are nucleic acids. DNA stores genetic information. RNA helps build proteins. Proteins, in turn, determine the structure and function of all your cells. Proteins consist of chains of amino acids. A proteins structure and function depends on the sequence of its amino acids. Instructions for this sequence are encoded in DNA. In eukaryotic cells, chromosomes are contained within the nucleus. But proteins are made in the cytoplasm at structures called ribosomes. How do the instructions in DNA reach the ribosomes in the cytoplasm? RNA is needed for this task. ",text,
L_0428,protein synthesis,T_2538,"RNA stands for ribonucleic acid. RNA is smaller than DNA. It can squeeze through pores in the membrane that encloses the nucleus. It copies instructions in DNA and carries them to a ribosome in the cytoplasm. Then it helps build the protein. RNA is not only smaller than DNA. It differs from DNA in other ways as well. It consists of one nucleotide chain rather than two chains as in DNA. It also contains the nitrogen base uracil (U) instead of thymine (T). In addition, it contains the sugar ribose instead of deoxyribose. You can see these differences in Figure 5.16. ",text,
L_0428,protein synthesis,T_2538,"RNA stands for ribonucleic acid. RNA is smaller than DNA. It can squeeze through pores in the membrane that encloses the nucleus. It copies instructions in DNA and carries them to a ribosome in the cytoplasm. Then it helps build the protein. RNA is not only smaller than DNA. It differs from DNA in other ways as well. It consists of one nucleotide chain rather than two chains as in DNA. It also contains the nitrogen base uracil (U) instead of thymine (T). In addition, it contains the sugar ribose instead of deoxyribose. You can see these differences in Figure 5.16. ",text,
L_0428,protein synthesis,T_2539,There are three different types of RNA. All three types are needed to make proteins. Messenger RNA (mRNA) copies genetic instructions from DNA in the nucleus. Then it carries the instructions to a ribosome in the cytoplasm. Ribosomal RNA (rRNA) helps form a ribosome. This is where the protein is made. Transfer RNA (tRNA) brings amino acids to the ribosome. The amino acids are then joined together to make the protein. ,text,
L_0428,protein synthesis,T_2540,"How is the information for making proteins encoded in DNA? The answer is the genetic code. The genetic code is based on the sequence of nitrogen bases in DNA. The four bases make up the letters of the code. Groups of three bases each make up code words. These three-letter code words are called codons. Each codon stands for one amino acid or else for a start or stop signal. There are 20 amino acids that make up proteins. With three bases per codon, there are 64 possible codons. This is more than enough to code for the 20 amino acids plus start and stop signals. You can see how to translate the genetic code in Figure 5.17. Start at the center of the chart for the first base of each three-base codon. Then work your way out from the center for the second and third bases. Find the codon AUG in Figure 5.17. It codes for the amino acid methionine. It also codes for the start signal. After an AUG start codon, the next three letters are read as the second codon. The next three letters after that are read as the third codon, and so on. You can see how this works in Figure 5.18. The figure shows the bases in a molecule ",text,
L_0428,protein synthesis,T_2540,"How is the information for making proteins encoded in DNA? The answer is the genetic code. The genetic code is based on the sequence of nitrogen bases in DNA. The four bases make up the letters of the code. Groups of three bases each make up code words. These three-letter code words are called codons. Each codon stands for one amino acid or else for a start or stop signal. There are 20 amino acids that make up proteins. With three bases per codon, there are 64 possible codons. This is more than enough to code for the 20 amino acids plus start and stop signals. You can see how to translate the genetic code in Figure 5.17. Start at the center of the chart for the first base of each three-base codon. Then work your way out from the center for the second and third bases. Find the codon AUG in Figure 5.17. It codes for the amino acid methionine. It also codes for the start signal. After an AUG start codon, the next three letters are read as the second codon. The next three letters after that are read as the third codon, and so on. You can see how this works in Figure 5.18. The figure shows the bases in a molecule ",text,
L_0428,protein synthesis,T_2541,The genetic code has three other important characteristics. The genetic code is the same in all living things. This shows that all organisms are related by descent from a common ancestor. Each codon codes for just one amino acid (or start or stop). This is necessary so the correct amino acid is always selected. Most amino acids are encoded by more than one codon. This is helpful. It reduces the risk of the wrong amino acid being selected if there is a mistake in the code. ,text,
L_0428,protein synthesis,T_2542,The process in which proteins are made is called protein synthesis. It occurs in two main steps. The steps are transcription and translation. Watch this video for a good introduction to both steps of protein synthesis: http://w MEDIA Click image to the left or use the URL below. URL: ,text,
L_0428,protein synthesis,T_2543,"Transcription is the first step in protein synthesis. It takes place in the nucleus. During transcription, a strand of DNA is copied to make a strand of mRNA. How does this happen? It occurs by the following steps, as shown in Figure 5.19. 1. An enzyme binds to the DNA. It signals the DNA to unwind. 2. After the DNA unwinds, the enzyme can read the bases in one of the DNA strands. 3. Using this strand of DNA as a template, nucleotides are joined together to make a complementary strand of mRNA. The mRNA contains bases that are complementary to the bases in the DNA strand. Translation is the second step in protein synthesis. It is shown in Figure 5.20. Translation takes place at a ribosome in the cytoplasm. During translation, the genetic code in mRNA is read to make a protein. Heres how it works: 1. 2. 3. 4. 5. The molecule of mRNA leaves the nucleus and moves to a ribosome. The ribosome consists of rRNA and proteins. It reads the sequence of codons in mRNA. Molecules of tRNA bring amino acids to the ribosome in the correct sequence. At the ribosome, the amino acids are joined together to form a chain of amino acids. The chain of amino acids keeps growing until a stop codon is reached. Then the chain is released from the ribosome. ",text,
L_0428,protein synthesis,T_2544,"Mutations have many possible causes. Some mutations occur when a mistake is made during DNA replication or transcription. Other mutations occur because of environmental factors. Anything in the environment that causes a mutation is known as a mutagen. Examples of mutagens are shown in Figure 5.21. They include ultraviolet rays in sunlight, chemicals in cigarette smoke, and certain viruses and bacteria. ",text,
L_0428,protein synthesis,T_2544,"Mutations have many possible causes. Some mutations occur when a mistake is made during DNA replication or transcription. Other mutations occur because of environmental factors. Anything in the environment that causes a mutation is known as a mutagen. Examples of mutagens are shown in Figure 5.21. They include ultraviolet rays in sunlight, chemicals in cigarette smoke, and certain viruses and bacteria. ",text,
L_0428,protein synthesis,T_2545,"Many mutations have no effect on the proteins they encode. These mutations are considered neutral. Occasionally, a mutation may make a protein even better than it was before. Or the protein might help the organism adapt to a new environment. These mutations are considered beneficial. An example is a mutation that helps bacteria resist antibiotics. Bacteria with the mutation increase in numbers, so the mutation becomes more common. Other mutations are harmful. They may even be deadly. Harmful mutations often result in a protein that no longer can do its job. Some harmful mutations cause cancer or other genetic disorders. Mutations also vary in their effects depending on whether they occur in gametes or in other cells of the body. Mutations that occur in gametes can be passed on to offspring. An offspring that inherits a mutation in a gamete will have the mutation in all of its cells. Mutations that occur in body cells cannot be passed on to offspring. They are confined to just one cell and its daughter cells. These mutations may have little effect on an organism. ",text,
L_0428,protein synthesis,T_2546,"The effect of a mutation is likely to depend as well on the type of mutation that occurs. A mutation that changes all or a large part of a chromosome is called a chromosomal mutation. This type of mutation tends to be very serious. Sometimes chromosomes are missing or extra copies are present. An example is the mutation that causes Down syndrome. In this case, there is an extra copy of one of the chromosomes. Deleting or inserting a nitrogen base causes a frameshift mutation. All of the codons following the mutation are misread. This may be disastrous. To see why, consider this English-language analogy. Take the sentence The big dog ate the red cat. If the second letter of big is deleted, then the sentence becomes: The bgd oga tet her edc at. Deleting a single letter makes the rest of the sentence impossible to read. Some mutations change just one or a few bases in DNA. A change in just one base is called a point mutation. Table 5.1 compares different types of point mutations and their effects. Type Silent Missense Nonsense Description mutated codon codes for the same amino acid mutated codon codes for a different amino acid mutated codon is a prema- ture stop codon Example CAA (glutamine) ! CAG (glutamine) CAA (glutamine) ! CCA (proline) CAA (glutamine) ! UAA (stop) Effect none variable serious ",text,
L_0432,darwins theory of evolution,T_2583,"Darwins theory of evolution by natural selection contains two major ideas: One idea is that evolution happens. Evolution is a change in the inherited traits of organisms over time. Living things have changed as descendants diverged from common ancestors in the past. The other idea is that evolution occurs by natural selection. Natural selection is the process in which living things with beneficial traits produce more offspring. As a result, their traits increase in the population over time. ",text,
L_0432,darwins theory of evolution,T_2584,"How did Darwin come up with the theory of evolution by natural selection? A major influence was an amazing scientific expedition he took on a ship called the Beagle. Darwin was only 22 years old when the ship set sail. The trip lasted for almost five years and circled the globe. Figure 7.2 shows the route the ship took. It set off from Plymouth, England in 1831. It wouldnt return to Plymouth until 1836. Imagine setting out for such an incredible adventure at age 22, and youll understand why the trip had such a big influence on Darwin. Darwins job on the voyage was to observe and collect specimens whenever the ship went ashore. This included plants, animals, rocks, and fossils. Darwin loved nature, so the job was ideal for him. During the long voyage, he made many observations that helped him form his theory of evolution. Some of his most important observations were made on the Galpagos Islands. The 16 Galpagos Islands lie 966 kilometers (about 600 miles) off the west coast of South America. (You can see their location on the map in Figure 7.2.) Some of the animals Darwin observed on the islands were giant tortoises and birds called finches. Watch this video for an excellent introduction to Darwin, his voyage, and the Galpagos: ",text,
L_0432,darwins theory of evolution,T_2585,"The Galpagos Islands are still famous for their giant tortoises. These gentle giants are found almost nowhere else in the world. Darwin was amazed by their huge size. He was also struck by the variety of shapes of their shells. You can see two examples in Figure 7.3. Each island had tortoises with a different shell shape. The local people even could tell which island a tortoise came from based on the shape of its shell. Darwin wondered how each island came to have its own type of tortoise. He found out that tortoises with dome- shaped shells lived on islands where the plants they ate were abundant and easy to reach. Tortoises with saddle- shaped shells, in contrast, lived on islands that were drier. On those islands, food was often scarce. The saddle shape of their shells allowed tortoises on those islands to reach up and graze on vegetation high above them. This made sense, but how had it happened? ",text,
L_0432,darwins theory of evolution,T_2585,"The Galpagos Islands are still famous for their giant tortoises. These gentle giants are found almost nowhere else in the world. Darwin was amazed by their huge size. He was also struck by the variety of shapes of their shells. You can see two examples in Figure 7.3. Each island had tortoises with a different shell shape. The local people even could tell which island a tortoise came from based on the shape of its shell. Darwin wondered how each island came to have its own type of tortoise. He found out that tortoises with dome- shaped shells lived on islands where the plants they ate were abundant and easy to reach. Tortoises with saddle- shaped shells, in contrast, lived on islands that were drier. On those islands, food was often scarce. The saddle shape of their shells allowed tortoises on those islands to reach up and graze on vegetation high above them. This made sense, but how had it happened? ",text,
L_0432,darwins theory of evolution,T_2586,"Darwin also observed that each of the Galpagos Islands had its own species of finches. The finches on different islands had beaks that differed in size and shape. You can see four examples in Figure 7.4. Darwin investigated further. He found that the different beaks seemed to suit the birds for the food available on their island. For example, finch number 1 in Figure 7.4 used its large, strong beak to crack open and eat big, tough seeds. Finch number 4 had a long, pointed beak that was ideal for eating insects. This seemed reasonable, but how had it come about? ",text,
L_0432,darwins theory of evolution,T_2587,"Besides his observations on the Beagle, other influences helped Darwin develop his theory of evolution by natural selection. These included his knowledge of plant and animal breeding and the ideas of other scientists. ",text,
L_0432,darwins theory of evolution,T_2588,"Darwin knew that people could breed plants and animals to have useful traits. By selecting which individuals were allowed to reproduce, they could change an organisms traits over several generations. Darwin called this type of change in organisms artificial selection. You can see an example in Figure 7.5. Keeping and breeding pigeons was a popular hobby in Darwins day. Both types of pigeons in the bottom row were bred from the common rock pigeon at the top of the figure. ",text,
L_0432,darwins theory of evolution,T_2589,"There were three other scientists in particular that influenced Darwin. Their names are Lamarck, Lyell, and Malthus. All three were somewhat older than Darwin, and he was familiar with their writings. Jean Baptiste Lamarck was a French naturalist. He was one of the first scientists to propose that species change over time. In other words, he proposed that evolution occurs. Lamarck also tried to explain how it happens, but he got that part wrong. Lamarck thought that the traits an organism developed during its life time could be passed on to its offspring. He called this the inheritance of acquired characteristics. Charles Lyell was an English geologist. He wrote a famous book called Principles of Geology. Darwin took the book with him on the Beagle. Lyell argued that geological processes such as erosion change Earths surface very gradually. To account for all the changes that had occurred on the planet, Earth must be a lot older than most people believed. Thomas Malthus was an English economist. He wrote a popular essay called On Population. He argued that human populations have the potential to grow faster than the resources they need. When populations get too big, disease and famine occur. These calamities control population size by killing off the weakest people. ",text,
L_0432,darwins theory of evolution,T_2590,"Darwin spent many years thinking about his own observations and the writings of Lamarck, Lyell, and Malthus. What did it all mean? How did it all fit together? The answer, of course, is the theory of evolution by natural selection. ",text,
L_0432,darwins theory of evolution,T_2591,"Heres how Darwin thought through his theory: Like Lamarck, Darwin assumed that species evolve, or change their traits over time. Fossils Darwin found on his voyage helped convince him that evolution occurs. From Lyell, Darwin realized that Earth is very old. This meant that living things had a long time in which to evolve. There was enough time to produce the great diversity of living things that Darwin had observed. From Malthus, Darwin saw that populations could grow faster than their resources. This overproduction of offspring led to a struggle for existence, in Darwins words. In this struggle, only the fittest survive. From Darwins knowledge of artificial selection, he knew how traits can change over time. Breeders artificially select the traits that they find beneficial. These traits become more common over many generations. In nature, Darwin reasoned, individuals with certain traits might be more likely to survive the struggle for existence and have offspring. Their traits would become more common over time. In this case, nature selects the traits that are beneficial. Thats why Darwin called this process natural selection. Darwin used the word fitness to refer to the ability to reproduce and pass traits to the next generation ",text,
L_0432,darwins theory of evolution,T_2592,Darwin finally published his theory of evolution by natural selection in 1859. He presented it in his book On the Origin of Species. The book is very detailed and includes a lot of evidence for the theory. Darwins book changed science forever. The theory of evolution by natural selection became the unifying theory of all life science. ,text,
L_0433,evidence for evolution,T_2593,"Fossils are the preserved remains or traces of organisms that lived during earlier ages. Remains that become fossils are generally the hard parts of organismsmainly bones, teeth, or shells. Traces include any evidence of life, such as footprints like the dinosaur footprint in Figure 7.7. Fossils are like a window into the past. They provide direct evidence of what life was like long ago. A scientist who studies fossils to learn about the evolution of living things is called a paleontologist. ",text,
L_0433,evidence for evolution,T_2594,"The soft parts of organisms almost always decompose quickly after death. Thats why most fossils consist of hard parts such as bones. Its rare even for hard parts to remain intact long enough to become fossils. Fossils form when water seeps through the remains and deposits minerals in them. The remains literally turn to stone. Remains are more likely to form fossils if they are covered quickly by sediments. Once in a while, remains are preserved almost unchanged. For example, they may be frozen in glaciers. Or they may be trapped in tree resin that hardens to form amber. Thats what happened to the wasp in Figure 7.8. The wasp lived about 20 million years ago, but even its fragile wings have been preserved by the amber. ",text,
L_0433,evidence for evolution,T_2595,"Fossils are useful for reconstructing the past only if they can be dated. Scientists need to determine when the organisms lived who left behind the fossils. Fossils can be dated in two different ways: absolute dating and relative dating. Absolute dating determines about how long ago a fossil organism lived. This gives the fossil an approximate age in years. Absolute dating is often based on the amount of carbon-14 or other radioactive element that remains in a fossil. You can learn how carbon-14 dating works by watching this short video: Relative dating determines which of two fossils is older or younger than the other but not their age in years. Relative dating is based on the positions of fossils in rock layers. Lower rock layers were laid down earlier, so they are assumed to contain older fossils. This is illustrated in Figure 7.9. ",text,
L_0433,evidence for evolution,T_2595,"Fossils are useful for reconstructing the past only if they can be dated. Scientists need to determine when the organisms lived who left behind the fossils. Fossils can be dated in two different ways: absolute dating and relative dating. Absolute dating determines about how long ago a fossil organism lived. This gives the fossil an approximate age in years. Absolute dating is often based on the amount of carbon-14 or other radioactive element that remains in a fossil. You can learn how carbon-14 dating works by watching this short video: Relative dating determines which of two fossils is older or younger than the other but not their age in years. Relative dating is based on the positions of fossils in rock layers. Lower rock layers were laid down earlier, so they are assumed to contain older fossils. This is illustrated in Figure 7.9. ",text,
L_0433,evidence for evolution,T_2596,"The evolution of whales is a good example of how fossils can help us understand evolution. Scientists have long known that mammals first evolved on land about 200 million years ago. Its been a mystery, however, how whales evolved. Whales are mammals that live completely in the water. Did they evolve from earlier land mammals? Or did they evolve from animals that already lived in the water? Starting in the late 1970s, a growing number of fossils have allowed scientists to piece together the story of whale evolution. The fossils represent ancient, whale-like animals. They show that an ancient land mammal made its way back to the sea more than 50 million years ago. It became the ancestor of modern whales. In doing so, it lost its legs and became adapted to life in the water. In Figure 7.10 you can see an artists rendition of such a whale ancestor. It had legs and could walk on land, but it was also a good swimmer. Watch this short video to learn more about the amazing story of whale evolution based on the fossils: ",text,
L_0433,evidence for evolution,T_2596,"The evolution of whales is a good example of how fossils can help us understand evolution. Scientists have long known that mammals first evolved on land about 200 million years ago. Its been a mystery, however, how whales evolved. Whales are mammals that live completely in the water. Did they evolve from earlier land mammals? Or did they evolve from animals that already lived in the water? Starting in the late 1970s, a growing number of fossils have allowed scientists to piece together the story of whale evolution. The fossils represent ancient, whale-like animals. They show that an ancient land mammal made its way back to the sea more than 50 million years ago. It became the ancestor of modern whales. In doing so, it lost its legs and became adapted to life in the water. In Figure 7.10 you can see an artists rendition of such a whale ancestor. It had legs and could walk on land, but it was also a good swimmer. Watch this short video to learn more about the amazing story of whale evolution based on the fossils: ",text,
L_0433,evidence for evolution,T_2597,"Scientists have learned a lot about evolution by comparing living organisms. They have compared body parts, embryos, and molecules such as DNA and proteins. ",text,
L_0433,evidence for evolution,T_2598,"Comparing body parts of different species may reveal evidence for evolution. For example, all mammals have front limbs that look quite different and are used for different purposes. Bats use their front limbs to fly, whales use them to swim, and cats use them to run and climb. However, the front limbs of all three animalsas well as humanshave the same basic underlying bone structure. You can see this in Figure 7.11. The similar bones provide evidence that all four animals evolved from a common ancestor. ",text,
L_0433,evidence for evolution,T_2599,"Some of the most interesting evidence for evolution comes from vestigial structures. These are body parts that are no longer used but are still present in modern organisms. Examples in humans include tail bones and the appendix. Human beings obviously dont have tails, but our ancestors did. We still have bones at the base of our spine that form a tail in other, related animals, such as monkeys. The appendix is a tiny remnant of a once-larger organ. In a distant ancestor, it was needed to digest food. If your appendix becomes infected, a surgeon can remove it. You wont miss it because it no longer has any purpose in the human body. ",text,
L_0433,evidence for evolution,T_2600,"An embryo is an organism in the earliest stages of development. Embryos of different species may look quite similar, even when the adult forms look very different. Look at the drawings of embryos in Figure 7.12. They represent very early life stages of a chicken, turtle, pig, and human being. The embryos look so similar that its hard to tell them apart. Such similarities provide evidence that all four types of animals are related. They help document that evolution has occurred. ",text,
L_0433,evidence for evolution,T_2601,"Scientists can compare the DNA or proteins of different species. If the molecules are similar, this shows that the species are related. The more similar the molecules are, the closer the relationship is likely to be. When molecules are used in this way, they are called molecular clocks. This method assumes that random mutations occur at a constant rate for a given protein or segment of DNA. Over time, the mutations add up. The longer the amount of time since species diverged, the more differences there will be in their DNA or proteins. Table 7.1 compares the DNA of four different organisms with modern human DNA. The DNA of chimpanzees is almost 99 percent the same as the DNA of modern humans. This shows that chimpanzees are very closely related to us. We are less closely related to the other organisms in the table. Its no surprise that grapes, which are plants, are less like us than the animals in the table. Organism Chimpanzee Cow Chicken Honeybee Grape Similarity with Human DNA (percent the same) 98.8 85 65 44 24 ",text,
L_0433,evidence for evolution,T_2602,"The best evidence for evolution comes from actually observing changes in organisms through time. In the 1970s, biologists Peter and Rosemary Grant went to the Galpagos Islands to do fieldwork. They wanted to re-study Darwins finches. They spent the next 40 years on the project. Their hard work paid off. They were able to document evolution by natural selection taking place in the finches. A period of very low rainfall occurred while the Grants were on the islands. The drought resulted in fewer seeds for the finches to eat. Birds with smaller beaks could eat only the smaller seeds. Birds with bigger beaks were better off. They could eat seeds of all sizes. Therefore, there was more food available to them. Many of the small-beaked birds died in the drought. More of the big-beaked birds survived and reproduced. Within just a couple of years, the average beak size in the finches increased. This was clearly evolution by natural selection. ",text,
L_0434,the scale of evolution,T_2603,"We now know how variation in traits is inherited. Variation in traits is controlled by different alleles for genes. Alleles, in turn, are passed to gametes and then to offspring. Evolution occurs because of changes in alleles over time. How long a time? That depends on the time scale of evolution you consider. Evolution that occurs over a short period of time is known as microevolution. It might take place in just a couple of generations. This scale of evolution occurs at the level of the population. The Grants observed evolution at this scale in populations of Darwins finches. Beak size in finch populations changed in just two years because of a serious drought. Evolution that occurs over a long period of time is called macroevolution. It might take place over millions of years. This scale of evolution occurs above the level of the species. Fossils provide evidence for evolution at this scale. The evolution of the horse family, shown in Figure 7.13, is an example of macroevolution. ",text,
L_0434,the scale of evolution,T_2604,Individuals dont evolve. Their alleles dont change over time. The unit of microevolution is the population. ,text,
L_0434,the scale of evolution,T_2605,"A population is a group of organisms of the same species that live in the same area. All the genes in all the members of a population make up the populations gene pool. For each gene, the gene pool includes all the different alleles in the population. The gene pool can be described by its allele frequencies for specific genes. The frequency of an allele is the number of copies of that allele divided by the total number of alleles for the gene in the gene pool. A simple example will help you understand these concepts. The data in Table 7.2 represent a population of 100 individuals. For each gene, the gene pool has a total of 200 alleles (2 per individual x 100 individuals). The gene in question exists as two different alleles, A and a. The number of A alleles in the gene pool is 140. Of these, 100 are in the 50 AA homozygotes. Another 40 are in the 40 Aa heterozygotes. The number of a alleles in the gene pool is 60. Of these, 40 are in the 40 Aa heterozygotes. Another 20 are in the 10 aa homozygotes. The frequency of the A allele is 140/200 = 0.7. The frequency of the a allele is 60/200 = 0.3. Genotype AA Aa aa Totals Number of Individuals 50 40 10 100 Number of A Alleles 100 (50 x 2) 40 (40 x 1) 0 (10 x 0) 140 Number of a Alleles 0 (50 x 0) 40 (40 x 1) 20 (10 x 2) 60 Evolution occurs in a population when its allele frequencies change over time. For example, the frequency of the A allele might change from 0.7 to 0.8. If that happens, evolution has occurred. What causes allele frequencies to change? The answer is forces of evolution. ",text,
L_0434,the scale of evolution,T_2606,"There are four major forces of evolution that cause allele frequencies to change. They are mutation, gene flow, genetic drift, and natural selection. Mutation creates new genetic variation in a gene pool This is how all new alleles first arise. Its the ultimate source of new genetic variation, so it is essential for evolution. However, for any given gene, the chance of a mutation occurring is very small. Therefore, mutation alone does not have much effect on allele frequencies. Gene flow is the movement of genes into or out of a gene pool It occurs when individuals migrate into or out of the population. How much gene flow changes allele frequencies depends on how many migrants there are and their genotypes. Genetic drift is a random change in allele frequencies. It occurs in small populations. Allele frequencies in the offspring may differ by chance from those in the parents. This is like tossing a coin just a few times. You may, by chance, get more or less than the expected 50 percent heads or tails. In the same way, you may get more or less than the expected allele frequencies in the small number of individuals in the next generation. The smaller the population is, the more allele frequencies may drift. Natural selection is a change in allele frequencies that occurs because some genotypes are more fit than others. Genotypes with greater fitness produce more offspring and pass more copies of their alleles to the next generation. This is the force of evolution that Darwin identified. Figure 23.12 shows how Darwin thought natural selection led to variation in finches on the Galpagos Islands. ",text,
L_0434,the scale of evolution,T_2607,What happens when forces of evolution work over a long period of time? The answer is macroevolution. An example is the evolution of a new species. ,text,
L_0434,the scale of evolution,T_2608,"The evolution of a new species is called speciation. A species is a group of organisms that can mate and produce fertile offspring together but not with members of other such groups. What must happen for a new species to arise? Some members of an existing species must change so they can no produce fertile offspring with the rest of the species. Speciation often occurs when some members of a species break off from the rest. The splinter group evolves in isolation from the original species. The original species also continues to evolve. Sooner or later, the splinter group becomes too different to breed with members of the original species. At that point, a new species has formed. A good example of speciation involves anole lizards, like the one pictured in Figure 7.15. There are about 150 different species of anole lizards in the Caribbean Islands. Scientists think that a single species of lizard first colonized one of the islands about 50 million years ago. A few lizards from this original species eventually reached each of the other islands, where they evolved in isolation. Anoles in different habitats evolved traits that affected mating. For example, they evolved skin flaps of different colors. Females didnt respond to male anoles with the wrong color skin flap. This prevented them from mating. Eventually, all the different species of anoles known today evolved. Watch this interesting video to learn more about anole speciation in the Caribbean: ",text,
L_0434,the scale of evolution,T_2609,"Sometimes two species evolve the same traits. It happens because they live in similar habitats. This is called convergent evolution. Caribbean Anoles demonstrate this as well. On each Caribbean island, anoles in similar habitats evolved the same traits. For example, anoles that lived on the forest floor evolved long legs for leaping and running on the ground. Anoles that lived on tree branches evolved short legs that helped them cling to small branches and twigs. Anoles that lived at the tops of trees evolved large toe pads that allowed them to walk on leaves without falling. On each of the islands, there were anole species that evolved in each of these same ways. ",text,
L_0434,the scale of evolution,T_2610,"Two species may often interact with each other and have a close relationship. Examples include flowers and the animals that pollinate them. When one of the two species evolves new traits, the other species may evolve matching traits. This is called coevolution. You can see an example of this in Figure 7.16. The very long beak of this hummingbird co-evolved with the tubular flowers it pollinates. Only this species of hummingbird can reach nectar deep in the flowers. ",text,
L_0434,the scale of evolution,T_2611,"Darwin thought that evolution occurs very slowly. This is likely if conditions are stable. But what if conditions are changing rapidly? Evolution is likely to occur more rapidly as well. For example, the Grants showed that evolution occurred in just a couple of years in Darwins finches. This happened when a severe drought killed off a lot of the plants that the birds needed for food. Millions of fossils have been found since Darwins time. They show that evolution may occur in fits and starts. Long period of little or gradual change may be interrupted by bursts of rapid change. The rate of evolution is influenced by how the environment is changing. Today, Earths climate is changing rapidly. How do you think this might affect the rate of evolution? ",text,
L_0435,history of life on earth,T_2612,Its hard to grasp the vast amounts of time since Earth formed and life first appeared. It may help to think of Earths history as a 24-hour day. ,text,
L_0435,history of life on earth,T_2613,"Figure 7.17 shows the history of Earth in a day. In this model, the planet forms at midnight. The first prokaryotes evolve around 3:00 am. Eukaryotes evolve at about 1:00 pm. Animals dont evolve until almost 8:00 pm. Humans appear only in the last minute of the day. Relating these major events in Earths history to a 24-hour day helps to put them in perspective. ",text,
L_0435,history of life on earth,T_2614,"Another tool for understanding the history of Earth and its life is the geologic time scale. You can see this time scale in Figure 7.18. It divides Earths history into eons, eras, and periods. These divisions are based on major changes in geology, climate, and the evolution of life. The geologic time scale organizes Earths history on the basis of important events instead of time alone. It also puts more focus on recent events, about which we know the most. ",text,
L_0435,history of life on earth,T_2615,"The Precambrian Supereon is the first major division of Earths history (see Figure 7.18). It covers the time from Earths formation 4.6 billion years ago to 544 million years ago. To see how life evolved during the Precambrian and beyond, watch this wonderful video. Its a good introduction to the rest of the lesson. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0435,history of life on earth,T_2616,"When Earth first formed, it was a fiery hot, barren ball. It had no oceans or atmosphere. Rivers of melted rock flowed over its surface. Gradually, the planet cooled and formed a solid crust. Gases from volcanoes formed an atmosphere, although it contained only a trace of oxygen. As the planet continued to cool, clouds formed and rain fell. Rainwater helped form oceans. The ancient atmosphere and oceans would be toxic to modern life, but they set the stage for life to begin. ",text,
L_0435,history of life on earth,T_2617,"All living things consist of organic molecules. Many scientists think that organic molecules evolved before cells, perhaps as early as 4 billion years ago. Its possible that lightning sparked chemical reactions in Earths early atmosphere. This could have created a soup of organic molecules from inorganic chemicals. Some scientists think that RNA was the first organic molecule to evolve. RNA can not only encode genetic instructions. Some RNA molecules can carry out chemical reactions. All living things are made of one or more cells. How the first cells evolved is not known for certain. Scientists speculate that lipid membranes grew around RNA molecules. The earliest cells may have consisted of little more than RNA inside a lipid membrane. You can see a model of such a cell in Figure 7.19. The first cells probably evolved between 3.8 and 4 billion years ago. Scientists think that one cell, called the Last Universal Common Ancestor (LUCA), gave rise to all of the following life on Earth. LUCA may have existed around 3.5 billion years ago. ",text,
L_0435,history of life on earth,T_2618,"The earliest cells were heterotrophs. They were unable to make food. Instead, they got energy by ""eating"" organic molecules in the soup around them. The earliest cells were also prokaryotes. They lacked a nucleus and other organelles. Gradually, these and other traits evolved. Photosynthesis evolved about 3 billion years ago. After that, certain cells could use sunlight to make food. These were the first autotrophs. They made food for themselves and other cells. They also added oxygen to the atmosphere. The oxygen was a waste product of photosynthesis. Oxygen was toxic to many cells. They had evolved in its absence. Many of them died out. The few that survived evolved a new way to use oxygen. They used it to get energy from food. This is the process of cellular respiration. The first eukaryotic cells probably evolved about 2 billion years ago. Thats when cells evolved organelles and a nucleus. Figure 7.20 shows one theory about the origin of organelles. According to this theory, a large cell engulfed small cells. The small cells took on special roles that helped the large cell function. In return, the small cells got nutrients from the large cell. Eventually, the large and small cells could no longer live apart. With their specialized organelles, eukaryotic cells were powerful and efficient. Eukaryotes would go on to evolve sexual reproduction. They would also evolve into multicellular organisms. The first multicellular organisms evolved about 1 billion years ago. ",text,
L_0435,history of life on earth,T_2619,"At the end of the Precambrian, a mass extinction occurred. In a mass extinction, the majority of species die out. The Precambrian mass extinction was the first of six mass extinctions that occurred on Earth. Its not certain what caused this first mass extinction. Changes in Earths geology and climate were no doubt involved. ",text,
L_0435,history of life on earth,T_2620,The Paleozoic Era lasted from 544 to 245 million years ago. It is divided into six periods. ,text,
L_0435,history of life on earth,T_2621,"The Precambrian mass extinction opened up many niches for new organisms to fill. As a result, the Cambrian Period began with an explosion of new kinds of living things. For example, many types of simple animals called sponges evolved. Trilobites were also very common. Sponges and trilobites were small ocean invertebrates. These are animals without a backbone. You can see examples of them in Figure 7.21. ",text,
L_0435,history of life on earth,T_2622,"During the Ordovician Period, the oceans became filled with many kinds of invertebrates. The first fish also evolved. Plants colonized the land for the first time. However, animals remained in the water. ",text,
L_0435,history of life on earth,T_2623,"Corals appeared in the oceans during the Silurian period. Fish continued to evolve. On land, vascular plants appeared. These are plants that have special tissues to circulate water and other substances. This allowed plants to become larger and colonize drier habitats. ",text,
L_0435,history of life on earth,T_2624,"During the Devonian Period, the first seed plants evolved. Seeds have a protective coat and contain stored food. This was a big advantage over other types of plant reproduction. Seed plants eventually became the most common type of plants on land. In the oceans, fish with lobe fins evolved. These fish could breathe air when they raised their head above water. This was a step in the evolution of animals that could live on land. ",text,
L_0435,history of life on earth,T_2625,"In the Carboniferous Period, forests of huge ferns and trees were widespread. You can see how these first forests might have looked in Figure 7.22. After the ferns and trees died, their remains eventually turned to coal. The first amphibians also evolved during this period. They could live on land but had to return to the water to lay their eggs. After amphibians, the earliest reptiles appeared. They were the first animals that could reproduce on land and move away from the water. ",text,
L_0435,history of life on earth,T_2626,"During the Permian Period, all the major landmasses moved together to form one supercontinent. The supercontinent has been named Pangaea. You can see how it looked in Figure 7.23. At this time, temperatures were extreme and the climate became very dry. As a result, plants and animals evolved ways to cope with dryness. For example, reptiles evolved leathery skin. This helped prevent water loss. Plants evolved waxy leaves for the same purpose. The Permian Period ended with Earths second mass extinction. During this event, most of Earths species went extinct. It was the most massive extinction ever recorded. Its not clear why it happened. One possible reason is that a very large meteorite struck Earth. Another possibility is the eruption of enormous volcanoes. Either event could create a huge amount of dust. The dust might block out sunlight for months. This would cool the planet and prevent photosynthesis. ",text,
L_0435,history of life on earth,T_2627,The Permian mass extinction paved the way for another burst of new life at the start of the Mesozoic Era. This era is known as the age of dinosaurs. It is divided into three periods. ,text,
L_0435,history of life on earth,T_2628,"During the Triassic Period, the first dinosaurs evolved from reptile ancestors. They eventually colonized the air and water in addition to the land. There were also forests of huge seed ferns and cone-bearing conifer trees in the Triassic Period. Modern corals, fish, and insects all evolved in this period as well. The supercontinent of Pangea started to break up. The Triassic Period ended in a mass extinction. The majority of species died out, but dinosaurs were spared. ",text,
L_0435,history of life on earth,T_2629,"The Triassic mass extinction gave dinosaurs the opportunity to really flourish during the Jurassic Period. Thats why this period is called the golden age of dinosaurs. The earliest birds also evolved during the Jurassic from dinosaur ancestors. In addition, all the major groups of mammals appeared. Flowering plants also appeared for the first time. New insects evolved to pollinate them. The continents continued to move apart. ",text,
L_0435,history of life on earth,T_2630,"During the Cretaceous Period, the dinosaurs reached their maximum size and distribution. For example, the well- known Tyrannosaurus rex weighed at least 7 tons! You can get an idea of how big it was from the T. rex skeleton in Figure 7.24. (Notice how small the person looks in the bottom left of the photo.) By the end of the Cretaceous, the continents were close to their present locations. The period ended with another mass extinction. This time, the dinosaurs went extinct. What happened to the dinosaurs? Some scientists think that a comet or asteroid may have crashed into Earth. This could darken the sky, shut down photosynthesis, and cause climate change. Other factors probably contributed to the mass extinction as well. ",text,
L_0435,history of life on earth,T_2631,The extinction of the dinosaurs at the end of the Mesozoic Era paved the way for mammals to take over. Thats why the Cenozoic Era is called the age of mammals. They soon became the dominant land animals on Earth. The Cenozoic is divided into two periods. ,text,
L_0435,history of life on earth,T_2632,"During the Tertiary Period, many new kinds of mammals evolved. For example, primates and human ancestors first appeared during this period. Many mammals also increased in size. Modern rain forests and grasslands appeared. Flowering plants and insects increased in numbers. ",text,
L_0435,history of life on earth,T_2633,"During the Quaternary Period, the climate cooled. This caused a series of ice ages. Glaciers advanced southward from the North Pole. They reached as far south as Chicago and New York City. Sea levels fell because so much water was frozen in glaciers. This exposed land bridges between continents. The land bridges allowed land animals to move to new areas. Some mammals adapted to the cold by evolving very large size and thick fur. An example is the woolly mammoth, shown in Figure 7.25. Other mammals moved closer to the equator. Those that couldnt adapt or move went extinct, along with many plants. The last ice age ended about 12,000 years ago. By then, our own species, Homo sapiens, had evolved. After that, we were eyewitnesses to the story of life. As a result, the recent past is less of a mystery than the billions of years before it. ",text,
L_0437,bacteria,T_2649,"Bacteria are the most abundant living things on Earth. They live in almost all environments. They are found in the air, ocean, soil, and intestines of animals. They are even found in rocks deep below Earths surface. Any surface that has not been sterilized is likely to be covered with bacteria. The total number of bacteria in the world is amazing. Its estimated to be about 5 million trillion trillion. If you write that number in digits, it has 30 zeroes! ",text,
L_0437,bacteria,T_2650,"Bacteria are the most diverse organisms on Earth. Thousands of species of bacteria have been discovered. Many more are thought to exist. The known species are classified on the basis of various traits. For example, they may be classified by the shape of their cells. They may also be classified by how they react to a dye called Gram stain. ",text,
L_0437,bacteria,T_2651,"Bacteria come in several different shapes. The different shapes can be seen by examining bacteria under a light microscope. Therefore, its relatively easy to classify them by shape. There are three types of bacteria based on shape: bacilli (bacillus, singular), or rod shaped. cocci (coccus, singular), or sphere shaped. spirilli (spirillus, singular), or spiral shaped. You can see a common example of each type of bacteria in Figure 8.10. ",text,
L_0437,bacteria,T_2652,"Different types of bacteria stain a different color when Gram stain is applied to them. This makes them easy to identify. Some stain purple and some stain red, as you can see in Figure 8.11. The two types differ in their outer layers. This explains why they stain differently. Bacteria that stain purple are called gram-positive bacteria. They have a thick cell wall without an outer membrane. Bacteria that stain red are called gram-negative bacteria. They have a thin cell wall with an outer membrane. ",text,
L_0437,bacteria,T_2652,"Different types of bacteria stain a different color when Gram stain is applied to them. This makes them easy to identify. Some stain purple and some stain red, as you can see in Figure 8.11. The two types differ in their outer layers. This explains why they stain differently. Bacteria that stain purple are called gram-positive bacteria. They have a thick cell wall without an outer membrane. Bacteria that stain red are called gram-negative bacteria. They have a thin cell wall with an outer membrane. ",text,
L_0437,bacteria,T_2653,"Bacteria and people have many important relationships. Bacteria make our lives easier in a variety of ways. In fact, we could not survive without them. On the other hand, many bacteria can make us sick. Some of them are even deadly. For a dramatic overview of the many roles of bacteria, watch this stunning video:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0437,bacteria,T_2654,"Bacteria help usand all other living thingsby decomposing wastes. In this way, they recycle carbon and nitrogen in ecosystems. In addition, photosynthetic cyanobacteria are important producers. On ancient Earth, they added oxygen to the atmosphere and changed the course of evolution forever. There are billions of bacteria inside the human digestive tract. They help us digest food. They also make vitamins and play other important roles. We use bacteria in many other ways as well. For example, we use them to: create medical products such as vaccines. transfer genes in gene therapy. make fuels such as ethanol. clean up oil spills. kill plant pests. ferment foods. Do you eat any of the fermented foods pictured in Figure 8.12? If so, you are eating bacteria and their wastes. Yum! ",text,
L_0437,bacteria,T_2655,"You have ten times as many bacterial cells as human cells in your body. Luckily for you, most of these bacteria are harmless. However, some of them can cause disease. Any organism that causes disease is called a pathogen. Diseases caused by bacterial pathogens include food poisoning, strep throat, and Lyme disease. Bacteria that cause disease may spread directly from person to person. For example, they may spread when people shake hands with, or sneeze on, other people. Bacteria may also spread through food, water, or objects that have become contaminated with them. Some bacteria are spread by vectors. A vector is an organism that spreads bacteria or other pathogens. Most vectors are animals, commonly insects. For example, deer ticks like the one in Figure 8.13 spread Lyme disease. Ticks carry Lyme disease bacteria from deer to people when they bite them. ",text,
L_0437,bacteria,T_2656,"Bacteria in food or water usually can be killed by heating it to a high temperature. Generally, this temperature is at least 71 C (160 F). Bacteria on surfaces such as countertops and floors can be killed with disinfectants, such as chlorine bleach. Bacterial infections in people can be treated with antibiotic drugs. These drugs kill bacteria and may quickly cure the disease. If youve ever had strep throat, you were probably prescribed an antibiotic to treat it. Some bacteria have developed antibiotic resistance. They have evolved traits that make them resistant to one or more antibiotic drugs. You can see how this happens in Figure 8.14. Its an example of natural selection. Some bacteria are now resistant to most common antibiotic drugs. These infections are very hard to treat. ",text,
L_0442,adulthood and aging,T_2690,"When is a person considered an adult? That depends. Most teens become physically mature by the age of 16 or so. But they are not adults in a legal sense until they are older. For example, in the U.S., you must be 18 to vote. Once adulthood begins, it can be divided into three stages: (1) early, (2) middle, and (3) late adulthood. ",text,
L_0442,adulthood and aging,T_2691,"Early adulthood starts at age 18 or 21. It continues until the mid-30s. During early adulthood, people are at their physical peak. They are also usually in good health. The ability to have children is greatest during early adulthood, as well. This is the stage of life when most people complete their education. They are likely to begin a career or take a full-time job. Many people also marry and start a family during early adulthood. ",text,
L_0442,adulthood and aging,T_2692,"Middle adulthood begins in the mid-30s. It continues until the mid-60s. During middle adulthood, people start to show signs of aging. Their hair slowly turns gray. Their skin develops wrinkles. The risk of health problems also increases during middle adulthood. For example, heart disease, cancer, and diabetes become more common during this time. This is the stage of life when people are most likely to achieve career goals. Their children also grow up and may leave home during this stage. ",text,
L_0442,adulthood and aging,T_2693,"Late adulthood begins in the mid-60s. It continues until death. This is the stage of life when most people retire from work. They are also likely to reflect on their life. They may focus on their grandchildren. During late adulthood, people are not as physically able. For example, they usually have less muscle and slower reflexes. Their immune system also doesnt work as well as it used to. As a result, they have a harder time fighting diseases like the flu. The risk of developing diseases such as heart disease and cancer continues to rise. Arthritis is also common. In arthritis, joints wear out and become stiff and painful. As many as one in four late adults may develop Alzheimers disease. In this disease, brain changes cause mental abilities to decrease. This family picture shows females in each of the three stages of life. Which stage does each represent? Despite problems such as these, many people remain healthy and active into their 80s or even 90s. Do you want to be one of them? Then adopt a healthy lifestyle now and follow it for life. Doing so will increase your chances of staying healthy and active to an old age. Exercising the body and brain help prevent the physical and mental effects of aging. ",text,
L_0449,aquatic biomes,T_2716,"Recall that terrestrial biomes are defined by their climate. Thats because plants and animals are adapted for certain amounts of temperature and moisture. However, would aquatic biomes be classified in the same way? No, that wouldnt make much senseall parts of an aquatic environment have plenty of water. Aquatic biomes can be generally classified based on the amount of salt in the water. Freshwater biomes have less than 1% salt and are typical of ponds and lakes, streams and rivers, and wetlands. Marine biomes have more salt and are characteristic of the oceans, coral reefs, and estuaries. Most aquatic organisms do not have to deal with extremes of temperature or moisture. Instead, their main limiting factors are the availability of sunlight and the concentration of dissolved oxygen and nutrients in the water. ",text,
L_0449,aquatic biomes,T_2717,"Aquatic biomes in the ocean are called marine biomes. Organisms that live in marine biomes must be adapted to the salt in the water. For example, many have organs for excreting excess salt. Marine biomes include the oceans, coral reefs, and estuaries ( Figure 1.1). The oceans are the largest of all the ecosystems. They can be divided into four separate zones based on the amount of sunlight. Ocean zones are also divided based on their depth and their distance from land. Each zone has a great diversity of species. Within a coral reef, the dominant organisms are corals. Corals consist partially of algae, which provide nutrients via photosynthesis. Corals also extend tentacles to obtain plankton from the water. Coral reefs include several species of microorganisms, invertebrates, fishes, sea urchins, octopuses, and sea stars. Estuaries are areas where freshwater streams or rivers merge with the ocean. An example of a marine biome, a kelp for- est, from Anacapa Island in the Channel Islands National Marine Sanctuary. ",text,
L_0449,aquatic biomes,T_2718,"Freshwater biomes are defined by their low salt concentration, usually less than 1%. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration, such as the ocean. There are different types of freshwater biomes: ponds and lakes ( Figure 1.2), streams and rivers, and wetlands. Ponds and lakes range in size from just a few square meters to thousands of square kilometers. Streams and rivers are bodies of flowing water moving in one direction. They can be found everywhere. They get their starts at headwaters, which may be springs, melting snow, or even lakes, and then travel all the way to their mouths, emptying into another water channel or the ocean. Wetlands are areas of standing water that support aquatic plants. Wetlands include marshes, swamps, and bogs. Lake Tahoe in Northern California is a freshwater biome. ",text,
L_0449,aquatic biomes,T_2719,"In large bodies of water, such as the ocean and lakes, the water can be divided into zones based on the amount of sunlight it receives: 1. The photic zone extends to a maximum depth of 200 meters (656 feet) below the surface of the water. This is where enough sunlight penetrates for photosynthesis to occur. Algae and other photosynthetic organisms can make food and support food webs. 2. The aphotic zone is water deeper than 200 meters. This is where too little sunlight penetrates for photosyn- thesis to occur. As a result, producers must make ""food"" by chemosynthesis, or the food must drift down from the water above. ",text,
L_0449,aquatic biomes,T_2720,"Water in lakes and the ocean also varies in the amount of dissolved oxygen and nutrients it contains: 1. Water near the surface of lakes and the ocean usually has more dissolved oxygen than does deeper water. This is because surface water absorbs oxygen from the air above it. 2. Water near shore generally has more dissolved nutrients than water farther from shore. This is because most nutrients enter the water from land. They are carried by runoff, streams, and rivers that empty into a body of water. 3. Water near the bottom of lakes and the ocean may contain more nutrients than water closer to the surface. When aquatic organisms die, they sink to the bottom. Decomposers near the bottom of the water break down the dead organisms and release their nutrients back into the water. ",text,
L_0454,autoimmune diseases,T_2733,"The immune system usually protects you from pathogens and other causes of disease. When the immune system is working properly, it keeps you from getting sick. But the immune system is like any other system of the body. It can break down or develop diseases. AIDS is an infectious disease of the immune system caused by a virus. Some diseases of the immune system are noninfectious. They include autoimmune diseases and allergies. ",text,
L_0454,autoimmune diseases,T_2734,"Does it make sense for an immune system to attack the cells it is meant to protect? No, but an immune system that does not function properly will attack its own cells. An autoimmune disease is a disease in which the immune system attacks the bodys own cells. One example is type 1 diabetes. In this disease, the immune system attacks cells of the pancreas. Other examples are multiple sclerosis and rheumatoid arthritis. In multiple sclerosis, the immune system attacks nerve cells. This causes weakness and pain. In rheumatoid arthritis, the immune system attacks the cells of joints. This causes joint damage and pain. Autoimmune diseases cannot be cured. But they can be helped with medicines that weaken the immune systems attack on normal cells. Other autoimmune diseases include celiac disease (damages to the small intestine), inflam- matory bowel disease (damage to the digestive tract), psoriasis (damage to the skin), and lupus (damage to the joints, skin, kidneys, heart, and lungs). ",text,
L_0454,autoimmune diseases,T_2735,"An allergy occurs when the immune system attacks a harmless substance that enters the body from the outside. A substance that causes an allergy is called an allergen. It is the immune system, not the allergen, that causes the symptoms of an allergy. Did you ever hear of hay fever? Its not really a fever at all. Its an allergy to plant pollens. People with this type of allergy have symptoms such as watery eyes, sneezing, and a runny nose. A common cause of hay fever is the pollen of ragweed. Many people are also allergic to poison ivy ( Figure 1.2). Skin contact with poison ivy leads to an itchy rash in people who are allergic to the plant. Ragweed is a common roadside weed found throughout the United States. Many people are allergic to its pollen. Some people are allergic to certain foods. Nuts and shellfish are common causes of food allergies. Other common causes of allergies include: Drugs, such as penicillin. Mold. Dust. The dead skin cells of dogs and cats, called dander. Stings of wasps and bees. Most allergies can be treated with medicines. Medicines used to treat allergies include antihistamines and corticos- teroids. These medicines help control the immune system when it attacks an allergen. Sometimes, allergies cause severe symptoms, a condition known as anaphylaxis. For example, they may cause the throat to swell so it is hard to breathe. Severe allergies may be life threatening. They require emergency medical care. ",text,
L_0457,bacteria in the digestive system,T_2745,"Your large intestine is not just made up of cells. It is also an ecosystem, home to trillions of bacteria known as the ""gut flora"" ( Figure 1.1). But dont worry, most of these bacteria are helpful. Friendly bacteria live mostly in the large intestine and part of the small intestine. The acidic environment of the stomach does not allow bacterial growth. Gut bacteria have several roles in the body. For example, intestinal bacteria: Produce vitamin B12 and vitamin K. Control the growth of harmful bacteria. Break down poisons in the large intestine. Break down some substances in food that cannot be digested, such as fiber and some starches and sugars. Bacteria produce enzymes that digest carbohydrates in plant cell walls. Most of the nutritional value of plant material would be wasted without these bacteria. These help us digest plant foods like spinach. Your intestines are home to trillions of bacteria. A wide range of friendly bacteria live in the gut. Bacteria begin to populate the human digestive system right after birth. Gut bacteria include Lactobacillus, the bacteria commonly used in probiotic foods such as yogurt, and E. coli bacteria. About a third of all bacteria in the gut are members of the Bacteroides species. Bacteroides are key in helping us digest plant food. It is estimated that 100 trillion bacteria live in the gut. This is more than the human cells that make up you. It has also been estimated that there are more bacteria in your mouth than people on the planet. There are over 7 billion people on the planet. The bacteria in your digestive system are from anywhere between 300 and 1000 species. As these bacteria are helpful, your body does not attack them. They actually appear to the bodys immune system as cells of the digestive system, not foreign invaders. The bacteria actually cover themselves with sugar molecules removed from the actual cells of the digestive system. This disguises the bacteria and protects them from the immune system. As the bacteria that live in the human gut are beneficial to us, and as the bacteria enjoy a safe environment to live, the relationship that we have with these tiny organisms is described as mutualism, a type of symbiotic relationship. Lastly, keep in mind the small size of bacteria. Together, all the bacteria in your gut may weight just about 2 pounds. ",text,
L_0458,bacteria nutrition,T_2746,"Like all organisms, bacteria need energy, and they can acquire this energy through a number of different ways. ",text,
L_0458,bacteria nutrition,T_2747,"Photosynthetic bacteria use the energy of the sun to make their own food. In the presence of sunlight, carbon dioxide and water are turned into glucose and oxygen. The glucose is then turned into usable energy. Glucose is like the ""food"" for the bacteria. An example of photosynthetic bacteria is cyanobacteria, as seen in the opening image. These bacteria are sometimes called blue-green algae, although they are not algae, due to their numerous chlorophyll molecules. ",text,
L_0458,bacteria nutrition,T_2748,"Bacteria known as decomposers break down wastes and dead organisms into smaller molecules. These bacteria use the organic substrates they break down to get their energy, carbon, and nutrients they need for survival. ",text,
L_0458,bacteria nutrition,T_2749,"Bacteria can also be chemotrophs. Chemosynthetic bacteria, or chemotrophs, obtain energy by breaking down chemical compounds in their environment. An example of one of these chemicals broken down by bacteria is nitrogen-containing ammonia. These bacteria are important because they help cycle nitrogen through the environ- ment for other living things to use. Nitrogen cannot be made by living organisms, so it must be continually recycled. Organisms need nitrogen to make organic compounds, such as DNA. ",text,
L_0458,bacteria nutrition,T_2750,"Some bacteria depend on other organisms for survival. For example, some bacteria live in the roots of legumes, such as pea plants ( Figure 1.1). The bacteria turn nitrogen-containing molecules into nitrogen that the plant can use. Meanwhile, the root provides nutrients to the bacteria. In this relationship, both the bacteria and the plant benefit, so it is known as a mutualism. Other mutualistic bacteria include gut microbes. These are bacteria that live in the intestines of animals. They are usually beneficial bacteria, needed by the host organism. These microbes obviously dont kill their host, as that would kill the bacteria as well. ",text,
L_0458,bacteria nutrition,T_2751,"Other bacteria are parasitic and can cause illness. In parasitism, the bacteria benefit, and the other organism is harmed. Harmful bacteria will be discussed in another concept. ",text,
L_0460,barriers to pathogens,T_2755,"It is the immune systems job to protect the body. Your body has many ways to protect you from pathogens. Your bodys defenses are like a castle. The outside of a castle was protected by a moat and high walls. Inside the castle, soldiers were ready to fight off any enemies that made it across the moat and over the walls. Like a castle, your body has a series of defenses. Only pathogens that get through all the defenses can harm you. The first line of defence includes both physical and chemical barriers that are always ready and prepared to defend the body from infection. Pathogens must make it past this first line of defense to cause harm. If this defense is broken, the second line of defense within your body is activated. Your bodys first line of defense is like a castles moat and walls. It keeps most pathogens out of your body. This is a non-specific type of defense, in that it tries to keep all pathogens out. The first line of defense includes different types of barriers. Being the ""first line"", it starts with the skin. The first line also includes tears, mucus, cilia, stomach acid, urine flow, and friendly bacteria. ",text,
L_0460,barriers to pathogens,T_2756,"The skin is a very important barrier to pathogens. The skin is the bodys largest organ. In adults, it covers an area of about 16 to 22 square feet! The skin is also the bodys most important defense against disease. It forms a physical barrier between the body and the outside world. The skin has several layers that stack on top of each other ( Figure The mouth and nose are not lined with skin. Instead, they are lined with mucous membranes. Other organs that are exposed to the outside world, including the lungs and stomach, are also lined with mucous membranes. Mucous membranes are not tough like skin, but they have other defenses. One defense of mucous membranes is the mucus they release. Mucus is a sticky, moist substance that covers mucous membranes. Most pathogens get stuck in the mucus before they can do harm to the body. Many mucous membranes also have cilia. Cilia in the lungs are pictured below ( Figure 1.2). Cilia are tiny finger-like projections. They move in waves and sweep mucus and trapped pathogens toward body openings. When you clear your throat or blow your nose, you remove mucus and pathogens from your body. ",text,
L_0460,barriers to pathogens,T_2757,"Most body fluids that you release from your body contain chemicals that kill pathogens. For example, mucus, sweat, tears, and saliva contain enzymes called lysozymes that kill pathogens. These enzymes can break down the cell walls of bacteria to kill them. The stomach also releases a very strong acid, called hydrochloric acid. This acid kills most pathogens that enter the stomach in food or water. Urine is also acidic, so few pathogens can grow in it. This is what the cilia lining the lungs look like when they are magnified. Their movements constantly sweep mucus and pathogens out of the lungs. Do they remind you of brushes? ",text,
L_0460,barriers to pathogens,T_2758,"You are not aware of them, but your skin is covered by millions (or more!) of bacteria. Millions more live inside your body. Most of these bacteria help defend your body from pathogens. How do they do it? They compete with harmful bacteria for food and space. This prevents the harmful bacteria from multiplying and making you sick. ",text,
L_0467,blood types,T_2774,"Do you know what your blood type is? Maybe you have heard people say that they have type A or type O blood. Blood type is a way to describe the type of antigens, or proteins, on the surface of red blood cells (RBCs). There are four blood types; A, B, AB, and O. 1. Type A blood has type A antigens on the RBCs in the blood. 2. Type AB blood has A and B antigens on the RBCs. 3. Type B has B antigens on the RBCs. 4. Type O does not have either A or B antigens. The ABO blood group system is important if a person needs a blood transfusion. A blood transfusion is the process of putting blood or blood products from one person into the circulatory system of another person. The blood type of the recipient needs to be carefully matched to the blood type of the donor. Thats because different blood types have different types of antibodies, or proteins, released by the blood cells. Antibodies attack strange substances in the body. This is a normal part of your immune response, which is your defense against disease. For example, imagine a person with type O blood was given type A blood. First, what type of antibodies do people with type O blood produce? They produce anti-A and anti-B antibodies. This means, if a person with type O blood received type A blood, the anti-A antibodies in the persons blood would attack the A antigens on the RBCs in the donor blood ( Figure 1.1). The antibodies would cause the RBCs to clump together, and the clumps could block a blood vessel. This clumping of blood cells could cause death. A person with type O blood has A and B antibodies in his/her plasma; if the person was to get type A blood instead of type O, his/her A antibodies would attach to the antigens on the RBCs and cause them to clump together. People with type A blood produce anti-B antibodies, and people with type B blood produce anti-A antibodies. People with type AB blood do not produce either antibody. ",text,
L_0467,blood types,T_2775,"The second most important blood group system in human blood is the Rhesus (Rh) factor. A person either has, or does not have, the Rh antigen on the surface of their RBCs. If they do have it, then the person is positive. If the person does not have the antigen, they are considered negative. ",text,
L_0467,blood types,T_2776,"Recall that people with type O blood do not have any antigens on their RBCs. As a result, type O blood can be given to people with blood types A, B, or AB. If there are no antigens on the RBCs, there cannot be an antibody reaction in the blood. People with type O blood are often called universal donors. The blood plasma of AB blood does not contain any anti-A or anti-B antibodies. People with type AB blood can receive any ABO blood type. People with type AB blood are called universal recipients because they can receive any blood type. The antigens and antibodies that define blood type are listed as follows ( Table 1.1). Blood Type Antigen Type Plasma Antibodies A B AB O A B A and B none anti-B anti-A none anti-A, anti-B Can Receive Blood from Types A,O B,O AB, A, B, O O Can Donate Blood to Types A, AB B, AB AB AB, A, B, O ",text,
L_0468,blood vessels,T_2777,"The blood vessels are an important part of the cardiovascular system. They connect the heart to every cell in the body. Arteries carry blood away from the heart, while veins return blood to the heart ( Figure 1.1). The right side of the heart pumps de- oxygenated blood into pulmonary circula- tion, while the left side pumps oxygenated blood into systemic circulation. ",text,
L_0468,blood vessels,T_2778,"There are specific veins and arteries that are more significant than others. The pulmonary arteries carry oxygen- poor blood away from the heart to the lungs. These are the only arteries that carry oxygen-poor blood. The aorta is the largest artery in the body. It carries oxygen-rich blood away from the heart. Further away from the heart, the aorta branches into smaller arteries, which eventually branch into capillaries. Capillaries are the smallest type of blood vessel; they connect very small arteries and veins. Gases and other substances are exchanged between cells and the blood across the very thin walls of capillaries. The veins that return oxygen-poor blood to the heart are the superior vena cava and the inferior vena cava. The pulmonary veins return oxygen-rich blood from the lungs to the heart. The pulmonary veins are the only veins that carry oxygen-rich blood. ",text,
L_0468,blood vessels,T_2779,"Pulmonary circulation is the part of the cardiovascular system that carries oxygen-poor blood away from the heart and brings it to the lungs. Oxygen-poor blood returns to the heart from the body and leaves the right ventricle through the pulmonary arteries, which carry the blood to each lung. Once at the lungs, the red blood cells release carbon dioxide and pick up oxygen when you breathe. The oxygen-rich blood then leaves the lungs through the pulmonary veins, which return it to the left side of the heart. This completes the pulmonary cycle. The oxygenated blood is then pumped to the body through systemic circulation, before returning again to pulmonary circulation. ",text,
L_0468,blood vessels,T_2780,"Systemic circulation is the part of the cardiovascular system that carries oxygen-rich blood away from the heart, to the body, and returns oxygen-poor blood back to the heart. Oxygen-rich blood leaves the left ventricle through the aorta. Then it travels to the bodys organs and tissues. The tissues and organs absorb the oxygen through the capillaries. Oxygen-poor blood is collected from the tissues and organs by tiny veins, which then flow into bigger veins, and, eventually, into the inferior vena cava and superior vena cava. This completes systemic circulation. The blood releases carbon dioxide and gets more oxygen in pulmonary circulation before returning to systemic circulation. The inferior vena cava returns blood from the body. The superior vena cava returns blood from the head. ",text,
L_0469,bony fish,T_2781,"There are about 27,000 species of bony fish ( Figure 1.1), which are divided into two classes: ray-finned fish and lobe-finned fish. Most bony fish are ray-finned. These thin fins consist of webs of skin over flexible spines. Lobe- finned fish, on the other hand, have fins that resemble stump-like appendages. Fins of bony fish: ray fin (left) and lobe fin (right). ",text,
L_0469,bony fish,T_2782,"Most fish are bony fish, making them the largest group of vertebrates in existence today. They are characterized by: 1. A head and pectoral girdles (arches supporting the forelimbs) that are covered with bones derived from the skin. 2. A lung or swim bladder, which helps the body create a balance between sinking and floating by either filling up with or emitting gases such as oxygen. Controlling the volume of this organ helps fish control their depth. 3. Jointed, segmented rods supporting the fins. 4. A cover over the gill called the operculum, which helps them breathe without having to swim. 5. The ability to see in color, unlike most other fish. ",text,
L_0469,bony fish,T_2783,"Most vertebrates are ray-finned fish, with close to 27,000 known species. By comparison, there are ""only"" about 10,000 species of birds. The ray-finned fish have fin rays, with fins supported by bony spines known as rays. The ray-finned fish are the dominant class of vertebrates, with nearly 99% of fish falling into this category. They live in all aquatic environments, from freshwater and marine environments from the deep sea to the highest mountain streams. ",text,
L_0469,bony fish,T_2784,"The lobe-finned fish are characterized by fleshy lobed fins, as opposed to the bony fins of the ray-finned fish. There are two types of living lobe-finned fish: the coelacanths and the lungfish. The pectoral and pelvic fins have joints resembling those of tetrapod (four-limbed land vertebrates) limbs. These fins evolved into legs of amphibians, the first tetrapod land vertebrates. They also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of ray-finned fish. All lobe-finned fishes possess teeth covered with true enamel. The lungfish also possess both gills and lungs, solidifying this class as the ancestors of amphibians. ",text,
L_0469,bony fish,T_2785,"The ocean sunfish is the most massive bony fish in the world, up to 11 feet long and weighing up to 5,070 pounds ( Figure 1.2). Other very large bony fish include the Atlantic blue marlin, the black marlin, some sturgeon species, the giant grouper, and the goliath grouper. The long-bodied oarfish can easily be over 30 feet long, but is not nearly as massive as the ocean sunfish. In contrast, the dwarf pygmy goby measures only 0.6 inches. Fish can also be quite valuable. In January 2013, at an auction in Tokyos Tsukiji fish market, a 222-kilogram (489-pound) tuna caught off northeastern Japan sold for 155.4 million yen, which is $1,760,000. An ocean sunfish, the most massive bony fish in the world, can reach up to 11 feet long and weigh up to 5,070 pounds! ",text,
L_0470,cancer,T_2786,"Cancer is a disease that causes cells to divide out of control. Normally, the body has systems that prevent cells from dividing out of control. But in the case of cancer, these systems fail. Cancer is usually caused by mutations. Mutations are random errors in genes. Mutations that lead to cancer usually happen to genes that control the cell cycle. Because of the mutations, abnormal cells divide uncontrollably. This often leads to the development of a tumor. A tumor is a mass of abnormal tissue. As a tumor grows, it may harm normal tissues around it. Anything that can cause cancer is called a carcinogen. Carcinogens may be pathogens, chemicals, or radiation. ",text,
L_0470,cancer,T_2787,Pathogens that cause cancer include the human papilloma virus (HPV) ( Figure 1.1) and the hepatitis B virus. HPV is spread through sexual contact. It can cause cancer of the reproductive system in females. The hepatitis B virus is spread through sexual contact or contact with blood containing the virus. It can cause cancer of the liver. ,text,
L_0470,cancer,T_2788,"Many different chemical substances cause cancer. Dozens of chemicals in tobacco smoke, including nicotine, have been shown to cause cancer ( Figure 1.2). In fact, tobacco smoke is one of the main sources of chemical carcinogens. Smoking tobacco increases the risk of cancer of the lung, mouth, throat, and bladder. Using smokeless tobacco can also cause cancer. Other chemicals that cause cancer include asbestos, formaldehyde, benzene, cadmium, and nickel. ",text,
L_0470,cancer,T_2788,"Many different chemical substances cause cancer. Dozens of chemicals in tobacco smoke, including nicotine, have been shown to cause cancer ( Figure 1.2). In fact, tobacco smoke is one of the main sources of chemical carcinogens. Smoking tobacco increases the risk of cancer of the lung, mouth, throat, and bladder. Using smokeless tobacco can also cause cancer. Other chemicals that cause cancer include asbestos, formaldehyde, benzene, cadmium, and nickel. ",text,
L_0470,cancer,T_2789,Forms of radiation that cause cancer include ultraviolet (UV) radiation and radon ( Figure 1.3). UV radiation is part of sunlight. It is the leading cause of skin cancer. Radon is a natural radioactive gas that seeps into buildings from the ground. It can cause lung cancer. ,text,
L_0470,cancer,T_2790,"Cancer is usually found in adults, especially in adults over the age of 50. The most common type of cancer in adult males is cancer of the prostate gland. The prostate gland is part of the male reproductive system. Prostate cancer makes up about one third of all cancers in men. The most common type of cancer in adult females is breast cancer. It makes up about one third of all cancers in women. In both men and women, lung cancer is the second most common type of cancer. Most cases of lung cancer happen in people who smoke. Cancer can also be found in children. But childhood cancer is rare. Leukemia is the main type of cancer in children. It makes up about one third of all childhood cancers. It happens when the body makes abnormal white blood cells. Sometimes cancer cells break away from a tumor. If they enter the bloodstream, they are carried throughout the body. Then, the cells may start growing in other tissues. This is usually how cancer spreads from one part of the body to another. Once this happens, cancer is very hard to stop or control. ",text,
L_0470,cancer,T_2791,"If leukemia is treated early, it usually can be cured. In fact, many cancers can be cured, which is known as remission, if treated early. Treatment of cancer often involves removing a tumor with surgery. This may be followed by other types of treatments. These treatments may include drugs (known as chemotherapy) and radiation therapy, which kill cancer cells. The sooner cancer is treated, the greater the chances of a cure. This is why it is important to know the warning signs of cancer. Having warning signs does not mean that you have cancer. However, you should see a doctor to be sure. Everyone should know the warning signs of cancer. Detecting and treating cancer early can often lead to a cure. Some warning signs of cancer include: Change in bowel or bladder habits. Sores that do not heal. Unusual bleeding or discharge. Lump in the breast or elsewhere. Chronic indigestion. Difficulty swallowing. Obvious changes in a wart or mole. Persistent cough or hoarseness. ",text,
L_0471,cardiovascular diseases,T_2792,"A cardiovascular disease (CVD) is any disease that affects the cardiovascular system. But the term is usually used to describe diseases that are linked to atherosclerosis. Atherosclerosis ( Figure 1.1) is an inflammation of the walls of arteries that causes swelling and a buildup of material called plaque. Plaque is made of cell pieces, fatty substances, calcium, and connective tissue that builds up around the area of inflammation. As a plaque grows, it stiffens and narrows the artery, which decreases the flow of blood through the artery. Atherosclerosis normally begins in late childhood and is typically found in most major arteries. It does not usually have any early symptoms. Causes of atherosclerosis include a high-fat diet, high cholesterol, smoking, obesity, and diabetes. Atherosclerosis becomes a threat to health when the plaque buildup prevents blood circulation in the heart or the brain. A blocked blood vessel in the heart can cause a heart attack. Blockage of the circulation in the brain can cause a stroke. Ways to prevent atherosclerosis include eating healthy foods, getting plenty of exercise and not smoking. These three factors are not as hard to control as you may think. If you smoke, STOP. Start a regular exercise program and watch what you eat. A diet high in saturated fat and cholesterol can raise your cholesterol levels, which makes more plaque available to line artery walls and narrow your arteries. Cholesterol and saturated fats are found mostly in animal products such Atherosclerosis is sometimes referred to as hardening of the arteries; plaque build- up decreases the blood flow through the artery. as meat, eggs, milk, and other dairy products. Check food labels to find the amount of saturated fat in a product. Also, avoid large amounts of salt and sugar. Be careful with processed foods, such as frozen dinners, as they can be high in fat, sugar, salt and cholesterol. Eat lots of fresh or frozen fruits and vegetables, smaller portions of lean meats and fish, and whole grains such as oats and whole wheat. Limit saturated fats like butter, instead choose unsaturated vegetable oils such as canola oil. ",text,
L_0471,cardiovascular diseases,T_2793,"Like any other muscle, your heart needs oxygen. Hearts have arteries that provide oxygen through the blood. They are known as coronary arteries. Coronary heart disease is the end result of the buildup of plaque within the walls of the coronary arteries. Coronary heart disease often does not have any symptoms. A symptom of coronary heart disease is chest pain. Occasional chest pain can happen during times of stress or physical activity. The pain of angina means the heart muscle fibers need more oxygen than they are getting. Most people with coronary heart disease often have no symptoms for many years until they have a heart attack. A heart attack happens when the blood cannot reach the heart because a blood vessel is blocked. If cardiac muscle is starved of oxygen for more than roughly five minutes, it will die. Cardiac muscle cells cannot be replaced, so once they die, they are dead forever. Coronary heart disease is the leading cause of death of adults in the United States. The image below shows the way in which a blocked coronary artery can cause a heart attack and cause part of the heart muscle to die ( Figure 1.2). Maybe one day stem cells will be used to replace dead cardiac muscle cells. ",text,
L_0471,cardiovascular diseases,T_2794,"Atherosclerosis in the arteries of the brain can also lead to a stroke. A stroke is a loss of brain function due to a blockage of the blood supply to the brain. Risk factors for stroke include old age, high blood pressure, having a previous stroke, diabetes, high cholesterol, and smoking. The best way to reduce the risk of stroke is to have low blood pressure. ",text,
L_0472,cardiovascular system,T_2795,"Your cardiovascular system has many jobs. At times the cardiovascular system can work like a pump, a heating system, or even a postal carrier. To do these tasks, your cardiovascular system works with other organ systems, such as the respiratory, endocrine, and nervous systems. The cardiovascular system (Figure 1.1) is made up of the heart, the blood vessels, and the blood. It moves nutrients, gases (like oxygen), and wastes to and from your cells. Every cell in your body depends on your cardiovascular system. If your cells dont receive nutrients, they cannot survive. The main function of the cardiovascular system is to deliver oxygen to each of your cells. Blood receives oxygen in your lungs (the main organs of the respiratory system) and then is pumped, by your heart, throughout your body. The oxygen then diffuses into your cells, and carbon dioxide, a waste product of cellular respiration, moves from your cells into your blood to be delivered back to your lungs and exhaled. Each cell in your body needs oxygen, as oxygen is used in cellular respiration to produce energy in the form of ATP. Without oxygen, lactic acid fermentation would occur in your cells, which can only be maintained for a brief period of time. Arteries carry blood full of oxygen (""oxygen-rich"") away from the heart and veins return oxygen-poor blood back to the heart. The cardiovascular system also plays a role in maintaining body temperature. It helps to keep you warm by moving warm blood around your body. Your blood vessels also control your body temperature to keep you from getting too hot or too cold. When your brain senses that your body temperature is increasing, it sends messages to the blood vessels in the skin to increase in diameter. Increasing the diameter of the blood vessels increases the amount of blood and heat that moves near the skins surface. The heat is then released from the skin. This helps you cool down. What do you think your blood vessels do when your body temperature is decreasing? The blood also carries hormones, which are chemical messenger molecules produced by organs of the endocrine system, through your body. Hormones are produced in one area of your body and have an effect on another area. To get to that other area, they must travel through your blood. An example is the hormone adrenaline, produced by the adrenal glands on top of the kidneys. Adrenaline has multiple effects on the heart (it quickens the heart rate), on muscles and on the airway. ",text,
L_0473,cardiovascular system health,T_2796,"There are many risk factors that can cause a person to develop cardiovascular disease. A risk factor is anything that is linked to an increased chance of developing a disease. Some of the risk factors for cardiovascular disease you cannot control, but there are many risk factors you can control. Risk factors you cannot control include: Age: The older a person is, the greater their chance of developing a cardiovascular disease. Gender: Men under age 64 are much more likely to die of coronary heart disease than women, although the gender difference decreases with age. Genetics: Family history of cardiovascular disease increases a persons chance of developing heart disease. Risk factors you can control include many lifestyle factors: Tobacco smoking: Giving up smoking or never starting to smoke is the best way to reduce the risk of heart disease. Diabetes: Diabetes can cause bodily changes, such as high cholesterol levels, which are are risk factors for cardiovascular disease. High cholesterol levels: High amounts of ""bad cholesterol,"" increase the risk of cardiovascular disease. Obesity: Having a very high percentage of body fat, especially if the fat is mostly found in the upper body, rather than the hips and thighs, increases risk significantly. High blood pressure: If the heart and blood vessels have to work harder than normal, this puts the cardiovas- cular system under a strain. Lack of physical activity: Aerobic activities, such as the one pictured below ( Figure 1.1), help keep your heart healthy. To reduce the risk of disease, you should be active for at least 60 minutes a day, five days a week. Poor eating habits: Eating mostly foods that do not have many nutrients other than fat or carbohydrate leads to high cholesterol levels, obesity, and cardiovascular disease ( Figure 1.2). 60 minutes a day of vigorous aerobic activity, such as basketball, is enough to help keep your cardiovascular system healthy. ",text,
L_0473,cardiovascular system health,T_2797,"Cholesterol cant dissolve in the blood. It has to be transported to and from the cells by carriers called lipoproteins. Low-density lipoprotein, or LDL, is known as ""bad"" cholesterol. High-density lipoprotein (HDL) is known as good cholesterol. When too much LDL cholesterol circulates in the blood, it can slowly build up in the inner walls of the The USDAs MyPyramid recommends that you limit the amount of such foods in your diet to occasional treats. arteries that feed the heart and brain. Together with other substances, it can form plaque, and lead to atherosclerosis. If a clot forms and blocks a narrowed artery, a heart attack or stroke can result. Cholesterol comes from the food you eat as well as being made by the body. To lower bad cholesterol, a diet low in saturated fat and dietary cholesterol should be followed. Regular aerobic exercise also lowers LDL cholesterol and increases HDL cholesterol. ",text,
L_0474,cartilaginous fish,T_2798,"The 1,000 or so species of cartilaginous fish are subdivided into two subclasses: the first includes sharks, rays, and skates; the second includes chimaera, sometimes called ghost sharks. Fish from this group range in size from the dwarf lanternshark, at 6.3 inches, to the over 50-foot whale shark. Sharks obviously have jaws, as do the other cartilaginous fish. These fish evolved from the jawless fish. So why did fish eventually evolve to have jaws? Such an adaptation would allow fish to eat a much wider variety of food, including plants and other organisms. Other characteristics of cartilaginous fish include: Paired fins. Paired nostrils. Scales. Two-chambered hearts. Skeletons made of cartilage rather than bone. Cartilage is supportive tissue that does not have as much calcium as bones, which makes bones rigid. Cartilage is softer and more flexible than bone. ",text,
L_0474,cartilaginous fish,T_2799,"Since they do not have bone marrow (as they have no bones), red blood cells are produced in the spleen, in special tissue around the reproductive organs, and in an organ called Leydigs organ, only found in cartilaginous fishes. The tough skin of this group of fish is covered with placoid scales, which are hard scales formed from modified teeth. The scales are covered with a hard enamel. The hard covering and the way the scales are arranged, gives the fish skin rough, sandpaper-like feel. The function of these scales is for protection against predators. The shape of sharks teeth differ according to their diet. Species that feed on mollusks and crustaceans have dense flattened teeth for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey, such as mammals, have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. Sharks continually shed and replace their teeth, with some shedding as much as 35,000 teeth in a lifetime. ",text,
L_0474,cartilaginous fish,T_2800,"The sharks, rays, and skates (which are similar to stingrays) are further broken into two superorders: 1. Rays and skates. 2. Sharks. Sharks are some of the most frequently studied cartilaginous fish. Sharks are distinguished by such features as: The number of gill slits. The number and type of fins. The type of teeth. The size of their jaws. Body shape. Their activity at night. An elongated, toothed snout used for slashing the fish that they eat, as seen in sawsharks. Teeth used for grasping and crushing shellfish, a characteristic of bullhead sharks. A whisker-like organ named barbels that help sharks find food, a characteristic of carpet sharks. A long snout (or nose-like area), characteristic of groundsharks. Ovoviviparous reproduction, where the eggs develop inside the mothers body after internal fertilization, and the young are born alive. This trait is characteristic of mackerel sharks. All sharks mate by internal fertilization. Some sharks then lay their eggs, others allow internal development. ",text,
L_0481,cellular respiration,T_2817,"How does the food you eat provide energy? When you need a quick boost of energy, you might reach for an apple or a candy bar. But cells do not ""eat"" apples or candy bars; these foods need to be broken down so that cells can use them. Through the process of cellular respiration, the energy in food is changed into energy that can be used by the bodys cells. Initially, the sugars in the food you eat are digested into the simple sugar glucose, a monosaccharide. Recall that glucose is the sugar produced by the plant during photosynthesis. The glucose, or the polysaccharide made from many glucose molecules, such as starch, is then passed to the organism that eats the plant. This organism could be you, or it could be the organism that you eat. Either way, it is the glucose molecules that holds the energy. ",text,
L_0481,cellular respiration,T_2818,"Specifically, during cellular respiration, the energy stored in glucose is transferred to ATP ( Figure 1.1). ATP, or adenosine triphosphate, is chemical energy the cell can use. It is the molecule that provides energy for your cells to perform work, such as moving your muscles as you walk down the street. But cellular respiration is slightly more complicated than just converting the energy from glucose into ATP. Cellular respiration can be described as the reverse or opposite of photosynthesis. During cellular respiration, glucose, in the presence of oxygen, is converted into carbon dioxide and water. Recall that carbon dioxide and water are the starting products of photosynthesis. What are the products of photosynthesis? The process can be summarized as: glucose + oxygen  carbon dioxide + water. During this process, the energy stored in glucose is transferred to ATP. Energy is stored in the bonds between the phosphate groups (PO4  ) of the ATP molecule. When ATP is broken down into ADP (adenosine diphosphate) and inorganic phosphate, energy is released. When ADP and inorganic phosphate are joined to form ATP, energy is stored. During cellular respiration, about 36 to 38 ATP molecules are produced for every glucose molecule. The structural formula for adenosine triphosphate (ATP). During cellular respi- ration, energy from the chemical bonds of the food you eat must be transferred to ATP. ",text,
L_0483,central nervous system,T_2825,"The central nervous system (CNS) ( Figure 1.1) is the largest part of the nervous system. It includes the brain and the spinal cord. The bony skull protects the brain. The spinal cord is protected within the bones of the spine, which are called vertebrae. ",text,
L_0483,central nervous system,T_2826,"What weighs about three pounds and contains up to 100 billion cells? The answer is the human brain. The brain is the control center of the nervous system. Its like the pilot of a plane. It tells other parts of the nervous system what to do. The brain is also the most complex organ in the body. Each of its 100 billion neurons has synapses connecting it with thousands of other neurons. All those neurons use a lot of energy. In fact, the adult brain uses almost a quarter of the total energy used by the body. The developing brain of a baby uses an even greater amount of the bodys total energy. The brain is the organ that lets us understand what we see, hear, or sense in other ways. It also allows us to use language, learn, think, and remember. The brain controls the organs in our body and our movements as well. The brain consists of three main parts, the cerebrum, the cerebellum, and the brain stem ( Figure 1.2). 1. The cerebrum is the largest part of the brain. It sits on top of the brain stem. The cerebrum controls functions that we are aware of, such as problem-solving and speech. It also controls voluntary movements, like waving to a friend. Whether you are doing your homework or jumping hurdles, you are using your cerebrum. 2. The cerebellum is the next largest part of the brain. It lies under the cerebrum and behind the brain stem. The cerebellum controls body position, coordination, and balance. Whether you are riding a bicycle or writing with a pen, you are using your cerebellum. 3. The brain stem is the smallest of the three main parts of the brain. It lies directly under the cerebrum. The brain stem controls basic body functions, such as breathing, heartbeat, and digestion. The brain stem also carries information back and forth between the cerebrum and spinal cord. The cerebrum is divided into a right and left half ( Figure 1.2). Each half of the cerebrum is called a hemisphere. The two hemispheres are connected by a thick bundle of axons called the corpus callosum. It lies deep inside the brain and carries messages back and forth between the two hemispheres. Did you know that the right hemisphere controls the left side of the body, and the left hemisphere controls the right side of the body? By connecting the two hemispheres, the corpus callosum allows this to happen. Each hemisphere of the cerebrum is divided into four parts, called lobes. The four lobes are the: 1. 2. 3. 4. Frontal. Parietal. Temporal. Occipital. Each lobe has different jobs. Some of the functions are listed below ( Table 1.1). Side view of the brain (right). Can you find the locations of the three major parts of the brain? Top view of the brain (left). Lobe Frontal Parietal Temporal Occipital Main Function(s) Speech, thinking, touch Speech, taste, reading Hearing, smell Sight ",text,
L_0483,central nervous system,T_2826,"What weighs about three pounds and contains up to 100 billion cells? The answer is the human brain. The brain is the control center of the nervous system. Its like the pilot of a plane. It tells other parts of the nervous system what to do. The brain is also the most complex organ in the body. Each of its 100 billion neurons has synapses connecting it with thousands of other neurons. All those neurons use a lot of energy. In fact, the adult brain uses almost a quarter of the total energy used by the body. The developing brain of a baby uses an even greater amount of the bodys total energy. The brain is the organ that lets us understand what we see, hear, or sense in other ways. It also allows us to use language, learn, think, and remember. The brain controls the organs in our body and our movements as well. The brain consists of three main parts, the cerebrum, the cerebellum, and the brain stem ( Figure 1.2). 1. The cerebrum is the largest part of the brain. It sits on top of the brain stem. The cerebrum controls functions that we are aware of, such as problem-solving and speech. It also controls voluntary movements, like waving to a friend. Whether you are doing your homework or jumping hurdles, you are using your cerebrum. 2. The cerebellum is the next largest part of the brain. It lies under the cerebrum and behind the brain stem. The cerebellum controls body position, coordination, and balance. Whether you are riding a bicycle or writing with a pen, you are using your cerebellum. 3. The brain stem is the smallest of the three main parts of the brain. It lies directly under the cerebrum. The brain stem controls basic body functions, such as breathing, heartbeat, and digestion. The brain stem also carries information back and forth between the cerebrum and spinal cord. The cerebrum is divided into a right and left half ( Figure 1.2). Each half of the cerebrum is called a hemisphere. The two hemispheres are connected by a thick bundle of axons called the corpus callosum. It lies deep inside the brain and carries messages back and forth between the two hemispheres. Did you know that the right hemisphere controls the left side of the body, and the left hemisphere controls the right side of the body? By connecting the two hemispheres, the corpus callosum allows this to happen. Each hemisphere of the cerebrum is divided into four parts, called lobes. The four lobes are the: 1. 2. 3. 4. Frontal. Parietal. Temporal. Occipital. Each lobe has different jobs. Some of the functions are listed below ( Table 1.1). Side view of the brain (right). Can you find the locations of the three major parts of the brain? Top view of the brain (left). Lobe Frontal Parietal Temporal Occipital Main Function(s) Speech, thinking, touch Speech, taste, reading Hearing, smell Sight ",text,
L_0483,central nervous system,T_2827,"The spinal cord is a long, tube-shaped bundle of neurons, protected by the vertebrae. It runs from the brain stem to the lower back. The main job of the spinal cord is to carry nerve impulses back and forth between the body and brain. The spinal cord is like a two-way highway. Messages about the body, both inside and out, pass through the spinal cord to the brain. Messages from the brain pass in the other direction through the spinal cord to tell the body what to do. ",text,
L_0485,chemistry of life,T_2834,,text,
L_0485,chemistry of life,T_2835,"If you pull a flower petal from a plant and break it in half, and then take that piece and break it in half again, and take the next piece and break it half, and so on, and so on, until you cannot even see the flower anymore, what do you think you will find? We know that the flower petal is made of cells, but what are cells made of? Scientists have broken down matter, or anything that takes up space and has masslike a cellinto the smallest pieces that cannot be broken down anymore. Every physical object, including rocks, animals, flowers, and your body, are all made up of matter. Matter is made up of a mixture of things called elements. Elements are substances that cannot be broken down into simpler substances. There are more than 100 known elements, and 92 occur naturally around us. The others have been made only in the laboratory. Inside of elements, you will find identical atoms. An atom is the simplest and smallest particle of matter that still has chemical properties of the element. Atoms are the building block of all of the elements that make up the matter in your body or any other living or non-living thing. Atoms are so small that only the most powerful microscopes can see them. Atoms themselves are composed of even smaller particles, including positively charged protons, uncharged neu- trons, and negatively charged electrons. Protons and neutrons are located in the center of the atom, or the nucleus, and the electrons move around the nucleus. How many protons an atom has determines what element it is. For example, hydrogen (H) has just one proton, helium (He) always has two protons ( Figure 1.1), while sodium (Na) always has 11. All the atoms of a particular element have the exact same number of protons, and the number of protons is that elements atomic number. An atom usually has the same number of protons and electrons, but sometimes an atom may gain or lose an electron, giving the atom a positive or negative charge. These atoms are known as ions and are depicted with a ""+"" or ""-"" sign. Ions, such as H+ , Na+ , K+ , or Cl have significant biological roles. An atom of Helium (He) contains two positively charged protons (red), two uncharged neutrons (blue), and two negatively charged electrons (yellow). ",text,
L_0485,chemistry of life,T_2836,"In 1869, a Russian scientist named Dmitri Mendeleev created the periodic table, which is a way of organizing elements according to their unique characteristics, like atomic number, density, boiling point, and other values ( Figure 1.2). Each element is represented by a one or two letter symbol. For example, H stands for hydrogen, and Au stands for gold. The vertical columns in the periodic table are known as groups, and elements in groups tend to have very similar properties. The table is also divided into rows, known as periods. ",text,
L_0485,chemistry of life,T_2837,"A molecule is any combination of two or more atoms. The oxygen in the air we breathe is two oxygen atoms connected by a chemical bond to form O2 , or molecular oxygen. A carbon dioxide molecule is a combination of one carbon atom and two oxygen atoms, CO2 . Because carbon dioxide includes two different elements, it is a compound as well as a molecule. A compound is any combination of two or more different elements. A compound has different properties from the elements that it contains. Elements and combinations of elements (compounds) make up all the many types of matter in the Universe. A chemical reaction is a process that breaks or forms the bonds between atoms of molecules and compounds. For example, two hydrogens and one oxygen bind together to form water, H2 O. The molecules that come together to start a chemical reaction are the reactants. So hydrogen and oxygen are the reactants. The product is the end result of a reaction. In this example, water is the product. Atoms also come together to form compounds much larger than water. It is some of these large compounds that come together to form the basis of the cell. So essentially, your cells are made out of compounds, which are made out of atoms. ",text,
L_0488,chromosomal disorders,T_2848,"Some children are born with genetic defects that are not carried by a single gene. Instead, an error in a larger part of the chromosome or even in an entire chromosome causes the disorder. Usually the error happens when the egg or sperm is forming. Having extra chromosomes or damaged chromosomes can cause disorders. ",text,
L_0488,chromosomal disorders,T_2849,"One common example of an extra-chromosome disorder is Down syndrome ( Figure 1.1). Children with Down syndrome are mentally disabled and also have physical deformities. Down syndrome occurs when a baby receives an extra chromosome 21 from one of his or her parents. Usually, a child will receive one chromosome 21 from the mother and one chromosome 21 from the father. In an individual with Down syndrome, however, there are three Chromosomes of a person with Down Syndrome. Notice the extra chromosome 21. copies of chromosome 21 ( Figure 1.2). Therefore, Down syndrome is also known as Trisomy 21. These people have 47 total chromosomes. Another example of a chromosomal disorder is Klinefelter syndrome, in which a male inherits an extra X chromosome. These individuals have an XXY genotype. They have underdeveloped sex organs and elongated limbs. They also have difficulty learning new things. ",text,
L_0488,chromosomal disorders,T_2849,"One common example of an extra-chromosome disorder is Down syndrome ( Figure 1.1). Children with Down syndrome are mentally disabled and also have physical deformities. Down syndrome occurs when a baby receives an extra chromosome 21 from one of his or her parents. Usually, a child will receive one chromosome 21 from the mother and one chromosome 21 from the father. In an individual with Down syndrome, however, there are three Chromosomes of a person with Down Syndrome. Notice the extra chromosome 21. copies of chromosome 21 ( Figure 1.2). Therefore, Down syndrome is also known as Trisomy 21. These people have 47 total chromosomes. Another example of a chromosomal disorder is Klinefelter syndrome, in which a male inherits an extra X chromosome. These individuals have an XXY genotype. They have underdeveloped sex organs and elongated limbs. They also have difficulty learning new things. ",text,
L_0488,chromosomal disorders,T_2850,"Chromosomal disorders also occur when part of a chromosome becomes damaged. For example, if a tiny portion of chromosome 5 is missing, the individual will have cri du chat (cats cry) syndrome. These individuals have misshapen facial features, and the infants cry resembles a cats cry. ",text,
L_0489,circulation and the lymphatic system,T_2851,"The lymphatic system is a network of vessels and tissues that carry a clear fluid called lymph. The lymphatic system ( Figure 1.1) spreads all around the body and filters and cleans the lymph of any debris, abnormal cells, or pathogens. Lymph vessels are tube-shaped, just like blood vessels, with about 500-600 lymph nodes (in an adult) attached. The lymphatic system works with the cardiovascular system to return body fluids to the blood. The lymphatic system and the cardiovascular system are often called the bodys two ""circulatory systems."" Organs of the lymphatic system include the tonsils, thymus gland and spleen. The thymus gland produces T cells or T-lymphocytes (see below) and the spleen and tonsils help in fighting infections. The spleens main function is to filter the blood, removing unwanted red blood cells. The spleen also detects viruses and bacteria and triggers the release of pathogen fighting cells. The lymphatic system helps return fluid that leaks from the blood vessels back to the cardiovascular system. ",text,
L_0489,circulation and the lymphatic system,T_2852,"You may think that your blood vessels have thick walls without any leaks, but thats not true. Blood vessels can leak just like any other pipe. The lymphatic system makes sure leaked blood returns back to the bloodstream. When a small amount of fluid leaks out from the blood vessels, it collects in the spaces between cells and tissues. Some of the fluid returns to the cardiovascular system, and the rest is collected by the lymph vessels of the lymphatic system ( Figure 1.2). The fluid that collects in the lymph vessels is called lymph. The lymphatic system then returns the lymph to the cardiovascular system. Unlike the cardiovascular system, the lymphatic system is not closed (meaning it is an open circulatory system that releases and collects fluid) and has no central pump (or heart). Lymph moves slowly in lymph vessels. It is moved along in the lymph vessels by the squeezing action of smooth muscles and skeletal muscles. Lymph capillaries collect fluid that leaks out from blood capillaries. The lymphatic vessels return the fluid to the cardiovas- cular system. ",text,
L_0489,circulation and the lymphatic system,T_2853,"The lymphatic system also plays an important role in the immune system. For example, the lymphatic system makes white blood cells that protect the body from diseases. Cells of the lymphatic system produce two types of white blood cells, T cells and B cells, that are involved in fighting specific pathogens. Lymph nodes, which are scattered throughout the lymphatic system, act as filters or traps for foreign particles and are important in the proper functioning of the immune system. The role of the lymphatic system in the immune response is discussed in additional concepts. ",text,
L_0494,connecting cellular respiration and photosynthesis,T_2865,"Photosynthesis and cellular respiration are connected through an important relationship. This relationship enables life to survive as we know it. The products of one process are the reactants of the other. Notice that the equation for cellular respiration is the direct opposite of photosynthesis: Cellular Respiration: C6 H12 O6 + 6O2  6CO2 + 6H2 O Photosynthesis: 6CO2 + 6H2 O  C6 H12 O6 + 6O2 Photosynthesis makes the glucose that is used in cellular respiration to make ATP. The glucose is then turned back into carbon dioxide, which is used in photosynthesis. While water is broken down to form oxygen during photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water. While photosynthesis requires carbon dioxide and releases oxygen, cellular respiration requires oxygen and releases carbon dioxide. It is the released oxygen that is used by us and most other organisms for cellular respiration. We breathe in that oxygen, which is carried through our blood to all our cells. In our cells, oxygen allows cellular respiration to proceed. Cellular respiration works best in the presence of oxygen. Without oxygen, much less ATP would be produced. Cellular respiration and photosynthesis are important parts of the carbon cycle. The carbon cycle is the pathways through which carbon is recycled in the biosphere. While cellular respiration releases carbon dioxide into the environment, photosynthesis pulls carbon dioxide out of the atmosphere. The exchange of carbon dioxide and oxygen during photosynthesis ( Figure 1.1) and cellular respiration worldwide helps to keep atmospheric oxygen and carbon dioxide at stable levels. Cellular respiration and photosynthesis are direct opposite reactions. Energy from the sun enters a plant and is con- verted into glucose during photosynthe- sis. Some of the energy is used to make ATP in the mitochondria during cellular respiration, and some is lost to the envi- ronment as heat. ",text,
L_0499,diabetes,T_2879,"Diabetes is a non-infectious disease in which the body is unable to control the amount of sugar in the blood. People with diabetes have high blood sugar, either because their bodies do not produce enough insulin, or because their cells do not respond to insulin. Insulin is a hormone that helps cells take up sugar from the blood. Without enough insulin, the blood contains too much sugar. This can damage blood vessels and other cells throughout the body. The kidneys work hard to filter out and remove some of the extra sugar. This leads to frequent urination and excessive thirst. There are two main types of diabetes, type 1 diabetes and type 2 diabetes. Type 1 diabetes makes up about 5-10% of all cases of diabetes in the United States. Type 2 diabetes accounts for most of the other cases. Both types of diabetes are more likely in people that have certain genes. Having a family member with diabetes increases the risk of developing the disease. Either type of diabetes can increase the chances of having other health problems. For example, people with diabetes are more likely to develop heart disease and kidney disease. Type 1 and type 2 diabetes are similar in these ways. However, the two types of diabetes have different causes. ",text,
L_0499,diabetes,T_2880,"Type 1 diabetes occurs when the immune system attacks normal cells of the pancreas. Since the cells in the pancreas are damaged, the pancreas cannot make insulin. Type 1 diabetes usually develops in childhood or adolescence. People with type 1 diabetes must frequently check the sugar in their blood. They use a meter to monitor their blood sugar ( Figure 1.1). Whenever their blood sugar starts to get too high, they need a shot of insulin. The insulin brings their blood sugar back to normal. There is no cure for type 1 diabetes. Therefore, insulin shots must be taken for life. Most people with this type of diabetes learn how to give themselves insulin shots. This is one type of meter used by people with diabetes to measure their blood sugar. Modern meters like this one need only a drop of blood and take less than a minute to use. ",text,
L_0499,diabetes,T_2881,"Type 2 diabetes occurs when body cells are no longer sensitive to insulin. The pancreas may still make insulin, but the cells of the body cannot use it efficiently. Being overweight and having high blood pressure increase the chances of developing type 2 diabetes. Type 2 diabetes usually develops in adulthood, but it is becoming more common in teens and children. This is because more young people are overweight, due to a high sugar and fat diet, now than ever before. Some cases of type 2 diabetes can be cured with weight loss. However, most people with the disease need to take medicine to control their blood sugar. Regular exercise and balanced eating also help, and should be a regular part of the treatment for these people. Like people with type 1 diabetes, people with type 2 diabetes must frequently check their blood sugar. ",text,
L_0499,diabetes,T_2882,"Common symptoms of diabetes include the following: frequent urination feeling very thirsty feeling very hungry, even though you are eating extreme fatigue blurry vision cuts or bruises that are slow to heal weight loss, even though you are eating more (type 1) tingling, pain, or numbness in the hands or feet (type 2) ",text,
L_0499,diabetes,T_2883,Complications of diabetes can include the following: eye complications foot complications skin complications high blood pressure hearing issues nerve damage kidney disease artery disease stroke stress ,text,
L_0501,digestive system organs,T_2887,"The mouth and stomach are just two of the organs of the digestive system. Other digestive system organs are the esophagus, small intestine, and large intestine. Below, you can see that the digestive organs form a long tube ( Figure 1.1). In adults, this tube is about 30 feet long! At one end of the tube is the mouth. At the other end is the anus. Food enters the mouth and then passes through the rest of the digestive system. Food waste leaves the body through the anus. The organs of the digestive system are lined with muscles. The muscles contract, or tighten, to push food through the system ( Figure 1.2). The muscles contract in waves. The waves pass through the digestive system like waves through a slinky. This movement of muscle contractions is called peristalsis. Without peristalsis, food would not be able to move through the digestive system. Peristalsis is an involuntary process, which means that it occurs without your conscious control. The liver, gallbladder, and pancreas are also organs of the digestive system ( Figure 1.1). Food does not pass through these three organs. However, these organs are important for digestion. They secrete or store enzymes or other chemicals that are needed to help digest food chemically. ",text,
L_0501,digestive system organs,T_2888,"The mouth is the first organ that food enters. But digestion may start even before you put the first bite of food into your mouth. Just seeing or smelling food can cause the release of saliva and digestive enzymes in your mouth. This diagram shows how muscles push food through the digestive system. Muscle contractions travel through the system in waves, pushing the food ahead of them. This is called peristalsis. Once you start eating, saliva wets the food, which makes it easier to break up and swallow. Digestive enzymes, including the enzyme amylase, start breaking down starches into sugars. Your tongue helps mix the food with the saliva and enzymes. Your teeth also help digest food. Your front teeth are sharp. They cut and tear food when you bite into it. Your back teeth are broad and flat. They grind food into smaller pieces when you chew. Chewing is part of mechanical digestion. Your tongue pushes the food to the back of your mouth so you can swallow it. When you swallow, the lump of chewed food passes down your throat to your esophagus. The esophagus is a narrow tube that carries food from the throat to the stomach. Food moves through the esophagus because of peristalsis. At the lower end of the esophagus, a circular muscle controls the opening to the stomach. The muscle relaxes to let food pass into the stomach. Then the muscle contracts again to prevent food from passing back into the esophagus. Some people think that gravity moves food through the esophagus. If that were true, food would move through the esophagus only when you are sitting or standing upright. In fact, because of peristalsis, food can move through the esophagus no matter what position you are ineven upside down! Just dont try to swallow food when you are upside downyou could choke! The stomach is a sac-like organ at the end of the esophagus. It has thick muscular walls. The muscles contract and relax. This moves the food around and helps break it into smaller pieces. Mixing the food around with the enzyme pepsin and other chemicals helps digest proteins. Water, salt, and simple sugars can be absorbed into the blood from the stomach. Most other substances are broken down further in the small intestine before they are absorbed. The stomach stores food until the small intestine is ready to receive it. A circular muscle controls the opening between the stomach and small intestine. When the small intestine is empty, the muscle relaxes. This lets food pass from the stomach into the small intestine. ",text,
L_0501,digestive system organs,T_2889,"The small intestine a is narrow tube that starts at the stomach and ends at the large intestine ( Figure 1.1). In adults, the small intestine is about 23 feet long. Chemical digestion takes place in the first part of the small intestine. Many enzymes and other chemicals are secreted here. The small intestine is also where most nutrients are absorbed into the blood. The later sections of the small intestines are covered with tiny projections called villi ( Figure 1.3). Villi contain very tiny blood vessels. Nutrients are absorbed into the blood through these tiny vessels. There are millions of villi, so, altogether, there is a very large area for absorption to take place. In fact, villi make the inner surface area of the small intestine 1,000 times larger than it would be without them. The entire inner surface area of the small intestine is about as big as a basketball court! The small intestine is much longer than the large intestine. So why is it called small? If you compare small and large intestines ( Figure 1.1), you will see the small intestine is smaller in width than the large intestine. ",text,
L_0501,digestive system organs,T_2890,"The large intestine is a wide tube that connects the small intestine with the anus. In adults, it is about five feet long. Waste enters the large intestine from the small intestine in a liquid state. As the waste moves through the large intestine, excess water is absorbed from it. After the excess water is absorbed, the remaining solid waste is called feces. Circular muscles control the anus. They relax to let the feces pass out of the body through the anus. After feces pass out of the body, they are called stool. Releasing the stool from the body is referred to as a bowel movement. ",text,
L_0502,diseases of the nervous system,T_2891,"The nervous system controls sensing, feeling, and thinking. It also controls movement and just about every other body function. Thats why problems with the nervous system can affect the entire body. Diseases of the nervous system include brain and spinal cord infections. Other problems of the nervous system range from very serious diseases, such as tumors, to less serious problems, such as tension headaches. Some of these diseases are present at birth. Others begin during childhood or adulthood. ",text,
L_0502,diseases of the nervous system,T_2892,"When you think of infections, you probably think of an ear infection or strep throat. You probably dont think of a brain or spinal cord infection. But bacteria and viruses can infect these organs as well as other parts of the body. Infections of the brain and spinal cord are not very common. But when they happen, they can be very serious. Thats why its important to know their symptoms. ",text,
L_0502,diseases of the nervous system,T_2893,"Encephalitis is a brain infection ( Figure 1.1). If you have encephalitis, you are likely to have a fever and headache or feel drowsy and confused. The disease is most often caused by viruses. The immune system tries to fight off a brain infection, just as it tries to fight off other infections. But sometimes this can do more harm than good. The immune systems response may cause swelling in the brain. With no room to expand, the brain pushes against the skull. This may injure the brain and even cause death. Medicines can help fight some viral infections of the brain, but not all infections. ",text,
L_0502,diseases of the nervous system,T_2894,"Meningitis is an infection of the membranes that cover the brain and spinal cord. If you have meningitis, you are likely to have a fever and a headache. Another telltale symptom is a stiff neck. Meningitis can be caused by viruses or bacteria. Viral meningitis often clears up on its own after a few days. Bacterial meningitis is much more serious ( Figure 1.2). It may cause brain damage and death. People with bacterial meningitis need emergency medical treatment. They are usually given antibiotics to kill the bacteria. A vaccine to prevent meningitis recently became available. It can be given to children as young as two years old. Many doctors recommend that children receive the vaccine no later than age 12 or 13, or before they begin high school. ",text,
L_0502,diseases of the nervous system,T_2895,"A condition called Reyes syndrome can occur in young people that take aspirin when they have a viral infection. The syndrome causes swelling of the brain and may be fatal. Fortunately, Reyes syndrome is very rare. The best way to prevent it is by not taking aspirin when you have a viral infection. Products like cold medicines often contain aspirin. So, read labels carefully when taking any medicines ( Figure 1.3). Since 1988, the U.S. Food and Drug Ad- ministration has required that all aspirin and aspirin-containing products carry a warning about Reyes syndrome. ",text,
L_0502,diseases of the nervous system,T_2896,"Like other parts of the body, the nervous system may develop tumors. A tumor is a mass of cells that grows out of control. A tumor in the brain may press on normal brain tissues. This can cause headaches, difficulty speaking, or other problems, depending on where the tumor is located. Pressure from a tumor can even cause permanent brain damage. In many cases, brain tumors can be removed with surgery. In other cases, tumors cant be removed without damaging the brain even more. In those cases, other types of treatments may be needed. Cerebral palsy is a disease caused by injury to the developing brain. The injury occurs before, during, or shortly after birth. Cerebral palsy is more common in babies that have a low weight at birth. But the cause of the brain injury is not often known. The disease usually affects the parts of the brain that control body movements. Symptoms range from weak muscles in mild cases to trouble walking and talking in more severe cases. There is no known cure for cerebral palsy. Epilepsy is a disease that causes seizures. A seizure is a period of lost consciousness that may include violent muscle contractions. It is caused by abnormal electrical activity in the brain. The cause of epilepsy may be an infection, a brain injury, or a tumor. The seizures of epilepsy can often be controlled with medicine. There is no known cure for the disease, but children with epilepsy may outgrow it by adulthood. A headache is a very common nervous system problem. Headaches may be a symptom of serious diseases, but they are more commonly due to muscle tension. A tension headache occurs when muscles in the shoulders, neck, and head become too tense. This often happens when people are stressed out. Just trying to relax may help relieve this type of headache. Mild pain relievers such as ibuprofen may also help. Sometimes relaxation is the best medicine for a tension headache and to help muscles get rid of pain. A migraine is a more severe type of headache. It occurs when blood vessels in the head dilate, or expand. This may be triggered by certain foods, bright lights, weather changes, or other factors. People with migraines may also have nausea or other symptoms. Fortunately, migraines can often be relieved with prescription drugs. There are many other nervous system diseases. They include multiple sclerosis, Huntingtons disease, Parkinsons disease, and Alzheimers disease. However, these diseases rarely, if ever, occur in young people. Their causes and symptoms are listed below ( Table 1.1). The diseases have no known cure, but medicines may help control their symptoms. Disease Multiple sclerosis Cause The immune system attacks and damages the central nervous sys- tem so neurons cannot function nor- mally. Symptoms Muscle weakness, difficulty mov- ing, problems with coordination, difficulty keeping the body bal- anced Parkinsons disease Alzheimers disease ",text,
L_0505,dna the genetic material,T_2901,"DNA is the material that makes up our chromosomes and stores our genetic information. When you build a house, you need a blueprint, a set of instructions that tells you how to build. The DNA is like the blueprint for living organisms. The genetic information is a set of instructions that tell your cells what to do. DNA is an abbreviation for deoxyribonucleic acid. As you may recall, nucleic acids are a type of macromolecule that store information. The deoxyribo part of the name refers to the name of the sugar that is contained in DNA, deoxyribose. DNA may provide the instructions to make up all living things, but it is actually a very simple molecule. DNA is made of a very long chain of nucleotides. In fact, in you, the smallest DNA molecule has well over 20 million nucleotides. ",text,
L_0505,dna the genetic material,T_2902,"Nucleotides are composed of three main parts: 1. a phosphate group. 2. a 5-carbon sugar (deoxyribose in DNA). 3. a nitrogen-containing base. The only difference between each nucleotide is the identity of the base. There are only four possible bases that make up each DNA nucleotide: adenine (A), guanine (G), thymine (T), and cytosine (C). ",text,
L_0505,dna the genetic material,T_2903,"The various sequences of the four nucleotide bases make up the genetic code of your cells. It may seem strange that there are only four letters in the alphabet of DNA. But since your chromosomes contain millions of nucleotides, there are many, many different combinations possible with those four letters. But how do all these pieces fit together? James Watson and Francis Crick won the Nobel Prize in 1962 for piecing together the structure of DNA. Together with the work of Rosalind Franklin and Maurice Wilkins, they determined that DNA is made of two strands of nucleotides formed into a double helix, or a two-stranded spiral, with the sugar and phosphate groups on the outside, and the paired bases connecting the two strands on the inside of the helix (Figure 1.1). ",text,
L_0505,dna the genetic material,T_2904,"The bases in DNA do not pair randomly. When Erwin Chargaff looked closely at the bases in DNA, he noticed that the percentage of adenine (A) in the DNA always equaled the percentage of thymine (T), and the percentage of guanine (G) always equaled the percentage of cytosine (C). Watson and Cricks model explained this result by suggesting that A always pairs with T, and G always pairs with C in the DNA helix. Therefore A and T, and G and C, are ""complementary bases,"" or bases that always pair together, known as a base-pair. The base-pairing rules state that A will always bind to T, and G will always bind to C (Figure 1.2). For example, if one DNA strand reads ATGCCAGT, the other strand will be made up of the complementary bases: TACGGTCA. Hydrogen bonds hold the complementary bases together, with two bonds forming between an A and a T, and three bonds between a G and a C. The chemical structure of DNA includes a chain of nucleotides consisting of a 5- carbon sugar, a phosphate group, and a nitrogen base. Notice how the sugar and phosphate group form the backbone of DNA (strands highlighted in pink), with the hydrogen bonds between the bases joining the two strands. ",text,
L_0507,echinoderms,T_2908,"Youre probably familiar with starfish and sand dollars ( Figure 1.1). They are both echinoderms. Sea urchins and sea cucumbers are also echinoderms. Whats similar between these three organisms? They all have radial symmetry. This means that the body is arranged around a central point. Echinoderms belong to the phylum Echinodermata. This phylum includes 7,000 living species. It is the largest animal phylum without freshwater or land-living members. ",text,
L_0507,echinoderms,T_2909,"As mentioned earlier, echinoderms show radial symmetry. Other key echinoderm features include an internal skeleton and spines, as well as a few organs and organ systems. Although echinoderms look like they have a hard exterior, they do not have an external skeleton. Instead, a thin outer skin covers an internal skeleton made of tiny plates and spines. This provides rigid support. Some groups of echinoderms, such as sea urchins ( Figure 1.2), have spines that protect the organism. Sea cucumbers use these spines to help them move. A starfish (left) and a keyhole sand dollar (right), showing the radial symmetry char- acteristic of the echinoderms. Starfish are also known as sea stars. Another echinoderm, a sea urchin (Echi- nus esculentus), showing its spines. Echinoderms have a unique water vascular system. This network of fluid-filled tubes helps them to breathe, eat, and move. Therefore, they can function without gill slits. Echinoderms also have a very simple digestive system, circulatory system, and nervous system. The digestive system often leads directly from the mouth to the anus. The echinoderms have an open circulatory system, meaning that fluid moves freely in the body cavity. But echinoderms have no heart. This may be due to their simple radial symmetry - a heart is not needed to pump the freely moving fluid. The echinoderm nervous system is a nerve net, or interconnected neurons with no central brain. Many echinoderms have amazing powers of regeneration. For example, some sea stars (starfish) are capable of regenerating lost arms. In some cases, lost arms have been observed to regenerate a second complete sea star! Sea cucumbers often release parts of their internal organs if they perceive danger. The released organs and tissues are then quickly regenerated. ",text,
L_0507,echinoderms,T_2909,"As mentioned earlier, echinoderms show radial symmetry. Other key echinoderm features include an internal skeleton and spines, as well as a few organs and organ systems. Although echinoderms look like they have a hard exterior, they do not have an external skeleton. Instead, a thin outer skin covers an internal skeleton made of tiny plates and spines. This provides rigid support. Some groups of echinoderms, such as sea urchins ( Figure 1.2), have spines that protect the organism. Sea cucumbers use these spines to help them move. A starfish (left) and a keyhole sand dollar (right), showing the radial symmetry char- acteristic of the echinoderms. Starfish are also known as sea stars. Another echinoderm, a sea urchin (Echi- nus esculentus), showing its spines. Echinoderms have a unique water vascular system. This network of fluid-filled tubes helps them to breathe, eat, and move. Therefore, they can function without gill slits. Echinoderms also have a very simple digestive system, circulatory system, and nervous system. The digestive system often leads directly from the mouth to the anus. The echinoderms have an open circulatory system, meaning that fluid moves freely in the body cavity. But echinoderms have no heart. This may be due to their simple radial symmetry - a heart is not needed to pump the freely moving fluid. The echinoderm nervous system is a nerve net, or interconnected neurons with no central brain. Many echinoderms have amazing powers of regeneration. For example, some sea stars (starfish) are capable of regenerating lost arms. In some cases, lost arms have been observed to regenerate a second complete sea star! Sea cucumbers often release parts of their internal organs if they perceive danger. The released organs and tissues are then quickly regenerated. ",text,
L_0507,echinoderms,T_2910,"Feeding strategies vary greatly among the different groups of echinoderms. Theres no one food or technique thats shared by all echinoderms. Different eating-methods include: 1. Passive filter-feeders, which are organisms that absorb suspended nutrients from passing water. Some echino- derms use their long arms to capture food particles floating past in the currents. 2. Grazers, such as sea urchins, are organisms that feed on available plants. Sea urchins are omnivorous, eating both plant and animals. The sea urchin mainly feeds on algae on the coral and rocks, along with decomposing matter such as dead fish, mussels, sponges, and barnacles. 3. Deposit feeders, which are organisms that feed on small pieces of organic matter, usually in the top layer of soil. Sea cucumbers are deposit feeders, living on the ocean floor. They eat the tiny scrap particles that are usually abundant in the environments that they inhabit. 4. Active hunters, which are organisms that actively hunt their prey. Many sea stars are predators, feeding on mollusks like clams by prying apart their shells and actually placing their stomach inside the mollusk shell to digest the meat. ",text,
L_0507,echinoderms,T_2911,"Echinoderms reproduce sexually. In most echinoderms, eggs and sperm cells are released into open water, and fertilization takes place when the eggs and sperm meet. This is called external fertilization, and is typical of many marine animals. The release of sperm and eggs often occurs when organisms are in the same place at the same time. Internal fertilization takes place in only a few species. Some species even take care of their offspring, like parents! ",text,
L_0509,effects of water pollution,T_2913,"Water pollutants can have an effect on both the ecology of ecosystems and on humans. As a result of water pollution, humans may not be able to use a waterway for recreation and fishing. Drinking water can also be affected if a toxin enters the groundwater. ",text,
L_0509,effects of water pollution,T_2914,"In a marine ecosystem, algae are the producers. Through photosynthesis, they provide glucose for the ecosystem. So, can too much algae be a bad thing? Eutrophication is an over-enrichment of chemical nutrients in a body of water. Usually these nutrients are the nitrogen and phosphorous found in fertilizers. Run-off from lawns or farms can wash fertilizers into rivers or coastal waters. Plants are not the only things that grow more quickly with added fertilizers. Algae like the excess nutrients in fertilizers too. When there are high levels of nutrients in the water, algae populations will grow large very quickly. This leads to overgrowths of algae called algal blooms. However, these algae do not live very long. They die and begin to decompose. This process uses oxygen, removing the oxygen from the water. Without oxygen, fish and shellfish cannot live, and this results in the death of these organisms ( Figure 1.1). Certain types of algal blooms can also create toxins. These toxins can enter shellfish. If humans eat these shellfish, then they can get very sick. These toxins cause neurological problems in humans. ",text,
L_0509,effects of water pollution,T_2915,"Ocean acidification occurs when excess carbon dioxide in the atmosphere causes the oceans to become acidic. Burning fossil fuels has led to an increase in carbon dioxide in the atmosphere. This carbon dioxide is then absorbed by the oceans, which lowers the pH of the water. Ocean acidification can kill corals and shellfish. It may also cause marine organisms to reproduce less, which could harm other organisms in the food chain. As a result, there also may be fewer marine organisms for humans to consume. ",text,
L_0509,effects of water pollution,T_2916,"Aquatic debris is trash that gets into fresh- and saltwater waterways. It comes from shipping accidents, landfill erosion, or the direct dumping of trash. Debris can be very dangerous to aquatic wildlife. Some animals may swallow plastic bags, mistaking them for food. Other animals can be strangled by floating trash like plastic six-pack rings. Wildlife can easily get tangled in nets ( Figure 1.2). Marine trash can harm different types of aquatic life. Pictured here is a marine turtle entangled in a net. How can you keep this from happening? ",text,
L_0509,effects of water pollution,T_2917,"Unsafe water supplies have drastic effects on human health. Waterborne diseases are diseases due to microscopic pathogens in fresh water. These diseases can be caused by protozoa, viruses, bacteria, and intestinal parasites. In many parts of the world there are no water treatment plants. If sewage or animal manure gets into a river, then people downstream will get sick when they drink the water. According to the World Health Organization (WHO), diarrheal disease is responsible for the deaths of 1.8 million people every year. It was estimated that 88% of the cases of diarrheal disease are caused by unsafe water supplies. ",text,
L_0510,energy pyramids,T_2918,"When an herbivore eats a plant, the energy in the plant tissues is used by the herbivore. But how much of that energy is transferred to the herbivore? Remember that plants are producers, bringing the energy into the ecosystem by converting sunlight into glucose. Does the plant use some of the energy for its own needs? Recall the energy is the ability to do work, and the plant has plenty or ""work"" to do. So of course it needs and uses energy. It converts the glucose it makes into ATP through cellular respiration just like other organisms. After the plant uses the energy from glucose for its own needs, the excess energy is available to the organism that eats the plant. The herbivore uses the energy from the plant to power its own life processes and to build more body tissues. However, only about 10% of the total energy from the plant gets stored in the herbivores body as extra body tissue. The rest of the energy is used by the herbivore and released as heat. The next consumer on the food chain that eats the herbivore will only store about 10% of the total energy from the herbivore in its own body. This means the carnivore will store only about 1% of the total energy that was originally in the plant. In other words, only about 10% of energy of one step in a food chain is stored in the next step in the food chain. The majority of the energy is used by the organism or released to the environment. Every time energy is transferred from one organism to another, there is a loss of energy. This loss of energy can be shown in an energy pyramid. An example of an energy pyramid is pictured below ( Figure 1.1). Since there is energy loss at each step in a food chain, it takes many producers to support just a few carnivores in a community. Each step of the food chain in the energy pyramid is called a trophic level. Plants or other photosynthetic organisms ( autotrophs) are found on the first trophic level, at the bottom of the pyramid. The next level will be the herbivores, and then the carnivores that eat the herbivores. The energy pyramid ( Figure 1.1) shows four levels of a food chain, from producers to carnivores. Because of the high rate of energy loss in food chains, there are usually only 4 or 5 trophic levels in the food chain or energy pyramid. There just is not enough energy to support any additional trophic levels. Heterotrophs are found in all levels of an energy pyramid other than the first level. ",text,
L_0511,enzymes in the digestive system,T_2919,"Chemical digestion could not take place without the help of digestive enzymes. An enzyme is a protein that speeds up chemical reactions in the body. Digestive enzymes speed up chemical reactions that break down large food molecules into small molecules. Did you ever use a wrench to tighten a bolt? You could tighten a bolt with your fingers, but it would be difficult and slow. If you use a wrench, you can tighten a bolt much more easily and quickly. Enzymes are like wrenches. They make it much easier and quicker for chemical reactions to take place. Like a wrench, enzymes can also be used over and over again. But you need the appropriate size and shape of the wrench to efficiently tighten the bolt, just like each enzyme is specific for the reaction it helps. Digestive enzymes are released, or secreted, by the organs of the digestive system. These enzymes include proteases that digest proteins, and nucleases that digest nucleic acids. Examples of digestive enzymes are: Amylase, produced in the mouth. It helps break down large starch molecules into smaller sugar molecules. Pepsin, produced in the stomach. Pepsin helps break down proteins into amino acids. Trypsin, produced in the pancreas. Trypsin also breaks down proteins. Pancreatic lipase, produced in the pancreas. It is used to break apart fats. Deoxyribonuclease and ribonuclease, produced in the pancreas. They are enzymes that break bonds in nucleic acids like DNA and RNA. Bile salts are bile acids that help to break down fat. Bile acids are made in the liver. When you eat a meal, bile is secreted into the intestine, where it breaks down the fats ( Figure 1.1). ",text,
L_0511,enzymes in the digestive system,T_2920,"If you are a typical teenager, you like to eat. For your body to break down, absorb and spread the nutrients from your food throughout your body, your digestive system and endocrine system need to work together. The endocrine system sends hormones around your body to communicate between cells. Essentially, hormones are chemical messenger molecules. Digestive hormones are made by cells lining the stomach and small intestine. These hormones cross into the blood where they can affect other parts of the digestive system. Some of these hormones are listed below. Gastrin, which signals the secretion of gastric acid. Cholecystokinin, which signals the secretion of pancreatic enzymes. Secretin, which signals secretion of water and bicarbonate from the pancreas. Ghrelin, which signals when you are hungry. Gastric inhibitory polypeptide, which stops or decreases gastric secretion. It also causes the release of insulin in response to high blood glucose levels. ",text,
L_0512,evolution acts on the phenotype,T_2921,"Natural selection acts on the phenotype (the traits or characteristics) of an individual. On the other hand, natural selection does not act on the underlying genotype (the genetic makeup) of an individual. For many traits, the homozygous genotype, AA, for example, has the same phenotype as the heterozygous Aa genotype. If both an AA and Aa individual have the same phenotype, the environment cannot distinguish between them. So natural selection cannot select for a homozygous individual over a heterozygous individual. Even if the ""aa"" phenotype is lethal, the recessive a allele, will be maintained in the population through heterozygous Aa individuals. Furthermore, the mating of two heterozygous individuals can produce homozygous recessive (aa) individuals. However, natural selection can and does differentiate between dominant and recessive phenotypes. ",text,
L_0512,evolution acts on the phenotype,T_2922,"Since natural selection acts on the phenotype, if an allele causes death in a homozygous individual, aa, for example, it will not cause death in a heterozygous Aa individual. These heterozygous Aa individuals will then act as carriers of the a allele, meaning that the a allele could be passed down to offspring. People who are carriers do not express the recessive phenotype, as they have a dominant allele. This allele is said to be kept in the populations gene pool. The gene pool is the complete set of genes and alleles within a population. For example, Tay-Sachs disease is a recessive human genetic disorder. That means only individuals with the homozygous recessive genotype, rr will be affected. Affected individuals usually die from complications of the disease in early childhood, at an age too young to reproduce. The two parents are each heterozygous (Rr) for the Tay-Sachs gene; they will not die in childhood and will be carriers of the disease gene. This deadly allele is kept in the gene pool even though it does not help humans adapt to their environment. This happens because evolution acts on the phenotype, not the genotype ( Figure 1.1). Tay-Sachs disease is inherited in the au- tosomal recessive pattern. Each parent is an unaffected carrier of the lethal allele. ",text,
L_0513,excretion,T_2923,"So what happens to your bodys wastes? Obviously, you must get rid of them. This is the job of the excretory system. You remove waste as a gas (carbon dioxide), as a liquid (urine and sweat), and as a solid. Excretion is the process of removing wastes and excess water from the body. Recall that carbon dioxide travels through the blood and is transferred to the lungs where it is exhaled. In the large intestine, the remains of food are turned into solid waste for excretion. How is waste other than carbon dioxide removed from the blood? That is the role of the kidneys. Urine is a liquid waste formed by the kidneys as they filter the blood. If you are getting plenty of fluids, your urine should be almost clear. But you might have noticed that sometimes your urine is darker than usual. Do you know why this happens? Sometimes your body is low on water and trying to reduce the amount of water lost in urine. Therefore, your urine gets darker than usual. Your body is striving to maintain homeostasis through the process of excretion. Urine helps remove excess water, salts, and nitrogen from your body. Your body also needs to remove the wastes that build up from cell activity and from digestion. If these wastes are not removed, your cells can stop working, and you can get very sick. The organs of your excretory system help to release wastes from the body. The organs of the excretory system are also parts of other organ systems. For example, your lungs are part of the respiratory system. Your lungs remove carbon dioxide from your body, so they are also part of the excretory system. More organs of the excretory system are listed below ( Table 1.1). Organ(s) Function Lungs Skin Remove carbon dioxide. Sweat glands remove water, salts, and other wastes. Removes solid waste and some wa- ter in the form of feces. Remove urea, salts, and excess wa- ter from the blood. Large intestine Kidneys Component of Other Organ Sys- tem Respiratory system Integumentary system Digestive system Urinary system ",text,
L_0514,excretory system problems,T_2924,The urinary system controls the amount of water in the body and removes wastes. Any problem with the urinary system can also affect many other body systems. ,text,
L_0514,excretory system problems,T_2925,"In some cases, certain mineral wastes can form kidney stones ( Figure 1.1). Stones form in the kidneys and may be found anywhere in the urinary system. Often, stones form when the urine becomes concentrated, allowing minerals to crystallize and stick together. They can vary in size, from small stones that can flow through your urinary system, to larger stones that cannot. Some stones cause great pain, while others cause very little pain. Some stones may need to be removed by surgery or ultrasound treatments. What are the symptoms of kidney stones? You may have a kidney stone if you have pain while urinating, see blood in your urine, and/or feel a sharp pain in your back or lower abdomen (the area between your chest and hips). The pain may last for a long or short time. You may also have nausea and vomiting with the pain. If you have a small stone that passes on its own easily, you may not experience any symptoms. If you have some of these symptoms, you should see your doctor. A kidney stone. The stones can form anywhere in the urinary system. ",text,
L_0514,excretory system problems,T_2926,"Kidney failure happens when the kidneys cannot remove wastes from the blood. If the kidneys are unable to filter wastes from the blood, the wastes build up in the body. Kidney failure can be caused by an accident that injures the kidneys, the loss of a lot of blood, or by some drugs and poisons. Kidney failure may lead to permanent loss of kidney function. But if the kidneys are not seriously damaged, they may recover. Chronic kidney disease is the slow decrease in kidney function that may lead to permanent kidney failure. A person who has lost kidney function may need to get kidney dialysis. Kidney dialysis is the process of filtering the blood of wastes using a machine. A dialysis machine ( Figure 1.2) filters waste from the blood by pumping the blood through a fake kidney. The filtered blood is then returned to the patients body. ",text,
L_0514,excretory system problems,T_2927,"Urinary tract infections (UTIs) are bacterial infections of any part of the urinary tract. When bacteria get into the bladder or kidney and produce more bacteria in the urine, they cause a UTI. The most common type of UTI is a bladder infection. Women get UTIs more often than men. UTIs are often treated with antibiotics. Most UTIs are not serious, but some infections can lead to serious problems. Long lasting kidney infections can cause permanent damage, including kidney scars, poor kidney function, high blood pressure, and other problems. Some sudden kidney infections can be life threatening, especially if the bacteria enter the bloodstream, a condition called septicemia. What are the signs and symptoms of a UTI? a burning feeling when you urinate, frequent or intense urges to urinate, even when you have little urine to pass, pain in your back or side below the ribs, cloudy, dark, bloody, or foul-smelling urine, fever or chills. You should see your doctor if you have signs of a UTI. Your doctor will diagnose a UTIs by asking about your symptoms and then testing a sample of your urine. ",text,
L_0515,features of populations,T_2928,"A population is a group of organisms of the same species, all living in the same area and interacting with each other. Since they live together in one area, members of the same species reproduce together. Ecologists who study populations determine how healthy or stable the populations are. They also study how the individuals of a species interact with each other and how populations interact with the environment. If a group of similar organisms in the same area cannot reproduce with members of the other group, then they are members of two distinct species and form two populations. Ecologists look at many factors that help to describe a population. First, ecologists can measure the number of individuals that make up the population, known as population size. They can then determine the population density, which is the number of individuals of the same species in an area. Population density can be expressed as number per area, such as 20 mice/acre, or 50 rabbits/square mile. Ecologists also study how individuals in a population are spread across an environment. This spacing of individuals within a population is called dispersion. Some species may be clumped or clustered ( Figure 1.1) in an area. Others may be evenly spaced ( Figure 1.2). Still others may be spaced randomly within an area. The population density and dispersion have an effect on reproduction and population size. What do you think the relationship is between population density, dispersion and size? Clumped species are closer together. This may allow for easier reproduction. A population of cacti in the Sonoran Desert generally shows even dispersion due to competition for water. Ecologists also study the birth and death rates of the population. Together these give the growth rate (the birth rate minus the death rate), which tells how fast (or slow) the population size is changing. The birth rate is the number of births within a population during a specific time period. The death rate is the number of deaths within a population during a specific time period. Knowing the birth and death rates of populations gives you information about a populations health. For example, when a population is made up of mostly young organisms and the birth rate is high, the population is growing. A population with equal birth and death rates will remain the same size. Populations that are decreasing in size have a higher death rate than birth rate. ",text,
L_0515,features of populations,T_2928,"A population is a group of organisms of the same species, all living in the same area and interacting with each other. Since they live together in one area, members of the same species reproduce together. Ecologists who study populations determine how healthy or stable the populations are. They also study how the individuals of a species interact with each other and how populations interact with the environment. If a group of similar organisms in the same area cannot reproduce with members of the other group, then they are members of two distinct species and form two populations. Ecologists look at many factors that help to describe a population. First, ecologists can measure the number of individuals that make up the population, known as population size. They can then determine the population density, which is the number of individuals of the same species in an area. Population density can be expressed as number per area, such as 20 mice/acre, or 50 rabbits/square mile. Ecologists also study how individuals in a population are spread across an environment. This spacing of individuals within a population is called dispersion. Some species may be clumped or clustered ( Figure 1.1) in an area. Others may be evenly spaced ( Figure 1.2). Still others may be spaced randomly within an area. The population density and dispersion have an effect on reproduction and population size. What do you think the relationship is between population density, dispersion and size? Clumped species are closer together. This may allow for easier reproduction. A population of cacti in the Sonoran Desert generally shows even dispersion due to competition for water. Ecologists also study the birth and death rates of the population. Together these give the growth rate (the birth rate minus the death rate), which tells how fast (or slow) the population size is changing. The birth rate is the number of births within a population during a specific time period. The death rate is the number of deaths within a population during a specific time period. Knowing the birth and death rates of populations gives you information about a populations health. For example, when a population is made up of mostly young organisms and the birth rate is high, the population is growing. A population with equal birth and death rates will remain the same size. Populations that are decreasing in size have a higher death rate than birth rate. ",text,
L_0516,female reproductive structures,T_2929,"The female reproductive organs include the vagina, uterus, fallopian tubes, and ovaries ( Figure 1.1). The breasts are not shown in this figure. They are not considered reproductive organs, even though they are involved in reproduction. They contain mammary glands that give milk to feed a baby. The milk leaves the breast through the nipple when the baby sucks on it. The vagina is a cylinder-shaped organ found inside of the female body. One end of the vagina opens at the outside of the body. The other end joins with the uterus. During sexual intercourse, sperm may be released into the vagina. If this occurs, the sperm will move through the vagina and into the uterus. During birth, a baby passes from the uterus to the vagina to leave the body. The uterus is a hollow organ with muscular walls. The part that connects the vagina with the uterus is called the cervix. The uterus is where a baby develops until birth. The walls of the uterus grow bigger as the baby grows. The muscular walls of the uterus push the baby out during birth. This drawing shows the organs of the female reproductive system. It shows the organs from the side. Find each organ in the drawing as you read about it in the text. The two ovaries are small, oval organs on either side of the uterus. Each ovary contains thousands of eggs, with about 1-2 million immature eggs present at birth and 40,000 immature eggs present at puberty, as most of the eggs die off. The eggs do not fully develop until a female has gone through puberty. About once a month, on average one egg completes development and is released by the ovary. The ovaries also secrete estrogen, the main female sex hormone. The two fallopian tubes are narrow tubes that open off from the uterus. Each tube reaches for one of the ovaries, but the tubes are not attached to the ovaries. The end of each fallopian tube by the ovary has fingers ( Figure 1.1). They sweep an egg into the fallopian tube. Then the egg passes through the fallopian tube to the uterus. If an egg is to be fertilized, this will occur in the fallopian tube. A fertilized egg then implants into the wall of the uterus, where it begins to develop. An unfertilized egg will flow through the uterus and be excreted from the body. ",text,
L_0517,female reproductive system,T_2930,"Most of the male reproductive organs are outside of the body. But female reproductive organs are inside of the body. The male and female organs also look very different and have different jobs. Two of the functions of the female reproductive system are similar to the functions of the male reproductive system. The female system: 1. Produces gametes, the reproductive cells, which are called eggs in females. 2. Secretes a major sex hormone, estrogen. One of the main roles of the female reproductive system is to produce eggs. Eggs ( Figure 1.1) are female gametes, and they are made in the ovaries. After puberty, females release only one egg at a time. Eggs are actually made in the body before birth, but they do not fully develop until later in life. Like sperm, eggs are produced by meiosis, so they contain half the number of chromosomes as the original cell. Another role of the female system is to secrete estrogen. Estrogen is the main sex hormone in females. Estrogen has two major roles: 1. During the teen years, estrogen causes the reproductive organs to develop. It also causes other female traits to develop. For example, it causes the breasts to grow. 2. During adulthood, estrogen is needed for a woman to release eggs. On average, a woman releases one egg each month from her ovaries. The female reproductive system has another important function. After puberty, the female reproductive system must prepare itself to accept a fertilized egg each cycle (about every month). This cycle is controlled by a well-planned and very complex interplay of hormones. If an egg is not fertilized, the system must prepare itself again the next cycle. The female reproductive system also supports a baby as it develops before birth, and it facilitates the babys birth at the end of pregnancy. ",text,
L_0518,fermentation,T_2931,"Sometimes cells need to obtain energy from sugar, but there is no oxygen present to complete cellular respiration. In this situation, cellular respiration can be anaerobic, occurring in the absence of oxygen. In this process, called fermentation, only the first step of respiration, glycolysis, occurs, producing two ATP; no additional ATP is produced. Therefore, the organism only obtains the two ATP molecules per glucose molecule from glycolysis. Compared to the 36-38 ATP produced under aerobic conditions, anaerobic respiration is not a very efficient process. Fermentation allows the first step of cellular respiration to continue and produce some ATP, even without oxygen. Yeast (single-celled eukaryotic organisms) perform alcoholic fermentation in the absence of oxygen. The products of alcoholic fermentation are ethyl alcohol (drinking alcohol) and carbon dioxide gas. This process is used to make common food and drinks. For example, alcoholic fermentation is used to bake bread. The carbon dioxide bubbles allow the bread to rise and become fluffy. Meanwhile, the alcohol evaporates. In wine making, the sugars of grapes are fermented to produce wine. The sugars are the starting materials for glycolysis. Animals and some bacteria and fungi carry out lactic acid fermentation. Lactic acid is a waste product of this process. Our muscles perform lactic acid fermentation during strenuous exercise, since oxygen cannot be delivered to the muscles quickly enough. The buildup of lactic acid is believed to make your muscles sore after exercise. Bacteria that produce lactic acid are used to make cheese and yogurt. The lactic acid causes the proteins in milk to thicken. Lactic acid also causes tooth decay, because bacteria use the sugars in your mouth for energy. Pictured below are some products of fermentation ( Figure 1.1). Products of fermentation include cheese (lactic acid fermentation) and wine (alco- holic fermentation). ",text,
L_0518,fermentation,T_2932,"Behind every fart is an army of gut bacteria undergoing some crazy biochemistry. These bacteria break down the remains of digested food through fermentation, creating gas in the process. Learn what these bacteria have in common with beer brewing at http://youtu.be/R1kxajH629A?list=PLzMhsCgGKd1hoofiKuifwy6qRXZs7NG6a . Click image to the left or use the URL below. URL: ",text,
L_0521,fish,T_2936,"What exactly is a fish? You probably think the answer is obvious. You may say that a fish is an animal that swims in the ocean or a lake, using fins. But as we saw with the mudskipper, not all fish spend all their time in water. So how do scientists define fish? Some characteristics of fish include: 1. They are ectothermic, meaning their temperature depends on the temperature of their environment. Ectother- mic animals are cold-blooded in that they cannot raise their body temperature on their own. This is unlike humans, whose temperature is controlled from inside the body. 2. They are covered with scales. 3. They have two sets of paired fins and several unpaired fins. 4. They also have a streamlined body that allows them to swim rapidly. Fish are aquatic vertebrates, meaning they have backbones. They became a dominant form of sea life and eventually evolved into land vertebrates. There are three classes of fish: Class Agnatha (the jawless fish), Class Chondrichthyes (the cartilaginous fish), and Class Osteichthyes (the bony fish). All have the characteristics of fish in common, though there are differences unique to each class. ",text,
L_0521,fish,T_2937,"In order to absorb oxygen from the water, fish use gills ( Figure 1.2). Gills take dissolved oxygen from water as the water flows over the surface of the gill. Gills help a fish breathe. ",text,
L_0521,fish,T_2938,"Fish reproduce sexually. They lay eggs that can be fertilized either inside or outside of the body. In most fish, the eggs develop outside of the mothers body. In the majority of these species, fertilization also takes place outside the mothers body. The male and female fish release their gametes into the surrounding water, where fertilization occurs. Female fish release very high numbers of eggs to increase the chances of fertilization. ",text,
L_0521,fish,T_2939,"Fish range in size from the 65-foot, 75,000 pound whale shark ( Figure 1.3) to the stout infantfish, which is about 0.33 inches (8.4 mm), and the Paedocypris progenetica carp species of the Indonesian island of Sumatra, which is about 0.31 inches (7.9 mm) long, making it also the smallest known vertebrate animal. The second-largest fish is the basking shark, which grows to about 40 feet and 8,000 pounds. Both of the large sharks may look ferocious, and would probably scare anyone who comes across one in the water, but both species are filter-feeders, and feed on tiny fish and plankton. The tiny carp species is unique in that it has the appearance of larvae, with a reduced skeleton lacking a cranium, which leaves the brain unprotected by bone. The fish lives in dark acidic waters, having a pH of 3. Keep in mind that whales are not fish, they are mammals. ",text,
L_0521,fish,T_2940,"There are exceptions to many of these fish traits. For example, tuna, swordfish, and some species of shark show some warm-blooded adaptations and are able to raise their body temperature significantly above that of the water around them. Some species of fish have a slower, more maneuverable swimming style, like eels and rays ( Figure 1.4). Body shape and the arrangement of fins are highly variable, and the surface of the skin may be naked, as in moray eels, or covered with scales. Scales can be of a variety of different types. ",text,
L_0521,fish,T_2941,"How are fish important? Of course, they are used as food ( Figure 1.5). In fact, people all over the world either catch fish in the wild or farm them in much the same way as cattle or chickens. Farming fish is known as aquaculture. Fish are also caught for recreation to display in the home or in a public aquarium. ",text,
L_0522,flatworms,T_2942,"The word ""worm"" is not very scientific. But it is a word that informally describes animals (usually invertebrates) that have long bodies with no arms or legs. (Snakes are vertebrates, so they are not usually described as worms.) Worms are the first significant group of animals with bilateral symmetry, meaning that the right side of their bodies is a mirror of the left. One type of worm is the flatworm. Worms in the phylum Platyhelminthes are called flatworms because they have flattened bodies. There are more than 18,500 known species of flatworms. ",text,
L_0522,flatworms,T_2943,"The main characteristics of flatworms ( Figure 1.1) include: 1. Flatworms have no true body cavity, but they do have bilateral symmetry. Due to the lack of a body cav- ity,flatworms are known as acoelomates. 2. Flatworms have an incomplete digestive system. This means that the digestive tract has only one opening. Digestion takes place in the gastrovascular cavity. 3. Flatworms do not have a respiratory system. Instead, they have pores that allow oxygen to enter through their body. Oxygen enters the pores by diffusion. 4. There are no blood vessels in the flatworms. Their gastrovascular cavity helps distribute nutrients throughout the body. 5. Flatworms have a ladder-like nervous system; two interconnected parallel nerve cords run the length of the body. 6. Most flatworms have a distinct head region that includes nerve cells and sensory organs, such as eyespots. The development of a head region, called cephalization, evolved at the same time as bilateral symmetry in animals. This process does not occur in cnidarians, which evolved prior to flatworms and have radial symmetry. Marine flatworms can be brightly colored, such as this one from the class Turbel- laria. These worms are mostly carnivores or scavengers. ",text,
L_0522,flatworms,T_2944,"Flatworms live in a variety of environments. Some species of flatworms are free-living organisms that feed on small organisms and rotting matter. These types of flatworms include marine flatworms and freshwater flatworms, such as Dugesia. Other types of flatworms are parasitic. That means they live inside another organism, called a host, in order to get the food and energy they need. For example, tapeworms have a head-like area with tiny hooks and suckers (known as the scolex) that help the worm attach to the intestines of an animal host ( Figure 1.2). There are over 11,000 species of parasitic flatworms. ",text,
L_0523,food and nutrients,T_2945,"Did you ever hear the old saying, An apple a day keeps the doctor away? Do apples really prevent you from getting sick? Probably not, but eating apples and other fresh fruits can help keep you healthy. Do you eat your vegetables? Maybe you do, but you may have friends who wont touch a piece of broccoli or asparagus. Should you eat these foods and food like them? The girls pictured in the Figure 1.1 are eating salads. Why do you need foods like these for good health? What role does food play in the body? Your body needs food for three reasons: 1. Food gives your body energy. You need energy for everything you do. Remember that cellular respiration converts the glucose in the food you eat into ATP, or cellular energy. Which has more glucose, a salad or a piece of meat? Do you remember what types of foods produce glucose? Recall that glucose is the product of photosynthesis. These girls are eating leafy green vegetables. Fresh vegetables such as these are excellent food choices for good health. 2. Food provides building materials for your body. Your body needs building materials so it can grow and repair itself. Specifically, it needs these materials to produce more cells and its components. 3. Food contains substances that help control body processes. Your body processes must be kept in balance for good health. For all these reasons, you must have a regular supply of nutrients. Nutrients are chemicals in food that your body needs. There are five types of nutrients. 1. 2. 3. 4. 5. Carbohydrates Proteins Lipids Vitamins Minerals Carbohydrates, proteins, and lipids are categories of organic compounds. They give your body energy, though carbohydrates are the main source of energy. Proteins provide building materials, such as amino acids to build your own proteins. Proteins, vitamins, and minerals also help control body processes. Carbohydrates include sugars such as the glucose made by photosynthesis. Often glucose is stored in large molecules such as starch. Proteins are found in foods like meats and nuts. Lipids includes fats and oils. Though you should stay away from many types of fats, others are needed by your body. Important vitamins include vitamins A, B (multiple types) C, D, and E. Important minerals include calcium and potassium. What should you drink to get calcium? Milk is a good source. ",text,
L_0525,fossils,T_2947,"Fossils are the preserved remains of animals, plants, and other organisms from the distant past. Examples of fossils include bones, teeth, and impressions. By studying fossils, evidence for evolution is revealed. Paleontologists are scientists who study fossils to learn about life in the past. Fossils allow these scientists to determine the features of extinct species. Paleontologists compare the features of species from different periods in history. With this information, they try to understand how species have evolved over millions of years ( Figure below). Until recently, fossils were the main source of evidence for evolution ( Figure below). Through studying fossils, we now know that todays organisms look much different in many cases than those that were alive in the past. Scientists have also shown that organisms were spread out differently across the planet. Earthquakes, volcanoes, shifting seas, and other movements of the continents have all affected where organisms live and how they adapted to their changing environments. ",text,
L_0525,fossils,T_2948,"There are many layers of rock in the Earths surface. Newer layers form on top of the older layers; the deepest rock layers are the oldest. Therefore, you can tell how old a fossil is by observing in which layer of rock it was found. Evolution of the horse. Fossil evi- dence, depicted by the skeletal frag- ments, demonstrates evolutionary mile- stones in this process. Notice the 57 million year evolution of the horse leg bones and teeth. Especially obvious is the transformation of the leg bones from having four distinct digits to that of todays horse. The fossils and the order in which fossils appear is called the fossil record. The fossil record provides evidence for when organisms lived on Earth, how species evolved, and how some species have gone extinct. Geologists use a method called radiometric dating to determine the exact age of rocks and fossils in each layer of rock. This technique, which is possible because radioactive materials decay at a known rate, measures how much of the radioactive materials in each rock layer have broken down ( Figure 1.3). Radiometric dating has been used to determine that the oldest known rocks on Earth are between 4 and 5 billion years old. The oldest fossils are between 3 and 4 billion years old. Remember that during Darwins time, people believed the Earth was just about 6,000 years old. The fossil record proves that Earth is much older than people once thought. ",text,
L_0525,fossils,T_2948,"There are many layers of rock in the Earths surface. Newer layers form on top of the older layers; the deepest rock layers are the oldest. Therefore, you can tell how old a fossil is by observing in which layer of rock it was found. Evolution of the horse. Fossil evi- dence, depicted by the skeletal frag- ments, demonstrates evolutionary mile- stones in this process. Notice the 57 million year evolution of the horse leg bones and teeth. Especially obvious is the transformation of the leg bones from having four distinct digits to that of todays horse. The fossils and the order in which fossils appear is called the fossil record. The fossil record provides evidence for when organisms lived on Earth, how species evolved, and how some species have gone extinct. Geologists use a method called radiometric dating to determine the exact age of rocks and fossils in each layer of rock. This technique, which is possible because radioactive materials decay at a known rate, measures how much of the radioactive materials in each rock layer have broken down ( Figure 1.3). Radiometric dating has been used to determine that the oldest known rocks on Earth are between 4 and 5 billion years old. The oldest fossils are between 3 and 4 billion years old. Remember that during Darwins time, people believed the Earth was just about 6,000 years old. The fossil record proves that Earth is much older than people once thought. ",text,
L_0525,fossils,T_2948,"There are many layers of rock in the Earths surface. Newer layers form on top of the older layers; the deepest rock layers are the oldest. Therefore, you can tell how old a fossil is by observing in which layer of rock it was found. Evolution of the horse. Fossil evi- dence, depicted by the skeletal frag- ments, demonstrates evolutionary mile- stones in this process. Notice the 57 million year evolution of the horse leg bones and teeth. Especially obvious is the transformation of the leg bones from having four distinct digits to that of todays horse. The fossils and the order in which fossils appear is called the fossil record. The fossil record provides evidence for when organisms lived on Earth, how species evolved, and how some species have gone extinct. Geologists use a method called radiometric dating to determine the exact age of rocks and fossils in each layer of rock. This technique, which is possible because radioactive materials decay at a known rate, measures how much of the radioactive materials in each rock layer have broken down ( Figure 1.3). Radiometric dating has been used to determine that the oldest known rocks on Earth are between 4 and 5 billion years old. The oldest fossils are between 3 and 4 billion years old. Remember that during Darwins time, people believed the Earth was just about 6,000 years old. The fossil record proves that Earth is much older than people once thought. ",text,
L_0533,genetic disorders,T_2968,"Many genetic disorders are caused by mutations in one or a few genes. Others are caused by chromosomal mutations. Some human genetic disorders are X-linked or Y-linked, which means the faulty gene is carried on these sex chromosomes. Other genetic disorders are carried on one of the other 22 pairs of chromosomes; these chromosomes are known as autosomes or autosomal (non-sex) chromosomes. Some genetic disorders are due to new mutations, others can be inherited from your parents. ",text,
L_0533,genetic disorders,T_2969,"Some genetic disorders are caused by recessive alleles of a single gene on an autosome. An example of autosomal recessive genetic disorders are Tay-Sachs disease and cystic fibrosis. Children with cystic fibrosis have excessively thick mucus in their lungs, which makes it difficult for them to breathe. The inheritance of this recessive allele is the same as any other recessive allele, so a Punnett square can be used to predict the probability that two carriers of the disease will have a child with cystic fibrosis. Recall that carriers have the recessive allele for a trait but do not express the trait. What are the possible genotypes of the offspring in the following table ( Table 1.1)? What are the possible phenotypes? F FF (normal) Ff (carrier) F f f Ff (carrier) ff (affected) According to this Punnett square, two parents that are carriers (Ff ) of the cystic fibrosis gene have a 25% chance of having a child with cystic fibrosis (ff ). The affected child must inherit two recessive alleles. The carrier parents are not affected. Tay-Sachs disease is a severe genetic disorder in which affected children do not live to adulthood, so the gene is not passed from an affected individual. Carriers of the Tay-Sachs gene are not affected. How does a child become affected with Tay-Sachs? ",text,
L_0533,genetic disorders,T_2970,"Huntingtons disease is an example of an autosomal dominant disorder. This means that if the dominant allele is present, then the person will express the disease. A child only has to inherit one dominant allele to have the disease. The disease causes the brains cells to break down, leading to muscle spasms and personality changes. Unlike most other genetic disorders, the symptoms usually do not become apparent until middle age. You can use a simple Punnett square to predict the inheritance of a dominant autosomal disorder, like Huntingtons disease. If one parent has Huntingtons disease, what is the chance of passing it on to the children? If you draw the Punnett square, you will find that there is a 50 percent chance of the disorder being passed on to the children. ",text,
L_0537,hardy weinberg theorem,T_2985,"Sometimes understanding how common a gene is within a population is necessary. Or, more specifically, you may want to know how common a certain form of that gene is within the population, such as a recessive form. This can be done using the Hardy-Weinberg model, but it can only be done if the frequencies of the genes are not changing. The Hardy-Weinberg model describes how a population can remain at genetic equilibrium, referred to as the Hardy-Weinberg equilibrium. Genetic equilibrium occurs when there is no evolution within the population. In other words, the frequency of alleles (variants of a gene) will be the same from one generation to another. At genetic equilibrium, the gene or allele frequencies are stablethey do not change. For example, lets assume that red hair is determined by the inheritance of a gene with two allelesR and r. The dominant allele, R, encodes for non-red hair, while the recessive allele, r, encodes for red hair. If a populations gene pool contains 90% R and 10% r alleles, then the next generation would also have 90% R and 10% r alleles. However, this only works under a strict set of conditions. The five conditions that must be met for genetic equilibrium to occur include: 1. 2. 3. 4. 5. No mutation (change) in the DNA sequence. No migration (moving into or out of a population). A very large population size. Random mating. No natural selection. These five conditions rarely occur in nature. When one or more of the conditions does not exist, then evolution can occur. As a result, allele frequencies are constantly changing, and populations are constantly evolving. As mutations and natural selection occur frequently in nature, it is difficult for a population to be at genetic equilibrium. The Hardy-Weinberg model also serves a mathematical formula used to predict allele frequencies in a population at genetic equilibrium. If you know the allele frequencies of one generation, you can use this formula to predict the next generation. Again, this only works if all five conditions are being met in a population. ",text,
L_0538,harmful bacteria,T_2986,"With so many species of bacteria, some are bound to be harmful. Harmful bacteria can make you sick. They can also ruin food and be used to hurt people. ",text,
L_0538,harmful bacteria,T_2987,"There are also ways that bacteria can be harmful to humans and other animals. Bacteria are responsible for many types of human illness ( Figure 1.1), including: Strep throat Tuberculosis Pneumonia Leprosy Lyme disease Luckily most of these can be treated with antibiotics, which kill the bacteria. It is important that when a medical doctor prescribes antibiotics for you, you take the medicine exactly as the doctor tells you. You need to make sure the bacteria is killed. ",text,
L_0538,harmful bacteria,T_2988,"Bacterial contamination of foods can lead to digestive problems, an illness known as food poisoning. Raw eggs and undercooked meats commonly carry the bacteria that can cause food poisoning. Food poisoning can be prevented by cooking meat thoroughly, which kills most microbes, and washing surfaces that have been in contact with raw meat. Washing your hands before and after handling food also helps prevent contamination. ",text,
L_0538,harmful bacteria,T_2989,"Some bacteria also have the potential to be used as biological weapons by terrorists. An example is anthrax, a disease caused by the bacterium Bacillus anthracis. Inhaling the spores of this bacterium can lead to a deadly infection, and, therefore, it is a dangerous weapon. In 2001, an act of terrorism in the United States involved B. anthracis spores sent in letters through the mail. ",text,
L_0538,harmful bacteria,T_2990,KidsHealth Food Poisoning at http://kidshealth.org/kid/ill_injure/sick/food_poisoning.html . 1. What are the common bacteria that cause food poisoning? 2. What steps can you take to keep your food safe? ,text,
L_0539,health hazards of air pollution,T_2991,"The World Health Organization (WHO) reports that 2.4 million people die each year from causes directly related to air pollution. This includes both outdoor and indoor air pollution. Worldwide, there are more deaths linked to air pollution each year than to car accidents. Research by the WHO also shows that the worst air quality is in countries with high poverty and population rates, such as Egypt, Sudan, Mongolia, and Indonesia. Respiratory system disorders are directly related to air pollution. These disorders have severe effects on human health, some leading to death directly related to air pollution. Air pollution related respiratory disorders include asthma, bronchitis, and emphysema. Asthma is a respiratory disorder characterized by wheezing, coughing, and a feeling of constriction in the chest. Bronchitis is inflammation of the membrane lining of the bronchial tubes of the lungs. Emphysema is a deadly lung disease characterized by abnormal enlargement of air spaces in the lungs and destruction of the lung tissue. Additional lung and heart diseases are also related to air pollution, as are respiratory allergies. Air pollution can also indirectly cause other health issues and even deaths. Air pollutants can cause an increase in cancer including lung cancer, eye problems, and other conditions. For example, using certain chemicals on farms, such as the insecticide DDT (dichlorodiphenyltrichloroethane) and toxic PCBs (polychlorinated biphenyl), can cause cancer. Indoors, pollutants such as radon or asbestos can also increase your cancer risk. Lastly, air pollution can lead to heart disease, including heart attack and stroke. ",text,
L_0539,health hazards of air pollution,T_2992,"Certain respiratory conditions can be made worse in people who live closer to or in large cites. Some studies have shown that people in urban areas suffer lower levels of lung function and more chronic bronchitis and emphysema. If you live in a city, you have seen smog. It is a low-hanging, fog-like cloud that seems to never leave the city ( Figure 1.1). Smog is caused by coal burning and by ozone produced by motor vehicle exhaust. Smog can cause eye irritation and respiratory problems. A layer of smog is typical for Cairo, Egypt. ",text,
L_0539,health hazards of air pollution,T_2993,"After reading about the effects of air pollution, both indoors and outdoors, you may wonder how you can avoid it. As for outdoor air pollution, if you hear in the news that the outdoor air quality is particularly bad, then it might make sense to wear a mask outdoors or to stay indoors. Because you have more control over your indoor air quality than the outdoor air quality, there are some simple steps you can take indoors to make sure the air quality is less polluted. These include: 1. 2. 3. 4. Make sure that vents and chimneys are working properly, and never burn charcoal indoors. Place carbon monoxide detectors in the home. Keep your home as clean as possible from pet dander, dust, dust mites, and mold. Make sure air conditioning systems are working properly. Are there any other ways you can think of to protect yourself from air pollution? ",text,
L_0540,health of the digestive system,T_2994,"Most of the time, you probably arent aware of your digestive system. It works well without causing any problems. But most people have problems with their digestive system at least once in a while. Did you ever eat something that didnt agree with you? Maybe you had a stomachache or felt sick to your stomach? Maybe you had diarrhea? These could be symptoms of foodborne illness, food allergies, or a food intolerance. ",text,
L_0540,health of the digestive system,T_2995,"Harmful bacteria can enter your digestive system in food and make you sick. This is called foodborne illness or food poisoning. The bacteria, or the toxins they produce, may cause vomiting or cramping, in addition to the symptoms mentioned above. Foodborne illnesses can also be caused by viruses and parasites. The most common foodborne illnesses happen within a few minutes to a few hours, and make you feel really sick, but last for only about a day or so. Others can take longer for the illness to appear. Some people believe that the taste of food will tell you if it is bad. As a rule, you probably should not eat bad tasting food, but many contaminated foods can still taste good. You can help prevent foodborne illness by following a few simple rules. Keep hot foods hot and cold foods cold. This helps prevent any bacteria in the foods from multiplying. Wash your hands before you prepare or eat food. This helps prevent bacteria on your hands from getting on the food. This is the easiest way to prevent foodborne illnesses. Wash your hands after you touch raw foods, such as meats, poultry, fish, or eggs. These foods often contain bacteria that your hands could transfer to your mouth. Cook meats, poultry, fish, and eggs thoroughly before eating them. The heat of cooking kills any bacteria the foods may contain, so they cannot make you sick. Refrigerate cooked food soon after a meal. Cooked food can be left out for up to two hours before they need to be placed in the cold. This will prevent the spread of bacteria. Cooked foods should not be left out all day. Bacteria that cause foodborne illnesses include Salmonella, a bacterium found in many foods, including raw and undercooked meat, poultry, dairy products, and seafood. Campylobacter jejuni is found in raw or undercooked chicken and unpasteurized milk. Several strains of E. coli can cause illnesses, and are found in raw or undercooked hamburger, unpasteurized fruit juices and milk, and even fresh produce. Vibrio is a bacterium that may contaminate fish or shellfish. Listeria has been found in raw and undercooked meats, unpasteurized milk, soft cheeses, and ready- to-eat deli meats and hot dogs. Most of these bacterial illnesses can be prevented with proper cooking of food and washing of hands. Common foodborne viruses include norovirus and hepatitis A virus. Norovirus, which causes inflammation of the stomach and intestines, has been a recent issue on cruise ships, infecting hundreds of passengers and crew on certain voyages. Hepatitis A causes inflammation of the liver, which is treated with rest and diet changes. Parasites are tiny organisms that live inside another organism. Giardia is a parasite spread through water contaminated with the stools of people or animals who are infected. Food preparers who are infected with parasites can also contaminate food if they do not thoroughly wash their hands after using the bathroom and before handling food. Trichinella is a type of roundworm parasite. People may be infected with this parasite by consuming raw or undercooked pork or wild game. ",text,
L_0540,health of the digestive system,T_2996,"Food allergies are like other allergies. They occur when the immune system reacts to harmless substances as though they were harmful. Almost ten percent of children have food allergies. Some of the foods most likely to cause allergies are shown below ( Figure 1.1). Eating foods you are allergic to may cause vomiting, diarrhea, or skin rashes. Some people are very allergic to certain foods. Eating even tiny amounts of the foods causes them to have serious symptoms, such as difficulty breathing. If they eat the foods by accident, they may need emergency medical treatment. Some of the foods that commonly cause allergies are shown here. They include nuts, eggs, grains, milk, and shellfish. Are you allergic to any of these foods? The most common food allergy symptoms include: tingling or itching in the mouth hives, itching or eczema, swelling of the lips, face, tongue and throat, or other parts of the body, wheezing, nasal congestion or trouble breathing, abdominal pain, diarrhea, nausea or vomiting, dizziness, lightheadedness or fainting. In some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can cause a coma or death. Anaphylaxis is vary rare. The vast majority of people will never have an anaphylactic reaction. The life-threatening symptoms of anaphylaxis include: constriction and tightening of the airway, a swollen throat or the sensation of a lump in your throat that makes it difficult to breathe, shock, with a severe drop in blood pressure, a rapid pulse, dizziness, lightheadedness or loss of consciousness. ",text,
L_0540,health of the digestive system,T_2997,"A food intolerance, or food sensitivity, is different from a food allergy. A food intolerance happens when the digestive system is unable to break down a certain type of food. This can result in stomach cramping, diarrhea, tiredness, and weight loss. Food intolerances are often mistakenly called allergies. Lactose intolerance is a food intolerance. A person who is lactose intolerant does not make enough lactase, the enzyme that breaks down the milk sugar, lactose. Lactose intolerance may be as high as 75% in some populations, but overall the percentage of affected individuals is much less. Still, well over 10% of the worlds population is lactose intolerant. ",text,
L_0541,hearing and balance,T_2998,What do listening to music and riding a bike have in common? It might surprise you to learn that both activities depend on your ears. The ears do more than just detect sound. They also sense the position of the body and help maintain balance. ,text,
L_0541,hearing and balance,T_2999,"Hearing is the ability to sense sound. Sound travels through the air in waves, much like the waves you see in the water pictured below ( Figure 1.1). Sound waves in air cause vibrations inside the ears. The ears sense the vibrations. The human ear is pictured below ( Figure 1.2). As you read about it, trace the path of sound waves through the ear. Assume a car horn blows in the distance. Sound waves spread through the air from the horn. Some of the sound waves reach your ear. The steps below show what happens next. They explain how your ears sense the sound. 1. The sound waves travel to the ear canal (external auditory canal in the figure). This is a tube-shaped opening in the ear. Sound waves travel through the air in all directions away from a sound, like waves traveling through water away from where a pebble was dropped. Read the names of the parts of the ear in the text; then find each of the parts in the diagram. Note that the round window is distinct from the oval window. 2. At the end of the ear canal, the sound waves hit the eardrum (tympanic membrane). This is a thin membrane that vibrates like the head of a drum when sound waves hit it. 3. The vibrations pass from the eardrum to the hammer (malleus). This is the first of three tiny bones that pass vibrations through the ear. 4. The hammer passes the vibrations to the anvil (incus), the second tiny bone that passes vibrations through the ear. 5. The anvil passes the vibrations to the stirrup (stapes), the third tiny bone that passes vibrations through the ear. 6. From the stirrup, the vibrations pass to the oval window. This is another membrane like the eardrum. 7. The oval window passes the vibrations to the cochlea. The cochlea is filled with liquid that moves when the vibrations pass through, like the waves in water when you drop a pebble into a pond. Tiny hair cells line the cochlea and bend when the liquid moves. When the hair cells bend, they release neurotransmitters. 8. The neurotransmitters trigger nerve impulses that travel to the brain through the auditory nerve (cochlear No doubt youve been warned that listening to loud music or other loud sounds can damage your hearing. Its true. In fact, repeated exposure to loud sounds is the most common cause of hearing loss. The reason? Very loud sounds can kill the tiny hair cells lining the cochlea. The hair cells do not generally grow back once they are destroyed, so this type of hearing loss is permanent. You can protect your hearing by avoiding loud sounds or wearing earplugs or other ear protectors. ",text,
L_0541,hearing and balance,T_2999,"Hearing is the ability to sense sound. Sound travels through the air in waves, much like the waves you see in the water pictured below ( Figure 1.1). Sound waves in air cause vibrations inside the ears. The ears sense the vibrations. The human ear is pictured below ( Figure 1.2). As you read about it, trace the path of sound waves through the ear. Assume a car horn blows in the distance. Sound waves spread through the air from the horn. Some of the sound waves reach your ear. The steps below show what happens next. They explain how your ears sense the sound. 1. The sound waves travel to the ear canal (external auditory canal in the figure). This is a tube-shaped opening in the ear. Sound waves travel through the air in all directions away from a sound, like waves traveling through water away from where a pebble was dropped. Read the names of the parts of the ear in the text; then find each of the parts in the diagram. Note that the round window is distinct from the oval window. 2. At the end of the ear canal, the sound waves hit the eardrum (tympanic membrane). This is a thin membrane that vibrates like the head of a drum when sound waves hit it. 3. The vibrations pass from the eardrum to the hammer (malleus). This is the first of three tiny bones that pass vibrations through the ear. 4. The hammer passes the vibrations to the anvil (incus), the second tiny bone that passes vibrations through the ear. 5. The anvil passes the vibrations to the stirrup (stapes), the third tiny bone that passes vibrations through the ear. 6. From the stirrup, the vibrations pass to the oval window. This is another membrane like the eardrum. 7. The oval window passes the vibrations to the cochlea. The cochlea is filled with liquid that moves when the vibrations pass through, like the waves in water when you drop a pebble into a pond. Tiny hair cells line the cochlea and bend when the liquid moves. When the hair cells bend, they release neurotransmitters. 8. The neurotransmitters trigger nerve impulses that travel to the brain through the auditory nerve (cochlear No doubt youve been warned that listening to loud music or other loud sounds can damage your hearing. Its true. In fact, repeated exposure to loud sounds is the most common cause of hearing loss. The reason? Very loud sounds can kill the tiny hair cells lining the cochlea. The hair cells do not generally grow back once they are destroyed, so this type of hearing loss is permanent. You can protect your hearing by avoiding loud sounds or wearing earplugs or other ear protectors. ",text,
L_0541,hearing and balance,T_3000,"Did you ever try to stand on one foot with your eyes closed? Try it and see what happens, but be careful! Its harder to keep your balance when you cant see. Your eyes obviously play a role in balance. But your ears play an even bigger role. The gymnast pictured below ( Figure 1.3) may not realize it, but her earsalong with her cerebellumare mostly responsible for her ability to perform on the balance beam. The parts of the ears involved in balance are the semicircular canals. Above, the semicircular canals are colored purple ( Figure 1.2). The canals contain liquid and are like the bottle of water pictured below ( Figure 1.4). When the bottle tips, the water surface moves up and down the sides of the bottle. When the body tips, the liquid in the semicircular canals moves up and down the sides of the canals. Tiny hair cells line the semicircular canals. Movement of the liquid inside the canals causes the hair cells to send nerve impulses. The nerve impulses travel to the cerebellum in the brain along the vestibular nerve. In response, the cerebellum sends commands to muscles to contract or relax so that the body stays balanced. ",text,
L_0542,heart,T_3001,"What does the heart look like? How does it pump blood? The heart is divided into four chambers ( Figure 1.1), or spaces: the left and right atria, and the left and right ventricles. An atrium (singular for atria) is one of the two small, thin-walled chambers on the top of the heart where the blood first enters. A ventricle is one of the two muscular V-shaped chambers that pump blood out of the heart. You can remember they are called ventricles because they are shaped like a ""V."" The atria receive the blood, and the ventricles pump the blood out of the heart. Each of the four chambers of the heart has a specific job. The right atrium receives oxygen-poor blood from the body. The right ventricle pumps oxygen-poor blood toward the lungs, where it receives oxygen. The left atrium receives oxygen-rich blood from the lungs. The left ventricle pumps oxygen-rich blood out of the heart to the rest of the body. ",text,
L_0542,heart,T_3002,"Blood flows through the heart in two separate loops. You can think of them as a left side loop and a right side loop. The right side of the heart collects oxygen-poor blood from the body and pumps it into the lungs, where it releases carbon dioxide and picks up oxygen. (Recall that carbon dioxide is a waste product that must be removed. It is removed when we exhale.) The left side carries the oxygen-rich blood back from the lungs into the left side of the heart, which then pumps the oxygen-rich blood to the rest of the body. The blood delivers oxygen to the cells of the body, where it is needed for cellular respiration, and returns to the heart oxygen-poor. To move blood through the heart, the cardiac muscle needs to contract in an organized way. Blood first enters the atria ( Figure 1.2). When the atria contract, blood is pushed into the ventricles. After the ventricles fill with blood, they contract, and blood is pushed out of the heart. The heart is mainly composed of cardiac muscle. These muscle cells contract in unison, causing the heart itself to contract and generating enough force to push the blood out. So how is the blood kept from flowing back on itself? Valves ( Figure 1.2) in the heart keep the blood flowing in one direction. The valves do this by opening and closing in one direction only. Blood only moves forward through the heart. The valves stop the blood from flowing backward. There are four valves of the heart. The two atrioventricular (AV) valves stop blood from moving from the ventricles to the atria. The two semilunar (SL) valves are found in the arteries leaving the heart, and they prevent blood from flowing back from the arteries into the ventricles. Why does a heart beat? The lub-dub sound of the heartbeat is caused by the closing of the AV valves (""lub"") and SL valves (""dub"") after blood has passed through them. ",text,
L_0543,helpful bacteria,T_3003,"Can we survive without bacteria? Could bacteria survive without us? No and yes. No, we could not survive without bacteria. And yes, bacteria could survive without us. ",text,
L_0543,helpful bacteria,T_3004,"Bacteria can be used to make cheese from milk. The bacteria turn the milk sugars into lactic acid. The acid is what causes the milk to curdle to form cheese. Bacteria are also involved in producing other foods. Yogurt is made by using bacteria to ferment milk ( Figure 1.1). Fermenting cabbage with bacteria produces sauerkraut. Yogurt is made from milk fermented with bacteria. The bacteria ingest natural milk sugars and release lactic acid as a waste product, which causes proteins in the milk to form into a solid mass, which becomes the yogurt. ",text,
L_0543,helpful bacteria,T_3005,"In the laboratory, bacteria can be changed to provide us with a variety of useful materials. Bacteria can be used as tiny factories to produce desired chemicals and medicines. For example, insulin, which is necessary to treat people with diabetes, can be produced using bacteria. Through the process of transformation, the human gene for insulin is placed into bacteria. The bacteria then use that gene to make a protein. The protein can be separated from the bacteria and then used to treat patients. The mass production of insulin by bacteria made this medicine much more affordable. During transformation, bacteria can take up any DNA from the environment. Therefore, transformation allows scientists to insert any DNA into a bacteria, potentially producing many different proteins. This makes the bacteria greatly useful to people. ",text,
L_0543,helpful bacteria,T_3006,"Bacteria also help you digest your food. Several species of bacteria, such as E. coli, are found in your digestive tract. In fact, in your gut, bacteria cells greatly outnumber your own cells! ",text,
L_0543,helpful bacteria,T_3007,"Bacteria are important in practically all ecosystems because many bacteria are decomposers. They break down dead materials and waste products and recycle nutrients back into the environment. The recycling of nutrients, such as nitrogen, by bacteria, is essential for living organisms. Organisms cannot produce nutrients, so they must come from other sources. We get nutrients from the food we eat; plants get them from the soil. How do these nutrients get into the soil? One way is from the actions of decomposers. Without decomposers, we would eventually run out of the materials we need to survive. We also depend on bacteria to decompose our wastes in sewage treatment plants. ",text,
L_0544,hiv and aids,T_3008,"HIV, or human immunodeficiency virus, causes AIDS. AIDS stands for ""acquired immune deficiency syndrome."" It is a condition that causes death and does not have a known cure. AIDS usually develops 10 to 15 years after a person is first infected with HIV. The development of AIDS can be delayed with proper medicines. The delay can be well over 20 years with the right medicines. Today, individuals who acquire HIV after 50 years of age can expect to reach an average human life span. ",text,
L_0544,hiv and aids,T_3009,"HIV spreads through contact between an infected persons body fluids and another persons bloodstream or mucus membranes, which are found in the mouth, nose, and genital areas. Body fluids that may contain HIV are blood, semen, vaginal fluid, and breast milk. The virus can spread through sexual contact or shared drug needles. It can also spread from an infected mother to her baby during childbirth or breastfeeding. Saliva can carry the HIV virus, but it wont spread it, unless the saliva gets into the bloodstream. Other body fluids such as urine and sweat do not contain the virus. HIV does not spread in any fluid in which the host cells cannot survive. Some people think they can become infected with HIV by donating blood or receiving donated blood. This is not true. The needles used to draw blood for donations are always new. Therefore, they cannot spread the virus. Donated blood is also tested to make sure it is does not contain HIV. HIV is not transmitted by day-to-day contact in the workplace, schools, or social settings. HIV is not transmitted through shaking hands, hugging, or a casual kiss. You cannot become infected from a toilet seat, a drinking fountain, a door knob, dishes, drinking glasses, food, or pets. ",text,
L_0544,hiv and aids,T_3010,"How does an HIV infection develop into AIDS? HIV destroys white blood cells called helper T cells. The cells are produced by the immune system. This is the body system that fights infections and other diseases. HIV invades helper T cells and uses them to produce more virus particles ( Figure 1.1). Then, the virus kills the helper T cells. As the number of viruses in the blood rises, the number of helper T cells falls. Without helper T cells, the immune system is unable to protect the body. The infected person cannot fight infections and other diseases because they do not have T cells. This is why people do not die from HIV. Instead, they die from another illness, like the common cold, that they cannot fight because they do not have helper T cells. Medications can slow down the increase of viruses in the blood. But the medications cannot remove the viruses from the body. At present, there is no cure for HIV infection. A vaccine against HIV could stop this disease, and such a vaccine is in development, though it could take many years before it can be given to prevent this virus. ",text,
L_0544,hiv and aids,T_3011,"AIDS is not really a single disease. It is a set of symptoms and other diseases. It results from years of damage to the immune system by HIV. AIDS occurs when helper T cells fall to a very low level, making it difficult for the affected person to fight various diseases and other infections. These people develop infections or cancers that people with a healthy immune systems can easily resist. These diseases are usually the cause of death of people with AIDS. The first known cases of AIDS occurred in 1981. Since then, AIDS has led to the deaths of more than 35 million people worldwide. Many of them were children. The greatest number of deaths occurred in Africa. It is also where medications to control HIV are least available. There are currently more people infected with HIV in Africa than any other part of the world. Well over 30 million people are living with HIV worldwide. ",text,
L_0545,homeostasis,T_3012,"When you walk outside on a cool day, does your body temperature drop? No, your body temperature stays stable at around 98.6 degrees Fahrenheit. Even when the temperature around you changes, your internal temperature stays the same. This ability of the body to maintain a stable internal environment despite a changing environment is called home- ostasis. Homeostasis doesnt just protect against temperature changes. Other aspects of your internal environment also stay stable. For example, your body closely regulates your fluid balance. You may have noticed that if you are slightly dehydrated, your urine is darker. Thats because the urine is more concentrated and less water is mixed in with it. ",text,
L_0545,homeostasis,T_3013,"So how does your body maintain homeostasis? The regulation of your internal environment is done primarily through negative feedback. Negative feedback is a response to a stimulus that keeps a variable close to a set value ( Figure For example, your body has an internal thermostat. During a winter day, in your house a thermostat senses the temperature in a room and responds by turning on or off the heater. Your body acts in much the same way. When body temperature rises, receptors in the skin and the brain sense the temperature change. The temperature change triggers a command from the brain. This command can cause several responses. If you are too hot, the skin makes sweat and blood vessels near the skin surface dilate. This response helps decrease body temperature. Another example of negative feedback has to do with blood glucose levels. When glucose (sugar) levels in the blood are too high, the pancreas secretes insulin to stimulate the absorption of glucose and the conversion of glucose into glycogen, which is stored in the liver. As blood glucose levels decrease, less insulin is produced. When glucose levels are too low, another hormone called glucagon is produced, which causes the liver to convert glycogen back to glucose. For additional information, see Homeostasis at  . Feedback Regulation. If a raise in body temperature (stimulus) is detected (recep- tor), a signal will cause the brain to main- tain homeostasis (response). Once the body temperature returns to normal, neg- ative feedback will cause the response to end. This sequence of stimulus-receptor- signal-response is used throughout the body to maintain homeostasis. ",text,
L_0545,homeostasis,T_3014,"Some processes in the body are regulated by positive feedback. Positive feedback is when a response to an event increases the likelihood of the event to continue. An example of positive feedback is milk production in nursing mothers. As the baby drinks her mothers milk, the hormone prolactin, a chemical signal, is released. The more the baby suckles, the more prolactin is released, which causes more milk to be produced. Other examples of positive feedback include contractions during childbirth. When constrictions in the uterus push a baby into the birth canal, additional contractions occur. ",text,
L_0546,how the eye works,T_3015,"Carbon is one of the most common elements found in living organisms. Chains of carbon molecules form the backbones of many organic molecules, such as carbohydrates, proteins, and lipids. Carbon is constantly cycling between living organisms and the atmosphere ( Figure 1.1). The cycling of carbon occurs through the carbon cycle. Living organisms cannot make their own carbon, so how is carbon incorporated into living organisms? In the atmosphere, carbon is in the form of carbon dioxide gas (CO2 ). Recall that plants and other producers capture the carbon dioxide and convert it to glucose (C6 H12 O6 ) through the process of photosynthesis. Then as animals eat plants or other animals, they gain the carbon from those organisms. The chemical equation of photosynthesis is 6CO2 + 6H2 O  C6 H12 O6 + 6O2 . How does this carbon in living things end up back in the atmosphere? Remember that we breathe out carbon dioxide. This carbon dioxide is generated through the process of cellular respiration, which has the reverse chemical reaction as photosynthesis. That means when our cells burn food (glucose) for energy, carbon dioxide is released. We, like all animals, exhale this carbon dioxide and return it back to the atmosphere. Also, carbon is released to the atmosphere as an organism dies and decomposes. Cellular respiration and photosynthesis can be described as a cycle, as one uses carbon dioxide (and water) and makes oxygen (and glucose), and the other uses oxygen (and glucose) and makes carbon dioxide (and water). The carbon cycle. The cycling of carbon dioxide in photosynthesis and cellular res- piration are main components of the car- bon cycle. Carbon is also returned to the atmosphere by the burning of fossil fuels and decomposition of organic matter. ",text,
L_0546,how the eye works,T_3016,"Millions of years ago, there were so many dead plants and animals that they could not completely decompose before they were buried. They were covered over by soil or sand, tar or ice. These dead plants and animals are organic matter made out of cells full of carbon-containing organic compounds (carbohydrates, lipids, proteins and nucleic acids). What happened to all this carbon? When organic matter is under pressure for millions of years, it forms fossil fuels. Fossil fuels are coal, oil, and natural gas. When humans dig up and use fossil fuels, we have an impact on the carbon cycle ( Figure 1.2). This carbon is not recycled until it is used by humans. The burning of fossil fuels releases more carbon dioxide into the atmosphere than is used by photosynthesis. So, there is more carbon dioxide entering the atmosphere than is coming out of it. Carbon dioxide is known as a greenhouse gas, since it lets in light energy but does not let heat escape, much like the panes of a greenhouse. The increase of greenhouse gasses in the atmosphere is contributing to a global rise in Earths temperature, known as global warming or global climate change. ",text,
L_0547,human causes of extinction,T_3017,"In addition to habitat destruction, other human-caused problems are also threatening many species. These include issues associated with climate change, pollution, and over-population. ",text,
L_0547,human causes of extinction,T_3018,"Another major cause of extinction is global warming, which is also known as global climate change. During the past century, the Earths average temperature has risen by almost 1C (about 1.3F). You may not think that is significant, but to organisms that live in the wild and are constantly adapting to their environments, any climate change can be hazardous. Recall that burning fossil fuels releases gasses into the atmosphere that warm the Earth. Our increased use of fossil fuels, such as coal and oil, is changing the Earths climate. Any long-term change in the climate can destroy the habitat of a species. Even a brief change in climate may be too stressful for an organism to survive. For example, if the seas increase in temperature, even briefly, it may be too warm for certain types of fish to reproduce. ",text,
L_0547,human causes of extinction,T_3019,"Pollution adds chemicals, noise, heat, or even light to an environment. This can have many different harmful effects on all kinds of organisms. For example, the pesticide DDT nearly eliminated the peregrine falcon in some parts of the world. This pesticide caused falcons to lay eggs with thinner shells. As a result, fewer falcon eggs survived to hatching. Populations of peregrine falcons declined rapidly. DDT was then banned in the U.S. and peregrine falcon populations have recovered. Water pollution threatens vital freshwater and marine resources throughout the world ( Figure 1.1). Specifically, industrial and agricultural chemicals, waste, and acid rain threaten water. As water is essential for all ecosystems, water pollution can result in the extinction of species. A bird that was the victim of an oil spill. About 58,000 gallons of oil spilled from a South Korea-bound container ship when it struck a tower supporting the San Francisco-Oakland Bay Bridge in dense fog in November, 2007. Finally, soil contamination can also result in extinction. Soil contamination can come from toxic industrial and municipal wastes ( Figure 1.2), salts from irrigation, and pesticides from agriculture. These all degrade the soil as well. As soil is the foundation of terrestrial ecosystems, this can result in extinction. ",text,
L_0547,human causes of extinction,T_3020,"Human populations are on the rise. The human population passed the 7 billion mark in October of 2011, and will pass 8 and 9 billion probably before the middle of the century. All these people will need resources such as places to live, food to eat, and water to drink, and they will use energy and create waste. Essentially, human population growth can effect all other causes of extinction. For example, more people on the Earth means more people contributing to global warming and pollution. More people also means more clearing of land for agriculture and development. Recall that development by humans often causes habitats to be destroyed. This destruction can force species to go extinct, or move somewhere else. ",text,
L_0548,human digestive system,T_3021,"Nutrients in the foods you eat are needed by the cells of your body. How do the nutrients in foods get to your body cells? What organs and processes break down the foods and make the nutrients available to cells? The organs are those of the digestive system. The processes are digestion and absorption. The digestive system is the body system that breaks down food and absorbs nutrients. It also gets rid of solid food waste. The digestive system is mainly one long tube from the mouth to the anus, known as the gastrointestinal tract (GI tract). The main organs of the digestive system include the esophagus, stomach and the intestine, and are pictured below ( Figure 1.1). The intestine is divided into the small and large intestine. The small intestine has three segments. The ileum is the longest segment of the small intestine, which is well over 10 feet long. The large intestine is about 5 feet long. This drawing shows the major organs of the digestive system. The liver, pancreas and gallbladder are also organs of the digestive system. Digestion is the process of breaking down food into nutrients. There are two types of digestion, mechanical and chemical. In mechanical digestion, large chunks of food are broken down into small pieces. Mechanical digestion begins in the mouth and involves physical processes, such as chewing. This process continues in the stomach as the food is mixed with digestive juices. In chemical digestion, large food molecules are broken down into small nutrient molecules. This is a chemical process which also begins in the mouth as saliva begins to break down food and continues in the stomach as stomach enzymes further digest the food. Absorption is the process that allows substances you eat to be taken up by the blood. After food is broken down into small nutrient molecules, the molecules are absorbed by the blood. After absorption, the nutrient molecules travel in the bloodstream to cells throughout the body. This happens mostly in the small intestine. Some substances in food cannot be broken down into nutrients. They remain behind in the digestive system after the nutrients are absorbed. Any substances in food that cannot be digested and absorbed pass out of the body as solid waste. The process of passing solid food waste out of the body is called elimination. ",text,
L_0550,human genome project,T_3025,"A persons genome is all of his or her genetic information. In other words, the human genome is all the information that makes us human. And unless you have an identical twin, your genome is unique. No one else has a genome just like yours, though all our genomes are similar. The Human Genome Project ( Figure 1.1) was an international effort to sequence all 3 billion bases that make up our DNA and to identify within this code more than 20,000 human genes. Scientists also completed a chromosome map, identifying where the genes are located on each of the chromosomes. The Human Genome Project was completed in 2003. Though the Human Genome Project is finished, analysis of the data will continue for many years. To say the Human Genome Project has been beneficial to mankind would be an understatement. Exciting applications of the Human Genome Project include the following: The genetic basis for many diseases can be more easily determined. Now there are tests for over 1,000 genetic disorders. The technologies developed during this effort, and since the completion of this project, will reduce the cost of sequencing a persons genome. This may eventually allow many people to sequence their individual genome. Analysis of your own genome could determine if you are at risk for specific diseases. Knowing you might be genetically prone to a certain disease would allow you to make preventive lifestyle changes or have medical screenings. To complete the Human Genome Project, all 23 pairs of chromosomes in the human body were sequenced. Each chromo- some contains thousands of genes. This is a karyotype, a visual representation of an individuals chromosomes lined up by size. The video Our Molecular Selves discusses the human genome, and is available at  or  . Genome, Unlocking Lifes Code is the Smithsonian National Museum of Natural Historys exhibit on the human genome. See http://unlockinglifescode.org to visit the exhibit. Click image to the left or use the URL below. URL: ",text,
L_0551,human population,T_3026,"How quickly is the human population growing? If we look at worldwide human population growth from 10,000 BCE through today, our growth looks like exponential growth. It increased very slowly at first, but later grew faster and faster as the population increased in size ( Figure 1.1). And recently, the human population has increased at a faster pace than ever before. It has taken only 12 years for the worlds population to increase from six billion to seven billion. Considering that in the year 1804, there were just one billion people, and in 1927, there were just two billion people (thats 123 years to increase from 1 to 2 billion), the recent increase in the human population growth rate is characteristic of exponential growth. Does this mean there are unlimited resources? Worldwide human population growth from 10,000 BCE through today. ",text,
L_0551,human population,T_3027,"On the other hand, if you look at human population growth in specific countries, you may see a different pattern. On the level of a country, the history of human population growth can be divided into five stages, as described in Table 1.1. Some countries have very high birth rates, in some countries the growth rate has stabilized, and in some countries the growth rate is in decline. Stage 1 2 3 4 5 Description Birth and death rates are high and population growth is stable. This occurred in early human history. Significant drop in death rate, resulting in exponential growth. This occurred in 18th- and 19th-century Eu- rope. Population size continues to grow. Birth rates equal death rates and populations become stable. Total population size may level off. The United Nations and the U.S. Census Bureau predict that by 2050, the Earth will be populated by 9.4 billion people. Other estimates predict 10 to 11 billion. ",text,
L_0551,human population,T_3028,"There are two different beliefs about what type of growth the human population will undergo in the future: 1. Neo-Malthusians believe that human population growth cannot continue without destroying the environment, and maybe humans themselves. 2. Cornucopians believe that the Earth can give humans a limitless amount of resources. They also believe that technology can solve problems caused by limited resources, such as lack of food. The Cornucopians believe that a larger population is good for technology and innovation. The 5-stage model above predicts that when all countries are industrialized, the human population will eventually level out. But many scientists and other Neo-Malthusians believe that humans have already gone over the Earths carrying capacity. That means, we may have already reached the maximum population size that can be supported, without destroying our resources and habitat. If this is true, then human overpopulation will lead to a lack of food and other resources. Overpopulation may also lead to increased disease, and/or war. These problems may cause the population of humans to crash. If these issues are not controlled, could the human population go extinct? Which of the above theories makes sense to you? Why? ",text,
L_0552,human skeletal system,T_3029,"How important is your skeleton? Can you imagine your body without it? You would be a wobbly pile of muscle and internal organs, and you would not be able to move. The adult human skeleton has 206 bones, some of which are named below ( Figure 1.1). Bones are made up of living tissue. They contain many different types of tissues. Cartilage, a dense connective tissue, is found at the end of bones and is made of tough protein fibers. Cartilage creates smooth surfaces for the movement of bones that are next to each other, like the bones of the knee. Ligaments are made of tough protein fibers and connect bones to each other. Your bones, cartilage, and ligaments make up your skeletal system. ",text,
L_0552,human skeletal system,T_3030,"Your skeletal system gives shape and form to your body, but it also plays other important roles. The main functions of the skeletal system include: The skeletal system is made up of bones, cartilage, and ligaments. The skeletal system has many important functions in your body. What bones protect the heart and lungs? What protects the brain? Support. The skeleton supports the body against the pull of gravity, meaning you dont fall over when you stand up. The large bones of the lower limbs support the rest of the body when standing. Protection. The skeleton supports and protects the soft organs of the body. For example, the skull surrounds the brain to protect it from injury. The bones of the rib cage help protect the heart and lungs. Movement. Bones work together with muscles to move the body. Making blood cells. Blood cells are mostly made inside certain types of bones. ",text,
L_0552,human skeletal system,T_3031,"Bones come in many different shapes and sizes, but they are all made of the same materials. Bones are organs, and recall that organs are made up of two or more types of tissues. The two main types of bone tissue are compact bone and spongy bone ( Figure 1.2). Compact bone makes up the dense outer layer of bones. Spongy bone is found at the center of the bone and is lighter and more porous than compact bone. Bones look tough, shiny, and white because they are covered by a layer called the periosteum. Many bones also contain a soft connective tissue called bone marrow in the pores of the spongy bone. Bone marrow is where blood cells are made. Bones are made up of different types of tissues. ",text,
L_0552,human skeletal system,T_3032,"Early in human development, the skeleton consists of only cartilage and other connective tissues. At this point, the skeleton is very flexible. As the fetus develops, hard bone begins to replace the cartilage, and the skeleton begins to harden. Not all of the cartilage, however, is replaced by bone. Cartilage remains in many places in your body, including your joints, your rib cage, your ears, and the tip of your nose. A baby is born with zones of cartilage in its bones that allow growth of the bones. These areas, called growth plates, allow the bones to grow longer as the child grows. By the time the child reaches an age of about 18 to 25 years, all of the cartilage in the growth plate has been replaced by bone. This stops the bone from growing any longer. Even though bones stop growing in length in early adulthood, they can continue to increase in thickness throughout life. This thickening occurs in response to strain from increased muscle activity and from weight-lifting exercises. ",text,
L_0568,indoor air pollution,T_3086,"Recall that air pollution is due to chemical substances and particles released into the air mainly by human actions. When most people think of air pollution, they think of the pollution outdoors. But it is just as easy to have indoor air pollution. Your home or school classroom probably doesnt get much fresh air. Sealing up your home reduces heating and cooling costs. But this also causes air pollution to stay trapped indoors. And people today usually spend a majority of their time indoors. So exposure to indoor air pollution can become a significant health risk. Indoor air pollutants include both chemical and biological pollutants. Chemical pollutants include the following: Radon, a radioactive gas released from the Earth in certain locations. It can become trapped inside buildings and increase your risk of cancer. Formaldehyde, a toxic gas emitted from building materials, such as carpeting and plywood. Volatile organic compounds (VOCs), which are given off by paint and solvents as they dry. They can cause cause long-term health effects. Secondhand smoke, which comes from breathing the smoke release from tobacco products. Secondhand smoke is also the smoke exhaled by a cigarette smoker. This smoke is extremely dangerous to human health. Carbon monoxide (CO), a toxic gas released by burning fossil fuels. It is often released indoors by faulty chimneys, gas-powered generators, or burning charcoal; it can be extremely dangerous. Dry cleaning fluids, such as tetrachloroethylene, which can be released from clothing days after dry cleaning. The past use of asbestos in factories and in homes. Asbestos is a very dangerous material, and it was used in many buildings ( Figure 1.1). Asbestos can cause cancer and other lung diseases. The use of asbestos is not allowed today. The use of asbestos in industry and do- mestic environments in the past, as in the asbestos-covered pipes in the oil-refining plant pictured here, has left a potentially very dangerous material in many busi- nesses. Biological sources of air pollution are also found indoors. These are produced from: Pet dander. Dust from tiny skin flakes and decomposed hair. Dust mites. Mold from walls, ceilings, and other structures. Air conditioning systems that can incubate certain bacteria and mold. Pollen, dust, and mold from houseplants, soil, and surrounding gardens. ",text,
L_0568,indoor air pollution,T_3087,"Can you avoid indoor air pollution? You cant go to school outside. But it is possible to reduce your exposure to air pollution. Some tips to decrease your exposure to indoor air pollution include: Using less toxic chemicals when possible. Limiting your exposure to pesticides and cleaning fluids by keeping them in a garage or shed. When using toxic chemicals, allowing fresh air to circulate through open windows and doors. Having detectors for radon and carbon monoxide in your home. What else could you do to reduce your exposure to air pollution? ",text,
L_0569,infancy and childhood,T_3088,"The first year after birth is called infancy. Infancy is a period when the baby grows very fast. During infancy, the baby doubles in length and triples in weight. Other important changes also happen during infancy: The babys teeth start to come in, usually at about six months of age ( Figure 1.1). The baby starts smiling, paying attention to other people, and grabbing toys. The baby begins making babbling sounds. By the end of the first year, the baby is starting to say a few words, such as mama and dada. The baby learns to sit, crawl, and stand. By the end of the first year, the baby may be starting to walk. Childhood begins after the babys first birthday and continues until the teen years. Between one and three years of age, a child is called a toddler. During the toddler stage, growth is still fast, but not as fast as it was during infancy. A toddler learns many new words. The child even starts putting together words in simple sentences. Motor skills also develop quickly during this stage. By age three, most children can run and climb steps. They can hold crayons and scribble with them. They can also feed themselves and use the toilet. From age three until the teens, growth is slower. The body also changes shape. The arms and legs get longer compared to the trunk. Children continue to develop new motor skills. For example, many young children learn how to ride a tricycle and then a bicycle. Most also learn how to play games and sports ( Figure 1.2). By age six, children start losing their baby teeth. Their permanent teeth begin coming in to replace them. They also start school and learn how to read and write. They develop friendships and become less dependent on their parents. ",text,
L_0569,infancy and childhood,T_3089,"There are numerous milestones that occur during the first few years of childhood. These include the use of language, walking and running, understanding simple concepts, pretend play, the development of fine motor skills, the development of independence, Children develop better motor skills as they get older. having temper tantrums, demonstrating separation anxiety, becoming fully potty-trained, showing natural curiosity. ",text,
L_0571,influences on darwin,T_3093,"When Darwin returned to England five years later, in 1836, at the end of his voyage, he did not rush to announce his discoveries. Unlike other naturalists before him, Darwin did not want to present any ideas unless he had strong evidence supporting them. Instead, once Darwin returned to England, he spent over twenty years examining specimens, talking with other scientists and collecting more information before he presented his theories. Some of Darwins ideas conflicted with widely held beliefs, including those from religious leaders. At that time, many people believed that organisms never change and never go extinct, and that the world was only about 6,000 years old, always existing in the same way, never changing. These beliefs delayed Darwin in presenting his findings. How did Darwin come up with his theories? Charles Darwin was influenced by the ideas of several people. 1. Before the voyage of the Beagle, Jean-Baptiste Lamarck proposed the idea that species change over time. However, Darwin differed with Lamarck on several key points. Lamarck proposed that traits acquired during ones lifetime could be passed to the next generation. Darwin did not agree with this. 2. The findings of Charles Lyell, a well-known geologist, also influenced Darwin. Lyells writings taught Darwin about geology, paleontology, and the changing Earth. Lyells findings suggested the Earth must be much older than 6,000 years. And the evolution of life, as Darwin was developing his ideas, would definitely take much longer than just 6,000 years. During the Voyage of the Beagle, Darwin observed fossils of sea life high up in the mountains. What must happen to the Earth for this to occur? Darwin, using the readings of Lyell, took this as evidence of a constantly changing Earth. 3. After the Voyage of the Beagle, another naturalist, Alfred Russel Wallace ( Figure 1.1), developed a similar theory of evolution by natural selection. Wallace toured South America and made similar observations to Darwins. Darwin and Wallace presented their theories and evidence in public together. Due to the large number of observations and conclusions he made, Darwin is mostly credited and associated with this theory. Alfred Wallace developed a similar theory of evolution by natural selection. Imagine developing a theory that conflicted with widely held beliefs of the time, as Darwin did. Imagine pulling together material from all these different people, adding his own findings, and turning it all into his theory. Imag- ine the torment Darwin must have endured during this time, knowing the skepticism that would follow the release of his findings. But, upon his death, Darwin was given one of the highest honors in England. Darwin is buried in Westminster Abbey, the final resting place of many of Englands kings and queens. Why was he buried in such an important spot? ",text,
L_0572,injuries of the nervous system,T_3094,"Injuries to the central nervous system may damage tissues of the brain or spinal cord. If an injury is mild, a person may have a full recovery. If an injury is severe, it may cause permanent disability or even death. Brain and spinal cord injuries most commonly occur because of car crashes or sports accidents. The best way to deal with such injuries is to try to prevent them. ",text,
L_0572,injuries of the nervous system,T_3095,"Brain injuries can range from mild to extremely severe, but even mild injuries need medical attention. Brain injuries can result from falls, car accidents, violence, sports injuries, and war and combat. Falls are the most common cause of brain injuries, particularly in older adults and young children. The mildest and most common type of brain injury is a concussion. This is a bruise on the surface of the brain. It may cause temporary problems such as headache, drowsiness, and confusion. Most concussions in young people occur when they are playing sports, especially contact sports like football. Other sports, like soccer, boxing, baseball, lacrosse, skateboarding, and hockey can also result in concussions. A concussion normally heals on its own in a few days. A single concussion is unlikely to cause permanent damage. But repeated concussions may lead to lasting problems. People who have had two or more concussions may have life-long difficulties with memory, learning, speech, or balance. For this reason, concussions are treated very seriously among athletes and in professional sports. You can see an animation of how a concussion occurs by visiting  A person with a serious brain injury usually suffers permanent brain damage. These brain injuries usually occur when an external mechanical force, such as a violent blow or jolt to the head or body, causes brain dysfunction. An object penetrating the skull, such as a bullet or a shattered piece of the skull, also can cause traumatic brain injury. As a result, the person may have trouble talking or controlling body movements. Symptoms depend on what part of the brain was injured. Serious brain injuries can also cause personality changes and problems with mental abilities such as memory. Medicines, counseling, and other treatments may help people with serious brain injuries recover from, or at least learn to cope with, their disabilities. Symptoms of severe brain injuries include the loss of consciousness from several minutes to hours, profound confusion, slurred speech, the inability to awaken from sleep, seizures, loss of coordination, persistent headache or headache that worsens. ",text,
L_0572,injuries of the nervous system,T_3096,"A spinal cord injury is damage to any part of the spinal cord or nerves at the end of the spinal canal. This injury often causes permanent changes in strength, sensation and other body functions below the site of the injury. Spinal cord injuries make it difficult for messages to travel between the brain and body. They may cause a person to lose the ability to feel or move parts of the body. This is called paralysis. Whether paralysis occursand what parts of the body are affected if it doesdepends on the location and seriousness of the injury. In addition to car crashes and sports injuries, diving accidents are a common cause of spinal cord injuries. Quadriplegia means your arms, hands, trunk, legs and pelvic organs are all affected by your spinal cord injury. Paraplegia means the paralysis affects all or part of the trunk, legs and pelvic organs. These people can still use their arms and hands. Some people recover from spinal cord injuries. But many people are paralyzed for life. Thanks to the work of Christopher Reeve ( Figure 1.1), more research is being done on spinal cord injuries now than ever before. For example, scientists are trying to discover ways to regrow damaged spinal cord neurons. If you suspect that someone has a back or neck injury: dont move the injured person as permanent paralysis and other serious complications may result, call 911 or your local emergency medical assistance number, keep the person very still, place heavy towels on both sides of the neck or hold the head and neck to prevent them from moving, until emergency care arrives, provide basic first aid, such as stopping any bleeding and making the person comfortable, without moving the head or neck. Former ""man of steel"" Superman star Christopher Reeve (September 25, 1952 October 10, 2004) was paralyzed from the neck down in a fall from a horse. The injury crushed his spinal cord so his brain could no longer communicate with his body. ",text,
L_0579,jawless fish,T_3111,"What defines a jawless fish? You can probably guess. A jawless fish is a fish without a jaw. But there are other features that are shared by this class of organisms. Why would such an organism evolve? These fish were the first vertebrates to evolve. Logically, this makes sense, in that the vertebral column would evolve first, with the more complex jaw bones evolving later. The early jawless fish are thought to have relied on filter feeding to capture their food, and most likely would have sucked water and debris from the seafloor into their mouth, releasing water and waste out of their gills. As other sea life evolved, these jawless fish began to feed on other fish species, and are now considered a pest in their habitat. Lampreys have no natural predators. ",text,
L_0579,jawless fish,T_3112,"Jawless fish are missing the following parts: 1. Jaws. 2. Paired fins. 3. A stomach. Characteristics they do have include: 1. A notochord, both in larvae and adults. Recall a notochord is a support rod that runs along the back of the fish. 2. Seven or more paired gill pouches. These organs take dissolved oxygen from water. 3. The branchial arches, a series of arches that support the gills of aquatic amphibians and fishes. They lie close to the bodys surface. 4. A light sensitive pineal eye, an eye-like structure that can detect light. 5. A cartilaginous skeleton, a skeleton made of a flexible rubber-like supportive material called cartilage. This is similar to the skeleton of cartilaginous fish, which includes sharks and rays. 6. A heart with two chambers. 7. Reproduction using external fertilization. 8. They are ectothermic. This means that their internal temperature depends on the temperature of their envi- ronment. ",text,
L_0579,jawless fish,T_3113,"Most scientists agree that the jawless fish are part of the the superclass Agnatha. They belong to the phylum Chordata, subphylum Vertebrata. There are two living groups of jawless fish, with about 100 species in total: lampreys and hagfish ( Figure 1.1). Although hagfish belong to the subphylum Vertebrata, they do not technically have vertebrae (though they do have a skull), whereas lampreys do have vertebrae. For this reason, scientists still disagree on the classification of jawless fish. A hagfish. ",text,
L_0580,keeping bones and joints healthy,T_3114,"You can help keep your bones and skeletal system healthy by eating well and getting enough exercise. Weight- bearing exercises help keep bones strong. Weight-bearing exercises and activities work against gravity. Such activities include basketball, tennis, gymnastics, karate, running, and walking. When the body is exercised regularly by performing weight-bearing activity, bones respond by adding more bone cells to increase their bone density. ",text,
L_0580,keeping bones and joints healthy,T_3115,"Did you know that what you eat as a teenager can affect how healthy your skeletal system will be in 30, 40, and even 50 years? Calcium and vitamin D are two of the most important nutrients for a healthy skeletal system. Your bones need calcium to grow properly. If you do not get enough calcium in your diet as a teenager, your bones may become weak and break easily later in life. Osteoporosis is a disease in which bones lose mass and become more fragile than they should be. Osteoporosis also makes bones more likely to break. Two of the easiest ways to prevent osteoporosis are eating a healthy diet that has the right amount of calcium and vitamin D and to do some sort of weight-bearing exercise every day. Foods that are a good source of calcium include milk, yogurt, and cheese. Non-dairy sources of calcium include Chinese cabbage, kale, and broccoli. Many fruit juices, fruit drinks, tofu, and cereals have calcium added to them. It is recommended that teenagers get 1300 mg of calcium every day. For example, one cup (8 fl. oz.) of milk provides about 300 mg of calcium, or about 30% of the daily requirement. Other sources of calcium are pictured in the Figure 1.1. There are many different sources of cal- cium. Getting enough calcium in your daily diet is important for good bone health. Vitamin D is unusual since you dont have to rely on your diet alone to get enough of this vitamin. Your skin makes vitamin D when exposed to sunlight. Pigments in the skin act like a filter that can prevent the skin from making vitamin D. As a result, people with darker skin need more time in the sun than people with lighter skin to make the same amount of vitamin D. You can also get vitamin D from foods. Fish is naturally rich in vitamin D. In the United States, vitamin D is added to other foods, including milk, soy milk, and breakfast cereals. Teenagers are recommended to get 5 micrograms (200 IU) of vitamin D every day. A 3 12 -ounce portion of cooked salmon provides 360 IU of vitamin D. A 8-ounce glass of milk is fortified with about 100 IU of vitamin D. ",text,
L_0580,keeping bones and joints healthy,T_3116,"Even though they are very strong, bones can fracture, or break. Fractures can happen at different places on a bone. They are usually caused by excess bending stress on the bone. Bending stress is what causes a pencil to break if you bend it too far. Soon after a fracture, the body begins to repair the break. The area becomes swollen and sore. Within a few days, bone cells travel to the break site and begin to rebuild the bone. It takes about two to three months before compact and spongy bone form at the break site. Sometimes the body needs extra help in repairing a broken bone. In such a case, a surgeon will piece a broken bone together with metal pins. Moving the broken pieces together will help keep the bone from moving and give the body a chance to repair the break. Below, a broken ulna has been repaired with pins ( Figure 1.2). The upper part of the ulna, just above the elbow joint, is broken, as you can see in the X-ray to the left. The x-ray to the right was taken after a surgeon inserted a system of pins and wires across the fracture to bring the two pieces of the ulna into close proximity. ",text,
L_0580,keeping bones and joints healthy,T_3117,"Osteoarthritis occurs when the cartilage at the ends of the bones breaks down. The break down of the cartilage leads to pain and stiffness in the joint. Decreased movement of the joint because of the pain may lead to weakening of the muscles that normally move the joint, and the ligaments surrounding the joint may become loose. Osteoarthritis is the most common form of arthritis. It has many contributing factors, including aging, sport injuries, fractures, and obesity. ",text,
L_0580,keeping bones and joints healthy,T_3118,"Recall that a ligament is a short band of tough connective tissue that connects bones together to form a joint. Ligaments can get injured when a joint gets twisted or bends too far. The protein fibers that make up a ligament can get strained or torn, causing swelling and pain. Injuries to ligaments are called sprains. Ankle sprains are a common type of sprain. ",text,
L_0580,keeping bones and joints healthy,T_3119,"Preventing injuries to your bones and ligaments is easier and much less painful than treating an injury. Wearing the correct safety equipment when performing activities that require such equipment can help prevent many common injuries. For example, wearing a bicycle helmet can help prevent a skull injury if you fall. Warming up and cooling down properly can help prevent ligament and muscle injuries. Stretching before and after activity also helps prevent injuries. ",text,
L_0581,keeping skin healthy,T_3120,"Your skin is your largest organ and constantly protects you from infections, so keeping your skin healthy is a good idea. ",text,
L_0581,keeping skin healthy,T_3121,"Some sunlight is good for your health. Vitamin D is made in the skin when it is exposed to sunlight. But getting too much sun can be unhealthy. A sunburn is a burn to the skin that is caused by overexposure to UV radiation from the suns rays or tanning beds. Light-skinned people, like the man pictured below ( Figure 1.1), get sunburned more quickly than people with darker skin. This is because pigments (melanin) in the skin act as a natural sunblock that help to protect the body from UV radiation. With over one million new cases each year, skin cancer, which is cancer that forms in the tissues of the skin, is the most common form of human cancer. Children and teens who have been sunburned are at a greater risk of developing skin cancer later in life. Long-term exposure to UV radiation is the leading cause of skin cancer. About 90 percent of skin cancers are linked to sun exposure. UV radiation damages the genetic material (DNA) of skin cells. This damage can cause the skin cells to grow out of control and form a tumor. Some of these tumors are very difficult to cure. For this reason you should always wear sunscreen with a high sun protection factor (SPF), a hat, and clothing when out in the sun. Sunburn is caused by overexposure to UV rays. Getting sunburned as a child or a teen, especially sunburn that causes blistering, increases the risk of developing skin cancer later in life. ",text,
L_0581,keeping skin healthy,T_3122,"Keeping your skin clean is important because dirty skin is more prone to infection. Bathing every day helps to keep your skin clean and healthy. Also, you know that taking a bath or shower helps prevent body odor. But where does body odor come from? During the day, sweat, oil, dirt, dust, and dead skin cells can build up on the skin surface. If not washed away, the mix of these materials can encourage the excess growth of bacteria. These bacteria feed on these substances and cause a smell that is commonly called body odor. ",text,
L_0581,keeping skin healthy,T_3123,"Conditions that irritate, clog or inflame your skin can cause symptoms such as redness, swelling, burning and itching. Allergies, irritants, your genetic background and certain diseases and immune system problems can cause numerous skin conditions. Many skin problems, such as acne, also affect your appearance. Acne Your skin has tiny holes called pores that that can become blocked by oil, bacteria, dead skin and dirt. When this occurs, you may develop a pimple. Acne is a skin condition that causes pimples, and is one of the more common skin problem among teenagers. A diet high in refined sugars or carbohydrates such as bread and chips can also lead to acne. Each pore on your skin is the opening to a follicle, which is made of a hair and sebaceous gland that releases sebum. Acne may result from too much sebum produced by the follicle, dead skin cells accumulating in the pore, or bacteria built up in the pore. Cleaning your skin daily with a mild soap to remove excess oil and dirt can help prevent acne. Cold Sores Cold sores are red, fluid-filled blisters that appear near the mouth or on other areas of the face, usually caused by herpes simplex virus type 1. Visible sores are contagious, but herpes may be spread even when sores cant be seen. You can catch the herpes simplex virus through kissing, sharing cosmetics, or sharing food with infected individuals. Once you catch herpes simplex virus, it cant be cured. Even after sores have healed, the virus remains in your body, and new cold sores can appear at any time. This is not to be confused with genital herpes, which is caused by herpes simplex virus type 2. Canker Sore A canker sore is a mouth ulcer or sore that is open and painful. They may be on the lips or inside of the lip or cheek. Canker sores are usually white or yellowish, surrounded by red, inflamed soft tissue. A canker sore can be either a simple canker or a complex canker. A simple canker sore reemerges about three to four times every year, and is the common type in people between the ages of 10 and 20. Canker sores are not contagious and usually heal on their own within a week or two. Causes of canker sores include a viral infection, stress, hormonal fluctuations, food allergies, immune system problems, or mouth injuries. ",text,
L_0582,keeping the nervous system healthy,T_3124,"The nervous system is such an important part of your body. You want it to work at its best so that you can be at your best. Your nervous system contains what is probably the most important part of your body, which, of course, is your brain. Your brain allows you to learn. It allows you to feel emotions like love, anger, and sadness. Your brain gives you the ability to see, hear, taste, touch, and smell. It works together with the nerves and spinal cord to send the signals that make your body move. Your nervous system lets you do things like run, jump, play sports, and do your homework. There are many choices you can make to keep your nervous system healthy. One obvious choice is to avoid using alcohol or other drugs. Not only will you avoid the injury that drugs themselves can cause, but you will also be less likely to get involved in other risky behaviors that could harm your nervous system. Another way to keep the nervous system healthy is to eat a variety of healthy foods. The minerals sodium, calcium, and potassium, and vitamins B1 and B12 are important for a healthy nervous system. Some foods that are good sources for these minerals and vitamins include milk, whole grains, beef steak, and kidney beans (shown in Figure 1.1). Your brain also needs healthy fats like those in nuts and fish. Recall that fats insulate the axons of neurons. These fats help build new connections between nerves and brain cells. These fats may improve memory and increase learning and intelligence. Water is also important for the nervous system, so drink plenty of water and other fluids. This helps prevent dehydration, which can cause confusion and memory problems. And get plenty of rest. Your brain requires plenty of rest so it can strengthen circuits that help with memory. A good nights sleep will help keep your brain functioning at its best. These foods are sources of nutrients needed for a healthy nervous system. Daily physical activity is also important for nervous system health. Regular exercise makes your heart more efficient at pumping blood to your brain. As a result, your brain gets more oxygen, which it needs to function normally. The saying use it or lose it applies to your brain as well as your body. This means that mental activity, not just physical activity, is important for nervous system health. Doing crossword puzzles, reading, and playing a musical instrument are just a few ways you can keep your brain active. You can also choose to practice safe behaviors to protect your nervous system from injury. To keep your nervous system safe, choose to: Bicycle helmets help protect from head injuries. Making healthy choices like this can help prevent nervous system injuries that could cause lifelong disability. Furthermore, make sure to exercise your nervous system on a daily basis. The simple act of writing requires that you use all the major components of your motor and sensory pathways. These include a number of different sensory receptors, peripheral nerves, synaptic connections within your spinal cord, major tracts within your spinal cord, and nerve tissue throughout your brain. All these components need to be utilized with great precision and coordination to produce neatly written words. What should you do? Spend a few minutes each day writing on paper as neatly as you can. This takes a lot more effort on the part of the nervous system than typing on a keyboard, as typing on a keyboard doesnt require as much fine motor control as writing on paper. If you dont want to write, then draw. Drawing with precision also requires use of all the major components of the sensory and motor divisions of the nervous system. ",text,
L_0582,keeping the nervous system healthy,T_3124,"The nervous system is such an important part of your body. You want it to work at its best so that you can be at your best. Your nervous system contains what is probably the most important part of your body, which, of course, is your brain. Your brain allows you to learn. It allows you to feel emotions like love, anger, and sadness. Your brain gives you the ability to see, hear, taste, touch, and smell. It works together with the nerves and spinal cord to send the signals that make your body move. Your nervous system lets you do things like run, jump, play sports, and do your homework. There are many choices you can make to keep your nervous system healthy. One obvious choice is to avoid using alcohol or other drugs. Not only will you avoid the injury that drugs themselves can cause, but you will also be less likely to get involved in other risky behaviors that could harm your nervous system. Another way to keep the nervous system healthy is to eat a variety of healthy foods. The minerals sodium, calcium, and potassium, and vitamins B1 and B12 are important for a healthy nervous system. Some foods that are good sources for these minerals and vitamins include milk, whole grains, beef steak, and kidney beans (shown in Figure 1.1). Your brain also needs healthy fats like those in nuts and fish. Recall that fats insulate the axons of neurons. These fats help build new connections between nerves and brain cells. These fats may improve memory and increase learning and intelligence. Water is also important for the nervous system, so drink plenty of water and other fluids. This helps prevent dehydration, which can cause confusion and memory problems. And get plenty of rest. Your brain requires plenty of rest so it can strengthen circuits that help with memory. A good nights sleep will help keep your brain functioning at its best. These foods are sources of nutrients needed for a healthy nervous system. Daily physical activity is also important for nervous system health. Regular exercise makes your heart more efficient at pumping blood to your brain. As a result, your brain gets more oxygen, which it needs to function normally. The saying use it or lose it applies to your brain as well as your body. This means that mental activity, not just physical activity, is important for nervous system health. Doing crossword puzzles, reading, and playing a musical instrument are just a few ways you can keep your brain active. You can also choose to practice safe behaviors to protect your nervous system from injury. To keep your nervous system safe, choose to: Bicycle helmets help protect from head injuries. Making healthy choices like this can help prevent nervous system injuries that could cause lifelong disability. Furthermore, make sure to exercise your nervous system on a daily basis. The simple act of writing requires that you use all the major components of your motor and sensory pathways. These include a number of different sensory receptors, peripheral nerves, synaptic connections within your spinal cord, major tracts within your spinal cord, and nerve tissue throughout your brain. All these components need to be utilized with great precision and coordination to produce neatly written words. What should you do? Spend a few minutes each day writing on paper as neatly as you can. This takes a lot more effort on the part of the nervous system than typing on a keyboard, as typing on a keyboard doesnt require as much fine motor control as writing on paper. If you dont want to write, then draw. Drawing with precision also requires use of all the major components of the sensory and motor divisions of the nervous system. ",text,
L_0583,kidneys,T_3125,"The kidneys ( Figure 1.1) are important organs in maintaining homeostasis, the ability of the body to maintain a stable internal environment despite a changing environment. Kidneys perform a number of homeostatic functions. They maintain the volume of body fluids. They maintain the balance of salt ions in body fluids. They excrete harmful nitrogen-containing molecules, such as urea, ammonia, and uric acid. There are many blood vessels in the kidneys ( Figure 1.1). The kidneys remove urea and other wastes from the blood through tiny filtering units called nephrons. Nephrons ( Figure 1.2) are tiny, tube-shaped structures found inside each kidney. Each kidney has up to a million nephrons. Each nephron collects a small amount of fluid and waste from a small group of capillaries. Structures of the kidney; fluid leaks from the capillaries and into the nephrons where the fluid forms urine then moves to the ureter and on to the bladder. Nitrogen-containing wastes, together with water and other wastes, form the urine as it passes through the nephrons and the kidney. The fluid within nephrons is carried out into a larger tube in the kidney called a ureter, which carries it to the bladder ( Figure 1.2). The kidneys never stop filtering waste products from the blood, so they are always producing urine. The amount of urine your kidneys produce is dependent on the amount of fluid in your body. Your body loses water through sweating, breathing, and urination. The water and other fluids you drink every day help to replace the lost water. This water ends up circulating in the blood because blood plasma is mostly water. ",text,
L_0583,kidneys,T_3126,"The process of urine formation is as follows: 1. Blood flows into the kidney through the renal artery. The renal artery connects to capillaries inside the kidney. Capillaries and nephrons lie very close to each other in the kidney. 2. The blood pressure within the capillaries causes water, salts, sugars, and urea to leave the capillaries and move into the nephron. 3. The water and salts move along through the tube-shaped nephron to a lower part of the nephron. 4. The fluid that remains in the nephron at this point is called urine. 5. The blood that leaves the kidney in the renal vein has much less waste than the blood that entered the kidney. 6. The urine is collected in the ureters and is moved to the urinary bladder, where it is stored. Nephrons filter about 14 cup of body fluid per minute. In a 24-hour period, nephrons filter 180 liters of fluid, and 1.5 liters of the fluid is released as urine. Urine enters the bladder through the ureters. Similar to a balloon, the walls of the bladder are stretchy. The stretchy walls allow the bladder to hold a large amount of urine. The bladder can hold about 1 12 to 2 21 cups of urine but may also hold more if the urine cannot be released immediately. How do you know when you have to urinate? Urination is the process of releasing urine from the body. Urine leaves the body through the urethra. Nerves in the bladder tell you when it is time to urinate. As the bladder first fills with urine, you may notice a feeling that you need to urinate. The urge to urinate becomes stronger as the bladder continues to fill up. The location of nephrons in the kidney. The fluid collects in the nephron tubules and moves to the bladder through the ureter. ",text,
L_0583,kidneys,T_3127,"The filtering action of the kidneys is controlled by the pituitary gland. The pituitary gland is about the size of a pea and is found below the brain ( Figure 1.3). The pituitary gland releases hormones that help the kidneys to filter water from the blood. The movement of water back into blood is controlled by a hormone called antidiuretic hormone (ADH). ADH is one of the hormones released from the pituitary gland in the brain. One of the most important roles of ADH is to control the bodys ability to hold onto water. If a person does not drink enough water, ADH is released. It causes the blood to reabsorb water from the kidneys. If the kidneys remove less water from the blood, what will the urine look like? It will look darker, because there is less water in it. When a person drinks a lot of water, then there will be a lot of water in the blood. The pituitary gland will then release a lower amount of ADH into the blood. This means less water will be reabsorbed by the blood. The kidneys then produce a large volume of urine. What color will this urine be? ",text,
L_0586,light reactions of photosynthesis,T_3135,,text,
L_0586,light reactions of photosynthesis,T_3136,"Photosynthesis takes place in the organelle of the plant cell known as the chloroplasts. Chloroplasts are one of the main differences between plant and animal cells. Animal cells do not have chloroplasts, so they cannot photosynthesize. Photosynthesis occurs in two stages. During the first stage, the energy from sunlight is absorbed by the chloroplast. Water is used, and oxygen is produced during this part of the process. During the second stage, carbon dioxide is used, and glucose is produced. Chloroplasts contain stacks of thylakoids, which are flattened sacs of membrane. Energy from sunlight is absorbed by the pigment chlorophyll in the thylakoid membrane. There are two separate parts of a chloroplast: the space inside the chloroplast itself, and the space inside the thylakoids ( Figure 1.1). The inner compartments inside the thylakoids are called the thylakoid space (or lumen). This is the site of the first part of photosynthesis. The interior space that surrounds the thylakoids is filled with a fluid called stroma. This is where carbon dioxide is used to produce glucose, the second part of photosynthesis. The chloroplast is the photosynthesis fac- tory of the plant. ",text,
L_0586,light reactions of photosynthesis,T_3137,"What goes into the plant cell to start photosynthesis? The reactants of photosynthesis are carbon dioxide and water. These are the molecules necessary to begin the process. But one more item is necessary, and that is sunlight. All three components, carbon dioxide, water, and the suns energy are necessary for photosynthesis to occur. These three components must meet in the chloroplast of the leaf cell for photosynthesis to occur. How do these three components get to the cells in the leaf? Chlorophyll is the green pigment in leaves that captures energy from the sun. Chlorophyll molecules are located in the thylakoid membranes inside chloroplasts. The veins in a plant carry water from the roots to the leaves. Carbon dioxide enters the leaf from the air through special openings called stomata ( Figure 1.2). ",text,
L_0586,light reactions of photosynthesis,T_3138,"What is produced by the plant cell during photosynthesis? The products of photosynthesis are glucose and oxygen. This means they are produced at the end of photosynthesis. Glucose, the food of plants, can be used to store energy in the form of large carbohydrate molecules. Glucose is a simple sugar molecule which can be combined with other glucose molecules to form large carbohydrates, such as starch. Oxygen is a waste product of photosynthesis. It is released into the atmosphere through the stomata. As you know, animals need oxygen to live. Without photosynthetic organisms like plants, there would not be enough oxygen in the atmosphere for animals to survive. ",text,
L_0586,light reactions of photosynthesis,T_3139,"The overall chemical reaction for photosynthesis is 6 molecules of carbon dioxide (CO2 ) and 6 molecules of water (H2 O), with the addition of solar energy. This produces 1 molecule of glucose (C6 H12 O6 ) and 6 molecules of oxygen Stomata are special pores that allow gasses to enter and exit the leaf. (O2 ). Using chemical symbols, the equation is represented as follows: 6CO2 + 6H2 O  C6 H12 O6 + 6O2 . Though this equation may not seem that complicated, photosynthesis is a series of chemical reactions divided into two stages, the light reactions and the Calvin cycle ( Figure 1.3). ",text,
L_0586,light reactions of photosynthesis,T_3140,"Photosynthesis begins with the light reactions. It is during these reactions that the energy from sunlight is absorbed by the pigment chlorophyll in the thylakoid membranes of the chloroplast. The energy is then temporarily transferred to two molecules, ATP and NADPH, which are used in the second stage of photosynthesis. ATP and NADPH are generated by two electron transport chains. During the light reactions, water is used and oxygen is produced. These reactions can only occur during daylight as the process needs sunlight to begin. ",text,
L_0586,light reactions of photosynthesis,T_3141,"The second stage of photosynthesis is the production of glucose from carbon dioxide. This process occurs in a continuous cycle, named after its discover, Melvin Calvin. The Calvin cycle uses CO2 and the energy temporarily stored in ATP and NADPH to make the sugar glucose. ",text,
L_0587,limiting factors to population growth,T_3142,"For a population to be healthy, factors such as food, nutrients, water and space, must be available. What happens when there are not resources to support the population? Limiting factors are resources or other factors in the environment that can lower the population growth rate. Limiting factors include a low food supply and lack of space. Limiting factors can lower birth rates, increase death rates, or lead to emigration. When organisms face limiting factors, they show logistic growth (S-shaped curve, curve B: Figure 1.1). Compe- tition for resources like food and space cause the growth rate to stop increasing, so the population levels off. This flat upper line on a growth curve is the carrying capacity. The carrying capacity (K) is the maximum population size that can be supported in a particular area without destroying the habitat. Limiting factors determine the carrying capacity of a population. Recall that when there are no limiting factors, the population grows exponentially. In exponential growth (J-shaped curve, curve A: Figure 1.1), as the population size increases, the growth rate also increases. Exponential and Logistic Growth. Curve A shows exponential growth. shows logistic growth. Curve B Notice that the carrying capacity (K) is also shown. ",text,
L_0587,limiting factors to population growth,T_3143,"If there are 12 hamburgers at a lunch table and 24 people sit down at a lunch table, will everyone be able to eat? At first, maybe you will split hamburgers in half, but if more and more people keep coming to sit at the lunch table, you will not be able to feed everyone. This is what happens in nature. But in nature, organisms that cannot get food will die or find a new place to live. It is possible for any resource to be a limiting factor, however, a resource such as food can have dramatic consequences on a population. In nature, when the population size is small, there is usually plenty of food and other resources for each individual. When there is plenty of food and other resources, organisms can easily reproduce, so the birth rate is high. As the population increases, the food supply, or the supply of another necessary resource, may decrease. When necessary resources, such as food, decrease, some individuals will die. Overall, the population cannot reproduce at the same rate, so the birth rates drop. This will cause the population growth rate to decrease. When the population decreases to a certain level where every individual can get enough food and other resources, and the birth and death rates become stable, the population has leveled off at its carrying capacity. ",text,
L_0587,limiting factors to population growth,T_3144,"Other limiting factors include light, water, nutrients or minerals, oxygen, the ability of an ecosystem to recycle nutrients and/or waste, disease and/or parasites, temperature, space, and predation. Can you think of some other factors that limit populations? Weather can also be a limiting factor. Whereas most plants like rain, an individual cactus-like Agave americana plant actually likes to grow when it is dry. Rainfall limits reproduction of this plant which, in turn, limits growth rate. Can you think of some other factors like this? Human activities can also limit the growth of populations. Such activities include use of pesticides, such as DDT, use of herbicides, and habitat destruction. ",text,
L_0590,male reproductive structures,T_3156,"The male reproductive organs include the penis, testes, and epididymis ( Figure 1.1). The figure also shows other parts of the male reproductive system. The penis is a cylinder-shaped organ. It contains the urethra. The urethra is a tube that carries urine out of the body. The urethra also carries sperm out of the body. This drawing shows the organs of the male reproductive system. It shows the organs from the side. Find each organ in the drawing as you read about it in the text. The two testes (singular, testis) are egg-shaped organs. They produce sperm and secrete testosterone. The testes are found inside of the scrotum. The scrotum is a sac that hangs down outside the body. The scrotum also contains the epididymis. The testes, being in the scrotum outside the body, allow the temperature of the sperm to be maintained at a few degrees lower than body temperature. This is necessary for the stability of these reproductive cells. The epididymis is a tube that is about six meters (20 feet) long in adults. It is tightly coiled, so it fits inside the scrotum. It rests on top of the testes. The epididymis is where sperm grow larger and mature. The epididymis also stores sperm until they leave the body. Other parts of the male reproductive system include the vas deferens and the prostate gland. Both of these structures are pictured below ( Figure 1.1). The vas deferens is a tube that carries sperm from the epididymis to the urethra. The prostate gland secretes a fluid that mixes with sperm to help form semen. The prostate gland is located beneath the bladder. Semen is a ""milky"" liquid that carries sperm through the urethra and out of the body. In addition to sperm cells, semen contains sugars (fructose) which provide energy to the sperm cells, and enzymes and other substances which help the sperm survive. ",text,
L_0591,male reproductive system,T_3157,"Dogs have puppies. Cats have kittens. All organisms reproduce, obviously including humans. Like other mammals, humans have a body system that controls reproduction. It is called the reproductive system. It is the only human body system that is very different in males and females. The male and female reproductive systems have different organs and different functions. The male reproductive system has two main functions: 1. Producing sperm. 2. Releasing testosterone into the body. Sperm are male gametes, or reproductive cells. When a male gamete meets a female gamete, they can form a new organism. Sperm form when certain cells in the male reproductive system divide by meiosis, resulting in cells with half the amount of DNA as a regular ""body"" cell. More precisely, sperm cells are haploid sex cells, having one set of chromosomes. Regular body cells are diploid, having two set of chromosomes. As there are 46 chromosomes in a diploid human cell, how many are in a human sperm cell? When males grow older, they produce millions of sperm each day. The male reproductive system also maintains and transports and delivers sperm and a protective fluid, known as semen. Testosterone is the main sex hormone in males. Hormones are chemicals that control many body processes. Testosterone has two major roles: During the teen years, testosterone causes the reproductive organs to mature. It also causes other male traits to develop. For example, it causes hair to grow on the face and allows for muscle growth. During adulthood, testosterone helps a man to produce sperm. When a hormone is released into the body, we say it is ""secreted."" Testosterone is secreted by males, but it is not the only sex hormone that males secrete. Males also secrete small amounts of estrogen. Even though estrogen is the main female sex hormone, scientists think that estrogen is needed for normal sperm production in males. ",text,
L_0599,menstrual cycle,T_3172,"The menstrual cycle is a series of changes in the reproductive system of mature females that repeats every month. While the egg and follicle are developing in the ovary, tissues are building up inside the uterus, the reproductive organ where the baby would develop. The uterus develops a thick lining covered in tiny blood vessels. This prepares the uterus to receive an egg that could develop into a child (a fertilized egg). The occurs during the first part of the cycle. Ovulation, the release of an egg from the ovary, occurs at about the midpoint of the cycle. This would be around day 14 of a 28 day cycle. The egg is swept into the fallopian tube. If sperm is present, fertilization may occur. As sperm can only survive in the fallopian tube for up to a few days, fertilization can only occur within those few days post-ovulation. If the egg is fertilized, the egg makes its way through the fallopian tube into the uterus, where it imbeds into the thick lining. When this occurs, the monthly cycle stops. The monthly cycle does not resume until the pregnancy is over. If a sperm does not enter an egg, the lining of the uterus breaks down. Blood and other tissues from the lining break off from the uterus. They pass through the vagina and out of the body. This is called menstruation. Menstruation is also called a menstrual period. It lasts about 4 days, on average. When the menstrual period ends, the cycle repeats. Some women feel discomfort during this process. Some people think that the average length of a menstrual period is the same as the normal length. They assume that shorter or longer menstrual periods are not normal. In fact, menstrual periods can vary from 1 to 8 days in length. This is usually normal. The average length of the cycle (time between menstrual periods) is about 28 days, but there is no normal cycle length. Some women experience cramping and pain before and during menstruation. ",text,
L_0601,microscopes,T_3176,"Microscopes, tools that you may get to use in your class, are some of the most important tools in biology ( Figure Microscopy is the study of small objects using microscopes. Look at your fingertips. Before microscopes were invented in 1595, the smallest things you could see on yourself were the tiny lines in your skin. But what else is hidden in your skin? ",text,
L_0601,microscopes,T_3177,"Over four hundred years ago, two Dutch spectacle makers, Zaccharias Janssen and his son Hans, were experimenting with several lenses in a tube. They discovered that nearby objects appeared greatly enlarged, or magnified. This was the forerunner of the compound microscope and of the telescope. In 1665, Robert Hooke, an English natural scientist, used a microscope to zoom in on a piece of cork - the stuff that makes up the stoppers in wine bottles, which is made from tree bark. Inside of cork, he discovered tiny structures, which he called cells. It turns out that cells are the smallest structural unit of living organisms. This finding eventually led to the development of the theory that all living things are made of cells. Without microscopes, this discovery would not have been possible, and the cell theory would not have been developed. Hookes discovery of the cell set the stage for other scientists to discover other types of organisms. After Hooke, the ""father of microscopy,"" Dutch scientist Antoine van Leeuwenhoek ( Figure 1.2) taught himself to make one of the first microscopes. In one of his early experiments, van Leeuwenhoek took a sample of scum from his own teeth and used his microscope to discover bacteria, the smallest living organism on the planet. Using microscopes, van Leeuwenhoek also discovered one-celled protists and sperm cells. Today, microscopes are used by all types of scientists, including cell biologists, microbiologists, virologists, forensic scientists, entomologists, taxonomists, and many other types. Antoine van Leeuwenhoek, a Dutch cloth merchant with a passion for microscopy. ",text,
L_0601,microscopes,T_3177,"Over four hundred years ago, two Dutch spectacle makers, Zaccharias Janssen and his son Hans, were experimenting with several lenses in a tube. They discovered that nearby objects appeared greatly enlarged, or magnified. This was the forerunner of the compound microscope and of the telescope. In 1665, Robert Hooke, an English natural scientist, used a microscope to zoom in on a piece of cork - the stuff that makes up the stoppers in wine bottles, which is made from tree bark. Inside of cork, he discovered tiny structures, which he called cells. It turns out that cells are the smallest structural unit of living organisms. This finding eventually led to the development of the theory that all living things are made of cells. Without microscopes, this discovery would not have been possible, and the cell theory would not have been developed. Hookes discovery of the cell set the stage for other scientists to discover other types of organisms. After Hooke, the ""father of microscopy,"" Dutch scientist Antoine van Leeuwenhoek ( Figure 1.2) taught himself to make one of the first microscopes. In one of his early experiments, van Leeuwenhoek took a sample of scum from his own teeth and used his microscope to discover bacteria, the smallest living organism on the planet. Using microscopes, van Leeuwenhoek also discovered one-celled protists and sperm cells. Today, microscopes are used by all types of scientists, including cell biologists, microbiologists, virologists, forensic scientists, entomologists, taxonomists, and many other types. Antoine van Leeuwenhoek, a Dutch cloth merchant with a passion for microscopy. ",text,
L_0601,microscopes,T_3178,"Some modern microscopes use light, as Hookes and van Leeuwenhoeks did. Others may use electron beams or sound waves. Researchers now use these four types of microscopes: 1. Light microscopes allow biologists to see small details of a specimen. Most of the microscopes used in schools and laboratories are light microscopes. Light microscopes use lenses, typically made of glass or plastic, to focus light either into the eye, a camera, or some other light detector. The most powerful light microscopes can make images up to 2,000 times larger. 2. Transmission electron microscopes (TEM) focus a beam of electrons through an object and can make an image up to two million times bigger, with a very clear image. 3. Scanning electron microscopes (SEM) allow scientists to find the shape and surface texture of extremely small objects, including a paperclip, a bedbug, or even an atom. These microscopes slide a beam of electrons across the surface of a specimen, producing detailed maps of the surface of objects. Magnification in a SEM can be controlled over a range from about 10 to 500,000 times. 4. Scanning acoustic microscopes use sound waves to scan a specimen. These microscopes are useful in biology and medical research. ",text,
L_0601,microscopes,T_3179,Scanning Electron Microscope at  (5:04) Click image to the left or use the URL below. URL:  1. How is the electron beam focused? 2. What part of a specimen does a scanning electron microscope look at? 3. Why is it important that a specimen for an electron microscope be placed in a vacuum? Why is this step unnecessary for a light microscope? ,text,
L_0606,mollusks,T_3188,"When you take a walk along a beach, what do you find there? Sand, the ocean, lots of sunlight. You may also find shells. The shells you find are most likely left by organisms in the phylum Mollusca. On the beach, you can find the shells of many different mollusks ( Figure 1.1), including clams, mussels, scallops, oysters, and snails. Mollusks are invertebrates that usually have a hard shell, a mantle, and a radula. Their glossy pearls, mother of pearl, and abalone shells are like pieces of jewelry. Some mollusks, such as squid and octopus, do not have shells. ",text,
L_0606,mollusks,T_3189,"The Mollusks body is often divided into different parts ( Figure 1.2): On the beach, you can find a wide variety of mollusk shells. 1. A head with eyes or tentacles. 2. In most species, a muscular foot, which helps the mollusk move. Some mollusks use the foot for burrowing into the sand, and others use it for jet-propulsion. 3. A mantle, or fold of the outer skin lining the shell. The mantle often releases calcium carbonate, which creates an external shell, just like the ones you find on the beach. The shell is made of chitin, a tough, semitransparent substance. 4. A mass housing the organs. 5. A complete digestive tract that begins at the mouth and runs to the anus. 6. Most ocean mollusks have a gill or gills to absorb oxygen from the water. 7. Many species have a feeding structure, the radula, found only in mollusks. The radula can be thought of as a ""tongue-like"" structure. The radula is made mostly of chitin. Types of radulae range from structures used to scrape algae off of rocks to the beaks of squid and octopuses. This is the basic body plan of a mollusk. Note the mantle, gills, and radula. Keep in mind the basic body plan can differ slightly among the mollusks. ",text,
L_0606,mollusks,T_3189,"The Mollusks body is often divided into different parts ( Figure 1.2): On the beach, you can find a wide variety of mollusk shells. 1. A head with eyes or tentacles. 2. In most species, a muscular foot, which helps the mollusk move. Some mollusks use the foot for burrowing into the sand, and others use it for jet-propulsion. 3. A mantle, or fold of the outer skin lining the shell. The mantle often releases calcium carbonate, which creates an external shell, just like the ones you find on the beach. The shell is made of chitin, a tough, semitransparent substance. 4. A mass housing the organs. 5. A complete digestive tract that begins at the mouth and runs to the anus. 6. Most ocean mollusks have a gill or gills to absorb oxygen from the water. 7. Many species have a feeding structure, the radula, found only in mollusks. The radula can be thought of as a ""tongue-like"" structure. The radula is made mostly of chitin. Types of radulae range from structures used to scrape algae off of rocks to the beaks of squid and octopuses. This is the basic body plan of a mollusk. Note the mantle, gills, and radula. Keep in mind the basic body plan can differ slightly among the mollusks. ",text,
L_0606,mollusks,T_3190,"Mollusks are probably most closely related to organisms in the phylum Annelida, also known as segmented worms. This phylum includes the earthworm and leech. Scientists believe these two groups are related because, when they are in the early stage of development, they look very similar. Mollusks also share features of their organ systems with segmented worms. Unlike segmented worms, however, mollusks do not have body segmentation. The basic mollusk body shape is usually quite different as well. ",text,
L_0607,muscles and exercise,T_3191,"Regular physical exercise is important in preventing lifestyle diseases such as cardiovascular disease, some types of cancer, type 2 diabetes, and obesity. Regular exercise also improves the health of the muscular system. Muscles that are exercised are bigger and stronger than muscles that are not exercised. Exercise improves both muscular strength and muscular endurance. Muscular strength is the ability of a muscle to use force during a contraction. Muscular endurance is the ability of a muscle to continue to contract over a long time without getting tired. Exercises are grouped into three types depending on the effect they have on the body: Aerobic exercises, such as cycling, walking, and running, increase muscular endurance and cardiovascular health. Anaerobic exercises, such as weight training or sprinting, increase muscle strength. Flexibility exercises, such as stretching, improve the range of motion of muscles and joints. Regular stretching helps people avoid activity-related injuries. ",text,
L_0607,muscles and exercise,T_3192,"Anaerobic exercises comprise brief periods of physical exertion and high-intensity, strength-training activities. Anaerobic exercises cause muscles to get bigger and stronger. Anaerobic exercises use a resistance against which the muscle has to work to lift or push away. The resistance can be a weight or a persons own body weight (Figure ",text,
L_0607,muscles and exercise,T_3193,"Aerobic exercises are exercises in which a low to moderate level of exertion can be sustained over long periods. These are exercises that cause your heart to beat faster and allow your muscles to use oxygen to contract. If you exercise aerobically, overtime, your muscles will not get easily tired, and you will use oxygen more efficiently. Aerobic exercise (Figure 1.2) also helps improve cardiac muscle. ",text,
L_0607,muscles and exercise,T_3194,"Sometimes muscles and tendons get injured when a person starts doing an activity before they have warmed up properly. A warm up is a slow increase in the intensity of a physical activity that prepares muscles for an activity. Warming up increases the blood flow to the muscles and increases the heart rate. Warmed-up muscles and tendons are less likely to get injured. For example, before running or playing soccer, a person might jog slowly to warm muscles and increase their heart rate. Even elite athletes need to warm up (Figure 1.3). When you dont do a proper warm-up, several types of injuries can occur. A strain happens when muscle or tendons tear. Strains are also known as ""pulled muscles."" Another common injury is tendinitis, the irritation of the tendons. Strains and tendinitis are usually treated with rest, cold compresses, and stretching exercises that a physical therapist designs for each patient. Injuries can also be prevented by proper rest and recovery. If you do not get enough rest, your body will become injured and will not react well to exercise, or improve. You can also rest by doing a different activity. For example, if you run, you can rest your running muscles and joints by swimming. Warming up before the game helps the players avoid injuries. Some warm-ups may include stretching exercises. ",text,
L_0608,muscles bones and movement,T_3195,"When skeletal muscles contract, bones move. But how do muscles make your bones move? A voluntary muscles usually works across a joint. It is attached to both the bones on either side of the joint by strong cords called tendons. A tendon is a tough band of connective tissue that connects a muscle to a bone. Tendons are similar to ligaments, except that ligaments join bones to each other. Muscles move the body by contracting against the skeleton. When muscles contract, they get shorter. By contracting, muscles pull on bones and allow the body to move. Muscles can only contract. They cannot actively extend, though they can move or relax back into the non-contracted neutral position. Therefore, to move bones in opposite directions, pairs of muscles must work in opposition. Each muscle in the pair works against the other to move bones at the joints of the body. The muscle that contracts to cause a joint to bend is called the flexor. The muscle that contracts to cause the joint to straighten is called the extensor. When one muscle is contracted, the other muscle from the pair is always elongated. For example, the biceps and triceps muscles work together to allow you to bend and straighten your elbow. When you want to bend your elbow, your biceps muscle contracts (Figure 1.1), and, at the same time, the triceps muscle relaxes. The biceps is the flexor, and the triceps is the extensor of your elbow joint. Other muscles that work together are the quadriceps and hamstrings used to bend and straighten the knee, and the pectorals and trapezius used to move the arms and shoulders forward and backward. During daily routines we do not use muscles equally. For example, we use our biceps more than our triceps due to lifting against gravity. ",text,
L_0608,muscles bones and movement,T_3196,"Smooth muscles and cardiac muscles are not attached to bone. Recall that these types of muscles are under involuntary control. Smooth muscle is responsible for the contractility of hollow organs, such as blood vessels, the gastrointestinal tract, the bladder, or the uterus. Like skeletal muscles, smooth muscle fibers do contract together, causing the muscle to shorten. Smooth muscles have numerous functions, including the following. The smooth muscle in the uterus helps a woman to push out her baby. In the bladder, smooth muscle helps to push out urine. Smooth muscles move food through the digestive tract. In arteries, smooth muscle movements maintain the arteries diameter. Smooth muscle regulates air flow in lungs. Smooth muscle in the lungs helps the airways to expand and contract as necessary. Smooth muscles in arteries and veins are largely responsible for regulation of blood pressure. Cardiac muscle also contracts and gets shorter. This muscle is found only in the heart. The sudden burst of contraction forces blood throughout your body. When the cardiac muscle relaxes, the heart fills with blood. This rhythmic contraction must continue for your whole life, luckily the heart muscle never gets tired. If your heart beats 75 times a minute, how many times does it beat in an hour? A day? A year? 85 years? ",text,
L_0609,mutations,T_3197,"The process of DNA replication is not always 100% accurate. Sometimes the wrong base is inserted in the new strand of DNA. This wrong base could become permanent. A permanent change in the sequence of DNA is known as a mutation. Small changes in the DNA sequence are usually point mutations, which is a change in a single nucleotide. Once DNA has a mutation, that mutation will be copied each time the DNA replicates. After cell division, each resulting cell will carry the mutation. A mutation may have no effect. However, sometimes a mutation can cause a protein to be made incorrectly. A defect in the protein can affect how well the protein works, or whether it works at all. Usually the loss of a protein function is detrimental to the organism. In rare circumstances, though, the mutation can be beneficial. Mutations are a mechanism for how species evolve. For example, suppose a mutation in an animals DNA causes the loss of an enzyme that makes a dark pigment in the animals skin. If the population of animals has moved to a light colored environment, the animals with the mutant gene would have a lighter skin color and be better camouflaged. So in this case, the mutation is beneficial. ",text,
L_0609,mutations,T_3198,"If a single base is deleted (called a deletion, which is also a point mutation), there can be huge effects on the organism, because this may cause a frameshift mutation. Remember that the bases in the mRNA are read in groups of three by the tRNA. If the reading frame is off by even one base, the resulting sequence will consist of an entirely different set of codons. The reading of an mRNA is like reading three-letter words of a sentence. Imagine the sentence: The big dog ate the red cat. If you take out the second letter from ""big,"" the frame will be shifted so now it will read: The bgd oga tet her edc at. One single deletion makes the whole sentence impossible to read. A point mutation that adds a base (known as an insertion) would also result in a frameshift. ",text,
L_0609,mutations,T_3199,"Mutations may also occur in chromosomes ( Figure 1.1). These mutations are going to be fairly large mutations, possible affecting many genes. Possible types of mutations in chromosomes include: 1. Deletion: When a segment of DNA is lost, so there is a missing segment in the chromosome. These usually result in many genes missing from the chromosome. 2. Duplication: When a segment of DNA is repeated, creating a longer chromosome. These usually result in multiple copies of genes in the chromosome. 3. Inversion: When a segment of DNA is flipped and then reattached to the same chromosome. 4. Insertion: When a segment of DNA from one chromosome is added to another, unrelated chromosome. 5. Translocation: When two segments from different chromosomes change positions. ",text,
L_0609,mutations,T_3200,"Many mutations are not caused by errors in replication. Mutations can happen spontaneously, and they can be caused by mutagens in the environment. Some chemicals, such as those found in tobacco smoke, can be mutagens. Sometimes mutagens can also cause cancer. Tobacco smoke, for example, is often linked to lung cancer. ",text,
L_0610,nails and hair,T_3201,"Along with the skin, the integumentary system includes the nails and hair. Both the nails and hair contain the tough protein, keratin. The keratin forms fibers, which makes your nails and hair tough and strong. Keratin is similar in toughness to chitin, the carbohydrate found in the exoskeleton of arthropods. ",text,
L_0610,nails and hair,T_3202,"Nails are similar to claws in other animals. They cover the tips of fingers and toes. Fingernails and toenails both grow from nail beds. As the nail grows, more cells are added at the nail bed. Older cells get pushed away from the nail bed and the nail grows longer. There are no nerve endings in the nail. Otherwise cutting your nails would hurt a lot! Nails act as protective plates over the fingertips and toes. Fingernails also help in sensing the environment. The area under your nail has many nerve endings. These nerve endings allow you to receive more information about objects you touch. The Guinness Book of World Records began tracking record fingernail lengths in 1955. At that time the record was 1 foot 10.75 inches long. The current record-holder for men is from India, with a record of 20 feet 2.25 inches for all nails on his left hand, the longest being his thumbnail at 4 feet 9.6 inches. The record for women is held by an American woman. The record is 28 feet (850 cm) for all nails of both hands, with the longest nail on her right thumb at 2 feet 11 inches. Since adult nails grow at about 3 mm a month (1/10 of an inch), how long would it take to grow such long nails? ",text,
L_0610,nails and hair,T_3203,"Hair is one of the defining characteristics of mammals. In fact, mammals are the only animals to have hair. Hair sticks out from the epidermis, but it grows from the dermis ( Figure 1.1). Hair grows from inside the hair follicle. New cells grow in the bottom part of the hair, called the bulb. Older cells get pushed up, and the hair grows longer. The cells that make up the hair strand are dead and filled with the rope-like protein keratin. Hair, hair follicle, and oil glands. The oil, called sebum, helps to prevent water loss from the skin. The sebaceous gland secretes sebum, which waterproofs the skin and hair. In humans, hair grows everywhere on the body except the soles of the feet and the palms of the hands, the lips, and the eyelids (except for eyelashes). Hair grows at a rate of about half an inch (1.25 cm) each month, or about 6 inches (15 cm) a year. Hair, especially on the head, helps to keep the body warm. The air traps a layer of warm air near the skin and acts like a warm blanket. Hair can also act as a filter. Nose hair helps to trap particles in the air that may otherwise travel to the lungs. Eyelashes shield eyes from dust and sunlight. Eyebrows stop salty sweat and rain from flowing into the eye. The worlds longest documented hair, according to Guinness World Records, belongs to Xie Qiuping of China at just under 18 feet 6 inches (5.627 m) when measured on May 8, 2004. She had been growing her hair since 1973 when she was 13 years old. ",text,
L_0613,nervous system,T_3210,"Michelle was riding her scooter when she hit a hole in the street and started to lose control. She thought she would fall, but, in the blink of an eye, she shifted her weight and kept her balance. Her heart was pounding, but at least she didnt get hurt. How was she able to react so quickly? Michelle can thank her nervous system for that ( Figure 1.1). The nervous system, together with the endocrine system, controls all the other organ systems. The nervous system sends one type of signal around the body, and the endocrine system sends another type of signal around the body. The endocrine system makes and releases chemical messenger molecules, or hormones, which tell other body parts that a change or a reaction is necessary. So what type of signal does the nervous system send? Controlling muscles and maintaining balance are just two of the roles of the nervous system. The nervous system also lets you: Sense your surroundings with your eyes and other sense organs. Sense the environment inside of your body, including temperature. Control your internal body systems and keep them in balance. Staying balanced when riding a scooter requires control over the bodys muscles. The nervous system controls the muscles and maintains balance. Prepare your body to fight or flee in an emergency. Use language, think, learn, and remember. The nervous system works by sending and receiving electrical signals. The main organs of the nervous system are the brain and the spinal cord. The signals are carried by nerves in the body, similar to the wires that carry electricity all over a house. The signals travel from all over the body to the spinal cord and up to the brain, as well as moving in the other direction. For example, when Michelle started to fall off her scooter, her nervous system sensed that she was losing her balance. It responded by sending messages from her brain to muscles in her body. Some muscles tightened while others relaxed. Maybe these actions moved her hips or her arms. The nervous system, working together with the muscular and skeletal systems, allowed Michelle to react to the situation. As a result, Michelles body became balanced again. The messages released by the nervous system traveled through nerves. Just like the electricity that travels through wires, nerve quickly carry the electrical messages around the body. Think about how quickly all this happens. It has to be really fast, otherwise Michelle would not have been able to react. What would happen if a car pulled out unexpectedly in front of Michelle? A signal would have to go from her eyes to her brain and then to her muscles. What allows the nervous system to react so fast. It starts with the special cell of the nervous system, the neuron. ",text,
L_0614,non infectious reproductive system disorders,T_3211,"Many disorders of the reproductive system are not sexually transmitted infections. They are not caused by pathogens, so they dont spread from person to person. They develop for other reasons. The disorders are different between males and females. In both genders, the disorders could cause a little discomfort, or they could cause death. ",text,
L_0614,non infectious reproductive system disorders,T_3212,"Most common disorders of the male reproductive system involve the testes. For example, injuries to the testes are very common. In teenagers, injuries to the testes most often occur while playing sports. An injury such as a strike or kick to the testes can be very painful. It may also cause bruising and swelling. Such injuries do not usually last very long. Another disorder of the testes is cancer. Cancer of the testes is most common in males aged 15 to 35. It occurs when cells in the testes grow out of control. The cells form a lump called a tumor. If found early, cancer of the testes usually can be easily cured with surgery. ",text,
L_0614,non infectious reproductive system disorders,T_3213,"Disorders of the female reproductive system may affect the vagina, uterus, or ovaries. They may also affect the breasts. One of the most common disorders is vaginitis. This is redness and itching of the vagina. It may be due to irritation by soap or bubble bath. Another possible cause of vaginitis is a yeast infection. Yeast normally grow in the vagina. A yeast infection happens when the yeast multiply too fast and cause symptoms. A yeast infection can be treated with medication. Bubble baths may be fun, but for women and girls they can cause irritation to the vagina. A common disorder of the ovaries is an ovarian cyst. A cyst is a sac filled with fluid or other material. An ovarian cyst is usually harmless, but it may cause pain. Most cysts slowly disappear and do not need treatment. Very large or painful cysts can be removed with surgery. Many teen girls have painful menstrual periods. They typically have cramping in the lower abdomen. Generally, this is nothing to worry about. Taking a warm bath or using a heating pad often helps. Exercise can help as well. A pain reliever like ibuprofen may also work. If the pain is severe, a doctor can prescribe stronger medicine to relieve the pain. The most common type of cancer in females is breast cancer. The cancer causes the cells of the breast to grow out of control and form a tumor. Breast cancer is rare in teens. It becomes more common as women get older. If breast cancer is found early, it usually can be cured with surgery. ",text,
L_0616,nonrenewable resources,T_3217,"A nonrenewable resource is a natural resource that is consumed or used up faster than it can be made by nature. Two main types of nonrenewable resources are fossil fuels and nuclear power. Fossil fuels, such as petroleum, coal, and natural gas, formed from plant and animal remains over periods from 50 to 350 million years ago. They took millions of years to form. Humans have been consuming fossil fuels for less than 200 years, yet remaining reserves of oil can supply our needs only until around the year 2055. Natural gas can only supply us until around 2085. Coal will last longer, until around the year 2250. That is why it is so important to develop alternate forms of energy, especially for our cars. Today, electric cars are becoming more and more common. Considering the year 2055 is not that far away, what would happen if we ran out of gasoline? Alternative use of energy, especially in transportation, must become a standard feature of all cars and trucks and planes by the middle of the century. Nuclear power is the use of nuclear energy ( nuclear fission) to create energy inside of a nuclear reactor ( Figure uranium fuel supplies, which will last to about the year 2100 (or longer) at current rates of use. However, new technologies could make some uranium fuel reserves more useful. Population growth, especially in developing countries, should make people think about how fast they are consuming resources. Governments around the world should seriously consider these issues. Developing nations will also increase demands on natural resources as they build more factories ( Figure 1.2). Improvements in technology, conservation of resources, and controls in population growth could all help to decrease the demand on natural resources. Aerial photo of the Bruce Nuclear Gener- ating Station near Kincardine, Ontario. Per capita energy consumption (2003) shows the unequal distribution of wealth, technology, and energy use. ",text,
L_0616,nonrenewable resources,T_3217,"A nonrenewable resource is a natural resource that is consumed or used up faster than it can be made by nature. Two main types of nonrenewable resources are fossil fuels and nuclear power. Fossil fuels, such as petroleum, coal, and natural gas, formed from plant and animal remains over periods from 50 to 350 million years ago. They took millions of years to form. Humans have been consuming fossil fuels for less than 200 years, yet remaining reserves of oil can supply our needs only until around the year 2055. Natural gas can only supply us until around 2085. Coal will last longer, until around the year 2250. That is why it is so important to develop alternate forms of energy, especially for our cars. Today, electric cars are becoming more and more common. Considering the year 2055 is not that far away, what would happen if we ran out of gasoline? Alternative use of energy, especially in transportation, must become a standard feature of all cars and trucks and planes by the middle of the century. Nuclear power is the use of nuclear energy ( nuclear fission) to create energy inside of a nuclear reactor ( Figure uranium fuel supplies, which will last to about the year 2100 (or longer) at current rates of use. However, new technologies could make some uranium fuel reserves more useful. Population growth, especially in developing countries, should make people think about how fast they are consuming resources. Governments around the world should seriously consider these issues. Developing nations will also increase demands on natural resources as they build more factories ( Figure 1.2). Improvements in technology, conservation of resources, and controls in population growth could all help to decrease the demand on natural resources. Aerial photo of the Bruce Nuclear Gener- ating Station near Kincardine, Ontario. Per capita energy consumption (2003) shows the unequal distribution of wealth, technology, and energy use. ",text,
L_0619,organic compounds,T_3223,"The main chemical components of living organisms are known as organic compounds. Organic compounds are molecules built around the element carbon (C). Living things are made up of very large molecules. These large molecules are called macromolecules because macro means large; they are made by smaller molecules bonding together. Our body gets these smaller molecules, the ""building blocks"" or monomers, of organic molecules from the food we eat. Which organic molecules do you recognize from the list below? The four main types of macromolecules found in living organisms, shown in Table 1.1, are: 1. 2. 3. 4. Proteins. Carbohydrates. Lipids. Nucleic Acids. Proteins C, H, O, N, S Enzymes, muscle fibers, antibodies Elements Examples Monomer building molecule) (small block Amino acids Carbohydrates C, H, O Sugar, glucose, starch, glycogen, cellulose Monosaccharides (simple sugars) Lipids C, H, O, P Fats, oils, waxes, steroids, phospho- lipids in membranes Often include fatty acids Nucleic Acids C, H, O, P, N DNA, RNA, ATP Nucleotides ",text,
L_0619,organic compounds,T_3224,"Carbohydrates are sugars, or long chains of sugars. An important role of carbohydrates is to store energy. Glucose ( Figure 1.1) is an important simple sugar molecule with the chemical formula C6 H12 O6 . Simple sugars are known as monosaccharides. Carbohydrates also include long chains of connected sugar molecules. These long chains often consist of hundreds or thousands of monosaccharides bonded together to form polysaccharides. Plants store sugar in polysaccharides called starch. Animals store sugar in polysaccharides called glycogen. You get the carbohydrates you need for energy from eating carbohydrate-rich foods, including fruits and vegetables, as well as grains, such as bread, rice, or corn. A molecule of glucose, a type of carbohy- drate. ",text,
L_0619,organic compounds,T_3225,"Proteins are molecules that have many different functions in living things. All proteins are made of monomers called amino acids ( Figure 1.2) that connect together like beads on a necklace ( Figure 1.3). There are only 20 common amino acids needed to build proteins. These amino acids form in thousands of different combinations, making about 100,000 or more unique proteins in humans. Proteins can differ in both the number and order of amino acids. It is the number and order of amino acids that determines the shape of the protein, and it is the shape (structure) of the protein that determines the unique function of the protein. Small proteins have just a few hundred amino acids. The largest proteins have more than 25,000 amino acids. This model shows the general structure of all amino acids. Only the side chain, R, varies from one amino acid to another. KEY: H = hydrogen, N = nitrogen, C = carbon, O = oxygen, R = variable side chain. Many important molecules in your body are proteins. Examples include enzymes, antibodies, and muscle fiber. Enzymes are a type of protein that speed up chemical reactions. They are known as ""biological catalysts."" For example, your stomach would not be able to break down food if it did not have special enzymes to speed up the rate of digestion. Antibodies that protect you against disease are proteins. Muscle fiber is mostly protein ( Figure 1.4). Muscle fibers are made mostly of protein. Its important for you and other animals to eat food with protein, because we cannot make certain amino acids on our own. You can get proteins from plant sources, such as beans, and from animal sources, like milk or meat. When you eat food with protein, your body breaks the proteins down into individual amino acids and uses them to build new proteins. You really are what you eat! ",text,
L_0619,organic compounds,T_3225,"Proteins are molecules that have many different functions in living things. All proteins are made of monomers called amino acids ( Figure 1.2) that connect together like beads on a necklace ( Figure 1.3). There are only 20 common amino acids needed to build proteins. These amino acids form in thousands of different combinations, making about 100,000 or more unique proteins in humans. Proteins can differ in both the number and order of amino acids. It is the number and order of amino acids that determines the shape of the protein, and it is the shape (structure) of the protein that determines the unique function of the protein. Small proteins have just a few hundred amino acids. The largest proteins have more than 25,000 amino acids. This model shows the general structure of all amino acids. Only the side chain, R, varies from one amino acid to another. KEY: H = hydrogen, N = nitrogen, C = carbon, O = oxygen, R = variable side chain. Many important molecules in your body are proteins. Examples include enzymes, antibodies, and muscle fiber. Enzymes are a type of protein that speed up chemical reactions. They are known as ""biological catalysts."" For example, your stomach would not be able to break down food if it did not have special enzymes to speed up the rate of digestion. Antibodies that protect you against disease are proteins. Muscle fiber is mostly protein ( Figure 1.4). Muscle fibers are made mostly of protein. Its important for you and other animals to eat food with protein, because we cannot make certain amino acids on our own. You can get proteins from plant sources, such as beans, and from animal sources, like milk or meat. When you eat food with protein, your body breaks the proteins down into individual amino acids and uses them to build new proteins. You really are what you eat! ",text,
L_0619,organic compounds,T_3225,"Proteins are molecules that have many different functions in living things. All proteins are made of monomers called amino acids ( Figure 1.2) that connect together like beads on a necklace ( Figure 1.3). There are only 20 common amino acids needed to build proteins. These amino acids form in thousands of different combinations, making about 100,000 or more unique proteins in humans. Proteins can differ in both the number and order of amino acids. It is the number and order of amino acids that determines the shape of the protein, and it is the shape (structure) of the protein that determines the unique function of the protein. Small proteins have just a few hundred amino acids. The largest proteins have more than 25,000 amino acids. This model shows the general structure of all amino acids. Only the side chain, R, varies from one amino acid to another. KEY: H = hydrogen, N = nitrogen, C = carbon, O = oxygen, R = variable side chain. Many important molecules in your body are proteins. Examples include enzymes, antibodies, and muscle fiber. Enzymes are a type of protein that speed up chemical reactions. They are known as ""biological catalysts."" For example, your stomach would not be able to break down food if it did not have special enzymes to speed up the rate of digestion. Antibodies that protect you against disease are proteins. Muscle fiber is mostly protein ( Figure 1.4). Muscle fibers are made mostly of protein. Its important for you and other animals to eat food with protein, because we cannot make certain amino acids on our own. You can get proteins from plant sources, such as beans, and from animal sources, like milk or meat. When you eat food with protein, your body breaks the proteins down into individual amino acids and uses them to build new proteins. You really are what you eat! ",text,
L_0619,organic compounds,T_3226,"Have you ever tried to put oil in water? They dont mix. Oil is a type of lipid. Lipids are molecules such as fats, oils, and waxes. The most common lipids in your diet are probably fats and oils. Fats are solid at room temperature, whereas oils are fluid. Animals use fats for long-term energy storage and to keep warm. Plants use oils for long- term energy storage. When preparing food, we often use animal fats, such as butter, or plant oils, such as olive oil or canola oil. There are many more type of lipids that are important to life. One of the most important are the phospholipids that make up the protective outer membrane of all cells ( Figure 1.5). These lipid membranes are impermeable to most water soluble compounds. ",text,
L_0619,organic compounds,T_3227,"Nucleic acids are long chains of nucleotides. Nucleotides are made of a sugar, a nitrogen-containing base, and a phosphate group. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two main nucleic acids. DNA is a double-stranded nucleic acid. DNA is the molecule that stores our genetic information ( Figure 1.6). The single- stranded RNA is involved in making proteins. ATP (adenosine triphosphate), known as the ""energy currency"" of the cell, is also a nucleic acid. ",text,
L_0621,organization of the human body,T_3232,"Cells are grouped together to carry out specific functions. A group of cells that work together form a tissue. Your body has four main types of tissues, as do the bodies of other animals. These tissues make up all structures and contents of your body. An example of each tissue type is pictured in the Figure 1.1. Your body has four main types of tissue: nervous tissue, epithelial tissue, connective tissue, and muscle tissue. They are found throughout your body. 1. Epithelial tissue is made up of layers of tightly packed cells that line the surfaces of the body. Examples of epithelial tissue include the skin, the lining of the mouth and nose, and the lining of the digestive system. 2. Connective tissue is made up of many different types of cells that are all involved in supporting and binding other tissues of the body. Examples include tendon, cartilage, and bone. Blood is also classified as a specialized connective tissue. 3. Muscle tissue is made up of bands of cells that contract and allow movement. 4. Nervous tissue is made up of nerve cells that sense stimuli and transmit signals. Nervous tissue is found in nerves, the spinal cord, and the brain. ",text,
L_0621,organization of the human body,T_3233,A single tissue alone cannot do all the jobs that are needed to keep you alive and healthy. Two or more tissues working together can do a lot more. An organ is a structure made of two or more tissues that work together. The heart ( Figure 1.2) is made up of the four types of tissues. The four different tissue types work to- gether in the heart as they do in the other organs. ,text,
L_0621,organization of the human body,T_3234,"Your heart pumps blood around your body. But how does your heart get blood to and from every cell in your body? Your heart is connected to blood vessels such as veins and arteries. Organs that work together form an organ system. Together, your heart, blood, and blood vessels form your cardiovascular system. What other organ systems can you think of? ",text,
L_0621,organization of the human body,T_3235,"Your bodys 12 organ systems are shown below ( Table 1.1). Your organ systems do not work alone in your body. They must all be able to work together. For example, one of the most important functions of organ systems is to provide cells with oxygen and nutrients and to remove toxic waste products such as carbon dioxide. A number of organ systems, including the cardiovascular and respiratory systems, all work together to do this. Organ System Cardiovascular Major Tissues and Organs Heart; blood vessels; blood Lymphatic Lymph nodes; lymph vessels Digestive Esophagus; stomach; small intes- tine; large intestine Pituitary gland, hypothalamus; adrenal glands; ovaries; testes Endocrine Function Transports oxygen, hormones, and nutrients to the body cells. Moves wastes and carbon dioxide away from cells. Defend against infection and dis- ease, moves lymph between tissues and the blood stream. Digests foods and absorbs nutrients, minerals, vitamins, and water. Produces hormones that communi- cate between cells. Organ System Integumentary Major Tissues and Organs Skin, hair, nails Muscular Cardiac (heart) muscle; skeletal muscle; smooth muscle; tendons Brain, spinal cord; nerves Nervous Reproductive Respiratory Female: uterus; vagina; fallopian tubes; ovaries Male: penis; testes; seminal vesi- cles Trachea, larynx, pharynx, lungs Skeletal Bones, cartilage; ligaments Urinary Kidneys; urinary bladder Immune Bone marrow; spleen; white blood cells Function Provides protection from injury and water loss, physical defense against infection by microorganisms, and temperature control. Involved in movement and heat pro- duction. Collects, transfers, and processes information. Produces gametes (sex cells) and sex hormones. Brings air to sites where gas ex- change can occur between the blood and cells (around body) or blood and air (lungs). Supports and protects soft tissues of body; produces blood cells; stores minerals. Removes extra water, salts, and waste products from blood and body; controls pH; controls water and salt balance. Defends against diseases. ",text,
L_0623,origins of life,T_3241,There is good evidence that life has probably existed on Earth for most of Earths history. Fossils of blue-green algae found in Australia are the oldest fossils of life forms on Earth. They are at least 3.5 billion years old ( Figure 1.1). ,text,
L_0623,origins of life,T_3242,"How did life begin? In order to answer this question, scientists need to know what kinds of materials were available at that time. We know that the ingredients for life were present at the beginning of Earths history. Scientists believe early Earth did not contain oxygen gas (photosynthesis had yet to evolve), but did contain other gases, including: nitrogen gas, carbon dioxide, carbon monoxide, water vapor, hydrogen sulfide. Some of the oldest fossils on Earth were found along the coast of Australia, similar to the area shown here. Where did these ingredients come from? Some chemicals were in water and volcanic gases ( Figure 1.2). Other chemicals would have come from meteorites in space. Energy to drive chemical reactions was provided by volcanic eruptions and lightning. Today, we have evidence that life on Earth came from random reactions between chem- ical compounds, which formed molecules, or groups of atoms bonded together. Small molecules, such as those present in the early atmosphere, can provide the components (including the elements C, H, N, O and S) to make larger molecules. These early molecules further reacted and eventually formed even larger molecules and organic compounds, such as amino acids (which combine to form proteins), and nucleotides (which form nucleic acids - RNA or DNA). These organic molecules eventually came together in the right combinations to form basic cells. The components that were necessary for the formation of the first cells are still being studied. How long did it take to develop the first life forms? As much as 1 billion years. Many scientists still study the origin of the first life forms because there are many questions left unanswered, such as, ""Did proteins or nucleic acids develop first?"" or ""What exactly were early Earths atmospheric conditions like?"" There is a lot of work still left to answer these and similar questions. Some clues to the origins of life on Earth come from studying the early life forms that developed in hot springs, such as the Grand Prismatic Spring at Yellowstone National Park. This spring is approxi- mately 250 feet deep and 300 feet wide. ",text,
L_0623,origins of life,T_3242,"How did life begin? In order to answer this question, scientists need to know what kinds of materials were available at that time. We know that the ingredients for life were present at the beginning of Earths history. Scientists believe early Earth did not contain oxygen gas (photosynthesis had yet to evolve), but did contain other gases, including: nitrogen gas, carbon dioxide, carbon monoxide, water vapor, hydrogen sulfide. Some of the oldest fossils on Earth were found along the coast of Australia, similar to the area shown here. Where did these ingredients come from? Some chemicals were in water and volcanic gases ( Figure 1.2). Other chemicals would have come from meteorites in space. Energy to drive chemical reactions was provided by volcanic eruptions and lightning. Today, we have evidence that life on Earth came from random reactions between chem- ical compounds, which formed molecules, or groups of atoms bonded together. Small molecules, such as those present in the early atmosphere, can provide the components (including the elements C, H, N, O and S) to make larger molecules. These early molecules further reacted and eventually formed even larger molecules and organic compounds, such as amino acids (which combine to form proteins), and nucleotides (which form nucleic acids - RNA or DNA). These organic molecules eventually came together in the right combinations to form basic cells. The components that were necessary for the formation of the first cells are still being studied. How long did it take to develop the first life forms? As much as 1 billion years. Many scientists still study the origin of the first life forms because there are many questions left unanswered, such as, ""Did proteins or nucleic acids develop first?"" or ""What exactly were early Earths atmospheric conditions like?"" There is a lot of work still left to answer these and similar questions. Some clues to the origins of life on Earth come from studying the early life forms that developed in hot springs, such as the Grand Prismatic Spring at Yellowstone National Park. This spring is approxi- mately 250 feet deep and 300 feet wide. ",text,
L_0624,outdoor air pollution,T_3243,"Air is all around us. Air is essential for life. Sometimes, humans can pollute the air. For example, releasing smoke and dust from factories and cars can cause air pollution. Air pollution is due to chemical substances and particles released into the air mainly by human actions. This pollution affects entire ecosystems around the world. Pollution can also cause many human health problems, and it can also cause death. Air pollution can be found both outdoors and indoors. Outdoor air pollution is made of chemical particles. When smoke or other pollutants enter the air, the particles found in the pollution mix with the air. Air is polluted when it contains many large toxic particles. Outdoor air pollution changes the natural characteristics of the atmosphere. Primary pollutants are added directly to the atmosphere. Fires add primary pollutants to the air. Particles released from the fire directly enter the air and cause pollution ( Figure 1.1). Burning of fossil fuels such as oil and coal is a major source of primary pollutants ( Figure Secondary pollutants are formed when primary pollutants interact with sunlight, air, or each other. They do not directly cause pollution. However, when they interact with other parts of the air, they do cause pollution. For example, ozone is created when some pollutants interact with sunlight. High levels of ozone in the atmosphere can cause problems for humans. Wildfires, either natural or human-caused, release particles into the air, one of the many causes of air pollution. A major source of air pollution is the burn- ing of fossil fuels from factories, power plants, and motor vehicles. ",text,
L_0624,outdoor air pollution,T_3243,"Air is all around us. Air is essential for life. Sometimes, humans can pollute the air. For example, releasing smoke and dust from factories and cars can cause air pollution. Air pollution is due to chemical substances and particles released into the air mainly by human actions. This pollution affects entire ecosystems around the world. Pollution can also cause many human health problems, and it can also cause death. Air pollution can be found both outdoors and indoors. Outdoor air pollution is made of chemical particles. When smoke or other pollutants enter the air, the particles found in the pollution mix with the air. Air is polluted when it contains many large toxic particles. Outdoor air pollution changes the natural characteristics of the atmosphere. Primary pollutants are added directly to the atmosphere. Fires add primary pollutants to the air. Particles released from the fire directly enter the air and cause pollution ( Figure 1.1). Burning of fossil fuels such as oil and coal is a major source of primary pollutants ( Figure Secondary pollutants are formed when primary pollutants interact with sunlight, air, or each other. They do not directly cause pollution. However, when they interact with other parts of the air, they do cause pollution. For example, ozone is created when some pollutants interact with sunlight. High levels of ozone in the atmosphere can cause problems for humans. Wildfires, either natural or human-caused, release particles into the air, one of the many causes of air pollution. A major source of air pollution is the burn- ing of fossil fuels from factories, power plants, and motor vehicles. ",text,
L_0624,outdoor air pollution,T_3244,"Most air pollutants can be traced to the burning of fossil fuels. Fossil fuels are burned during many processes, including in power plants to create electricity, in factories to make machinery run, in power stoves and furnaces for heating, and in waste facilities. Perhaps one of the biggest uses of fossil fuels is in transportation. Fossil fuels are used in cars, trains, and planes. Air pollution can also be caused by agriculture, such as cattle ranching and the use of fertilizers and pesticides. Other sources of air pollution include the production of plastics, refrigerants, and aerosols, in nuclear power and defense, from landfills and mining, and from biological warfare. ",text,
L_0624,outdoor air pollution,T_3245,"One result of air pollution is acid rain. Acid rain is precipitation with a low (acidic) pH. This rain can be very destructive to wildlife. When acid rain falls in forests, freshwater habitats, or soils, it can kill insects and aquatic life. It causes this damage because of its very low pH. Sulfur oxides and nitrogen oxides in the air both cause acid rain to form ( Figure 1.3). Sulfur oxides are chemicals that are released from coal-fired power plants. Nitrogen oxides are released from motor vehicle exhaust. A forest in the Jizera Mountains of the Czech Republic shows effects caused by acid rain. What do you observe? ",text,
L_0624,outdoor air pollution,T_3246,"Pollutants also affect the atmosphere through their contribution to global warming. Global warming is an increase in the Earths temperature. It is thought to be caused mostly by the increase of greenhouse gases like carbon dioxide. Greenhouse gases can be released by factories that burn fossil fuels. Over the past 20 years, burning fossil fuels has produced about three-quarters of the carbon dioxide from human activity. The rest of the carbon dioxide in the atmosphere is there because of deforestation, or cutting down trees ( Figure 1.4). Trees absorb carbon dioxide during cellular respiration, so when trees are cut down, they cannot remove carbon dioxide from the air. This increase in global temperature will cause the sea level to rise. It is also expected to produce an increase in extreme weather events and change the amount of precipitation. Global warming may also cause food shortages and species extinction. ",text,
L_0626,pathogens,T_3250,"Has this ever happened to you? A student sitting next to you in class has a cold. The other student is coughing and sneezing, but you feel fine. Two days later, you come down with a cold, too. Diseases like colds are contagious. Contagious diseases are also called infectious diseases. An infectious disease is a disease that spreads from person to person. Infectious diseases are caused by pathogens. A pathogen is a living thing or virus that causes disease. Pathogens are commonly called germs. They can travel from one person to another. ",text,
L_0626,pathogens,T_3251,"Living things that cause human diseases include bacteria, fungi, and protozoa. Most infectious diseases caused by these organisms can be cured with medicines. For example, medicines called antibiotics can cure most diseases caused by bacteria. Bacteria are one-celled organisms without a nucleus. Although most bacteria are harmless, some cause diseases. Worldwide, the most common disease caused by bacteria is tuberculosis (TB). TB is a serious disease of the lungs. Another common disease caused by bacteria is strep throat. You may have had strep throat yourself. Bacteria that cause strep throat are shown below ( Figure 1.1). Some types of pneumonia and many cases of illnesses from food are also caused by bacteria. The structures that look like strings of beads are bacteria. They belong to the genus Streptococcus. Bacteria of this genus cause diseases such as strep throat and pneumonia. They are shown here 900 times bigger than their actual size. Fungi are simple eukaryotic organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athletes foot. Both are skin diseases that are not usually serious. A ringworm infection is pictured below ( Figure 1.2). A more serious fungus disease is histoplasmosis. It is a lung infection. Though fungal infections can be annoying, they are rarely as serious or deadly as bacterial or viral infections. Ringworm isnt a worm at all. Its a disease caused by a fungus. The fungus causes a ring-shaped rash on the skin, like the one shown here. Protozoa are one-celled organisms with a nucleus, making them eukaryotic organisms. They cause diseases such as malaria. Malaria is a serious disease that is common in warm climates. The protozoa infect people when they are bit by a mosquito. More than a million people die of malaria each year. Other protozoa cause diarrhea. An example is Giardia lamblia ( Figure 1.3). Viruses are nonliving collections of protein and DNA that must reproduce inside of living cells. Viruses cause many common diseases. For example, viruses cause colds and the flu. Cold sores are caused by the virus Herpes simplex This picture shows a one-celled organism called Giardia lamblia. It is a protozoan that causes diarrhea. ( Figure 1.4). Antibiotics do not affect viruses, because antibiotics only kill bacteria. But medicines called antiviral drugs can treat many diseases caused by viruses. Keep in mind that viruses are nonliving, so can they be killed? ",text,
L_0626,pathogens,T_3251,"Living things that cause human diseases include bacteria, fungi, and protozoa. Most infectious diseases caused by these organisms can be cured with medicines. For example, medicines called antibiotics can cure most diseases caused by bacteria. Bacteria are one-celled organisms without a nucleus. Although most bacteria are harmless, some cause diseases. Worldwide, the most common disease caused by bacteria is tuberculosis (TB). TB is a serious disease of the lungs. Another common disease caused by bacteria is strep throat. You may have had strep throat yourself. Bacteria that cause strep throat are shown below ( Figure 1.1). Some types of pneumonia and many cases of illnesses from food are also caused by bacteria. The structures that look like strings of beads are bacteria. They belong to the genus Streptococcus. Bacteria of this genus cause diseases such as strep throat and pneumonia. They are shown here 900 times bigger than their actual size. Fungi are simple eukaryotic organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athletes foot. Both are skin diseases that are not usually serious. A ringworm infection is pictured below ( Figure 1.2). A more serious fungus disease is histoplasmosis. It is a lung infection. Though fungal infections can be annoying, they are rarely as serious or deadly as bacterial or viral infections. Ringworm isnt a worm at all. Its a disease caused by a fungus. The fungus causes a ring-shaped rash on the skin, like the one shown here. Protozoa are one-celled organisms with a nucleus, making them eukaryotic organisms. They cause diseases such as malaria. Malaria is a serious disease that is common in warm climates. The protozoa infect people when they are bit by a mosquito. More than a million people die of malaria each year. Other protozoa cause diarrhea. An example is Giardia lamblia ( Figure 1.3). Viruses are nonliving collections of protein and DNA that must reproduce inside of living cells. Viruses cause many common diseases. For example, viruses cause colds and the flu. Cold sores are caused by the virus Herpes simplex This picture shows a one-celled organism called Giardia lamblia. It is a protozoan that causes diarrhea. ( Figure 1.4). Antibiotics do not affect viruses, because antibiotics only kill bacteria. But medicines called antiviral drugs can treat many diseases caused by viruses. Keep in mind that viruses are nonliving, so can they be killed? ",text,
L_0626,pathogens,T_3251,"Living things that cause human diseases include bacteria, fungi, and protozoa. Most infectious diseases caused by these organisms can be cured with medicines. For example, medicines called antibiotics can cure most diseases caused by bacteria. Bacteria are one-celled organisms without a nucleus. Although most bacteria are harmless, some cause diseases. Worldwide, the most common disease caused by bacteria is tuberculosis (TB). TB is a serious disease of the lungs. Another common disease caused by bacteria is strep throat. You may have had strep throat yourself. Bacteria that cause strep throat are shown below ( Figure 1.1). Some types of pneumonia and many cases of illnesses from food are also caused by bacteria. The structures that look like strings of beads are bacteria. They belong to the genus Streptococcus. Bacteria of this genus cause diseases such as strep throat and pneumonia. They are shown here 900 times bigger than their actual size. Fungi are simple eukaryotic organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athletes foot. Both are skin diseases that are not usually serious. A ringworm infection is pictured below ( Figure 1.2). A more serious fungus disease is histoplasmosis. It is a lung infection. Though fungal infections can be annoying, they are rarely as serious or deadly as bacterial or viral infections. Ringworm isnt a worm at all. Its a disease caused by a fungus. The fungus causes a ring-shaped rash on the skin, like the one shown here. Protozoa are one-celled organisms with a nucleus, making them eukaryotic organisms. They cause diseases such as malaria. Malaria is a serious disease that is common in warm climates. The protozoa infect people when they are bit by a mosquito. More than a million people die of malaria each year. Other protozoa cause diarrhea. An example is Giardia lamblia ( Figure 1.3). Viruses are nonliving collections of protein and DNA that must reproduce inside of living cells. Viruses cause many common diseases. For example, viruses cause colds and the flu. Cold sores are caused by the virus Herpes simplex This picture shows a one-celled organism called Giardia lamblia. It is a protozoan that causes diarrhea. ( Figure 1.4). Antibiotics do not affect viruses, because antibiotics only kill bacteria. But medicines called antiviral drugs can treat many diseases caused by viruses. Keep in mind that viruses are nonliving, so can they be killed? ",text,
L_0626,pathogens,T_3251,"Living things that cause human diseases include bacteria, fungi, and protozoa. Most infectious diseases caused by these organisms can be cured with medicines. For example, medicines called antibiotics can cure most diseases caused by bacteria. Bacteria are one-celled organisms without a nucleus. Although most bacteria are harmless, some cause diseases. Worldwide, the most common disease caused by bacteria is tuberculosis (TB). TB is a serious disease of the lungs. Another common disease caused by bacteria is strep throat. You may have had strep throat yourself. Bacteria that cause strep throat are shown below ( Figure 1.1). Some types of pneumonia and many cases of illnesses from food are also caused by bacteria. The structures that look like strings of beads are bacteria. They belong to the genus Streptococcus. Bacteria of this genus cause diseases such as strep throat and pneumonia. They are shown here 900 times bigger than their actual size. Fungi are simple eukaryotic organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athletes foot. Both are skin diseases that are not usually serious. A ringworm infection is pictured below ( Figure 1.2). A more serious fungus disease is histoplasmosis. It is a lung infection. Though fungal infections can be annoying, they are rarely as serious or deadly as bacterial or viral infections. Ringworm isnt a worm at all. Its a disease caused by a fungus. The fungus causes a ring-shaped rash on the skin, like the one shown here. Protozoa are one-celled organisms with a nucleus, making them eukaryotic organisms. They cause diseases such as malaria. Malaria is a serious disease that is common in warm climates. The protozoa infect people when they are bit by a mosquito. More than a million people die of malaria each year. Other protozoa cause diarrhea. An example is Giardia lamblia ( Figure 1.3). Viruses are nonliving collections of protein and DNA that must reproduce inside of living cells. Viruses cause many common diseases. For example, viruses cause colds and the flu. Cold sores are caused by the virus Herpes simplex This picture shows a one-celled organism called Giardia lamblia. It is a protozoan that causes diarrhea. ( Figure 1.4). Antibiotics do not affect viruses, because antibiotics only kill bacteria. But medicines called antiviral drugs can treat many diseases caused by viruses. Keep in mind that viruses are nonliving, so can they be killed? ",text,
L_0626,pathogens,T_3252,"Different pathogens spread in different ways. Some pathogens spread through food. They cause food borne illnesses, which are discussed in a previous concept. Some pathogens spread through water. Giardia lamblia is one example. Water can be boiled to kill Giardia and most other pathogens. Several pathogens spread through sexual contact. HIV is one example, which is discussed in the next concept. Other pathogens that spread through sexual contact are discussed in a separate concept. Many pathogens that cause respiratory diseases spread by droplets in the air. Droplets are released when a person sneezes or coughs. Thousands of tiny droplets are released when a person sneezes ( Figure 1.5). Each droplet can contain thousands of pathogens. Viruses that cause colds and the flu can spread in this way. You may get sick if you breathe in the pathogens. As this picture shows, thousands of tiny droplets are released into the air when a person sneezes. Each droplet may carry thousands of pathogens. You cant normally see the droplets from a sneeze because they are so small. However, you can breathe them in, along with any pathogens they carry. This is how many diseases of the respiratory system are spread. ",text,
L_0626,pathogens,T_3253,"Other pathogens spread when they get on objects or surfaces. A fungus may spread in this way. For example, you can pick up the fungus that causes athletes foot by wearing shoes that an infected person has worn. You can also pick up this fungus from the floor of a public shower or other damp areas. After acne, athletes foot is the most common skin disease in the United States. Therefore, the chance of coming in contact with the fungus in one of these ways is fairly high. Bacteria that cause the skin disease impetigo, which causes blisters, can spread when people share towels or clothes. The bacteria can also spread through direct skin contact in sports like wrestling. ",text,
L_0626,pathogens,T_3254,"Still other pathogens are spread by vectors. A vector is an organism that carries pathogens from one person or animal to another. Most vectors are insects, such as ticks and mosquitoes. These insects tend to transfer protozoan or viral parasites. When an insect bites an infected person or animal, it picks up the pathogen. Then the pathogen travels to the next person or animal it bites. Ticks carry the bacteria that cause Lyme disease. Mosquitoes ( Figure serious symptoms may develop. Other diseases spread by mosquitoes include Dengue Fever and Yellow Fever. The first case of West Nile virus in North America occurred in 1999. Within just a few years, the virus had spread throughout most of the United States. Birds as well as humans can be infected with the virus. Birds often fly long distances. This is one reason why West Nile virus spread so quickly. ",text,
L_0627,pedigree analysis,T_3255,"A pedigree is a chart that shows the inheritance of a trait over several generations. A pedigree is commonly created for families, and it outlines the inheritance patterns of genetic disorders and traits. A pedigree can help predict the probability that offspring will inherit a genetic disorder. Pictured below is a pedigree displaying recessive inheritance of a disorder through three generations ( Figure 1.1). From studying a pedigree, scientists can determine the following: If the trait is sex-linked (on the X or Y chromosome) or autosomal (on a chromosome that does not determine sex). If the trait is inherited in a dominant or recessive fashion. Sometimes pedigrees can also help determine whether individuals with the trait are heterozygous (two different alleles) or homozygous (two of the same allele). Some points to keep in mind when analyzing a pedigree are: 1. With autosomal recessive inheritance, all affected individuals will be homozygous recessive. 2. With dominant inheritance, all affected individuals will have at least one dominant allele. They will be either homozygous dominant or heterozygous. 3. With sex-linked inheritance, more males (XY) than females (XX) usually have the trait. Sex-linked inheritance is usually recessive. ",text,
L_0628,peripheral nervous system,T_3256,"There are other nerves in your body that are not found in the brain or spinal cord. The peripheral nervous system (PNS) ( Figure 1.1) contains all the nerves in the body that are found outside of the central nervous system. They include nerves of the hands, arms, feet, legs, and trunk. They also include nerves of the scalp, neck, and face. Nerves that send and receive messages to the internal organs are also part of the peripheral nervous system. The peripheral nervous system is divided into two parts, the sensory division and the motor division. How these divisions of the peripheral nervous system are related to the rest of the nervous system is shown below ( Figure 1.2). Refer to the figure as you read more about the peripheral nervous system in the text that follows. ",text,
L_0628,peripheral nervous system,T_3257,"The sensory division carries messages from sense organs and internal organs to the central nervous system. Human beings have several senses. They include sight, hearing, balance, touch, taste, and smell. We have special sense organs for each of these senses. What is the sense organ for sight? For hearing? Sensory neurons in each sense organ receive stimuli, or messages from the environment that cause a response in the body. For example, sensory neurons in the eyes send messages to the brain about light. Sensory neurons in the skin send messages to the brain about touch. Our sense organs recognize sensations, but they dont tell us what we are sensing. For example, when you breathe in chemicals given off by baking cookies, your nose does not tell you that you are smelling cookies. Thats your brains job. The sense organs send messages about sights, smells, and other stimuli to the brain ( Figure 1.3). The brain then reads the messages and tells you what they mean. A certain area of the brain receives and interprets information from each sense organ. For example, information from the nose is received and interpreted by the temporal lobe of the cerebrum. Which senses would be stimulated by these raspberries? ",text,
L_0628,peripheral nervous system,T_3257,"The sensory division carries messages from sense organs and internal organs to the central nervous system. Human beings have several senses. They include sight, hearing, balance, touch, taste, and smell. We have special sense organs for each of these senses. What is the sense organ for sight? For hearing? Sensory neurons in each sense organ receive stimuli, or messages from the environment that cause a response in the body. For example, sensory neurons in the eyes send messages to the brain about light. Sensory neurons in the skin send messages to the brain about touch. Our sense organs recognize sensations, but they dont tell us what we are sensing. For example, when you breathe in chemicals given off by baking cookies, your nose does not tell you that you are smelling cookies. Thats your brains job. The sense organs send messages about sights, smells, and other stimuli to the brain ( Figure 1.3). The brain then reads the messages and tells you what they mean. A certain area of the brain receives and interprets information from each sense organ. For example, information from the nose is received and interpreted by the temporal lobe of the cerebrum. Which senses would be stimulated by these raspberries? ",text,
L_0628,peripheral nervous system,T_3258,"The motor division of the peripheral system carries messages from the central nervous system to internal organs and muscles. The motor division is also divided into two parts ( Figure 1.2), the somatic nervous system and the autonomic nervous system. The somatic nervous system carries messages that control body movements. It is responsible for activities that are under your control, such as waving your hand or kicking a ball. The girl pictured below ( Figure 1.4) is using her somatic nervous system to control the muscles needed to play the violin. Her brain sends messages to motor neurons that move her hands so she can play. Without the messages from her brain, she would not be able to move her hands and play the violin. The autonomic nervous system carries nerve impulses to internal organs. It controls activities that are not under your control, such as sweating and digesting food. The autonomic nervous system has two parts: 1. The sympathetic division controls internal organs and glands during emergencies. It prepares the body for fight or flight ( Figure 1.5). For example, it increases the heart rate and the flow of blood to the legs, so you can run away from danger. 2. The parasympathetic division controls internal organs and glands during the rest of the time. It controls processes like digestion, heartbeat, and breathing when there is not an emergency. Have you ever become frightened and felt your heart start pounding? How does this happen? The answer is your autonomic nervous system. The sympathetic division prepared you to deal with a possible emergency by increasing ",text,
L_0628,peripheral nervous system,T_3258,"The motor division of the peripheral system carries messages from the central nervous system to internal organs and muscles. The motor division is also divided into two parts ( Figure 1.2), the somatic nervous system and the autonomic nervous system. The somatic nervous system carries messages that control body movements. It is responsible for activities that are under your control, such as waving your hand or kicking a ball. The girl pictured below ( Figure 1.4) is using her somatic nervous system to control the muscles needed to play the violin. Her brain sends messages to motor neurons that move her hands so she can play. Without the messages from her brain, she would not be able to move her hands and play the violin. The autonomic nervous system carries nerve impulses to internal organs. It controls activities that are not under your control, such as sweating and digesting food. The autonomic nervous system has two parts: 1. The sympathetic division controls internal organs and glands during emergencies. It prepares the body for fight or flight ( Figure 1.5). For example, it increases the heart rate and the flow of blood to the legs, so you can run away from danger. 2. The parasympathetic division controls internal organs and glands during the rest of the time. It controls processes like digestion, heartbeat, and breathing when there is not an emergency. Have you ever become frightened and felt your heart start pounding? How does this happen? The answer is your autonomic nervous system. The sympathetic division prepared you to deal with a possible emergency by increasing ",text,
L_0629,photosynthesis,T_3259,"If a plant gets hungry, it cannot walk to a local restaurant and buy a slice of pizza. So, how does a plant get the food it needs to survive? Plants are producers, which means they are able to make, or produce, their own food. They also produce the ""food"" for other organisms. Plants are also autotrophs. Autotrophs are the organisms that collect the energy from the sun and turn it into organic compounds. Using the energy from the sun, they produce complex organic compounds from simple inorganic molecules. So once again, how does a plant get the food it needs to survive? Through photosynthesis. Photosynthesis is the process plants use to make their own food from the suns energy, carbon dioxide, and water. During photosynthesis, carbon dioxide and water combine with solar energy to create glucose, a carbohydrate (C6 H12 O6 ), and oxygen. The process can be summarized as: in the presence of sunlight, carbon dioxide + water  glucose + oxygen. Glucose, the main product of photosynthesis, is a sugar that acts as the ""food"" source for plants. The glucose is then converted into usable chemical energy, ATP, during cellular respiration. The oxygen formed during photosynthesis, which is necessary for animal life, is essentially a waste product of the photosynthesis process. Actually, almost all organisms obtain their energy from photosynthetic organisms. For example, if a bird eats a caterpillar, then the bird gets the energy that the caterpillar gets from the plants it eats. So the bird indirectly gets energy that began with the glucose formed through photosynthesis. Therefore, the process of photosynthesis is central to sustaining life on Earth. In eukaryotic organisms, photosynthesis occurs in chloroplasts. Only cells with chloroplastsplant cells and algal (protist) cellscan perform photosynthesis. Animal cells and fungal cells do not have chloroplasts and, therefore, cannot photosynthesize. That is why these organisms, as well as the non- photosynthetic protists, rely on other organisms to obtain their energy. These organisms are heterotrophs. The Photosynthesis Song explaining photosynthesis, can be heard at  Click image to the left or use the URL below. URL: ",text,
L_0629,photosynthesis,T_3260,Why do leaves change color each fall? This MIT video demonstrates an experiment about the different pigments in leaves. See the video at  . Click image to the left or use the URL below. URL: ,text,
L_0637,polygenic traits,T_3277,"Another exception to Mendels rules is polygenic inheritance, which occurs when a trait is controlled by more than one gene. This means that each dominant allele ""adds"" to the expression of the next dominant allele. Usually, traits are polygenic when there is wide variation in the trait. For example, humans can be many different sizes. Height is a polygenic trait, controlled by at least three genes with six alleles. If you are dominant for all of the alleles for height, then you will be very tall. There is also a wide range of skin color across people. Skin color is also a polygenic trait, as are hair and eye color. Polygenic inheritance often results in a bell shaped curve when you analyze the population ( Figure 1.1). That means that most people fall in the middle of the phenotypic range, such as average height, while very few people are at the extremes, such as very tall or very short. At one end of the curve will be individuals who are recessive for all the alleles (for example, aabbcc); at the other end will be individuals who are dominant for all the alleles (for example, AABBCC). Through the middle of the curve will be individuals who have a combination of dominant and recessive alleles (for example, AaBbCc or AaBBcc). ",text,
L_0638,population growth patterns,T_3278,What does population growth mean? You can probably guess that it means the number of individuals in a population is increasing. The population growth rate tells you how quickly a population is increasing or decreasing. What determines the population growth rate for a particular population? ,text,
L_0638,population growth patterns,T_3279,"Population growth rate depends on birth rates and death rates, as well as migration. First, we will consider the effects of birth and death rates. You can predict the growth rate by using this simple equation: growth rate = birth rate death rate. If the birth rate is larger than the death rate, then the population grows. If the death rate is larger than the birth rate, what will happen to the population? The population size will decrease. If the birth and death rates are equal, then the population size will not change. Factors that affect population growth are: 1. 2. 3. 4. 5. 6. Age of organisms at first reproduction. How often an organism reproduces. The number of offspring of an organism. The presence or absence of parental care. How long an organism is able to reproduce. The death rate of offspring. For an ecosystem to be stable, populations in that system must be healthy, and that usually means reproducing as much as their environment allows. Do organisms reproduce yearly or every few years? Do organisms reproduce for much of their life, or just part of their life? Do organisms produce many offspring at once, or just a few, or even just one? Do many newborn organisms die, or do the majority survive? All these factors play a role in the growth of a population. Organisms can use different strategies to increase their reproduction rate. Altricial organisms are helpless at birth, and their parents give them a lot of care. This care is often seen in bird species. ( Figure 1.1). Altricial birds are usually born blind and without feathers. Compared to precocial organisms, altricial organisms have a longer period of development before they reach maturity. Precocial organisms, such as the geese shown below, can take care of themselves at birth and do not require help from their parents ( Figure 1.1). In order to reproduce as much as possible, altricial and precocial organisms must use very different strategies. (left) A hummingbird nest with young il- lustrates an altricial reproductive strategy, with a few small eggs, helpless young, and intensive parental care. (right) The Canada goose shows a precocial repro- ductive strategy. It lays a large number of large eggs, producing well-developed young. ",text,
L_0638,population growth patterns,T_3280,"Migration is the movement of individual organisms into, or out of, a population. Migration affects population growth rate. There are two types of migration: 1. Immigration is the movement of individuals into a population from other areas. This increases the population size and growth rate. 2. Emigration is the movement of individuals out of a population. This decreases the population size and growth rate. The earlier growth rate equation can be modified to account for migration: growth rate = (birth rate + immigration rate) (death rate + emigration rate). One type of migration that you are probably familiar with is the migration of birds. Maybe you have heard that birds fly south for the winter. In the fall, birds fly thousands of miles to the south where it is warmer. In the spring, they return to their homes. ( Figure 1.2). Monarch butterflies also migrate from Mexico to the northern U.S. in the summer and back to Mexico in the winter. These types of migrations move entire populations from one location to another. A flock of barnacle geese fly in formation during the autumn migration. ",text,
L_0638,population growth patterns,T_3281,"Population growth can be described with two models, based on the size of the population and necessary resources. These two types of growth are known as exponential growth and logistic growth. If a population is given unlimited amounts of resources, such as food and water, land if needed, moisture, oxygen, and other environmental factors, it will grow exponentially. Exponential growth occurs as a population grows larger, dramatically increasing the growth rate. This is shown as a ""J-shaped"" curve below ( Figure 1.3). You can see that the population grows slowly at first, but as time passes, growth occurs more and more rapidly. Growth of populations according to ex- ponential (or J-curve) growth model (left) and logistic (or S-curve) growth model (right). Time is plotted on the x-axis, and population size is plotted on the y-axis. In nature, organisms do not usually have ideal environments with unlimited food. In nature, there are limits. Sometimes, there will be plenty of food. Sometimes, a fire will wipe out all of the available nutrients. Sometimes a predator will kill many individuals in a population. How do you think these limits affect the way organisms grow? ",text,
L_0640,pregnancy and childbirth,T_3283,"While a woman is pregnant, the developing baby may be called an embryo or a fetus. Do these mean the same thing? No, in the very early stages the developing baby is called an embryo, while in the later stages it is called a fetus. When the ball of cells first implants into the uterus, it is called an embryo. The embryo stage lasts until the end of the 8th week after fertilization. After that point until birth, the developing baby is called a fetus. ",text,
L_0640,pregnancy and childbirth,T_3284,"During the embryo stage, the baby grows in size. 3rd week after fertilization: Cells of different types start to develop. Cells that will form muscles and skin, for example, start to develop at this time. 4th week after fertilization: Body organs begin to form. 8th week after fertilization: All the major organs have started to develop. Pictured below are some of the changes that take place during the 4th and 8th weeks ( Figure 1.1). Look closely at the two embryos in the figure. Do you think that the older embryo looks more human? Notice that it has arms and legs and lacks a tail. The face has also started to form, and it is much bigger. Embryonic Development (Weeks 48). Most organs develop in the embryo during weeks four through eight. (Note: the drawings of the embryos are not to scale.) ",text,
L_0640,pregnancy and childbirth,T_3285,"There are also many changes that take place after the embryo becomes a fetus. Some of the differences between them are obvious. For example, the fetus has ears and eyelids. Its fingers and toes are also fully formed. The fetus even has fingernails and toenails. In addition, the reproductive organs have developed to make the baby a male or female. The brain and lungs are also developing quickly. The fetus has started to move around inside the uterus. This is usually when the mother first feels the fetus moving. By the 28th week, the fetus is starting to look much more like a baby. Eyelashes and eyebrows are present. Hair has started to grow on the head. The body of the fetus is also starting to fill out as muscles and bones develop. Babies born after the 28th week are usually able to survive. However, they need help breathing because their lungs are not yet fully mature. A baby should not be delivered prior to this time, unless absolutely necessary. A baby born prior to week 28 will need considerable medical intervention to survive. During the last several weeks of the fetal period, all of the organs become mature. The most obvious change, however, is an increase in body size. The fetus rapidly puts on body fat and gains weight during the last couple of months. By the end of the 38th week, all of the organs are working, and the fetus is ready to be born. This is when birth normally occurs. A baby born before this time is considered premature. ",text,
L_0640,pregnancy and childbirth,T_3286,"During pregnancy, other structures also develop inside the mothers uterus. They are the amniotic sac, placenta, and umbilical cord ( Figure 1.2). Surrounding the fetus is the fluid-filled amniotic sac. The placenta and umbilical cord are also shown here. They provide a connection between the mothers and fetuss blood for the transfer of nutrients and gases. The amniotic sac is a membrane that surrounds the fetus. It is filled with water and dissolved substances, known as amniotic fluid. Imagine placing a small plastic toy inside a balloon and then filling the balloon with water. The toy would be cushioned and protected by the water. It would also be able to move freely inside the balloon. The amniotic sac and its fluid are like a water-filled balloon. They cushion and protect the fetus. They also let the fetus move freely inside the uterus. The placenta is a spongy mass of blood vessels. Some of the vessels come from the mother. Some come from the fetus. The placenta is attached to the inside of the mothers uterus. The fetus is connected to the placenta by a tube called the umbilical cord. The cord contains two arteries and a vein. Substances pass back and forth between the mothers and fetuss blood through the placenta and cord. Oxygen and nutrients pass from the mother to the fetus. Carbon dioxide passes from the fetus to the mother. It is important for the mother to eat plenty of nutritious foods during pregnancy. She must take in enough nutrients for the fetus as well as for herself. She needs extra calories, proteins, and lipids. She also needs more vitamins and minerals. In addition to eating well, the mother must avoid substances that could harm the embryo or fetus. These include alcohol, illegal drugs, and some medicines. It is especially important for her to avoid these substances during the first eight weeks after fertilization. This is when all the major organs are forming. Exposure to harmful substances during this time could damage the developing body systems. ",text,
L_0640,pregnancy and childbirth,T_3287,"During childbirth, a baby passes from the uterus, through the vagina, and out of the mothers body. Childbirth usually starts when the amniotic sac breaks. Then, the muscles of the uterus start contracting. The contractions get stronger and closer together. They may go on for hours. Eventually, the contractions squeeze the baby out of the uterus. Once the baby enters the vagina, the mother starts pushing. She soon pushes the baby through the vagina and out of her body. As soon as the baby is born, the umbilical cord is cut. After the cord is cut, the baby can no longer get rid of carbon dioxide through the cord and placenta. As a result, carbon dioxide builds up in the babys blood. This triggers the baby to start breathing. The amniotic sac and placenta pass through the vagina and out of the body shortly after the birth of the baby. ",text,
L_0641,preserving water sources,T_3288,"It might seem like there is plenty of water on Earth, but thats not really the case. Water is a limited resource. That means that it is used faster than it is replaced. Theoretically, at some point in time, the supply of fresh water could run out. Though this is unlikely, it is possible. But it is a significant issue in parts of the world with large populations. As these populations continue to grow, the supply of water becomes an increasingly important issue. Even though we have lots of water in our oceans, we cannot use that water whenever we want. It takes special equipment, such as a desalination plant, and a lot of energy (and money) to convert salt water into fresh water. Of all the water on Earth, only about 1% can be used for drinking water. Almost all of the rest of the water is either salt water in the ocean or ice in glaciers and ice caps. As a result, there are water shortages many places in the world. Since we have such a limited supply of water, it is important to preserve our water supplies. Therefore, steps have been taken to prevent water pollution. Technologies have also been developed to conserve water and prevent water pollution. Sub-Saharan African countries have the most vulnerable water supplies. Some scientists believe of a potential future crisis in both Asia and Africa from pollution and depletion of natural water resources. Many countries in the Middle East are at an extreme risk of water shortages. Diminished water supplies could increase the risk of both internal conflicts or wars between countries. ",text,
L_0641,preserving water sources,T_3289,"In the U.S., concern over water pollution has resulted in many federal laws. Some of these laws go all the way back to the 1800s! The laws prohibit the disposal of any waste into the nations rivers, lakes, streams, and other bodies of water, unless a person first has a permit. Growing concern for controlling water pollutants led to the enactment of the Clean Water Act in 1972. The Clean Water Act set water quality standards. It also limits the pollution that can enter the waterways. Other countries are also actively preventing water pollution and purifying water ( Figure 1.1). A water purification station in France. Contaminants are removed to make clean water. ",text,
L_0641,preserving water sources,T_3290,"Fresh water is also preserved by purifying wastewater. Wastewater is water that has been used for cleaning, washing, flushing, or manufacturing. It includes the water that goes down your shower drain and that is flushed down your toilet. Instead of dumping wastewater directly into rivers, wastewater can be purified at a water treatment plant ( Figure 1.2). When wastewater is recycled, waterborne diseases caused by pathogens in sewage can be prevented. What are some ways you can save water in your own house? ",text,
L_0642,preventing infectious diseases,T_3291,"Infectious diseases are diseases that spread from person to person. They are caused by pathogens such as bacteria, viruses or fungi. What can you do to avoid infectious diseases? Eating right and getting plenty of sleep are a good start. These habits will help keep your immune system healthy. With a healthy immune system, you will be able to fight off many pathogens. The next best way is to avoid pathogens. Though this is difficult, there are steps you can take to limit your exposure to pathogens. Here are the ten best ways to prevent the spread of infectious diseases. 1. Wash your hands frequently. 2. Dont share personal items. 3. Cover your mouth when you cough or sneeze. 4. 5. 6. 7. 8. 9. 10. Get vaccinated. Use safe cooking practices. Be a smart traveler. Practice safe sex. Dont pick your nose (or your mouth or eyes either). Exercise caution with animals. Watch the news, and be aware of disease outbreaks. ",text,
L_0642,preventing infectious diseases,T_3292,"You can also take steps to avoid pathogens in the first place. The best way to avoid pathogens is to wash your hands often. You should wash your hands after using the bathroom or handling raw meat or fish. You should also wash your hands before eating or preparing food. In addition, you should also wash the food that your eat, and the utensils and countertop where food is prepared. In addition, you should wash your hands after being around sick people. The correct way to wash your hands is demonstrated below ( Figure 1.1). If soap and water arent available, use some hand sanitizer. The best way to prevent diseases spread by vectors is to avoid contact with the vectors. Recall that a vector is an organism that carries pathogens from one person or animal to another. For example, ticks and mosquitoes are vectors, so you should wear long sleeves and long pants when appropriate to avoid tick and mosquito bites. Using insect repellent can also reduce your risk of insect bites. Many infectious diseases can be prevented with vaccinations. Immunization can drastically reduce your chances of contracting many diseases. You will read more about vaccinations in another concept. Vaccinations can help prevent measles, mumps, chicken pox, and several other diseases. If you do develop an infectious disease, try to avoid infecting others. Stay home from school until you are well. Also, take steps to keep your germs to yourself. Cover your mouth and nose with a tissue when you sneeze or cough, Watching the news will allow you to make informed decisions. If an outbreak of bad beef due to a bacterial infection is in the news, dont buy beef for a while. If tomatoes are making people sick, dont eat tomatoes until the outbreak is over. If a place has an unhealthy water supply, boil the water or drink bottled water. Local news can tell you of restaurants to avoid due to unhealthy conditions. And so on. ",text,
L_0643,preventing noninfectious diseases,T_3293,"Noninfectious diseases cant be passed from one person to another. Instead, these types of diseases are caused by factors such as the environment, genetics, and lifestyle. Examples of inherited noninfectious conditions include cystic fibrosis and Down syndrome. If youre born with these conditions, you must learn how to manage the symptoms. Examples of conditions caused by environmental or lifestyle factors include heart disease and skin cancer. We cant change our genetic codes, but there are plenty of ways to prevent other noninfectious diseases. For example, cutting down on exposure to cigarette smoke and the suns rays will prevent certain types of cancer. It is a fact that most chronic noninfectious diseases can be prevented. The chronic noninfectious diseases that cause the most deaths in many developed countries are largely preventable. These diseases are heart disease, stroke, diabetes and cancer, and though they do have some genetic components, they also have many lifestyle components. For example, some cancers have genetic risks, but people at high risk for cancers can have screening examinations to catch them early or sometimes can take other steps to prevent the cancers. Heart disease, stroke and diabetes are mostly linked to lifestyle choices, even when family history puts a person at higher risk for the diseases. Most allergies can be prevented by avoiding the substances that cause them. For example, you can avoid pollens by staying indoors as much as possible. You can learn to recognize plants like poison ivy and not touch them. A good way to remember how to avoid poison ivy is ""leaves of three, let it be."" Some people receive allergy shots to help prevent allergic reactions. The shots contain tiny amounts of allergens, which are the substances that cause an allergic reaction. After many months or years of shots, the immune system gets used to the allergens and no longer responds to them. Type 1 diabetes and other autoimmune diseases cannot be prevented. But choosing a healthy lifestyle can help prevent type 2 diabetes. Getting plenty of exercise, avoiding high-fat foods, and staying at a healthy weight can reduce the risk of developing this type of diabetes. This is especially important for people who have family members with the disease. Making these healthy lifestyle choices can also help prevent some types of cancer. In addition, you can lower the risk of cancer by avoiding carcinogens, which are substances that cause cancer. For example, you can reduce your risk of lung cancer by not smoking. You can reduce your risk of skin cancer by using sunscreen. How to choose a sunscreen that offers the most protection is explained below ( Figure 1.1). Some people think that tanning beds are a safe way to get a tan. This is a myth. Tanning beds expose the skin to UV radiation. Any exposure to UV radiation increases the risk of skin cancer. It doesnt matter whether the radiation comes from tanning lamps or the sun. Overall, people in many developed countries are contributing to higher rates of noninfectious diseases (heart disease, stroke, diabetes and cancer) by taking advantage of technology and social environments that encourage a less active lifestyle, and also encourages faster and cheaper meals. For example, many children now spend more time on their computer or watching TV then playing outdoors. The ""faster and cheaper"" meals are usually less healthy than other meals. Even though many people are living longer, they can choose to live more healthily by adopting regular exercise routines and healthy eating habits. When you choose a sunscreen, select one with an SPF (sun protection factor) of 30 or higher. Also, choose a sunscreen that protects against both UVB and UVA radiation. ",text,
L_0645,process of cellular respiration,T_3298,"Cellular respiration is the process of extracting energy in the form of ATP from the glucose in the food you eat. How does cellular respiration happen inside of the cell? Cellular respiration is a three step process. Briefly: 1. In stage one, glucose is broken down in the cytoplasm of the cell in a process called glycolysis. 2. In stage two, the pyruvate molecules are transported into the mitochondria. The mitochondria are the organelles known as the energy ""powerhouses"" of the cells (Figure 1.1). In the mitochondria, the pyruvate, which have been converted into a 2-carbon molecule, enter the Krebs cycle. Notice that mitochondria have an inner membrane with many folds, called cristae. These cristae greatly increase the membrane surface area where many of the cellular respiration reactions take place. 3. In stage three, the energy in the energy carriers enters an electron transport chain. During this step, this energy is used to produce ATP. Oxygen is needed to help the process of turning glucose into ATP. The initial step releases just two molecules of ATP for each glucose. The later steps release much more ATP. Most of the reactions of cellular respira- tion are carried out in the mitochondria. ",text,
L_0645,process of cellular respiration,T_3299,What goes into the cell? Oxygen and glucose are both reactants of cellular respiration. Oxygen enters the body when an organism breathes. Glucose enters the body when an organism eats. ,text,
L_0645,process of cellular respiration,T_3300,"What does the cell produce? The products of cellular respiration are carbon dioxide and water. Carbon dioxide is transported from your mitochondria out of your cell, to your red blood cells, and back to your lungs to be exhaled. ATP is generated in the process. When one molecule of glucose is broken down, it can be converted to a net total of 36 or 38 molecules of ATP. This only occurs in the presence of oxygen. ",text,
L_0645,process of cellular respiration,T_3301,"The overall chemical reaction for cellular respiration is one molecule of glucose (C6 H12 O6 ) and six molecules of oxygen (O2 ) yields six molecules of carbon dioxide (CO2 ) and six molecules of water (H2 O). Using chemical symbols the equation is represented as follows: C6 H12 O6 + 6O2  6CO2 + 6H2 O ATP is generated during the process. Though this equation may not seem that complicated, cellular respiration is a series of chemical reactions divided into three stages: glycolysis, the Krebs cycle, and the electron transport chain. ",text,
L_0645,process of cellular respiration,T_3302,"Stage one of cellular respiration is glycolysis. Glycolysis is the splitting, or lysis of glucose. Glycolysis converts the 6-carbon glucose into two 3-carbon pyruvate molecules. This process occurs in the cytoplasm of the cell, and it occurs in the presence or absence of oxygen. During glycolysis a small amount of NADH is made as are four ATP. Two ATP are used during this process, leaving a net gain of two ATP from glycolysis. The NADH temporarily holds energy, which will be used in stage three. ",text,
L_0645,process of cellular respiration,T_3303,"In the presence of oxygen, under aerobic conditions, pyruvate enters the mitochondria to proceed into the Krebs cycle. The second stage of cellular respiration is the transfer of the energy in pyruvate, which is the energy initially in glucose, into two energy carriers, NADH and FADH2 . A small amount of ATP is also made during this process. This process occurs in a continuous cycle, named after its discover, Hans Krebs. The Krebs cycle uses a 2-carbon molecule (acetyl-CoA) derived from pyruvate and produces carbon dioxide. ",text,
L_0645,process of cellular respiration,T_3304,"Stage three of cellular respiration is the use of NADH and FADH2 to generate ATP. This occurs in two parts. First, the NADH and FADH2 enter an electron transport chain, where their energy is used to pump, by active transport, protons (H+ ) into the intermembrane space of mitochondria. This establishes a proton gradient across the inner membrane. These protons then flow down their concentration gradient, moving back into the matrix by facilitated diffusion. During this process, ATP is made by adding inorganic phosphate to ADP. Most of the ATP produced during cellular respiration is made during this stage. For each glucose that starts cellular respiration, in the presence of oxygen (aerobic conditions), 36-38 ATP are generated. Without oxygen, under anaerobic conditions, much less (only two!) ATP are produced. ",text,
L_0646,processes of breathing,T_3305,"Breathing is only part of the process of bringing oxygen to where it is needed in the body. After oxygen enters the lungs, what happens? 1. The oxygen enters the bloodstream from the alveoli, tiny sacs in the lungs where gas exchange takes place ( Figure 1.1). The transfer of oxygen into the blood is through simple diffusion. 2. The oxygen-rich blood returns to the heart. 3. Oxygen-rich blood is then pumped through the aorta, the large artery that receives blood directly from the heart. 4. From the aorta, oxygen-rich blood travels to the smaller arteries and, finally, to the capillaries, the smallest type of blood vessel. 5. The oxygen molecules move, by diffusion, out of the capillaries and into the body cells. 6. While oxygen moves from the capillaries and into body cells, carbon dioxide moves from the cells into the capillaries. Gas exchange is the movement of oxygen into the blood and carbon dioxide out of the blood. 7. Carbon dioxide is brought, through the blood, back to the heart and then to the lungs. Then it is released into the air during exhalation. Why is oxygen needed by each cell in your body? To make ATP, the usable form of cellular energy. Oxygen is needed in the final stage of cellular respiration, which is the process of converting glucose into ATP. This process is much more efficient in the presence of oxygen. Without oxygen, much less ATP is produced. As ATP is needed for the cells to function properly, every cell in your body needs oxygen. Getting that oxygen begins with inhaling. The oxygen moves into your blood, where it travels to every cell in your body. ",text,
L_0647,producers,T_3306,"Energy is the ability to do work. In organisms, this work can be physical work, like walking or jumping, or it can be the work used to carry out the chemical processes in their cells. Every biochemical reaction that occurs in an organisms cells needs energy. All organisms need a constant supply of energy to stay alive. Some organisms can get the energy directly from the sun. Other organisms get their energy from other organisms. Through predator-prey relationships, the energy of one organism is passed on to another. Energy is constantly flowing through a community. With just a few exceptions, all life on Earth depends on the suns energy for survival. The energy of the sun is first captured by producers ( Figure 1.1), organisms that can make their own food. Many producers make their own food through the process of photosynthesis. The ""food"" the producers make is the sugar, glucose. Producers make food for the rest of the ecosystem. As energy is not recycled, energy must consistently be captured by producers. This energy is then passed on to the organisms that eat the producers, and then to the organisms that eat those organisms, and so on. Recall that the only required ingredients needed for photosynthesis are sunlight, carbon dioxide (CO2 ), and wa- ter (H2 O). From these simple inorganic ingredients, photosynthetic organisms produce the carbohydrate glucose (C6 H12 O6 ), and other complex organic compounds. Essentially, these producers are changing the energy from the sunlight into a usable form of energy. They are also making the oxygen that we breathe. Oxygen is a waste product of photosynthesis. The survival of every ecosystem is dependent on the producers. Without producers capturing the energy from the sun and turning it into glucose, an ecosystem could not exist. On land, plants are the dominant producers. Phytoplankton, tiny photosynthetic organisms, are the most common producers in the oceans and lakes. Algae, which is the green layer you might see floating on a pond, are an example of phytoplankton. There are also bacteria that use chemical processes to produce food. They get their energy from sources other than the sun, but they are still called producers. This process is known as chemosynthesis, and is common in ecosystems without sunlight, such as certain marine ecosystems. Producers include (a) plants, (b) algae, and (c) diatoms. ",text,
L_0652,puberty and adolescence,T_3317,"Puberty is the stage of life when a child becomes sexually mature. Puberty lasts from about 12 to 18 years of age in boys and from about 10 to 16 years of age in girls. The age when puberty begins is different from one child to another. Children that begin puberty much earlier or later than their peers may feel self-conscious. They may also worry that something is wrong with them. Usually, an early or late puberty is perfectly normal. In boys, puberty begins when the pituitary gland tells the testes to secrete testosterone. Testosterone causes the following to happen: 1. 2. 3. 4. The penis and testes grow. The testes start making sperm. Pubic and facial hair grow. The shoulders broaden, and the voice becomes deeper. In girls, puberty begins when the pituitary gland tells the ovaries to secrete estrogen. Estrogen causes the following to happen: 1. 2. 3. 4. 5. The uterus and ovaries grow. The ovaries start releasing eggs. The menstrual cycle begins. Pubic hair grows. The hips widen, and the breasts develop. Boys and girls are close to the same height during childhood. In both boys and girls, growth in height and weight is very fast during puberty. But boys grow faster than girls during puberty. Their period of fast growth also lasts longer. By the end of puberty, boys are an average of 10 centimeters (4 inches) taller than girls. ",text,
L_0652,puberty and adolescence,T_3318,"Adolescence is the period of life between the start of puberty and the beginning of adulthood. Adolescence includes the physical changes of puberty. It also includes many other changes, including significant mental, emotional, and social changes. During adolescence: Teenagers develop new thinking abilities. For example, they can think about abstract ideas, such as freedom. They are also better at thinking logically. They are usually better at solving problems as well. Teenagers try to establish a sense of who they are as individuals. They may try to become more independent from their parents. Most teens also have emotional ups and downs. This is partly due to changing hormone levels. Teenagers usually spend much more time with peers than with family members. ",text,
L_0654,recombinant dna,T_3320,"Recombinant DNA is the combination of DNA from two different sources. For example, it is possible to place a human gene into bacterial DNA. Recombinant DNA technology is useful in gene cloning and in identifying the function of a gene. Recombinant DNA technology can also be used to produce useful proteins, such as insulin. To treat diabetes, many people need insulin. Previously, insulin had been taken from animals. Through recombinant DNA technology, bacteria were created that carry the human gene which codes for the production of insulin. These bacteria become tiny factories that produce this protein. Recombinant DNA technology helps create insulin so it can be used by humans. Recombinant DNA technology is used in gene cloning. A clone is an exact genetic copy. Genes are cloned for many reasons, including use in medicine and in agriculture. Below are the steps used to copy, or clone, a gene: 1. A gene or piece of DNA is put in a vector, or carrier molecule, producing a recombinant DNA molecule. 2. The vector is placed into a host cell, such as a bacterium. 3. The gene is copied (or cloned) inside of the bacterium. As the bacterial DNA is copied, so is the vector DNA. As the bacteria divide, the recombinant DNA molecules are divided between the new cells. Over a 12- to 24-hour period, millions of copies of the cloned DNA are made. 4. The cloned DNA can produce a protein (like insulin) that can be used in medicine or in research. ",text,
L_0654,recombinant dna,T_3321,"Bacteria have small rings of DNA in the cytoplasm, called plasmids ( Figure 1.1). A plasmid is not part of the bacterial chromosome, but an additional pieced of DNA. When putting foreign DNA into a bacterium, the plasmids are often used as a vector. Viruses can also be used as vectors. The manipulation of the plasmid DNA, and then the insertion of the recombinant plasmid into a bacterium, is an invaluable tool in scientific research. This image shows a drawing of a plasmid. The plasmid has two large segments and one small segment depicted. The two large segments (green and blue) indicate antibiotic resistances usually used in a screening procedure. The antibiotic resis- tance segments ensure only bacteria with the plasmid will grow. The small segment (red) indicates an origin of replication. The origin of replication is where DNA replication starts, copying the plasmid. ",text,
L_0655,reduce reuse and recycle,T_3322,"Why conserve resources? During your lifetime, it is possible that the world may run out of some nonrenewable resources, especially as the population passes 8 then 9 billion people. So it is necessary to try to make these resources last as long as possible. You may have heard people say, ""Reduce, Reuse, Recycle."" You may know that this is the slogan of the campaign to conserve resources. But what do each one of those words truly mean? ",text,
L_0655,reduce reuse and recycle,T_3323,"What exactly does it mean to reduce? Reducing means decreasing the amount of waste we create. That could also mean cutting down on use of natural resources. In addition, many ways to reduce also result in saving money. Minimizing of waste may be difficult to achieve for individuals and households, but here are some starting points that you can include in your daily routine to reduce the use of resources: Turn lights off when not using them. Turn the television off when no one is watching. Replace burned out bulbs with ones that are more energy-efficient ( Figure 1.1). Reduce water use by turning off faucets when not using water. Use low-flow shower heads, which save on water and use less energy. Use low-flush and composting toilets. Put kitchen and garden waste into a compost pile. In the summer, change filters on your air conditioner and use as little air conditioning as possible. The use of air conditioning uses a lot of energy. In winter, make sure your furnace is working properly and make sure there is enough insulation on windows and doors. Mend broken or worn items instead of buying new ones. When you go shopping for items, buy quantities you know you will use without waste. Walk or bicycle instead of using an automobile, in order to save on fuel usage and costs, and to cut down on pollution. When buying a new vehicle, check into hybrid, semi-hybrid, or electric models to cut down on gas usage and air pollution. These fluorescent light bulbs are much more energy efficient than standard light bulbs. ",text,
L_0655,reduce reuse and recycle,T_3324,"Lets now look at what we can reuse. Reusing includes using the same item again for the same function and also using an item again for a new function. Reuse can have both economic and environmental benefits. New packaging regulations are helping society to move towards these goals. Water is a resource that can be reused for numerous purposes. You may not drink used water, but it is quite useful for other purposes. Some ways of reusing resources include: Use reusable bags when shopping. Use gray water. Water that has been used for laundry, for example, can be used to water the garden or flush toilets. At the town level, purified sewage water can be used for fountains, watering public parks or golf courses, fire fighting, and irrigating crops. Rain can be caught in rain barrels and used to water your garden. What are some other ways to reuse resources? ",text,
L_0655,reduce reuse and recycle,T_3325,"Now we move on to recycle. Sometimes it may be difficult to understand the differences between reusing and recycling. Recycling involves processing used materials in order to make them suitable for other uses. That usually means taking a used item, breaking it down, and reusing the pieces. Even though recycling requires extra energy, it does often make use of items which are broken, worn out, or cannot be reused. The things that are commonly recycled include: Batteries. Biodegradable waste. Electronics. Iron and steel. Aluminum ( Figure 1.2). Glass. Paper. Plastic. Textiles, such as clothing. Timber. Tires. Each type of recyclable requires a different recycling technique. Here are some things you can do to recycle in your home, school, or community: Laws can also be created to make sure people and companies reduce, reuse, and recycle. Individuals can vote for leaders who stand for sustainable ecological practices. They can also tell their leaders to make wise use of natural resources. You can also influence companies. If you and your family only buy from companies and restaurants that support recycling or eco-friendly packaging, then other companies will also change to be more environmentally friendly. ",text,
L_0656,renewable resources and alternative energy sources,T_3326,"A resource is renewable if it is remade by natural processes at the same rate that humans use it up. Sunlight and wind are renewable resources because they will not be used up ( Figure 1.1). The rising and falling of ocean tides is another example of a resource in unlimited supply. A sustainable resource is a resource that is used in a way that meets the needs of the present without keeping future generations from meeting their needs. People can sustainably harvest wood, cork, and bamboo. Farmers can also grow crops sustainably by not planting the same crop in their soil year after year. Planting the same crop each year can remove nutrients from the soil. This means that wood, cork, bamboo, and crops can be sustainable resources. ",text,
L_0656,renewable resources and alternative energy sources,T_3327,"A nonrenewable resource is one that cannot be replaced as easily as it is consumed. Fossil fuels are an example of nonrenewable resources. They take millions of years to form naturally, and so they cannot be replaced as fast as they are consumed. To take the place of fossil fuel use, alternative energy resources are being developed. These alternative energy sources often utilize renewable resources. The following are examples of sustainable alternative energy resources: Solar power, which uses solar cells to turn sunlight into electricity ( Figure 1.2). The electricity can be used to power anything that uses normal coal-generated electricity. Wind power, which uses windmills to transform wind energy into electricity. It is used for less than 1% of the worlds energy needs. But wind energy is growing fast. Every year, 30% more wind energy is used to create electricity. Hydropower ( Figure 1.3), which uses the energy of moving water to turn turbines (similar to windmills) or water wheels, that create electricity. This form of energy produces no waste or pollution. It is a renewable resource. Geothermal power, which uses the natural flow of heat from the Earths core to produce steam. This steam is used to turn turbines which create electricity. Biomass is the mass of biological organisms. It is usually used to describe the amount of organic matter in a trophic level of an ecosystem. Biomass production involves using organic matter (""biomass"") from plants to create electricity. Using corn to make ethanol fuel is an example of biomass generated energy. Biomass is generally renewable. Tides in the ocean can also turn a turbine to create electricity. This energy can then be stored until needed ( Figure 1.4). Dam of the tidal power plant in the Rance River, Bretagne, France ",text,
L_0656,renewable resources and alternative energy sources,T_3327,"A nonrenewable resource is one that cannot be replaced as easily as it is consumed. Fossil fuels are an example of nonrenewable resources. They take millions of years to form naturally, and so they cannot be replaced as fast as they are consumed. To take the place of fossil fuel use, alternative energy resources are being developed. These alternative energy sources often utilize renewable resources. The following are examples of sustainable alternative energy resources: Solar power, which uses solar cells to turn sunlight into electricity ( Figure 1.2). The electricity can be used to power anything that uses normal coal-generated electricity. Wind power, which uses windmills to transform wind energy into electricity. It is used for less than 1% of the worlds energy needs. But wind energy is growing fast. Every year, 30% more wind energy is used to create electricity. Hydropower ( Figure 1.3), which uses the energy of moving water to turn turbines (similar to windmills) or water wheels, that create electricity. This form of energy produces no waste or pollution. It is a renewable resource. Geothermal power, which uses the natural flow of heat from the Earths core to produce steam. This steam is used to turn turbines which create electricity. Biomass is the mass of biological organisms. It is usually used to describe the amount of organic matter in a trophic level of an ecosystem. Biomass production involves using organic matter (""biomass"") from plants to create electricity. Using corn to make ethanol fuel is an example of biomass generated energy. Biomass is generally renewable. Tides in the ocean can also turn a turbine to create electricity. This energy can then be stored until needed ( Figure 1.4). Dam of the tidal power plant in the Rance River, Bretagne, France ",text,
L_0656,renewable resources and alternative energy sources,T_3327,"A nonrenewable resource is one that cannot be replaced as easily as it is consumed. Fossil fuels are an example of nonrenewable resources. They take millions of years to form naturally, and so they cannot be replaced as fast as they are consumed. To take the place of fossil fuel use, alternative energy resources are being developed. These alternative energy sources often utilize renewable resources. The following are examples of sustainable alternative energy resources: Solar power, which uses solar cells to turn sunlight into electricity ( Figure 1.2). The electricity can be used to power anything that uses normal coal-generated electricity. Wind power, which uses windmills to transform wind energy into electricity. It is used for less than 1% of the worlds energy needs. But wind energy is growing fast. Every year, 30% more wind energy is used to create electricity. Hydropower ( Figure 1.3), which uses the energy of moving water to turn turbines (similar to windmills) or water wheels, that create electricity. This form of energy produces no waste or pollution. It is a renewable resource. Geothermal power, which uses the natural flow of heat from the Earths core to produce steam. This steam is used to turn turbines which create electricity. Biomass is the mass of biological organisms. It is usually used to describe the amount of organic matter in a trophic level of an ecosystem. Biomass production involves using organic matter (""biomass"") from plants to create electricity. Using corn to make ethanol fuel is an example of biomass generated energy. Biomass is generally renewable. Tides in the ocean can also turn a turbine to create electricity. This energy can then be stored until needed ( Figure 1.4). Dam of the tidal power plant in the Rance River, Bretagne, France ",text,
L_0656,renewable resources and alternative energy sources,T_3327,"A nonrenewable resource is one that cannot be replaced as easily as it is consumed. Fossil fuels are an example of nonrenewable resources. They take millions of years to form naturally, and so they cannot be replaced as fast as they are consumed. To take the place of fossil fuel use, alternative energy resources are being developed. These alternative energy sources often utilize renewable resources. The following are examples of sustainable alternative energy resources: Solar power, which uses solar cells to turn sunlight into electricity ( Figure 1.2). The electricity can be used to power anything that uses normal coal-generated electricity. Wind power, which uses windmills to transform wind energy into electricity. It is used for less than 1% of the worlds energy needs. But wind energy is growing fast. Every year, 30% more wind energy is used to create electricity. Hydropower ( Figure 1.3), which uses the energy of moving water to turn turbines (similar to windmills) or water wheels, that create electricity. This form of energy produces no waste or pollution. It is a renewable resource. Geothermal power, which uses the natural flow of heat from the Earths core to produce steam. This steam is used to turn turbines which create electricity. Biomass is the mass of biological organisms. It is usually used to describe the amount of organic matter in a trophic level of an ecosystem. Biomass production involves using organic matter (""biomass"") from plants to create electricity. Using corn to make ethanol fuel is an example of biomass generated energy. Biomass is generally renewable. Tides in the ocean can also turn a turbine to create electricity. This energy can then be stored until needed ( Figure 1.4). Dam of the tidal power plant in the Rance River, Bretagne, France ",text,
L_0656,renewable resources and alternative energy sources,T_3328,"Scientists at the Massachusetts of Technology are turning trash into coal, which can readily be used to heat homes and cook food in developing countries. This coal burns cleaner than that from fossil fuels. It also save a tremendous amount of energy. See http://youtu.be/GzhFgEYiVyY?list=PLzMhsCgGKd1hoofiKuifwy6qRXZs7NG6a for more information. Click image to the left or use the URL below. URL: ",text,
L_0659,reproductive system health,T_3336,"As was discussed in previous concepts, both infectious and noninfectious diseases of the reproductive system can be very serious. But there are ways to keep your reproductive system healthy. What can you do to keep your reproductive system healthy? You can start by making the right choices for overall good health. To be as healthy as you can be, you should: Eat a balanced diet that is high in fiber and low in fat. Drink plenty of water. Get regular exercise. Maintain a healthy weight. Get enough sleep. Avoid using tobacco, alcohol, or other drugs. Manage stress in healthy ways. Keeping your genitals clean is also very important. A daily shower or bath is all that it takes. Females do not need to use special feminine hygiene products. In fact, using them may do more harm than good because they can irritate the vagina or other reproductive structures. You should also avoid other behaviors that can put you at risk. Do not get into contact with another persons blood or other body fluids. For example, never get a tattoo or piercing unless you are sure that the needles have not been used before. This is one of the most important ways to prevent an STI. Of course, the only way to be fully protected against STIs is to refrain from sexual activity. If you are a boy, you should always wear a protective cup when you play contact sports. Contact sports include football, boxing, and hockey. Wearing a cup will help protect the testes from injury. You should also do a monthly self-exam to check for cancer of the testes. If you are a girl and use tampons, be sure to change them every four to six hours. Leaving tampons in for too long can put you at risk of toxic shock syndrome. This is a serious condition. Signs and symptoms of toxic shock syndrome develop suddenly, and the disease can be fatal. The disease involves fever, shock, and problems with the function of several body organs. Girls should also get in the habit of doing a monthly self-exam to check for breast cancer. Although breast cancer is rare in teens, its a good idea to start doing the exam when you are young. It will help you get to know what is normal for you. ",text,
L_0661,respiration,T_3340,"Most of the time, you breathe without thinking about it. Breathing is mostly an involuntary action that is controlled by a part of your brain that also controls your heart beat. If you swim, do yoga, or sing, you know you can control your breathing, however. Taking air into the body through the nose and mouth is called inhalation. Pushing air out of the body through the nose or mouth is called exhalation. The woman pictured below is exhaling before she surfaces from the pool water (Figure 1.1). How do lungs allow air in? Air moves into and out of the lungs by the movement of muscles. The most important muscle in the process of breathing is the diaphragm, a sheet of muscle that spreads across the bottom of the rib cage. The diaphragm and rib muscles contract and relax to move air into and out of the lungs. During inhalation, the diaphragm contracts and moves downward. The rib muscles contract and cause the ribs to move outward. This causes the chest volume to increase. Because the chest volume is larger, the air pressure inside the lungs is lower than the air pressure outside. This difference in air pressures causes air to be sucked into the lungs. When the diaphragm and rib muscles relax, air is pushed out of the lungs. Exhalation is similar to letting the air out of a balloon. How does the inhaled oxygen get into the bloodstream? The exchange of gasses between the lungs and the blood happens in tiny sacs called alveoli. The walls of the alveoli are very thin and allow gases to pass though them. The alveoli are lined with capillaries (Figure 1.2). Oxygen moves from the alveoli to the blood in the capillaries that surround the alveoli. At the same time, carbon dioxide moves in the opposite direction, from capillary blood to the alveoli. The gases move by simple diffusion, passing from an area of high concentration to an area of low concentration. For example, initially there is more oxygen in the alveoli than in the blood, so oxygen moves by diffusion from the alveoli into the blood. ",text,
L_0661,respiration,T_3340,"Most of the time, you breathe without thinking about it. Breathing is mostly an involuntary action that is controlled by a part of your brain that also controls your heart beat. If you swim, do yoga, or sing, you know you can control your breathing, however. Taking air into the body through the nose and mouth is called inhalation. Pushing air out of the body through the nose or mouth is called exhalation. The woman pictured below is exhaling before she surfaces from the pool water (Figure 1.1). How do lungs allow air in? Air moves into and out of the lungs by the movement of muscles. The most important muscle in the process of breathing is the diaphragm, a sheet of muscle that spreads across the bottom of the rib cage. The diaphragm and rib muscles contract and relax to move air into and out of the lungs. During inhalation, the diaphragm contracts and moves downward. The rib muscles contract and cause the ribs to move outward. This causes the chest volume to increase. Because the chest volume is larger, the air pressure inside the lungs is lower than the air pressure outside. This difference in air pressures causes air to be sucked into the lungs. When the diaphragm and rib muscles relax, air is pushed out of the lungs. Exhalation is similar to letting the air out of a balloon. How does the inhaled oxygen get into the bloodstream? The exchange of gasses between the lungs and the blood happens in tiny sacs called alveoli. The walls of the alveoli are very thin and allow gases to pass though them. The alveoli are lined with capillaries (Figure 1.2). Oxygen moves from the alveoli to the blood in the capillaries that surround the alveoli. At the same time, carbon dioxide moves in the opposite direction, from capillary blood to the alveoli. The gases move by simple diffusion, passing from an area of high concentration to an area of low concentration. For example, initially there is more oxygen in the alveoli than in the blood, so oxygen moves by diffusion from the alveoli into the blood. ",text,
L_0661,respiration,T_3341,"The process of getting oxygen into the body and releasing carbon dioxide is called respiration. Sometimes breathing is called respiration, but there is much more to respiration than just breathing. Breathing is only the movement of oxygen into the body and carbon dioxide out of the body. The process of respiration also includes the exchange of oxygen and carbon dioxide between the blood and the cells of the body. ",text,
L_0662,respiratory system diseases,T_3342,"Respiratory diseases are diseases of the lungs, bronchial tubes, trachea, nose, and throat ( Figure 1.1). These diseases can range from a mild cold to a severe case of pneumonia. Respiratory diseases are common. Many are easily treated, while others may cause severe illness or death. Some respiratory diseases are caused by bacteria or viruses, while others are caused by environmental pollutants, such as tobacco smoke. Some diseases are genetic and, therefore, are inherited. This boy is suffering from whooping cough (also known as pertussis), which gets its name from the loud whooping sound that is made when the person inhales during a coughing fit. ",text,
L_0662,respiratory system diseases,T_3343,"Bronchitis is an inflammation of the bronchi, the air passages that conduct air into the lungs. The bronchi become red and swollen with infection. Acute bronchitis is usually caused by viruses or bacteria, and may last several days or weeks. It is characterized by a cough that produces phlegm, or mucus. Symptoms include shortness of breath and wheezing. Acute bronchitis is usually treated with antibiotics. ",text,
L_0662,respiratory system diseases,T_3344,"Asthma is a chronic illness in which the bronchioles, the tiny branches into which the bronchi are divided, become inflamed and narrow ( Figure 1.2). The muscles around the bronchioles contract, which narrows the airways. Large amounts of mucus are also made by the cells in the lungs. People with asthma have difficulty breathing. Their chests feel tight, and they wheeze. Asthma can be caused by different things, such as allergies. Asthma can also be caused by cold air, warm air, moist air, exercise, or stress. The most common asthma triggers are illnesses, like the common cold. Asthma is not contagious and cannot be passed on to other people. Children and adolescents who have asthma can still lead active lives if they control their asthma. Asthma can be controlled by taking medication and by avoiding contact with environmental triggers for asthma, like smoking. ",text,
L_0662,respiratory system diseases,T_3345,"Pneumonia is an illness that occurs when the alveoli, the tiny sacs in the lungs where gas exchange takes place, become inflamed and filled with fluid. When a person has pneumonia, gas exchange cannot occur properly across the alveoli. Pneumonia can be caused by many things. Infection by bacteria, viruses, fungi, or parasites can cause pneumonia. An injury caused by chemicals or a physical injury to the lungs can also cause pneumonia. Symptoms of pneumonia include cough, chest pain, fever, and difficulty breathing. Treatment depends on the cause of pneumonia. Bacterial pneumonia is treated with antibiotics. Pneumonia is a common illness that affects people in all age groups. It is a leading cause of death among the elderly and people who are chronically and terminally ill. ",text,
L_0662,respiratory system diseases,T_3346,"Tuberculosis (TB) is a common and often deadly disease caused by a genus of bacterium called Mycobacterium. Tuberculosis most commonly attacks the lungs but can also affect other parts of the body. TB is a chronic disease, but most people who become infected do not develop the full disease. Symptoms include a cough, which usually contains mucus and coughing up blood. The TB bacteria are spread in the air when people who have the disease cough, sneeze, or spit, so it is very contagious. To help prevent the spread of the disease, public health notices, such as the one pictured below ( Figure 1.3), remind people how to stop the spread of the disease. A public health notice from the early 20th century reminded people that TB could be spread very easily. ",text,
L_0662,respiratory system diseases,T_3347,"Lung cancer is a disease in which the cells found in the lungs grow out of control. The growing mass of cells can form a tumor that pushes into nearby tissues. The tumor will affect how these tissues work. Lung cancer is the most common cause of cancer-related death in men, and the second most common in women. It is responsible for 1.3 million deaths worldwide every year ( Figure 1.4). The most common symptoms are shortness of breath, coughing (including coughing up blood), and weight loss. The most common cause of lung cancer is exposure to tobacco smoke. The inside of a lung showing cancerous tissue. ",text,
L_0662,respiratory system diseases,T_3348,"Emphysema is a chronic lung disease caused by the breakdown of the lung tissue. Symptoms of emphysema include shortness of breath, especially during exercise, and chronic cough, usually due to cigarette smoking, and wheezing, especially during expiration. Damage to the alveoli ( Figure 1.5), is not curable. Smoking is the leading cause of emphysema. ",text,
L_0662,respiratory system diseases,T_3349,"Many respiratory diseases are caused by pathogens. A pathogen is an organism that causes disease in another organism. Certain bacteria, viruses, and fungi are pathogens of the respiratory system. The common cold and flu are caused by viruses. The influenza virus that causes the flu is pictured below ( Figure 1.6). Tuberculosis, whooping cough, and acute bronchitis are caused by bacteria. The pathogens that cause colds, flu, and TB can be passed from person to person by coughing, sneezing, and spitting. Illnesses caused by bacteria can be treated with antibiotics. Those caused by viruses cannot. Pollution is another common cause of respiratory disease. The quality of the air you breathe can affect the health of your lungs. Asthma, heart and lung diseases, allergies, and several types of cancers are all linked to air quality. Air pollution is not just found outdoors; indoor air pollution can also be responsible for health problems. Smoking is the major cause of chronic respiratory disease as well as cardiovascular disease and cancer. Exposure to tobacco smoke by smoking or by breathing air that contains tobacco smoke is the leading cause of preventable death in the United States. Regular smokers die about 10 years earlier than nonsmokers do. The Centers for Disease Control and Prevention (CDC) describes tobacco use as ""the single most important preventable risk to human health The lung of a smoker who had emphysema (left). Tar, a sticky, black substance found in tobacco smoke, is evident. Chronic obstructive pulmonary disease (right), is a tobacco-related disease that is characterized by emphysema. This represents the influenza virus that causes the swine flu, or H1N1. The Center for Disease Control and Prevention recommends that children between the ages of 6 months and 19 years get a flu vaccination each year. in developed countries and an important cause of [early] death worldwide."" Simply stated: Stopping smoking can prevent many respiratory diseases. ",text,
L_0662,respiratory system diseases,T_3349,"Many respiratory diseases are caused by pathogens. A pathogen is an organism that causes disease in another organism. Certain bacteria, viruses, and fungi are pathogens of the respiratory system. The common cold and flu are caused by viruses. The influenza virus that causes the flu is pictured below ( Figure 1.6). Tuberculosis, whooping cough, and acute bronchitis are caused by bacteria. The pathogens that cause colds, flu, and TB can be passed from person to person by coughing, sneezing, and spitting. Illnesses caused by bacteria can be treated with antibiotics. Those caused by viruses cannot. Pollution is another common cause of respiratory disease. The quality of the air you breathe can affect the health of your lungs. Asthma, heart and lung diseases, allergies, and several types of cancers are all linked to air quality. Air pollution is not just found outdoors; indoor air pollution can also be responsible for health problems. Smoking is the major cause of chronic respiratory disease as well as cardiovascular disease and cancer. Exposure to tobacco smoke by smoking or by breathing air that contains tobacco smoke is the leading cause of preventable death in the United States. Regular smokers die about 10 years earlier than nonsmokers do. The Centers for Disease Control and Prevention (CDC) describes tobacco use as ""the single most important preventable risk to human health The lung of a smoker who had emphysema (left). Tar, a sticky, black substance found in tobacco smoke, is evident. Chronic obstructive pulmonary disease (right), is a tobacco-related disease that is characterized by emphysema. This represents the influenza virus that causes the swine flu, or H1N1. The Center for Disease Control and Prevention recommends that children between the ages of 6 months and 19 years get a flu vaccination each year. in developed countries and an important cause of [early] death worldwide."" Simply stated: Stopping smoking can prevent many respiratory diseases. ",text,
L_0663,respiratory system health,T_3350,"We know that many respiratory illnesses are caused by bacteria or viruses. There are steps you can take to help the spread of these pathogens, and also to prevent you from catching one. Furthermore, many respiratory illnesses are caused by poor habits, such as smoking. Many of the diseases related to smoking are called lifestyle diseases. Lifestyle diseases are diseases that are caused by choices that people make in their daily lives. For example, the choice to smoke can lead to emphysema, cancer and heart disease in later life. But you can make healthy choices instead. There are many things you can do to keep yourself healthy. ",text,
L_0663,respiratory system health,T_3351,"Cigarette smoking can cause serious diseases, so not smoking or quitting now are the most effective ways to reduce your risk of developing chronic respiratory diseases, such as lung cancer. Avoiding (or stopping) smoking is the single best way to prevent many respiratory and cardiovascular diseases. Also, do your best to avoid secondhand smoke. ",text,
L_0663,respiratory system health,T_3352,"Eating healthy foods, getting enough sleep, and being active every day can help keep your respiratory system, cardiovascular system and immune system strong. Getting enough exercise makes your lungs stronger and better at giving your body the oxygen it needs. It also helps to boost your body fight germs that could make you sick. These can also, of course, keep your skeletal and muscular systems strong. ",text,
L_0663,respiratory system health,T_3353,"Washing your hands often, especially after sneezing, coughing, or blowing your nose, helps to protect you and others from diseases. Washing your hands for 20 seconds with soap and warm water can help prevent colds and flu. In one respect, you can think of hand washing as a survival skill. Some viruses and bacteria can live from 20 minutes to two hours or more on surfaces like cafeteria tables, doorknobs, and desks. Washing your hands often can remove many of these pathogens. Never touch your mouth, nose, or eyes without washing your hands. ",text,
L_0663,respiratory system health,T_3354,"Do not go to school or to other public places when you are sick. You risk spreading your illness to other people. You may also get even sicker if you catch something else. Do not share food and other things that go in the mouth, as in guzzling milk from the carton or double dipping chips. You never know what pathogens can be lurking around. Cover your mouth with a tissue when you cough or sneeze and to dispose of the tissue yourself. No time to grab a tissue. Cough or sneeze into the inside of your elbow instead of your hands. ",text,
L_0663,respiratory system health,T_3355,"Getting the recommended vaccinations can help prevent diseases, such as whooping cough and flu. In fact, a yearly flu vaccine is recommended for everyone who is at least 6 months of age. The flu vaccine is especially important for people who are at high risk of developing serious complications (like pneumonia) if they get sick with the flu. People who have certain medical conditions including asthma, diabetes, and chronic lung disease, pregnant women, and people younger than 5 years (and especially those younger than 2), and people 65 years and older should also make sure they get the yearly flu vaccine. Seeking medical help for diseases like asthma can help stop the disease from getting worse. If you are unsure if you should go to the doctor, call the doctors office and ask. ",text,
L_0664,respiratory system organs,T_3356,"Your respiratory system is made up of the tissues and organs that allow oxygen to enter your body and carbon dioxide to leave your body. Organs in your respiratory system include your: Nose. Mouth. Larynx. Pharynx. Lungs. Diaphragm. The organs of the respiratory system move air into and out of the body. These structures are shown below (Figure 1.1). What do you think is the purpose of each of these organs? The nose and the nasal cavity filter, warm, and moisten the air you breathe. The nose hairs and the mucus produced by the cells in the nose catch particles in the air and keep them from entering the lungs. Behind the nasal cavity, air passes through the pharynx, a long tube. Both food and air pass through the pharynx. The larynx, also called the ""voice box,"" is found just below the pharynx. Your voice comes from your larynx. Air from the lungs passes across thin tissues in the larynx and produces sound. The trachea, or windpipe, is a long tube that leads down to the lungs, where it divides into the right and left bronchi. The bronchi branch out into smaller bronchioles in each lung. There is small flap called the epiglottis that covers your trachea when you eat or drink. The muscle controlling the epiglottis is involuntary and prevents food from entering your lungs or wind pipe. The bronchioles lead to the alveoli. Alveoli are the little sacs at the end of the bronchioles (Figure 1.2). They look like little bunches of grapes. Oxygen is exchanged for carbon dioxide in the alveoli. That means oxygen enters the blood, and carbon dioxide moves out of the blood. The gases are exchanged between the blood and alveoli by simple diffusion. The diaphragm is a sheet of muscle that spreads across the bottom of the rib cage. When the diaphragm contracts, the chest volume gets larger, and the lungs take in air. When the diaphragm relaxes, the chest volume gets smaller, and air is pushed out of the lungs. ""Grape-like"" alveoli in the lungs. ",text,
L_0664,respiratory system organs,T_3356,"Your respiratory system is made up of the tissues and organs that allow oxygen to enter your body and carbon dioxide to leave your body. Organs in your respiratory system include your: Nose. Mouth. Larynx. Pharynx. Lungs. Diaphragm. The organs of the respiratory system move air into and out of the body. These structures are shown below (Figure 1.1). What do you think is the purpose of each of these organs? The nose and the nasal cavity filter, warm, and moisten the air you breathe. The nose hairs and the mucus produced by the cells in the nose catch particles in the air and keep them from entering the lungs. Behind the nasal cavity, air passes through the pharynx, a long tube. Both food and air pass through the pharynx. The larynx, also called the ""voice box,"" is found just below the pharynx. Your voice comes from your larynx. Air from the lungs passes across thin tissues in the larynx and produces sound. The trachea, or windpipe, is a long tube that leads down to the lungs, where it divides into the right and left bronchi. The bronchi branch out into smaller bronchioles in each lung. There is small flap called the epiglottis that covers your trachea when you eat or drink. The muscle controlling the epiglottis is involuntary and prevents food from entering your lungs or wind pipe. The bronchioles lead to the alveoli. Alveoli are the little sacs at the end of the bronchioles (Figure 1.2). They look like little bunches of grapes. Oxygen is exchanged for carbon dioxide in the alveoli. That means oxygen enters the blood, and carbon dioxide moves out of the blood. The gases are exchanged between the blood and alveoli by simple diffusion. The diaphragm is a sheet of muscle that spreads across the bottom of the rib cage. When the diaphragm contracts, the chest volume gets larger, and the lungs take in air. When the diaphragm relaxes, the chest volume gets smaller, and air is pushed out of the lungs. ""Grape-like"" alveoli in the lungs. ",text,
L_0665,rna,T_3357,"DNA contains the instructions to create proteins, but it does not make proteins itself. DNA is located in the nucleus, which it never leaves, while proteins are made on ribosomes in the cytoplasm. So DNA needs a messenger to bring its instructions to a ribosome located outside of the nucleus. DNA sends out a message, in the form of RNA (ribonucleic acid), describing how to make the protein. There are three types of RNA directly involved in protein synthesis: Messenger RNA ( mRNA) carries the instructions from the nucleus to the cytoplasm. mRNA is produced in the nucleus, as are all RNAs. The other two forms of RNA, ribosomal RNA ( rRNA) and transfer RNA ( tRNA), are involved in the process of ordering the amino acids to make the protein. rRNA becomes part of the ribosome, which is the site of protein synthesis, and tRNA brings an amino acid to the ribosome so it can be added to a growing chain during protein synthesis. There are numerous tRNAs, as each tRNA is specific for an amino acid. The amino acid actually attaches to the tRNA during this process. More about RNAs will be discussed during the Transcription and Translation Concepts. All three RNAs are nucleic acids, made of nucleotides, similar to DNA ( Figure 1.1). The RNA nucleotide is different from the DNA nucleotide in the following ways: RNA contains a different kind of sugar, called ribose. In RNA, the base uracil (U) replaces the thymine (T) found in DNA. RNA is a single strand molecule. A comparison of DNA and RNA, with the bases of each shown. Notice that in RNA, uracil replaces thymine. ",text,
L_0667,roundworms,T_3362,"The word ""worm"" is not very scientific. This informal term describes animals (usually invertebrates) that have long bodies with no arms or legs. Worms with round, non-segmented bodies are known as nematodes or roundworms ( Figure 1.1). They are classified in the phylum Nematoda, which has over 28,000 known species. Some scientists believe there could be over a million species of Nematodes. Nematodes are slender bilaterally symmetrical worms, typically less than 2.5 mm long. The smallest nematodes are microscopic, while free-living species can reach as much as 5 cm, and some parasitic species are larger still, reaching over a meter in length. The worm body is often covered with ridges, rings, bristles, or other distinctive structures. The radially symmetrical head of a nematode also has distinct features. The head is covered with sensory bristles and, in many cases, solid ""head-shields"" around the mouth region. The mouth has either three or six lips arranged around the mouth opening, which often have a series of teeth on their inner edges. Nematodes can be parasites of plants and animals. ",text,
L_0667,roundworms,T_3363,"1. Unlike the flatworms, the roundworms have a body cavity with internal organs. 2. A roundworm has a complete digestive system, which includes both a mouth and an anus. This is a significant difference from the incomplete digestive system of flatworms. The roundworm digestive system also include a large digestive organ known as the gut. Digestive enzymes that start to break down food are produced here. There is no stomach, but there is an intestine which produces enzymes that help absorb nutrients. The last portion of the intestine forms a rectum, which expels waste through the anus. 3. Roundworms also have a simple nervous system with a primitive brain. There are four nerves that run the length of the body and are connected from the top to the bottom of the body. At the anterior end of the animal (the head region), the nerves branch from a circular ring which serves as the brain. The head of a nematode has a few tiny sense organs, including chemoreceptors, which sense chemicals. Though still a relatively simple structure, the nervous system of roundworms is very different from that of the cnidarian nerve net. ",text,
L_0667,roundworms,T_3364,"Roundworms can be free-living organisms, but they are probably best known for their role as significant plant and animal parasites. Most Nematodes are parasitic, with over 16,000 parasitic species described. Heartworms, which cause serious disease in dogs while living in the heart and blood vessels, are a type of roundworm. Roundworms can also cause disease in humans. Elephantiasis, a disease characterized by the extreme swelling of the limbs ( Figure Most parasitic roundworm eggs or larvae are found in the soil and enter the human body when a person picks them up on the hands and then transfers them to the mouth. The eggs or larvae also can enter the human body directly through the skin. The best solution to these diseases is to try to prevent these diseases rather than treat or cure them. Diseases caused by roundworms are more common in developing countries. Many parasitic diseases caused by roundworms result from poor personal hygiene. Contributing factors may include lack of a clean water supply, inadequate sanitation measures, crowded living conditions, combined with a lack of access to health care and low levels of education. ",text,
L_0675,segmented worms,T_3388,"When you think of worms, you probably picture earthworms. There are actually many types of worms, including flatworms, roundworms, and segmented worms. Earthworms are segmented worms. Segmented worms are in the phylum Annelida, which has over 22,000 known species. These worms are known as the segmented worms because their bodies are segmented, or separated into repeating units. Besides the earthworm, the segmented worms also include leeches and some marine worms. Most segmented worms like the earthworm, feed on dead organic matter. Leeches (Figure 1.1), however, can live in fresh water and suck blood from their animal host. You may have noticed many earthworms in soil. Earthworms support terrestrial ecosystems both as prey and by aerating and enriching soil. ",text,
L_0675,segmented worms,T_3389,"Segmented worms have a number of characteristic features. 1. The basic form consists of multiple segments, each of which has the same sets of organs and, in most, a pair of parapodia that many species use for locomotion. 2. Segmented worms have a well-developed body cavity filled with fluid. This fluid-filled cavity serves as a hydroskeleton, a supportive structure that helps move the worms muscles. Only the most primitive worms (the flatworms) lack a body cavity. 3. Segmented worms also tend to have organ systems that are more developed than the roundworms or flat- worms. Earthworms, for example, have a complete digestive tract with two openings, as well as an esophagus and intestines. The circulatory system consists of paired hearts and blood vessels. Actually there are five pairs of hearts that pump blood along the two main vessels. And the nervous system consists of the brain and a ventral nerve cord. ",text,
L_0675,segmented worms,T_3390,The following table compares the three worm phyla (Table 1.1). Phylum Platyhelminthes Nematoda Annelida Common Name Flatworm Roundworm Segmented worm Body Cavity Segmented No Yes Yes No No Yes Digestive System Incomplete Complete Complete ,text,
L_0676,sex linked inheritance,T_3391,"What determines if a baby is a male or female? Recall that you have 23 pairs of chromosomesand one of those pairs is the sex chromosomes. Everyone has two sex chromosomes. Your sex chromosomes can be X or Y. Females have two X chromosomes (XX), while males have one X chromosome and one Y chromosome (XY). If a baby inherits an X chromosome from the father and an X chromosome from the mother, what will be the childs sex? The baby will have two X chromosomes, so it will be female. If the fathers sperm carries the Y chromosome, the child will be male. Notice that a mother can only pass on an X chromosome, so the sex of the baby is determined by the father. The father has a 50 percent chance of passing on the Y or X chromosome, so there is a 50 percent chance that a child will be male, and there is a 50 percent chance a child will be female. This 50:50 chance occurs for each baby. A couples first five children could all be boys. The sixth child still has a 50:50 chance of being a girl. One special pattern of inheritance that doesnt fit Mendels rules is sex-linked inheritance, referring to the inher- itance of traits that are located on genes on the sex chromosomes. Since males and females do not have the same sex chromosomes, there will be differences between the sexes in how these sex-linked traitstraits linked to genes located on the sex chromosomesare expressed. Sex-linked traits usually refer to traits due to genes on the X chromosome. One example of a sex-linked trait is red-green colorblindness. People with this type of colorblindness cannot tell the difference between red and green. They often see these colors as shades of brown ( Figure 1.1). Boys are much more likely to be colorblind than girls ( Table 1.1). This is because colorblindness is a sex-linked, recessive trait. Boys only have one X chromosome, so if that chromosome carries the gene for colorblindness, they will be colorblind. As girls have two X chromosomes, a girl can have one X chromosome with the colorblind gene and one X chromosome with a normal gene for color vision. Since colorblindness is recessive, the dominant normal gene will mask the recessive colorblind gene. Females with one colorblindness allele and one normal allele are referred to as carriers. They carry the allele but do not express it. How would a female become colorblind? She would have to inherit two genes for colorblindness, which is very unlikely. Many sex-linked traits are inherited in a recessive manner. Xc Xc X (carrier female) Xc Y (colorblind male) X Y X XX (normal female) XY (normal male) According to this Punnett square ( Table 1.1), the son of a woman who carries the colorblindness trait and a male with normal vision has a 50% chance of being colorblind. ",text,
L_0677,sexually transmitted infections,T_3392,"A sexually transmitted infection (STI) is an infection that spreads through sexual contact. STIs are caused by pathogens, a living thing or virus that causes infection. The pathogens enter the body through the reproductive organs. Many STIs also spread through body fluids, such as blood. For example, a shared tattoo needle is one way an STI could spread. Some STIs can also spread from a mother to her baby during childbirth. STIs are more common in teens and young adults than in older people. One reason is that young people are more likely to take risks. They also may not know how STIs spread. They are likely to believe myths about STIs ( Table Myth If you are sexually active with just one person, you cant get STIs. If you dont have any symptoms, then you dont have an STI. Getting STIs is no big deal, because STIs can be cured with medicine. Fact The only way to avoid the risk of STIs is to practice abstinence from sexual activity. Many STIs do not cause symptoms, especially in fe- males. Only some STIs can be cured with medicine; other STIs cannot be cured. Most STIs are caused by bacteria or viruses. STIs caused by bacteria usually can be cured with drugs called antibiotics. But antibiotics are not effective against viruses. Therefore, STIs caused by viruses are not treated with antibiotics. Other drugs may be used to help control the symptoms of viral STIs, but they cannot be cured. Once you have a viral STI, you are usually infected for life. ",text,
L_0677,sexually transmitted infections,T_3393,"In the U.S., chlamydia is the most common STI caused by bacteria. Females are more likely than males to develop the infection. Rates of chlamydia among U.S. females in 2006 are shown below ( Figure 1.1). Rates were much higher in teens and young women than in other age groups. Chlamydia may cause a burning feeling during urination. It may also cause a discharge (leaking of fluids) from the vagina or penis. But in many cases it causes no symptoms. As a result, people do not know they are infected, so they dont go to the doctor for help. If chlamydia goes untreated, it may cause more serious problems in females. It may cause infections of the uterus, fallopian tubes, or ovaries. These infections may leave a woman unable to have children. Gonorrhea is another common STI. Gonorrhea may cause pain during urination. It may also cause a discharge from the vagina or penis. On the other hand, some people with gonorrhea have no symptoms. As a result, they dont seek treatment. Without treatment, gonorrhea may lead to infection of other reproductive organs. This can happen in males as well as females. Syphilis is a very serious STI. Luckily, it is less common than chlamydia or gonorrhea. Syphilis usually begins with a small sore on the genitals. This is followed a few months later by a rash and flu-like symptoms. If syphilis is not treated, it may damage the heart, brain, and other organs. It can even cause death. ",text,
L_0677,sexually transmitted infections,T_3394,"Genital warts are an STI caused by human papilloma virus, or HPV. They are one of the most common STIs in teenagers. HPV infections cannot be cured. But a new vaccine called Gardasil can prevent most HPV infections in females. Many doctors recommend that females between the ages of 9 and 26 years receive the vaccine. Preventing HPV infections in females is important because HPV can also cause cancer of the cervix. A related herpes virus causes cold sores on the lips ( Figure 1.2). Both viruses cause painful blisters. In the case of genital herpes, the blisters are on the penis or around the vaginal opening. The blisters go away on their own, but the virus remains in the body. The blisters may come back repeatedly, especially when a person is under stress. There is no cure for genital herpes. But drugs can help prevent or shorten outbreaks. Researchers are trying to find a vaccine to prevent genital herpes. Hepatitis B is a disease of the liver. It is caused by a virus called hepatitis B, which can be passed through sexual activity. Hepatitis B causes vomiting. It also causes yellowing of the skin and eyes. The disease goes away on its own in some people. Other people are sick for the rest of their lives. In these people, the virus usually damages the liver. It may also lead to liver cancer. Medicines can help prevent liver damage in these people. There is also a vaccine to protect against hepatitis B. HIV stands for ""human immunodeficiency virus."" It is the virus that causes AIDS. HIV and AIDS are described in a previous concept. HIV can spread through sexual contact. It can also spread through body fluids such as blood. There is no cure for HIV infection, and AIDS can cause death, although AIDS can be delayed for several years with medication. Researchers are trying to find a vaccine to prevent HIV infection. ",text,
L_0678,skeletal system joints,T_3395,"A joint is a point at which two or more bones meet. There are three main types of joints in the body: 1. Fixed joints do not allow any bone movement. Many of the joints in your skull are fixed ( Figure 1.1). There are eight bones that fuse together to form the cranium. The joints between these bones do not allow movement, which helps protect the brain. 2. Partly movable joints allow only a little movement. Your backbone has partly movable joints between the vertebrae ( Figure 1.2). The skull has fixed joints. Fixed joints do not allow any movement of the bones, which protects the brain from injury. 3. Movable joints allow the most movement. Movable joints are also the most common type of joint in your body. Your fingers, toes, hips, elbows, and knees all provide examples of movable joints. The surfaces of bones at movable joints are covered with a smooth layer of cartilage. The cartilage reduces friction between the bones. Ligaments often cross a joint, holding two nones together. For example, there are numerous ligaments connecting the leg bones across the knee joint. ",text,
L_0678,skeletal system joints,T_3395,"A joint is a point at which two or more bones meet. There are three main types of joints in the body: 1. Fixed joints do not allow any bone movement. Many of the joints in your skull are fixed ( Figure 1.1). There are eight bones that fuse together to form the cranium. The joints between these bones do not allow movement, which helps protect the brain. 2. Partly movable joints allow only a little movement. Your backbone has partly movable joints between the vertebrae ( Figure 1.2). The skull has fixed joints. Fixed joints do not allow any movement of the bones, which protects the brain from injury. 3. Movable joints allow the most movement. Movable joints are also the most common type of joint in your body. Your fingers, toes, hips, elbows, and knees all provide examples of movable joints. The surfaces of bones at movable joints are covered with a smooth layer of cartilage. The cartilage reduces friction between the bones. Ligaments often cross a joint, holding two nones together. For example, there are numerous ligaments connecting the leg bones across the knee joint. ",text,
L_0678,skeletal system joints,T_3396,"Four types of movable joints are discussed here. 1. In a ball-and-socket joint, the ball-shaped surface of one bone fits into the cup-like shape of another. Exam- ples of a ball-and-socket joint include the hip ( Figure 1.3) and the shoulder. 2. In a hinge joint, the ends of the bones are shaped in a way that allows motion in two directions, forward and backward. Examples of hinge joints are the knees ( Figure 1.4) and elbows. 3. The pivot joint ( Figure 1.5) only allows rotating movement. An example of a pivot joint is the joint between the radius and ulna that allows you to turn the palm of your hand up and down. 4. A gliding joint is a joint which allows only gliding movement. The gliding joint allows one bone to slide over the other. The gliding joint in your wrist allows you to flex your wrist. It also allows you to make very small side-to-side motions. There are also gliding joints in your ankles. ",text,
L_0678,skeletal system joints,T_3396,"Four types of movable joints are discussed here. 1. In a ball-and-socket joint, the ball-shaped surface of one bone fits into the cup-like shape of another. Exam- ples of a ball-and-socket joint include the hip ( Figure 1.3) and the shoulder. 2. In a hinge joint, the ends of the bones are shaped in a way that allows motion in two directions, forward and backward. Examples of hinge joints are the knees ( Figure 1.4) and elbows. 3. The pivot joint ( Figure 1.5) only allows rotating movement. An example of a pivot joint is the joint between the radius and ulna that allows you to turn the palm of your hand up and down. 4. A gliding joint is a joint which allows only gliding movement. The gliding joint allows one bone to slide over the other. The gliding joint in your wrist allows you to flex your wrist. It also allows you to make very small side-to-side motions. There are also gliding joints in your ankles. ",text,
L_0678,skeletal system joints,T_3396,"Four types of movable joints are discussed here. 1. In a ball-and-socket joint, the ball-shaped surface of one bone fits into the cup-like shape of another. Exam- ples of a ball-and-socket joint include the hip ( Figure 1.3) and the shoulder. 2. In a hinge joint, the ends of the bones are shaped in a way that allows motion in two directions, forward and backward. Examples of hinge joints are the knees ( Figure 1.4) and elbows. 3. The pivot joint ( Figure 1.5) only allows rotating movement. An example of a pivot joint is the joint between the radius and ulna that allows you to turn the palm of your hand up and down. 4. A gliding joint is a joint which allows only gliding movement. The gliding joint allows one bone to slide over the other. The gliding joint in your wrist allows you to flex your wrist. It also allows you to make very small side-to-side motions. There are also gliding joints in your ankles. ",text,
L_0679,skin,T_3397,"Did you know that you see the largest organ in your body every day? You wash it, dry it, cover it up to stay warm, and uncover it to cool off. Yes, your skin is your bodys largest organ. Your skin is part of your integumentary system ( Figure 1.1), which is the outer covering of your body. The integumentary system is made up of your skin, hair, and nails. Skin acts as a barrier that stops water and other things, like soap and dirt, from getting into your body. ",text,
L_0679,skin,T_3398,"The skin has many important functions. The skin: Provides a barrier. It keeps organisms that could harm the body out. It stops water from entering or leaving the body. Controls body temperature. It does this by making sweat (or perspiration), a watery substance that cools the body when it evaporates. Gathers information about your environment. Special nerve endings in your skin sense heat, pressure, cold, and pain. Helps the body get rid of some types of waste, which are removed in sweat. Acts as a sun block. A pigment called melanin blocks sunlight from getting to deeper layers of skin cells, which are easily damaged by sunlight. ",text,
L_0679,skin,T_3399,"Your skin is always exposed to your external environment, so it gets cut, scratched, and worn down. You also naturally shed many skin cells every day. Your body replaces damaged or missing skin cells by growing more of them. Did you know that the layer of skin you can see is actually dead? As the dead cells are shed or removed from the upper layer, they are replaced by the skin cells below them. Two different layers make up the skin: the epidermis and the dermis ( Figure 1.2). A fatty layer lies under the dermis, but it is not part of your skin. ",text,
L_0679,skin,T_3400,"The epidermis is the outermost layer of the skin. It forms the waterproof, protective wrap over the bodys surface. Although the top layer of epidermis is only about as thick as a sheet of paper, it is made up of 25 to 30 layers of cells. The epidermis also contains cells that produce melanin. Melanin is the brownish pigment that gives skin and hair their color. Melanin-producing cells are found in the bottom layer of the epidermis. The epidermis does not have any blood vessels. The lower part of the epidermis receives blood by diffusion from blood vessels of the dermis. Skin is made up of two layers, the epider- mis on top and the dermis below. The tissue below the dermis is called the hy- podermis, but it is not part of the skin. ",text,
L_0679,skin,T_3401,"The dermis is the layer of skin directly under the epidermis. It is made of a tough connective tissue. The dermis contains hair follicles, sweat glands, oil glands, and blood vessels ( Figure 1.2). It also holds many nerve endings that give you your sense of touch, pressure, heat, and pain. Do you ever notice how your hair stands up when you are cold or afraid? Tiny muscles in the dermis pull on hair follicles which cause hair to stand up. The resulting little bumps in the skin are commonly called ""goosebumps"" ( Figure 1.3). ",text,
L_0679,skin,T_3402,"Glands and hair follicles open out into the epidermis, but they start in the dermis. Oil glands ( Figure 1.2) release, or secrete an oily substance, called sebum, into the hair follicle. Sebum waterproofs hair and the skin surface to prevent them from drying out. It can also stop the growth of bacteria on the skin. It is odorless, but the breakdown of sebum by bacteria can cause odors. If an oil gland becomes plugged and infected, it develops into a pimple. Up to 85% of teenagers get pimples, which usually go away by adulthood. Frequent washing can help decrease the amount of sebum on the skin. Sweat glands ( Figure 1.2) open to the skin surface through skin pores. They are found all over the body. Evaporation of sweat from the skin surface helps to lower skin temperature. The skin also releases excess water, salts, sugars, and other wastes, such as ammonia and urea, in sweat. The Integumentary System Song can be heard at  . Goosebumps are caused by tiny mus- cles in the dermis that pull on hair folli- cles, which causes the hairs to stand up straight. ",text,
L_0680,smooth skeletal and cardiac muscles,T_3403,"The muscular system consists of all the muscles in the body. This is the body system that allows us to move. You also depend on many muscles to keep you alive. Your heart, which is mostly muscle, pumps blood around your body. Each muscle in the body is made up of cells called muscle fibers. Muscle fibers are long, thin cells that can do something that other cells cannot dothey are able to get shorter. Shortening of muscle fibers is called contraction. Muscle fibers can contract because they are made of proteins, called actin and myosin, that form long filaments (or fibers). When muscles contract, these protein filaments slide or glide past one another, shortening the length of the cell. When your muscles relax, the length extends back to the previous position. Nearly all movement in the body is the result of muscle contraction. You can control some muscle movements. However, certain muscle movements happen without you thinking about them. Muscles that are under your conscious control are called voluntary muscles. Muscles that are not under your conscious control are called involuntary muscles. Muscle tissue is one of the four types of tissue found in animals. There are three different types of muscle in the body ( Figure 1.1): 1. Skeletal muscle is made up of voluntary muscles, usually attached to the skeleton. Skeletal muscles move the body. They can also contract involuntarily by reflexes. For example, you can choose to move your arm, but your arm would move automatically if you were to burn your finger on a stove top. This voluntary contraction begins with a thought process. A signal from your brain tells your muscles to contract or relax. Quickly contract and relax the muscles in your fingers a few times. Think about how quickly these signals must travel throughout your body to make this happen. 2. Smooth muscle is composed of involuntary muscles found within the walls of organs and structures such as the esophagus, stomach, intestines, and blood vessels. These muscles push materials like food or blood through organs. Unlike skeletal muscle, smooth muscle can never be under your control. 3. Cardiac muscle is also an involuntary muscle, found only in the heart. The cardiac muscle fibers all contract together, generating enough force to push blood throughout the body. What would happen if this muscle was under conscious or voluntary control? There are three types of muscles in the body: cardiac, skeletal, and smooth. ",text,
L_0682,sources of water pollution,T_3407,"While to many people clean water may seem limitless and everywhere, to many others this is not so. Water pollution is a serious issue facing hundreds of millions of people world-wide, having harmful effects on the lives of those people. Water is not in unlimited supply and cannot just be made fresh when it is wanted. Water is actually a limited resource, and for many people, fresh, unpolluted water is hard to find. A limited resource is one that we use faster than we can remake it. It is a resource that can be used up. Water pollution happens when contaminants enter water bodies. Contaminants are any substances that harm the health of the environment or humans. Most contaminants enter the water because of humans. Surface water (river or lake) can be exposed to and contaminated by acid rain, storm water runoff, pesticide runoff, and industrial waste. This water is cleaned somewhat by exposure to sunlight, aeration, and microorganisms in the water. Groundwater (private wells and some public water supplies) generally takes longer to become contaminated, but the natural clean- ing process also may take much longer. Groundwater can be contaminated by disease-producing pathogens, careless disposal of hazardous household chemical-containing products, agricultural chemicals, and leaking underground storage tanks. Water pollution can cause harmful effects to ecology and human health. Shown is the pollution in Jakarta, Indonesia. Natural events, like storms, volcanic eruptions and earthquakes can cause major changes in water quality. But human-caused contaminants have a much greater impact on the quality of the water supply. Water is considered polluted either when it does not support a human use, like clean drinking water, or a use for other animals and plants. The overgrowth of algae, known as an algal bloom, can result from the runoff of fertilizer into bodies of water. This excess of nutrients allows the algae to grow beyond control, bring harm to the rest of the ecosystem. The main sources of water pollution can be grouped into two categories: Point source pollution results from the contaminants that enter a waterway or water body through a single site. Examples of this include untreated sewage, wastewater from a sewage treatment plant, and leaking underground tanks. Nonpoint source pollution is contamination that does not come from a single point source. Instead, it happens when there is a buildup of small amounts of contaminants that collect from a large area. Examples of this include fertilizer runoff from many farms flowing into groundwater or streams. ",text,
L_0688,taste and smell,T_3422,"The senses of taste and smell are more complicated than many people might think and have a surprisingly large impact on behavior, perception and overall health. Imagine your sense of smell disappearing as you age. Though this doesnt usually happen, it could provide clues about diseases of the nervous system. What about differences in taste? Do all foods taste the same to all people? Are there some foods you would never eat because you dont like the taste? Does this food taste good to other people? Genetic differences in taste could help predict what we eat, how well our metabolism works, and even whether or not were overweight. These two senses actually work together to provide some of the basic sensations of everyday life. ",text,
L_0688,taste and smell,T_3423,"Your sense of taste is controlled by sensory neurons, or nerve cells, on your tongue that sense the chemicals in food. The neurons are grouped in bundles within taste buds. Each taste bud actually has a pore that opens out to the surface of the tongue enabling molecules and ions taken into the mouth to reach the receptor cells inside. There are five different types of taste neurons on the tongue. Each type detects a different taste. The tastes are: 1. Sweet, which is produced by the presence of sugars, such as the common table sugar sucrose, and a few other substances. 2. Salty, which is produced primarily by the presence of sodium ions. Common salt is sodium chloride, NaCl. The use of salt can donate the sodium ion producing this taste. 3. Sour, which is the taste that detects acidity. The most common food group that contains naturally sour foods is fruit, such as lemon, grape, orange, and sometimes melon. Children show a greater enjoyment of sour flavors than adults, and sour candy such as Lemon Drops, Shock Tarts and sour versions of Skittles and Starburst, is popular. Many of these candies contain citric acid. 4. Bitter is an unpleasant, sharp, or disagreeable taste. Common bitter foods and beverages include coffee, unsweetened cocoa, beer (due to hops), olives, and citrus peel. 5. Umami, which is a meaty or savory taste. This taste can be found in fish, shellfish, cured meats, mushrooms, cheese, tomatoes, grains, and beans. A single taste bud contains 50100 taste cells representing all 5 taste sensations. A stimulated taste receptor cell triggers action potentials in a nearby sensory neuron, which send messages to the brain about the taste. The brain then decides what tastes you are sensing. ",text,
L_0688,taste and smell,T_3424,"Your sense of smell also involves sensory neurons that sense chemicals. The neurons are found in the nose, and they detect chemicals in the air. Unlike taste neurons, which can detect only five different tastes, the sensory neurons in the nose can detect thousands of different odors. Have you ever noticed that you lose your sense of taste when your nose is stuffed up? Thats because your sense of smell greatly affects your ability to taste food. As you eat, molecules of food chemicals enter your nose (actually your nasal cavity). You experience the taste and smell at the same time. Being able to smell as well as taste food greatly increases the number of different flavors you are able to sense. For example, you can use your sense of taste alone to learn that a food is sweet, but you have to also use your sense of smell to learn that the food tastes like strawberry cheesecake. Specific scents are often associated with our memories of places and events. Thats because scents are more novel or specific than shapes or other things you might see. So an odor similar to that of your grandmothers kitchen or pantry might be more quickly associated with your memories of that place than a similar sight, which might be more generalized. ",text,
L_0691,the carbon cycle,T_3428,"Carbon is one of the most common elements found in living organisms. Chains of carbon molecules form the backbones of many organic molecules, such as carbohydrates, proteins, and lipids. Carbon is constantly cycling between living organisms and the atmosphere ( Figure 1.1). The cycling of carbon occurs through the carbon cycle. Living organisms cannot make their own carbon, so how is carbon incorporated into living organisms? In the atmosphere, carbon is in the form of carbon dioxide gas (CO2 ). Recall that plants and other producers capture the carbon dioxide and convert it to glucose (C6 H12 O6 ) through the process of photosynthesis. Then as animals eat plants or other animals, they gain the carbon from those organisms. The chemical equation of photosynthesis is 6CO2 + 6H2 O  C6 H12 O6 + 6O2 . How does this carbon in living things end up back in the atmosphere? Remember that we breathe out carbon dioxide. This carbon dioxide is generated through the process of cellular respiration, which has the reverse chemical reaction as photosynthesis. That means when our cells burn food (glucose) for energy, carbon dioxide is released. We, like all animals, exhale this carbon dioxide and return it back to the atmosphere. Also, carbon is released to the atmosphere as an organism dies and decomposes. Cellular respiration and photosynthesis can be described as a cycle, as one uses carbon dioxide (and water) and makes oxygen (and glucose), and the other uses oxygen (and glucose) and makes carbon dioxide (and water). The carbon cycle. The cycling of car- bon dioxide in photosynthesis and cellular respiration are main components of the carbon cycle. Carbon is also returned to the atmosphere by the burning of organic matter (combustion) and fossil fuels and decomposition of organic matter. ",text,
L_0691,the carbon cycle,T_3429,"Millions of years ago, there were so many dead plants and animals that they could not completely decompose before they were buried. They were covered over by soil or sand, tar or ice. These dead plants and animals are organic matter made out of cells full of carbon-containing organic compounds (carbohydrates, lipids, proteins and nucleic acids). What happened to all this carbon? When organic matter is under pressure for millions of years, it forms fossil fuels. Fossil fuels are coal, oil, and natural gas. When humans dig up and use fossil fuels, we have an impact on the carbon cycle ( Figure 1.2). This carbon is not recycled until it is used by humans. The burning of fossil fuels releases more carbon dioxide into the atmosphere than is used by photosynthesis. So, there is more carbon dioxide entering the atmosphere than is coming out of it. Carbon dioxide is known as a greenhouse gas, since it lets in light energy but does not let heat escape, much like the panes of a greenhouse. The increase of greenhouse gasses in the atmosphere is contributing to a global rise in Earths temperature, known as global warming or global climate change. ",text,
L_0692,the nitrogen cycle,T_3430,"Like water and carbon, nitrogen is also repeatedly recycled through the biosphere. This process is called the nitrogen cycle. Nitrogen is one of the most common elements in living organisms. It is important for creating both proteins and nucleic acids, like DNA. The air that we breathe is mostly nitrogen gas (N2 ), but, unfortunately, animals and plants cannot use the nitrogen when it is a gas. In fact, plants often die from a lack of nitrogen even through they are surrounded by plenty of nitrogen gas. Nitrogen gas (N2 ) has two nitrogen atoms connected by a very strong triple bond. Most plants and animals cannot use the nitrogen in nitrogen gas because they cannot break that triple bond. In order for plants to make use of nitrogen, it must be transformed into molecules they can use. This can be accomplished several different ways ( Figure 1.1). Lightning: When lightening strikes, nitrogen gas is transformed into nitrate (NO3  ) that plants can use. Nitrogen fixation: Special nitrogen-fixing bacteria can also transform nitrogen gas into useful forms. These bacteria live in the roots of plants in the pea family. They turn the nitrogen gas into ammonium (NH4 + ) (a process called ammonification). In water environments, bacteria in the water can also fix nitrogen gas into ammonium. Ammonium can be used by aquatic plants as a source of nitrogen. Nitrogen also is released to the environment by decaying organisms or decaying wastes. These wastes release nitrogen in the form of ammonium. Ammonium in the soil can be turned into nitrate by a two-step process completed by two different types of bacteria. In the form of nitrate, nitrogen can be used by plants through the process of assimilation. It is then passed along to animals when they eat the plants. ",text,
L_0692,the nitrogen cycle,T_3431,"Turning nitrate back into nitrogen gas, the process of denitrification, happens through the work of denitrifying bacteria. These bacteria often live in swamps and lakes. They take in the nitrate and release it back to the atmosphere as nitrogen gas. Just like the carbon cycle, human activities impact the nitrogen cycle. These human activities include the burning of fossil fuels, which release nitrogen oxide gasses into the atmosphere. Releasing nitrogen oxide back into the atmosphere leads to problems like acid rain. ",text,
L_0693,the water cycle,T_3432,"Whereas energy flows through an ecosystem, water and elements like carbon and nitrogen are recycled. Water and nutrients are constantly being recycled through the environment. This process through which water or a chemical element is continuously recycled in an ecosystem is called a biogeochemical cycle. This recycling process involves both the living organisms (biotic components) and nonliving things (abiotic factors) in the ecosystem. Through biogeochemical cycles, water and other chemical elements are constantly being passed through living organisms to non-living matter and back again, over and over. Three important biogeochemical cycles are the water cycle, carbon cycle, and nitrogen cycle. The biogeochemical cycle that recycles water is the water cycle. The water cycle involves a series of interconnected pathways involving both the biotic and abiotic components of the biosphere. Water is obviously an extremely important aspect of every ecosystem. Life cannot exist without water. Many organisms contain a large amount of water in their bodies, and many live in water, so the water cycle is essential to life on Earth. Water continuously moves between living organisms, such as plants, and non-living things, such as clouds, rivers, and oceans ( Figure The water cycle does not have a real starting or ending point. It is an endless recycling process that involves the oceans, lakes and other bodies of water, as well as the land surfaces and the atmosphere. The steps in the water cycle are as follows, starting with the water in the oceans: 1. Water evaporates from the surface of the oceans, leaving behind salts. As the water vapor rises, it collects and is stored in clouds. 2. As water cools in the clouds, condensation occurs. Condensation is when gases turn back into liquids. 3. Condensation creates precipitation. Precipitation includes rain, snow, hail, and sleet. The precipitation allows the water to return again to the Earths surface. 4. When precipitation lands on land, the water can sink into the ground to become part of our underground water reserves, also known as groundwater. Much of this underground water is stored in aquifers, which are porous layers of rock that can hold water. ",text,
L_0693,the water cycle,T_3433,"Most precipitation that occurs over land, however, is not absorbed by the soil and is called runoff. This runoff collects in streams and rivers and eventually flows back into the ocean. ",text,
L_0693,the water cycle,T_3434,"Water also moves through the living organisms in an ecosystem. Plants soak up large amounts of water through their roots. The water then moves up the plant and evaporates from the leaves in a process called transpiration. The process of transpiration, like evaporation, returns water back into the atmosphere. ",text,
L_0694,timeline of evolution,T_3435,"For life to evolve from simple single-celled organisms to many millions of species of prokaryotic species to simple eukaryotic species to all the protists, fungi, plants, and animals, took some time. Well over 3 billion years. ",text,
L_0694,timeline of evolution,T_3436,"How old is Earth? How was it formed? How did life begin on Earth? These questions have fascinated scientists for centuries. During the 1800s, geologists, paleontologists, and naturalists found several forms of physical evidence that confirmed that Earth is very old. The evidence includes: Fossils of ancient sea life on dry land far from oceans. This supported the idea that the Earth changed over time and that some dry land today was once covered by oceans. The many layers of rock. When people realized that rock layers represent the order in which rocks and fossils appeared, they were able to trace the history of Earth and life on Earth. Indications that volcanic eruptions, earthquakes, and erosion that happened long ago shaped much of the Earths surface. This supported the idea of an older Earth. The Earth is at least as old as its oldest rocks. The oldest rock minerals found on Earth so far are crystals that are at least 4.404 billion years old. These tiny crystals were found in Australia. Likewise, Earth cannot be older than the solar system. The oldest possible age of Earth is 4.57 billion years old, the age of the solar system. Therefore, the age of Earth is between 4.4 and 4.57 billion years. ",text,
L_0694,timeline of evolution,T_3437,Geologists and other Earth scientists use geologic time scales to describe when events happened in the history of Earth. The time scales can be used to show when both geologic events and events affecting plant and animal life occurred. The geologic time scale pictured below ( Figure 1.1) illustrates the timing of events like: Earthquakes. Volcanic eruptions. Major erosion. Meteorites hitting Earth. The first signs of life forms. Mass extinctions. ,text,
L_0694,timeline of evolution,T_3438,"Life on Earth began about 3.5 to 4 billion years ago. The first life forms were single-celled organisms similar to bacteria. These first life forms were, of course, very basic, and this then allowed for the evolution of more complex life forms. The first multicellular organisms did not appear until about 610 million years ago. Many different types of organisms evolved during the next ten million years, in an event called the Cambrian Explosion. This sudden burst of evolution may have been caused by some environmental changes that made the Earths environment more suitable for a wider variety of life forms. Plants and fungi did not appear until roughly 500 million years ago. They were soon followed by arthropods (insects and spiders). Next came the amphibians about 300 million years ago, followed by mammals around 200 million years ago and birds around 100 million years ago. Even though large life forms have been very successful on Earth, most of the life forms on Earth today are still prokaryotessmall, relatively simple single-celled organisms. As it is difficult to identify, observe and study such small forms of life, most of these organisms remain unknown to scientists. Advancing technologies, however, do allow for the identification and study of such organisms. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common; in fact, it is estimated that 99% of the species that have ever lived on Earth no longer exist. The basic timeline of a 4.6 billion-year-old Earth includes the following: About 3.5 - 3.8 billion years of simple cells (prokaryotes). 3 billion years of photosynthesis. 2 billion years of complex cells (eukaryotes). 1 billion years of multicellular life. 600 million years of simple animals. 570 million years of arthropods (ancestors of insects, arachnids and crustaceans). 550 million years of complex animals. 500 million years of fish and proto-amphibians. 475 million years of land plants. 400 million years of insects and seeds. 360 million years of amphibians. 300 million years of reptiles. 200 million years of mammals. 150 million years of birds. 130 million years of flowers. 65 million years since the non-avian dinosaurs died out. 2.5 million years since the appearance of Homo. 200,000 years since the appearance of modern humans. 25,000 years since Neanderthals died out. ",text,
L_0695,touch,T_3439,"When you look at the prickly cactus pictured below ( Figure 1.1), does the word ""ouch"" come to mind? Touching the cactus would be painful. Touch is the sense of pain, pressure, or temperature. Touch depends on sensory neurons, or nerve cells, in the skin. The skin on the palms of the hands, soles of the feet, and face has the most sensory neurons and is especially sensitive to touch. The tongue and lips are very sensitive to touch as well. Neurons that sense pain are also found inside the body in muscles, joints, and organs. If you have a stomach ache or pain from a sprained ankle, its because of these sensory neurons found inside of your body. The following example shows how messages about touch travel from sensory neurons to the brain, as well as how the brain responds to the messages. Suppose you wanted to test the temperature of the water in a lake before jumping in. You might stick one bare foot in the water. Neurons in the skin on your foot would sense the temperature of the water and send a message about it to your central nervous system. The frontal lobe of the cerebrum would process the information. It might decide that the water is really cold and send a message to your muscles to pull your foot out of the water. In some cases, messages about pain or temperature dont travel all the way to and from the brain. Instead, they travel only as far as the spinal cord, and the spinal cord responds to the messages by giving orders to the muscles. This allows you to respond to pain more quickly. When messages avoid the brain in this way, it forms a reflex arc, like the one shown below ( Figure 1.2). ",text,
L_0695,touch,T_3440,"Our sense of touch is controlled by a huge network of nerve endings and touch receptors. This system is responsible for all the sensations we feel, including cold, hot, smooth, rough, pressure, tickle, itch, pain, vibrations, and more. There are four main types of receptors: mechanoreceptors, thermoreceptors, pain receptors, and proprioceptors. Mechanoreceptors perceive sensations such as pressure, vibrations, and texture. Your brain gets an enormous amount of information about the texture of objects through your fingertips because the ridges that make up your fingerprints are full of these sensitive receptors. Thermoreceptors perceive sensations related to the temperature of objects. There are two basic categories of thermoreceptors: hot receptors and cold receptors. The highest concentration of thermoreceptors can be found in the face and ears. Pain receptors, or nociceptor detect pain or stimuli that can or does cause damage to the skin and other tissues of the body. There are over three million pain receptors throughout the body, found in skin, muscles, bones, blood vessels, and some organs. Proprioceptors detect the position of different parts of the body in relation to each other and the surrounding environment. These receptors are found in joints, tendons and muscles, and allow us to do fundamental things such as feeding or clothing ourselves. ",text,
L_0697,transcription of dna to rna,T_3444,"DNA is located in the nucleus. Proteins are made on ribosomes in the cytoplasm. Remember that information in a gene is converted into mRNA, which carries the information to the ribosome. In the nucleus, mRNA is created by using the DNA in a gene as a template. A template is a model provided for others to copy. The process of constructing an mRNA molecule from DNA is known as transcription ( Figure 1.1 and Figure of double stranded DNA. In transcription, only one strand of DNA is used as a template. First, the double helix of DNA unwinds and an enzyme, RNA Polymerase, builds the mRNA using the DNA as a template. The nucleotides follow basically the same base pairing rules as in DNA to form the correct sequence in the mRNA. This time, however, uracil (U) pairs with each adenine (A) in the DNA. For example, a DNA sequence ACGGGTAAGG will be transcribed into the mRNA sequence UGCCCAUUCC. In this manner, the information of the DNA is passed on to the mRNA. The mRNA will carry this code to the ribosomes to tell them how to make a protein. As not all genes are used in every cell, a gene must be ""turned on"" or expressed when the gene product is needed by the cell. Only the information in a gene that is being expressed is transcribed into an mRNA. Transcription is when RNA is created from a DNA template. Each gene (a) contains triplets of bases (b) that are transcribed into RNA (c). Every triplet in the DNA, or codon in the mRNA, encodes for a unique amino acid. Base-pairing ensures the accuracy of transcription. Notice how the helix must unwind for transcription to take place. The new mRNA is shown in green. ",text,
L_0697,transcription of dna to rna,T_3444,"DNA is located in the nucleus. Proteins are made on ribosomes in the cytoplasm. Remember that information in a gene is converted into mRNA, which carries the information to the ribosome. In the nucleus, mRNA is created by using the DNA in a gene as a template. A template is a model provided for others to copy. The process of constructing an mRNA molecule from DNA is known as transcription ( Figure 1.1 and Figure of double stranded DNA. In transcription, only one strand of DNA is used as a template. First, the double helix of DNA unwinds and an enzyme, RNA Polymerase, builds the mRNA using the DNA as a template. The nucleotides follow basically the same base pairing rules as in DNA to form the correct sequence in the mRNA. This time, however, uracil (U) pairs with each adenine (A) in the DNA. For example, a DNA sequence ACGGGTAAGG will be transcribed into the mRNA sequence UGCCCAUUCC. In this manner, the information of the DNA is passed on to the mRNA. The mRNA will carry this code to the ribosomes to tell them how to make a protein. As not all genes are used in every cell, a gene must be ""turned on"" or expressed when the gene product is needed by the cell. Only the information in a gene that is being expressed is transcribed into an mRNA. Transcription is when RNA is created from a DNA template. Each gene (a) contains triplets of bases (b) that are transcribed into RNA (c). Every triplet in the DNA, or codon in the mRNA, encodes for a unique amino acid. Base-pairing ensures the accuracy of transcription. Notice how the helix must unwind for transcription to take place. The new mRNA is shown in green. ",text,
L_0698,translation of rna to protein,T_3445,"The mRNA, which is transcribed from the DNA in the nucleus, carries the directions for the protein-making process. mRNA tells the ribosome ( Figure 1.1) how to create a specific protein. Ribosomes translate RNA into a protein with a specific amino acid sequence. The tRNA binds and brings to the ribosome the amino acid encoded by the mRNA. The process of reading the mRNA code in the ribosome to make a protein is called translation ( Figure 1.2): the mRNA is translated from the language of nucleic acids (nucleotides) to the language of proteins (amino acids). Sets of three bases, called codons, are read in the ribosome, the organelle responsible for making proteins. This summary of how genes are ex- pressed shows that DNA is transcribed into RNA, which is translated, in turn, to protein. The one letter code represents amino acids. The following are the steps involved in translation: mRNA travels to the ribosome from the nucleus. The following steps occur in the ribosome: The base code in the mRNA determines the order of the amino acids in the protein. The genetic code in mRNA is read in words of three letters (triplets), called codons. Each codon codes for an amino acid. There are 20 amino acids used to make proteins, and different codons code for different amino acids. For example, GGU codes for the amino acid glycine, while GUC codes for valine. tRNA reads the mRNA code and brings a specific amino acid to attach to the growing chain of amino acids. The anticodon on the tRNA binds to the codon on the mRNA. Each tRNA carries only one type of amino acid and only recognizes one specific codon. For example, a GGC anticodon will bind to a CCG codon, and a CGA anticodon will bind to a GCU codon. tRNA is released from the amino acid. Three codons, UGA, UAA, and UAG, indicate that the protein should stop adding amino acids. They are called stop codons and do not code for an amino acid. Once tRNA comes to a stop codon, the protein is set free from the ribosome. The following chart ( Figure 1.3) is used to determine which amino acids correspond to which codons. ",text,
L_0698,translation of rna to protein,T_3445,"The mRNA, which is transcribed from the DNA in the nucleus, carries the directions for the protein-making process. mRNA tells the ribosome ( Figure 1.1) how to create a specific protein. Ribosomes translate RNA into a protein with a specific amino acid sequence. The tRNA binds and brings to the ribosome the amino acid encoded by the mRNA. The process of reading the mRNA code in the ribosome to make a protein is called translation ( Figure 1.2): the mRNA is translated from the language of nucleic acids (nucleotides) to the language of proteins (amino acids). Sets of three bases, called codons, are read in the ribosome, the organelle responsible for making proteins. This summary of how genes are ex- pressed shows that DNA is transcribed into RNA, which is translated, in turn, to protein. The one letter code represents amino acids. The following are the steps involved in translation: mRNA travels to the ribosome from the nucleus. The following steps occur in the ribosome: The base code in the mRNA determines the order of the amino acids in the protein. The genetic code in mRNA is read in words of three letters (triplets), called codons. Each codon codes for an amino acid. There are 20 amino acids used to make proteins, and different codons code for different amino acids. For example, GGU codes for the amino acid glycine, while GUC codes for valine. tRNA reads the mRNA code and brings a specific amino acid to attach to the growing chain of amino acids. The anticodon on the tRNA binds to the codon on the mRNA. Each tRNA carries only one type of amino acid and only recognizes one specific codon. For example, a GGC anticodon will bind to a CCG codon, and a CGA anticodon will bind to a GCU codon. tRNA is released from the amino acid. Three codons, UGA, UAA, and UAG, indicate that the protein should stop adding amino acids. They are called stop codons and do not code for an amino acid. Once tRNA comes to a stop codon, the protein is set free from the ribosome. The following chart ( Figure 1.3) is used to determine which amino acids correspond to which codons. ",text,
L_0698,translation of rna to protein,T_3445,"The mRNA, which is transcribed from the DNA in the nucleus, carries the directions for the protein-making process. mRNA tells the ribosome ( Figure 1.1) how to create a specific protein. Ribosomes translate RNA into a protein with a specific amino acid sequence. The tRNA binds and brings to the ribosome the amino acid encoded by the mRNA. The process of reading the mRNA code in the ribosome to make a protein is called translation ( Figure 1.2): the mRNA is translated from the language of nucleic acids (nucleotides) to the language of proteins (amino acids). Sets of three bases, called codons, are read in the ribosome, the organelle responsible for making proteins. This summary of how genes are ex- pressed shows that DNA is transcribed into RNA, which is translated, in turn, to protein. The one letter code represents amino acids. The following are the steps involved in translation: mRNA travels to the ribosome from the nucleus. The following steps occur in the ribosome: The base code in the mRNA determines the order of the amino acids in the protein. The genetic code in mRNA is read in words of three letters (triplets), called codons. Each codon codes for an amino acid. There are 20 amino acids used to make proteins, and different codons code for different amino acids. For example, GGU codes for the amino acid glycine, while GUC codes for valine. tRNA reads the mRNA code and brings a specific amino acid to attach to the growing chain of amino acids. The anticodon on the tRNA binds to the codon on the mRNA. Each tRNA carries only one type of amino acid and only recognizes one specific codon. For example, a GGC anticodon will bind to a CCG codon, and a CGA anticodon will bind to a GCU codon. tRNA is released from the amino acid. Three codons, UGA, UAA, and UAG, indicate that the protein should stop adding amino acids. They are called stop codons and do not code for an amino acid. Once tRNA comes to a stop codon, the protein is set free from the ribosome. The following chart ( Figure 1.3) is used to determine which amino acids correspond to which codons. ",text,
L_0702,types of echinoderms,T_3459,"The echinoderms can be divided into two major groups: 1. Eleutherozoa are the echinoderms that can move. This group includes the starfish and most other echinoderms. 2. Pelmatozoa are the immobile echinoderms. This group includes crinoids, such as the feather stars. Listed below are the four main classes of echinoderms present in the Eleutherozoa Group ( Table 1.1). Class Asteroidea Ophiuroidea Representative Organisms Starfish and asteroids Brittle stars ( Figure 1.1) Echinoidea Sea urchins and sand dollars Holothuroidea Sea cucumbers Characteristics Capture prey for their own food. Bottom feeders with long, narrow, flexible arms that allow relatively fast movement. Have movable spines which are used for movement, defense, and sensing the environment. Armless, elongated, generally soft- ",text,
L_0702,types of echinoderms,T_3460,"Echinoderms are spread all over the world at almost all depths, latitudes, and environments in the ocean. Most feather stars (crinoids) live in shallow water. In the deep ocean, sea cucumbers are common, sometimes making up 90% of the organisms. Most echinoderms, however, are found in reefs just lying beneath the surface of the water. No echinoderms are found in freshwater habitats or on land. This makes Echinodermata the largest animal phylum to only have ocean-based species. ",text,
L_0702,types of echinoderms,T_3461,"While almost all echinoderms live on the sea floor, some sea-lilies can swim at great speeds for brief periods of time, and a few sea cucumbers are fully floating. Some echinoderms find other ways of moving. For example, crinoids attach themselves to floating logs, and some sea cucumbers move by attaching to the sides of fish. On the underside side of a sea star, there are hundreds of tiny feet usually arranged into several rows on each ray of the star. These are called tube feet, or podia, and are filled with seawater in most echinoderms. The water vascular system within the body of the animal is also filled with seawater. By expanding and contracting chambers within the water vascular system, the echinoderm can force water into certain tube feet to extend them. The animal has muscles in the tube feet, which are used to retract them. By expanding and retracting the right tube feet in the proper order, the animal can walk. ",text,
L_0702,types of echinoderms,T_3462,Sea cucumbers at National Geographic http://animals.nationalgeographic.com/animals/invertebrates/sea-cucu 1. Where do sea cucumbers live? 2. How do sea cucumbers eat? ,text,
L_0704,types of nutrients,T_3467,"Carbohydrates, proteins, and lipids contain energy. When your body digests food, it breaks down the molecules of these nutrients. This releases the energy so your body can use it. ",text,
L_0704,types of nutrients,T_3468,"Carbohydrates are nutrients that include sugars, starches, and fiber. There are two types of carbohydrates: simple and complex. Pictured below are some foods that are good sources of carbohydrates ( Figure 1.1). ",text,
L_0704,types of nutrients,T_3469,"Sugars are small, simple carbohydrates that are found in foods such as fruits and milk. The sugar found in fruits is called fructose. The sugar found in milk is called lactose. These sugars are broken down by the body to form glucose (C6 H12 O6 ), the simplest sugar of all. Up to the age of 13 years, you need about 130 grams of carbohydrates a day. Most of the carbohydrates should be complex. They are broken down by the body more slowly than simple carbohydrates. There- fore, they provide energy longer and more steadily. Where does glucose come from? Recall that glucose is the product of photosynthesis, so some organisms such as plants are able to make their own glucose. As animals cannot photosynthesize, they must eat to obtain carbohydrates. Through the process of cellular respiration, glucose is converted by cells into energy that is usable by the cell (ATP). ",text,
L_0704,types of nutrients,T_3470,"Starch is a large, complex carbohydrate made of thousands of glucose units (monomers) joined together. Starches are found in foods such as vegetables and grains. Starches are broken down by the body into sugars that provide energy. Breads and pasta are good sources of complex carbohydrates. Fiber is another type of large, complex carbohydrate that is partly indigestible. Unlike sugars and starches, fiber does not provide energy. However, it has other important roles in the body. For example, fiber is important for maintaining the health of your gastrointestinal tract. Eating foods high in fiber also helps fill you up without providing too many calories. Most fruits and vegetables are high in fiber. Some examples are pictured below ( Figure 1.2). ",text,
L_0704,types of nutrients,T_3471,"Proteins are nutrients made up of smaller molecules called amino acids. Recall that there are 20 different amino acids arranged like ""beads on a string"" to form proteins. These amino acid chains then fold up into a three- dimensional molecule, giving the protein a specific function. Proteins have several important roles in the body. For example, proteins make up antibodies, muscle fibers and enzymes that help control cell and body processes. You need to make sure you have enough protein in your diet to obtain the necessary amino acids to make your proteins. Between the ages of 9 and 13 years, girls need about 26 grams of fiber per day, and boys need about 31 grams of fiber per day. If you eat more than you need for these purposes, the extra protein is used for energy. The image below shows how many grams of protein you need each day ( Figure 1.3). It also shows some foods that are good sources of protein. ",text,
L_0704,types of nutrients,T_3472,"Lipids are nutrients, such as fats that store energy. Lipids also have several other roles in the body. For example, lipids protect nerves and make up the membranes that surround cells. Fats are one type of lipid. Stored fat gives your body energy to use for later. Its like having money in a savings account: its there in case you need it. Stored fat also cushions and protects internal organs. In addition, it insulates the body. It helps keep you warm in cold weather. Between the ages of 9 and 13 years, you need about 34 grams of proteins a day. Seafood and eggs are other good sources of protein. There are two main types of fats, saturated and unsaturated. 1. Saturated fats can be unhealthy, even in very small amounts. They are found mainly in animal foods, such as meats, whole milk, and eggs. So even though these foods are good sources of proteins, they should be eaten in limited amounts. Saturated lipids increase cholesterol levels in the blood. Too much cholesterol in the blood Another type of lipid is called trans fat. Trans fats are manufactured and added to certain foods to keep them fresher for longer. Foods that contain trans fats include cakes, cookies, fried foods, and margarine. Eating foods that contain trans fats increases the risk of heart disease. Beginning with Denmark in 2003, many nations now limit the amount of trans fat that can be in food products or ban these products all together. On January 1, 2008, Calgary became the first city in Canada to ban trans fats from restaurants and fast food chains. Beginning in 2010, California banned trans fats from restaurant products, and in 2011, from all retail baked goods. ",text,
L_0705,urinary system,T_3473,"Sometimes, the urinary system ( Figure 1.1) is called the excretory system. But the urinary system is only one part of the excretory system. Recall that the excretory system is also made up of the skin, lungs, and large intestine, as well as the kidneys. The urinary system is the organ system that makes, stores, and gets rid of urine. ",text,
L_0705,urinary system,T_3474,"1. As you can see above ( Figure 1.1), the kidneys are two bean-shaped organs. Kidneys filter and clean the blood and form urine. They are about the size of your fists and are found near the middle of the back, just below your ribcage. 2. Ureters are tube-shaped and bring urine from the kidneys to the urinary bladder. 3. The urinary bladder is a hollow and muscular organ. It is shaped a little like a balloon. It is the organ that collects urine. 4. Urine leaves the body through the urethra. The kidneys filter the blood that passes through them, and the urinary bladder stores the urine until it is released from the body. ",text,
L_0705,urinary system,T_3475,"Urine is a liquid that is formed by the kidneys when they filter wastes from the blood. Urine contains mostly water, but it also contains salts and nitrogen-containing molecules. The amount of urine released from the body depends on many things. Some of these include the amount of fluid and food a person consumes and how much fluid they have lost from sweating and breathing. Urine ranges from colorless to dark yellow but is usually a pale yellow color. Light yellow urine contains mostly water. The darker the urine, the less water it contains. The urinary system also removes a type of waste called urea from your blood. Urea is a nitrogen-containing molecule that is made when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea and other wastes are carried in the bloodstream to the kidneys, where they are removed and form urine. ",text,
L_0709,vision correction,T_3488,You probably know people who need eyeglasses or contact lenses to see clearly. Maybe you need them yourself. Lenses are used to correct vision problems. Two of the most common vision problems are myopia and hyperopia. ,text,
L_0709,vision correction,T_3489,"Myopia is also called nearsightedness. It affects about one third of people. People with myopia can see nearby objects clearly, but distant objects appear blurry. The picture below shows how a person with myopia might see two boys that are a few meters away ( Figure 1.1). In myopia, the eye is too long. Below, you can see how images are focused on the retina of someone with myopia ( Figure 1.2). Myopia is corrected with a concave lens, which curves inward like the inside of a bowl. The lens changes the focus, so images fall on the retina as they should. Generally, nearsightedness first occurs in school-age children. There is some evidence that myopia is inherited. If one or both of your parents need glasses, there is an increased chance that you will too. Individuals who spend a lot of time reading, working or playing at a computer, or doing other close visual work may also be more likely to develop nearsightedness. Because the eye continues to grow during childhood, myopia typically progresses until On the left, you can see how a person with normal vision sees two boys. The right image shows how a person with myopia sees the boys. The eye of a person with myopia is longer than normal. As a result, images are focused in front of the retina (top left). A concave lens is used to correct myopia to help focus images on the retina (top right). Farsightedness, or hyperopia, oc- curs when objects are focused in back of the retina (bottom left). It is corrected with a convex lens (bottom right). about age 20. However, nearsightedness may also develop in adults due to visual stress or health conditions such as diabetes. A common sign of nearsightedness is difficulty seeing distant objects like a movie screen or the TV, or the whiteboard or chalkboard in school. Eyeglasses or contact lenses can easily help with myopia. Depending on the amount of myopia, you may only need to wear glasses or contact lenses for certain activities, like watching a movie or driving a car. Or, if you are very nearsighted, they may need to be worn all the time. ",text,
L_0709,vision correction,T_3489,"Myopia is also called nearsightedness. It affects about one third of people. People with myopia can see nearby objects clearly, but distant objects appear blurry. The picture below shows how a person with myopia might see two boys that are a few meters away ( Figure 1.1). In myopia, the eye is too long. Below, you can see how images are focused on the retina of someone with myopia ( Figure 1.2). Myopia is corrected with a concave lens, which curves inward like the inside of a bowl. The lens changes the focus, so images fall on the retina as they should. Generally, nearsightedness first occurs in school-age children. There is some evidence that myopia is inherited. If one or both of your parents need glasses, there is an increased chance that you will too. Individuals who spend a lot of time reading, working or playing at a computer, or doing other close visual work may also be more likely to develop nearsightedness. Because the eye continues to grow during childhood, myopia typically progresses until On the left, you can see how a person with normal vision sees two boys. The right image shows how a person with myopia sees the boys. The eye of a person with myopia is longer than normal. As a result, images are focused in front of the retina (top left). A concave lens is used to correct myopia to help focus images on the retina (top right). Farsightedness, or hyperopia, oc- curs when objects are focused in back of the retina (bottom left). It is corrected with a convex lens (bottom right). about age 20. However, nearsightedness may also develop in adults due to visual stress or health conditions such as diabetes. A common sign of nearsightedness is difficulty seeing distant objects like a movie screen or the TV, or the whiteboard or chalkboard in school. Eyeglasses or contact lenses can easily help with myopia. Depending on the amount of myopia, you may only need to wear glasses or contact lenses for certain activities, like watching a movie or driving a car. Or, if you are very nearsighted, they may need to be worn all the time. ",text,
L_0709,vision correction,T_3490,"Farsightedness is also known as hyperopia. It affects about one fourth of people. People with hyperopia can see distant objects clearly, but nearby objects appear blurry. In hyperopia, the eye is too short. This results in images being focused in back of the retina ( Figure 1.2). Hyperopia is corrected with a convex lens, which curves outward like the outside of a bowl. The lens changes the focus so that images fall on the retina as they should. Common signs of farsightedness include difficulty in concentrating and maintaining a clear focus on close objects, eye strain, fatigue and headaches after close work, and aching or burning eyes, especially after intense concentration on close work. In addition to lenses, many cases of myopia and hyperopia can be corrected with surgery. For example, a procedure called LASIK (Laser-Assisted in situ Keratomileusis) uses a laser to permanently change the shape of the cornea so light is correctly focused on the retina. ",text,
L_0710,vitamins and minerals,T_3491,"Vitamins and minerals are also nutrients. They do not provide energy, but they are needed for good health. ",text,
L_0710,vitamins and minerals,T_3492,"Vitamins are organic compounds that the body needs in small amounts to function properly. Humans need 13 different vitamins. Some of them are listed below ( Table 1.1). The table also shows how much of each vitamin you need every day. Vitamins have many roles in the body. For example, Vitamin A helps maintain good vision. Vitamin B9 helps form red blood cells. Vitamin K is needed for blood to clot when you have a cut or other wound. Vitamin Necessary for Available from Daily Amount Required (at ages 913 years) Vitamin Necessary for Available from A Good vision B1 Healthy nerves B3 Healthy skin and nerves B9 Red blood cells B12 Healthy nerves C Growth and repair of tis- sues Healthy bones and teeth Blood to clot Carrots, spinach, milk, eggs Whole wheat, peas, meat, beans, fish, peanuts Beets, liver, pork, turkey, fish, peanuts Liver, peas, dried beans, leafy green vegetables Meat, liver, milk, shell- fish, eggs Oranges, grapefruits, red peppers, broccoli Milk, salmon, tuna, eggs Spinach, brussels sprouts, milk, eggs D K Daily Amount Required (at ages 913 years) 600 g (1 g = 1  106 g) 0.9 mg (1 mg = 1  103 g) 12 mg 300 g 1.8 g 45 mg 5 g 60 g Some vitamins are produced in the body. For example, vitamin D is made in the skin when it is exposed to sunlight. Vitamins B12 and K are produced by bacteria that normally live inside the body. Most other vitamins must come from foods. Foods that are good sources of vitamins include whole grains, vegetables, fruits, and milk ( Table 1.1). Not getting enough vitamins can cause health problems. For example, too little vitamin C causes a disease called scurvy. People with scurvy have bleeding gums, nosebleeds, and other symptoms. ",text,
L_0710,vitamins and minerals,T_3493,"Minerals are chemical elements that are needed for body processes. Minerals that you need in relatively large amounts are listed below ( Table 1.2). Minerals that you need in smaller amounts include iodine, iron, and zinc. Minerals have many important roles in the body. For example, calcium and phosphorus are needed for strong bones and teeth. Potassium and sodium are needed for muscles and nerves to work normally. Mineral Necessary for Available from Calcium Strong bones and teeth Chloride Magnesium Proper balance of water and salts in body Strong bones Phosphorus Strong bones and teeth Potassium Muscles and nerves to work normally Muscles and nerves to work normally Milk, soy milk, leafy green vegetables Table salt, most packaged foods Whole grains, leafy green vegetables, nuts Meat, poultry, whole grains Meats, grains, bananas, orange juice Table salt, most packaged foods Sodium Daily Amount Required (at ages 913 years) 1,300 mg 2.3 g 240 mg 1,250 mg 4.5 g 1.5 g Your body cannot produce any of the minerals that it needs. Instead, you must get minerals from the foods you eat. Good sources of minerals include milk, leafy green vegetables, and whole grains ( Table 1.2). Not getting enough minerals can cause health problems. For example, too little calcium may cause osteoporosis. This is a disease in which bones become soft and break easily. Getting too much of some minerals can also cause health problems. Many people get too much sodium. Sodium is added to most packaged foods. People often add more sodium to their food by using table salt. Too much sodium causes high blood pressure in some people. ",text,
L_0716,acids and bases,T_3517,"An acid is an ionic compound that produces positive hydrogen ions (H+ ) when dissolved in water. An example is hydrogen chloride (HCl). When it dissolves in water, its hydrogen ions and negative chloride ions (Cl ) separate, forming hydrochloric acid. This can be represented by the equation: HCl H2 O + ! H + Cl ",text,
L_0716,acids and bases,T_3518,"You already know that a sour taste is one property of acids. (Never taste an unknown substance to see whether it is an acid!) Acids have certain other properties as well. For example, acids can conduct electricity because they consist of charged particles in solution. Acids also react with metals to produce hydrogen gas. For example, when hydrochloric acid (HCl) reacts with the metal magnesium (Mg), it produces magnesium chloride (MgCl2 ) and hydrogen (H2 ). This is a single replacement reaction, represented by the chemical equation: Mg + 2HCl ! H2 + MgCl2 You can see an online demonstration of a similar reaction at this URL: ",text,
L_0716,acids and bases,T_3519,"Certain compounds, called indicators, change color when acids come into contact with them. They can be used to detect acids. An example of an indicator is a compound called litmus. It is placed on small strips of paper that may be red or blue. If you place a few drops of acid on a strip of blue litmus paper, the paper will turn red. You can see this in Figure 10.6. Litmus isnt the only indicator for detecting acids. Red cabbage juice also works well, as you can see in this entertaining video:  . ",text,
L_0716,acids and bases,T_3520,"Acids have many important uses, especially in industry. For example, sulfuric acid is used to manufacture a variety of different products, including paper, paint, and detergent. Some other uses of acids are illustrated in Figure 10.7. ",text,
L_0716,acids and bases,T_3521,"A base is an ionic compound that produces negative hydroxide ions (OH ) when dissolved in water. For example, when the compound sodium hydroxide (NaOH) dissolves in water, it produces hydroxide ions and positive sodium ions (Na+ ). This can be represented by the equation: NaOH H2 O ! OH + Na+ ",text,
L_0716,acids and bases,T_3522,"All bases share certain properties, including a bitter taste. (Never taste an unknown substance to see whether it is a base!) Did you ever taste unsweetened cocoa powder? It tastes bitter because it is a base. Bases also feel slippery. Think about how slippery soap feels. Soap is also a base. Like acids, bases conduct electricity because they consist of charged particles in solution. ",text,
L_0716,acids and bases,T_3523,"Bases change the color of certain compounds, and this property can be used to detect them. A common indicator of bases is red litmus paper. Bases turn red litmus paper blue. You can see an example in Figure 10.8. Red cabbage juice can detect bases as well as acids, as youll see by reviewing this video:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0716,acids and bases,T_3524,"Bases are used for a variety of purposes. For example, soaps contain bases such as potassium hydroxide. Other uses of bases are pictured in Figure 10.9. ",text,
L_0716,acids and bases,T_3525,The acid in vinegar is weak enough to safely eat on a salad. The acid in a car battery is strong enough to eat through skin. The base in antacid tablets is weak enough to take for an upset stomach. The base in drain cleaner is strong enough to cause serious burns. What causes these differences in strength of acids and bases? ,text,
L_0716,acids and bases,T_3526,"The strength of an acid depends on the concentration of hydrogen ions it produces when dissolved in water. A stronger acid produces a greater concentration of ions than a weaker acid. For example, when hydrogen chloride is added to water, all of it breaks down into H+ and Cl ions. Therefore, it is a strong acid. On the other hand, only about 1 percent of acetic acid breaks down into ions, so it is a weak acid. The strength of a base depends on the concentration of hydroxide ions it produces when dissolved in water. For example, sodium hydroxide completely breaks down into ions in water, so it is a strong base. However, only a fraction of ammonia breaks down into ions, so it is a weak base. ",text,
L_0716,acids and bases,T_3527,"The strength of acids and bases is measured on a scale called the pH scale (see Figure 10.10). The symbol pH represents acidity, or the concentration of hydrogen ions (H+ ) in a solution. Pure water, which is neutral, has a pH of 7. With a higher concentration of hydrogen ions, a solution is more acidic but has a lower pH. Therefore, acids have a pH less than 7, and the strongest acids have a pH close to zero. Bases have a pH greater than 7, and the strongest bases have a pH close to 14. You can watch a video about the pH scale at this URL:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0716,acids and bases,T_3528,"Acidity is an important factor for living things. For example, many plants grow best in soil that has a pH between 6 and 7. Fish also need a pH close to 7. Some air pollutants form acids when dissolved in water droplets in the air. This results in acid fog and acid rain, which may have a pH of 4 or even lower (see Figure 10.10). Figure 10.11 shows the effects of acid fog and acid rain on a forest. Acid rain also lowers the pH of surface waters such as streams and lakes. As a result, the water became too acidic for fish and many other water organisms to survive. Even normal (not acid) rain is slightly acidic. Thats because carbon dioxide in the air dissolves in raindrops, producing a weak acid called carbonic acid. When acidic rainwater soaks into the ground, it can slowly dissolve rocks, particularly those containing calcium carbonate. This is how water forms caves, like the one that opened this chapter. ",text,
L_0716,acids and bases,T_3529,"As you read above, an acid produces positive hydrogen ions and a base produces negative hydroxide ions. If an acid and base react together, the hydrogen and hydroxide ions combine to form water. This is represented by the equation: H+ + OH ! H2 O An acid also produces negative ions, and a base also produces positive ions. For example, the acid hydrogen chloride (HCl), when dissolved in water, produces negative chloride ions (Cl ) as well as hydrogen ions. The base sodium hydroxide (NaOH) produces positive sodium ions (Na+ ) in addition to hydroxide ions. These other ions also combine when the acid and base react. They form sodium chloride (NaCl). This is represented by the equation: Na+ + Cl ! NaCl Sodium chloride is called table salt, but salt is a more general term. A salt is any ionic compound that forms when an acid and base react. It consists of a positive ion from the base and a negative ion from the acid. Like pure water, a salt is neutral in pH. Thats why reactions of acids and bases are called neutralization reactions. Another example of a neutralization reaction is described in Figure 10.12. You can learn more about salts and how they form at this URL:  (13:21). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0716,acids and bases,T_3529,"As you read above, an acid produces positive hydrogen ions and a base produces negative hydroxide ions. If an acid and base react together, the hydrogen and hydroxide ions combine to form water. This is represented by the equation: H+ + OH ! H2 O An acid also produces negative ions, and a base also produces positive ions. For example, the acid hydrogen chloride (HCl), when dissolved in water, produces negative chloride ions (Cl ) as well as hydrogen ions. The base sodium hydroxide (NaOH) produces positive sodium ions (Na+ ) in addition to hydroxide ions. These other ions also combine when the acid and base react. They form sodium chloride (NaCl). This is represented by the equation: Na+ + Cl ! NaCl Sodium chloride is called table salt, but salt is a more general term. A salt is any ionic compound that forms when an acid and base react. It consists of a positive ion from the base and a negative ion from the acid. Like pure water, a salt is neutral in pH. Thats why reactions of acids and bases are called neutralization reactions. Another example of a neutralization reaction is described in Figure 10.12. You can learn more about salts and how they form at this URL:  (13:21). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0716,acids and bases,T_3529,"As you read above, an acid produces positive hydrogen ions and a base produces negative hydroxide ions. If an acid and base react together, the hydrogen and hydroxide ions combine to form water. This is represented by the equation: H+ + OH ! H2 O An acid also produces negative ions, and a base also produces positive ions. For example, the acid hydrogen chloride (HCl), when dissolved in water, produces negative chloride ions (Cl ) as well as hydrogen ions. The base sodium hydroxide (NaOH) produces positive sodium ions (Na+ ) in addition to hydroxide ions. These other ions also combine when the acid and base react. They form sodium chloride (NaCl). This is represented by the equation: Na+ + Cl ! NaCl Sodium chloride is called table salt, but salt is a more general term. A salt is any ionic compound that forms when an acid and base react. It consists of a positive ion from the base and a negative ion from the acid. Like pure water, a salt is neutral in pH. Thats why reactions of acids and bases are called neutralization reactions. Another example of a neutralization reaction is described in Figure 10.12. You can learn more about salts and how they form at this URL:  (13:21). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0717,radioactivity,T_3530,"Radioactivity is the ability of an atom to emit, or give off, charged particles and energy from the nucleus. The charged particles and energy are called by the general term radiation. Only unstable nuclei emit radiation. When they do, they gain or lose protons. Then the atoms become different elements. (Be careful not to confuse this radiation with electromagnetic radiation, which has to do with the light given off by atoms as they absorb and then emit energy.) ",text,
L_0717,radioactivity,T_3531,"Radioactivity was discovered in 1896 by a French physicist named Antoine Henri Becquerel. Becquerel was experimenting with uranium, which glows after being exposed to sunlight. Becquerel wanted to see if the glow was caused by rays of energy, like rays of light and X-rays. He placed a bit of uranium on a photographic plate. The plate was similar to film thats used today to take X-rays. You can see an example of an X-ray in Figure 11.1. As Becquerel predicted, the uranium left an image on the photographic plate. This meant that uranium gives off rays after being exposed to sunlight. Becquerel was a good scientist, so he wanted to repeat his experiment to confirm his results. He placed more uranium on another photographic plate. However, the day had turned cloudy, so he tucked the plate and uranium in a drawer to try again another day. He wasnt expecting the uranium to leave an image on the plate without being exposed to sunlight. To his surprise, there was an image on the plate in the drawer the next day. Becquerel had discovered that uranium gives off rays without getting energy from light. He had discovered radioactivity, for which he received a Nobel prize. To learn more about the importance of Becquerels research, go to this URL: http://nobelprize.org/no Another scientist, who worked with Becquerel, actually came up with the term ""radioactivity."" The other scientist was the French chemist Marie Curie. She went on to discover the radioactive elements polonium and radium. She won two Nobel Prizes for her discoveries. You can learn more about Marie Curie at this URL: http://nobelprize.or ",text,
L_0717,radioactivity,T_3532,"Isotopes are atoms of the same element that differ from each other because they have different numbers of neutrons. Many elements have one or more isotopes that are radioactive. Radioactive isotopes are called radioisotopes. An example of a radioisotope is carbon-14. All carbon atoms have 6 protons, and most have 6 neutrons. These carbon atoms are called carbon-12, where 12 is the mass number (6 protons + 6 neutrons). A tiny percentage of carbon atoms have 8 neutrons instead of the usual 6. These atoms are called carbon-14 (6 protons + 8 neutrons). The nuclei of carbon-14 are unstable because they have too many neutrons. To be stable, a small nucleus like carbon, with just 6 protons, must have a 1:1 ratio of protons to neutrons. In other words, it must have the same number of neutrons as protons. In a large nucleus, with many protons, the ratio must be 2:1 or even 3:1 protons to neutrons. In elements with more than 83 protons, all the isotopes are radioactive (see Figure 11.2). The force of repulsion among all those protons overcomes the strong force holding them together. This makes the nuclei unstable and radioactive. Elements with more than 92 protons have such unstable nuclei that these elements do not even exist in nature. They exist only if they are created in a lab. ",text,
L_0717,radioactivity,T_3533,"A low level of radiation occurs naturally in the environment. This is called background radiation. It comes from various sources. One source is rocks, which may contain small amounts of radioactive elements such as uranium. Another source is cosmic rays. These are charged particles that arrive on Earth from outer space. Background radiation is generally considered to be safe for living things. A source of radiation that may be more dangerous is radon. Radon is a radioactive gas that forms in rocks underground. It can seep into basements and get trapped inside buildings. Then it may build up and become harmful to people who breathe it. Other sources of radiation are described in the interactive animation at this URL: http://w ",text,
L_0717,radioactivity,T_3534,"You may have seen a sign like the one in Figure 11.3. It warns people that there is radiation in the area. Exposure to radiation can be very dangerous. Radiation damages living things by knocking electrons out of atoms and changing them to ions. Radiation also breaks bonds in DNA and other biochemical compounds. A single large exposure to radiation can burn the skin and cause radiation sickness. Symptoms of this illness include extreme fatigue, destruction of blood cells, and loss of hair. Long-term exposure to lower levels of radiation can cause cancer. For example, radon in buildings can cause lung cancer. Marie Curie died of cancer, most likely because of exposure to radiation in her research. To learn more about the harmful health effects of radiation, go to this URL:  . Nonliving things can also be damaged by radiation. For example, high levels of radiation can remove electrons from metals. This may weaken metals in nuclear power plants and space vehicles, both of which are exposed to very high levels of radiation. ",text,
L_0717,radioactivity,T_3535,"One reason radiation is dangerous is that it cant be detected with the senses. You normally cant see it, smell it, hear it, or feel it. Fortunately, there are devices such as Geiger counters that can detect radiation. A Geiger counter, like the one in Figure 11.4, has a tube that contains atoms of a gas. If radiation enters the tube, it turns gas atoms to ions that carry electric current. The current causes the Geiger counter to click. The faster the clicks occur, the higher the level of radiation. You can see a video about the Geiger counter and how it was invented at the URL below. ",text,
L_0717,radioactivity,T_3536,"Despite its dangers, radioactivity has several uses. It can be used to determine the ages of ancient rocks and fossils. This use of radioactivity is explained in this chapters ""Radioactive Decay"" lesson. Radioactivity can also be used as a source of power to generate electricity. This use of radioactivity is covered later on in this chapter in the lesson ""Nuclear Energy."" Radioactivity can even be used to diagnose and treat diseases, including cancer. Cancer cells grow rapidly and take up a lot of glucose for energy. Glucose containing radioactive elements can be given to patients. Cancer cells will take up more of the glucose than normal cells do and give off radiation. The radiation can be detected with special machines (see Figure 11.5). Radioactive elements taken up by cancer cells may also be used to kill the cells and treat the disease. You can learn more about medical uses of radiation at the URL below. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0718,radioactive decay,T_3537,"There are three types of radioactive decay: alpha, beta, and gamma decay. In all three types, nuclei emit radiation, but the nature of that radiation differs from one type of decay to another. You can watch a video about the three types at this URL:  (17:02). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0718,radioactive decay,T_3538,"Alpha decay occurs when an unstable nucleus emits an alpha particle and energy. The diagram in Figure 11.6 represents alpha decay. An alpha particle contains two protons and two neutrons, giving it a charge of +2. A helium nucleus has two protons and two neutrons, so an alpha particle is represented in nuclear equations by the symbol 4 He. 2 The superscript 4 is the mass number (2 protons + 2 neutrons). The subscript 2 is the charge of the particle as well as the number of protons. An example of alpha decay is the decay of uranium-238 to thorium-234. In this reaction, uranium loses two protons and two neutrons to become the element thorium. The reaction can be represented by this equation: 238 92 U 4 !234 90 Th +2 He + Energy If you count the number of protons and neutrons on each side of this equation, youll see that the numbers are the same on both sides of the arrow. This means that the equation is balanced. The thorium-234 produced in this reaction is unstable, so it will undergo radioactive decay as well. The alpha particle (42 He) produced in the reaction can pick up two electrons to form the element helium. This is how most of Earths helium formed. Problem Solving ? 4 Problem: Fill in the missing subscript and superscript to balance this nuclear equation: 208 84 Po !? Pb +2 He + Energy Solution: The subscript is 82, and the superscript is 204. You Try It! ? 4 Problem: Fill in the missing subscript and superscript to balance this nuclear equation: 222 ? Ra !86 Rn+2 He+Energy ",text,
L_0718,radioactive decay,T_3539,"Beta decay occurs when an unstable nucleus emits a beta particle and energy. A beta particle is an electron. It has a charge of -1. In nuclear equations, a beta particle is represented by the symbol 01 e. The subscript -1 represents the particles charge, and the superscript 0 shows that the particle has virtually no mass. Nuclei contain only protons and neutrons, so how can a nucleus emit an electron? A neutron first breaks down into a proton and an electron (see Figure 11.7). Then the electron is emitted from the nucleus, while the proton stays inside the nucleus. The proton increases the atomic number by one, thus changing one element into another. An example of beta decay is the decay of thorium-234 to protactinium-234. In this reaction, thorium loses a neutron and gains a proton to become protactinium. The reaction can be represented by this equation: 234 90 Th !234 91 Pa + 0 1 e + Energy The protactinium-234 produced in this reaction is radioactive and decays to another element. The electron produced in the reaction (plus another electron) can combine with an alpha particle to form helium. Problem Solving Problem: Fill in the missing subscript and superscript in this nuclear equation: 131 I 53 !?? Xe + 14 C ? !?7 N + Solution: The subscript is 54, and the superscript is 131. 0 e + Energy 1 You Try It! Problem: Fill in the missing subscript and superscript in this nuclear equation: 0 e + Energy 1 ",text,
L_0718,radioactive decay,T_3540,"In alpha and beta decay, both particles and energy are emitted. In gamma decay, only energy is emitted. Gamma decay occurs when an unstable nucleus gives off gamma rays. Gamma rays, like rays of visible light and X-rays, are waves of energy that travel through space at the speed of light. Gamma rays have the greatest amount of energy of all such waves. By itself, gamma decay doesnt cause one element to change into another, but it is released in nuclear reactions that do. Some of the energy released in alpha and beta decay is in the form of gamma rays. You can learn more about gamma radiation at this URL:  (2:45). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0718,radioactive decay,T_3541,The different types of radiation vary in how far they are able to travel and what they can penetrate (see Figure 11.8 and the URL below). MEDIA Click image to the left or use the URL below. URL:  Alpha particles can travel only a few centimeters through air. They cannot pass through a sheet of paper or thin layer of clothing. They may burn the skin but cannot penetrate tissues beneath the skin. Beta particles can travel up to a meter through air. They can pass through paper and cloth but not through a sheet of aluminum. They can penetrate and damage tissues beneath the skin. Gamma rays can travel thousands of meters through air. They can pass through a sheet of aluminum as well as paper and cloth. They can be stopped only by several centimeters of lead or several meters of concrete. They can penetrate and damage organs deep inside the body. ,text,
L_0718,radioactive decay,T_3542,"A radioactive isotope decays at a certain constant rate. The rate is measured in a unit called the half-life. This is the length of time it takes for half of a given amount of the isotope to decay. The concept of half-life is illustrated in Figure 11.9 for the beta decay of phosphorus-32 to sulfur-32. The half-life of this radioisotope is 14 days. After 14 days, half of the original amount of phosphorus-32 has decayed. After another 14 days, half of the remaining amount (or one-quarter of the original amount) has decayed, and so on. Different radioactive isotopes vary greatly in their rate of decay. As you can see from the examples in Table 11.1, the half-life of a radioisotope can be as short as a split second or as long as several billion years. You can simulate radioactive decay of radioisotopes with different half-lives at the URL below. Some radioisotopes decay much more quickly than others. Isotope Uranium-238 Potassium-40 Carbon-14 Hydrogen-3 Radon-222 Polonium-214 Half-life 4.47 billion years 1.28 billion years 5,730 years 12.3 years 3.82 days 0.00016 seconds Problem Solving Problem: If you had a gram of carbon-14, how many years would it take for radioactive decay to reduce it to one-quarter of a gram? Solution: One gram would decay to one-quarter of a gram in 2 half-lives years. 1 2 12 = 1 4 , or 2  5,730 years = 11,460 You Try It! Problem: What fraction of a given amount of hydrogen-3 would be left after 36.9 years of decay? ",text,
L_0718,radioactive decay,T_3543,Radioactive isotopes can be used to estimate the ages of fossils and rocks. The method is called radioactive dating. Carbon-14 dating is an example of radioactive dating. It is illustrated in the video at this URL:  MEDIA Click image to the left or use the URL below. URL: ,text,
L_0718,radioactive decay,T_3544,"Carbon-14 forms naturally in Earths atmosphere when cosmic rays strike atoms of nitrogen-14. Living things take in and use carbon-14, just as they do carbon-12. The carbon-14 in living things gradually decays to nitrogen-14. However, it is constantly replaced because living things keep taking in carbon-14. As a result, there is a fixed ratio of carbon-14 to carbon-12 in organisms as long as they are alive. This is illustrated in the top part of Figure 11.10. After organisms die, the carbon-14 they already contain continues to decay, but it is no longer replaced (see bottom part of Figure 11.10). Therefore, the carbon-14 in a dead organism constantly declines at a fixed rate equal to the half-life of carbon-14. Half of the remaining carbon-14 decays every 5,730 years. If you measure how much carbon- 14 is left in a fossil, you can determine how many half-lives (and how many years) have passed since the organism died. ",text,
L_0718,radioactive decay,T_3545,"Carbon-14 has a relatively short half-life (see Table 11.1). After about 50,000 years, too little carbon-14 is left in a fossil to be measured. Therefore, carbon-14 dating can only be used to date fossils that are less than 50,000 years old. Radioisotopes with a longer half-life, such as potassium-40, must be used to date older fossils and rocks. ",text,
L_0719,nuclear energy,T_3546,"Nuclear fission is the splitting of the nucleus of an atom into two smaller nuclei. This type of reaction releases a great deal of energy from a very small amount of matter. For example, nuclear fission of a tiny pellet of uranium-235, like the one pictured in Figure 11.11, can release as much energy as burning 1,000 kilograms of coal! Nuclear fission of uranium-235 can be represented by this equation: 235 92 U + 1 141 Neutron !92 36 Kr + 56 Ba + 3 Neutrons + Energy As shown in Figure 11.12, the reaction begins when a nucleus of uranium-235 absorbs a neutron. This can happen naturally or when a neutron is deliberately crashed into a uranium nucleus in a nuclear power plant. In either case, the nucleus of uranium becomes very unstable and splits in two. In this example, it forms krypton-92 and barium-141. The reaction also releases three neutrons and a great deal of energy. ",text,
L_0719,nuclear energy,T_3547,"The neutrons released in this nuclear fission reaction may be captured by other uranium nuclei and cause them to fission as well. This can start a nuclear chain reaction (see Figure 11.13). In a chain reaction, one fission reaction leads to others, which lead to others, and so on. A nuclear chain reaction is similar to a pile of wood burning. If you start one piece of wood burning, enough heat is produced by the burning wood to start the rest of the pile burning without any further help from you. You can see another example of a chain reaction at this URL: ",text,
L_0719,nuclear energy,T_3547,"The neutrons released in this nuclear fission reaction may be captured by other uranium nuclei and cause them to fission as well. This can start a nuclear chain reaction (see Figure 11.13). In a chain reaction, one fission reaction leads to others, which lead to others, and so on. A nuclear chain reaction is similar to a pile of wood burning. If you start one piece of wood burning, enough heat is produced by the burning wood to start the rest of the pile burning without any further help from you. You can see another example of a chain reaction at this URL: ",text,
L_0719,nuclear energy,T_3547,"The neutrons released in this nuclear fission reaction may be captured by other uranium nuclei and cause them to fission as well. This can start a nuclear chain reaction (see Figure 11.13). In a chain reaction, one fission reaction leads to others, which lead to others, and so on. A nuclear chain reaction is similar to a pile of wood burning. If you start one piece of wood burning, enough heat is produced by the burning wood to start the rest of the pile burning without any further help from you. You can see another example of a chain reaction at this URL: ",text,
L_0719,nuclear energy,T_3548,"If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb. If a nuclear chain reaction is controlled, it produces energy more slowly. This is what occurs in a nuclear power plant. The reaction may be controlled by inserting rods of material that do not undergo fission into the core of fissioning material (see Figure 11.14). The radiation from the controlled fission is used to heat water and turn it to steam. The steam is under pressure and causes a turbine to spin. The spinning turbine runs a generator, which produces electricity. ",text,
L_0719,nuclear energy,T_3549,"In the U.S., the majority of electricity is produced by burning coal or other fossil fuels. This causes air pollution, acid rain, and global warming. Fossil fuels are also limited and may eventually run out. Like fossil fuels, radioactive elements are limited. In fact, they are relatively rare, so they could run out sooner rather than later. On the other hand, nuclear fission does not release air pollution or cause the other environmental problems associated with burning fossil fuels. This is the major advantage of using nuclear fission as a source of energy. The main concern over the use of nuclear fission is the risk of radiation. Accidents at nuclear power plants can release harmful radiation that endangers people and other living things. Even without accidents, the used fuel that is left after nuclear fission reactions is still radioactive and very dangerous. It takes thousands of years for it to decay until it no longer releases harmful radiation. Therefore, used fuel must be stored securely to people and other living things. You can learn more about the problem of radioactive waste at this URL: ",text,
L_0719,nuclear energy,T_3550,"Nuclear fusion is the opposite of nuclear fission. In fusion, two or more small nuclei combine to form a single, larger nucleus. An example is shown in Figure 11.15. In this example, two hydrogen nuclei fuse to form a helium nucleus. A neutron and a great deal of energy are also released. In fact, fusion releases even more energy than fission does. ",text,
L_0719,nuclear energy,T_3551,"Nuclear fusion of hydrogen to form helium occurs naturally in the sun and other stars. It takes place only at extremely high temperatures. Thats because a great deal of energy is needed to overcome the force of repulsion between positively charged nuclei. The suns energy comes from fusion in its core, where temperatures reach millions of Kelvin (see Figure 11.16). ",text,
L_0719,nuclear energy,T_3552,"Scientists are searching for ways to create controlled nuclear fusion reactions on Earth. Their goal is develop nuclear fusion power plants, where the energy from fusion of hydrogen nuclei can be converted to electricity. How this might work is shown in Figure 11.17. The use of nuclear fusion for energy has several pros. Unlike nuclear fission, which involves dangerous radioiso- topes, nuclear fusion involves hydrogen and helium. These elements are harmless. Hydrogen is also very plentiful. There is a huge amount of hydrogen in ocean water. The hydrogen in just a gallon of water could produce as much energy by nuclear fusion as burning 1,140 liters (300 gallons) of gasoline! The hydrogen in the oceans would generate enough energy to supply all the worlds people for a very long time. Unfortunately, using energy from nuclear fusion is far from a reality. Scientists are a long way from developing the necessary technology. One problem is raising temperatures high enough for fusion to take place. Another problem is that matter this hot exists only in the plasma state. There are no known materials that can contain plasma, although a magnet might be able to do it. Thats because plasma consists of ions and responds to magnetism. You can learn more about research on nuclear fusion at the URL below. ",text,
L_0719,nuclear energy,T_3552,"Scientists are searching for ways to create controlled nuclear fusion reactions on Earth. Their goal is develop nuclear fusion power plants, where the energy from fusion of hydrogen nuclei can be converted to electricity. How this might work is shown in Figure 11.17. The use of nuclear fusion for energy has several pros. Unlike nuclear fission, which involves dangerous radioiso- topes, nuclear fusion involves hydrogen and helium. These elements are harmless. Hydrogen is also very plentiful. There is a huge amount of hydrogen in ocean water. The hydrogen in just a gallon of water could produce as much energy by nuclear fusion as burning 1,140 liters (300 gallons) of gasoline! The hydrogen in the oceans would generate enough energy to supply all the worlds people for a very long time. Unfortunately, using energy from nuclear fusion is far from a reality. Scientists are a long way from developing the necessary technology. One problem is raising temperatures high enough for fusion to take place. Another problem is that matter this hot exists only in the plasma state. There are no known materials that can contain plasma, although a magnet might be able to do it. Thats because plasma consists of ions and responds to magnetism. You can learn more about research on nuclear fusion at the URL below. ",text,
L_0719,nuclear energy,T_3553,"Probably the most famous equation in the world is E = mc2 . You may have heard of it. You may have even seen it on a tee shirt or coffee mug. Its a simple equation that was derived in 1905 by the physicist Albert Einstein (see Figure 11.18). Although the equation is simple, it is incredibly important. It changed how scientists view two of the most basic concepts in science: matter and energy. The equation shows that matter and energy are two forms of the same thing. It also shows how matter and energy are related. In addition, Einsteins equation explains why nuclear fission and nuclear fusion produce so much energy. You can listen to a recording of Einstein explaining his famous equation at this URL: ",text,
L_0719,nuclear energy,T_3554,"In Einsteins equation, the variable E stands for energy and the variable m stands for mass. The c in the equation is a constant. It stands for the speed of light. The speed of light is 300,000 kilometers (186,000 miles) per second, so c2 is a very big number, no matter what units are used to measure it. Einsteins equation means that the energy in a given amount of matter is equal to its mass times the square of the speed of light. Thats a huge amount of energy from even a tiny amount of mass. Suppose, for example, that you have 1 gram of matter. Thats about the mass of a paperclip. Multiplying that mass by the square of the speed of light yields enough energy to power 3,600 homes for a year! ",text,
L_0719,nuclear energy,T_3555,"When the nucleus of a radioisotope undergoes fission or fusion, it loses a tiny amount of mass. What happens to the lost mass? It isnt really lost at all. It is converted to energy. How much energy? E = mc2 . The change in mass is tiny, but it results in a great deal of energy. What about the laws of conservation of mass and conservation of energy? Do they not apply to nuclear reactions? We dont need to throw out these laws. Instead, we just need to combine them. It is more correct to say that the sum of mass and energy is always conserved in a nuclear reaction. Mass may change to energy, but the amount of mass and energy combined remains the same. ",text,
L_0720,distance and direction,T_3556,"Assume that a school bus, like the one in Figure 12.2, passes by as you stand on the sidewalk. Its obvious to you that the bus is moving. It is moving relative to you and the trees across the street. But what about to the children inside the bus? They arent moving relative to each other. If they look only at the other children sitting near them, they will not appear to be moving. They may only be able to tell that the bus is moving by looking out the window and seeing you and the trees whizzing by. This example shows that how we perceive motion depends on our frame of reference. Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving. What is your frame of reference if you are standing on the sidewalk and see the bus go by? How can you tell the bus is moving? The video at the URL below illustrates other examples of how frame of reference is related to motion. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0720,distance and direction,T_3556,"Assume that a school bus, like the one in Figure 12.2, passes by as you stand on the sidewalk. Its obvious to you that the bus is moving. It is moving relative to you and the trees across the street. But what about to the children inside the bus? They arent moving relative to each other. If they look only at the other children sitting near them, they will not appear to be moving. They may only be able to tell that the bus is moving by looking out the window and seeing you and the trees whizzing by. This example shows that how we perceive motion depends on our frame of reference. Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving. What is your frame of reference if you are standing on the sidewalk and see the bus go by? How can you tell the bus is moving? The video at the URL below illustrates other examples of how frame of reference is related to motion. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0720,distance and direction,T_3557,"Did you ever go to a track meet like the one pictured in Figure 12.3? Running events in track include 100-meter sprints and 2000-meter races. Races are named for their distance. Distance is the length of the route between two points. The length of the route in a race is the distance between the starting and finishing lines. In a 100-meter sprint, for example, the distance is 100 meters. ",text,
L_0720,distance and direction,T_3558,"The SI unit for distance is the meter (1 m = 3.28 ft). Short distances may be measured in centimeters (1 cm = 0.01 m). Long distances may be measured in kilometers (1 km = 1000 m). For example, you might measure the distance a frogs tongue moves in centimeters and the distance a cheetah moves in kilometers. ",text,
L_0720,distance and direction,T_3559,Maps can often be used to measure distance. Look at the map in Figure 12.4. Find Mias house and the school. You can use the map key to directly measure the distance between these two points. The distance is 2 kilometers. Measure it yourself to see if you agree. ,text,
L_0720,distance and direction,T_3560,"Things dont always move in straight lines like the route from Mias house to the school. Sometimes they change direction as they move. For example, the route from Mias house to the post office changes from west to north at the school (see Figure 12.4). To find the total distance of a route that changes direction, you must add up the distances traveled in each direction. From Mias house to the school, for example, the distance is 2 kilometers. From the school to the post office, the distance is 1 kilometer. Therefore, the total distance from Mias house to the post office is 3 kilometers. You Try It! Problem: What is the distance from the post office to the park in Figure 12.4? Direction is just as important as distance in describing motion. For example, if Mia told a friend how to reach the post office from her house, she couldnt just say, ""go 3 kilometers."" The friend might end up at the park instead of the post office. Mia would have to be more specific. She could say, ""go west for 2 kilometers and then go north for 1 kilometer."" When both distance and direction are considered, motion is a vector. A vector is a quantity that includes both size and direction. A vector is represented by an arrow. The length of the arrow represents distance. The way the arrow points shows direction. The red arrows in Figure 12.4 are vectors for Mias route to the school and post office. If you want to learn more about vectors, watch the videos at these URLs:  (5:27) MEDIA Click image to the left or use the URL below. URL:  You Try It! Problem: Draw vectors to represent the route from the post office to the park in Figure 12.4. ",text,
L_0721,speed and velocity,T_3561,"Speed is an important aspect of motion. It is a measure of how fast or slow something moves. It depends on how far something travels and how long it takes to travel that far. Speed can be calculated using this general formula: speed = distance time A familiar example is the speed of a car. In the U.S., this is usually expressed in miles per hour (see Figure 12.6). If your family makes a car trip that covers 120 miles and takes 3 hours, then the cars speed is: speed = 120 mi = 40 mi/h 3h The speed of a car may also be expressed in kilometers per hour (km/h). The SI unit for speed is meters per second (m/s). ",text,
L_0721,speed and velocity,T_3562,"When you travel by car, you usually dont move at a constant speed. Instead you go faster or slower depending on speed limits, traffic, traffic lights, and many other factors. For example, you might travel 65 miles per hour on a highway but only 20 miles per hour on a city street (see Figure 12.7). You might come to a complete stop at traffic lights, slow down as you turn corners, and speed up to pass other cars. The speed of a moving car or other object at a given instant is called its instantaneous speed. It may vary from moment to moment, so it is hard to calculate. Its easier to calculate the average speed of a moving object than the instantaneous speed. The average speed is the total distance traveled divided by the total time it took to travel that distance. To calculate the average speed, you can use the general formula for speed that was given above. Suppose, for example, that you took a 75-mile car trip with your family. Your instantaneous speed would vary throughout the trip. If the trip took a total of 1.5 hours, your average speed for the trip would be: average speed = 75 mi = 50 mi/h 1.5 h You can see a video about instantaneous and average speed and how to calculate them at this URL:  MEDIA Click image to the left or use the URL below. URL:  You Try It! Problem: Terri rode her bike very slowly to the top of a big hill. Then she coasted back down the hill at a much faster speed. The distance from the bottom to the top of the hill is 3 kilometers. It took Terri 15 minutes to make the round trip. What was her average speed for the entire trip? ",text,
L_0721,speed and velocity,T_3563,The motion of an object can be represented by a distance-time graph like the one in Figure 12.8. A distance-time graph shows how the distance from the starting point changes over time. The graph in Figure 12.8 represents a bike trip. The trip began at 7:30 AM (A) and ended at 12:30 PM (F). The rider traveled from the starting point to a destination and then returned to the starting point again. ,text,
L_0721,speed and velocity,T_3564,"In a distance-time graph, the speed of the object is represented by the slope, or steepness, of the graph line. If the line is straight, like the line between A and B in Figure 12.8, then the speed is constant. The average speed can be calculated from the graph. The change in distance (represented by Dd) divided by the change in time (represented by Dt): speed = Dd Dt For example, the speed between A and B in Figure 12.8 is: speed = Dd 20 km 0 km 20 km = = = 20 km/h Dt 8:30 7:30 h 1h If the graph line is horizontal, as it is between B and C, then the slope and the speed are zero: speed = Dd 20 km 20 km 0 km = = = 0 km/h Dt 9:00 8:30 h 0.5 h You Try It! Problem: In Figure 12.8, calculate the speed of the rider between C and D. ",text,
L_0721,speed and velocity,T_3565,"If you know the speed of a moving object, you can also calculate the distance it will travel in a given amount of time. To do so, you would use this version of the general speed formula: distance = speed  time For example, if a car travels at a speed of 60 km/h for 2 hours, then the distance traveled is: distance = 60 km/h  2 h = 120 km You Try It! Problem: If Maria runs at a speed of 2 m/s, how far will she run in 60 seconds? ",text,
L_0721,speed and velocity,T_3566,"Speed tells you only how fast an object is moving. It doesnt tell you the direction the object is moving. The measure of both speed and direction is called velocity. Velocity is a vector that can be represented by an arrow. The length of the arrow represents speed, and the way the arrow points represents direction. The three arrows in Figure directions. They represent objects moving at the same speed but in different directions. Vector C is shorter than vector A or B but points in the same direction as vector A. It represents an object moving at a slower speed than A or B but in the same direction as A. If youre still not sure of the difference between speed and velocity, watch the cartoon at this URL:  (2:10). MEDIA Click image to the left or use the URL below. URL:  In general, if two objects are moving at the same speed and in the same direction, they have the same velocity. If two objects are moving at the same speed but in different directions (like A and B in Figure 12.9), they have different velocities. If two objects are moving in the same direction but at a different speed (like A and C in Figure 12.9), they have different velocities. A moving object that changes direction also has a different velocity, even if its speed does not change. ",text,
L_0722,acceleration,T_3567,"Acceleration is a measure of the change in velocity of a moving object. It shows how quickly velocity changes. Acceleration may reflect a change in speed, a change in direction, or both. Because acceleration includes both a size (speed) and direction, it is a vector. People commonly think of acceleration as an increase in speed, but a decrease in speed is also acceleration. In this case, acceleration is negative. Negative acceleration may be called deceleration. A change in direction without a change in speed is acceleration as well. You can see several examples of acceleration in Figure 12.11. If you are accelerating, you may be able to feel the change in velocity. This is true whether you change your speed or your direction. Think about what it feels like to ride in a car. As the car speeds up, you feel as though you are being pressed against the seat. The opposite occurs when the car slows down, especially if the change in speed is ",text,
L_0722,acceleration,T_3568,"Calculating acceleration is complicated if both speed and direction are changing. Its easier to calculate acceleration when only speed is changing. To calculate acceleration without a change in direction, you just divide the change in velocity (represented by Dv) by the change in time (represented by Dt). The formula for acceleration in this case is: Acceleration = Dv Dt Consider this example. The cyclist in Figure 12.12 speeds up as he goes downhill on this straight trail. His velocity changes from 1 meter per second at the top of the hill to 6 meters per second at the bottom. If it takes 5 seconds for him to reach the bottom, what is his acceleration, on average, as he flies down the hill? Acceleration = Dv 6 m/s 1 m/s 5 m/s 1 m/s = = = = 1 m/s2 Dt 5s 5s 1m In words, this means that for each second the cyclist travels downhill, his velocity increases by 1 meter per second (on average). The answer to this problem is expressed in the SI unit for acceleration: m/s2 (""meters per second squared""). You Try It! Problem: Tranh slowed his skateboard as he approached the street. He went from 8 m/s to 2 m/s in a period of 3 seconds. What was his acceleration? ",text,
L_0722,acceleration,T_3569,"The acceleration of an object can be represented by a velocity-time graph like the one in Figure 12.13. A velocity- time graph shows how velocity changes over time. It is similar to a distance-time graph except the y axis represents velocity instead of distance. The graph in Figure 12.13 represents the velocity of a sprinter on a straight track. The runner speeds up for the first 4 seconds of the race, then runs at a constant velocity for the next 3 seconds, and finally slows to a stop during the last 3 seconds of the race. In a velocity-time graph, acceleration is represented by the slope of the graph line. If the line slopes upward, like the line between A and B in Figure 12.13, velocity is increasing, so acceleration is positive. If the line is horizontal, as it is between B and C, velocity is not changing, so acceleration is zero. If the line slopes downward, like the line between C and D, velocity is decreasing, so acceleration is negative. You can review the concept of acceleration as well as other chapter concepts by watching the musical video at this URL: ",text,
L_0723,what is force,T_3570,"Force is defined as a push or a pull acting on an object. Examples of forces include friction and gravity. Both are covered in detail later in this chapter. Another example of force is applied force. It occurs when a person or thing applies force to an object, like the girl pushing the swing in Figure 13.1. The force of the push causes the swing to move. ",text,
L_0723,what is force,T_3571,"Force is a vector because it has both size and direction. For example, the girl in Figure 13.1 is pushing the swing away from herself. Thats the direction of the force. She can give the swing a strong push or a weak push. Thats the size, or strength, of the force. Like other vectors, forces can be represented with arrows. Figure 13.2 shows some examples. The length of each arrow represents the strength of the force, and the way the arrow points represents the direction of the force. How could you use an arrow to represent the girls push on the swing in Figure 13.1? ",text,
L_0723,what is force,T_3571,"Force is a vector because it has both size and direction. For example, the girl in Figure 13.1 is pushing the swing away from herself. Thats the direction of the force. She can give the swing a strong push or a weak push. Thats the size, or strength, of the force. Like other vectors, forces can be represented with arrows. Figure 13.2 shows some examples. The length of each arrow represents the strength of the force, and the way the arrow points represents the direction of the force. How could you use an arrow to represent the girls push on the swing in Figure 13.1? ",text,
L_0723,what is force,T_3572,"The SI unit of force is the newton (N). One newton is the amount of force that causes a mass of 1 kilogram to accelerate at 1 m/s2 . Thus, the newton can also be expressed as kgm/s2 . The newton was named for the scientist Sir Isaac Newton, who is famous for his law of gravity. Youll learn more about Sir Isaac Newton later in the chapter. ",text,
L_0723,what is force,T_3573,"More than one force may act on an object at the same time. In fact, just about all objects on Earth have at least two forces acting on them at all times. One force is gravity, which pulls objects down toward the center of Earth. The other force is an upward force that may be provided by the ground or other surface. Consider the example in Figure 13.3. A book is resting on a table. Gravity pulls the book downward with a force of 20 newtons. At the same time, the table pushes the book upward with a force of 20 newtons. The combined forces acting on the book  or any other object  are called the net force. This is the overall force acting on an object that takes into account all of the individual forces acting on the object. You can learn more about the concept of net force at this URL:  . ",text,
L_0723,what is force,T_3574,"When two forces act on an object in opposite directions, like the book on the table, the net force is equal to the difference between the two forces. In other words, one force is subtracted from the other to calculate the net force. If the opposing forces are equal in strength, the net force is zero. Thats what happens with the book on the table. The upward force minus the downward force equals zero (20 N up - 20 N down = 0 N). Because the forces on the book are balanced, the book remains on the table and doesnt move. In addition to these downward and upward forces, which generally cancel each other out, forces may push or pull an object in other directions. Look at the dogs playing tug-of-war in Figure 13.4. One dog is pulling on the rope with a force of 10 newtons to the left. The other dog is pulling on the rope with a force of 12 newtons to the right. These opposing forces are not equal in strength, so they are unbalanced. When opposing forces are unbalanced, the net force is greater than zero. The net force on the rope is 2 newtons to the right, so the rope will move to the right. ",text,
L_0723,what is force,T_3575,"Two forces may act on an object in the same direction. You can see an example of this in Figure 13.5. After the man on the left lifts up the couch, he will push the couch to the right with a force of 25 newtons. At the same time, the man to the right is pulling the couch to the right with a force of 20 newtons. When two forces act in the same direction, the net force is equal to the sum of the forces. This always results in a stronger force than either of the individual forces alone. In this case, the net force on the couch is 45 newtons to the right, so the couch will move to the right. You Try It! Problem: The boys in the drawing above are about to kick the soccer ball in opposite directions. What will be the net force on the ball? In which direction will the ball move? ",text,
L_0723,what is force,T_3575,"Two forces may act on an object in the same direction. You can see an example of this in Figure 13.5. After the man on the left lifts up the couch, he will push the couch to the right with a force of 25 newtons. At the same time, the man to the right is pulling the couch to the right with a force of 20 newtons. When two forces act in the same direction, the net force is equal to the sum of the forces. This always results in a stronger force than either of the individual forces alone. In this case, the net force on the couch is 45 newtons to the right, so the couch will move to the right. You Try It! Problem: The boys in the drawing above are about to kick the soccer ball in opposite directions. What will be the net force on the ball? In which direction will the ball move? ",text,
L_0724,friction,T_3576,"Friction is a force that opposes motion between two surfaces that are touching. Friction can work for or against us. For example, putting sand on an icy sidewalk increases friction so you are less likely to slip. On the other hand, too much friction between moving parts in a car engine can cause the parts to wear out. Other examples of friction are illustrated in Figure 13.7. You can see an animation showing how friction opposes motion at this URL: http://w ",text,
L_0724,friction,T_3577,"Friction occurs because no surface is perfectly smooth. Even surfaces that look smooth to the unaided eye appear rough or bumpy when viewed under a microscope. Look at the metal surfaces in Figure 13.8. The metal foil is so smooth that it is shiny. However, when highly magnified, the surface of metal appears to be very bumpy. All those mountains and valleys catch and grab the mountains and valleys of any other surface that contacts the metal. This creates friction. ",text,
L_0724,friction,T_3578,Rougher surfaces have more friction between them than smoother surfaces. Thats why we put sand on icy sidewalks and roads. The blades of skates are much smoother than the soles of shoes. Thats why you cant slide as far across ice with shoes as you can with skates (see Figure 13.9). The rougher surface of shoes causes more friction and slows you down. Heavier objects also have more friction because they press together with greater force. Did you ever try to push boxes or furniture across the floor? Its harder to overcome friction between heavier objects and the floor than it is between lighter objects and the floor. ,text,
L_0724,friction,T_3579,"You know that friction produces heat. Thats why rubbing your hands together makes them warmer. But do you know why the rubbing produces heat? Friction causes the molecules on rubbing surfaces to move faster, so they have more heat energy. Heat from friction can be useful. It not only warms your hands. It also lets you light a match (see Figure 13.10). On the other hand, heat from friction can be a problem inside a car engine. It can cause the car to overheat. To reduce friction, oil is added to the engine. Oil coats the surfaces of moving parts and makes them slippery so there is less friction. ",text,
L_0724,friction,T_3580,"There are different ways you could move heavy boxes. You could pick them up and carry them. You could slide them across the floor. Or you could put them on a dolly like the one in Figure 13.11 and roll them across the floor. This example illustrates three types of friction: static friction, sliding friction, and rolling friction. Another type of friction is fluid friction. All four types of friction are described below. In each type, friction works opposite the direction of the force applied to a move an object. You can see a video demonstration of the different types of friction at this URL:  (1:07). ",text,
L_0724,friction,T_3581,"Static friction acts on objects when they are resting on a surface. For example, if you are walking on a sidewalk, there is static friction between your shoes and the concrete each time you put down your foot (see Figure 13.12). Without this static friction, your feet would slip out from under you, making it difficult to walk. Static friction also allows you to sit in a chair without sliding to the floor. Can you think of other examples of static friction? ",text,
L_0724,friction,T_3582,"Sliding friction is friction that acts on objects when they are sliding over a surface. Sliding friction is weaker than static friction. Thats why its easier to slide a piece of furniture over the floor after you start it moving than it is to get it moving in the first place. Sliding friction can be useful. For example, you use sliding friction when you write with a pencil and when you put on your bikes brakes. ",text,
L_0724,friction,T_3583,"Rolling friction is friction that acts on objects when they are rolling over a surface. Rolling friction is much weaker than sliding friction or static friction. This explains why it is much easier to move boxes on a wheeled dolly than by carrying or sliding them. It also explains why most forms of ground transportation use wheels, including cars, 4-wheelers, bicycles, roller skates, and skateboards. Ball bearings are another use of rolling friction (see Figure ",text,
L_0724,friction,T_3584,"Fluid friction is friction that acts on objects that are moving through a fluid. A fluid is a substance that can flow and take the shape of its container. Fluids include liquids and gases. If youve ever tried to push your open hand through the water in a tub or pool, then youve experienced fluid friction between your hand and the water. When a skydiver is falling toward Earth with a parachute, fluid friction between the parachute and the air slows the descent (see Figure 13.14). Fluid pressure with the air is called air resistance. The faster or larger a moving object is, the greater is the fluid friction resisting its motion. The very large surface area of a parachute, for example, has greater air resistance than a skydivers body. ",text,
L_0725,gravity,T_3585,"Gravity has traditionally been defined as a force of attraction between two masses. According to this conception of gravity, anything that has mass, no matter how small, exerts gravity on other matter. The effect of gravity is that objects exert a pull on other objects. Unlike friction, which acts only between objects that are touching, gravity also acts between objects that are not touching. In fact, gravity can act over very long distances. ",text,
L_0725,gravity,T_3586,"You are already very familiar with Earths gravity. It constantly pulls you toward the center of the planet. It prevents you and everything else on Earth from being flung out into space as the planet spins on its axis. It also pulls objects above the surface, from meteors to skydivers, down to the ground. Gravity between Earth and the moon and between Earth and artificial satellites keeps all these objects circling around Earth. Gravity also keeps Earth moving around the sun. ",text,
L_0725,gravity,T_3587,"Weight measures the force of gravity pulling on an object. Because weight measures force, the SI unit for weight is the newton (N). On Earth, a mass of 1 kilogram has a weight of about 10 newtons because of the pull of Earths gravity On the moon, which has less gravity, the same mass would weigh less. Weight is measured with a scale, like the spring scale in Figure 13.16. The scale measures the force with which gravity pulls an object downward. ",text,
L_0725,gravity,T_3588,"People have known about gravity for thousands of years. After all, they constantly experienced gravity in their daily lives. They knew that things always fall toward the ground. However, it wasnt until Sir Isaac Newton developed his law of gravity in the late 1600s that people really began to understand gravity. Newton is pictured in Figure 13.17. ",text,
L_0725,gravity,T_3589,"Newton was the first one to suggest that gravity is universal and affects all objects in the universe. Thats why his law of gravity is called the law of universal gravitation. Universal gravitation means that the force that causes an apple to fall from a tree to the ground is the same force that causes the moon to keep moving around Earth. Universal gravitation also means that while Earth exerts a pull on you, you exert a pull on Earth. In fact, there is gravity between you and every mass around you  your desk, your book, your pen. Even tiny molecules of gas are attracted to one another by the force of gravity. Newtons law had a huge impact on how people thought about the universe. It explains the motion of objects not only on Earth but in outer space as well. You can learn more about Newtons law of gravity in the video at this URL: ",text,
L_0725,gravity,T_3590,"Newtons law also states that the strength of gravity between any two objects depends on two factors: the masses of the objects and the distance between them. Objects with greater mass have a stronger force of gravity. For example, because Earth is so massive, it attracts you and your desk more strongly than you and your desk attract each other. Thats why you and the desk remain in place on the floor rather than moving toward one another. Objects that are closer together have a stronger force of gravity. For example, the moon is closer to Earth than it is to the more massive sun, so the force of gravity is greater between the moon and Earth than between the moon and the sun. Thats why the moon circles around Earth rather than the sun. This is illustrated in Figure You can apply these relationships among mass, distance, and gravity by designing your own roller coaster at this URL:  . ",text,
L_0725,gravity,T_3591,"Newtons idea of gravity can predict the motion of most but not all objects. In the early 1900s, Albert Einstein came up with a theory of gravity that is better at predicting how all objects move. Einstein showed mathematically that gravity is not really a force in the sense that Newton thought. Instead, gravity is a result of the warping, or curving, of space and time. Imagine a bowling ball pressing down on a trampoline. The surface of the trampoline would curve downward instead of being flat. Einstein theorized that Earth and other very massive bodies affect space and time around them in a similar way. This idea is represented in Figure 13.19. According to Einstein, objects curve toward one another because of the curves in space and time, not because they are pulling on each other with a force of attraction as Newton thought. You can see an animation of Einsteins theory of gravity at this URL: http://einstein. theory of gravity, go to this URL: ",text,
L_0725,gravity,T_3591,"Newtons idea of gravity can predict the motion of most but not all objects. In the early 1900s, Albert Einstein came up with a theory of gravity that is better at predicting how all objects move. Einstein showed mathematically that gravity is not really a force in the sense that Newton thought. Instead, gravity is a result of the warping, or curving, of space and time. Imagine a bowling ball pressing down on a trampoline. The surface of the trampoline would curve downward instead of being flat. Einstein theorized that Earth and other very massive bodies affect space and time around them in a similar way. This idea is represented in Figure 13.19. According to Einstein, objects curve toward one another because of the curves in space and time, not because they are pulling on each other with a force of attraction as Newton thought. You can see an animation of Einsteins theory of gravity at this URL: http://einstein. theory of gravity, go to this URL: ",text,
L_0725,gravity,T_3592,Regardless of what gravity is  a force between masses or the result of curves in space and time  the effects of gravity on motion are well known. You already know that gravity causes objects to fall down to the ground. Gravity affects the motion of objects in other ways as well. ,text,
L_0725,gravity,T_3593,"When gravity pulls objects toward the ground, it causes them to accelerate. Acceleration due to gravity equals 9.8 m/s2 . In other words, the velocity at which an object falls toward Earth increases each second by 9.8 m/s. Therefore, after 1 second, an object is falling at a velocity of 9.8 m/s. After 2 seconds, it is falling at a velocity of 19.6 m/s (9.8 m/s  2), and so on. This is illustrated in Figure 13.20. You can compare the acceleration due to gravity on Earth, the moon, and Mars with the interactive animation called ""Freefall"" at this URL: http://jersey.uoregon.edu/vlab/ . You might think that an object with greater mass would accelerate faster than an object with less mass. After all, its greater mass means that it is pulled by a stronger force of gravity. However, a more massive object accelerates at the same rate as a less massive object. The reason? The more massive object is harder to move because of its greater mass. As a result, it ends up moving at the same acceleration as the less massive object. Consider a bowling ball and a basketball. The bowling ball has greater mass than the basketball. However, if you were to drop both balls at the same time from the same distance above the ground, they would reach the ground together. This is true of all falling objects, unless air resistance affects one object more than another. For example, a falling leaf is slowed down by air resistance more than a falling acorn because of the leafs greater surface area. However, if the leaf and acorn were to fall in the absence of air (that is, in a vacuum), they would reach the ground at the same time. ",text,
L_0725,gravity,T_3594,"Earths gravity also affects the acceleration of objects that start out moving horizontally, or parallel to the ground. Look at Figure 13.21. A cannon shoots a cannon ball straight ahead, giving the ball horizontal motion. At the same time, gravity pulls the ball down toward the ground. Both forces acting together cause the ball to move in a curved path. This is called projectile motion. Projectile motion also applies to other moving objects, such as arrows shot from a bow. To hit the bulls eye of a target with an arrow, you actually have to aim for a spot above the bulls eye. Thats because by the time the arrow reaches the target, it has started to curve downward toward the ground. Figure 13.22 shows what happens if you aim at the bulls eye instead of above it. You can access interactive animations of projectile motion at these URLs: http://phet.colorado.edu/en/simulation/projectile-motion http://jersey.uoregon.edu/vlab/ (Select the applet entitled Cannon.) ",text,
L_0725,gravity,T_3595,"The moon moves around Earth in a circular path called an orbit. Why doesnt Earths gravity pull the moon down to the ground instead? The moon has enough forward velocity to partly counter the force of Earths gravity. It constantly falls toward Earth, but it stays far enough away from Earth so that it actually falls around the planet. As a result, the moon keeps orbiting Earth and never crashes into it. The diagram in Figure 13.23 shows how this happens. You can explore gravity and orbital motion in depth with the animation at this URL: http://phet.colorado You can see an animated version of this diagram at: http://en.wikipedia.org/wiki/File:Orbital_motion.gif . ",text,
L_0725,gravity,T_3595,"The moon moves around Earth in a circular path called an orbit. Why doesnt Earths gravity pull the moon down to the ground instead? The moon has enough forward velocity to partly counter the force of Earths gravity. It constantly falls toward Earth, but it stays far enough away from Earth so that it actually falls around the planet. As a result, the moon keeps orbiting Earth and never crashes into it. The diagram in Figure 13.23 shows how this happens. You can explore gravity and orbital motion in depth with the animation at this URL: http://phet.colorado You can see an animated version of this diagram at: http://en.wikipedia.org/wiki/File:Orbital_motion.gif . ",text,
L_0726,elastic force,T_3596,"Something that is elastic can return to its original shape after being stretched or compressed. This property is called elasticity. As you stretch or compress an elastic material, it resists the change in shape. It exerts a counter force in the opposite direction. This force is called elastic force. Elastic force causes the material to spring back to its original shape as soon as the stretching or compressing force is released. You can watch a demonstration of elastic force at this URL:  (3:57). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0726,elastic force,T_3597,"Elastic force can be very useful. You probably use it yourself every day. A few common uses of elastic force are pictured in Figure 13.25. Did you ever use a resistance band like the one in the figure? When you pull on the band, it stretches but doesnt break. The resistance you feel when you pull on it is elastic force. The resistance of the band to stretching is what gives your muscles a workout. After you stop pulling on the band, it returns to its original shape, ready for the next workout. Springs like the ones in Figure 13.26 also have elastic force when they are stretched or compressed. And like stretchy materials, they return to their original shape when the stretching or compressing force is released. Because of these properties, springs are used in scales to measure weight. They also cushion the ride in a car and provide springy support beneath a mattress. Can you think of other uses of springs? ",text,
L_0727,newtons first law,T_3598,"Newtons first law of motion states that an objects motion will not change unless an unbalanced force acts on the object. If the object is at rest, it will stay at rest. If the object is in motion, it will stay in motion and its velocity will remain the same. In other words, neither the direction nor the speed of the object will change as long as the net force acting on it is zero. You can watch a video about Newtons first law at this URL: http://videos.howstuffworks.com/ Look at the pool balls in Figure 14.2. When a pool player pushes the pool stick against the white ball, the white ball is set into motion. Once the white ball is rolling, it rolls all the way across the table and stops moving only after it crashes into the cluster of colored balls. Then, the force of the collision starts the colored balls moving. Some may roll until they bounce off the raised sides of the table. Some may fall down into the holes at the edges of the table. None of these motions will occur, however, unless that initial push of the pool stick is applied. As long as the net force on the balls is zero, they will remain at rest. ",text,
L_0727,newtons first law,T_3599,"Newtons first law of motion is also called the law of inertia. Inertia is the tendency of an object to resist a change in its motion. If an object is already at rest, inertia will keep it at rest. If the object is already moving, inertia will keep it moving. Think about what happens when you are riding in a car that stops suddenly. Your body moves forward on the seat. Why? The brakes stop the car but not your body, so your body keeps moving forward because of inertia. Thats why its important to always wear a seat belt. Inertia also explains the amusement park ride in Figure 14.1. The car keeps changing direction, but the riders keep moving in the same direction as before. They slide to the opposite side of the car as a result. You can see an animation of inertia at this URL: ",text,
L_0727,newtons first law,T_3600,"The inertia of an object depends on its mass. Objects with greater mass also have greater inertia. Think how hard it would be to push a big box full of books, like the one in Figure 14.3. Then think how easy it would be to push the box if it was empty. The full box is harder to move because it has greater mass and therefore greater inertia. ",text,
L_0727,newtons first law,T_3601,"To change the motion of an object, inertia must be overcome by an unbalanced force acting on the object. Until the soccer player kicks the ball in Figure 14.4, the ball remains motionless on the ground. However, when the ball is kicked, the force on it is suddenly unbalanced. The ball starts moving across the field because its inertia has been overcome. ",text,
L_0728,newtons second law,T_3602,"Newton determined that two factors affect the acceleration of an object: the net force acting on the object and the objects mass. The relationships between these two factors and motion make up Newtons second law of motion. This law states that the acceleration of an object equals the net force acting on the object divided by the objects mass. This can be represented by the equation: Net force , or Mass F a= m Acceleration = You can watch a video about how Newtons second law of motion applies to football at this URL: http://science36 ",text,
L_0728,newtons second law,T_3603,"Newtons second law shows that there is a direct relationship between force and acceleration. The greater the force that is applied to an object of a given mass, the more the object will accelerate. For example, doubling the force on the object doubles its acceleration. The relationship between mass and acceleration, on the other hand, is an inverse relationship. The greater the mass of an object, the less it will accelerate when a given force is applied. For example, doubling the mass of an object results in only half as much acceleration for the same amount of force. Consider the example of a batter, like the boy in Figure 14.6. The harder he hits the ball, the greater will be its acceleration. It will travel faster and farther if he hits it with more force. What if the batter hits a baseball and a softball with the same amount of force? The softball will accelerate less than the baseball because the softball has greater mass. As a result, it wont travel as fast or as far as the baseball. ",text,
L_0728,newtons second law,T_3604,"The equation for acceleration given above can be used to calculate the acceleration of an object that is acted on by an unbalanced force. For example, assume you are pushing a large wooden trunk, like the one shown in Figure acceleration of the trunk, substitute these values in the equation for acceleration: a= F 20 N 2N = = m 10 kg kg Recall that one newton (1 N) is the force needed to cause a 1-kilogram mass to accelerate at 1 m/s2 . Therefore, force can also be expressed in the unit kgm/s2 . This way of expressing force can be substituted for newtons in the solution to the problem: a= 2 N 2 kg  m/s2 = = 2 m/s2 kg kg Why are there no kilograms in the final answer to this problem? The kilogram units in the numerator and denominator of the fraction cancel out. As a result, the answer is expressed in the correct units for acceleration: m/s2 . You Try It! Problem: Assume that you add the weights to the trunk in Figure 14.7. If you push the trunk and weights with a force of 20 N, what will be the trunks acceleration? Need more practice? You can find additional problems at this URL: ",text,
L_0728,newtons second law,T_3605,"Newtons second law of motion explains the weight of objects. Weight is a measure of the force of gravity pulling on an object of a given mass. Its the force (F) in the acceleration equation that was introduced above: a= F m This equation can also be written as: F = ma The acceleration due to gravity of an object equals 9.8 m/s2 , so if you know the mass of an object, you can calculate its weight as: F = m  9.8 m/s2 As this equation shows, weight is directly related to mass. As an objects mass increases, so does its weight. For example, if mass doubles, weight doubles as well. You can learn more about weight and acceleration at this URL: Problem Solving Problem: Daisy has a mass of 35 kilograms. How much does she weigh? Solution: Use the formula: F = m  9.8 m/s2 . F = 35 kg  9.8 m/s2 = 343.0 kg  m/s2 = 343.0 N You Try It! Problem: Daisys dad has a mass is 70 kg, which is twice Daisys mass. Predict how much Daisys dad weighs. Then calculate his weight to see if your prediction is correct. Helpful Hints The equation for calculating weight (F = m  a) works only when the correct units of measurement are used. Mass must be in kilograms (kg). Acceleration must be in m/s2 . Weight (F) is expressed in kgm/s2 or in newtons (N). ",text,
L_0729,newtons third law,T_3606,"Newtons third law of motion states that every action has an equal and opposite reaction. This means that forces always act in pairs. First an action occurs, such as the skateboarders pushing together. Then a reaction occurs that is equal in strength to the action but in the opposite direction. In the case of the skateboarders, they move apart, and the distance they move depends on how hard they first pushed together. You can see other examples of actions and reactions in Figure 14.9. You can watch a video about actions and reactions at this URL:  You might think that actions and reactions would cancel each other out like balanced forces do. Balanced forces, which are also equal and opposite, cancel each other out because they act on the same object. Action and reaction forces, in contrast, act on different objects, so they dont cancel each other out and, in fact, often result in motion. For example, in Figure 14.9, the kangaroos action acts on the ground, but the grounds reaction acts on the kangaroo. As a result, the kangaroo jumps away from the ground. One of the action-reaction examples in the Figure 14.9 does not result in motion. Do you know which one it is? ",text,
L_0729,newtons third law,T_3607,"What if a friend asked you to play catch with a bowling ball, like the one pictured in Figure 14.10? Hopefully, you would refuse to play! A bowling ball would be too heavy to catch without risk of injury assuming you could even throw it. Thats because a bowling ball has a lot of mass. This gives it a great deal of momentum. Momentum is a property of a moving object that makes the object hard to stop. It equals the objects mass times its velocity. It can be represented by the equation: Momentum = Mass  Velocity This equation shows that momentum is directly related to both mass and velocity. An object has greater momentum if it has greater mass, greater velocity, or both. For example, a bowling ball has greater momentum than a softball when both are moving at the same velocity because the bowling ball has greater mass. However, a softball moving at a very high velocity say, 100 miles an hour would have greater momentum than a slow-rolling bowling ball. If an object isnt moving at all, it has no momentum. Thats because its velocity is zero, and zero times anything is zero. ",text,
L_0729,newtons third law,T_3608,"Momentum can be calculated by multiplying an objects mass in kilograms (kg) by its velocity in meters per second (m/s). For example, assume that a golf ball has a mass of 0.05 kg. If the ball is traveling at a velocity of 50 m/s, its momentum is: Momentum = 0.05 kg  50 m/s = 2.5 kg  m/s Note that the SI unit for momentum is kgm/s. Problem Solving Problem: What is the momentum of a 40-kg child who is running straight ahead with a velocity of 2 m/s? Solution: The child has momentum of: 40 kg  2 m/s = 80 kgm/s. You Try It! Problem: Which football player has greater momentum? Player A: mass = 60 kg; velocity = 2.5 m/s Player B: mass = 65 kg; velocity = 2.0 m/s ",text,
L_0729,newtons third law,T_3609,"When an action and reaction occur, momentum is transferred from one object to the other. However, the com- bined momentum of the objects remains the same. In other words, momentum is conserved. This is the law of conservation of momentum. Consider the example of a truck colliding with a car, which is illustrated in Figure 14.11. Both vehicles are moving in the same direction before and after the collision, but the truck is moving faster than the car before the collision occurs. During the collision, the truck transfers some of its momentum to the car. After the collision, the truck is moving slower and the car is moving faster than before the collision occurred. Nonetheless, their combined momentum is the same both before and after the collision. You can see an animation showing how momentum is conserved in a head-on collision at this URL:  . ",text,
L_0729,newtons third law,T_3610,"Paul Doherty of the Exploratorium performs a ""sit-down"" lecture on one of Sir Issac Newtons most famous laws. For more information on Newtons laws of motion, see http://science.kqed.org/quest/video/quest-lab-newtons-laws- MEDIA Click image to the left or use the URL below. URL: ",text,
L_0729,newtons third law,T_3611,"At UC Berkeley, a team of undergrads is experimenting with velocity, force, and aerodynamics. But you wont find them in a lab  they work on a baseball diamond, throwing fast balls, sliders and curve balls. QUEST discovers how the principles of physics can make the difference between a strike and a home run. For more information on the physics of baseball, see http://science.kqed.org/quest/video/out-of-the-park-the-physics-of-baseball/ . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0731,buoyancy of fluids,T_3623,Buoyancy is the ability of a fluid to exert an upward force on any object placed in the fluid. This upward force is called buoyant force. ,text,
L_0731,buoyancy of fluids,T_3624,"What explains buoyant force? Recall from the earlier lesson ""Pressure of Fluids"" that a fluid exerts pressure in all directions but the pressure is greater at greater depth. Therefore, the fluid below an object exerts greater force on the object than the fluid above the object. This is illustrated in Figure 15.12. Buoyant force explains why objects may float in water. No doubt youve noticed, however, that some objects do not float in water. If buoyant force applies to all objects in fluids, why do some objects sink instead of float? The answer has to do with their weight. ",text,
L_0731,buoyancy of fluids,T_3625,"Weight is a measure of the force of gravity pulling down on an object. Buoyant force pushes up on an object. Weight and buoyant force together determine whether an object sinks or floats. This is illustrated in Figure 15.13. If an objects weight is the same as the buoyant force acting on the object, then the object floats. This is the example on the left in Figure 15.13. If an objects weight is greater than the buoyant force acting on the object, then the object sinks. This is the example on the right in Figure 15.13. Because of buoyant force, objects seem lighter in water. You may have noticed this when you went swimming and could easily pick up a friend or sibling under the water. Some of the persons weight was countered by the buoyant force of the water. ",text,
L_0731,buoyancy of fluids,T_3626,"Density, or the amount of mass in a given volume, is also related to buoyancy. Thats because density affects weight. A given volume of a denser substance is heavier than the same volume of a less dense substance. For example, ice is less dense than liquid water. This explains why ice cubes float in a glass of water. This and other examples of density and buoyant force are illustrated in Figure 15.14 and in the video at this URL:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0731,buoyancy of fluids,T_3627,"Did you ever notice that when you get into a bathtub of water the level of the water rises? More than 2200 years ago, a Greek mathematician named Archimedes noticed the same thing. He observed that both a body and the water in a tub cant occupy the same space at the same time. As a result, some of the water is displaced, or moved out of the way. How much water is displaced? Archimedes determined that the volume of displaced water equals the volume of the submerged object. So more water is displaced by a bigger body than a smaller one. What does displacement have to do with buoyant force? Everything! Archimedes discovered that the buoyant force acting on an object in a fluid equals the weight of the fluid displaced by the object. This is known as Archimedes law (or Archimedes Principle). Archimedes law explains why some objects float in fluids even though they are very heavy. Remember the oil tanker that opened this chapter? It is extremely heavy, yet it stays afloat. If a steel ball with the same weight as the ship were put into water, it would sink to the bottom (see Figure 15.15). Thats because the volume of water displaced by the steel ball weighs less than the ball. As a result, the buoyant force is not as great as the force of gravity acting on the ball. The design of the ships hull, on the other hand, causes it to displace much more water than the ball. In fact, the weight of the displaced water is greater than the weight of the ship, so the buoyant force is greater than the force of gravity acting on the ship. As a result, the ship floats. You can check your understanding of Archimedes law by doing the brainteaser at this URL:  . For an entertaining video presentation of Archimedes law, go to this URL: http://videos.howstuffworks.com/disc ",text,
L_0732,work,T_3628,"Work is defined differently in physics than in everyday language. In physics, work means the use of force to move an object. The teen who is playing tennis in Figure 16.1 is using force to move her tennis racket, so she is doing work. The teen who is studying isnt moving anything, so she is not doing work. Not all force that is used to move an object does work. For work to be done, the force must be applied in the same direction that the object moves. If a force is applied in a different direction than the object moves, no work is done. Figure 16.2 illustrates this point. The stick person applies an upward force on the box when raising it from the ground to chest height. Work is done because the force is applied in the same direction as the box is moving. However, as the stick person walks from left to right while holding the box at chest height, no more work is done by the persons arms holding the box up. Thats because the force supporting the box acts in a different direction than the box is moving. A small amount of work in the horizontal direction is performed when the person is accelerating during the first step of the walk across the room. But other than that, there is no work, because there is no net force acting on the box horizontally. ",text,
L_0732,work,T_3629,"Work is directly related to both the force applied to an object and the distance the object moves. It can be represented by the equation: Work = Force  Distance This equation shows that the greater the force that is used to move an object or the farther the object is moved, the more work that is done. You can see a short video introduction to work as the product of force and distance at this link:  . To see the effects of force and distance on work, compare the weight lifters in Figure 16.3. The two weight lifters on the left are lifting the same amount of weight, but the bottom weight lifter is lifting the weight a longer distance. Therefore, this weight lifter is doing more work. The two weight lifters on the bottom right are both lifting the weight the same distance, but the weight lifter on the left is lifting a heavier weight. Therefore, this weight lifter is doing more work. ",text,
L_0732,work,T_3630,"The equation for work given above can be used to calculate the amount of work that is done if force and distance are known. For example, assume that one of the weight lifters in Figure 16.2 lifts a weight of 400 newtons over his head to a height of 2.2 meters off the ground. The amount of work he does is: Work = 400 N  2.2 m = 880 N  m Notice that the unit for work is the newton  meter. This is the SI unit for work, also called the joule (J). One joule equals the amount of work that is done when 1 newton of force moves an object over a distance of 1 meter. Problem Solving Problem: Todd pushed a 500 N box 4 meters across the floor. How much work did he do? Solution: Use the equation Work = Force  Distance. Work = 500 N  4 m = 2000 N  m, or 2000 J You Try It! Problem: Lara lifted a 100 N box 1.5 meters above the floor. How much work did she do? ",text,
L_0732,work,T_3631,"Did you ever rake leaves, like the woman in Figure 16.4? It can take a long time to do all that work. But if you use an electric leaf blower, like the man in the figure, the job gets done much sooner. Both the leaf blower and the rake do the work of removing leaves from the yard, but the leaf blower has more power. Thats why it can do the same amount of work in less time. ",text,
L_0732,work,T_3632,"Power is a measure of the amount of work that can be done in a given amount of time. Power can be represented by the equation: Power = Work Time In this equation, work is measured in joules and time is measured in seconds, so power is expressed in joules per second (J/s). This is the SI unit for work, also known as the watt (W). A watt equals 1 joule of work per second. The watt is named for James Watt, a Scottish inventor you will read about below. You may already be familiar with watts. Thats because light bulbs and small appliances such as hair dryers are labeled with the watts of power they provide. For example, the hair dryer in Figure 16.5 is labeled ""2000 watts."" This amount of power could also be expressed kilowatts. A kilowatt equals 1000 watts, so the 2000-watt hair dryer produces 2 kilowatts of power. Compared with a less powerful device, a more powerful device can either do more work in the same time or do the same work in less time. For example, compared with a low-power microwave, a high-power microwave can cook more food in the same time or the same amount of food in less time. ",text,
L_0732,work,T_3632,"Power is a measure of the amount of work that can be done in a given amount of time. Power can be represented by the equation: Power = Work Time In this equation, work is measured in joules and time is measured in seconds, so power is expressed in joules per second (J/s). This is the SI unit for work, also known as the watt (W). A watt equals 1 joule of work per second. The watt is named for James Watt, a Scottish inventor you will read about below. You may already be familiar with watts. Thats because light bulbs and small appliances such as hair dryers are labeled with the watts of power they provide. For example, the hair dryer in Figure 16.5 is labeled ""2000 watts."" This amount of power could also be expressed kilowatts. A kilowatt equals 1000 watts, so the 2000-watt hair dryer produces 2 kilowatts of power. Compared with a less powerful device, a more powerful device can either do more work in the same time or do the same work in less time. For example, compared with a low-power microwave, a high-power microwave can cook more food in the same time or the same amount of food in less time. ",text,
L_0732,work,T_3633,"Power can be calculated using the formula above, if the amount of work and time are known. For example, assume that a small engine does 3000 joules of work in 2 seconds. Then the power of the motor is: Power = 3000 J = 1500 J/s, or 1500 W 2s You can also calculate work if you know power and time by rewriting the power equation above as: Work = Power  Time For example, if you use a 2000-watt hair dryer for 30 seconds, how much work is done? First express 2000 watts in J/s and then substitute this value for power in the work equation: Work = 2000 J/s  30 s = 60, 000 J For a video presentation on calculating power and work, go to this link:  Problem Solving Problem: An electric mixer does 2500 joules of work in 5 seconds. What is its power? Solution: Use the equation: Power = Work Time . Power = 2500 J = 500 J/s, or 500 W 5s You Try It! Problem: How much work can be done in 30 seconds by a 1000-watt microwave? ",text,
L_0732,work,T_3634,"Sometimes power is measured in a unit called the horsepower. One horsepower is the amount of work a horse can do in 1 minute. It equals 745 watts of power. The horsepower was introduced by James Watt, who invented the first powerful steam engine in the 1770s. Watts steam engine led to a revolution in industry and agriculture because of its power. Watt wanted to impress people with the power of his steam engine, so he compared it with something familiar to people of his time: the power of workhorses, like those pictured in Figure 16.6. Watt said his steam engine could produce the power of 20 horses, or 20 horsepower. The most powerful engines today may produce more than 100,000 horsepower! How many watts of power is that? ",text,
L_0733,machines,T_3635,"A machine is any device that makes work easier by changing a force. When you use a machine, you apply force to the machine. This force is called the input force. The machine, in turn, applies force to an object. This force is called the output force. Recall that work equals force multiplied by distance: Work = Force  Distance The force you apply to a machine is applied over a given distance, called the input distance. The force applied by the machine to the object is also applied over a distance, called the output distance. The output distance may or may not be the same as the input distance. Machines make work easier by increasing the amount of force that is applied, increasing the distance over which the force is applied, or changing the direction in which the force is applied. Contrary to popular belief, machines do not increase the amount of work that is done. They just change how the work is done. So if a machine increases the force applied, it must apply the force over a shorter distance. Similarly, if a machine increases the distance over which the force is applied, it must apply less force. ",text,
L_0733,machines,T_3636,"Examples of machines that increase force are doorknobs and nutcrackers. Figure 16.8 explains how these machines work. In each case, the force applied by the user is less than the force applied by the machine, but the machine applies the force over a shorter distance. ",text,
L_0733,machines,T_3637,"Examples of machines that increase the distance over which force is applied are paddles and hammers. Figure 16.9 explains how these machines work. In each case, the machine increases the distance over which the force is applied, but it reduces the strength of the applied force. ",text,
L_0733,machines,T_3638,"Some machines change the direction of the force applied by the user. They may or may not also change the strength of the force or the distance over which it is applied. Two examples of machines that work in this way are claw hammers and the rope systems (pulleys) that raise or lower flags on flagpoles. Figure 16.10 explains how these machines work. In each case, the direction of the force applied by the user is reversed by the machine. How does this make it easier to do the job? ",text,
L_0733,machines,T_3639,"An exoskeleton suit may seem like science fiction, turning ordinary humans into super heroes. But wearable robots are moving forward into reality. And for paraplegics, the ability to stand and walk that these machines provide is a super power. QUEST meets Austin Whitney and Tamara Mena, two ""Exoskeleton Test Pilots"" who are now putting this new technology through its paces. For more information on exoskeleton suits, see http://science.kqed.org/ques MEDIA Click image to the left or use the URL below. URL: ",text,
L_0733,machines,T_3640,"You read above that machines do not increase the work done on an object. In other words, you cant get more work out of a machine than you put into it. In fact, machines always do less work on the object than the user does on the machine. Thats because all machines must use some of the work put into them to overcome friction. How much work? It depends on the efficiency of the machine. Efficiency is the percent of input work that becomes output work. It is a measure of how well a machine reduces friction. ",text,
L_0733,machines,T_3641,"Consider the ramp in Figure 16.11. Its easier to push the heavy piece of furniture up the ramp to the truck than to lift it straight up off the ground. However, pushing the furniture over the surface of the ramp creates a lot of friction. Some of the force applied to moving the furniture must be used to overcome the friction. It would be more efficient to use a dolly on wheels to roll the furniture up the ramp. Thats because rolling friction is much less than sliding friction. As a result, the efficiency of the ramp would be greater with a dolly. ",text,
L_0733,machines,T_3642,"Efficiency can be calculated with the equation: Efficiency = Output work 100% Input work Consider a machine that puts out 6000 joules of work. To produce that much work from the machine requires the user to put in 8000 joules of work. To find the efficiency of the machine, substitute these values into the equation for efficiency: Efficiency = 6000 J 100% = 75% 8000 J You Try It! Problem: Rani puts 10,000 joules of work into a car jack. The car jack, in turn, puts out 7000 joules of work to raise up the car. What is the efficiency of the jack? ",text,
L_0733,machines,T_3643,Another measure of the effectiveness of a machine is its mechanical advantage. Mechanical advantage is the number of times a machine multiplies the input force. It can be calculated with the equation: Mechanical Advantage = Output force Input force This equation computes the actual mechanical advantage of a machine. It takes into account the reduction in output force that is due to friction. It shows how much a machine actually multiplies force when it used in the real world. ,text,
L_0733,machines,T_3644,"It can be difficult to measure the input and output forces needed to calculate actual mechanical advantage. Its usually much easier to measure the input and output distances. These measurements can then be used to calculate the ideal mechanical advantage. The ideal mechanical advantage represents the multiplication of input force that would be achieved in the absence of friction. Therefore, it is greater than the actual mechanical advantage because all machines use up some work in overcoming friction. Ideal mechanical advantage is calculated with the equation: Ideal Mechanical Advantage = Input distance Output distance Compare this equation with the equation above for actual mechanical advantage. Notice how the input and output values are switched. This makes sense when you recall that when a machine increases force, it decreases distance and vice versa. You can watch a video about actual and ideal mechanical advantage at this link: http://video.goo Consider the simple ramp in Figure 16.12. A ramp can be used to raise an object up off the ground. The input distance is the length of the sloped surface of the ramp. The output distance is the height of the ramp, or the vertical distance the object is raised. Therefore, the ideal mechanical advantage of the ramp is: Ideal Mechanical Advantage = 6m =3 2m An ideal mechanical advantage of 3 means that the ramp ideally (in the absence of friction) multiplies the output force by a factor of 3. ",text,
L_0733,machines,T_3645,"As you read above, some machines increase the force put into the machine, while other machines increase the distance over which the force is applied. Still other machines change only the direction of the force. Which way a machine works affects its mechanical advantage. For machines that increase force including ramps, doorknobs, and nutcrackers the output force is greater than the input force. Therefore, the mechanical advantage is greater than 1. For machines that increase the distance over which force is applied, such as paddles and hammers, the output force is less than the input force. Therefore, the mechanical advantage is less than 1. For machines that change only the direction of the force, such as the rope systems on flagpoles, the output force is the same as the input force. Therefore, the mechanical advantage is equal to 1. ",text,
L_0734,simple machines,T_3646,"The man in Figure 16.14 is using a ramp to move a heavy dryer up to the back of a truck. The highway in the figure switches back and forth so it climbs up the steep hillside. Both the ramp and the highway are examples of inclined planes. An inclined plane is a simple machine consisting of a sloping surface that connects lower and higher elevations. The sloping surface of the inclined plane supports part of the weight of the object as it moves up the slope. As a result, it takes less force to move the object uphill. The trade-off is that the object must be moved over a greater distance than if it were moved straight up to the higher elevation. On the other hand, the output force is greater than the input force because it is applied over a shorter distance. Like other simple machines, the ideal mechanical advantage of an inclined plane is given by: Ideal Mechanical Advantage = Input distance Output distance For an inclined plane, the input distance is the length of the sloping surface, and the output distance is the maximum height of the inclined plane. This was illustrated in Figure 16.12. Because the sloping surface is always greater than the height of the inclined plane, the ideal mechanical advantage of an inclined plane is always greater than 1. An inclined plane with a longer sloping surface relative to its height has a gentler slope. An inclined plane with a gentler slope has a greater mechanical advantage and requires less input force to move an object to a higher elevation. ",text,
L_0734,simple machines,T_3647,Two simple machines that are based on the inclined plane are the wedge and the screw. Both increase the force used to move an object because the input force is applied over a greater distance than the output force. ,text,
L_0734,simple machines,T_3648,"Imagine trying to slice a tomato with a fork or spoon instead of a knife, like the one in Figure 16.15. The knife makes the job a lot easier because of the wedge shape of the blade. A wedge is a simple machine that consists of two inclined planes. But unlike one inclined plane, a wedge works only when it moves. It has a thin end and thick end, and the thin end is forced into an object to cut or split it. The chisel in Figure 16.15 is another example of a wedge. The input force is applied to the thick end of a wedge, and it acts over the length of the wedge. The output force pushes against the object on both sides of the wedge, so the output distance is the thickness of the wedge. Therefore, the ideal mechanical advantage of a wedge can be calculated as: Ideal Mechanical Advantage = Length of wedge Maximum thickness of wedge The length of a wedge is always greater than its maximum thickness. As a result, the ideal mechanical advantage of a wedge is always greater than 1. ",text,
L_0734,simple machines,T_3649,"The spiral staircase in Figure 16.16 also contains an inclined plane. Do you see it? The stairs that wrap around the inside of the walls make up the inclined plane. The spiral staircase is an example of a screw. A screw is a simple machine that consists of an inclined plane wrapped around a cylinder or cone. No doubt you are familiar with screws like the wood screw in Figure 16.16. The screw top of the container in the figure is another example. Screws move objects to a higher elevation (or greater depth) by increasing the force applied. When you use a wood screw, you apply force to turn the inclined plane. The output force pushes the screw into the wood. It acts along the length of the cylinder around which the inclined plane is wrapped. Therefore, the ideal mechanical advantage of a screw is calculated as: Ideal Mechanical Advantage = Length of inclined plane Length of screw The length of the inclined plane is always greater than the length of the screw. As a result, the mechanical advantage of a screw is always greater than 1. Look at the collection of screws and bolts in Figure 16.17. In some of them, the turns (or threads) of the inclined plane are closer together. The closer together the threads are, the longer the inclined plane is relative to the length of the screw or bolt, so the greater its mechanical advantage is. Therefore, if the threads are closer together, you need to apply less force to penetrate the wood or other object. The trade-off is that more turns of the screw or bolt are needed to do the job because the distance over which the input force must be applied is greater. ",text,
L_0734,simple machines,T_3649,"The spiral staircase in Figure 16.16 also contains an inclined plane. Do you see it? The stairs that wrap around the inside of the walls make up the inclined plane. The spiral staircase is an example of a screw. A screw is a simple machine that consists of an inclined plane wrapped around a cylinder or cone. No doubt you are familiar with screws like the wood screw in Figure 16.16. The screw top of the container in the figure is another example. Screws move objects to a higher elevation (or greater depth) by increasing the force applied. When you use a wood screw, you apply force to turn the inclined plane. The output force pushes the screw into the wood. It acts along the length of the cylinder around which the inclined plane is wrapped. Therefore, the ideal mechanical advantage of a screw is calculated as: Ideal Mechanical Advantage = Length of inclined plane Length of screw The length of the inclined plane is always greater than the length of the screw. As a result, the mechanical advantage of a screw is always greater than 1. Look at the collection of screws and bolts in Figure 16.17. In some of them, the turns (or threads) of the inclined plane are closer together. The closer together the threads are, the longer the inclined plane is relative to the length of the screw or bolt, so the greater its mechanical advantage is. Therefore, if the threads are closer together, you need to apply less force to penetrate the wood or other object. The trade-off is that more turns of the screw or bolt are needed to do the job because the distance over which the input force must be applied is greater. ",text,
L_0734,simple machines,T_3650,"Did you ever use a hammer to pull a nail out of a board? If not, you can see how its done in Figure 16.18. When you pull down on the handle of the hammer, the claw end pulls up on the nail. A hammer is an example of a lever. A lever is a simple machine consisting of a bar that rotates around a fixed point called the fulcrum. For a video introduction to levers using skateboards as examples, go to this link:  MEDIA Click image to the left or use the URL below. URL:  A lever may or may not increase the force applied, and it may or may not change the direction of the force. It all depends on the location of the input and output forces relative to the fulcrum. In this regard, there are three basic types of levers, called first-class, second-class, and third-class levers. Figure 16.19 describes the three classes. ",text,
L_0734,simple machines,T_3651,"All three classes of levers make work easier, but they do so in different ways. When the input and output forces are on opposite sides of the fulcrum, the lever changes the direction of the applied force. This occurs only with a first-class lever. When both the input and output forces are on the same side of the fulcrum, the direction of the applied force does not change. This occurs with both second- and third-class levers. When the input force is applied farther from the fulcrum, the input distance is greater than the output distance, so the ideal mechanical advantage is greater than 1. This always occurs with second-class levers and may occur with first-class levers. When the input force is applied closer to the fulcrum, the input distance is less than the output distance, so the ideal mechanical advantage is less than 1. This always occurs with third-class levers and may occur with first-class levers. When both forces are the same distance from the fulcrum, the input distance equals the output distance, so the ideal mechanical advantage equals 1. This occurs only with first class-levers. ",text,
L_0734,simple machines,T_3652,"You may be wondering why you would use a third-class lever when it doesnt change the direction or strength of the applied force. The advantage of a third-class lever is that the output force is applied over a greater distance than the input force. This means that the output end of the lever must move faster than the input end. Why would this be useful when you are moving a hockey stick or baseball bat, both of which are third-class levers? ",text,
L_0734,simple machines,T_3653,"Did you ever ride on a Ferris wheel, like the one pictured in Figure 16.20? If you did, then you know how thrilling the ride can be. A Ferris wheel is an example of a wheel and axle. A wheel and axle is a simple machine that consists of two connected rings or cylinders, one inside the other, which both turn in the same direction around a single center point. The smaller, inner ring or cylinder is called the axle. The bigger, outer ring or cylinder is called the wheel. The car steering wheel in Figure 16.20 is another example of a wheel and axle. In a wheel and axle, force may be applied either to the wheel or to the axle. In both cases, the direction of the force does not change, but the force is either increased or applied over a greater distance. When the input force is applied to the axle, as it is with a Ferris wheel, the wheel turns with less force, so the ideal mechanical advantage is less than 1. However, the wheel turns over a greater distance, so it turns faster than the axle. The speed of the wheel is one reason that the Ferris wheel ride is so exciting. When the input force is applied to the wheel, as it is with a steering wheel, the axle turns over a shorter distance but with greater force, so the ideal mechanical advantage is greater than 1. This allows you to turn the steering wheel with relatively little effort, while the axle of the steering wheel applies enough force to turn the car. ",text,
L_0734,simple machines,T_3654,"Another simple machine that uses a wheel is the pulley. A pulley is a simple machine that consists of a rope and grooved wheel. The rope fits into the groove in the wheel, and pulling on the rope turns the wheel. Figure 16.21 shows two common uses of pulleys. Some pulleys are attached to a beam or other secure surface and remain fixed in place. They are called fixed pulleys. Other pulleys are attached to the object being moved and are moveable themselves. They are called moveable pulleys. Sometimes, fixed and moveable pulleys are used together. They make up a compound pulley. The three types of pulleys are compared in Figure 16.22. In all three types, the ideal mechanical advantage is equal to the number of rope segments pulling up on the object. The more rope segments that are helping to do the lifting work, the less force that is needed for the job. You can experiment with an interactive animation of compound pulleys with various numbers of pulleys at this link:  . In a single fixed pulley, only one rope segment lifts the object, so the ideal mechanical advantage is 1. This type of pulley doesnt increase the force, but it does change the direction of the force. This allows you to use your weight to pull on one end of the rope and more easily raise the object attached to the other end. In a single moveable pulley, two rope segments lift the object, so the ideal mechanical advantage is 2. This type of pulley doesnt change the direction of the force, but it does increase the force. In a compound pulley, two or more rope segments lift the object, so the ideal mechanical advantage is equal to or greater than 2. This type of pulley may or may not change the direction of the force, depending on the number and arrangement of pulleys. When several pulleys are combined, the increase in force may be very great. To learn more about the mechanical advantage of different types of pulleys, watch the video at this link: http://video ",text,
L_0735,compound machines,T_3655,"A compound machine is a machine that consists of more than one simple machine. Some compound machines consist of just two simple machines. For example, a wheelbarrow consists of a lever, as you read earlier in the lesson ""Simple Machines,"" and also a wheel and axle. Other compound machines, such as cars, consist of hundreds or even thousands of simple machines. Two common examples of compound machines are scissors and fishing rods with reels. To view a young students compound machine invention that includes several simple machines, watch the video at this link:  . To see if you can identify the simple machines in a lawn mower, go to the URL below and click on Find the Simple Machines. ",text,
L_0735,compound machines,T_3656,"Look at the scissors in Figure 16.24. As you can see from the figure, scissors consist of two levers and two wedges. You apply force to the handle ends of the levers, and the output force is exerted by the blade ends of the levers. The fulcrum of both levers is where they are joined together. Notice that the fulcrum lies between the input and output points, so the levers are first-class levers. They change the direction of force. They may or may not also increase force, depending on the relative lengths of the handles and blades. The blades themselves are wedges, with a sharp cutting edge and a thicker dull edge. ",text,
L_0735,compound machines,T_3657,"The fishing rod with reel shown in Figure 16.25 is another compound machine. The rod is a third-class lever, with the fulcrum on one end of the rod, the input force close to the fulcrum, and the output force at the other end of the rod. The output distance is greater than the input distance, so the angler can fling the fishing line far out into the water with just a flick of the wrist. The reel is a wheel and axle that works as a pulley. The fishing line is wrapped around the wheel. Using the handle to turn the axle of the wheel winds or unwinds the line. ",text,
L_0735,compound machines,T_3658,"Riding a bicycle might be easy. But the forces that allow humans to balance atop a bicycle are complex. QUEST visits Davis  a city that loves its bicycles  to take a ride on a research bicycle and explore a collection of antique bicycles. Scientists say studying the complicated physics of bicycling can lead to the design of safer, and more efficient bikes. For more information on the science of riding a bicycle, see  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0735,compound machines,T_3659,"Because compound machines have more moving parts than simple machines, they generally have more friction to overcome. As a result, compound machines tend to have lower efficiency than simple machines. When a compound machine consists of a large number of simple machines, friction may become a serious problem, and it may produce a lot of heat. Lubricants such as oil or grease may be used to coat the moving parts so they slide over each other more easily. This is how a cars friction is reduced. Compound machines have a greater mechanical advantage than simple machines. Thats because the mechanical advantage of a compound machine equals the product of the mechanical advantages of all its component simple machines. The greater the number of simple machines it contains, the greater is its mechanical advantage. ",text,
L_0736,types of energy,T_3660,"The concept of energy was first introduced in the chapter ""States of Matter,"" where it is defined as the ability to cause change in matter. Energy can also be defined as the ability to do work. Work is done whenever a force is used to move matter. When work is done, energy is transferred from one object to another. For example, when the batter in Figure 17.2 uses energy to swing the bat, she transfers energy to the bat. The moving bat, in turn, transfers energy to the ball. Like work, energy is measured in the joule (J), or newtonmeter (Nm). Energy exists in different forms, which you can read about in the lesson ""Forms of Energy"" later in the chapter. Some forms of energy are mechanical, electrical, and chemical energy. Most forms of energy can also be classified as kinetic or potential energy. Kinetic and potential forms of mechanical energy are the focus of this lesson. Mechanical energy is the energy of objects that are moving or have the potential to move. ",text,
L_0736,types of energy,T_3661,"What do all the photos in Figure 17.3 have in common? All of them show things that are moving. Kinetic energy is the energy of moving matter. Anything that is moving has kinetic energy from the atoms in matter to the planets in solar systems. Things with kinetic energy can do work. For example, the hammer in the photo is doing the work of pounding the nail into the board. You can see a cartoon introduction to kinetic energy and its relation to work at this URL:  . The amount of kinetic energy in a moving object depends on its mass and velocity. An object with greater mass or greater velocity has more kinetic energy. The kinetic energy of a moving object can be calculated with the equation: 1 Kinetic Energy (KE) = mass  velocity2 2 This equation for kinetic energy shows that velocity affects kinetic energy more than mass does. For example, if mass doubles, kinetic energy also doubles. But if velocity doubles, kinetic energy increases by a factor of four. Thats because velocity is squared in the equation. You can see for yourself how mass and velocity affect kinetic energy by working through the problems below. Problem Solving Problem: Juan has a mass of 50 kg. If he is running at a velocity of 2 m/s, how much kinetic energy does he have? Solution: Use the formula: KE = 12 mass  velocity2 1 50 kg  (2 m/s2 ) 2 = 100 kg  m2 /s2 = 100 N  m, or 100 J KE = You Try It! Problem: What is Juans kinetic energy if he runs at a velocity of 4 m/s? Problem: Juans dad has a mass of 100 kg. How much kinetic energy does he have if he runs at a velocity of 2 m/s? ",text,
L_0736,types of energy,T_3662,"Did you ever see a scene like the one in Figure 17.4? In many parts of the world, trees lose their leaves in autumn. The leaves turn color and then fall from the trees to the ground. As the leaves are falling, they have kinetic energy. While they are still attached to the trees they also have energy, but its not because of motion. Instead, they have stored energy, called potential energy. An object has potential energy because of its position or shape. For example leaves on trees have potential energy because they could fall due to the pull of gravity. ",text,
L_0736,types of energy,T_3663,"Potential energy due to the position of an object above Earth is called gravitational potential energy. Like the leaves on trees, anything that is raised up above Earths surface has the potential to fall because of gravity. You can see examples of people with gravitational potential energy in Figure 17.5. Gravitational potential energy depends on an objects weight and its height above the ground. It can be calculated with the equation: Gravitational potential energy (GPE) = weight  height Consider the diver in Figure 17.5. If he weighs 70 newtons and the diving board is 5 meters above Earths surface, then his potential energy is: GPE = 70 N  5 m = 350 N  m, or 350 J ",text,
L_0736,types of energy,T_3664,"Potential energy due to an objects shape is called elastic potential energy. This energy results when elastic objects are stretched or compressed. Their elasticity gives them the potential to return to their original shape. For example, the rubber band in Figure 17.6 has been stretched, but it will spring back to its original shape when released. Springs like the handspring in the figure have elastic potential energy when they are compressed. What will happen when the handspring is released? ",text,
L_0736,types of energy,T_3665,"Remember the diver in Figure 17.5? What happens when he jumps off the diving board? His gravitational potential energy changes to kinetic energy as he falls toward the water. However, he can regain his potential energy by getting out of the water and climbing back up to the diving board. This requires an input of kinetic energy. These changes in energy are examples of energy conversion, the process in which energy changes from one type or form to another. ",text,
L_0736,types of energy,T_3666,"The law of conservation of energy applies to energy conversions. Energy is not used up when it changes form, although some energy may be used to overcome friction, and this energy is usually given off as heat. For example, the divers kinetic energy at the bottom of his fall is the same as his potential energy when he was on the diving board, except for a small amount of heat resulting from friction with the air as he falls. ",text,
L_0736,types of energy,T_3667,There are many other examples of energy conversions between potential and kinetic energy. Figure 17.7 describes how potential energy changes to kinetic energy and back again on swings and trampolines. You can see an animation of changes between potential and kinetic energy on a ramp at the URL below. Can you think of other examples? ,text,
L_0736,types of energy,T_3668,"QUEST teams up with Make Magazine to construct the latest must have, do-it-yourself device hacks and science projects. This week well show you how to make a tabletop linear accelerator that demonstrates the finer points of kinetic energy by shooting a steel ball. For more information on the tabletop linear accelerator, see http://science.k MEDIA Click image to the left or use the URL below. URL: ",text,
L_0737,forms of energy,T_3669,"Energy, or the ability to do work, can exist in many different forms. The photo in Figure 17.8 represents six of the eight different forms of energy that are described in this lesson. The guitarist gets the energy he needs to perform from chemical energy in food. He uses mechanical energy to pluck the strings of the guitar. The stage lights use electrical energy and give off both light energy and thermal energy, commonly called heat. The guitar also uses electrical energy, and it produces sound energy when the guitarist plucks the strings. For an introduction to all these forms of energy, go to this URL:  . For an interactive animation about the different forms of energy, visit this URL:  After you read below about different forms of energy, you can check your knowledge by doing the drag and drop quiz at this URL:  . ",text,
L_0737,forms of energy,T_3670,"Mechanical energy is the energy of an object that is moving or has the potential to move. It is the sum of an objects kinetic and potential energy. In Figure 17.9, the basketball has mechanical energy because it is moving. The arrow in the same figure has mechanical energy because it has the potential to move due to the elasticity of the bow. What are some other examples of mechanical energy? ",text,
L_0737,forms of energy,T_3671,"Energy is stored in the bonds between atoms that make up compounds. This energy is called chemical energy, and it is a form of potential energy. If the bonds between atoms are broken, the energy is released and can do work. The wood in the fireplace in Figure 17.10 has chemical energy. The energy is released as thermal energy when the wood burns. People and many other living things meet their energy needs with chemical energy stored in food. When food molecules are broken down, the energy is released and may be used to do work. ",text,
L_0737,forms of energy,T_3672,"Electrons are negatively charged particles in atoms. Moving electrons have a form of kinetic energy called electrical energy. If youve ever experienced an electric outage, then you know how hard it is to get by without electrical energy. Most of the electrical energy we use is produced by power plants and arrives in our homes through wires. Two other sources of electrical energy are pictured in Figure 17.11. ",text,
L_0737,forms of energy,T_3673,"The nuclei of atoms are held together by powerful forces. This gives them a tremendous amount of stored energy, called nuclear energy. The energy can be released and used to do work. This happens in nuclear power plants when nuclei fission, or split apart. It also happens in the sun and other stars when nuclei fuse, or join together. Some of the suns energy travels to Earth, where it warms the planet and provides the energy for photosynthesis (see Figure ",text,
L_0737,forms of energy,T_3674,"The atoms that make up matter are in constant motion, so they have kinetic energy. All that motion gives matter thermal energy. Thermal energy is defined as the total kinetic energy of all the atoms that make up an object. It depends on how fast the atoms are moving and how many atoms the object has. Therefore, an object with more mass has greater thermal energy than an object with less mass, even if their individual atoms are moving at the same speed. You can see an example of this in Figure 17.13. ",text,
L_0737,forms of energy,T_3674,"The atoms that make up matter are in constant motion, so they have kinetic energy. All that motion gives matter thermal energy. Thermal energy is defined as the total kinetic energy of all the atoms that make up an object. It depends on how fast the atoms are moving and how many atoms the object has. Therefore, an object with more mass has greater thermal energy than an object with less mass, even if their individual atoms are moving at the same speed. You can see an example of this in Figure 17.13. ",text,
L_0737,forms of energy,T_3675,"Energy that the sun and other stars release into space is called electromagnetic energy. This form of energy travels through space as electrical and magnetic waves. Electromagnetic energy is commonly called light. It includes visible light, as well as radio waves, microwaves, and X rays (Figure 17.14). ",text,
L_0737,forms of energy,T_3676,"The drummer in Figure 17.15 is hitting the drumheads with drumsticks. This causes the drumheads to vibrate. The vibrations pass to surrounding air particles and then from one air particle to another in a wave of energy called sound energy. We hear sound when the sound waves reach our ears. Sound energy can travel through air, water, and other substances, but not through empty space. Thats because the energy needs particles of matter to pass it on. ",text,
L_0737,forms of energy,T_3677,"Energy often changes from one form to another. For example, the mechanical energy of a moving drumstick changes to sound energy when it strikes the drumhead and causes it to vibrate. Any form of energy can change into any other form. Frequently, one form of energy changes into two or more different forms. For example, when wood burns, the woods chemical energy changes to both thermal energy and light energy. Other examples of energy conversions are described in Figure 17.16. You can see still others at this URL: http://fi.edu/guide/hughes/energychangeex.html . You can check your understanding of how energy changes form by doing the quizzes at these URLs:  Energy is conserved in energy conversions. No energy is lost when energy changes form, although some may be released as thermal energy due to friction. For example, not all of the energy put into a steam turbine in Figure 17.16 changes to electrical energy. Some changes to thermal energy because of friction of the turning blades and other moving parts. The more efficient a device is, the greater the percentage of usable energy it produces. Appliances with an ""Energy Star"" label like the one in Figure 17.17 use energy efficiently and thereby reduce energy use. ",text,
L_0738,energy resources,T_3678,Nonrenewable resources are natural resources that are limited in supply and cannot be replaced except over millions of years. Nonrenewable energy resources include fossil fuels and radioactive elements such as uranium. ,text,
L_0738,energy resources,T_3679,"Fossil fuels are mixtures of hydrocarbons that formed over millions of years from the remains of dead organisms. They include petroleum (commonly called oil), natural gas, and coal. Fossil fuels provide most of the energy used in the world today. They are burned in power plants to produce electrical energy, and they also fuel cars, heat homes, and supply energy for many other purposes. You can see examples of their use in Figure 17.19. Fossil fuels contain stored chemical energy that came originally from the sun. Ancient plants changed energy in ",text,
L_0738,energy resources,T_3679,"Fossil fuels are mixtures of hydrocarbons that formed over millions of years from the remains of dead organisms. They include petroleum (commonly called oil), natural gas, and coal. Fossil fuels provide most of the energy used in the world today. They are burned in power plants to produce electrical energy, and they also fuel cars, heat homes, and supply energy for many other purposes. You can see examples of their use in Figure 17.19. Fossil fuels contain stored chemical energy that came originally from the sun. Ancient plants changed energy in ",text,
L_0738,energy resources,T_3680,"Like fossil fuels, the radioactive element uranium can be used to generate electrical energy in power plants. In a nuclear power plant, the nuclei of uranium atoms are split in the process of nuclear fission. This process releases a tremendous amount of energy from just a small amount of uranium. The total supply of uranium in the world is quite limited, however, and cannot be replaced once it is used up. This makes nuclear energy a nonrenewable resource. Although using nuclear energy does not release carbon dioxide or cause air pollution, it does produce dangerous radioactive wastes. Accidents at nuclear power plants also have the potential to release large amounts of radioactive material into the environment. Figure 17.21 describes the nuclear disaster caused by a Japanese tsunami in 2011. You can learn more about the disaster and its aftermath at the URLs below. ",text,
L_0738,energy resources,T_3681,"President Obama says the United States needs new nuclear reactors, to meet the countrys energy demands and counter climate change. But can nuclear power be produced more safely and affordably? A scientist at the University of California, Berkeley, is working to do just that. For more information about nuclear energy, see http://science.k MEDIA Click image to the left or use the URL below. URL: ",text,
L_0738,energy resources,T_3682,"Renewable resources are natural resources that can be replaced in a relatively short period of time or are virtually limitless in supply. Renewable energy resources include sunlight, moving water, wind, biomass, and geothermal energy. Each of these energy resources is described in Table 17.1. Resources such as sunlight and wind are limitless in supply, so they will never run out. Besides their availability, renewable energy resources also have the advantage of producing little if any pollution and not contributing to global warming. The technology needed to gather energy from renewable resources is currently expensive to install, but most of the resources themselves are free for the taking. here? Renewable Energy Resource Sunlight The energy in sunlight, or solar energy, can be used to heat homes. It can also be used to produce electricity in solar cells. However, solar energy may not be practical in areas that are often cloudy. Example Solar panels on the roof of this house generate enough electricity to supply a familys needs. Moving Water When water falls downhill, its potential energy is con- verted to kinetic energy that can turn a turbine and generate electricity. The water may fall naturally over a waterfall or flow through a dam. A drawback of dams is that they flood land upstream and reduce water flow downstream. Either effect may harm ecosystems. Wind Wind is moving air, so it has kinetic energy that can do work. Remember the wind turbines that opened this chapter? Wind turbines change the kinetic energy of the wind to electrical energy. Only certain areas of the world get enough steady wind to produce much electricity. Many people also think that wind turbines are noisy and unattractive in the landscape. Water flowing through Hoover dam between Arizona and Nevada generates electricity for both of these states and also by southern California. The dam spans the Colorado River. This old-fashioned windmill captures wind energy that is used for pumping water out of a well. Windmills like this one have been used for centuries. Renewable Energy Resource Biomass The stored chemical energy of trees and other plants is called biomass energy. When plant materials are burned, they produce thermal energy that can be used for heating, cooking, or generating electricity. Biomassespecially woodis an important energy source in countries where most people cant afford fossil fuels. Some plants can also be used to make ethanol, a fuel that is added to gasoline. Ethanol produces less pollution than gasoline, but large areas of land are needed to grow the plants needed to make it. Geothermal Heat below Earths surfacecalled geothermal en- ergycan be used to produce electricity. A power plant pumps water underground where it is heated. Then it pumps the water back to the plant and uses its thermal energy to generate electricity. On a small scale, geothermal energy can be used to heat homes. Installing a geothermal system can be very costly, how- ever, because of the need to drill through underground rocks. Example This large machine is harvesting and grinding plants to be used for biomass energy. This geothermal power plant is located in Italy where hot magma is close to the surface. ",text,
L_0738,energy resources,T_3683,"The largest solar thermal plant in the world opens in Californias Mojave Desert, after a debate that pitted renewable energy against a threatened tortoise. The Ivanpah solar plant is one of seven big solar farms scheduled to open in California in the coming months, as a result of the states push to produce one third of its electricity from renewable energy. Some 30 states have similar mandates. For more information on this solar plant, see http://science.kqed.org/ MEDIA Click image to the left or use the URL below. URL: ",text,
L_0738,energy resources,T_3684,"On the windswept tarmac of the former Alameda Naval Air Station, an inventive group of scientists and engineers are test-flying a kite-like tethered wing that may someday help revolutionize clean energy. QUEST explores the potential of wind energy and new airborne wind turbines designed to harness the stronger and more consistent winds found at higher altitudes. For more information on wind energy, see http://science.kqed.org/quest/video/airborne MEDIA Click image to the left or use the URL below. URL: ",text,
L_0738,energy resources,T_3685,"Solar and wind power may get the headlines when it comes to renewable energy. But another type of clean power is heating up in the hills just north of Sonoma wine country. Geothermal power uses heat from deep inside the Earth to generate electricity. The Geysers, the worlds largest power-producing geothermal field, has been providing electricity for roughly 850,000 Northern California households, and is set to expand even further. For more information on geothermal energy, see http://science.kqed.org/quest/video/geothermal-heats-up/ . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0738,energy resources,T_3686,"Figure 17.22 shows the mix of energy resources used worldwide in 2006. Fossil fuels still provide most of the worlds energy, with oil being the single most commonly used energy resource. Natural gas is used less than the other two fossil fuels, but even natural gas is used more than all renewable energy resources combined. Wind, solar, and geothermal energy contribute the least to global energy use, despite the fact that they are virtually limitless in supply and nonpolluting. ",text,
L_0738,energy resources,T_3687,"People in the richer nations of the world use far more energy, especially energy from fossil fuels, than people in the poorer nations do. Figure 17.23 compares the amounts of oil used by the top ten oil-consuming nations. The U.S. uses more oil than several other top-ten countries combined. If you also consider the population size in these countries, the differences are even more stunning. The average person in the U.S. uses a whopping 23 barrels of oil a year! In comparison, the average person in India or China uses just 1 or 2 barrels a year. Because richer nations use more fossil fuels, they also cause more air pollution and global warming than poorer nations do. ",text,
L_0738,energy resources,T_3688,We can reduce our use of energy resources and the pollution they cause by conserving energy. Conservation means saving resources by using them more efficiently or not using them at all. Figure 17.24 shows several ways that people can conserve energy in their daily lives. You can find more energy-saving tips at the URL below. What do you do to save energy? What else could you do? ,text,
L_0738,energy resources,T_3688,We can reduce our use of energy resources and the pollution they cause by conserving energy. Conservation means saving resources by using them more efficiently or not using them at all. Figure 17.24 shows several ways that people can conserve energy in their daily lives. You can find more energy-saving tips at the URL below. What do you do to save energy? What else could you do? ,text,
L_0738,energy resources,T_3688,We can reduce our use of energy resources and the pollution they cause by conserving energy. Conservation means saving resources by using them more efficiently or not using them at all. Figure 17.24 shows several ways that people can conserve energy in their daily lives. You can find more energy-saving tips at the URL below. What do you do to save energy? What else could you do? ,text,
L_0738,energy resources,T_3689,"QUEST teams up with Climate Watch to give you an inside look at home energy efficiency. Tag along with Sustainable Spaces on a home efficiency ""green-up"" and learn tips on how to make your home more energy efficient. For more information on home energy audits, see http://science.kqed.org/quest/video/web-extra-home-energy-audit/ . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0738,energy resources,T_3690,"With the race on to reduce global warming and fossil fuel dependency, experts in alternative energy see a bright future for renewable resources like wind, solar, hydro-power and geothermal energy. QUEST and Climate Watch team up to look at the ""Smart Grid"" of the future and how it might be improved to more cleanly and efficiently keep the lights on in California. For more information on the ""Smart Grid"", see http://science.kqed.org/quest/video/clim MEDIA Click image to the left or use the URL below. URL: ",text,
L_0739,temperature and heat,T_3691,"No doubt you already have a good idea of what temperature is. You might define it as how hot or cold something feels. In physics, temperature is defined as the average kinetic energy of the particles in an object. When particles move more quickly, temperature is higher and an object feels warmer. When particles move more slowly, temperature is lower and an object feels cooler. ",text,
L_0739,temperature and heat,T_3692,"If two objects have the same mass, the object with the higher temperature has greater thermal energy. Temperature affects thermal energy, but temperature isnt the same thing as thermal energy. Thats because an objects mass also affects its thermal energy. The examples in Figure 18.1 make this clear. In the figure, the particles of cocoa are moving faster than the particles of bathwater. Therefore, the cocoa has a higher temperature. However, the bath water has more thermal energy because there is so much more of it. It has many more moving particles. Bill Nye the Science Guy cleverly discusses these concepts at this URL:  MEDIA Click image to the left or use the URL below. URL:  If youre still not clear about the relationship between temperature and thermal energy, watch the animation ""Tem- perature"" at this URL:  . ",text,
L_0739,temperature and heat,T_3693,"Temperature is measured with a thermometer. A thermometer shows how hot or cold something is relative to two reference temperatures, usually the freezing and boiling points of water. Scientists often use the Celsius scale for temperature. On this scale, the freezing point of water is 0C and the boiling point is 100C. To learn more about measuring temperature, watch the animation Measuring Temperature at this URL:  Did you ever wonder how a thermometer works? Look at the thermometer in Figure 18.2. Particles of the red liquid have greater energy when they are warmer, so they move more and spread apart. This causes the liquid to expand and rise higher in the glass tube. Like the liquid in a thermometer, most types of matter expand to some degree when they get warmer. Gases usually expand the most when heated, followed by liquids. Solids generally expand the least. (Water is an exception; it takes up more space as a solid than as a liquid.) ",text,
L_0739,temperature and heat,T_3694,"Something that has a high temperature is said to be hot. Does temperature measure heat? Is heat just another word for thermal energy? The answer to both questions is no. Heat is the transfer of thermal energy between objects that have different temperatures. Thermal energy always moves from an object with a higher temperature to an object with a lower temperature. When thermal energy is transferred in this way, the warm object becomes cooler and the cool object becomes warmer. Sooner or later, both objects will have the same temperature. Only then does the transfer of thermal energy end. For a visual explanation of these concepts, watch the animation ""Temperature vs. Heat"" at this URL:  . ",text,
L_0739,temperature and heat,T_3695,"Figure 18.3 illustrates an example of thermal energy transfer. Before the spoon was put into the steaming hot coffee, it was cool to the touch. Once in the coffee, the spoon heated up quickly. The fast-moving particles of the coffee transferred some of their energy to the slower-moving particles of the spoon. The spoon particles started moving faster and became warmer, causing the temperature of the spoon to rise. Because the coffee particles lost some of their kinetic energy to the spoon particles, the coffee particles started to move more slowly. This caused the temperature of the coffee to fall. Before long, the coffee and spoon had the same temperature. ",text,
L_0739,temperature and heat,T_3696,"The girls in Figure 18.4 are having fun at the beach. Its a warm, sunny day, and the sand feels hot under their bare hands and feet. The water, in contrast, feels much cooler. Why does the sand get so hot while the water does not? The answer has to do with specific heat. Specific heat is the amount of energy (in joules) needed to raise the temperature of 1 gram of a substance by 1C. Specific heat is a property that is specific to a given type of matter. Table 18.1 lists the specific heat of four different substances. Metals such as iron have relatively low specific heat. It doesnt take much energy to raise their temperature. Thats why a metal spoon heats up quickly when placed in hot coffee. Sand also has a relatively low specific heat, whereas water has a very high specific heat. It takes a lot more energy to increase the temperature of water than sand. This explains why the sand on a beach gets hot while the water stays cool. Differences in the specific heat of water and land also affect climate. To learn how, watch the video at this URL:  MEDIA Click image to the left or use the URL below. URL:  In Table 18.1, how much greater is the specific heat of water than sand? Substances iron sand wood water Specific Heat (joules) 0.45 0.67 1.76 4.18 ",text,
L_0739,temperature and heat,T_3697,"The roadway across the Golden Gate Bridge rises and falls as much as 16 feet depending on the temperature. When the sun hits the bridge, the metal expands and the bridge cables stretch. As the fog rolls in, the cables contract and the bridge goes up. Curators from the Outdoor Exploratorium in San Francisco have set up a scope two miles away so you can see how the bridge is moving up or down depending on the weather. For more information on how the bridge moves due to temperature, see http://science.kqed.org/quest/video/quest-lab-bridge-thermometer/ . Heat is the transfer of thermal energy between objects that have different temperatures. Thermal energy always moves from an object with a higher temperature to an object with a lower temperature. Specific heat is the amount of energy (in joules) needed to raise the temperature of 1 gram of a substance by 1C. Substances differ in their specific heat. ",text,
L_0740,transfer of thermal energy,T_3698,"Conduction is the transfer of thermal energy between particles of matter that are touching. When energetic particles collide with nearby particles, they transfer some of their thermal energy. From particle to particle, like dominoes falling, thermal energy moves throughout a substance. In Figure 18.5, conduction occurs between particles of the metal in the pot and between particles of the pot and the water. Figure 18.6 shows additional examples of conduction. For a deeper understanding of this method of heat transfer, watch the animation ""Conduction"" at this URL: http://w ",text,
L_0740,transfer of thermal energy,T_3699,"Conduction is usually faster in liquids and certain solids than in gases. Materials that are good conductors of thermal energy are called thermal conductors. Metals are excellent thermal conductors. They have freely moving electrons that can transfer energy quickly and easily. Thats why the metal pot in Figure 18.5 soon gets hot all over, even though it gains thermal energy from the fire only at the bottom of the pot. In Figure 18.6, the metal heating element of the curling iron heats up almost instantly and quickly transfers energy to the strands of hair that it touches. ",text,
L_0740,transfer of thermal energy,T_3700,"Particles of gases are farther apart and have fewer collisions, so they are not good at transferring thermal energy. Materials that are poor thermal conductors are called thermal insulators. Figure 18.7 shows several examples. Fluffy yellow insulation inside the roof of a home is full of air. The air prevents the transfer of thermal energy into the house on hot days and out of the house on cold days. A puffy down jacket keeps you warm in the winter for the same reason. Its feather filling holds trapped air that prevents energy transfer from your warm body to the cold air outside. Solids like plastic and wood are also good thermal insulators. Thats why pot handles and cooking utensils are often made of these materials. ",text,
L_0740,transfer of thermal energy,T_3701,"Everyday, women living in the refugee camps of Darfur, Sudan must walk for up to seven hours outside the safety of the camps to collect firewood for cooking, putting them at risk for violent attacks. Now, researchers at Lawrence Berkeley National Laboratory have engineered a more efficient wood-burning stove, which is greatly reducing both the womens need for firewood and the threats against them. For more information on these stoves, see http://scien MEDIA Click image to the left or use the URL below. URL: ",text,
L_0740,transfer of thermal energy,T_3702,"Convection is the transfer of thermal energy by particles moving through a fluid. Particles transfer energy by moving from warmer to cooler areas. Thats how energy is transferred in the soup in Figure 18.7. Particles of soup near the bottom of the pot get hot first. They have more energy so they spread out and become less dense. With lower density, these particles rise to the top of the pot (see Figure 18.8). By the time they reach the top of the pot they have cooled off. They have less energy to move apart, so they become denser. With greater density, the particles sink to the bottom of the pot, and the cycle repeats. This loop of moving particles is called a convection current. Convection currents move thermal energy through many fluids, including molten rock inside Earth, water in the oceans, and air in the atmosphere. In the atmosphere, convection currents create wind. You can see one way this happens in Figure 18.9. Land heats up and cools off faster than water because it has lower specific heat. Therefore, land is warmer during the day and cooler at night than water. Air close to the surface gains or loses heat as well. Warm air rises because it is less dense, and when it does, cool air moves in to take its place. This creates a convection current that carries air from the warmer to the cooler area. You can learn more about convection currents by watching ""Convection"" at this URL:  . ",text,
L_0740,transfer of thermal energy,T_3702,"Convection is the transfer of thermal energy by particles moving through a fluid. Particles transfer energy by moving from warmer to cooler areas. Thats how energy is transferred in the soup in Figure 18.7. Particles of soup near the bottom of the pot get hot first. They have more energy so they spread out and become less dense. With lower density, these particles rise to the top of the pot (see Figure 18.8). By the time they reach the top of the pot they have cooled off. They have less energy to move apart, so they become denser. With greater density, the particles sink to the bottom of the pot, and the cycle repeats. This loop of moving particles is called a convection current. Convection currents move thermal energy through many fluids, including molten rock inside Earth, water in the oceans, and air in the atmosphere. In the atmosphere, convection currents create wind. You can see one way this happens in Figure 18.9. Land heats up and cools off faster than water because it has lower specific heat. Therefore, land is warmer during the day and cooler at night than water. Air close to the surface gains or loses heat as well. Warm air rises because it is less dense, and when it does, cool air moves in to take its place. This creates a convection current that carries air from the warmer to the cooler area. You can learn more about convection currents by watching ""Convection"" at this URL:  . ",text,
L_0740,transfer of thermal energy,T_3703,"Both conduction and convection transfer energy through matter. Radiation is the only way of transferring energy that doesnt require matter. Radiation is the transfer of energy by waves that can travel through empty space. When the waves reach objects, they transfer energy to the objects, causing them to warm up. This is how the suns energy reaches Earth and heats its surface (see Figure 18.10). Radiation is also how thermal energy from a campfire warms people nearby. You might be surprised to learn that all objects radiate thermal energy, including people. In fact, when a room is full of people, it may feel noticeably warmer because of all the thermal energy the people radiate! To learn more about thermal radiation, watch ""Radiation"" at the URL below. ",text,
L_0741,using thermal energy,T_3704,Warming homes and other buildings is an obvious way that thermal energy can be used. Two common types of home heating systems are hot-water and warm-air heating systems. Both types are described below. You can watch an animation showing how a solar heating system works at this URL: ,text,
L_0741,using thermal energy,T_3705,"A hot-water heating system uses thermal energy to heat water and then pumps the hot water throughout the building in a system of pipes and radiators. You can see a diagram of this type of heating system in Figure 18.12. Typically, the water is heated in a boiler that burns natural gas or heating oil. There is usually a radiator in each room that gets warm when the hot water flows through it. The radiator transfers thermal energy to the air around it by conduction and radiation. The warm air then circulates throughout the room in convection currents. The hot water cools as it flows through the system and transfers its thermal energy. When it finally returns to the boiler, it is heated again and the cycle repeats. ",text,
L_0741,using thermal energy,T_3706,"A warm-air heating system uses thermal energy to heat air. It then forces the warm air through a system of ducts. You can see a diagram of this type of heating system in Figure 18.13. Typically, the air is heated in a furnace that burns natural gas or heating oil. When the air is warm, a fan blows it through the ducts and out through vents that are located in each room. Warm air blowing out of a vent moves across the room, pushing cold air out of the way. The cold air enters an intake vent on the opposite side of the room and returns to the furnace with the help of another fan. In the furnace, the cold air is heated, and the cycle repeats. ",text,
L_0741,using thermal energy,T_3707,"Its easy to see how thermal energy can be used to keep things warm. But did you know that thermal energy can also be used to keep things cool? Cooling systems such as air conditioners and refrigerators transfer thermal energy in order to keep homes and cars cool or to keep food cold. In a refrigerator, for example, thermal energy is transferred from the cool air inside the refrigerator to the warmer air in the kitchen. You read in this chapters ""Transfer of Thermal Energy"" lesson that thermal energy always moves from a warmer area to a cooler area, so how can it move from the cooler refrigerator to the warmer room? The answer is work. The refrigerator does work to transfer thermal energy in this way. Doing this work takes energy, which is usually provided by electricity. Figure 18.14 explains how a refrigerator does its work. For an animated demonstration of how a refrigerator works, go to this URL:  The key to how a refrigerator or other cooling system works is the refrigerant. A refrigerant is a substance, such as FreonTM, that has a low boiling point and changes between liquid and gaseous states as it passes through the cooling system. As a liquid, the refrigerant absorbs thermal energy from the cool air inside the refrigerator and changes to a gas. As a gas, it releases thermal energy to the warm air outside the refrigerator and changes back to a liquid. ",text,
L_0741,using thermal energy,T_3708,A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the energy to do work. Two basic types of combustion engines are external and internal combustion engines. ,text,
L_0741,using thermal energy,T_3709,"An external combustion engine burns fuel externally, or outside the engine. The burning fuel releases thermal energy that is used to turn water to steam. The pressure of the steam is then used to move a piston back and forth in a cylinder. The kinetic energy of the moving piston can be used to turn a turbine or other device. Figure 18.15 explains in greater detail how this type of engine works. You can see an animated version of an external combustion engine at this URL: http://science.howstuffworks.com/transport/engines-equipment/steam1.htm . ",text,
L_0741,using thermal energy,T_3710,"An internal combustion engine (see Figure 18.16) burns fuel internally, or inside the engine. This type of engine is found in most cars and other motor vehicles. It works in these steps, which keep repeating: 1. A mixture of fuel and air is pulled into a cylinder through a valve, which then closes. 2. The piston is pushed upward, compressing the fuel-air mixture in the closed cylinder. The mixture is now under a lot of pressure and very warm. 3. A spark from a spark plug is used to ignite the fuel-air mixture, causing it to burn explosively within the confined space of the closed cylinder. 4. The pressure of the hot gases from combustion forces the piston downward. 5. When the piston moves up again, it forces the exhaust gases of combustion out of the cylinder though another valve. Then the process repeats. In a car, the piston is connected by the piston rod to the crankshaft. The crankshaft rotates when the piston moves up and down. The kinetic energy of the moving crankshaft is used to turn the driveshaft, which causes the wheels of the car to turn. Most cars have at least four cylinders connected to the crankshaft. Their pistons move up and down in sequence, one after the other. You can watch animations of internal combustion engines in action at these URLs: http://auto.howstuffworks.com/engine1.htm ",text,
L_0742,characteristics of waves,T_3711,"A mechanical wave is a disturbance in matter that transfers energy from place to place. A mechanical wave starts when matter is disturbed. An example of a mechanical wave is pictured in Figure 19.1. A drop of water falls into a pond. This disturbs the water in the pond. What happens next? The disturbance travels outward from the drop in all directions. This is the wave. A source of energy is needed to start a mechanical wave. In this case, the energy comes from the falling drop of water. ",text,
L_0742,characteristics of waves,T_3712,"The energy of a mechanical wave can travel only through matter. This matter is called the medium (plural, media). The medium in Figure 19.1 is a liquid the water in the pond. But the medium of a mechanical wave can be any state of matter, including a solid or a gas. Its important to note that particles of matter in the medium dont actually travel along with the wave. Only the energy travels. The particles of the medium just vibrate, or move back-and- forth or up-and-down in one spot, always returning to their original positions. As the particles vibrate, they pass the energy of the disturbance to the particles next to them, which pass the energy to the particles next to them, and so on. ",text,
L_0742,characteristics of waves,T_3713,"There are three types of mechanical waves. They differ in how they travel through a medium. The three types are transverse, longitudinal, and surface waves. All three types are described in detail below. ",text,
L_0742,characteristics of waves,T_3714,"A transverse wave is a wave in which the medium vibrates at right angles to the direction that the wave travels. An example of a transverse wave is a wave in a rope, like the one pictured in Figure 19.2. In this wave, energy is provided by a persons hand moving one end of the rope up and down. The direction of the wave is down the length of the rope away from the persons hand. The rope itself moves up and down as the wave passes through it. You can see a brief video of a transverse wave in a rope at this URL:  . To see a transverse wave in slow motion, go to this URL:  (0:22). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0742,characteristics of waves,T_3715,"A transverse wave can be characterized by the high and low points reached by particles of the medium as the wave passes through. This is illustrated in Figure 19.3. The high points are called crests, and the low points are called troughs. ",text,
L_0742,characteristics of waves,T_3716,"Another example of transverse waves occurs with earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called secondary, or S, waves. An S wave is illustrated in Figure 19.4. ",text,
L_0742,characteristics of waves,T_3716,"Another example of transverse waves occurs with earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called secondary, or S, waves. An S wave is illustrated in Figure 19.4. ",text,
L_0742,characteristics of waves,T_3716,"Another example of transverse waves occurs with earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called secondary, or S, waves. An S wave is illustrated in Figure 19.4. ",text,
L_0742,characteristics of waves,T_3717,"A longitudinal wave is a wave in which the medium vibrates in the same direction that the wave travels. An example of a longitudinal wave is a wave in a spring, like the one in Figure 19.5. In this wave, the energy is provided by a persons hand pushing and pulling the spring. The coils of the spring first crowd closer together and then spread farther apart as the disturbance passes through them. The direction of the wave is down the length of the spring, or the same direction in which the coils move. You can see a video of a longitudinal wave in a spring at this URL: http ",text,
L_0742,characteristics of waves,T_3718,"A longitudinal wave can be characterized by the compressions and rarefactions of the medium. This is illustrated in Figure 19.6. Compressions are the places where the coils are crowded together, and rarefactions are the places where the coils are spread apart. ",text,
L_0742,characteristics of waves,T_3719,"Earthquakes cause longitudinal waves as well as transverse waves. The disturbance that causes an earthquake sends longitudinal waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called primary, or P, waves. They are illustrated in Figure 19.7. ",text,
L_0742,characteristics of waves,T_3719,"Earthquakes cause longitudinal waves as well as transverse waves. The disturbance that causes an earthquake sends longitudinal waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called primary, or P, waves. They are illustrated in Figure 19.7. ",text,
L_0742,characteristics of waves,T_3720,"A surface wave is a wave that travels along the surface of a medium. It combines a transverse wave and a longitudinal wave. Ocean waves are surface waves. They travel on the surface of the water between the ocean and the air. In a surface wave, particles of the medium move up and down as well as back and forth. This gives them an overall circular motion. This is illustrated in Figure 19.8 and at the URL below. MEDIA Click image to the left or use the URL below. URL:  In deep water, particles of water just move in circles. They dont actually move closer to shore with the energy of the waves. However, near the shore where the water is shallow, the waves behave differently. They start to drag on the bottom, creating friction (see Figure 19.9). The friction slows down the bottoms of the waves, while the tops of the waves keep moving at the same speed. This causes the waves to get steeper until they topple over and crash on the shore. The crashing waves carry water onto the shore as surf. ",text,
L_0743,measuring waves,T_3721,The height of a wave is its amplitude. Another measure of wave size is wavelength. Both wave amplitude and wave- length are described in detail below. Figure 19.11 shows these wave measures for both transverse and longitudinal waves. You can also simulate waves with different amplitudes and wavelengths by doing the interactive animation at this URL: http://sci-culture.com/advancedpoll/GCSE/sine%20wave%20simulator.html . ,text,
L_0743,measuring waves,T_3722,"Wave amplitude is the maximum distance the particles of a medium move from their resting position when a wave passes through. The resting position is where the particles would be in the absence of a wave. In a transverse wave, wave amplitude is the height of each crest above the resting position. The higher the crests are, the greater the amplitude. In a longitudinal wave, amplitude is a measure of how compressed particles of the medium become when the wave passes through. The closer together the particles are, the greater the amplitude. What determines a waves amplitude? It depends on the energy of the disturbance that causes the wave. A wave caused by a disturbance with more energy has greater amplitude. Imagine dropping a small pebble into a pond of still water. Tiny ripples will move out from the disturbance in concentric circles, like those in Figure 19.1. The ripples are low-amplitude waves. Now imagine throwing a big boulder into the pond. Very large waves will be generated by the disturbance. These waves are high-amplitude waves. ",text,
L_0743,measuring waves,T_3723,Another important measure of wave size is wavelength. Wavelength is the distance between two corresponding points on adjacent waves (see Figure 19.11). Wavelength can be measured as the distance between two adjacent crests of a transverse wave or two adjacent compressions of a longitudinal wave. It is usually measured in meters. Wavelength is related to the energy of a wave. Short-wavelength waves have more energy than long-wavelength waves of the same amplitude. You can see examples of waves with shorter and longer wavelengths in Figure 19.12. ,text,
L_0743,measuring waves,T_3724,"Imagine making transverse waves in a rope, like the waves in Figure 19.2. You tie one end of the rope to a doorknob or other fixed point and move the other end up and down with your hand. You can move the rope up and down slowly or quickly. How quickly you move the rope determines the frequency of the waves. ",text,
L_0743,measuring waves,T_3725,"The number of waves that pass a fixed point in a given amount of time is wave frequency. Wave frequency can be measured by counting the number of crests or compressions that pass the point in 1 second or other time period. The higher the number is, the greater is the frequency of the wave. The SI unit for wave frequency is the hertz (Hz), where 1 hertz equals 1 wave passing a fixed point in 1 second. Figure 19.13 shows high-frequency and low- frequency transverse waves. You can simulate transverse waves with different frequencies at this URL: http://zonal The frequency of a wave is the same as the frequency of the vibrations that caused the wave. For example, to generate a higher-frequency wave in a rope, you must move the rope up and down more quickly. This takes more energy, so a higher-frequency wave has more energy than a lower-frequency wave with the same amplitude. ",text,
L_0743,measuring waves,T_3726,"Assume that you move one end of a rope up and down just once. How long will take the wave to travel down the rope to the other end? This depends on the speed of the wave. Wave speed is how far the wave travels in a given amount of time, such as how many meters it travels per second. Wave speed is not the same thing as wave frequency, but it is related to frequency and also to wavelength. This equation shows how the three factors are related: Speed = Wavelength  Frequency In this equation, wavelength is measured in meters and frequency is measured in hertz, or number of waves per second. Therefore, wave speed is given in meters per second. The equation for wave speed can be used to calculate the speed of a wave when both wavelength and wave frequency are known. Consider an ocean wave with a wavelength of 3 meters and a frequency of 1 hertz. The speed of the wave is: Speed = 3 m  1 wave/s = 3 m/s You Try It! Problem: Jera made a wave in a spring by pushing and pulling on one end. The wavelength is 0.1 m, and the wave frequency is 0.2 m/s. What is the speed of the wave? If you want more practice calculating wave speed from wavelength and frequency, try the problems at this URL: http The equation for wave speed (above) can be rewritten as: Frequency = Speed Speed or Wavelength = Wavelength Frequency Therefore, if you know the speed of a wave and either the wavelength or wave frequency, you can calculate the missing value. For example, suppose that a wave is traveling at a speed of 2 meters per second and has a wavelength of 1 meter. Then the frequency of the wave is: Frequency = 2 m/s = 2 waves/s, or 2 Hz 1m You Try It! Problem: A wave is traveling at a speed of 2 m/s and has a frequency of 2 Hz. What is its wavelength? ",text,
L_0743,measuring waves,T_3727,"The speed of most waves depends on the medium through which they are traveling. Generally, waves travel fastest through solids and slowest through gases. Thats because particles are closest together in solids and farthest apart in gases. When particles are farther apart, it takes longer for the energy of the disturbance to pass from particle to particle. ",text,
L_0743,measuring waves,T_3728,"The organizers of the famous Maverick surf contest have voted that the conditions are right for hanging ten this weekend. The monster waves at Mavericks attract big wave surfers from around the world. But what exactly makes these Half Moon Bay waves so big? For more information on waves, see http://science.kqed.org/quest/video/scie MEDIA Click image to the left or use the URL below. URL: ",text,
L_0744,wave interactions and interference,T_3729,"Waves interact with matter in several ways. The interactions occur when waves pass from one medium to another. Besides bouncing back like an echo, waves may bend or spread out when they strike a new medium. These three ways that waves may interact with matter are called reflection, refraction, and diffraction. Each type of interaction is described in detail below. For animations of the three types of wave interactions, go to this URL: ",text,
L_0744,wave interactions and interference,T_3730,"An echo is an example of wave reflection. Reflection occurs when waves bounce back from a barrier they cannot pass through. Reflection can happen with any type of waves, not just sound waves. For example, Figure 19.15 shows the reflection of ocean waves off a rocky coast. Light waves can also be reflected. In fact, thats how we see most objects. Light from a light source, such as the sun or a light bulb, shines on the object and some of the light is reflected. When the reflected light enters our eyes, we can see the object. Reflected waves have the same speed and frequency as the original waves before they were reflected. However, the direction of the reflected waves is different. When waves strike an obstacle head on, the reflected waves bounce straight back in the direction they came from. When waves strike an obstacle at any other angle, they bounce back at the same angle but in a different direction. This is illustrated in Figure 19.16. ",text,
L_0744,wave interactions and interference,T_3730,"An echo is an example of wave reflection. Reflection occurs when waves bounce back from a barrier they cannot pass through. Reflection can happen with any type of waves, not just sound waves. For example, Figure 19.15 shows the reflection of ocean waves off a rocky coast. Light waves can also be reflected. In fact, thats how we see most objects. Light from a light source, such as the sun or a light bulb, shines on the object and some of the light is reflected. When the reflected light enters our eyes, we can see the object. Reflected waves have the same speed and frequency as the original waves before they were reflected. However, the direction of the reflected waves is different. When waves strike an obstacle head on, the reflected waves bounce straight back in the direction they came from. When waves strike an obstacle at any other angle, they bounce back at the same angle but in a different direction. This is illustrated in Figure 19.16. ",text,
L_0744,wave interactions and interference,T_3731,"Refraction is another way that waves interact with matter. Refraction occurs when waves bend as they enter a new medium at an angle. You can see an example of refraction in Figure 19.17. Light bends when it passes from air to water. The bending of the light causes the pencil to appear broken. Why do waves bend as they enter a new medium? Waves usually travel at different speeds in different media. For example, light travels more slowly in water than air. This causes it to refract when it passes from air to water. ",text,
L_0744,wave interactions and interference,T_3731,"Refraction is another way that waves interact with matter. Refraction occurs when waves bend as they enter a new medium at an angle. You can see an example of refraction in Figure 19.17. Light bends when it passes from air to water. The bending of the light causes the pencil to appear broken. Why do waves bend as they enter a new medium? Waves usually travel at different speeds in different media. For example, light travels more slowly in water than air. This causes it to refract when it passes from air to water. ",text,
L_0744,wave interactions and interference,T_3732,"Did you ever notice that when youre walking down a street, you can hear sounds around the corners of buildings? Figure 19.18 shows why this happens. As you can see from the figure, sound waves spread out and travel around obstacles. This is called diffraction. It also occurs when waves pass through an opening in an obstacle. All waves may be diffracted, but it is more pronounced in some types of waves than others. For example, sound waves bend around corners much more than light does. Thats why you can hear but not see around corners. For a given type of waves, such as sound waves, how much the waves diffract depends on two factors: the size of the obstacle or opening in the obstacle and the wavelength. This is illustrated in Figure 19.19. Diffraction is minor if the length of the obstacle or opening is greater than the wavelength. Diffraction is major if the length of the obstacle or opening is less than the wavelength. ",text,
L_0744,wave interactions and interference,T_3732,"Did you ever notice that when youre walking down a street, you can hear sounds around the corners of buildings? Figure 19.18 shows why this happens. As you can see from the figure, sound waves spread out and travel around obstacles. This is called diffraction. It also occurs when waves pass through an opening in an obstacle. All waves may be diffracted, but it is more pronounced in some types of waves than others. For example, sound waves bend around corners much more than light does. Thats why you can hear but not see around corners. For a given type of waves, such as sound waves, how much the waves diffract depends on two factors: the size of the obstacle or opening in the obstacle and the wavelength. This is illustrated in Figure 19.19. Diffraction is minor if the length of the obstacle or opening is greater than the wavelength. Diffraction is major if the length of the obstacle or opening is less than the wavelength. ",text,
L_0744,wave interactions and interference,T_3733,"Waves interact not only with matter in the ways described above. Waves also interact with other waves. This is called wave interference. Wave interference may occur when two waves that are traveling in opposite directions meet. The two waves pass through each other, and this affects their amplitude. How amplitude is affected depends on the type of interference. Interference can be constructive or destructive. ",text,
L_0744,wave interactions and interference,T_3734,"Constructive interference occurs when the crests of one wave overlap the crests of the other wave. This is illustrated in Figure 19.20. As the waves pass through each other, the crests combine to produce a wave with greater amplitude. You can see an animation of constructive interference at this URL: http://phys23p.sl.psu.edu/phys_anim/waves/em ",text,
L_0744,wave interactions and interference,T_3735,"Destructive interference occurs when the crests of one wave overlap the troughs of another wave. This is illustrated in Figure 19.21. As the waves pass through each other, the crests and troughs cancel each other out to produce a wave with less amplitude. You can see an animation of destructive interference at this URL: http://phys23p.sl.psu.ed ",text,
L_0744,wave interactions and interference,T_3736,"When a wave is reflected straight back from an obstacle, the reflected wave interferes with the original wave and creates a standing wave. This is a wave that appears to be standing still. A standing wave occurs because of a combination of constructive and destructive interference between a wave and its reflected wave. You can see animations of standing waves at the URLs below. http://skullsinthestars.com/2008/05/04/classic-science-paper-otto-wieners-experiment-1890/  Its easy to generate a standing wave in a rope by tying one end to a fixed object and moving the other end up and down. When waves reach the fixed object, they are reflected back. The original wave and the reflected wave interfere to produce a standing wave. Try it yourself and see if the wave appears to stand still. ",text,
L_0748,characteristics of sound,T_3770,"Why does a tree make sound when it crashes to the ground? How does the sound reach peoples ears if they happen to be in the forest? And in general, how do sounds get started, and how do they travel? Keep reading to find out. ",text,
L_0748,characteristics of sound,T_3771,"All sounds begin with vibrating matter. It could be the ground vibrating when a tree comes crashing down. Or it could be guitar strings vibrating when they are plucked. You can see a guitar string vibrating in Figure 20.2. The vibrating string repeatedly pushes against the air particles next to it. The pressure of the vibrating string causes these air particles to vibrate. The air particles alternately push together and spread apart. This starts waves of vibrations that travel through the air in all directions away from the strings. The vibrations pass through the air as longitudinal waves, with individual air particles vibrating back and forth in the same direction that the waves travel. You can see an animation of sound waves moving through air at this URL: ",text,
L_0748,characteristics of sound,T_3772,"Sound waves are mechanical waves, so they can travel only though matter and not through empty space. This was demonstrated in the 1600s by a scientist named Robert Boyle. Boyle placed a ticking clock in a sealed glass jar. The clock could be heard ticking through the air and glass of the jar. Then Boyle pumped the air out of the jar. The clock was still running, but the ticking could no longer be heard. Thats because the sound couldnt travel away from the clock without air particles to pass the sound energy along. You can see an online demonstration of the same experimentwith a modern twistat this URL:  (4:06). MEDIA Click image to the left or use the URL below. URL:  Sound waves can travel through many different kinds of matter. Most of the sounds we hear travel through air, but sounds can also travel through liquids such as water and solids such as glass and metal. If you swim underwater or even submerge your ears in bathwater any sounds you hear have traveled to your ears through water. You can tell that sounds travel through glass and other solids because you can hear loud outdoor sounds such as sirens through closed windows and doors. ",text,
L_0748,characteristics of sound,T_3773,"Sound has certain characteristic properties because of the way sound energy travels in waves. Properties of sound include speed, loudness, and pitch. ",text,
L_0748,characteristics of sound,T_3774,"The speed of sound is the distance that sound waves travel in a given amount of time. You probably already know that sound travels more slowly than light. Thats why you usually see the flash of lightning before you hear the boom of thunder. However, the speed of sound isnt constant. It varies depending on the medium of the sound waves. Table 20.1 lists the speed of sound in several different media. Generally, sound waves travel fastest through solids and slowest through gases. Thats because the particles of solids are close together and can quickly pass the energy of vibrations to nearby particles. You can explore the speed of sound in different media at this URL:  Medium (20C) Air Water Wood Glass Aluminum Speed of Sound Waves (m/s) 343 1437 3850 4540 6320 The speed of sound also depends on the temperature of the medium. For a given medium such as air, sound has a slower speed at lower temperatures. You can compare the speed of sound in air at different temperatures in Table transfer the energy of the sound waves. The amount of water vapor in the air affects the speed of sound as well. Do you think sound travels faster or slower when the air contains more water vapor? (Hint: Compare the speed of sound in water and air in Table 20.1.) Temperature of Air 0C 20C 100C Speed of Sound (m/s) 331 343 386 KQED: Speed of Sound Along with cable cars and seagulls, the Golden Gate Bridge foghorn is one of San Franciscos most iconic sounds. But did you know that if you hear that foghorn off in the distance, you can calculate how many miles you are from the bridge? Using the Speed of Sound exhibit at the Outdoor Exploratorium at Fort Mason, Shawn Lani shows us how sound perception is affected by distance. For more information on the speed of sound, see http://science.kqed. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0748,characteristics of sound,T_3775,"A friend whispers to you in class in a voice so soft that you have to lean very close to hear what hes saying. Later that day, your friend shouts to you across the football field. Now his voice is loud enough for you to hear him clearly even though hes many meters away. Obviously, sounds can vary in loudness. Loudness refers to how loud or soft a sound seems to a listener. The loudness of sound is determined, in turn, by the intensity of sound. Intensity is a measure of the amount of energy in sound waves. The unit of intensity is the decibel (dB). You can see typical decibel levels of several different sounds in Figure 20.3. As decibel levels get higher, sound waves have greater intensity and sounds are louder. For every 10-decibel increase in the intensity of sound, loudness is 10 times greater. Therefore, a 30-decibel ""quiet"" room is 10 times louder than a 20-decibel whisper, and a 40- decibel light rainfall is 100 times louder than a 20-decibel whisper. How much louder than a 20-decibel whisper is the 60-decibel sound of a vacuum cleaner? The intensity of sound waves determines the loudness of sounds, but what determines intensity? Intensity is a function of two factors: the amplitude of the sound waves and how far they have traveled from the source of the sound. Remember that sound waves start at a source of vibrations and spread out from the source in all directions. The farther the sound waves travel away from the source, the more spread out their energy becomes. This is illustrated in Figure 20.4. The decrease in intensity with distance from a sound source explains why even loud sounds fade away as you move farther from the source. It also explains why low-amplitude sounds can be heard only over short distances. For a video demonstration of the amplitude and loudness of sounds, go to this URL: interactive animation at this URL: ",text,
L_0748,characteristics of sound,T_3775,"A friend whispers to you in class in a voice so soft that you have to lean very close to hear what hes saying. Later that day, your friend shouts to you across the football field. Now his voice is loud enough for you to hear him clearly even though hes many meters away. Obviously, sounds can vary in loudness. Loudness refers to how loud or soft a sound seems to a listener. The loudness of sound is determined, in turn, by the intensity of sound. Intensity is a measure of the amount of energy in sound waves. The unit of intensity is the decibel (dB). You can see typical decibel levels of several different sounds in Figure 20.3. As decibel levels get higher, sound waves have greater intensity and sounds are louder. For every 10-decibel increase in the intensity of sound, loudness is 10 times greater. Therefore, a 30-decibel ""quiet"" room is 10 times louder than a 20-decibel whisper, and a 40- decibel light rainfall is 100 times louder than a 20-decibel whisper. How much louder than a 20-decibel whisper is the 60-decibel sound of a vacuum cleaner? The intensity of sound waves determines the loudness of sounds, but what determines intensity? Intensity is a function of two factors: the amplitude of the sound waves and how far they have traveled from the source of the sound. Remember that sound waves start at a source of vibrations and spread out from the source in all directions. The farther the sound waves travel away from the source, the more spread out their energy becomes. This is illustrated in Figure 20.4. The decrease in intensity with distance from a sound source explains why even loud sounds fade away as you move farther from the source. It also explains why low-amplitude sounds can be heard only over short distances. For a video demonstration of the amplitude and loudness of sounds, go to this URL: interactive animation at this URL: ",text,
L_0748,characteristics of sound,T_3776,"A marching band is parading down the street. You can hear it coming from several blocks away. When the different instruments finally pass by you, their distinctive sounds can be heard. The tiny piccolos trill their bird-like high notes, and the big tubas rumble out their booming bass notes (see Figure 20.5). Clearly, some sounds are higher or lower than others. But do you know why? How high or low a sound seems to a listener is its pitch. Pitch, in turn, depends on the frequency of sound waves. Recall that the frequency of waves is the number of waves that pass a fixed point in a given amount of time. High-pitched sounds, like the sounds of a piccolo, have high-frequency waves. Low-pitched sounds, like the sounds of a tuba, have low-frequency waves. For a video demonstration of frequency and pitch, go to this URL:  (3:20). MEDIA Click image to the left or use the URL below. URL:  To explore an interactive animation of sound wave frequency, go to this URL:  The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. Human beings can normally hear sounds with a frequency between about 20 Hz and 20,000 Hz. Sounds with frequencies below 20 hertz are called infrasound. Sounds with frequencies above 20,000 hertz are called ultrasound. Some other animals can hear sounds in the ultrasound range. For example, dogs can hear sounds with frequencies as high as 50,000 Hz. You may have seen special whistles that dogs but not people can hear. The whistles produce a sound with a frequency too high for the human ear to detect. Other animals can hear even higher-frequency sounds. Bats, for example, can hear sounds with frequencies higher than 100,000 Hz. ",text,
L_0748,characteristics of sound,T_3777,"Look at the police car in Figure 20.6. The sound waves from its siren travel outward in all directions. Because the car is racing forward (toward the right), the sound waves get bunched up in front of the car and spread out behind it. As the car approaches the person on the right (position B), the sound waves get closer and closer together. In other words, they have a higher frequency. This makes the siren sound higher in pitch. After the car speeds by the person on the left (position A), the sound waves get more and more spread out, so they have a lower frequency. This makes the siren sound lower in pitch. A change in the frequency of sound waves, relative to a stationary listener, when the source of the sound waves is moving is called the Doppler effect. Youve probably experienced the Doppler effect yourself. The next time a vehicle with a siren races by, listen for the change in pitch. For an online animation of the Doppler effect, go to the URL below. ",text,
L_0749,hearing sound,T_3778,"Figure 20.7 shows the three main parts of the ear: the outer, middle, and inner ear. It also shows the specific structures in each part. The roles of these structures in hearing are described below and in the animations at these URLS:  (1:43) MEDIA Click image to the left or use the URL below. URL: ",text,
L_0749,hearing sound,T_3779,"The outer ear includes the pinna, ear canal, and eardrum. The pinna is the only part of the ear that extends outward from the head. Its position and shape make it good at catching sound waves and funneling them into the ear canal. The ear canal is a tube that carries sound waves into the ear. The sound waves travel through the air inside the ear canal to the eardrum. The eardrum is like the head of a drum. Its a thin membrane stretched tight across the end of the ear canal. The eardrum vibrates when sound waves strike it, and it sends the vibrations on to the middle ear. ",text,
L_0749,hearing sound,T_3780,"The middle ear contains three tiny bones (ossicles) called the hammer, anvil, and stirrup. If you look at these bones in Figure 20.7, you might notice that they resemble the objects for which they are named. The three bones transmit vibrations from the eardrum to the inner ear. They also amplify the vibrations. The arrangement of the three bones allows them to work together as a lever that increases the amplitude of the waves as they pass to the inner ear. ",text,
L_0749,hearing sound,T_3781,"The stirrup passes the amplified sound waves to the inner ear through the oval window (see Figure 20.7). When the oval window vibrates, it causes the cochlea to vibrate as well. The cochlea is a shell-like structure that is full of fluid and lined with nerve cells called hair cells. Each hair cell has tiny hair-like projections, as you can see in Figure and this triggers electrical impulses. The electrical impulses travel to the brain through nerves. Only after the nerve impulses reach the brain do we hear the sound. ",text,
L_0749,hearing sound,T_3782,"All these structures of the ear must work well for normal hearing. Damage to any of them, through illness or injury, may cause hearing loss. Total hearing loss is called deafness. To learn more about hearing loss, watch the animation at this URL:  (1:39). MEDIA Click image to the left or use the URL below. URL:  Most adults experience at least some hearing loss as they get older. The most common cause is exposure to loud sounds, which damage hair cells. The louder a sound is, the less exposure is needed for damage to occur. Even a single brief exposure to a sound louder than 115 decibels can cause hearing loss. Figure 20.9 shows the relationship between loudness, exposure time, and hearing loss. ",text,
L_0749,hearing sound,T_3782,"All these structures of the ear must work well for normal hearing. Damage to any of them, through illness or injury, may cause hearing loss. Total hearing loss is called deafness. To learn more about hearing loss, watch the animation at this URL:  (1:39). MEDIA Click image to the left or use the URL below. URL:  Most adults experience at least some hearing loss as they get older. The most common cause is exposure to loud sounds, which damage hair cells. The louder a sound is, the less exposure is needed for damage to occur. Even a single brief exposure to a sound louder than 115 decibels can cause hearing loss. Figure 20.9 shows the relationship between loudness, exposure time, and hearing loss. ",text,
L_0749,hearing sound,T_3783,"Hearing loss caused by loud sounds is permanent. However, this type of hearing loss can be prevented by protecting the ears from loud sounds. ",text,
L_0749,hearing sound,T_3784,People who work in jobs that expose them to loud sounds must wear hearing protectors. Examples include construc- tion workers who work around loud machinery for many hours each day (see Figure 20.10). But anyone exposed to loud sounds for longer than the permissible exposure time should wear hearing protectors. Many home and yard chores and even recreational activities are loud enough to cause hearing loss if people are exposed to them for very long. ,text,
L_0749,hearing sound,T_3785,"You can see two different types of hearing protectors in Figure 20.11. Earplugs are simple hearing protectors that just muffle sounds by partially blocking all sound waves from entering the ears. This type of hearing protector is suitable for lower noise levels, such as the noise of a lawnmower or snowmobile engine. Electronic ear protectors work differently. They identify high-amplitude sound waves and send sound waves through them in the opposite direction. This causes destructive interference with the waves, which reduces their amplitude to zero or nearly zero. This changes even the loudest sounds to just a soft hiss. Sounds that people need to hear, such as the voices of co-workers, are not interfered with in this way and may be amplified instead so they can be heard more clearly. This type of hearing protector is recommended for higher noise levels and situations where its important to be able to hear lower-decibel sounds. ",text,
L_0750,using sound,T_3786,"People have been using sound to make music for thousands of years. They have invented many different kinds of musical instruments for this purpose. Despite their diversity, however, musical instruments share certain similarities. All musical instruments create sound by causing matter to vibrate. The vibrations start sound waves moving through the air. Most musical instruments use resonance to amplify the sound waves and make the sounds louder. Resonance occurs when an object vibrates in response to sound waves of a certain frequency. In a musical instrument such as a guitar, the whole instrument and the air inside it may vibrate when a single string is plucked. This causes constructive interference with the sound waves, which increases their amplitude. Most musical instruments have a way of changing the frequency of the sound waves they produce. This changes the pitch of the sounds. There are three basic categories of musical instruments: percussion, wind, and stringed instruments. In Figure ",text,
L_0750,using sound,T_3787,"Researchers at Lawrence Berkeley National Laboratory are pioneering a new way to recover 100-year-old record- ings. Found on fragile wax cylinders and early lacquer records, the sounds reveal a rich acoustic heritage, including languages long lost. For more information on how to recover recordings, see http://science.kqed.org/quest/video/ MEDIA Click image to the left or use the URL below. URL: ",text,
L_0750,using sound,T_3788,"Ultrasound has frequencies higher than the human ear can detect (higher than 20,000 hertz). Although we cant hear ultrasound, it is very useful. Uses include echolocation, sonar, and ultrasonography. ",text,
L_0750,using sound,T_3789,"Animals such as bats, whales, and dolphins send out ultrasound waves and use their echoes, or reflected waves, to identify the locations of objects they cannot see. This is called echolocation. Animals use echolocation to find prey and avoid running into objects in the dark. Figure 20.13 and the animation at the URL below show how a bat uses echolocation to locate insect prey. ",text,
L_0750,using sound,T_3790,"Sonar uses ultrasound in a way that is similar to echolocation. Sonar stands for sound navigation and ranging. It is used to locate underwater objects such as sunken ships or to determine how deep the water is. A sonar device is usually located on a boat at the surface of the water. The device is both a sender and a receiver (see Figure 20.14). It sends out ultrasound waves and detects reflected waves that bounce off underwater objects or the bottom of the water. If you watch the video at the URL below, you can see how sonar is used on a submarine. The distance to underwater objects or the bottom of the water can be calculated from the known speed of sound in water and the time it takes for the waves to travel to the object. The equation for the calculation is: Distance = Speed  Time Assume, for example, that a sonar device on a ship sends an ultrasound wave to the bottom of the ocean. The speed of the sound through ocean water is 1437 m/s, and the wave travels to the bottom and back in 2 seconds. What is the distance from the surface to the bottom of the water? The sound wave travels to the bottom and back in 2 seconds, so it travels from the surface to the bottom in 1 second. Therefore, the distance from the surface to the bottom is: Distance = 1437 m/s  1 s = 1437 m You Try It! Problem: The sonar device on a ship sends an ultrasound wave to the bottom of the water at speed of 1437 m/s. The wave is reflected back to the device in 4 seconds. How deep is the water? ",text,
L_0750,using sound,T_3791,"Ultrasound can be used to ""see"" inside the human body. This use of ultrasound is called ultrasonography. Harmless ultrasound waves are sent inside the body, and the reflected waves are used to create an image on a screen. This technology is used to examine internal organs and unborn babies without risk to the patient. You can see an ultrasound image in Figure 20.15. You can see an animation showing how ultrasonography works at this URL: ",text,
L_0750,using sound,T_3792,"In this QUEST web extra, Stanford University astrophysicist Todd Hoeksema explains how solar sound waves are a vital ingredient to the science of helioseismology, in which the interior properties of the sun are probed by analyzing and tracking the surface sound waves that bounce into and out of the Sun. For more information on solar sound waves, see http://science.kqed.org/quest/video/web-extra-music-of-the-sun/ . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0751,electromagnetic waves,T_3793,"An electromagnetic wave is a wave that consists of vibrating electric and magnetic fields. A familiar example will help you understand the fields that make up an electromagnetic wave. Think about a common bar magnet. It exerts magnetic force in an area surrounding it, called the magnetic field. You can see the magnetic field of a bar magnet in Figure 21.1. Because of this force field, a magnet can exert force on objects without touching them. They just have to be in its magnetic field. An electric field is similar to a magnetic field (see Figure 21.1). An electric field is an area of electrical force surrounding a charged particle. Like a magnetic field, an electric field can exert force on objects over a distance without actually touching them. ",text,
L_0751,electromagnetic waves,T_3794,"An electromagnetic wave begins when an electrically charged particle vibrates. This is illustrated in Figure 21.2. When a charged particle vibrates, it causes the electric field surrounding it to vibrate as well. A vibrating electric field, in turn, creates a vibrating magnetic field (you can learn how this happens in the chapter ""Electromagnetism""). The two types of vibrating fields combine to create an electromagnetic wave. You can see an animation of an electromagnetic wave at this URL:  (1:31). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0751,electromagnetic waves,T_3795,"As you can see in Figure 21.2, the electric and magnetic fields that make up an electromagnetic wave occur are at right angles to each other. Both fields are also at right angles to the direction that the wave travels. Therefore, an electromagnetic wave is a transverse wave. ",text,
L_0751,electromagnetic waves,T_3796,"Unlike a mechanical transverse wave, which requires a medium, an electromagnetic transverse wave can travel through space without a medium. Waves traveling through a medium lose some energy to the medium. However, when an electromagnetic wave travels through space, no energy is lost, so the wave doesnt get weaker as it travels. However, the energy is ""diluted"" as it spreads out over an ever-larger area as it travels away from the source. This is similar to the way a sound wave spreads out and becomes less intense farther from the sound source. ",text,
L_0751,electromagnetic waves,T_3797,"Electromagnetic waves can travel through matter as well as across space. When they strike matter, they interact with it in the same ways that mechanical waves interact with matter. They may reflect (bounce back), refract (bend when traveling through different materials), or diffract (bend around objects). They may also be converted to other forms of energy. Microwaves are a familiar example. They are a type of electromagnetic wave that you can read about later on in this chapter, in the lesson ""The Electromagnetic Spectrum."" When microwaves strike food in a microwave oven, they are converted to thermal energy, which heats the food. ",text,
L_0751,electromagnetic waves,T_3798,"Electromagnetic radiation behaves like waves of energy most of the time, but sometimes it behaves like particles. As evidence accumulated for this dual nature of electromagnetic radiation, the famous physicist Albert Einstein developed a new theory about electromagnetic radiation, called the wave-particle theory. This theory explains how electromagnetic radiation can behave as both a wave and a particle. In brief, when an electron returns to a lower energy level, it is thought to give off a tiny ""packet"" of energy called a photon (see Figure 21.3). The amount of energy in a photon may vary. It depends on the frequency of electromagnetic radiation. The higher the frequency is, the more energy a photon has. ",text,
L_0751,electromagnetic waves,T_3799,"The most important source of electromagnetic radiation on Earth is the sun. Electromagnetic waves travel from the sun to Earth across space and provide virtually all the energy that supports life on our planet. Many other sources of electromagnetic waves that people use depend on technology. Radio waves, microwaves, and X rays are examples. We use these electromagnetic waves for communications, cooking, medicine, and many other purposes. Youll learn about all these types of electromagnetic waves in this chapters lesson on ""The Electromagnetic Spectrum."" ",text,
L_0752,properties of electromagnetic waves,T_3800,"All electromagnetic waves travel at the same speed through empty space. That speed, called the speed of light, is 300 million meters per second (3.0  108 m/s). Nothing else in the universe is known to travel this fast. If you could move that fast, you would be able to travel around Earth 7.5 times in just 1 second! The sun is about 150 million kilometers (93 million miles) from Earth, but it takes electromagnetic radiation only 8 minutes to reach Earth from the sun. Electromagnetic waves travel more slowly through a medium, and their speed may vary from one medium to another. For example, light travels more slowly through water than it does through air (see Figure 21.4). You can learn more about the speed of light at this URL: http://videos.howstuffworks.com/discovery/29407-assignme ",text,
L_0752,properties of electromagnetic waves,T_3801,"Although all electromagnetic waves travel at the same speed, they may differ in their wavelength and frequency. ",text,
L_0752,properties of electromagnetic waves,T_3802,Wavelength and frequency are defined in the same way for electromagnetic waves as they are for mechanical waves. Both properties are illustrated in Figure 21.5. Wavelength is the distance between corresponding points of adjacent waves. Wavelengths of electromagnetic waves range from many kilometers to a tiny fraction of a millimeter. Frequency is the number of waves that pass a fixed point in a given amount of time. Frequencies of electro- magnetic waves range from thousands to trillions of waves per second. Higher frequency waves have greater energy. ,text,
L_0752,properties of electromagnetic waves,T_3803,"The speed of a wave is a product of its wavelength and frequency. Because all electromagnetic waves travel at the same speed through space, a wave with a shorter wavelength must have a higher frequency, and vice versa. This relationship is represented by the equation: Speed = Wavelength  Frequency The equation for wave speed can be rewritten as: Frequency = Speed Speed or Wavelength = Wavelength Frequency Therefore, if either wavelength or frequency is known, the missing value can be calculated. Consider an electromag- netic wave that has a wavelength of 3 meters. Its speed, like the speed of all electromagnetic waves, is 3.0  108 meters per second. Its frequency can be found by substituting these values into the frequency equation: Frequency = 3.0  108 m/s = 1.0  108 waves/s, or 1.0  108 hertz (Hz) 3.0 m You Try It! Problem: What is the wavelength of an electromagnetic wave that has a frequency of 3.0  108 hertz? For more practice calculating the frequency and wavelength of electromagnetic waves, go to these URLs: ",text,
L_0753,the electromagnetic spectrum,T_3804,"Electromagnetic radiation occurs in waves of different wavelengths and frequencies. Infrared light and visible light make up just a small part of the full range of electromagnetic radiation, which is called the electromagnetic spectrum. The electromagnetic spectrum is summarized in the diagram in Figure 21.7. On the far left of the diagram are radio waves, which include microwaves. They have the longest wavelengths and lowest frequencies of all electromagnetic waves. They also have the least amount of energy. On the far right are X rays and gamma rays. The have the shortest wavelengths and highest frequencies of all electromagnetic waves. They also have the greatest amount of energy. Between these two extremes, wavelength, frequency, and energy change continuously from one side of the spectrum to the other. Waves in this middle section of the electromagnetic spectrum are commonly called light. As you will read below, the properties of electromagnetic waves influence how the different waves behave and how they can be used. ",text,
L_0753,the electromagnetic spectrum,T_3804,"Electromagnetic radiation occurs in waves of different wavelengths and frequencies. Infrared light and visible light make up just a small part of the full range of electromagnetic radiation, which is called the electromagnetic spectrum. The electromagnetic spectrum is summarized in the diagram in Figure 21.7. On the far left of the diagram are radio waves, which include microwaves. They have the longest wavelengths and lowest frequencies of all electromagnetic waves. They also have the least amount of energy. On the far right are X rays and gamma rays. The have the shortest wavelengths and highest frequencies of all electromagnetic waves. They also have the greatest amount of energy. Between these two extremes, wavelength, frequency, and energy change continuously from one side of the spectrum to the other. Waves in this middle section of the electromagnetic spectrum are commonly called light. As you will read below, the properties of electromagnetic waves influence how the different waves behave and how they can be used. ",text,
L_0753,the electromagnetic spectrum,T_3805,"Radio waves are the broad range of electromagnetic waves with the longest wavelengths and lowest frequencies. In Figure 21.7, you can see that the wavelength of radio waves may be longer than a soccer field. With their low frequencies, radio waves have the least energy of electromagnetic waves, but they still are extremely useful. They are used for radio and television broadcasts, microwave ovens, cell phone transmissions, and radar. You can learn more about radio waves, including how they were discovered, at this URL:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0753,the electromagnetic spectrum,T_3806,"In radio broadcasts, sounds are encoded in radio waves that are sent out through the atmosphere from a radio tower. A receiver detects the radio waves and changes them back to sounds. Youve probably listened to both AM and FM radio stations. How sounds are encoded in radio waves differs between AM and FM broadcasts. AM stands for amplitude modulation. In AM broadcasts, sound signals are encoded by changing the amplitude of radio waves. AM broadcasts use longerwavelength radio waves than FM broadcasts. Because of their longer wavelengths, AM radio waves reflect off a layer of the upper atmosphere called the ionosphere. You can see how this happens in Figure 21.8. This allows AM radio waves to reach radio receivers that are very far away from the radio tower. FM stands for frequency modulation. In FM broadcasts, sound signals are encoded by changing the frequency of radio waves. Frequency modulation allows FM waves to encode more information than does amplitude modulation, so FM broadcasts usually sound clearer than AM broadcasts. However, because of their shorter wavelength, FM waves do not reflect off the ionosphere. Instead, they pass right through it and out into space (see Figure 21.8). As a result, FM waves cannot reach very distant receivers. ",text,
L_0753,the electromagnetic spectrum,T_3807,"Television broadcasts also use radio waves. Sounds are encoded with frequency modulation, and pictures are encoded with amplitude modulation. The encoded radio waves are broadcast from a TV tower like the one in Figure 21.9. When the waves are received by television sets, they are decoded and changed back to sounds and pictures. ",text,
L_0753,the electromagnetic spectrum,T_3808,"The shortest wavelength, highest frequency radio waves are called microwaves (see Figure 21.7). Microwaves have more energy than other radio waves. Thats why they are useful for heating food in microwave ovens. Microwaves have other important uses as well, including cell phone transmissions and radar, which is a device for determining the presence and location of an object by measuring the time for the echo of a radio wave to return from it and the direction from which it returns. These uses are described in Figure 21.10. You can learn more about microwaves and their uses in the video at this URL:  (3:23). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0753,the electromagnetic spectrum,T_3809,"Mid-wavelength electromagnetic waves are commonly called light. This range of electromagnetic waves has shorter wavelengths and higher frequencies than radio waves, but not as short and high as X rays and gamma rays. Light includes visible light, infrared light, and ultraviolet light. If you look back at Figure 21.7, you can see where these different types of light waves fall in the electromagnetic spectrum. ",text,
L_0753,the electromagnetic spectrum,T_3810,"The only light that people can see is called visible light. It refers to a very narrow range of wavelengths in the electromagnetic spectrum that falls between infrared light and ultraviolet light. Within the visible range, we see light of different wavelengths as different colors of light, from red light, which has the longest wavelength, to violet light, which has the shortest wavelength. You can see the spectrum of colors of visible light in Figure 21.11. When all of the wavelengths are combined, as they are in sunlight, visible light appears white. You can learn more about visible light in the chapter ""Visible Light"" and at the URL below. ",text,
L_0753,the electromagnetic spectrum,T_3810,"The only light that people can see is called visible light. It refers to a very narrow range of wavelengths in the electromagnetic spectrum that falls between infrared light and ultraviolet light. Within the visible range, we see light of different wavelengths as different colors of light, from red light, which has the longest wavelength, to violet light, which has the shortest wavelength. You can see the spectrum of colors of visible light in Figure 21.11. When all of the wavelengths are combined, as they are in sunlight, visible light appears white. You can learn more about visible light in the chapter ""Visible Light"" and at the URL below. ",text,
L_0753,the electromagnetic spectrum,T_3811,"Light with the longest wavelengths is called infrared light. The term infrared means ""below red."" Infrared light is the range of light waves that have longer wavelengths than red light in the visible spectrum. You cant see infrared light waves, but you can feel them as heat on your skin. The sun gives off infrared light as do fires and living things. The picture of a cat that opened this chapter was made with a camera that detects infrared light waves and changes their energy to colored light in the visible range. Night vision goggles, which are used by law enforcement and the military, also detect infrared light waves. The goggles convert the invisible waves to visible images. For a deeper understanding of infrared light, watch the video at this URL:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0753,the electromagnetic spectrum,T_3812,"Light with wavelengths shorter than visible light is called ultraviolet light. The term ultraviolet means ""above violet."" Ultraviolet light is the range of light waves that have shorter wavelengths than violet light in the visible spectrum. Humans cant see ultraviolet light, but it is very useful nonetheless. It has higher-frequency waves than visible light, so it has more energy. It can be used to kill bacteria in food and to sterilize laboratory equipment (see Figure 21.12). The human skin also makes vitamin D when it is exposed to ultraviolet light. Vitamin D is needed for strong bones and teeth. You can learn more about ultraviolet light and its discovery at this URL:  MEDIA Click image to the left or use the URL below. URL:  Too much exposure to ultraviolet light can cause sunburn and skin cancer. You can protect your skin from ultraviolet light by wearing clothing that covers your skin and by applying sunscreen to any exposed areas. The SPF, or sun- protection factor, of sunscreen gives a rough idea of how long it protects the skin from sunburn (see Figure 21.13). A sunscreen with a higher SPF protects the skin longer. You should use sunscreen with an SPF of at least 15 even on cloudy days, because ultraviolet light can travel through clouds. Sunscreen should be applied liberally and often. You can learn more about the effects of ultraviolet light on the skin at this URL:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0753,the electromagnetic spectrum,T_3813,"The shortest-wavelength, highest-frequency electromagnetic waves are X rays and gamma rays. These rays have so much energy that they can pass through many materials. This makes them potentially very harmful, but it also makes them useful for certain purposes. ",text,
L_0753,the electromagnetic spectrum,T_3814,"X rays are high-energy electromagnetic waves. They have enough energy to pass through soft tissues such as skin but not enough to pass through bones and teeth, which are very dense. The bright areas on the X ray film in Figure also to screen luggage at airports (see Figure 21.14). Too much X ray exposure may cause cancer. If youve had dental X rays, you may have noticed that a heavy apron was placed over your body to protect it from stray X rays. The apron is made of lead, which X rays cannot pass through. You can learn about the discovery of X rays as well as other uses of X rays at this URL: ",text,
L_0753,the electromagnetic spectrum,T_3815,"Gamma rays are the most energetic of all electromagnetic waves. They can pass through most materials, including bones and teeth. Nonetheless, even these waves are useful. For example, they can be used to treat cancer. A medical device sends gamma rays the site of the cancer, and the rays destroy the cancerous cells. If you want to learn more about gamma rays, watch the video at the URL below. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0753,the electromagnetic spectrum,T_3816,"Scientists in Berkeley have developed a powerful new microscope which uses X rays to scan a whole cell and in a manner of minutes, generate a 3D view of the cell and its genetic material. This groundbreaking tool is helping to advance research into the development of biofuels, the treatment of malaria and it may even help to more rapidly diagnose cancer. For more information on X ray microscopes, see http://science.kqed.org/quest/video/x-ray-micros MEDIA Click image to the left or use the URL below. URL: ",text,
L_0754,the light we see,T_3817,Look at the classroom in Figure 22.1. It has several sources of visible light. One source of visible light is the sun. Sunlight enters the classroom through the windows. The sun provides virtually all of the visible light that living things need. Visible light travels across space from the sun to Earth in electromagnetic waves. But how does the sun produce light? Read on to find out. ,text,
L_0754,the light we see,T_3818,"The sun and other stars produce light because they are so hot. They glow with light due to their extremely high temperatures. This way of producing light is called incandescence. Some objects produce light without becoming very hot. They generate light through chemical reactions or other processes. Producing light without heat is called luminescence. Objects that produce light by luminescence are said to be luminous. Luminescence, in turn, can occur in different ways: One type of luminescence is called fluorescence. In this process, a substance absorbs shorter-wavelength light, such as ultraviolet light, and then gives off light in the visible range of wavelengths. Certain minerals produce light in this way. Another type of luminescence is called electroluminescence. In this process, a substance gives off light when an electric current runs through it. Some gases produce light in this way. A third type of luminescence is called bioluminescence. This is the production of light by living things as a result of chemical reactions. Examples of bioluminescent organisms are pictured in Figure 22.2. You can learn more about bioluminescence in the video at this URL:  Many other objects appear to produce their own light, but they actually just reflect light from another source. The moon is a good example. It appears to glow in the sky from its own light, but in reality it is just reflecting light from the sun. Objects like the moon that are lit up by another source of light are said to be illuminated. Everything you can see that doesnt produce its own light is illuminated. ",text,
L_0754,the light we see,T_3819,"The classroom in Figure 22.1 has artificial light sources in addition to natural sunlight. There are fluorescent lights on the ceiling of the room. There are also projectors on the ceiling that are shining light on screens. In these and most other artificial light sources, electricity provides the energy and some type of light bulb converts the electrical energy to visible light. How a light bulb produces visible light varies by type of bulb, as you can see in Table 22.1. Incandescent light bulbs, which produce light by incandescence, give off a lot of heat as well as light, so they waste energy. Other light bulbs produce light by luminescence, so they produce little if any heat. These light bulbs use energy more efficiently. Which types of light bulbs do you use? Type of Light Bulb Incandescent Light Description An incandescent light bulb produces visible light by incandescence. The bulb contains a thin wire filament made of tungsten. When electric current passes through the filament, it gets extremely hot and glows. You can learn more about incandescent light bulbs at the URL below. Fluorescent Light A fluorescent light bulb produces visible light by flu- orescence. The bulb contains mercury gas that gives off ultraviolet light when electricity passes through it. The inside of the bulb is coated with a substance called phosphor. The phosphor absorbs the ultraviolet light and then gives off most of the energy as visible light. You can learn more about fluorescent light bulbs at this URL: http://science.discovery.com/videos/deco Type of Light Bulb Neon Light Vapor Light LED Light Description A neon light produces visible light by electrolumines- cence. The bulb is a glass tube that contains the noble gas neon. When electricity passes through the gas, it excites electrons of neon atoms, causing them to give off visible light. Neon produces red light. Other noble gases are also used in lights, and they produce light of different colors. For example, krypton produces violet light, and argon produces blue light. A vapor light produces visible light by electrolumi- nescence. The bulb contains a small amount of solid sodium or mercury as well as a mixture of neon and argon gases. When an electric current passes through the gases, it causes the solid sodium or mercury to change to a gas and emit visible light. Sodium vapor lights, like these streetlights, produce yellowish light. Mercury vapor lights produce bluish light. Vapor lights are very bright and energy efficient. The bulbs are also long lasting. LED stands for light-emitting diode. This type of light contains a material, called a semi-conductor, which gives off visible light when a current runs through it. LED lights are used for traffic lights and indicator lights on computers, cars, and many other devices. This type of light is very reliable and durable. ",text,
L_0754,the light we see,T_3820,"When visible light strikes matter, it interacts with it. How light interacts with matter depends on the type of matter. ",text,
L_0754,the light we see,T_3821,"Light may interact with matter in several ways. Light may be reflected by matter. Reflected light bounces back when it strikes matter. Reflection of light is similar to reflection of sound waves. You can read more about reflection of light later on in this chapter in the lesson Optics. Light may be refracted by matter. The light is bent when it passes from one type of matter to another. Refraction of light is similar to refraction of sound waves. You can also read more about refraction of light in the lesson Optics. Light may pass through matter. This is called transmission of light. As light is transmitted, it may be scattered by particles of matter and spread out in all directions. This is called scattering of light. Light may be absorbed by matter. This is called absorption of light. When light is absorbed, it doesnt reflect from or pass through matter. Instead, its energy is transferred to particles of matter, which may increase the temperature of matter. ",text,
L_0754,the light we see,T_3822,"Matter can be classified on the basis of how light interacts with it. Matter may be transparent, translucent, or opaque. Each type of matter is illustrated in Figure 22.3. Transparent matter is matter that transmits light without scattering it. Examples of transparent matter include air, pure water, and clear glass. You can see clearly through a transparent object, such as the revolving glass doors in the figure, because all the light passes straight through it. Translucent matter is matter that transmits but scatters light. Light passes through a translucent object but you cannot see clearly through the object because the light is scattered in all directions. The frosted glass doors in the figure are translucent. Opaque matter is matter that does not let any light pass through it. Matter may be opaque because it absorbs light, reflects light, or does both. Examples of opaque objects are solid wooden doors and glass mirrors. A wooden door absorbs most of the light that strikes it and reflects just a few wavelengths of visible light. A mirror, which is a sheet of glass with a shiny metal coating on the back, reflects all the light that strikes it. ",text,
L_0754,the light we see,T_3823,"Visible light consists of a range of wavelengths. The wavelength of visible light determines the color that the light appears. As you can see in Figure 22.4, light with the longest wavelength appears red, and light with the shortest wavelength appears violet. In between is a continuum of all the other colors of light. Only a few colors of light are represented in the figure. ",text,
L_0754,the light we see,T_3824,"A prism, like the one in Figure 22.5, can be used to separate visible light into its different colors. A prism is a pyramid-shaped object made of transparent matter, usually clear glass. It transmits light but slows it down. When light passes from the air to the glass of the prism, the change in speed causes the light to bend. Different wavelengths of light bend at different angles. This causes the beam of light to separate into light of different wavelengths. What we see is a rainbow of colors. Look back at the rainbow that opened this chapter. Do you see all the different colors of light, from red at the top to violet at the bottom? Individual raindrops act as tiny prisms. They separate sunlight into its different wavelengths and create a rainbow. For an animated version of Figure 22.5, go to the URL: http://en.wikipedia.org/wiki/File:Light_dispersion_conce ",text,
L_0754,the light we see,T_3825,"We see an opaque object, such as the apple in Figure 22.6, because it reflects some wavelengths of visible light. The wavelengths that are reflected determine the color that the object appears. For example, the apple in the figure appears red because it reflects red light and absorbs light of other wavelengths. We see a transparent or translucent object, such as the bottle in Figure 22.6, because it transmits light. The wavelength of the transmitted light determines the color that the object appears. For example, the bottle in the figure appears blue because it transmits blue light. The color of light that strikes an object may also affect the color that the object appears. For example, if only blue light strikes a red apple, the blue light is absorbed and no light is reflected. When no light reflects from an object, it looks black. Black isnt a color. It is the absence of light. ",text,
L_0754,the light we see,T_3826,"The human eye can distinguish only red, green, and blue light. These three colors of light are called primary colors. All other colors of light can be created by combining the primary colors. As you can see in Figure 22.7, when red and green light combine, they form yellow. When red and blue light combine, they form magenta, a dark pinkish color, and when blue and green light combine, they form cyan, a bluish green color. Yellow, magenta, and cyan are called the secondary colors of light. Look at the center of the diagram in Figure 22.7. When all three primary colors combine, they form white light. White is the color of the full spectrum of visible light when all of its wavelengths are combined. You can explore the colors of visible light and how they combine with the interactive animations at this URL:  . ",text,
L_0754,the light we see,T_3826,"The human eye can distinguish only red, green, and blue light. These three colors of light are called primary colors. All other colors of light can be created by combining the primary colors. As you can see in Figure 22.7, when red and green light combine, they form yellow. When red and blue light combine, they form magenta, a dark pinkish color, and when blue and green light combine, they form cyan, a bluish green color. Yellow, magenta, and cyan are called the secondary colors of light. Look at the center of the diagram in Figure 22.7. When all three primary colors combine, they form white light. White is the color of the full spectrum of visible light when all of its wavelengths are combined. You can explore the colors of visible light and how they combine with the interactive animations at this URL:  . ",text,
L_0754,the light we see,T_3826,"The human eye can distinguish only red, green, and blue light. These three colors of light are called primary colors. All other colors of light can be created by combining the primary colors. As you can see in Figure 22.7, when red and green light combine, they form yellow. When red and blue light combine, they form magenta, a dark pinkish color, and when blue and green light combine, they form cyan, a bluish green color. Yellow, magenta, and cyan are called the secondary colors of light. Look at the center of the diagram in Figure 22.7. When all three primary colors combine, they form white light. White is the color of the full spectrum of visible light when all of its wavelengths are combined. You can explore the colors of visible light and how they combine with the interactive animations at this URL:  . ",text,
L_0754,the light we see,T_3826,"The human eye can distinguish only red, green, and blue light. These three colors of light are called primary colors. All other colors of light can be created by combining the primary colors. As you can see in Figure 22.7, when red and green light combine, they form yellow. When red and blue light combine, they form magenta, a dark pinkish color, and when blue and green light combine, they form cyan, a bluish green color. Yellow, magenta, and cyan are called the secondary colors of light. Look at the center of the diagram in Figure 22.7. When all three primary colors combine, they form white light. White is the color of the full spectrum of visible light when all of its wavelengths are combined. You can explore the colors of visible light and how they combine with the interactive animations at this URL:  . ",text,
L_0754,the light we see,T_3827,"Many objects have color because they contain pigments. A pigment is a substance that colors materials by reflecting light of certain wavelengths and absorbing light of other wavelengths. A very common pigment is chlorophyll, which is found in plants. This dark green pigment absorbs all but green wavelengths of visible light. It is responsible for capturing the light energy needed for photosynthesis. Pigments are also found in paints, inks, and dyes. Just three pigments, called primary pigments, can be combined to produce all other colors. The primary pigment colors are the same as the secondary colors of light: cyan, magenta, and yellow. The printer ink cartridges in Figure 22.8 come in just these three colors. They are the only colors needed for full-color printing. ",text,
L_0754,the light we see,T_3828,"Artist Kate Nichols longed to paint with the iridescent colors of butterfly wings, but no such pigments existed. So she became the first artist-in-residence at Lawrence Berkeley National Laboratory to synthesize nanoparticles and incorporate them into her artwork. From the laboratory to the studio, see how Kate uses the phenomenon known as ""structural color"" to transform nanotechnology into creativity. For more information on using nanoparticles to create colors, see http://science.kqed.org/quest/video/science-on-the-spot-color-by-nano-the-art-of-kate-nichols/ . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0755,optics,T_3829,Almost all surfaces reflect some of the light that strikes them. The still water of the lake in Figure 22.9 reflects almost all of the light that strikes it. The reflected light forms an image of nearby objects. An image is a copy of an object that is formed by reflected or refracted light. ,text,
L_0755,optics,T_3830,"If a surface is extremely smooth, like very still water, then an image formed by reflection is sharp and clear. This is called regular reflection. If the surface is even slightly rough, an image may not form, or if there is an image, it is blurry or fuzzy. This is called diffuse reflection. Both types of reflection are represented in Figure 22.10. You can also see animations of both types of reflection at this URL: http://toolboxes.flexiblelearning.net.au/demosites/serie In Figure 22.10, the waves of light are represented by arrows called rays. Rays that strike the surface are referred to as incident rays, and rays that reflect off the surface are known as reflected rays. In regular reflection, all the rays are reflected in the same direction. This explains why regular reflection forms a clear image. In diffuse reflection, in contrast, the rays are reflected in many different directions. This is why diffuse reflection forms, at best, a blurry image. ",text,
L_0755,optics,T_3831,"One thing is true of both regular and diffuse reflection. The angle at which the reflected rays bounce off the surface is equal to the angle at which the incident rays strike the surface. This is the law of reflection, and it applies to the reflection of all light. The law is illustrated in Figure 22.11 and in the animation at this URL: ",text,
L_0755,optics,T_3832,"Mirrors are usually made of glass with a shiny metal backing that reflects all the light that strikes it. Mirrors may have flat or curved surfaces. The shape of a mirrors surface determines the type of image the mirror forms. For example, the image may be real or virtual. A real image forms in front of a mirror where reflected light rays actually meet. It is a true image that could be projected on a screen. A virtual image appears to be on the other side of the mirror. Of course, reflected rays dont actually go behind a mirror, so a virtual image doesnt really exist. It just appears to exist to the human eye and brain. ",text,
L_0755,optics,T_3833,"Most mirrors are plane mirrors. A plane mirror has a flat reflective surface and forms only virtual images. The image formed by a plane mirror is also life sized. But something is different about the image compared with the real object in front of the mirror. Left and right are reversed. Look at the man shaving in Figure 22.12. He is using his right hand to hold the razor, but his image appears to be holding the razor in the left hand. Almost all plane mirrors reverse left and right in this way. ",text,
L_0755,optics,T_3834,"Some mirrors have a curved rather than flat surface. Curved mirrors can be concave or convex. A concave mirror is shaped like the inside of a bowl. This type of mirror forms either real or virtual images, depending on where the object is placed relative to the focal point. The focal point is the point in front of the mirror where the reflected rays intersect. You can see how concave mirrors form images in Figure 22.13 and in the interactive animation at the URL below. The animation allows you to move an object to see how its position affects the image. Concave mirrors are used behind car headlights. They focus the light and make it brighter. They are also used in some telescopes. ",text,
L_0755,optics,T_3834,"Some mirrors have a curved rather than flat surface. Curved mirrors can be concave or convex. A concave mirror is shaped like the inside of a bowl. This type of mirror forms either real or virtual images, depending on where the object is placed relative to the focal point. The focal point is the point in front of the mirror where the reflected rays intersect. You can see how concave mirrors form images in Figure 22.13 and in the interactive animation at the URL below. The animation allows you to move an object to see how its position affects the image. Concave mirrors are used behind car headlights. They focus the light and make it brighter. They are also used in some telescopes. ",text,
L_0755,optics,T_3835,"The other type of curved mirror, a convex mirror, is shaped like the outside of a bowl. This type of mirror forms only virtual images. The image is always right-side up and smaller than the actual object, which makes the object appear farther away than it really is. You can see how a convex mirror forms an image in Figure 22.14 and in the animation at the URL below. Because of their shape, convex mirrors can gather and reflect light from a wide area. This is why they are used as side mirrors on cars. They give the driver a wider view of the area around the vehicle than a plane mirror would. ",text,
L_0755,optics,T_3836,"Although the speed of light is constant in a vacuum, light travels at different speeds in different kinds of matter. For example, light travels more slowly in glass than in air. Therefore, when light passes from air to glass, it slows down. If light strikes a sheet of glass straight on, or perpendicular to the glass, it slows down but passes straight through. However, if light enters the glass at an angle other than 90 , the wave refracts, or bends. This is illustrated in Figure change in speed, the more light bends. ",text,
L_0755,optics,T_3836,"Although the speed of light is constant in a vacuum, light travels at different speeds in different kinds of matter. For example, light travels more slowly in glass than in air. Therefore, when light passes from air to glass, it slows down. If light strikes a sheet of glass straight on, or perpendicular to the glass, it slows down but passes straight through. However, if light enters the glass at an angle other than 90 , the wave refracts, or bends. This is illustrated in Figure change in speed, the more light bends. ",text,
L_0755,optics,T_3837,"Lenses make use of the refraction of light to create images. A lens is a transparent object, typically made of glass, with one or two curved surfaces. The more curved the surface of a lens is, the more it refracts light. Like mirrors, lenses may be concave or convex. ",text,
L_0755,optics,T_3838,"Concave lenses are thicker at the edges than in the middle. They cause rays of light to diverge, or spread apart. Figure 22.16 shows how a concave lens forms an image. The image is always virtual and on the same side of the lens as the object. The image is also right-side up and smaller than the object. Concave lenses are used in cameras. They focus reduced images inside the camera, where they are captured and stored. You can explore the formation of images by a concave lens with the interactive animation at this URL: http://phet.colorado.edu/sims/geometric-opti ",text,
L_0755,optics,T_3839,"Convex lenses are thicker in the middle than at the edges. They cause rays of light to converge, or meet, at a point called the focus (F). Convex lenses form either real or virtual images. It depends on how close an object is to the lens relative to the focus. Figure 22.17 shows how a convex lens works. You can also interact with an animated convex lens at the URL below. An example of a convex lens is a hand lens. ",text,
L_0755,optics,T_3840,"Mirrors and lenses are used in optical instruments to reflect and refract light. Optical instruments include micro- scopes, telescopes, cameras, and lasers. ",text,
L_0755,optics,T_3841,"A light microscope is an instrument that uses lenses to make enlarged images of objects that are too small for the unaided eye to see. A common type of light microscope is a compound microscope, like the one in Figure 22.18. A compound microscope has at least two convex lenses: one or more objective lenses and one or more eyepiece lenses. The objective lenses are close to the object being viewed. They form an enlarged image of the object inside the microscope. The eyepiece lenses are close to the viewers eyes. They form an enlarged image of the first image. The magnifications of all the lenses are multiplied together to yield the overall magnification of the microscope. Some light microscopes can magnify objects more than 1000 times! For more on light microscopes and the images they create, watch the video at this URL:  (7:29). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0755,optics,T_3841,"A light microscope is an instrument that uses lenses to make enlarged images of objects that are too small for the unaided eye to see. A common type of light microscope is a compound microscope, like the one in Figure 22.18. A compound microscope has at least two convex lenses: one or more objective lenses and one or more eyepiece lenses. The objective lenses are close to the object being viewed. They form an enlarged image of the object inside the microscope. The eyepiece lenses are close to the viewers eyes. They form an enlarged image of the first image. The magnifications of all the lenses are multiplied together to yield the overall magnification of the microscope. Some light microscopes can magnify objects more than 1000 times! For more on light microscopes and the images they create, watch the video at this URL:  (7:29). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0755,optics,T_3842,"Like microscopes, telescopes use convex lenses to make enlarged images. However, telescopes make enlarged images of objectssuch as distant starsthat only appear tiny because they are very far away. There are two basic types of telescopes: reflecting telescopes and refracting telescopes. The two types are compared in Figure 22.19. You can learn more about telescopes and how they evolved in the video at this URL: ",text,
L_0755,optics,T_3843,"A camera is an optical instrument that records an image of an object. The image may be recorded on film or it may be detected by an electronic sensor that stores the image digitally. Regardless of how the image is recorded, all cameras form images in the same basic way, as demonstrated in Figure 22.20 and at the URL below. Light passes through the lens at the front of the camera and enters the camera through an opening called the aperture. As light passes through the lens, it forms a reduced real image. The image focuses on film (or a sensor) at the back of the camera. The lens may be moved back and forth to bring the image into focus. The shutter controls the amount of light that strikes the film (or sensor). It stays open longer in dim light to let more light in. For a series of animations showing how a camera works, go to this URL:  . ",text,
L_0755,optics,T_3843,"A camera is an optical instrument that records an image of an object. The image may be recorded on film or it may be detected by an electronic sensor that stores the image digitally. Regardless of how the image is recorded, all cameras form images in the same basic way, as demonstrated in Figure 22.20 and at the URL below. Light passes through the lens at the front of the camera and enters the camera through an opening called the aperture. As light passes through the lens, it forms a reduced real image. The image focuses on film (or a sensor) at the back of the camera. The lens may be moved back and forth to bring the image into focus. The shutter controls the amount of light that strikes the film (or sensor). It stays open longer in dim light to let more light in. For a series of animations showing how a camera works, go to this URL:  . ",text,
L_0755,optics,T_3844,"Did you ever see a cat chase after a laser light, like the one in Figure 22.21? A laser is a device that produces a very focused beam of light of just one wavelength and color. Waves of laser light are synchronized so the crests and troughs of the waves line up (see Figure 22.21). Laser light is created in a tube like the one shown in Figure 22.22. Electrons in a material such as a ruby crystal are stimulated to radiate photons of light of one wavelength. At each end of the tube is a concave mirror. The photons of light bounce back and forth in the tube off the mirrors. This focuses the light. The mirror at one end of the tube is partly transparent. A constant stream of photons passes through the transparent part, forming the laser beam. You can see an animation showing how a laser works at this URL:  (1:12). MEDIA Click image to the left or use the URL below. URL:  Besides entertaining a cat, laser light has many other uses. It is used to scan bar codes, for example, and to carry communication signals in optical fibers. Optical fibers are extremely thin glass tubes that are used to guide laser light (see Figure 22.23). Sounds or pictures are encoded in pulses of laser light, which are then sent through an optical fiber. All of the light reflects off the inside of the fiber, so none of it escapes. As a result, the signal remains strong even over long distances. More than one signal can travel through an optic fiber at the same time, as you can see in Figure 22.23. Optical fibers are used to carry telephone, cable TV, and Internet signals. ",text,
L_0755,optics,T_3844,"Did you ever see a cat chase after a laser light, like the one in Figure 22.21? A laser is a device that produces a very focused beam of light of just one wavelength and color. Waves of laser light are synchronized so the crests and troughs of the waves line up (see Figure 22.21). Laser light is created in a tube like the one shown in Figure 22.22. Electrons in a material such as a ruby crystal are stimulated to radiate photons of light of one wavelength. At each end of the tube is a concave mirror. The photons of light bounce back and forth in the tube off the mirrors. This focuses the light. The mirror at one end of the tube is partly transparent. A constant stream of photons passes through the transparent part, forming the laser beam. You can see an animation showing how a laser works at this URL:  (1:12). MEDIA Click image to the left or use the URL below. URL:  Besides entertaining a cat, laser light has many other uses. It is used to scan bar codes, for example, and to carry communication signals in optical fibers. Optical fibers are extremely thin glass tubes that are used to guide laser light (see Figure 22.23). Sounds or pictures are encoded in pulses of laser light, which are then sent through an optical fiber. All of the light reflects off the inside of the fiber, so none of it escapes. As a result, the signal remains strong even over long distances. More than one signal can travel through an optic fiber at the same time, as you can see in Figure 22.23. Optical fibers are used to carry telephone, cable TV, and Internet signals. ",text,
L_0756,vision,T_3845,"The structure of the human eye is shown in Figure 22.24. Find each structure in the diagram as you read about it below. The cornea is the transparent outer covering of the eye. It protects the eye and also acts as a convex lens, helping to focus light that enters the eye. The pupil is an opening in the front of the eye. It looks black because it doesnt reflect any light. It allows light to enter the eye. The pupil automatically gets bigger or smaller to let more or less light in as needed. The iris is the colored part of the eye. It controls the size of the pupil. The lens is a convex lens that fine-tunes the focus so an image forms on the back of the eye. Tiny muscles control the shape of the lens to focus images of close or distant objects. The retina is a membrane lining the back of the eye. The retina has nerve cells called rods and cones that change images to electrical signals. Rods are good at sensing dim light but cant distinguish different colors of light. Cones can sense colors but not in dim light. There are three different types of cones. Each type senses one of the three primary colors of light. The optic nerve carries electrical signals from the rods and cones to the brain. ",text,
L_0756,vision,T_3846,"As just described, the eyes collect and focus visible light. The lens and other structures of the eye work together to focus a real image on the retina. The image is upside-down and reduced in size, as you can see in Figure 22.25. The image reaches the brain as electrical signals that travel through the optic nerve. The brain interprets the signals as shape, color, and brightness. It also interprets the image as though it were right-side up. The brain does this automatically, so what we see is always right-side up. The brain also tells us what we are seeing. ",text,
L_0756,vision,T_3847,"Many people have vision problems. The problems often can be corrected with contact lenses or lenses in eyeglasses. Some vision problems can also be corrected with laser surgery, which reshapes the cornea. Two of the most common vision problems are nearsightedness and farsightedness. You may even have one of these conditions yourself. Both are illustrated in Figure 22.26 and in the video at this URL:  (1:08). MEDIA Click image to the left or use the URL below. URL:  Nearsightedness, or myopia, is the condition in which nearby objects are seen clearly, but distant objects are blurry. It occurs when the eyeball is longer than normal. This causes images to be focused in front of the retina. Myopia can be corrected with concave lenses. The lenses focus images farther back in the eye, so they are on the retina instead of in front of it. Farsightedness, or hyperopia, is the condition in which distant objects are seen clearly, but nearby objects are blurry. It occurs when the eyeball is shorter than normal. This causes images to be focused in back of the retina. Hyperopia can be corrected with convex lenses. The lenses focus images farther forward in the eye, so they are on the retina instead of behind it. ",text,
L_0761,magnets and magnetism,T_3883,"A magnet is an object that attracts certain materials such as iron. Youre probably familiar with common bar magnets, like the one in Figure 24.2. Like all magnets, this bar magnet has north and south poles and attracts objects such as paper clips that contain iron. ",text,
L_0761,magnets and magnetism,T_3884,"All magnets have two magnetic poles. The poles are regions where the magnet is strongest. The poles are called north and south because they always line up with Earths north-south axis if the magnet is allowed to move freely. (Earths axis is the imaginary line around which the planet rotates.) What do you suppose would happen if you cut the bar magnet in Figure 24.2 in half along the line between the north and south poles? Both halves would also have north and south poles. If you cut each of the halves in half, all those pieces would have north and south poles as well. Pieces of a magnet always have both north and south poles no matter how many times you cut the magnet. ",text,
L_0761,magnets and magnetism,T_3885,"The force that a magnet exerts on certain materials is called magnetic force. Like electric force, magnetic force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. ",text,
L_0761,magnets and magnetism,T_3886,"Like the electric field that surrounds a charged particle, a magnetic field surrounds a magnet. This is the area around the magnet where it exerts magnetic force. Figure 24.3 shows the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. To see an animated magnetic field of a bar magnet, go to this URL: http://elgg.norfolk.e2bn.org/jsmith112/files/68/149/ When two magnets are brought close together, their magnetic fields interact. You can see how in Figure 24.4. The drawings show how lines of force of north and south poles attract each other whereas those of two north poles repel each other. The animations at the URL below show how magnetic field lines change as two or more magnets move in relation to each other. You can take an animated quiz to check your understanding of magnetic field interactions at this URL: http://elgg. ",text,
L_0761,magnets and magnetism,T_3887,"Magnetism is the ability of a material to be attracted by a magnet and to act as a magnet. No doubt youve handled refrigerator magnets like the ones in Figure 24.5. You probably know first-hand that they stick to a metal refrigerator but not to surfaces such as wooden doors and glass windows. Wood and glass arent attracted to a magnet, whereas the steel refrigerator is. Obviously, only certain materials respond to magnetic force. ",text,
L_0761,magnets and magnetism,T_3887,"Magnetism is the ability of a material to be attracted by a magnet and to act as a magnet. No doubt youve handled refrigerator magnets like the ones in Figure 24.5. You probably know first-hand that they stick to a metal refrigerator but not to surfaces such as wooden doors and glass windows. Wood and glass arent attracted to a magnet, whereas the steel refrigerator is. Obviously, only certain materials respond to magnetic force. ",text,
L_0761,magnets and magnetism,T_3888,"Magnetism is due to the movement of electrons within atoms of matter. When electrons spin around the nucleus of an atom, it causes the atom to become a tiny magnet, with north and south poles and a magnetic field. In most materials, the electrons orbiting the nuclei of the atoms are arranged in such a way that the materials have no magnetic properties. Also, in most types of matter, the north and south poles of atoms point in all different directions, so overall the matter is not magnetic. Examples of nonmagnetic materials include wood, glass, plastic, paper, copper, and aluminum. These materials are not attracted to magnets and cannot become magnets. In other materials, electrons fill the orbitals of the atoms that make up the material in a way to allow for each atom to have a tiny magnetic field, giving each atom a tiny north and south pole. There are large areas where the north and south poles of atoms are all lined up in the same direction. These areas are called magnetic domains. Generally, the magnetic domains point in different directions, so the material is still not magnetic. However, the material can be magnetized by placing it in a magnetic field. When this happens, all the magnetic domains become aligned, and the material becomes a magnet. This is illustrated in Figure 24.6. Materials that can be magnetized are called ferromagnetic materials. They include iron, cobalt, and nickel. ",text,
L_0761,magnets and magnetism,T_3889,"Materials that have been magnetized may become temporary or permanent magnets. An example of each type of magnet is described below. Both are demonstrated in Figure 24.7. If you bring a bar magnet close to pile of paper clips, the paper clips will become temporarily magnetized, as all their magnetic domains align. As a result, the paper clips will stick to the magnet and also to each other. However, if you remove the paper clips from the bar magnets magnetic field, their magnetic domains will no longer align. As a result, the paper clips will no longer be magnetized or stick together. If you stroke an iron nail with a bar magnet, the nail will become a permanent (or at least long-lasting) magnet. Its magnetic domains will remain aligned even after you remove it from the magnetic field of the bar magnet. Permanent magnets can be demagnetized, however, if they are dropped or heated to high temperatures. These actions move the magnetic domains out of alignment. ",text,
L_0761,magnets and magnetism,T_3889,"Materials that have been magnetized may become temporary or permanent magnets. An example of each type of magnet is described below. Both are demonstrated in Figure 24.7. If you bring a bar magnet close to pile of paper clips, the paper clips will become temporarily magnetized, as all their magnetic domains align. As a result, the paper clips will stick to the magnet and also to each other. However, if you remove the paper clips from the bar magnets magnetic field, their magnetic domains will no longer align. As a result, the paper clips will no longer be magnetized or stick together. If you stroke an iron nail with a bar magnet, the nail will become a permanent (or at least long-lasting) magnet. Its magnetic domains will remain aligned even after you remove it from the magnetic field of the bar magnet. Permanent magnets can be demagnetized, however, if they are dropped or heated to high temperatures. These actions move the magnetic domains out of alignment. ",text,
L_0762,earth as a magnet,T_3890,"Imagine a huge bar magnet passing through Earths axis, as illustrated in Figure 24.10. This is a good representation of Earth as a magnet. Like a bar magnet, Earth has north and south magnetic poles and a magnetic field. ",text,
L_0762,earth as a magnet,T_3891,"Although a compass always points north, it doesnt point to Earths geographic north pole, which is located at 90 north latitude (see Figure 24.11). Instead, it points to Earths magnetic north pole, which is located at about 80 north latitude. Earths magnetic south pole is also located several degrees of latitude away from the geographic south pole. A compass pointer has north and south poles, and its north pole points to Earths magnetic north pole. Why does this happen if opposite poles attract? Why doesnt the compass needle point south instead? The answer may surprise you. Earths magnetic north pole is actually the south pole of magnet Earth! Its called the magnetic north pole to avoid confusion. Because its close to the geographic north pole, it would be confusing to call it the magnetic south pole. ",text,
L_0762,earth as a magnet,T_3892,"Like all magnets, Earth has a magnetic field. Earths magnetic field is called the magnetosphere. It is a huge region that extends outward from Earth for several thousand kilometers but is strongest at the poles. You can see the extent of the magnetosphere in Figure 24.12. For an animated version of the magnetosphere, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: ",text,
L_0762,earth as a magnet,T_3892,"Like all magnets, Earth has a magnetic field. Earths magnetic field is called the magnetosphere. It is a huge region that extends outward from Earth for several thousand kilometers but is strongest at the poles. You can see the extent of the magnetosphere in Figure 24.12. For an animated version of the magnetosphere, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: ",text,
L_0762,earth as a magnet,T_3893,"Do you like to read science fiction? Science fiction writers are really creative. For example, an author might write about a time in the distant past when compasses pointed south instead of north. Actually, this idea isnt fictionits a fact! Earths magnetic poles have switched places repeatedly over the past hundreds of millions of years, each time reversing Earths magnetic field. This is illustrated in Figure 24.13. Scientists dont know for certain why magnetic reversals occur, but there is hard evidence showing that they have occurred. The evidence comes from rocks on the ocean floor. Look at Figure 24.14, which shows a ridge on the ocean floor. At the center of the ridge, hot magma pushes up through the crust and hardens into rock. Once the magma hardens, the alignment of magnetic domains in the rock is frozen in place forever. The newly hardened rock is then gradually pushed away from the ridge in both directions as more magma erupts and newer rock forms. Rock samples from many places on the ocean floor reveal that magnetic domains of rocks from different time periods are aligned in opposite directions. The evidence shows that Earths magnetic field reversed hundreds of times over the last 330 million years. The last reversal was less than a million years ago. What might happen if a magnetic reversal occurred in your lifetime? How might it affect you? You can learn more about Earths magnetic reversals at this URL:  . ",text,
L_0762,earth as a magnet,T_3894,"The idea that Earth is a magnet is far from new. It was first proposed in 1600 by a British physician named William Gilbert. However, explaining why Earth acts like a magnet is a relatively recent discovery. It had to wait until the development of technologies such as seismographs, which detect and measure earthquake waves. Then scientists could learn about Earths inner structure (see Figure 24.15). They discovered that Earth has an inner and outer core and that the outer core consists of liquid metals, mainly iron and nickel. Scientists think that Earths magnetic field is generated by the movement of charged particles through the molten metals in the outer core. The particles move as Earth spins on its axis. The video at the URL below takes a closer look at how this occurs. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0762,earth as a magnet,T_3894,"The idea that Earth is a magnet is far from new. It was first proposed in 1600 by a British physician named William Gilbert. However, explaining why Earth acts like a magnet is a relatively recent discovery. It had to wait until the development of technologies such as seismographs, which detect and measure earthquake waves. Then scientists could learn about Earths inner structure (see Figure 24.15). They discovered that Earth has an inner and outer core and that the outer core consists of liquid metals, mainly iron and nickel. Scientists think that Earths magnetic field is generated by the movement of charged particles through the molten metals in the outer core. The particles move as Earth spins on its axis. The video at the URL below takes a closer look at how this occurs. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0762,earth as a magnet,T_3895,"Earths magnetic field helps protect Earth and its organisms from harmful particles given off by the sun. Most of the particles are attracted to the north and south magnetic poles, where Earths magnetic field is strongest. This is also where relatively few organisms live. Another benefit of Earths magnetic field is its use for navigation. People use compasses to detect Earths magnetic north pole and tell direction. Many animals have natural ""compasses"" that work just as well. Birds like the garden warbler in Figure 24.16 use Earths magnetic field to guide their annual migrations. Recent research suggests that warblers and other migrating birds have structures in their eyes that let them see Earths magnetic field as a visual pattern. You can learn more about animals and Earths magnetic field, including the potential effects of magnetic field reversals, at this URL:  . ",text,
L_0762,earth as a magnet,T_3896,"Northern California residents may not be able to see the northern lights like people in Alaska can, but Bay Area scientists are playing a key role in understanding them. Find out more about the spectacular light shows up north and what scientists at UC Berkeley are discovering about the Earths magnetic field. For more information on the northern lights, see http://science.kqed.org/quest/video/illuminating-the-northern-lights/ . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0767,types of matter,T_3921,An element is a pure substance. It cannot be separated into any other substances. There are more than 90 different elements that occur in nature. Some are much more common than others. Hydrogen is the most common element in the universe. Oxygen is the most common element in Earths crust. Figure 3.7 shows other examples of elements. Still others are described in the video below. MEDIA Click image to the left or use the URL below. URL: ,text,
L_0767,types of matter,T_3922,"Each element has a unique set of properties that make it different from all other elements. As a result, elements can be identified by their properties. For example, the elements iron and nickel are both metals that are good conductors of heat and electricity. However, iron is attracted by a magnet, whereas nickel is not. How could you use this property to separate iron objects from nickel objects? ",text,
L_0767,types of matter,T_3923,"The idea of elements is not new. It dates back about 2500 years to ancient Greece. The ancient Greek philosopher Aristotle thought that all matter consists of just four elements. He identified the elements as earth, air, water, and fire. He thought that different kinds of matter contain only these four elements but in different combinations. Aristotles ideas about elements were accepted for the next 2000 years. Then, scientists started discovering the many unique substances we call elements today. You can read when and how each of the elements was discovered at the link below. Scientists soon realized that there are far more than just four elements. Eventually, they discovered a total of 92 naturally occurring elements. ",text,
L_0767,types of matter,T_3924,"The smallest particle of an element that still has the elements properties is an atom. All the atoms of an element are alike, and they are different from the atoms of all other elements. For example, atoms of gold are the same whether they are found in a gold nugget or a gold ring (see Figure 3.8). All gold atoms have the same structure and properties. ",text,
L_0767,types of matter,T_3925,"There are millions of different substances in the world. Thats because elements can combine in many different ways to form new substances. In fact, most elements are found in compounds. A compound is a unique substance that forms when two or more elements combine chemically. An example is water, which forms when hydrogen and oxygen combine chemically. A compound always has the same components in the same proportions. It also has the same composition throughout. You can learn more about compounds and how they form by watching this video: MEDIA Click image to the left or use the URL below. URL: ",text,
L_0767,types of matter,T_3926,"A compound has different properties than the substances it contains. For example, hydrogen and oxygen are gases at room temperature. But when they combine chemically, they form liquid water. Another example is table salt, or sodium chloride. It contains sodium and chlorine. Sodium is a silvery solid that reacts explosively with water, and chlorine is a poisonous gas (see Figure 3.9). But together, sodium and chlorine form a harmless, unreactive compound that you can safely sprinkle on food. ",text,
L_0767,types of matter,T_3927,"The smallest particle of a compound that still has the compounds properties is a molecule. A molecule consists of two or more atoms that are joined together. For example, a molecule of water consists of two hydrogen atoms joined to one oxygen atom (see Figure 3.10). You can learn more about molecules at this link:  Some compounds form crystals instead of molecules. A crystal is a rigid, lattice-like framework of many atoms bonded together. Table salt is an example of a compound that forms crystals (see Figure 3.11). Its crystals are made up of many sodium and chloride ions. Ions are electrically charged forms of atoms. You can actually watch crystals forming in this video:  . ",text,
L_0767,types of matter,T_3927,"The smallest particle of a compound that still has the compounds properties is a molecule. A molecule consists of two or more atoms that are joined together. For example, a molecule of water consists of two hydrogen atoms joined to one oxygen atom (see Figure 3.10). You can learn more about molecules at this link:  Some compounds form crystals instead of molecules. A crystal is a rigid, lattice-like framework of many atoms bonded together. Table salt is an example of a compound that forms crystals (see Figure 3.11). Its crystals are made up of many sodium and chloride ions. Ions are electrically charged forms of atoms. You can actually watch crystals forming in this video:  . ",text,
L_0767,types of matter,T_3928,"Not all combined substances are compounds. Some are mixtures. A mixture is a combination of two or more substances in any proportion. The substances in a mixture may be elements or compounds. The substances dont combine chemically to form a new substance, as they do in a compound. Instead, they keep their original properties and just intermix. Examples of mixtures include salt and water in the ocean and gases in the atmosphere. Other examples are pictured in Figure 3.12. ",text,
L_0767,types of matter,T_3929,"Some mixtures are homogeneous. This means they have the same composition throughout. An example is salt water in the ocean. Ocean water everywhere is about 3.5 percent salt. Some mixtures are heterogeneous. This means they vary in their composition. An example is trail mix. No two samples of trail mix, even from the same package, are likely to be exactly the same. One sample might have more raisins, another might have more nuts. ",text,
L_0767,types of matter,T_3930,"Mixtures have different properties depending on the size of their particles. Three types of mixtures based on particle size are described below. Figure 3.13 shows examples of each type. You can watch videos about the three types of mixtures at these links: MEDIA Click image to the left or use the URL below. URL:  MEDIA Click image to the left or use the URL below. URL:  A solution is a homogeneous mixture with tiny particles. An example is salt water. The particles of a solution are too small to reflect light. As a result, you cannot see them. Thats why salt water looks the same as pure water. The particles of solutions are also too small to settle or be filtered out of the mixture. A suspension is a heterogeneous mixture with large particles. An example is muddy water. The particles of a suspension are big enough to reflect light, so you can see them. They are also big enough to settle or be filtered out. Anything that you have to shake before using, such as salad dressing, is usually a suspension. A colloid is a homogeneous mixture with medium-sized particles. Examples include homogenized milk and gelatin. The particles of a colloid are large enough to reflect light, so you can see them. But they are too small to settle or filter out of the mixture. ",text,
L_0767,types of matter,T_3931,"The components of a mixture keep their own identity when they combine. Therefore, they usually can be easily separated again. Their different physical properties are used to separate them. For example, oil is less dense than water, so a mixture of oil and water can be separated by letting it stand until the oil floats to the top. Other ways of separating mixtures are shown in Figure 3.14 and in the videos below.  (2:30) MEDIA Click image to the left or use the URL below. URL:  (2:41) MEDIA Click image to the left or use the URL below. URL: ",text,
L_0772,inside the atom,T_3963,"Figure 5.1 represents a simple model of an atom. You will learn about more complex models in later lessons, but this model is a good place to start. You can see similar, animated models of atoms at this URL: http://web.jjay.cuny ",text,
L_0772,inside the atom,T_3964,"At the center of an atom is the nucleus (plural, nuclei). The nucleus contains most of the atoms mass. However, in size, its just a tiny part of the atom. The model in Figure 5.1 is not to scale. If an atom were the size of a football stadium, the nucleus would be only about the size of a pea. The nucleus, in turn, consists of two types of particles, called protons and neutrons. These particles are tightly packed inside the nucleus. Constantly moving about the nucleus are other particles called electrons. You can see a video about all three types of atomic particles at this URL:  (1:57). ",text,
L_0772,inside the atom,T_3965,"A proton is a particle in the nucleus of an atom that has a positive electric charge. All protons are identical. It is the number of protons that gives atoms of different elements their unique properties. Atoms of each type of element have a characteristic number of protons. For example, each atom of carbon has six protons, as you can see in Figure ",text,
L_0772,inside the atom,T_3966,"A neutron is a particle in the nucleus of an atom that has no electric charge. Atoms of an element often have the same number of neutrons as protons. For example, most carbon atoms have six neutrons as well as six protons. This is also shown in Figure 5.2. ",text,
L_0772,inside the atom,T_3967,"An electron is a particle outside the nucleus of an atom that has a negative electric charge. The charge of an electron is opposite but equal to the charge of a proton. Atoms have the same number of electrons as protons. As a result, the negative and positive charges ""cancel out."" This makes atoms electrically neutral. For example, a carbon atom has six electrons that ""cancel out"" its six protons. ",text,
L_0772,inside the atom,T_3968,"When it comes to atomic particles, opposites attract. Negative electrons are attracted to positive protons. This force of attraction keeps the electrons moving about the nucleus. An analogy is the way planets orbit the sun. What about particles with the same charge, such as protons in the nucleus? They push apart, or repel, each other. So why doesnt the nucleus fly apart? The reason is a force of attraction between protons and neutrons called the strong force. The name of the strong force suits it. It is stronger than the electric force pushing protons apart. However, the strong force affects only nearby particles (see Figure 5.3). It is not effective if the nucleus gets too big. This puts an upper limit on the number of protons an atom can have and remain stable. You can learn more about atomic forces in the colorful tutorial at this URL:  . ",text,
L_0772,inside the atom,T_3969,"Electrons have almost no mass. Instead, almost all the mass of an atom is in its protons and neutrons in the nucleus. The nucleus is very small, but it is densely packed with matter. The SI unit for the mass of an atom is the atomic mass unit (amu). One atomic mass unit equals the mass of a proton, which is about 1.7  10 24 g. Each neutron also has a mass of 1 amu. Therefore, the sum of the protons and neutrons in an atom is about equal to the atoms total mass in atomic mass units. Two numbers are commonly used to distinguish atoms: atomic number and mass number. Figure 5.4 shows how these numbers are usually written. The atomic number is the number of protons in an atom. This number is unique for atoms of each kind of element. For example, the atomic number of all helium atoms is 2. The mass number is the number of protons plus the number of neutrons in an atom. For example, most atoms of helium have 2 neutrons, so their mass number is 2 + 2 = 4. This mass number means that an atom of helium has a mass of about 4 amu. Problem Solving Problem: An atom has an atomic number of 12 and a mass number of 24. How many protons and neutrons does the atom have? Solution: The number of protons is the same as the atomic number, or 12. The number of neutrons is equal to the mass number minus the atomic number, or 24 12 = 12. You Try It! Problem: An atom has an atomic number of 8 and a mass number of 16. How many neutrons does it have? What is the atoms mass in atomic mass units? ",text,
L_0772,inside the atom,T_3970,"The number of protons per atom is always the same for a given element. However, the number of neutrons may vary, and the number of electrons can change. ",text,
L_0772,inside the atom,T_3971,"Sometimes atoms lose or gain electrons. Then they become ions. Ions have a positive or negative charge. Thats because they do not have the same number of electrons as protons. If atoms lose electrons, they become positive ions, or cations. If atoms gain electrons, they become negative ions, or anions. Consider the example of fluorine in Figure 5.5. A fluorine atom has nine protons and nine electrons, so it is electrically neutral. If a fluorine atom gains an electron, it becomes a fluoride ion with a negative charge of minus one. ",text,
L_0772,inside the atom,T_3972,"Some atoms of the same element may have different numbers of neutrons. For example, some carbon atoms have seven or eight neutrons instead of the usual six. Atoms of the same element that differ in number of neutrons are called isotopes. Many isotopes occur naturally. Usually one or two isotopes of an element are the most stable and common. Different isotopes of an element generally have the same chemical properties. Thats because they have the same numbers of protons and electrons. For a video explanation of isotopes, go to this URL:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0772,inside the atom,T_3973,Hydrogen is a good example of isotopes because it has the simplest atoms. Three isotopes of hydrogen are modeled in Figure 5.6. Most hydrogen atoms have just one proton and one electron and lack a neutron. They are just called hydrogen. Some hydrogen atoms have one neutron. These atoms are the isotope named deuterium. Other hydrogen atoms have two neutrons. These atoms are the isotope named tritium. ,text,
L_0772,inside the atom,T_3974,"For most other elements, isotopes are named for their mass number. For example, carbon atoms with the usual 6 neutrons have a mass number of 12 (6 protons + 6 neutrons = 12), so they are called carbon-12. Carbon atoms with 7 neutrons have an atomic mass of 13 (6 protons + 7 neutrons = 13). These atoms are the isotope called carbon-13. Some carbon atoms have 8 neutrons. What is the name of this isotope of carbon? You can learn more about this isotope at the URL below. It is used by scientists to estimate the ages of rocks and fossils. ",text,
L_0772,inside the atom,T_3975,Remember the quarks from the first page of this chapter? Quarks are even tinier particles of matter that make up protons and neutrons. There are three quarks in each proton and three quarks in each neutron. The charges of quarks are balanced exactly right to give a positive charge to a proton and a neutral charge to a neutron. It might seem strange that quarks are never found alone but only as components of other particles. This is because the quarks are held together by very strange particles called gluons. ,text,
L_0772,inside the atom,T_3976,"Gluons make quarks attract each other more strongly the farther apart the quarks get. To understand how gluons work, imagine holding a rubber band between your fingers. If you try to move your hands apart, they will be pulled back together by the rubber band. The farther apart you move your hands, the stronger the force of the rubber band pulling your hands together. Gluons work the same way on quarks inside protons and neutrons (and other, really rare particles too). If you were to move your hands apart with enough force, the rubber band holding them together would break. The same is true of quarks. If they are given enough energy, they pull apart with enough force to ""break"" the binding from the gluons. However, all the energy that is put into a particle to make this possible is then used to create a new set of quarks and gluons. And so a new proton or neutron appears. ",text,
L_0772,inside the atom,T_3977,"The existence of quarks was first proposed in the 1960s. Since then, scientists have done experiments to show that quarks really do exist. In fact, they have identified six different types of quarks. However, much remains to be learned about these tiny, fundamental particles of matter. They are very difficult and expensive to study. If you want to learn more about them, including how they are studied, the URL below is a good place to start. ",text,
L_0772,inside the atom,T_3978,"QUEST journeys back to find out how physicists on the UC Berkeley campus in the 1930s, and at the Stanford Linear Accelerator Center in the 1970s, created ""atom smashers"" that led to key discoveries about the tiny constituents of the atom and paved the way for the Large Hadron Collider in Switzerland. For more information on particle accelerators, see http://science.kqed.org/quest/video/homegrown-particle-accelerators/ . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0773,history of the atom,T_3979,"The history of the atom begins around 450 B.C. with a Greek philosopher named Democritus (see Figure 5.7). Democritus wondered what would happen if you cut a piece of matter, such as an apple, into smaller and smaller pieces. He thought that a point would be reached where matter could not be cut into still smaller pieces. He called these ""uncuttable"" pieces atomos. This is where the modern term atom comes from. Democritus was an important philosopher. However, he was less influential than the Greek philosopher Aristotle, who lived about 100 years after Democritus. Aristotle rejected Democrituss idea of atoms. In fact, Aristotle thought ",text,
L_0773,history of the atom,T_3980,"Around 1800, a British chemist named John Dalton revived Democrituss early ideas about the atom. Dalton is pictured in Figure 5.8. He made a living by teaching and just did research in his spare time. Nonetheless, from his research results, he developed one of the most important theories in science. ",text,
L_0773,history of the atom,T_3981,"Dalton did many experiments that provided evidence for atoms. For example, he studied the pressure of gases. He concluded that gases must consist of tiny particles in constant motion. Dalton also researched the properties of compounds. He showed that a compound always consists of the same elements in the same ratio. On the other hand, different compounds always consist of different elements or ratios. This can happen, Dalton reasoned, only if elements are made of tiny particles that can combine in an endless variety of ways. From his research, Dalton developed a theory of the atom. You can learn more about Dalton and his research by watching the video at this URL:  (9:03). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0773,history of the atom,T_3982,The atomic theory Dalton developed consists of three ideas: All substances are made of atoms. Atoms are the smallest particles of matter. They cannot be divided into smaller particles. They also cannot be created or destroyed. All atoms of the same element are alike and have the same mass. Atoms of different elements are different and have different masses. Atoms join together to form compounds. A given compound always consists of the same kinds of atoms in the same ratio. Daltons theory was soon widely accepted. Most of it is still accepted today. The only part that is no longer accepted is his idea that atoms are the smallest particles. Scientists now know that atoms consist of even smaller particles. ,text,
L_0773,history of the atom,T_3983,"Dalton incorrectly thought that atoms are tiny solid particles of matter. He used solid wooden balls to model them. The sketch in the Figure 5.9 shows how Daltons model atoms looked. He made holes in the balls so they could be joined together with hooks. In this way, the balls could be used to model compounds. When later scientists discovered subatomic particles (particles smaller than the atom itself), they realized that Daltons models were too simple. They didnt show that atoms consist of even smaller particles. Models including these smaller particles were later developed. ",text,
L_0773,history of the atom,T_3984,The next major advance in the history of the atom was the discovery of electrons. These were the first subatomic particles to be identified. They were discovered in 1897 by a British physicist named J. J. Thomson. You can learn more about Thomson and his discovery at this online exhibit:  . ,text,
L_0773,history of the atom,T_3985,"Thomson was interested in electricity. He did experiments in which he passed an electric current through a vacuum tube. The experiments are described in Figure 5.10. Thomsons experiments showed that an electric current consists of flowing, negatively charged particles. Why was this discovery important? Many scientists of Thomsons time thought that electric current consists of rays, like rays of light, and that it is positive rather than negative. Thomsons experiments also showed that the negative particles are all alike and smaller than atoms. Thomson concluded that the negative particles couldnt be fundamental units of matter because they are all alike. Instead, they must be parts of atoms. The negative particles were later named electrons. ",text,
L_0773,history of the atom,T_3986,"Thomson knew that atoms are neutral in electric charge. So how could atoms contain negative particles? Thomson thought that the rest of the atom must be positive to cancel out the negative charge. He said that an atom is like a plum pudding, which has plums scattered through it. Thats why Thomsons model of the atom is called the plum pudding model. You can see it in Figure 5.11. It shows the atom as a sphere of positive charge (the pudding) with negative electrons (the plums) scattered through it. ",text,
L_0773,history of the atom,T_3987,A physicist from New Zealand named Ernest Rutherford made the next major discovery about atoms. He discovered the nucleus. You can watch a video about Rutherford and his discovery at this URL:  MEDIA Click image to the left or use the URL below. URL: ,text,
L_0773,history of the atom,T_3988,"In 1899, Rutherford discovered that some elements give off positively charged particles. He named them alpha particles (a). In 1911, he used alpha particles to study atoms. He aimed a beam of alpha particles at a very thin sheet of gold foil. Outside the foil, he placed a screen of material that glowed when alpha particles struck it. If Thomsons plum pudding model were correct, the alpha particles should be deflected a little as they passed through the foil. Why? The positive ""pudding"" part of gold atoms would slightly repel the positive alpha particles. This would cause the alpha particles to change course. But Rutherford got a surprise. Most of the alpha particles passed straight through the foil as though they were moving through empty space. Even more surprising, a few of the alpha particles bounced back from the foil as though they had struck a wall. This is called back scattering. It happened only in very small areas at the centers of the gold atoms. ",text,
L_0773,history of the atom,T_3989,"Based on his results, Rutherford concluded that all the positive charge of an atom is concentrated in a small central area. He called this area the nucleus. Rutherford later discovered that the nucleus contains positively charged particles. He named the positive particles protons. Rutherford also predicted the existence of neutrons in the nucleus. However, he failed to find them. One of his students, a physicist named James Chadwick, went on to discover neutrons in 1932. You learn how at this URL:  . ",text,
L_0773,history of the atom,T_3990,"Rutherfords discoveries meant that Thomsons plum pudding model was incorrect. Positive charge is not spread out everywhere in an atom. It is all concentrated in the tiny nucleus. The rest of the atom is empty space, except for the electrons moving randomly through it. In Rutherfords model, electrons move around the nucleus in random orbits. He compared them to planets orbiting a star. Thats why Rutherfords model is called the planetary model. You can see it in Figure 5.13. ",text,
L_0773,history of the atom,T_3990,"Rutherfords discoveries meant that Thomsons plum pudding model was incorrect. Positive charge is not spread out everywhere in an atom. It is all concentrated in the tiny nucleus. The rest of the atom is empty space, except for the electrons moving randomly through it. In Rutherfords model, electrons move around the nucleus in random orbits. He compared them to planets orbiting a star. Thats why Rutherfords model is called the planetary model. You can see it in Figure 5.13. ",text,
L_0774,modern atomic theory,T_3991,"Bohrs research focused on electrons. In 1913, he discovered evidence that the orbits of electrons are located at fixed distances from the nucleus. Remember, Rutherford thought that electrons orbit the nucleus at random. Figure 5.14 shows Bohrs model of the atom. ",text,
L_0774,modern atomic theory,T_3992,"Basic to Bohrs model is the idea of energy levels. Energy levels are areas located at fixed distances from the nucleus of the atom. They are the only places where electrons can be found. Energy levels are a little like rungs on a ladder. You can stand on one rung or another but not between the rungs. The same goes for electrons. They can occupy one energy level or another but not the space between energy levels. The model of an atom in Figure 5.15 has six energy levels. The level with the least energy is the one closest to the nucleus. As you go farther from the nucleus, the levels have more and more energy. Electrons can jump from one energy level to another. If an atom absorbs energy, some of its electrons can jump to a higher energy level. If electrons jump to a lower energy level, the atom emits, or gives off, energy. You can see an animation at this happening at the URL below. ",text,
L_0774,modern atomic theory,T_3992,"Basic to Bohrs model is the idea of energy levels. Energy levels are areas located at fixed distances from the nucleus of the atom. They are the only places where electrons can be found. Energy levels are a little like rungs on a ladder. You can stand on one rung or another but not between the rungs. The same goes for electrons. They can occupy one energy level or another but not the space between energy levels. The model of an atom in Figure 5.15 has six energy levels. The level with the least energy is the one closest to the nucleus. As you go farther from the nucleus, the levels have more and more energy. Electrons can jump from one energy level to another. If an atom absorbs energy, some of its electrons can jump to a higher energy level. If electrons jump to a lower energy level, the atom emits, or gives off, energy. You can see an animation at this happening at the URL below. ",text,
L_0774,modern atomic theory,T_3993,"Bohrs idea of energy levels is still useful today. It helps explain how matter behaves. For example, when chemicals in fireworks explode, their atoms absorb energy. Some of their electrons jump to a higher energy level. When the electrons move back to their original energy level, they give off the energy as light. Different chemicals have different arrangements of electrons, so they give off light of different colors. This explains the blue- and purple- colored fireworks in Figure 5.16. ",text,
L_0774,modern atomic theory,T_3994,"In the 1920s, physicists discovered that electrons do not travel in fixed paths. In fact, they found that electrons only have a certain chance of being in any particular place. They could only describe where electrons are with mathematical formulas. Thats because electrons have wave-like properties as well as properties of particles of matter. It is the ""wave nature"" of electrons that lets them exist only at certain distances from the nucleus. The negative electrons are attracted to the positive nucleus. However, because the electrons behave like waves, they bend around the nucleus instead of falling toward it. Electrons exist only where the wave is stable. These are the orbitals. They do not exist where the wave is not stable. These are the places between orbitals. ",text,
L_0774,modern atomic theory,T_3995,"Today, these ideas about electrons are represented by the electron cloud model. The electron cloud is an area around the nucleus where electrons are likely to be. Figure 5.17 shows an electron cloud model for a helium atom. ",text,
L_0774,modern atomic theory,T_3996,"Some regions of the electron cloud are denser than others. The denser regions are areas where electrons are most likely to be. These regions are called orbitals. Each orbital has a maximum of just two electrons. Different energy levels in the cloud have different numbers of orbitals. Therefore, different energy levels have different maximum numbers of electrons. Table 5.1 lists the number of orbitals and electrons for the first four energy levels. Energy levels farther from the nucleus have more orbitals. Therefore, these levels can hold more electrons. Energy Level Number of Orbitals 1 2 3 4 1 4 9 16 Max. No. of Electrons (@ 2 per orbital) 2 8 18 32 Figure 5.18 shows the arrangement of electrons in an atom of magnesium as an example. The most stable arrange- ment of electrons occurs when electrons fill the orbitals at the lowest energy levels first before more are added at higher levels. You can learn more about orbitals and their electrons at the URL below: ",text,
L_0774,modern atomic theory,T_3996,"Some regions of the electron cloud are denser than others. The denser regions are areas where electrons are most likely to be. These regions are called orbitals. Each orbital has a maximum of just two electrons. Different energy levels in the cloud have different numbers of orbitals. Therefore, different energy levels have different maximum numbers of electrons. Table 5.1 lists the number of orbitals and electrons for the first four energy levels. Energy levels farther from the nucleus have more orbitals. Therefore, these levels can hold more electrons. Energy Level Number of Orbitals 1 2 3 4 1 4 9 16 Max. No. of Electrons (@ 2 per orbital) 2 8 18 32 Figure 5.18 shows the arrangement of electrons in an atom of magnesium as an example. The most stable arrange- ment of electrons occurs when electrons fill the orbitals at the lowest energy levels first before more are added at higher levels. You can learn more about orbitals and their electrons at the URL below: ",text,
L_0775,how elements are organized,T_3997,"Mendeleev was a teacher as well as a chemist. He was writing a chemistry textbook and needed a way to organize the elements so it would be easier for students to learn about them. He made a set of cards of the elements, similar to a deck of playing cards, with one element per card. On the card, he wrote the elements name, atomic mass, and known properties. He arranged and rearranged the cards in many different ways, looking for a pattern. He finally found it when he placed the elements in order by atomic mass. ",text,
L_0775,how elements are organized,T_3998,"You can see how Mendeleev organized the elements in Figure 6.2. From left to right across each row, elements are arranged by increasing atomic mass. Mendeleev discovered that if he placed eight elements in each row and then continued on to the next row, the columns of the table would contain elements with similar properties. He called the columns groups. They are sometimes called families, because elements within a group are similar but not identical to one another, like people in a family. Mendeleevs table of the elements is called a periodic table because of its repeating pattern. Anything that keeps repeating is referred to as periodic. Other examples of things that are periodic include the monthly phases of the moon and the daily cycle of night and day. The term period refers to the interval between repetitions. In a periodic table, the periods are the rows of the table. In Mendeleevs table, each period contains eight elements, and then the pattern repeats in the next row. ",text,
L_0775,how elements are organized,T_3999,"Did you notice the blanks in Mendeleevs table (Figure 6.2)? They are spaces that Mendeleev left for elements that had not yet been discovered when he created his table. He predicted that these missing elements would eventually be discovered. Based on their position in the table, he could even predict their properties. For example, he predicted a missing element in row 5 of his group 3. He said it would have an atomic mass of about 68 and be a soft metal like other group 3 elements. Scientists searched for the missing element. They found it a few years later and named it gallium. Scientists searched for the other missing elements. Eventually, all of them were found. An important measure of a good model is its ability to make accurate predictions. This makes it a useful model. Clearly, Mendeleevs periodic table was a useful model. It helped scientists discover new elements and make sense of those that were already known. ",text,
L_0775,how elements are organized,T_4000,A periodic table is still used today to classify the elements. Figure 6.3 shows the modern periodic table. You can see an interactive version at this URL:  . ,text,
L_0775,how elements are organized,T_4001,"In the modern periodic table, elements are organized by atomic number. The atomic number is the number of protons in an atom of an element. This number is unique for each element, so it seems like an obvious way to organize the elements. (Mendeleev used atomic mass instead of atomic number because protons had not yet been discovered when he made his table.) In the modern table, atomic number increases from left to right across each period. It also increases from top to bottom within each group. How is this like Mendeleevs table? ",text,
L_0775,how elements are organized,T_4002,"Besides atomic number, the periodic table includes each elements chemical symbol and class. Some tables include other information as well. The chemical symbol consists of one or two letters that come from the chemicals name in English or another language. The first letter is always written in upper case. The second letter, if there is one, is always written in lower case. For example, the symbol for lead is Pb. It comes from the Latin word plumbum, which means ""lead."" Find lead in Figure 6.3. What is its atomic number? You can access videos about lead and other elements in the modern periodic table at this URL:  . The classes of elements are metals, metalloids, and nonmetals. They are color-coded in the table. Blue stands for metals, orange for metalloids, and green for nonmetals. You can read about each of these three classes of elements later in the chapter, in the lesson ""Classes of Elements."" ",text,
L_0775,how elements are organized,T_4003,"Rows of the modern table are called periods, as they are in Mendeleevs table. From left to right across a period, each element has one more proton than the element before it. In each period, elements change from metals on the left side of the table, to metalloids, and then to nonmetals on the right. Figure 6.4 shows this for period 4. Some periods in the modern periodic table are longer than others. For example, period 1 contains only two elements. Periods 6 and 7, in contrast, are so long that some of their elements are placed below the main part of the table. They are the elements starting with lanthanum (La) in period 6 and actinium (Ac) in period 7. Some elements in period 7 have not yet been named. They are represented by temporary symbols, such as Uub. Many of these elements have only recently been shown to exist. Elements 114 and 116 were added to the table in 2011. Four more elements (113, 115, 117, and 118) were approved for addition in December 2015 and will be named at some later date. ",text,
L_0775,how elements are organized,T_4004,"Columns of the modern table are called groups, as they are in Mendeleevs table. However, the modern table has many more groups  18 to be exact. Elements in the same group have similar properties. For example, all elements in group 18 are colorless, odorless gases. You can read about the different groups of elements in this chapters lesson on ""Groups of Elements."" ",text,
L_0776,classes of elements,T_4005,"Metals are elements that are good conductors of electricity. They are the largest of the three classes of elements. In fact, most elements are metals. Look back at the modern periodic table (Figure 6.3) in this chapters lesson ""How Elements Are Organized."" Find the metals in the table. They are all the elements that are color-coded blue. Examples include sodium (Na), silver (Ag), and zinc (Zn). Metals have relatively high melting points, so almost all are solids at room temperature. The only exception is mercury (Hg), which is a liquid. Most metals are also good conductors of heat. Thats why they are used for cooking pots and stovetops. Metals have other characteristic properties as well. Most are shiny, ductile, and malleable. These properties are illustrated in Figure 6.5. You can dig deeper into the properties of metals at this URL: ",text,
L_0776,classes of elements,T_4006,"Nonmetals are elements that do not conduct electricity. They are the second largest class of elements. Find the nonmetals in Figure 6.3. They are all the elements on the right side of the table that are color-coded green. Examples of nonmetals include helium (He), carbon (C), and oxygen (O). Nonmetals generally have properties that are the opposite of those of metals. They also tend to vary more in their properties than metals do. For example, nonmetals have relatively low boiling points, so many of them are gases at room temperature. But several nonmetals are solids, including carbon and phosphorus (P). One nonmetal, bromine (Br), is a liquid at room temperature. Generally, nonmetals are also poor conductors of heat. In fact, they may be used for insulation. For example, the down filling in a down jacket is mostly air, which consists mainly of nitrogen (N) and oxygen (O). These nonmetal gases are poor conductors of heat, so they keep body heat in and cold air out. Solid nonmetals are dull rather than shiny. They are also brittle rather than ductile or malleable. You can see examples of solid nonmetals in Figure 6.6. You can learn more about specific nonmetals with the interactive table at this URL: http://library.thinkquest.org/36 ",text,
L_0776,classes of elements,T_4007,"Metalloids are elements that fall between metals and nonmetals in the periodic table. Just seven elements are metalloids, so they are the smallest class of elements. In Figure 6.3, they are color-coded orange. Examples of metalloids include boron (B), silicon (Si), and germanium (Ge). Metalloids have some properties of metals and some properties of nonmetals. For example, many metalloids can conduct electricity but only at certain temperatures. These metalloids are called semiconductors. Silicon is an example. It is used in computer chips. It is also the most common metalloid on Earth. It is shiny like a metal but brittle like a nonmetal. You see a sample of silicon in Figure 6.7. The figure also shows other examples of metalloids. You can learn more about the properties of metalloids at this URL: http://library.thinkquest.org/3659/p ",text,
L_0776,classes of elements,T_4008,"From left to right across the periodic table, each element has one more proton than the element to its left. Because atoms are always electrically neutral, for each added proton, one electron is also added. Electrons are added first to the lowest energy level possible until that level is full. Only then are electrons added to the next higher energy level. ",text,
L_0776,classes of elements,T_4009,"The increase in electrons across the periodic table explains why elements go from metals to metalloids and then to nonmetals from left to right across the table. Look at period 2 in Figure 6.8 as an example. Lithium (Li) is a metal, boron (B) a metalloid, and fluorine (F) and neon (Ne) are nonmetals. The inner energy level is full for all four elements. This level has just one orbital and can hold a maximum of two electrons. The outer energy level is a different story. This level has four orbitals and can hold a maximum of eight electrons. Lithium has just one electron in this level, boron has three, fluorine has seven, and neon has eight. ",text,
L_0776,classes of elements,T_4010,"The electrons in the outer energy level of an atom are called valence electrons. It is valence electrons that are potentially involved in chemical reactions. The number of valence electrons determines an elements reactivity, or how likely the element is to react with other elements. The number of valence electrons also determines whether the element can conduct electric current. Thats because electric current is the flow of electrons. Table 6.1 shows how these properties vary in elements from each class. Metals such as lithium have an outer energy level that is almost empty. They ""want"" to give up their few valence electrons so they will have a full outer energy level. As a result, metals are very reactive and good conductors of electricity. Metalloids such as boron have an outer energy level that is about half full. These elements need to gain or lose too many electrons for a full outer energy level to come about easily. As a result, these elements are not very reactive. They may be able to conduct electricity but not very well. Some nonmetals, such as bromine, have an outer energy level that is almost full. They ""want"" to gain electrons so they will have a full outer energy level. As a result, these nonmetals are very reactive. Because they only accept electrons and do not give them up, they do not conduct electricity. Other nonmetals, such as neon, have a completely full outer energy level. Their electrons are already in the most stable arrangement possible. They are unreactive and do not conduct electricity. Element Description Element Lithium Description Lithium (Li) is a highly reactive metal. It has just one electron in its outer energy level. Lithium reacts explosively with water (see picture). It can react with moisture on skin and cause serious burns. Boron Boron (B) is a metalloid. It has three valence electrons and is less reactive than lithium. Boron compounds dissolved in water form boric acid. Dilute boric acid is weak enough to use as eye wash. Bromine Bromine (Br) is an extremely reactive nonmetal. In fact, reactions with fluorine are often explosive, as you can see in the URL below. Neon (Ne) is a nonmetal gas with a completely filled outer energy level. This makes it unreactive, so it doesnt combine with other elements. Neon is used for lighted signs like this one. You can learn why neon gives off light at this link:  Neon ",text,
L_0777,groups of elements,T_4011,"All the elements in group 1 have just one valence electron, so they are highly reactive. Group 1 is shown in Figure element in the universe. All the other elements in group 1 are alkali metals. They are the most reactive of all metals, and along with the elements in group 17, the most reactive elements. Because alkali metals are so reactive, they are only found in nature combined with other elements. The alkali metals are soft. Most are soft enough to cut with a knife. They are also low in density. Some of them even float on water. All are solids at room temperature. You can see a video demonstrating the reactivity of alkali metals with water at this URL:  (2:22). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0777,groups of elements,T_4012,"The alkaline Earth metals include all the elements in group 2 (see Figure 6.10). These metals have just two valence electrons, so they are very reactive, although not quite as reactive as the alkali metals. In nature, they are always found combined with other elements. Alkaline Earth metals are silvery grey in color. They are harder and denser than the alkali metals. All are solids at room temperature. ",text,
L_0777,groups of elements,T_4013,"Groups 3-12 of the periodic table contain transition metals (see Figure 6.11). Transition metals have more valence electrons and are less reactive than metals in the first two metal groups. The transition metals are shiny. Many are silver colored. They tend to be very hard, with high melting and boiling points. All except mercury (Hg) are solids at room temperature. Transition metals include the elements that are placed below the periodic table. Those that follow lanthanum (La) are called lanthanides. They are all shiny, relatively reactive metals. Those that follow Actinium (Ac) are called actinides. They are all radioactive metals. This means they are unstable. They break down into different, more stable elements. You can read more about radioactive elements in the chapter Nuclear Chemistry. Many of the actinides do not occur in nature but are made in laboratories. ",text,
L_0777,groups of elements,T_4013,"Groups 3-12 of the periodic table contain transition metals (see Figure 6.11). Transition metals have more valence electrons and are less reactive than metals in the first two metal groups. The transition metals are shiny. Many are silver colored. They tend to be very hard, with high melting and boiling points. All except mercury (Hg) are solids at room temperature. Transition metals include the elements that are placed below the periodic table. Those that follow lanthanum (La) are called lanthanides. They are all shiny, relatively reactive metals. Those that follow Actinium (Ac) are called actinides. They are all radioactive metals. This means they are unstable. They break down into different, more stable elements. You can read more about radioactive elements in the chapter Nuclear Chemistry. Many of the actinides do not occur in nature but are made in laboratories. ",text,
L_0777,groups of elements,T_4014,"Groups 13-16 each contain one or more metalloids. These groups are shown in Figure 6.12. Group 13 is called the boron group. The only metalloid in this group is boron (B). The other four elements are metals. All group 13 elements have three valence electrons and are fairly reactive. All are solids at room temperature. Group 14 is called the carbon group. Carbon (C) is a nonmetal. The next two elements are metalloids, and the final two are metals. All the elements in the carbon group have four valence electrons. They are not very reactive. All are solids at room temperature. Group 15 is called the nitrogen group. The first two elements in this group are nonmetals. These are followed by two metalloids and one metal. All the elements in the nitrogen group have five valence electrons, but they vary in their reactivity. Nitrogen (N) in not reactive at all. Phosphorus (P), in contrast, is quite reactive. In fact, it is found naturally only in combination with other substances. Nitrogen is a gas at room temperature. The other group 15 elements are solids. Group 16 is called the oxygen group. The first three elements in this group are nonmetals. They are followed by one metalloid and one metal. All the elements in the oxygen group have six valence electrons, and all are ",text,
L_0777,groups of elements,T_4015,"Elements in group 17 are called halogens (see Figure 6.13). They are highly reactive nonmetals with seven valence electrons. The halogens react violently with alkali metals, which have one valence electron. The two elements combine to form a salt. For example, the halogen chlorine (Cl) and the alkali metal sodium (Na) react to form table salt, or sodium chloride (NaCl). The halogen group includes gases, liquids, and solids. For example, chlorine is a gas at room temperature, bromine (Br) is a liquid, and iodine (I) is a solid. You can watch a video demonstrating the reactivity of halogens at this URL:  . ",text,
L_0777,groups of elements,T_4016,"Group 18 elements are nonmetals called noble gases (see Figure 6.14). They are all colorless, odorless gases. Their outer energy level is also full, so they are the least reactive elements. In nature, they seldom combine with other substances. For a short video about the noble gases and their properties, go to this URL: ",text,
L_0778,introduction to chemical bonds,T_4017,"Elements form compounds when they combine chemically. Their atoms join together to form molecules, crystals, or other structures. The atoms are held together by chemical bonds. A chemical bond is a force of attraction between atoms or ions. It occurs when atoms share or transfer valence electrons. Valence electrons are the electrons in the outer energy level of an atom. You can learn more about chemical bonds in this video:  MEDIA Click image to the left or use the URL below. URL:  Look at the example of water in Figure 7.1. A water molecule consists of two atoms of hydrogen and one atom of oxygen. Each hydrogen atom has just one electron. The oxygen atom has six valence electrons. In a water molecule, two hydrogen atoms share their two electrons with the six valence electrons of one oxygen atom. By sharing electrons, each atom has electrons available to fill its sole or outer energy level. This gives it a more stable arrangement of electrons that takes less energy to maintain. ",text,
L_0778,introduction to chemical bonds,T_4018,"Water (H2 O) is an example of a chemical compound. Water molecules always consist of two atoms of hydrogen and one atom of oxygen. Like water, all other chemical compounds consist of a fixed ratio of elements. It doesnt matter how much or how little of a compound there is. It always has the same composition. ",text,
L_0778,introduction to chemical bonds,T_4019,"Elements are represented by chemical symbols. Examples are H for hydrogen and O for oxygen. Compounds are represented by chemical formulas. Youve already seen the chemical formula for water. Its H2 O. The subscript 2 after the H shows that there are two atoms of hydrogen in a molecule of water. The O for oxygen has no subscript. When there is just one atom of an element in a molecule, no subscript is used. Table 7.1 shows some other examples of compounds and their chemical formulas. Name of Compound Electron Dot Diagram Numbers of Atoms Chemical Formula Name of Compound Hydrogen chloride Electron Dot Diagram Numbers of Atoms H=1 Cl = 1 Chemical Formula HCl Methane C=1 H=4 CH4 Hydrogen peroxide H=2 O=2 H2 O2 Carbon dioxide C=1 O=2 CO2 Problem Solving Problem: A molecule of ammonia consists of one atom of nitrogen (N) and three atoms of hydrogen (H). What is its chemical formula? Solution: The chemical formula is NH3 . You Try It! Problem: A molecule of nitrogen dioxide consists of one atom of nitrogen (N) and two atoms of oxygen (O). What is its chemical formula? ",text,
L_0778,introduction to chemical bonds,T_4020,"The same elements may combine in different ratios. If they do, they form different compounds. Figure 7.2 shows some examples. Both water (H2 O) and hydrogen peroxide (H2 O2 ) consist of hydrogen and oxygen. However, they have different ratios of the two elements. As a result, water and hydrogen peroxide are different compounds with different properties. If youve ever used hydrogen peroxide to disinfect a cut, then you know that it is very different from water! Both carbon dioxide (CO2 ) and carbon monoxide (CO) consist of carbon and oxygen, but in different ratios. How do their properties differ? ",text,
L_0778,introduction to chemical bonds,T_4021,"There are different types of compounds. They differ in the nature of the bonds that hold their atoms together. The type of bonds in a compound determines many of its properties. Three types of bonds are ionic, covalent, and metallic bonds. You will read about these three types in later lessons. You can also learn more about them by watching this video:  (7:18). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0778,introduction to chemical bonds,T_4022,"Chocolate: Its been revered for millennia by cultures throughout the world. But while its easy to appreciate all of its delicious forms, creating this confection is a complex culinary feat. Local chocolate makers explain the elaborate engineering and chemistry behind this tasty treat. And learn why its actually good for your health! For more information on the science of chocolate, see http://science.kqed.org/quest/video/the-sweet-science-of-chocolate/ . MEDIA Click image to the left or use the URL below. URL: ",text,
L_0779,ionic bonds,T_4023,"An ionic bond is the force of attraction that holds together positive and negative ions. It forms when atoms of a metallic element give up electrons to atoms of a nonmetallic element. Figure 7.3 shows how this happens. In row 1 of Figure 7.3, an atom of sodium donates an electron to an atom of chlorine (Cl). By losing an electron, the sodium atom becomes a sodium ion. It now has one less electron than protons, giving it a charge of +1. Positive ions such as sodium are given the same name as the element. The chemical symbol has a plus sign to distinguish the ion from an atom of the element. The symbol for a sodium ion is Na+ . By gaining an electron, the chlorine atom becomes a chloride ion. It now has one more electron than protons, giving it a charge of -1. Negative ions are named by adding the suffix ide to the first part of the element name. The symbol for chloride is Cl . Sodium and chloride ions have equal but opposite charges. Opposites attract, so sodium and chloride ions attract each other. They cling together in a strong ionic bond. You can see this in row 2 of Figure 7.3. Brackets separate the ions in the diagram to show that the ions in the compound do not share electrons. You can see animations of sodium chloride forming at these URLs: http://web.jjay.cuny.edu/~acarpi/NSC/salt.htm ",text,
L_0779,ionic bonds,T_4024,"Ionic bonds form only between metals and nonmetals. Metals ""want"" to give up electrons, and nonmetals ""want"" to gain electrons. Find sodium (Na) in Figure 7.4. Sodium is an alkali metal in group 1. Like other group 1 elements, it has just one valence electron. If sodium loses that one electron, it will have a full outer energy level. Now find fluorine (F) in Figure 7.4. Fluorine is a halogen in group 17. It has seven valence electrons. If fluorine gains one electron, it will have a full outer energy level. After sodium gives up its valence electron to fluorine, both atoms have a more stable arrangement of electrons. ",text,
L_0779,ionic bonds,T_4025,"It takes energy to remove valence electrons from an atom. The force of attraction between the negative electrons and positive nucleus must be overcome. The amount of energy needed depends on the element. Less energy is needed to remove just one or a few electrons than many. This explains why sodium and other alkali metals form positive ions so easily. Less energy is also needed to remove electrons from larger atoms in the same group. For example, in group 1, it takes less energy to remove an electron from francium (Fr) at the bottom of the group than from lithium (Li) at the top of the group (see Figure 7.4). In bigger atoms, valence electrons are farther from the nucleus. As a result, the force of attraction between the electrons and nucleus is weaker. What happens when an atom gains an electron and becomes a negative ion? Energy is released. Halogens release the most energy when they form ions. As a result, they are very reactive. ",text,
L_0779,ionic bonds,T_4026,"Ionic compounds contain ions of metals and nonmetals held together by ionic bonds. Ionic compounds do not form molecules. Instead, many positive and negative ions bond together to form a structure called a crystal. You can see an example of a crystal in Figure 7.5. It shows the ionic compound sodium chloride. Positive sodium ions (Na+ ) alternate with negative chloride ions (Cl ). The oppositely charged ions are strongly attracted to each other. Helpful Hints Naming Ionic Compounds Ionic compounds are named for their positive and negative ions. The name of the positive ",text,
L_0779,ionic bonds,T_4027,"The crystal structure of ionic compounds is strong and rigid. It takes a lot of energy to break all those strong ionic bonds. As a result, ionic compounds are solids with high melting and boiling points (see Table 7.2). The rigid crystals are brittle and more likely to break than bend when struck. As a result, ionic crystals tend to shatter. You can learn more about the properties of ionic compounds by watching the video at this URL:  MEDIA Click image to the left or use the URL below. URL:  Compare the melting and boiling points of these ionic compounds with those of water (0C and 100C), which is not an ionic compound. Ionic Compound Sodium chloride (NaCl) Calcium chloride (CaCl2 ) Barium oxide (BaO) Iron bromide (FeBr3 ) Melting Point (C) 801 772 1923 684 Boiling Point (C) 1413 1935 2000 934 Solid ionic compounds are poor conductors of electricity. The strong bonds between ions lock them into place in the crystal. However, in the liquid state, ionic compounds are good conductors of electricity. Most ionic compounds dissolve easily in water. When they dissolve, they separate into individual ions. The ions can move freely, so they are good conductors of electricity. Dissolved ionic compounds are called electrolytes. ",text,
L_0779,ionic bonds,T_4028,Ionic compounds have many uses. Some are shown in Figure 7.6. Many ionic compounds are used in industry. The human body also needs several ions for good health. Having low levels of the ions can endanger important functions such as heartbeat. Solutions of ionic compounds can be used to restore the ions. ,text,
L_0780,covalent bonds,T_4029,"A covalent bond is the force of attraction that holds together two atoms that share a pair of electrons. The shared electrons are attracted to the nuclei of both atoms. Covalent bonds form only between atoms of nonmetals. The two atoms may be the same or different elements. If the bonds form between atoms of different elements, a covalent compound forms. Covalent compounds are described in detail later in the lesson. To see a video about covalent bonding, go to this URL:  (6:20). MEDIA Click image to the left or use the URL below. URL:  Figure 7.7 shows an example of a covalent bond forming between two atoms of the same element, in this case two atoms of hydrogen. The two atoms share a pair of electrons. Hydrogen normally occurs in two-atom, or diatomic, molecules like this (di- means ""two""). Several other elements also normally occur as diatomic molecules: nitrogen, oxygen, and all but one of the halogens (fluorine, chlorine, bromine, and iodine). ",text,
L_0780,covalent bonds,T_4030,"Covalent bonds form because they give atoms a more stable arrangement of electrons. Look at the hydrogen atoms in Figure 7.7. Alone, each hydrogen atom has just one electron. By sharing electrons with another hydrogen atom, it has two electrons: its own and the one in the other hydrogen atom. The shared electrons are attracted to both hydrogen nuclei. This force of attraction holds the two atoms together as a molecule of hydrogen. Some atoms need to share more than one pair of electrons to have a full outer energy level. For example, an oxygen atom has six valence electrons. It needs two more electrons to fill its outer energy level. Therefore, it must form two covalent bonds. This can happen in many different ways. One way is shown in Figure 7.8. The oxygen atom in the figure has covalent bonds with two hydrogen atoms. This forms the covalent compound water. ",text,
L_0780,covalent bonds,T_4031,"In some covalent bonds, electrons are not shared equally between the two atoms. These are called polar bonds. Figure 7.9 shows this for water. The oxygen atom attracts the shared electrons more strongly because its nucleus has more positively charged protons. As a result, the oxygen atom becomes slightly negative in charge. The hydrogen atoms attract the electrons less strongly. They become slightly positive in charge. For another example of polar bonds, see the video at this URL:  (0:52). MEDIA Click image to the left or use the URL below. URL:  In other covalent bonds, electrons are shared equally. These bonds are called nonpolar bonds. Neither atom attracts the shared electrons more strongly. As a result, the atoms remain neutral. Figure 7.10 shows an example of nonpolar bonds. ",text,
L_0780,covalent bonds,T_4031,"In some covalent bonds, electrons are not shared equally between the two atoms. These are called polar bonds. Figure 7.9 shows this for water. The oxygen atom attracts the shared electrons more strongly because its nucleus has more positively charged protons. As a result, the oxygen atom becomes slightly negative in charge. The hydrogen atoms attract the electrons less strongly. They become slightly positive in charge. For another example of polar bonds, see the video at this URL:  (0:52). MEDIA Click image to the left or use the URL below. URL:  In other covalent bonds, electrons are shared equally. These bonds are called nonpolar bonds. Neither atom attracts the shared electrons more strongly. As a result, the atoms remain neutral. Figure 7.10 shows an example of nonpolar bonds. ",text,
L_0780,covalent bonds,T_4032,"Covalent bonds between atoms of different elements form covalent compounds. The smallest, simplest covalent compounds have molecules with just two atoms. An example is hydrogen chloride (HCl). It consists of one hydrogen atom and one chlorine atom. The largest, most complex covalent molecules have thousands of atoms. Examples include proteins and carbohydrates. These are compounds in living things. Helpful Hints Naming Covalent Compounds Follow these rules in naming simple covalent compounds: The element closer to the left of the periodic table is named first. The second element gets the suffix ide. Prefixes such as di- (2) and tri- (3) show the number of each atom in the compound. These are written with subscripts in the chemical formula. Example: The gas that consists of one carbon atom and two oxygen atoms is named carbon dioxide. Its chemical formula is CO2 . You Try It! Problem: What is the name of the compound that contains three oxygen atoms and two nitrogen atoms? What is its chemical formula? ",text,
L_0780,covalent bonds,T_4033,"Covalent compounds have different properties than ionic compounds because of their bonds. Covalent compounds exist as individual molecules rather than crystals. It takes less energy for individual molecules than ions in a crystal to pull apart. As a result, covalent compounds have lower melting and boiling points than ionic compounds. Many are gases or liquids at room temperature. Covalent compounds have shared electrons. These are not free to move like the transferred electrons of ionic compounds. This makes covalent compounds poor conductors of electricity. Many covalent compounds also do not dissolve in water as all ionic compounds do. ",text,
L_0780,covalent bonds,T_4034,"Having polar bonds may make a covalent compound polar. A polar compound is one in which there is a slight difference in charge between opposite ends of the molecule. All polar compounds contain polar bonds. But having polar bonds does not necessarily result in a polar compound. It depends on how the atoms are arranged. This is illustrated in Figure 7.11. Both molecules in the figure contain polar bonds, but only formaldehyde is a polar compound. Why is carbon dioxide nonpolar? The molecules of polar compounds are attracted to each other. You can see this in Figure 7.12 for water. A bond forms between the positive hydrogen end of one water molecule and the negative oxygen end of another water molecule. This type of bond is called a hydrogen bond. Hydrogen bonds are weak, but they still must be overcome when a polar substance changes from a solid to a liquid or from a liquid to a gas. As a result, polar covalent compounds may have higher melting and boiling points than nonpolar covalent compounds. To learn more about hydrogen bonding and when it occurs, see the video at this URL:  (0:58). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0780,covalent bonds,T_4034,"Having polar bonds may make a covalent compound polar. A polar compound is one in which there is a slight difference in charge between opposite ends of the molecule. All polar compounds contain polar bonds. But having polar bonds does not necessarily result in a polar compound. It depends on how the atoms are arranged. This is illustrated in Figure 7.11. Both molecules in the figure contain polar bonds, but only formaldehyde is a polar compound. Why is carbon dioxide nonpolar? The molecules of polar compounds are attracted to each other. You can see this in Figure 7.12 for water. A bond forms between the positive hydrogen end of one water molecule and the negative oxygen end of another water molecule. This type of bond is called a hydrogen bond. Hydrogen bonds are weak, but they still must be overcome when a polar substance changes from a solid to a liquid or from a liquid to a gas. As a result, polar covalent compounds may have higher melting and boiling points than nonpolar covalent compounds. To learn more about hydrogen bonding and when it occurs, see the video at this URL:  (0:58). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0781,metallic bonds,T_4035,"A metallic bond is the force of attraction between a positive metal ion and the valence electrons it shares with other ions of the metal. The positive ions form a lattice-like structure. You can see an example in Figure 7.13. (For an animated version, go to the URL below.) The ions are held together in the lattice by bonds with the valence electrons around them. These valence electrons include their own and those of other ions. Why do metallic bonds form? Recall that metals ""want"" to give up their valence electrons. This means that their valence electrons move freely. The electrons form a ""sea"" of negative charge surrounding the positive ions. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0781,metallic bonds,T_4036,"Because of their freely moving electrons, metals are good conductors of electricity. Metals also can be shaped without breaking. They are ductile (can be shaped into wires) and malleable (can be shaped into thin sheets). Metals have these properties because of the nature of their metallic bonds. A metallic lattice, like the one in Figure 7.13, may resemble a rigid ionic crystal. However, it is much more flexible. Look at Figure 7.14. It shows a blacksmith hammering a piece of red-hot iron in order to shape it. Why doesnt the iron shatter, as an ionic crystal would? The ions of the metal can move within the ""sea"" of electrons without breaking the metallic bonds that hold them together. The ions can shift closer together or farther apart. In this way, the metal can change shape without breaking. You can learn more about metallic bonds and the properties of metals at this URL:  (6:12). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0781,metallic bonds,T_4037,"Metals are useful for many purposes because of their unique properties. However, pure metals may be less useful than mixtures of metals. For example, iron is not as strong as steel, which is a mixture of iron and small amounts of carbon. Steel is so strong that it can hold up huge bridges, like the one Figure 7.15. Steel is also used to make skyscrapers, cargo ships, cars, and trains. Steel is an example of an alloy. An alloy is a mixture of a metal with one or more other elements. The other elements may be metals, nonmetals, or both. An alloy is a solid solution. It is formed by melting a metal and dissolving the other elements in it. The molten solution is then allowed to cool and harden. Several other examples of alloys and their uses are shown in Figure 7.16. You can learn about an amazing alloy called memory wire at the URL below. If you have braces on your teeth, you may even have this alloy in your mouth! ",text,
L_0781,metallic bonds,T_4037,"Metals are useful for many purposes because of their unique properties. However, pure metals may be less useful than mixtures of metals. For example, iron is not as strong as steel, which is a mixture of iron and small amounts of carbon. Steel is so strong that it can hold up huge bridges, like the one Figure 7.15. Steel is also used to make skyscrapers, cargo ships, cars, and trains. Steel is an example of an alloy. An alloy is a mixture of a metal with one or more other elements. The other elements may be metals, nonmetals, or both. An alloy is a solid solution. It is formed by melting a metal and dissolving the other elements in it. The molten solution is then allowed to cool and harden. Several other examples of alloys and their uses are shown in Figure 7.16. You can learn about an amazing alloy called memory wire at the URL below. If you have braces on your teeth, you may even have this alloy in your mouth! ",text,
L_0782,introduction to chemical reactions,T_4038,"A chemical reaction is a process in which some substances change into different substances. Substances that start a chemical reaction are called reactants. Substances that are produced in the reaction are called products. Reactants and products can be elements or compounds. A chemical reaction can be represented by this general equation: Reactants ! Products The arrow (!) shows the direction in which the reaction occurs. The reaction may occur quickly or slowly. For example, foam shoots out of a fire extinguisher as soon as the lever is pressed. But it might take years for metal to rust. ",text,
L_0782,introduction to chemical reactions,T_4039,"In chemical reactions, bonds break in the reactants and new bonds form in the products. The reactants and prod- ucts contain the same atoms, but they are rearranged during the reaction. As a result, the atoms are in different combinations in the products than they were in the reactants. Look at the example in Figure 8.2. It shows how water forms. Bonds break in molecules of hydrogen and oxygen. Then new bonds form in molecules of water. In both reactants and products, there are four hydrogen atoms and two oxygen atoms. But the atoms are combined differently in water. You can see another example at this URL: http://w ",text,
L_0782,introduction to chemical reactions,T_4040,"The arrow in Figure 8.2 shows that the reaction goes from left to right, from hydrogen and oxygen to water. The reaction can also go in the reverse direction. If an electric current passes through water, water molecules break down into molecules of hydrogen and oxygen. This reaction would be represented by a right-to-left arrow ( ) in Figure Many other reactions can also go in both forward and reverse directions. Often, a point is reached at which the forward and reverse reactions occur at the same rate. When this happens, there is no overall change in the amount of reactants and products. This point is called equilibrium, which refers to a balance between any opposing changes. You can see an animation of a chemical reaction reaching equilibrium at this URL: ",text,
L_0782,introduction to chemical reactions,T_4041,"Not all changes in matter involve chemical reactions. For example, there are no chemical reactions involved in changes of state. When liquid water freezes or evaporates, it is still water. No bonds are broken and no new products are formed. How can you tell whether a change in matter involves a chemical reaction? Often, there is evidence. Four common signs that a chemical reaction has occurred are: Change in color: the products are a different color than the reactants. Change in temperature: heat is released or absorbed during the reaction. Production of a gas: gas bubbles are released during the reaction. Production of a solid: a solid settles out of a liquid solution. The solid is called a precipitate. You can see examples of each type of evidence in Figure 8.3 and at this URL:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0783,chemical equations,T_4042,"A chemical equation is a symbolic representation of a chemical reaction. It is a shorthand way of showing how atoms are rearranged in the reaction. The general form of a chemical equation was introduced in this chapters lesson ""Introduction to Chemical Reactions."" It is: Reactants ! Products Consider the simple example in Figure 8.4. When carbon (C) reacts with oxygen (O2 ), it produces carbon dioxide (CO2 ). The chemical equation for this reaction is: C + O2 ! CO2 The reactants are one atom of carbon and one molecule of oxygen. When there is more than one reactant, they are separated by plus signs (+). The product is one molecule of carbon dioxide. If more than one product were produced, plus signs would be used between them as well. ",text,
L_0783,chemical equations,T_4043,"Some chemical equations are more challenging to write. Consider the reaction in which hydrogen (H2 ) and oxygen (O2 ) combine to form water (H2 O). Hydrogen and oxygen are the reactants, and water is the product. To write a chemical equation for this reaction, you would start by writing symbols for the reactants and products: Equation 1: H2 + O2 ! H2 O Like equations in math, equations in chemistry must balance. There must be the same number of each type of atom in the products as there is in the reactants. In equation 1, count the number of hydrogen and oxygen atoms on each side of the arrow. There are two hydrogen atoms in both reactants and products. There are two oxygen atoms in the reactants but only one in the product. Therefore, equation 1 is not balanced. ",text,
L_0783,chemical equations,T_4044,"Coefficients are used to balance chemical equations. A coefficient is a number placed in front of a chemical symbol or formula. It shows how many atoms or molecules of the substance are involved in the reaction. For example, two molecules of hydrogen would be written as 2H2 . A coefficient of 1 usually isnt written. Coefficients can be used to balance equation 1 (above) as follows: Equation 2: 2H2 + O2 ! 2H2 O Equation 2 shows that two molecules of hydrogen react with one molecule of oxygen to produce two molecules of water. The two molecules of hydrogen each contain two hydrogen atoms. There are now four hydrogen atoms in both reactants and products. Is equation 2 balanced? Count the oxygen atoms to find out. ",text,
L_0783,chemical equations,T_4045,"Balancing a chemical equation involves a certain amount of trial and error. In general, however, you should follow these steps: 1. Count the number of each type of atom in reactants and products. Does the same number of each atom appear on both sides of the arrow? If not, the equation is not balanced, and you need to go to step 2. 2. Add coefficients to increase the number of atoms or molecules of reactants or products. Use the smallest coefficients possible. 3. Repeat steps 1 and 2 until the equation is balanced. Helpful Hint When you balance chemical equations, never change the subscripts in chemical formulas. Changing subscripts changes the substances involved in the reaction. Change only the coefficients. Work through the Problem Solving examples below. Then do the You Try It! problems to check your understand- ing. If you need more help, go to this URL:  (14:28). MEDIA Click image to the left or use the URL below. URL:  Problem Solving Problem: Balance this chemical equation: N2 + H2 ! NH3 Hints for balancing 1. Two N are needed in the products to match the two N (N2 ) in the reactants. Add the coefficient 2 in front of NH3 . Now N is balanced. 2. Six H are now needed in the reactants to match the six H in the products. Add the coefficient 3 in front of H2 . Now H is balanced. Solution: N2 + 3H2 ! 2NH3 Problem: Balance this chemical equation: CH4 + O2 ! CO2 + H2 O Solution: CH4 + 2O2 ! CO2 + 2H2 O You Try It! Problem: Balance these chemical equations: Zn + HCl ! ZnCl2 + H2 Cu + O2 ! CuO ",text,
L_0783,chemical equations,T_4046,"Why must chemical equations be balanced? Its the law! Matter cannot be created or destroyed in chemical reactions. This is the law of conservation of mass. In every chemical reaction, the same mass of matter must end up in the products as started in the reactants. Balanced chemical equations show that mass is conserved in chemical reactions. How do scientists know that mass is always conserved in chemical reactions? Careful experiments in the 1700s by a French chemist named Antoine Lavoisier led to this conclusion. For this and other contributions, Lavoisier has been called the father of modern chemistry. Lavoisier carefully measured the mass of reactants and products in many different chemical reactions. He carried out the reactions inside a sealed jar, like the one in Figure 8.5. As a result, any gases involved in the reactions were captured and could be measured. In every case, the total mass of the jar and its contents was the same after the reaction as it was before the reaction took place. This showed that matter was neither created nor destroyed in the reactions. Another outcome of Lavoisiers research was his discovery of oxygen. You can learn more about Lavoisier and his important research at: ",text,
L_0784,types of chemical reactions,T_4047,"A synthesis reaction occurs when two or more reactants combine to form a single product. A synthesis reaction can be represented by the general equation: A+B !C In this general equation (and others like it in this lesson), the letters A, B,C, and so on represent atoms or ions of elements. The arrow shows the direction of the reaction. The letters on the left side of the arrow are the reactants that begin the chemical reaction. The letters on the right side of the arrow are the product of the reaction. Two examples of synthesis reactions are described below. You can see more examples at this URL: ",text,
L_0784,types of chemical reactions,T_4048,"An example of a synthesis reaction is the combination of sodium (Na) and chlorine (Cl) to produce sodium chloride (NaCl). This reaction is represented by the chemical equation: 2Na + Cl2 ! 2NaCl Sodium is a highly reactive metal, and chlorine is a poisonous gas (see Figure 8.6). The compound they synthesize has very different properties. It is table salt, which is neither reactive nor poisonous. In fact, salt is a necessary component of the human diet. ",text,
L_0784,types of chemical reactions,T_4049,"Another example of a synthesis reaction is illustrated in Figure 8.7. The brown haze in the air over the city of Los Angeles is smog. A major component of smog is nitrogen dioxide (NO2 ). It forms when nitric oxide (NO), from sources such as car exhaust, combines with oxygen (O2 ) in the air. The equation for this reaction is: 2NO + O2 ! 2NO2 Nitrogen dioxide is a toxic gas with a sharp odor. It can irritate the eyes and throat and trigger asthma attacks. It is a major air pollutant. ",text,
L_0784,types of chemical reactions,T_4050,"A decomposition reaction is the reverse of a synthesis reaction. In a decomposition reaction, one reactant breaks down into two or more products. This can be represented by the general equation: AB ! A + B Two examples of decomposition reactions are described below. You can see other examples at this URL: http://w ",text,
L_0784,types of chemical reactions,T_4051,"An example of a decomposition reaction is the breakdown of carbonic acid (H2 CO3 ) to produce water (H2 O) and carbon dioxide (CO2 ). The equation for this reaction is: H2 CO3 ! H2 O + CO2 Carbonic acid is synthesized in the reverse reaction. It forms when carbon dioxide dissolves in water. For example, some of the carbon dioxide in the atmosphere dissolves in the ocean and forms carbonic acid. The amount of carbon dioxide in the atmosphere has increased over recent decades (see Figure 8.8). As a result, the acidity of ocean water is also increasing. How do you think this might affect ocean life? ",text,
L_0784,types of chemical reactions,T_4052,"Another example of a decomposition reaction is illustrated in Figure 8.9. Water (H2 O) decomposes to hydrogen (H2 ) and oxygen (O2 ) when an electric current passes through it. This reaction is represented by the equation: 2H2 O ! 2H2 + O2 What is the reverse of this decomposition reaction? (Hint: How is water synthesized? You can look at this chapters ""Introduction to Chemical Reactions"" lesson to find out.) ",text,
L_0784,types of chemical reactions,T_4053,Replacement reactions involve ions. They occur when ions switch places in compounds. There are two types of replacement reactions: single and double. Both types are described below. ,text,
L_0784,types of chemical reactions,T_4054,"A single replacement reaction occurs when one ion takes the place of another in a single compound. This type of reaction has the general equation: A + BC ! B + AC Do you see how A has replaced B in the compound? The compound BC has become the compound AC. An example of a single replacement reaction occurs when potassium (K) reacts with water (H2 O). A colorless solid called potassium hydroxide (KOH) forms, and hydrogen gas (H2 ) is released. The equation for the reaction is: 2K + 2H2 O ! 2KOH + H2 Potassium is a highly reactive group 1 alkali metal, so its reaction with water is explosive. You can actually watch this reaction occurring at: http://commons.wikimedia.org/wiki/File:Potassium_water_20.theora.ogv . ",text,
L_0784,types of chemical reactions,T_4055,A double replacement reaction occurs when two compounds exchange ions. This produces two new compounds. A double replacement reaction can be represented by the general equation: AB +CD ! AD +CB Do you see how B and D have changed places? Both reactant compounds have changed. An example of a double replacement reaction is sodium chloride (NaCl) reacting with silver fluoride (AgF). This reaction is represented by the equation: NaCl + AgF ! NaF + AgCl Cl and F have changed places. Can you name the products of this reaction? ,text,
L_0784,types of chemical reactions,T_4056,A combustion reaction occurs when a substance reacts quickly with oxygen (O2 ). You can see an example of a combustion reaction in Figure 8.10. Combustion is commonly called burning. The substance that burns is usually referred to as fuel. The products of a combustion reaction include carbon dioxide (CO2 ) and water (H2 O). The reaction typically gives off heat and light as well. The general equation for a combustion reaction can be represented by: Fuel + O2 ! CO2 + H2 O ,text,
L_0784,types of chemical reactions,T_4057,"The fuel that burns in a combustion reaction is often a substance called a hydrocarbon. A hydrocarbon is a compound that contains only carbon (C) and hydrogen (H). Fossil fuels, such as natural gas, consist of hydrocarbons. Natural gas is a fuel that is commonly used in home furnaces and gas stoves (see Figure 8.11). The main component of natural gas is the hydrocarbon called methane (CH4 ). The combustion of methane is represented by the equation: CH4 + 2O2 ! CO2 + 2H2 O ",text,
L_0784,types of chemical reactions,T_4058,"Your own body cells burn fuel in combustion reactions. The fuel is glucose (C6 H12 O6 ), a simple sugar. The process in which combustion of glucose occurs in body cells is called cellular respiration. This combustion reaction provides energy for life processes. Cellular respiration can be summed up by the equation: C6 H12 O6 + 6O2 ! 6CO2 + 6H2 O Where does glucose come from? It is produced by plants during photosynthesis. In this process, carbon dioxide and water combine to form glucose. Which type of chemical reaction is photosynthesis? ",text,
L_0785,chemical reactions and energy,T_4059,"In an endothermic reaction, it takes more energy to break bonds in the reactants than is released when new bonds form in the products. The word ""endothermic"" literally means ""taking in heat."" A constant input of energy, often in the form of heat, is needed in an endothermic reaction. Not enough energy is released when products form to break more bonds in the reactants. Additional energy is needed to keep the reaction going. The general equation for an endothermic reaction is: Reactants + Energy ! Products In many endothermic reactions, heat is absorbed from the surroundings. As a result, the temperature drops. The drop in temperature may be great enough to cause liquid products to freeze. Thats what happens in the endothermic reaction at this URL:  One of the most important endothermic reactions is photosynthesis. In this reaction, plants synthesize glucose (C6 H12 O6 ) from carbon dioxide (CO2 ) and water (H2 O). They also release oxygen (O2 ). The energy for photo- synthesis comes from light (see Figure 8.12). Without light energy, photosynthesis cannot occur. The chemical equation for photosynthesis is: 6CO2 + 6H2 O ! C6 H12 O6 + 6O2 ",text,
L_0785,chemical reactions and energy,T_4060,"In an exothermic reaction, it takes less energy to break bonds in the reactants than is released when new bonds form in the products. The word ""exothermic"" literally means ""turning out heat."" Energy, often in the form of heat, is released as an exothermic reaction occurs. The general equation for an exothermic reaction is: Reactants ! Products + Energy If the energy is released as heat, an exothermic reaction results in a rise in temperature. Thats what happens in the exothermic reaction at the URL below. Combustion reactions are examples of exothermic reactions. When substances burn, they usually give off energy as heat and light. Look at the big bonfire in Figure 8.13. You can see the light energy it is giving off. If you were standing near the fire, you would also feel its heat. ",text,
L_0785,chemical reactions and energy,T_4061,"Whether a reaction absorbs energy or releases energy, there is no overall change in the amount of energy. Energy cannot be created or destroyed. This is the law of conservation of energy. Energy can change form for example, from electricity to light but the same amount of energy always remains. If energy cannot be destroyed, what happens to the energy that is absorbed in an endothermic reaction? The energy is stored in the chemical bonds of the products. This form of energy is called chemical energy. In an endothermic reaction, the products have more stored chemical energy than the reactants. In an exothermic reaction, the opposite is true. The products have less stored chemical energy than the reactants. The excess energy in the reactants is released to the surroundings when the reaction occurs. The graphs in Figure 8.14 show the chemical energy of reactants and products in each type of reaction. ",text,
L_0785,chemical reactions and energy,T_4061,"Whether a reaction absorbs energy or releases energy, there is no overall change in the amount of energy. Energy cannot be created or destroyed. This is the law of conservation of energy. Energy can change form for example, from electricity to light but the same amount of energy always remains. If energy cannot be destroyed, what happens to the energy that is absorbed in an endothermic reaction? The energy is stored in the chemical bonds of the products. This form of energy is called chemical energy. In an endothermic reaction, the products have more stored chemical energy than the reactants. In an exothermic reaction, the opposite is true. The products have less stored chemical energy than the reactants. The excess energy in the reactants is released to the surroundings when the reaction occurs. The graphs in Figure 8.14 show the chemical energy of reactants and products in each type of reaction. ",text,
L_0785,chemical reactions and energy,T_4062,"All chemical reactions, even exothermic reactions, need a certain amount of energy to get started. This energy is called activation energy. For example, activation energy is needed to start a car. Turning the key causes a spark that activates the burning of gasoline in the engine. The combustion of gas wont occur without the spark of energy to begin the reaction. Why is activation energy needed? A reaction wont occur unless atoms or molecules of reactants come together. This happens only if the particles are moving, and movement takes energy. Often, reactants have to overcome forces that push them apart. This takes energy as well. Still more energy is needed to start breaking bonds in reactants. The graphs in Figure 8.15 show the changes in energy in endothermic and exothermic reactions. Both reactions need the same amount of activation energy in order to begin. You have probably used activation energy to start a chemical reaction. For example, if youve ever used a match to light a campfire, then you provided the activation energy needed to start a combustion reaction. Combustion is exothermic. Once a fire starts to burn, it releases enough energy to activate the next reaction, and the next, and so on. However, wood will not burst into flames on its own. ",text,
L_0785,chemical reactions and energy,T_4063,"Any factor that helps reactants come together so they can react lowers the amount of activation energy needed to start the reaction. If the activation energy is lowered, more reactant particles can react, and the reaction occurs more quickly. How fast a reaction occurs is called the reaction rate. Factors that affect the reaction rate include: temperature of reactants concentration of reactants surface area of reactants presence of catalysts ",text,
L_0785,chemical reactions and energy,T_4064,"When the temperature of reactants is higher, the rate of the reaction is faster. At higher temperatures, particles of reactants have more energy, so they move faster. They are more likely to bump into one another and to collide with greater force. For example, when you fry an egg, turning up the heat causes the egg to cook faster. The same principle explains why storing food in a cold refrigerator reduces the rate at which food spoils (see Figure 8.16). Both food frying and food spoiling are chemical reactions that happen faster at higher temperatures. ",text,
L_0785,chemical reactions and energy,T_4065,"Concentration is the number of particles of a substance in a given volume. When the concentration of reactants is higher, the reaction rate is faster. At higher concentrations, particles of reactants are crowded closer together, so they are more likely to collide and react. Did you ever see a sign like the one in Figure 8.17? You might see it where someone is using a tank of pure oxygen for a breathing problem. The greater concentration of oxygen in the air makes combustion rapid if a fire starts burning. ",text,
L_0785,chemical reactions and energy,T_4066,"When a solid substance is involved in a chemical reaction, only the matter at the surface of the solid is exposed to other reactants. If a solid has more surface area, more of it is exposed and able to react. Therefore, increasing the surface area of solid reactants increases the reaction rate. For example, crushing a solid into a powder exposes more of the substance to other reactants. This may greatly speed up the reaction. You can see another example in Figure 8.18. Iron rusts when it combines with oxygen in the air. The iron hammer head and iron nails will both rust eventually. Which will rust faster? ",text,
L_0785,chemical reactions and energy,T_4067,"Some reactions need extra help to occur quickly. They need another substance, called a catalyst. A catalyst is a substance that increases the rate of a chemical reaction but is not changed or used up in the reaction. The catalyst can go on to catalyze many more reactions. Catalysts are not reactants, but they help reactants come together so they can react. You can see one way this happens in the animation at the URL below. By helping reactants come together, a catalyst decreases the activation energy needed to start a chemical reaction. This speeds up the reaction. Living things depend on catalysts to speed up many chemical reactions inside their cells. Catalysts in living things are called enzymes. Enzymes may be extremely effective. A reaction that takes a split second to occur with an enzyme might take billions of years without it! ",text,
L_0786,properties of carbon,T_4068,"Carbon is a nonmetal in group 14 of the periodic table. Like other group 14 compounds, carbon has four valence electrons. Valence electrons are the electrons in the outer energy level of an atom that are involved in chemical bonds. The valence electrons of carbon are shown in Figure 9.1. ",text,
L_0786,properties of carbon,T_4069,"Because it has four valence electrons, carbon needs four more electrons to fill its outer energy level. It can achieve this by forming four covalent bonds. Covalent bonds are chemical bonds that form between nonmetals. In a covalent bond, two atoms share a pair of electrons. By forming four covalent bonds, carbon shares four pairs of electrons, thus filling its outer energy level. A carbon atom can form bonds with other carbon atoms or with the atoms of other elements. Carbon often forms bonds with hydrogen. You can see an example in Figure 9.2. The compound represented in the figure is methane (CH4 ). The carbon atom in a methane molecule forms bonds with four hydrogen atoms. The diagram on the left shows all the shared electrons. The diagram on the right represents each pair of shared electrons with a dash (). This type of diagram is called a structural formula. ",text,
L_0786,properties of carbon,T_4070,"Carbon can form single, double, or even triple bonds with other carbon atoms. In a single bond, two carbon atoms share one pair of electrons. In a double bond, they share two pairs of electrons, and in a triple bond they share three pairs of electrons. Examples of compounds with these types of bonds are shown in Figure 9.3. ",text,
L_0786,properties of carbon,T_4071,"Because of carbons ability to form so many covalent bonds, it often forms polymers. A polymer is a large molecule that consists of many smaller molecules joined together by covalent bonds. The smaller molecules are called monomers. (The prefix mono means ""one,"" and the prefix poly means ""many."") Polymers may consist of just one type of monomer or of more than one type. Polymers are a little like the strings of beads in Figure 9.4. What do the individual beads represent? Many polymers occur naturally. You will read about natural polymers in this chapters ""Hydrocarbons"" and ""Carbon and Living Things"" lessons. Other polymers are synthetic. This means that they are produced in labs or factories. Synthetic polymers are created in synthesis reactions in which monomers bond together to form much larger compounds. Plastics are examples of synthetic polymers. The plastic items in Figure 9.5 are all made of polythene (also called polyethylene). It consists of repeating monomers of ethene (C2 H4 ). To learn more about polymers and how they form, go to this URL:  (2:13). ",text,
L_0786,properties of carbon,T_4071,"Because of carbons ability to form so many covalent bonds, it often forms polymers. A polymer is a large molecule that consists of many smaller molecules joined together by covalent bonds. The smaller molecules are called monomers. (The prefix mono means ""one,"" and the prefix poly means ""many."") Polymers may consist of just one type of monomer or of more than one type. Polymers are a little like the strings of beads in Figure 9.4. What do the individual beads represent? Many polymers occur naturally. You will read about natural polymers in this chapters ""Hydrocarbons"" and ""Carbon and Living Things"" lessons. Other polymers are synthetic. This means that they are produced in labs or factories. Synthetic polymers are created in synthesis reactions in which monomers bond together to form much larger compounds. Plastics are examples of synthetic polymers. The plastic items in Figure 9.5 are all made of polythene (also called polyethylene). It consists of repeating monomers of ethene (C2 H4 ). To learn more about polymers and how they form, go to this URL:  (2:13). ",text,
L_0786,properties of carbon,T_4072,"Exploratorium Staff Scientist Julie Yu changes and manipulates the physical and chemical properties of plastic bottles by exposing them to heat. This is how plastic bags and bottles can be recycled and used over and over again. For more information on properties of plastic, see http://science.kqed.org/quest/video/quest-lab-properties-of-plas MEDIA Click image to the left or use the URL below. URL: ",text,
L_0786,properties of carbon,T_4073,"Pure carbon can exist in different forms, depending on how its atoms are arranged. The forms include diamond, graphite, and fullerenes. All three forms exist as crystals, but they have different structures. Their different structures, in turn, give them different properties. You can learn more about them in Table 9.1. atoms affect the properties of the substances formed? Structure Diamond crystal Description Diamond Diamond is a form of carbon in which each carbon atom is bonded to four other carbon atoms. This forms a strong, rigid, three- dimensional structure. Diamond is the hardest natural substance. It is used for cutting and grinding tools as well as for rings and other pieces of jewelry. Graphite Graphite is a form of carbon in which carbon atoms are arranged in layers. Bonds are strong between carbon atoms within each layer but relatively weak between atoms in different layers. The weak bonds between layers allow the layers to slide over one another. This makes graphite relatively soft and slippery. It is used as a lubricant. It also makes up the ""lead"" in pencils. Fullerene A fullerene (also called a bucky- ball) is a form of carbon in which carbon atoms are arranged in hol- low spheres. Each carbon atom is bonded to three others by sin- gle covalent bonds. The pattern of atoms resembles the pattern on the surface of a soccer ball. Fullerenes were first discovered in 1985. They have been found in soot and me- teorites. Possible commercial uses of fullerenes are under investiga- tion. To learn how this form of carbon got its funny names, go to this URL:  This metal cutter has a diamond blade. ",text,
L_0787,hydrocarbons,T_4074,"Hydrocarbons are compounds that contain only carbon and hydrogen. Hydrocarbons are the simplest type of carbon-based compounds. Nonetheless, they can vary greatly in size. The smallest hydrocarbons have just one or two carbon atoms, but large hydrocarbons may have hundreds. The size of hydrocarbon molecules influences their properties. For example, it influences their boiling and melting points. As a result, some hydrocarbons are gases at room temperature, while others are liquids or solids. Hydrocarbons are generally nonpolar and do not dissolve in water. In fact, they tend to repel water. Thats why they are used in floor wax and similar products. Hydrocarbons can be classified in two basic classes. The classes are saturated hydrocarbons and unsaturated hydrocarbons. This classification is based on the number of bonds between carbon atoms. You can learn more about both types of hydrocarbons at this URL:  (6:41). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0787,hydrocarbons,T_4075,"Saturated hydrocarbons contain only single bonds between carbon atoms. They are the simplest hydrocarbons. They are called saturated because each carbon atom is bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogen. You can see an example of a saturated hydrocarbon in Figure Saturated hydrocarbons are given the general name of alkanes. The name of specific alkanes always ends in -ane. The first part of the name indicates how many carbon atoms each molecule of the alkane has. The smallest alkane is methane. It has just one carbon atom. The next largest is ethane, with two carbon atoms. The chemical formulas and properties of methane, ethane, and several other alkanes are listed in Table 9.2. The boiling and melting points of alkanes are determined mainly by the number of carbon atoms they have. Alkanes with more carbon atoms generally have higher boiling and melting points. This table shows only alkanes with relatively few carbon atoms. Some alkanes have many more carbon atoms. What properties might larger alkanes have? For example, do you think that any of them might be solids? Alkane Methane Ethane Propane Butane Pentane Hexane Heptane Octane Chemical Formula CH4 C2 H6 C3 H8 C4 H10 C5 H12 C6 H14 C7 H16 C8 H18 Boiling Point (C) -162 -89 -42 0 36 69 98 126 Melting Point (C) -183 -172 -188 -138 -130 -95 -91 -57 State (at 20C) gas gas gas gas liquid liquid liquid liquid ",text,
L_0787,hydrocarbons,T_4076,"Structural formulas are often used to represent hydrocarbon compounds because the molecules can have different shapes, or structures. Hydrocarbons may form straight chains, branched chains, or rings. Figure 9.8 shows an example of an alkane with each shape. In straight-chain molecules, all the carbon atoms are lined up in a row like cars of a train. They form what is called the backbone of the molecule. In branched-chain molecules, at least one of the carbon atoms branches off to the side from the backbone. In cyclic molecules, the chain of carbon atoms is joined at the two ends to form a ring. ",text,
L_0787,hydrocarbons,T_4077,"Even compounds with the same number of carbon and hydrogen atoms can have different shapes. These compounds are called isomers. Look at the examples in Figure 9.9. The figure shows the structural formulas of butane and its isomer iso-butane. Both molecules have four carbon atoms and ten hydrogen atoms (C4 H10 ), but the atoms are arranged differently. Butane is a straight-chain molecule. Iso-butane is branched. You can see three-dimensional models of these two isomers at the URLs below. You can rotate the molecule models to get a better idea of their shapes. ",text,
L_0787,hydrocarbons,T_4078,"Ring-shaped alkanes are called cycloalkanes. They usually contain just five or six carbon atoms because larger rings are not very stable. However, rings can join together to create larger molecules consisting of two or more rings. Compared with the straight- and branched-chain alkanes, cycloalkanes have higher boiling and melting points. ",text,
L_0787,hydrocarbons,T_4079,"Unsaturated hydrocarbons contain at least one double or triple bond between carbon atoms. As a result, the carbon atoms are unable to bond with as many hydrogen atoms as they would if they were joined only by single bonds. This makes them unsaturated with hydrogen. Unsaturated hydrocarbons are classified on the basis of their bonds as alkenes, alkynes, or aromatic hydrocarbons. ",text,
L_0787,hydrocarbons,T_4080,"Unsaturated hydrocarbons that contain at least one double bond are called alkenes. The name of a specific alkene always ends in ene, with a prefix indicating the number of carbon atoms. Figure 9.10 shows the structural formula for the smallest alkene. It has just two carbon atoms and is named ethene. Ethene is produced by most fruits and vegetables. It speeds up ripening and also rotting. Figure 9.11 shows the effects of ethene on bananas. Like alkanes, alkenes can have different shapes. They can form straight chains, branched chains, or rings. Alkenes can also form isomers, or compounds with the same atoms but different shapes. Generally, the physical properties of alkenes are similar to those of alkanes. Smaller alkenes, such as ethene, have relatively high boiling and melting points. They are gases at room temperature. Larger alkenes have lower boiling and melting points. They are liquids or waxy solids at room temperature. ",text,
L_0787,hydrocarbons,T_4081,"Unsaturated hydrocarbons that contain at least one triple bond are called alkynes. The name of specific alkynes always end in yne, with a prefix for the number of carbon atoms. Figure 9.12 shows the smallest alkyne, called ethyne, which has just two carbon atoms. Ethyne is also called acetylene. It is burned in acetylene torches, like the one in Figure 9.13. Acetylene produces so much heat when it burns that it can melt metal. Breaking all those bonds between carbon atoms releases a lot of energy. Alkynes may form straight or branched chains. They rarely occur as cycloalkynes. In fact, alkynes of all shapes are relatively rare, at least in nature. ",text,
L_0787,hydrocarbons,T_4081,"Unsaturated hydrocarbons that contain at least one triple bond are called alkynes. The name of specific alkynes always end in yne, with a prefix for the number of carbon atoms. Figure 9.12 shows the smallest alkyne, called ethyne, which has just two carbon atoms. Ethyne is also called acetylene. It is burned in acetylene torches, like the one in Figure 9.13. Acetylene produces so much heat when it burns that it can melt metal. Breaking all those bonds between carbon atoms releases a lot of energy. Alkynes may form straight or branched chains. They rarely occur as cycloalkynes. In fact, alkynes of all shapes are relatively rare, at least in nature. ",text,
L_0787,hydrocarbons,T_4081,"Unsaturated hydrocarbons that contain at least one triple bond are called alkynes. The name of specific alkynes always end in yne, with a prefix for the number of carbon atoms. Figure 9.12 shows the smallest alkyne, called ethyne, which has just two carbon atoms. Ethyne is also called acetylene. It is burned in acetylene torches, like the one in Figure 9.13. Acetylene produces so much heat when it burns that it can melt metal. Breaking all those bonds between carbon atoms releases a lot of energy. Alkynes may form straight or branched chains. They rarely occur as cycloalkynes. In fact, alkynes of all shapes are relatively rare, at least in nature. ",text,
L_0787,hydrocarbons,T_4082,"Unsaturated cyclic hydrocarbons are called aromatic hydrocarbons. Thats because they have a strong aroma, or scent. Their molecules consist of six carbon atoms in a ring shape, connected by alternating single and double bonds. Aromatic hydrocarbons may have a single ring or multiple rings joined together by bonds between their carbon atoms. Benzene is the smallest aromatic hydrocarbon. It has just one ring. You can see its structural formula in Figure 9.14. Benzene has many uses. For example, it is used in air fresheners and mothballs because of its strong scent. You can learn more about benzene and other aromatic hydrocarbons at this URL:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0787,hydrocarbons,T_4083,"It is hard to overstate the importance of hydrocarbons to modern life. Hydrocarbons have even been called the driving force of western civilization. You saw some ways they are used in Figure 9.6. Several other ways are illustrated in Figure 9.15. Their most important use is as fuels. Gasoline, natural gas, fuel oil, diesel fuel, jet fuel, coal, kerosene, and propane are just some of the hydrocarbon compounds that are burned for fuel. Hydrocarbons are also used to manufacture many products, including plastics and synthetic fabrics such as polyester. The main source of hydrocarbons is fossil fuels coal, petroleum, and natural gas. Fossil fuels form over hundreds of millions of years when dead organisms are covered with sediments and put under great pressure. Giant ferns in ancient swamps turned into coal deposits. Dead organisms in ancient seas gradually formed deposits of petroleum and natural gas. You can read more about these sources of hydrocarbons in the chapter Introduction to Energy and at the URL below. ",text,
L_0788,carbon and living things,T_4084,"A biochemical compound is any carbon-based compound found in living things. Like hydrocarbons, all biochemi- cal compounds contain hydrogen as well as carbon. However, biochemical compounds also contain other elements, such as oxygen and nitrogen. Almost all biochemical compounds are polymers. They consist of many, smaller monomer molecules. Biochemical polymers are referred to as macromolecules. The prefix macro means ""large,"" and many biochemical molecules are very large indeed. They may contain thousands of monomer molecules. Biochemical compounds make up the cells and tissues of organisms. They are also involved in life processes, such as making and using food for energy. Given their diversity of functions, its not surprising that there are millions of different biochemical compounds. However, they can be grouped into just four main classes: carbohydrates, proteins, lipids, and nucleic acids. The classes are summarized in Table 9.3 and described in the rest of this lesson. Class Carbohydrates Elements carbon hydrogen oxygen Examples sugars starches cellulose Proteins carbon hydrogen oxygen nitrogen sulfur carbon hydrogen oxygen carbon hydrogen oxygen nitrogen phosphorus enzymes hormones Lipids Nucleic acids Functions provide energy to cells store energy in plants makes up the cell walls of plants speed up biochemical re- actions regulate life processes fats oils store energy in animals store energy in plants DNA RNA stores genetic information in cells helps cells make proteins ",text,
L_0788,carbon and living things,T_4085,"Carbohydrates are biochemical compounds that include sugars, starches, and cellulose. They contain oxygen in addition to carbon and hydrogen. Organisms use carbohydrates mainly for energy. ",text,
L_0788,carbon and living things,T_4086,"Sugars are simple carbohydrates. Molecules of sugar have just a few carbon atoms. The simplest sugar is glucose (C6 H12 O6 ). Glucose is the sugar that the cells of living things use for energy. Plants and some other organisms make glucose in the process of photosynthesis. Living things that cannot make glucose obtain it by consuming plants or these other organisms. You can see the structural formula of glucose and two other sugars in Figure 9.16. The other sugars in the figure are fructose and sucrose. Fructose is an isomer of glucose. It is found in fruits. It has the same atoms as glucose, but they are arranged differently. Sucrose is table sugar. It consists of one molecule of glucose and one molecule of fructose. ",text,
L_0788,carbon and living things,T_4087,"Starches are complex carbohydrates. They are polymers of glucose. They consist of hundreds of glucose monomers bonded together. Plants make starch to store extra sugars. Consumers get starch from plants. Common sources of starch in the human diet are pictured in Figure 9.17. Our digestive system breaks down starch to simple sugars, which our cells use for energy. ",text,
L_0788,carbon and living things,T_4087,"Starches are complex carbohydrates. They are polymers of glucose. They consist of hundreds of glucose monomers bonded together. Plants make starch to store extra sugars. Consumers get starch from plants. Common sources of starch in the human diet are pictured in Figure 9.17. Our digestive system breaks down starch to simple sugars, which our cells use for energy. ",text,
L_0788,carbon and living things,T_4088,"Cellulose is another complex carbohydrate that is a polymer of glucose. However, the glucose molecules are bonded together differently in cellulose than they are in starches. Cellulose molecules bundle together to form long, tough fibers (see Figure 9.18). Have you ever eaten raw celery? If you have, then you probably noticed that the stalks contain long, stringy fibers. The fibers are mostly cellulose. Cellulose is the most abundant biochemical compound. It makes up the cell walls of plants and gives support to trunks and stems. Cellulose also provides needed fiber in the human diet. We cant digest cellulose, but it helps keep food wastes moving through the digestive tract. ",text,
L_0788,carbon and living things,T_4089,"Proteins are biochemical compounds that contain oxygen, nitrogen, and sulfur in addition to carbon and hydrogen. Protein molecules consist of one or more chains of small molecules called amino acids. ",text,
L_0788,carbon and living things,T_4090,"Amino acids are the ""building blocks"" of proteins. There are 20 different common amino acids. The structural formula of the simplest amino acid, called glycine, is shown in Figure 9.19. Other amino acids have a similar structure. The sequence of amino acids and the number of amino acid chains in a protein determine the proteins shape. The shape of a protein, in turn, determines its function. Shapes may be very complex. You can learn more about the structure of proteins at the URL below. MEDIA Click image to the left or use the URL below. URL: ",text,
L_0788,carbon and living things,T_4091,"Proteins are the most common biochemicals. They have many different functions, including: making up tissues as components of muscle. speeding up biochemical reactions as enzymes. regulating life processes as hormones. helping defend against infections as antibodies. transporting materials as components of the blood (see the example in Figure 9.20). ",text,
L_0788,carbon and living things,T_4092,"Lipids are biochemical compounds such as fats and oils. Organisms use lipids to store energy. In addition to carbon and hydrogen, lipids contain oxygen. ",text,
L_0788,carbon and living things,T_4093,"Lipids are made up of long carbon chains called fatty acids. Like hydrocarbons, fatty acids may be saturated or unsaturated. Figure 9.21 shows structural formulas for two small fatty acids. One is saturated and one is unsaturated. In saturated fatty acids, there are only single bonds between carbon atoms. As a result, the carbons are saturated with hydrogen atoms. Saturated fatty acids are found in fats. Fats are solid lipids that animals use to store energy. In unsaturated fatty acids, there is at least one double bond between carbon atoms. As a result, some carbons are not bonded to as many hydrogen atoms as possible. Unsaturated fatty acids are found in oils. Oils are liquid lipids that plants use to store energy. ",text,
L_0788,carbon and living things,T_4094,"Some lipids contain the element phosphorus as well as oxygen, carbon, and hydrogen. These lipids are called phospholipids. Two layers of phospholipid molecules make up most of the cell membrane in the cells of living things. Figure 9.22 shows how phospholipid molecules are arranged in a cell membrane. One end (the head) of each phospholipid molecule is polar and attracts water. This end is called hydrophilic (""water loving""). The other end (the tail) is nonpolar and repels water. This end is called hydrophobic (""water hating""). The nonpolar tails are on the inside of the membrane. The polar heads are on the outside of the membrane. These differences in polarity allow some molecules to pass through the membrane while keeping others out. You can see how this works in the video at the URL below. ",text,
L_0788,carbon and living things,T_4095,"Nucleic acids are biochemical molecules that contain oxygen, nitrogen, and phosphorus in addition to carbon and hydrogen. There are two main types of nucleic acids. They are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). ",text,
L_0788,carbon and living things,T_4096,"Nucleic acids consist of chains of small molecules called nucleotides. The structure of a nucleotide is shown in Figure 9.23. Each nucleotide contains a phosphate group (PO4 ), a sugar (C5 H8 O4 ) in DNA, and a nitrogen- containing base. (A base is a compound that is not neither acidic nor neutral.) There are four different nitrogenous bases in DNA. They are adenine, thymine, guanine, and cytosine. In RNA, the only difference is that thymine is replaced with a different base, uracil. DNA consists of two long chains of nucleotides. Nitrogen bases on the two chains form hydrogen bonds with each other. Adenine always bonds with thymine, and guanine always bonds with cytosine. These bonds hold the two chains together and give DNA is characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in Figure 9.24. Sugars and phosphate groups form the ""backbone"" of each chain of DNA. The bonded bases are called base pairs. RNA, in contrast to DNA, consists of just one chain of nucleotides. Determining the structure of DNA was a big scientific breakthrough. You can read the interesting story of its discovery at the URL below. ",text,
L_0788,carbon and living things,T_4096,"Nucleic acids consist of chains of small molecules called nucleotides. The structure of a nucleotide is shown in Figure 9.23. Each nucleotide contains a phosphate group (PO4 ), a sugar (C5 H8 O4 ) in DNA, and a nitrogen- containing base. (A base is a compound that is not neither acidic nor neutral.) There are four different nitrogenous bases in DNA. They are adenine, thymine, guanine, and cytosine. In RNA, the only difference is that thymine is replaced with a different base, uracil. DNA consists of two long chains of nucleotides. Nitrogen bases on the two chains form hydrogen bonds with each other. Adenine always bonds with thymine, and guanine always bonds with cytosine. These bonds hold the two chains together and give DNA is characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in Figure 9.24. Sugars and phosphate groups form the ""backbone"" of each chain of DNA. The bonded bases are called base pairs. RNA, in contrast to DNA, consists of just one chain of nucleotides. Determining the structure of DNA was a big scientific breakthrough. You can read the interesting story of its discovery at the URL below. ",text,
L_0788,carbon and living things,T_4097,"DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in the nucleotide chains of DNA. RNA ""reads"" the genetic code in DNA and is involved in the synthesis of proteins based on the code. This video shows how:  (2:51). MEDIA Click image to the left or use the URL below. URL: ",text,
L_0789,biochemical reactions,T_4098,Most of the energy used by living things comes either directly or indirectly from the sun. Sunlight provides the energy for photosynthesis. This is the process in which plants and certain other organisms (see Figure 9.26) synthesize glucose (C6 H12 O6 ). The process uses carbon dioxide and water and also produces oxygen. The overall chemical equation for photosynthesis is: 6CO2 + 6H2 O + Light Energy ! C6 H12 O6 + 6O2 Photosynthesis changes light energy to chemical energy. The chemical energy is stored in the bonds of glucose molecules. Glucose is used for energy by the cells of almost all living things. Plants make their own glucose. Other organisms get glucose by consuming plants (or organisms that consume plants). How do living things get energy from glucose? The answer is cellular respiration. ,text,
L_0789,biochemical reactions,T_4098,Most of the energy used by living things comes either directly or indirectly from the sun. Sunlight provides the energy for photosynthesis. This is the process in which plants and certain other organisms (see Figure 9.26) synthesize glucose (C6 H12 O6 ). The process uses carbon dioxide and water and also produces oxygen. The overall chemical equation for photosynthesis is: 6CO2 + 6H2 O + Light Energy ! C6 H12 O6 + 6O2 Photosynthesis changes light energy to chemical energy. The chemical energy is stored in the bonds of glucose molecules. Glucose is used for energy by the cells of almost all living things. Plants make their own glucose. Other organisms get glucose by consuming plants (or organisms that consume plants). How do living things get energy from glucose? The answer is cellular respiration. ,text,
L_0789,biochemical reactions,T_4099,"Cellular respiration is the process in which the cells of living things break down glucose with oxygen to produce carbon dioxide, water, and energy. The overall chemical equation for cellular respiration is: C6 H12 O6 + 6O2 ! 6CO2 + 6H2 O + Heat and Chemical Energy Cellular respiration releases some of the energy in glucose as heat. It uses the rest of the energy to form many, even smaller molecules. The smaller molecules contain just the right amount of energy to power chemical reactions inside cells. You can look at cellular respiration in more detail at this URL:  MEDIA Click image to the left or use the URL below. URL: ",text,
L_0789,biochemical reactions,T_4100,"Human body temperature must remain within a narrow range around 37C (98.6F). At this temperature, most biochemical reactions would occur too slowly to keep us alive. Thats where enzymes come in. Enzymes are biochemical catalysts. They speed up biochemical reactions, not only in humans but in virtually all living things. Most enzymes are proteins. Two are described in Figure 9.27. ",text,
L_0790,acceleration,T_4101,"Acceleration is a measure of the change in velocity of a moving object. It measures the rate at which velocity changes. Velocity, in turn, is a measure of the speed and direction of motion, so a change in velocity may reflect a change in speed, a change in direction, or both. Both velocity and acceleration are vectors. A vector is any measurement that has both size and direction. People commonly think of acceleration as in increase in speed, but a decrease in speed is also acceleration. In this case, acceleration is negative and called deceleration. A change in direction without a change in speed is acceleration as well. Q: Can you think of an example of acceleration that doesnt involve a change in speed? A: Driving at a constant speed around a bend in a road is one example. Use your imagination to think of others. ",text,
L_0790,acceleration,T_4102,"You can see several examples of acceleration in the pictures from the Figure 1.1. In each example, velocity is changing but in different ways. For example, direction may be changing but not speed, or vice versa. Figure out what is moving and how its moving in each of the photos. Q: Describe how velocity is changing in each of the motions you identified from the Figure 1.1. A: You should describe how both direction and speed are changing. For example, the boy on the carousel is moving up and down and around in a circle, so his direction is constantly changing, but his speed changes only at the beginning and end of the ride. The skydiver is falling straight down toward the ground so her direction isnt changing, but her speed keeps increasing as she falls until she opens her parachute. ",text,
L_0790,acceleration,T_4103,"If you are accelerating, you may be able to feel the change in velocity. This is true whether the change is in speed, direction, or both. You often feel acceleration when you ride in a car. As the car speeds up, you feel as though you are being pressed against the seat. When the car slows down, you feel like you are being pushed forward, especially if the change in speed is sudden. If the car changes direction and turns right, you feel as though you are being pushed to the left. With a left turn, you feel a push to the right. The next time you ride in a car, notice how it feels as the car accelerates in each of these ways. ",text,
L_0791,acceleration due to gravity,T_4104,"Gravity is a force that pulls objects down toward the ground. When objects fall to the ground, gravity causes them to accelerate. Acceleration is a change in velocity, and velocity, in turn, is a measure of the speed and direction of motion. Gravity causes an object to fall toward the ground at a faster and faster velocity the longer the object falls. In fact, its velocity increases by 9.8 m/s2, so by 1 second after an object starts falling, its velocity is 9.8 m/s. By 2 seconds after it starts falling, its velocity is 19.6 m/s (9.8 m/s + 9.8 m/s), and so on. The acceleration of a falling object due to gravity is illustrated in the Figure 1.1. Q: In this diagram, the boy drops the object at time t= 0 s. By t = 1 s, the object is falling at a velocity of 9.8 m/s. What is its velocity by t = 5 s? What will its velocity be at t = 6 s if it keeps falling? A: Its velocity at t = 5 s is 49.0 m/s, and at t = 6 s, it will be 58.8 m/s (49.0 m/s + 9.8 m/s). ",text,
L_0791,acceleration due to gravity,T_4105,"What if you were to drop a bowling ball and a soccer ball at the same time from the same distance above the ground? The bowling ball has greater mass than the basketball, so the pull of gravity on it is greater. Would it fall to the ground faster? No, the bowling ball and basketball would reach the ground at the same time. The reason? The more massive bowling ball is also harder to move because of its greater mass, so it ends up moving at the same acceleration as the soccer ball. This is true of all falling objects. They all accelerate at the same rate due to gravity, unless air resistance affects one object more than another. For example, a falling leaf is slowed down by air resistance more than a falling acorn because of the leafs greater surface area. Q: If a leaf and an acorn were to fall to the ground in the absence of air (that is, in a vacuum), how would this affect their acceleration due to gravity? A: They would both accelerate at the same rate and reach the ground at the same time. ",text,
L_0792,accuracy and precision,T_4106,"The accuracy of a measurement is how close the measurement is to the true value. If you were to hit four different golf balls toward an over-sized hole, all of them might land in the hole. These shots would all be accurate because they all landed in the hole. This is illustrated in the sketch below. ",text,
L_0792,accuracy and precision,T_4107,"As you can see from the sketch above, the four golf balls did not land as close to one another as they could have. Each one landed in a different part of the hole. Therefore, these shots are not very precise. The precision of measurements is how close they are to each other. If you make the same measurement twice, the answers are precise if they are the same or at least very close to one another. The golf balls in the sketch below landed quite close together in a cluster, so they would be considered precise. However, they are all far from the hole, so they are not accurate. Q: If you were to hit four golf balls toward a hole and your shots were both accurate and precise, where would the balls land? A: All four golf balls would land in the hole (accurate) and also very close to one another (precise). ",text,
L_0793,acid base neutralization,T_4108,"An acid is a compound that produces positive hydrogen ions (H+ ) and negative nonmetal ions when it dissolves in water. (Ions are atoms that have become charged by losing or gaining electrons.) Hydrochloric acid (HCl) is an example of an acid. When it dissolves in water, it produces positive hydrogen ions and negative chloride ions (Cl ). This can be represented by the chemical equation: H O 2 HCl H+ + Cl A base is a compound that produces negative hydroxide ions (OH ) and positive metal ions when it dissolves in water. For example, when the base sodium hydroxide (NaOH) dissolves in water, it produces negative hydroxide ions and positive sodium ions (Na+ ). This can be represented by the chemical equation: H O 2 NaOH OH + Na+ Q: If you were to combine acid and base solutions, what products do you think would be produced? A: Combining acid and base solutions produces water and a neutral ionic compound. ",text,
L_0793,acid base neutralization,T_4109,"When an acid and a base react, the reaction is called a neutralization reaction. Thats because the reaction produces neutral products. Water is always one product, and a salt is also produced. A salt is a neutral ionic compound. Lets see how a neutralization reaction produces both water and a salt, using as an example the reaction between solutions of hydrochloric acid and sodium hydroxide. The overall equation for this reaction is: NaOH + HCl  H2 O and NaCl Now lets break this reaction down into two parts to see how each product forms. Positive hydrogen ions from HCl and negative hydroxide ions from NaOH combine to form water. This part of the reaction can be represented by the equation: H+ + OH  H2 O Positive sodium ions from NaOH and negative chloride ions from HCL combine to form the salt sodium chloride (NaCl), commonly called table salt. This part of the reaction can be represented by the equation: Na+ + Cl  NaCl Another example of a neutralization reaction can be seen in the Figure 1.1. Q: What products are produced when antacid tablets react with hydrochloric acid in the stomach? A: The products are water and the salt calcium chloride (CaCl2 ). Carbon dioxide (CO2 ) is also produced. The reaction is represented by the chemical equation: CaCO3 + 2HCl  H2 O + CaCl2 + CO2 ",text,
L_0794,activation energy,T_4110,"Chemical reactions also need energy to be activated. They require a certain amount of energy just to get started. This energy is called activation energy. For example, activation energy is needed to start a car engine. Turning the key causes a spark that activates the burning of gasoline in the engine. The combustion of gas wont occur without the spark of energy to begin the reaction. Q: Why is activation energy needed? Why wont a reaction occur without it? A: A reaction wont occur unless atoms or molecules of reactants come together. This happens only if the particles are moving, and movement takes energy. Often, reactants have to overcome forces that push them apart. This takes energy as well. Still more energy is needed to start breaking bonds in reactants. ",text,
L_0794,activation energy,T_4111,"Some chemical reactions need a constant input of energy to take place. They are called endothermic reactions. Other chemical reactions release energy when they occur, so they can keep going without any added energy. They are called exothermic reactions. Q: It makes sense that endothermic reactions need activation energy. But do exothermic reactions also need activation energy? A: All chemical reactions need energy to get started, even exothermic reactions. Look at the Figure 1.1. They compare energy changes that occur during endothermic and exothermic reactions. From the graphs, you can see that both types of reactions need the same amount of activation energy in order to get started. Only after it starts does the exothermic reaction produce more energy than it uses. ",text,
L_0794,activation energy,T_4112,"You have probably used activation energy to start a chemical reaction. For example, if youve ever struck a match to light it, then you provided the activation energy needed to start a combustion reaction. When you struck the match on the box, the friction started the match head burning. Combustion is exothermic. Once a match starts to burn, it releases enough energy to activate the next reaction, and the next, and so on. However, the match wont burst into flames on its own. ",text,
L_0796,alkaline earth metals,T_4116,"Barium (Ba) is one of six elements in group 2 of the periodic table, which is shown in Figure 1.1. Elements in this group are called alkaline Earth metals. These metals are silver or gray in color. They are relatively soft and low in density, although not as soft and lightweight as alkali metals. ",text,
L_0796,alkaline earth metals,T_4117,"All alkaline Earth metals have similar properties because they all have two valence electrons. They readily give up their two valence electrons to achieve a full outer energy level, which is the most stable arrangement of electrons. As a result, they are very reactive, although not quite as reactive as the alkali metals in group 1. For example, alkaline Earth metals will react with cold water, but not explosively as alkali metals do. Because of their reactivity, alkaline Earth metals never exist as pure substances in nature. Instead, they are always found combined with other elements. The reactivity of alkaline Earth metals increases from the top to the bottom of the group. Thats because the atoms get bigger from the top to the bottom, so the valence electrons are farther from the nucleus. When valence electrons are farther from the nucleus, they are attracted less strongly by the nucleus and more easily removed from the atom. This makes the atom more reactive. Q: Alkali metals have just one valence electron. Why are alkaline Earth metals less reactive than alkali metals? A: It takes more energy to remove two valence electrons from an atom than one valence electron. This makes alkaline Earth metals with their two valence electrons less reactive than alkali metals with their one valence electron. ",text,
L_0796,alkaline earth metals,T_4118,"For a better understanding of alkaline Earth metals, lets take a closer look at two of them: calcium (Ca) and strontium (Sr). Calcium is a soft, gray, nontoxic alkaline Earth metal. Although pure calcium doesnt exist in nature, calcium compounds are very common in Earths crust and in sea water. Calcium is also the most abundant metal in the human body, occurring as calcium compounds such as calcium phosphate and calcium carbonate. These calcium compounds are found in bones and make them hard and strong. The skeleton of the average adult contains about a kilogram of calcium. Because calciumlike bariumabsorbs x-rays, bones show up white in x-ray images. Calcium is an important component of a healthy human diet. Good food sources of calcium are pictured in Figure Q: What health problems might result from a diet low in calcium? A: Children who dont get enough calcium while their bones are forming may develop a deficiency disease called rickets, in which their bones are softer than normal and become bent and stunted. Adults who dont get enough calcium may develop a condition called osteoporosis, in which the bones lose calcium and become weak and brittle. People with osteoporosis are at high risk of bone fractures. Strontium is a silver-colored alkaline Earth metal that is even softer than calcium. Strontium compounds are quite common and have a variety of usesfrom fireworks to cement to toothpaste. In fireworks, strontium compounds produce deep red explosions. In toothpaste, the compound strontium chloride reduces tooth sensitivity. ",text,
L_0797,alloys,T_4119,"An alloy is a mixture of a metal with one or more other elements. The other elements may be metals, nonmetals, or both. An alloy is formed by melting a metal and dissolving the other elements in it. The molten solution is then allowed to cool and harden. Alloys generally have more useful properties than pure metals. Several examples of alloys are described and pictured below. If you have braces on your teeth, you might even have this alloy in your mouth! Click image to the left or use the URL below. URL: ",text,
L_0797,alloys,T_4120,"Most metal objects are made of alloys rather than pure metals. Objects made of four different alloys are shown in the Figure 1.1. Brass saxophone: Brass is an alloy of copper and zinc. It is softer than bronze and easier to shape. Its also very shiny. Notice the curved pieces in this shiny brass saxophone. Brass is used for shap- ing many other curved objects, such as doorknobs and plumbing fixtures. Stain- less steel sink: Stainless steel is a type of steel that contains nickel and chromium in addition to carbon and iron. It is shiny, strong, and resistant to rusting. This makes it useful for sinks, eating utensils, and other objects that are exposed to wa- ter. ""Gold"" bracelet: Pure gold is relatively soft, so it is rarely used for jewelry. Most ""gold"" jewelry is actually made of an alloy of gold, copper and silver. Bronze statue: Bronze was the first alloy ever made. The earliest bronze dates back many thou- sands of years. Bronze is a mixture of copper and tin. Both copper and tin are relatively soft metals, but mixed together in bronze they are much harder. Bronze has been used for statues, coins, and other objects. Q: Sterling silver is an alloy that is used to make fine jewelry. What elements do you think sterling silver contains? What properties might sterling silver have that make it more useful than pure silver? A: Most sterling silver is about 93 percent silver and about 7 percent copper. Sterling silver is harder and stronger than pure silver, while retaining the malleability and luster of pure silver. ",text,
L_0798,alpha decay,T_4121,"Radioactive elements and isotopes have unstable nuclei. To become more stable, the nuclei undergo radioactive decay. In radioactive decay, the nuclei give off, or emit, radiation in the form of energy and often particles as well. There are several types of radioactive decay, including alpha, beta, and gamma decay. Energy is emitted in all three types of decay, but only alpha and beta decay also emit particles. ",text,
L_0798,alpha decay,T_4122,"Alpha decay occurs when a nucleus is unstable because it has too many protons. The Figure 1.1 shows what happens during alpha decay. The nucleus emits an alpha particle and energy. An alpha particle consists of two protons and two neutrons, which is actually a helium nucleus. Losing the protons and neutrons makes the nucleus more stable. ",text,
L_0798,alpha decay,T_4123,"Radioactive nuclei and particles are represented by nuclear symbols that indicate their numbers of protons and neutrons. For example, an alpha particle (helium nucleus) is represented by the symbol 42 He, where He is the chemical symbol for helium, the subscript 2 is the number of protons, and the superscript 4 is the mass number (2 protons + 2 neutrons). Nuclear symbols are used to write nuclear equations for radioactive decay. Lets consider an example. Uranium-238 undergoes alpha decay to become thorium-234. (The numbers following the chemical names refer to the number of protons plus neutrons.) In this reaction, uranium-238 loses two protons and two neutrons to become the element thorium-234. The reaction can be represented by this nuclear equation: 238 U 92 4 234 90 Th + 2 He + Energy If you count the number of protons (subscripts) as well as the number of protons plus neutrons (superscripts), youll see that the total numbers are the same on both sides of the arrow. This means that the equation is balanced. The thorium-234 produced in this reaction is also unstable, so it will undergo radioactive decay as well. The alpha particle (42 He) produced in the reaction can join with two free electrons to form the element helium. This is how most of Earths helium formed. Q: Fill in the missing subscript and superscript to balance the following nuclear equation for alpha decay of Polonium-210. 210 Po 84 ?? Pb + 42 He + Energy A: The subscript of Pb is 82, and the superscript is 206. This means that the new element produced in the reaction has 82 protons. You can find the element with this number of protons in the periodic table. It is the element lead (Pb). The new element also has 124 neutrons (206 - 82 protons = 124 neutrons). ",text,
L_0798,alpha decay,T_4124,"All types of radioactive decay pose risks to living things, but alpha decay is the least dangerous. Thats because alpha particles are relatively heavy, so they can travel only a few centimeters through the air. They also are not very penetrating. For example, they cant pass through a sheet of paper or thin layer of clothing. They may burn the skin, but they cant penetrate to the tissues underneath the skin. However, if alpha particles are emitted inside the body, they can do more damage. One way this can happen is by inhaling cigarette smoke. People who smoke actually inhale the radioactive element polonium-210. It undergoes alpha decay in the lungs. Over time, exposure to alpha particles may cause lung cancer. ",text,
L_0800,archimedes law,T_4128,"Did you ever notice when you get into a bathtub of water that the level of the water rises? More than 2000 years ago, a Greek mathematician named Archimedes noticed the same thing. He observed that both a body and the water in a tub cant occupy the same space at the same time. As a result, some of the water is displaced, or moved out of the way. How much water is displaced? Archimedes determined that the volume of displaced water equals the volume of the submerged object. So more water is displaced by a bigger body than a smaller one. Q: If you jump into swimming pool, how much water does your body displace? A: The water displaced by your body is equal to your bodys volume. Depending on your size, this volume might be about 0.07 m3 . ",text,
L_0800,archimedes law,T_4129,Objects such as ships may float in a fluid like water because of buoyant force. This is an upward force that a fluid exerts on any object that is placed in it. Archimedes discovered that the buoyant force acting on an object equals the weight of the fluid displaced by the object. This is known as Archimedes law (or Archimedes principle). ,text,
L_0800,archimedes law,T_4130,"Archimedes law explains why some objects float in fluids even though they are very heavy. It all depends on how much fluid they displace. The cruise ship pictured in the opening image is extremely heavy, yet it stays afloat. If a steel ball with the same weight as the ship were placed in water, it would sink to the bottom. This is modeled in the Figure 1.1. The reason the ball sinks is that its shape is very compact, so it displaces relatively little water. The volume of water displaced by the steel ball weighs less than the ball itself, so the buoyant force is not as great as the force of gravity pulling down on the ball. Thus, the ball sinks. Now look at the ships hull in the Figure 1.1. Its shape causes the ship to displace much more water than the ball. In fact, the weight of the displaced water is greater than the weight of the ship. As a result, the buoyant force is greater than the force of gravity acting on the ship, so the ship floats. Q: Why might you be more likely to float in water if you stretch out your body rather than curl up into a ball? A: You would displace more water by stretching out your body, so there would be more buoyant force acting on it. Therefore, you would be more likely to float in this position. ",text,
L_0801,artificial light,T_4131,"If youre like most people, you dont give it a thought when you flick a switch to turn on a lightat least not until the power goes out and youre left in the dark! When you flick on a light switch, electricity normally flows through the light, and some type of light bulb converts the electrical energy to visible light. This can happen in various ways, depending on the type of light bulb. Several different types of light bulbs are described below. All of them are examples of artificial light, as opposed to natural light from the sun or other sources in nature. ",text,
L_0801,artificial light,T_4132,"An incandescent light bulb like the one pictured in the Figure 1.1 produces visible light by incandescence. Incan- descence occurs when something gets so hot that it glows. An incandescent light bulb contains a thin wire filament made of tungsten. When electric current passes through the filament, it gets extremely hot and emits light. ",text,
L_0801,artificial light,T_4133,A fluorescent light bulb produces visible light by fluorescence. Fluorescence occurs when a substance absorbs shorter-wavelength ultraviolet light and then gives off the energy as visible light. The compact fluorescent light bulb (CFL) in the Figure 1.2 contains mercury gas that gives off ultraviolet light when electricity passes through it. The inside of the bulb is coated with a substance called phosphor. Phosphor absorbs the ultraviolet light and then gives off most of the energy as visible light. ,text,
L_0801,artificial light,T_4133,A fluorescent light bulb produces visible light by fluorescence. Fluorescence occurs when a substance absorbs shorter-wavelength ultraviolet light and then gives off the energy as visible light. The compact fluorescent light bulb (CFL) in the Figure 1.2 contains mercury gas that gives off ultraviolet light when electricity passes through it. The inside of the bulb is coated with a substance called phosphor. Phosphor absorbs the ultraviolet light and then gives off most of the energy as visible light. ,text,
L_0801,artificial light,T_4134,"A neon light produces visible light by electroluminescence. In this process, neon or some other gas gives off light when an electric current passes through it. Other halogen gases besides neonincluding krypton and argonalso produce light in this way. The word OPEN in the sign 1.3 is a neon light. It is a long glass tube that contains neon gas. When electricity passes through the gas, it excites electrons of neon atoms, and the electrons jump to a higher energy level. As the excited electrons return to their original energy level, they give off visible light. Neon produces red light. Other gases produce light of different colors. For example, krypton produces violet light, and argon produces blue light. ",text,
L_0801,artificial light,T_4135,"A vapor light also produces visible light by electroluminescence The bulb contains a small amount of solid sodium or mercury as well as a mixture of neon and argon gases. When an electric current passes through the gases, it causes the solid sodium or mercury to change to a gas and emit visible light. Sodium vapor lights, like the streetlight pictured in the Figure 1.4, produce yellowish light. Mercury vapor lights produce bluish light. In addition to lighting city streets, vapor lights are used to light highways and stadiums. The bulbs are very bright and long lasting so they are a good choice for these places. ",text,
L_0801,artificial light,T_4136,"LED stands for light-emitting diode. An LED light contains a material called a semi-conductor, which gives off visible light when an electric current flows through it. LED lights are used for traffic lights (see Figure 1.5) and also indicator lights on computers, cars, and many other devices. This type of light is very reliable and durable. Q: Some light bulbs produce a lot of heat in addition to visible light, so they waste energy. Other bulbs produce much less heat, so they use energy more efficiently. Which light bulbs described above would you place in each category? A: Incandescent light bulbs, which produce light by incandescence, give off a lot of heat as well as light, so they waste energy. The other light bulbs produce light by some type of luminescence, in which light is produced without heat. These light bulbs use energy more efficiently. Which types of light bulbs do you use? ",text,
L_0802,atomic forces,T_4137,"Electromagnetic force is a force of attraction or repulsion between all electrically charged particles. This force is transferred between charged particles of matter by fundamental force-carrying particles called photons. Because of electromagnetic force, particles with opposite charges attract each other and particles with the same charge repel each other. Inside the atom, two types of subatomic particles have electric charge: electrons, which have an electric charge of -1, and protons, which have an opposite but equal electric charge of +1. The model of an atom in the Figure 1.1 shows both types of charged particles. Protons are found inside the nucleus at the center of the atom, and they give the nucleus a positive charge. (There are also neutrons in the nucleus, but they have no electric charge.) Negative electrons stay in the area surrounding the positive nucleus because of the electromagnetic force of attraction between them. Q: Why do you think protons cluster together in the nucleus of the atom instead of repelling each other because of their like charges? A: The electromagnetic force of repulsion between positively charged protons is overcome by a stronger force, called the strong nuclear force. ",text,
L_0802,atomic forces,T_4138,"The strong nuclear force is a force of attraction between fundamental particles called quarks, which have a type of charge called color charge. The strong nuclear force is transferred between quarks by fundamental force-carrying particles called gluons. Both protons and neutrons consist of quarks. The exchange of gluons holds quarks together within a proton or neutron. Excess, or residual, strong force holds together protons and neutrons in the nucleus. The strong nuclear force is strong enough to overcome the electromagnetic force of repulsion pushing protons apart. Both forces are represented in the Figure 1.2. The strong nuclear force works only over very short distances. As a result, it isnt effective if the nucleus gets too big. As more protons are added to the nucleus, the electromagnetic force of repulsion between them gets stronger, while the strong nuclear force of attraction between them gets weaker. This puts an upper limit on the number of protons an atom can have and remain stable. If atoms have more than 83 protons, the electromagnetic repulsion between them is greater than the strong nuclear force of attraction between them. This makes the nucleus unstable, or radioactive, so it breaks down. The following video discusses the strong nuclear force and its role in the atom. The types of quarks found in protons and neutrons are called up quarks (u) and down quarks (d). Each proton consists of two up quarks and one down quark (uud), and each neutron consists of one up quark and two down quarks (udd). This diagram represents two protons. Click image to the left or use the URL below. URL: ",text,
L_0802,atomic forces,T_4139,"The weak nuclear force is transferred by the exchange of force-carrying fundamental particles called W and Z bosons. This force is also a very short-range force that works only within the nucleus of the atom. It is much weaker than the strong force or electromagnetic force that are also at work inside the atom. Unlike these other two forces, the weak nuclear force does not bind subatomic particles together in an atom. Instead, it changes subatomic particles from one type to another. The Figure 1.3 shows one way this can happen. In this figure, an up quark in a proton is changed by the weak force to a down quark. This changes the proton (uud) to a neutron (udd). Q: If the weak force causes a proton to change to a neutron, how does this change the atom? A: The resulting atom represents a different element. Thats because each element has a unique number of protons. For example, all atoms of helium have two protons. If one of the protons in a helium atom changes to a neutron, the resulting atom would have just one proton, so the atom would no longer be a helium atom. Instead it would be a hydrogen atom, because all hydrogen atoms have a single proton. ",text,
L_0803,atomic nucleus,T_4140,"The nucleus (plural, nuclei) is a positively charged region at the center of the atom. It consists of two types of subatomic particles packed tightly together. The particles are protons, which have a positive electric charge, and neutrons, which are neutral in electric charge. Outside of the nucleus, an atom is mostly empty space, with orbiting negative particles called electrons whizzing through it. The Figure 1.1 shows these parts of the atom. ",text,
L_0803,atomic nucleus,T_4141,"The nucleus of the atom is extremely small. Its radius is only about 1/100,000 of the total radius of the atom. If an atom were the size of a football stadium, the nucleus would be about the size of a pea! Click image to the left or use the URL below. URL:  Electrons have virtually no mass, but protons and neutrons have a lot of mass for their size. As a result, the nucleus has virtually all the mass of an atom. Given its great mass and tiny size, the nucleus is very dense. If an object the size of a penny had the same density as the nucleus of an atom, its mass would be greater than 30 million tons! Click image to the left or use the URL below. URL: ",text,
L_0803,atomic nucleus,T_4142,"Particles with opposite electric charges attract each other. This explains why negative electrons orbit the positive nucleus. Particles with the same electric charge repel each other. This means that the positive protons in the nucleus push apart from one another. So why doesnt the nucleus fly apart? An even stronger forcecalled the strong nuclear forceholds protons and neutrons together in the nucleus. Click image to the left or use the URL below. URL:  Q: Can you guess why an atomic bomb releases so much energy when it explodes? A: When an atomic bomb explodes, the nuclei of atoms undergo a process called fission, in which they split apart. This releases the huge amount of energy that was holding together subatomic particles in the nucleus. ",text,
L_0804,atomic number,T_4143,"Its often useful to have ways to signify different people or objects like athletes on teams. The same is true of atoms. Its important to be able to distinguish atoms of one element from atoms of other elements. Elements are pure substances that make up all other matter, so each one is given a unique name. The names of elements are also represented by unique one- or two-letter symbols, such as H for hydrogen, C for carbon, and He for helium. You can see other examples in the Figure 1.1. Q: The table shown above is called the periodic table of the elements. Each symbol stands for a different element. What do you think the symbol K stands for? A: The symbol K stands for the element potassium. The symbol comes from the Latin name for potassium, which is kalium. The symbols in the table above would be more useful if they revealed more information about the atoms they represent. For example, it would be useful to know the numbers of protons and neutrons in the atoms. Thats where atomic number and mass number come in. ",text,
L_0804,atomic number,T_4144,"The number of protons in an atom is called its atomic number. This number is very important because it is unique for atoms of a given element. All atoms of an element have the same number of protons, and every element has a different number of protons in its atoms. For example, all helium atoms have two protons, and no other elements have atoms with two protons. In the case of helium, the atomic number is 2. The atomic number of an element is usually written in front of and slightly below the elements symbol, like in the Figure 1.2 for helium. Atoms are neutral in electrical charge because they have the same number of negative electrons as positive protons. Therefore, the atomic number of an atom also tells you how many electrons the atom has. This, in turn, determines many of the atoms properties. ",text,
L_0804,atomic number,T_4145,"There is another number in the box above for helium. That number is the mass number, which is the mass of the atom in a unit called the atomic mass unit (amu). One atomic mass unit is the mass of a proton, or about 1.67 1027 kilograms, which is an extremely small mass. A neutron has just a tiny bit more mass than a proton, so its mass is often assumed to be one atomic mass unit as well. Because electrons have virtually no mass, just about all the mass of an atom is in its protons and neutrons. Therefore, the total number of protons and neutrons in an atom determines its mass in atomic mass units. Consider helium again. Most helium atoms have two neutrons in addition to two protons. Therefore the mass of most helium atoms is 4 atomic mass units (2 amu for the protons + 2 amu for the neutrons). However, some helium atoms have more or less than two neutrons. Atoms with the same number of protons but different numbers of neutrons are called isotopes. Because the number of neutrons can vary for a given element, the mass numbers of different atoms of an element may also vary. For example, some helium atoms have three neutrons instead of two. Therefore, they have a different mass number than the one given in the box above. Q: What is the mass number of a helium atom that has three neutrons? A: The mass number is the number of protons plus the number of neutrons. For helium atoms with three neutrons, the mass number is 2 (protons) + 3 (neutrons) = 5. Q: How would you represent this isotope of helium to show its atomic number and mass number? A: You would represent it by the elements symbol and both numbers, with the mass number on top and the atomic number on the bottom: 5 2 He ",text,
L_0806,balancing chemical equations,T_4153,"A chemical equation represents the changes that occur during a chemical reaction. A chemical equation has the general form: Reactants  Products An example of a simple chemical reaction is the reaction in which hydrogen (H2 ) and oxygen (O2 ) combine to produce water (H2 O). In this reaction, the reactants are hydrogen and oxygen and the product is water. To write the chemical equation for this reaction, you would start by writing the reactants on the left and the product on the right, with an arrow between them to show the direction in which the reaction occurs: Equation 1: H2 + O2  H2 O Q: Look closely at equation 1. Theres something wrong with it. Do you see what it is? A: All chemical equations must be balanced. This means that there must be the same number of each type of atom on both sides of the arrow. Thats because mass is always conserved in chemical reactions. Count the number of hydrogen and oxygen atoms on each side of the arrow. There are two hydrogen atoms in both reactants and products. There are two oxygen atoms in the reactants but only one in the product. Therefore, equation 1 is not balanced. ",text,
L_0806,balancing chemical equations,T_4154,"Coefficients are used to balance chemical equations. A coefficient is a number placed in front of a chemical symbol or formula. It shows how many atoms or molecules of the substance are involved in the reaction. For example, two molecules of hydrogen would be written as 2 H2 , and two molecules of water would be written 2 H2 O. A coefficient of 1 usually isnt written. Coefficients can be used to balance equation 1 (above) as follows: Equation 2: 2 H2 + O2  2 H2 O Equation 2 shows that two molecules of hydrogen react with one molecule of oxygen to produce two molecules of water. The two molecules of hydrogen each contain two hydrogen atoms and so do the two molecules of water. Therefore, there are now four hydrogen atoms in both reactants and products. Q: Is equation 2 balanced? A: Count the oxygen atoms to find out. There are two oxygen atoms in the one molecule of oxygen in the reactants. There are also two oxygen atoms in the products, one in each of the two water molecules. Therefore, equation 2 is balanced. ",text,
L_0806,balancing chemical equations,T_4155,"Balancing a chemical equation involves a certain amount of trial and error. In general, however, you should follow these steps: 1. Count each type of atom in reactants and products. Does the same number of each atom appear on both sides of the arrow? If not, the equation is not balanced, and you need to go to step 2. 2. Place coefficients, as needed, in front of the symbols or formulas to increase the number of atoms or molecules of the substances. Use the smallest coefficients possible. Warning! Never change the subscripts in chemical formulas. Changing subscripts changes the substances involved in the reaction. Change only the coefficients. 3. Repeat steps 1 and 2 until the equation is balanced. Q: Balance this chemical equation for the reaction in which nitrogen (N2 ) and hydrogen (H2 ) combine to form ammonia (NH3 ): N2 + H2  NH3 A: First count the nitrogen atoms on both sides of the arrow. There are two nitrogen atoms in the reactants so there must be two in the products as well. Place the coefficient 2 in front of NH3 to balance nitrogen: N2 + H2  2 NH3 Now count the hydrogen atoms on both sides of the arrow. There are six hydrogen atoms in the products so there must also be six in the reactants. Place the coefficient 3 in front of H2 to balance hydrogen: N2 + 3 H2  2 NH3 ",text,
L_0808,beta decay,T_4158,"Atoms with unstable nuclei are radioactive. To become more stable, the nuclei undergo radioactive decay. In radioactive decay, the nuclei emit energy and usually particles of matter as well. There are several types of radioactive decay, including alpha, beta, and gamma decay. Energy is emitted in all three types of decay, but only alpha and beta decay also emit particles. ",text,
L_0808,beta decay,T_4159,"Beta decay occurs when an unstable nucleus emits a beta particle and energy. A beta particle is either an electron or a positron. An electron is a negatively charged particle, and a positron is a positively charged electron (or anti- electron). When the beta particle is an electron, the decay is called beta-minus decay. When the beta particle is a positron, the decay is called beta-plus decay. Beta-minus decay occurs when a nucleus has too many neutrons relative to protons, and beta-plus decay occurs when a nucleus has too few neutrons relative to protons. Q: Nuclei contain only protons and neutrons, so how can a nucleus emit an electron in beta-minus decay or a positron in beta-plus decay? A: Beta decay begins with a proton or neutron. You can see how in the Figure 1.1. Q: How does beta decay change an atom to a different element? A: In beta-minus decay an atom gains a proton, and it beta-plus decay it loses a proton. In each case, the atom becomes a different element because it has a different number of protons. ",text,
L_0808,beta decay,T_4160,"Radioactive nuclei and particles are represented by nuclear symbols.. For example, a beta-minus particle (electron) is represented by the symbol 01 e. The subscript -1 represents the particles charge, and the superscript 0 shows that the particle has virtually no mass (no protons or neutrons). Another example is the radioactive nucleus of thorium-234. It is represented by the symbol 234 90 Th, where the subscript 90 stands for the number of protons and the superscript 234 for the number of protons plus neutrons. Nuclear symbols are used to write nuclear equations for radioactive decay. Lets consider the example of the beta- minus decay of thorium-234 to protactinium-234. This reaction is represented by the equation: 234 Th 90 0 234 91 Pa + 1 e + energy The equation shows that thorium-234 becomes protactinium-234 and loses a beta particle and energy. The protactinium- 234 produced in the reaction is also radioactive, so it will decay as well. A nuclear equation is balanced if the total numbers of protons and neutrons are the same on both sides of the arrow. If you compare the subscripts and superscripts on both sides of the equation above, youll see that they are the same. Q: What happens to the electron produced in the reaction above? A: Along with another electron, it can combine with an alpha particle to form a helium atom. An alpha particle, which is emitted during alpha decay, consists of two protons and two neutrons. Q: Try to balance the following nuclear equation for beta-minus decay by filling in the missing subscript and superscript. 131 I 53 ?? Xe + 01 e + energy A: The subscript of Xe is 54, and the superscript is 131. ",text,
L_0808,beta decay,T_4161,Beta particles can travel about a meter through air. They can pass through a sheet of paper or a layer of cloth but not through a sheet of aluminum or a few centimeters of wood. They can also penetrate the skin and damage underlying tissues. They are even more harmful if they are ingested or inhaled. ,text,
L_0809,biochemical compound classification,T_4162,"Glucose is an example of a biochemical compound. The prefix bio- comes from the Greek word that means life. A biochemical compound is any carbon-based compound that is found in living things. Biochemical compounds make up the cells and tissues of living things. They are also involved in all life processes, including making and using food for energy. Given their diversity of functions, its not surprising that there are millions of different biochemical compounds. Q: Plants make food in the process of photosynthesis. What biochemical compound is synthesized in photosynthe- sis? A: Glucose is synthesized in photosynthesis. Virtually all living things use glucose for energy, but glucose is just one of many examples of biochemical compounds that are found in most or all living things. In fact the similarity in biochemical compounds between living things provides some of the best evidence for the evolution of species from common ancestors. A classic example is the biochemical compound called cytochrome c. It is found in all living organisms because it performs essential life functions. Only slight variations in the molecule exist between closely related species, as you can see in the Figure and the single-celled tetrahymena (pictured in the Figure 1.1), the cytochrome c molecule is nearly 50 percent the same. ",text,
L_0809,biochemical compound classification,T_4163,"All biochemical molecules contain hydrogen and oxygen as well as carbon. They may also contain nitrogen, phosphorus, and/or sulfur. Almost all biochemical compounds are polymers. Polymers are large molecules that consist of many smaller, repeating molecules, called monomers. Glucose is a monomer of biochemical compounds called starches. In starches and all other biochemical polymers, monomers are joined together by covalent bonds, in which atoms share pairs of valence electrons. Click image to the left or use the URL below. URL: ",text,
L_0809,biochemical compound classification,T_4164,"Most biochemical molecules are macromolecules. The prefix macro- means large, and many biochemical molecules are very large indeed. They may contain thousands of monomer molecules. The largest known biochemical molecule is called titin. It plays an important role in muscle contraction. The human form of the molecule contains more than 34,000 monomers. Its chemical formula is C169723 H270464 N45688 O52243 S912 . Its chemical name contains almost 190,000 letters, and it has been called the longest word in any language. ",text,
L_0809,biochemical compound classification,T_4165,"Although there are millions of biochemical compounds, all of them can be grouped into just four main classes: carbohydrates, proteins, lipids, and nucleic acids. The classes are summarized in the Table 1.1. Class Carbohydrates Elements carbon hydrogen oxygen Examples sugars starches cellulose Proteins carbon hydrogen oxygen nitrogen sulfur carbon hydrogen oxygen carbon hydrogen oxygen nitrogen phosphorus enzymes hormones Lipids Nucleic acids Functions provide energy to cells store energy in plants makes up the cell walls of plants speed up biochemical re- actions regulate life processes fats oils store energy in animals store energy in plants DNA RNA stores genetic information in cells helps cells make proteins Q: In which class of biochemical compounds would you place glucose? A: Glucose is a sugar in the class carbohydrates. Like other carbohydrates, it contains only carbon, hydrogen, and oxygen. It provides energy to the cells of living things. Q: Look back at the chemical formula for titin. In which class of biochemical compounds should it be placed? A: Titin is a protein. You can tell because it contains sulfur, and proteins are the only biochemical compounds that contain this element. ",text,
L_0810,biochemical reaction chemistry,T_4166,Chemical reactions that take place inside living things are called biochemical reactions (bio- means life). Its not just for energy that living things depend on biochemical reactions. Every function and structure of a living organism depends on thousands of biochemical reactions taking place in each cell. The sum of all these biochemical reactions is called metabolism. ,text,
L_0810,biochemical reaction chemistry,T_4167,"Biochemical reactions of metabolism can be divided into two general categories: catabolic reactions and anabolic reactions. Catabolic reactions involve breaking bonds. Larger molecules are broken down to smaller ones. For example, complex carbohydrates are broken down to simple sugars. Catabolic reactions release energy, so they are exothermic. Anabolic reactions involve forming bonds. Smaller molecules are combined to form larger ones. For example, simple sugars are combined to form complex carbohydrates. Anabolic reactions require energy, so they are endothermic. Q: Imagine! Each of the trillions of cells in your body is continuously performing thousands of catabolic and anabolic reactions. Thats an amazing number of biochemical reactionsfar more than the number of reactions that might take place in a lab or factory. How can so many biochemical reactions take place simultaneously in our cells? A: So many reactions can occur because biochemical reactions are amazingly fast. Q: In a lab or factory, reactants can be heated to very high temperatures or placed under great pressure so they will react very quickly. These ways of speeding up chemical reactions cant occur inside the delicate cells of living things. So how do cells speed up biochemical reactions? A: The answer is enzymes. ",text,
L_0810,biochemical reaction chemistry,T_4168,"Enzymes are proteins that increase the rate of chemical reactions by reducing the amount of activation energy needed for reactants to start reacting. Enzymes are synthesized in the cells that need them, based on instructions encoded in the cells DNA. Enzymes arent changed or used up in the reactions they catalyze, so they can be used to speed up the same reaction over and over again. Enzymes are highly specific for certain chemical reactions, so they are very effective. A reaction that would take years to occur without its enzyme might occur in a split second with the enzyme. Enzymes are also very efficient, so waste products rarely form. ",text,
L_0810,biochemical reaction chemistry,T_4169,"Some of the most important biochemical reactions are the reactions involved in photosynthesis and cellular respira- tion. Together, these two processes provide energy to almost all of Earths organisms. The two processes are closely related, as you can see in the Figure 1.1. In photosynthesis, light energy from the sun is converted to stored chemical energy in glucose. In cellular respiration, stored energy is released from glucose and stored in smaller amounts that cells can use. A: In photosynthesis, carbon dioxide (CO2 ) and water (H2 O) are the reactants. They combine using energy from light to produce oxygen (O2 ) and glucose (C6 H12 O6 ). Oxygen and glucose, in turn, are the reactants in cellular respiration. They combine to produce carbon dioxide, water, and energy. ",text,
L_0811,bohrs atomic model,T_4170,"The existence of the atom was first demonstrated around 1800 by John Dalton. Then, close to a century went by before J.J. Thomson discovered the first subatomic particle, the negatively charged electron. Because atoms are neutral in charge, Thomson thought that they must consist of a sphere of positive charge with electrons scattered through it. In 1910, Ernest Rutherford showed that this idea was incorrect. He demonstrated that all of the positive charge of an atom is actually concentrated in a tiny central region called the nucleus. Rutherford surmised that electrons move around the nucleus like planets around the sun. Rutherfords idea of atomic structure was an improvement on Thomsons model, but it wasnt the last word. Rutherford focused on the nucleus and didnt really clarify where the electrons were in the empty space surrounding the nucleus. The next major advance in atomic history occurred in 1913, when the Danish scientist Niels Bohr published a description of a more detailed model of the atom. His model identified more clearly where electrons could be found. Although later scientists would develop more refined atomic models, Bohrs model was basically correct and much of it is still accepted today. It is also a very useful model because it explains the properties of different elements. Bohr received the 1922 Nobel prize in physics for his contribution to our understanding of the structure of the atom. You can see a picture of Bohr 1.1. ",text,
L_0811,bohrs atomic model,T_4171,"As a young man, Bohr worked in Rutherfords lab in England. Because Rutherfords model was weak on the position of the electrons, Bohr focused on them. He hypothesized that electrons can move around the nucleus only at fixed distances from the nucleus based on the amount of energy they have. He called these fixed distances energy levels, or electron shells. He thought of them as concentric spheres, with the nucleus at the center of each sphere. In other words, the shells consisted of sphere within sphere within sphere. Furthermore, electrons with less energy would be found at lower energy levels, closer to the nucleus. Those with more energy would be found at higher energy levels, farther from the nucleus. Bohr also hypothesized that if an electron absorbed just the right amount of energy, it would jump to the next higher energy level. Conversely, if it lost the same amount of energy, it would jump back to its original energy level. However, an electron could never exist in between two energy levels. These ideas are illustrated in the Figure 1.2. Q: How is an atom like a ladder? A: Energy levels in an atom are like the rungs of a ladder. Just as you can stand only on the rungs and not in between them, electrons can orbit the nucleus only at fixed distances from the nucleus and not in between them. ",text,
L_0811,bohrs atomic model,T_4172,"Bohrs model of the atom is actually a combination of two different ideas: Rutherfords atomic model of electrons orbiting the nucleus and German scientist Max Plancks idea of a quantum, which Planck published in 1901. A quantum (plural, quanta) is the minimum amount of energy that can be absorbed or released by matter. It is a discrete, or distinct, amount of energy. If energy were water and you wanted to add it to matter in the form of a drinking glass, you couldnt simply pour the water continuously into the glass. Instead, you could add it only in small fixed quantities, for example, by the teaspoonful. Bohr reasoned that if electrons can absorb or lose only fixed quantities of energy, then they must vary in their energy by these fixed amounts. Thus, they can occupy only fixed energy levels around the nucleus that correspond to quantum increases in energy. This is a two-dimensional model of a three-dimensional atom. The concen- tric circles actually represent concentric spheres. Q: The idea that energy is transferred only in discrete units, or quanta, was revolutionary when Max Planck first proposed it in 1901. However, what scientists already knew about matter may have made it easier for them to accept the idea of energy quanta. Can you explain? A: Scientists already knew that matter exists in discrete units called atoms. This idea had been demonstrated by John Dalton around 1800. Knowing this may have made it easier for scientists to accept the idea that energy exists in discrete units as well. ",text,
L_0813,bond polarity,T_4176,"Covalent bonds are chemical bonds between atoms of nonmetals that share valence electrons. In some covalent bonds, electrons are not shared equally between the two atoms. These are called polar covalent bonds. The Figure than the hydrogen atoms do because the nucleus of the oxygen atom has more positively charged protons. As a result, the oxygen atom becomes slightly negative in charge, and the hydrogen atoms become slightly positive in charge. Click image to the left or use the URL below. URL:  In other covalent bonds, electrons are shared equally. These bonds are called nonpolar covalent bonds. Neither atom attracts the shared electrons more strongly. As a result, the atoms remain neutral in charge. The oxygen (O2 ) molecule in the Figure 1.2 has two nonpolar bonds. The two oxygen nuclei have an equal force of attraction for their four shared electrons. ",text,
L_0813,bond polarity,T_4176,"Covalent bonds are chemical bonds between atoms of nonmetals that share valence electrons. In some covalent bonds, electrons are not shared equally between the two atoms. These are called polar covalent bonds. The Figure than the hydrogen atoms do because the nucleus of the oxygen atom has more positively charged protons. As a result, the oxygen atom becomes slightly negative in charge, and the hydrogen atoms become slightly positive in charge. Click image to the left or use the URL below. URL:  In other covalent bonds, electrons are shared equally. These bonds are called nonpolar covalent bonds. Neither atom attracts the shared electrons more strongly. As a result, the atoms remain neutral in charge. The oxygen (O2 ) molecule in the Figure 1.2 has two nonpolar bonds. The two oxygen nuclei have an equal force of attraction for their four shared electrons. ",text,
L_0813,bond polarity,T_4177,"A covalent compound is a compound in which atoms are held together by covalent bonds. If the covalent bonds are polar, then the covalent compound as a whole may be polar. A polar covalent compound is one in which there is a slight difference in electric charge between opposite sides of the molecule. All polar compounds contain polar bonds. But having polar bonds does not necessarily result in a polar compound. It depends on how the atoms are arranged. This is illustrated in the Figure 1.3. In both molecules, the oxygen atoms attract electrons more strongly than the carbon or hydrogen atoms do, so both molecules have polar bonds. However, only formaldehyde is a polar compound. Carbon dioxide is nonpolar. Q: Why is carbon dioxide nonpolar? A: The symmetrical arrangement of atoms in carbon dioxide results in opposites sides of the molecule having the same charge. ",text,
L_0815,buoyancy,T_4182,"Buoyant force is an upward force that fluids exert on any object that is placed in them. The ability of fluids to exert this force is called buoyancy. What explains buoyant force? A fluid exerts pressure in all directions, but the pressure is greater at greater depth. Therefore, the fluid below an object, where the fluid is deeper, exerts greater pressure on the object than the fluid above it. You can see in the Figure 1.1 how this works. Buoyant force explains why the girl pictured above can float in water. Q: Youve probably noticed that some things dont float in water. For example, if you drop a stone in water, it will sink to the bottom rather than floating. If buoyant force applies to all objects in fluids, why do some objects sink instead of float? A: The answer has to do with their weight. ",text,
L_0815,buoyancy,T_4183,"Weight is a measure of the force of gravity pulling down on an object, whereas buoyant force pushes up on an object. Which force is greater determines whether an object sinks or floats. Look at the Figure 1.2. On the left, the objects weight is the same as the buoyant force acting on it, so the object floats. On the right, the objects weight is greater than the buoyant force acting on it, so the object sinks. ",text,
L_0815,buoyancy,T_4183,"Weight is a measure of the force of gravity pulling down on an object, whereas buoyant force pushes up on an object. Which force is greater determines whether an object sinks or floats. Look at the Figure 1.2. On the left, the objects weight is the same as the buoyant force acting on it, so the object floats. On the right, the objects weight is greater than the buoyant force acting on it, so the object sinks. ",text,
L_0815,buoyancy,T_4184,"Density, or the amount of mass in a given volume, is also related to the ability of an object to float. Thats because density affects weight. A given volume of a denser substance is heavier than the same volume of a less dense substance. For example, ice is less dense than liquid water. This explains why the giant ice berg in the Figure 1.3 is floating in the ocean. Q: Can you think of more examples of substances that float in a fluid because they are low in density? A: Oil is less dense than water, so oil from a spill floats on ocean water. Helium is less dense than air, so balloons filled with helium float in air. ",text,
L_0816,calculating acceleration from force and mass,T_4185,"A change in an objects motionsuch as Xander speeding up on his scooteris called acceleration. Acceleration occurs whenever an object is acted upon by an unbalanced force. The greater the net force acting on the object, the greater its acceleration will be, but the mass of the object also affects its acceleration. The smaller its mass is, the greater its acceleration for a given amount of force. Newtons second law of motion summarizes these relationships. According to this law, the acceleration of an object equals the net force acting on it divided by its mass. This can be represented by the equation: Acceleration = Net force Mass or a = F m ",text,
L_0816,calculating acceleration from force and mass,T_4186,"This equation for acceleration can be used to calculate the acceleration of an object that is acted on by a net force. For example, Xander and his scooter have a total mass of 50 kilograms. Assume that the net force acting on Xander and the scooter is 25 Newtons. What is his acceleration? Substitute the relevant values into the equation for acceleration: F = 25 N = 0.5 N a= m 50 kg kg The Newton is the SI unit for force. It is defined as the force needed to cause a 1-kilogram mass to accelerate at 1 m/s2 . Therefore, force can also be expressed in the unit kg  m/s2 . This way of expressing force can be substituted for Newtons in Xanders acceleration so the answer is expressed in the SI unit for acceleration, which is m/s2 : 2 0.5 kgm/s a = 0.5kgN = = 0.5 m/s2 kg Q: Why are there no kilograms in the final answer to this problem? A: The kilogram units in the numerator and denominator of the fraction cancel out. As a result, the answer is expressed in the correct SI units for acceleration. ",text,
L_0816,calculating acceleration from force and mass,T_4187,"Its often easier to measure the mass and acceleration of an object than the net force acting on it. Mass can be measured with a balance, and average acceleration can be calculated from velocity and time. However, net force may be a combination of many unseen forces, such as gravity, friction with surfaces, and air resistance. Therefore, it may be more useful to know how to calculate the net force acting on an object from its mass and acceleration. The equation for acceleration above can be rewritten to solve for net force as: Net Force = Mass  Acceleration, or F=ma Look at Xander in the Figure 1.1. Hes riding his scooter down a ramp. Assume that his acceleration is 0.8 m/s2 . How much force does it take for him to accelerate at this rate? Substitute the relevant values into the equation for force to find the answer: F = m  a = 50 kg  0.8 m/s2 = 40 kg  m/s2 , or 40 N Q: If Xander and his scooter actually had a mass of 40 kg instead of 50 kg, how much force would it take for him to accelerate at 0.8 m/s2 ? ",text,
L_0817,calculating acceleration from velocity and time,T_4188,"Calculating acceleration is complicated if both speed and direction are changing or if you want to know acceleration at any given instant in time. However, its relatively easy to calculate average acceleration over a period of time when only speed is changing. Then acceleration is the change in velocity (represented by v) divided by the change in time (represented by t): acceleration = v t ",text,
L_0817,calculating acceleration from velocity and time,T_4189,"Look at the cyclist in the Figure 1.1. With the help of gravity, he speeds up as he goes downhill on a straight part of the trail. His velocity changes from 1 meter per second at the top of the hill to 6 meters per second by the time he reaches the bottom. If it takes him 5 seconds to reach the bottom, what is his average acceleration as he races down the hill? v t 6 m/s  1 m/s = 5s 5 m/s = 5s 1 m/s = 1s = 1 m/s2 acceleration = In words, this means that for each second the cyclist travels downhill, his velocity (in this case, his speed) increases by 1 meter per second on average. Note that the answer to this problem is expressed in m/s2 , which is the SI unit for acceleration. Q: The cyclist slows down at the end of the race. His velocity changes from 6 m/s to 2 m/s during a period of 4 seconds without any change in direction. What was his average acceleration during these 4 seconds? A: Use the equation given above for acceleration: v t 6 m/s  2 m/s = 4s 4 m/s = 4s 1 m/s = 1s = 1 m/s2 acceleration = ",text,
L_0819,calculating work,T_4195,Work is the use of force to move an object. It is directly related to both the force applied to the object and the distance the object moves. Work can be calculated with this equation: Work = Force x Distance. ,text,
L_0819,calculating work,T_4196,"The equation for work can be used to calculate work if force and distance are known. To use the equation, force is expressed in Newtons (N), and distance is expressed in meters (m). For example, assume that Clarissa uses 100 Newtons of force to push the mower and that she pushes it for a total of 200 meters as she cuts the grass in her grandmothers yard. Then, the amount of work Clarissa does is: Work = 100 N  200 m = 20,000 N  m Notice that the unit for work in the answer is the Newton  meter (N  m). This is the SI unit for work, also called the joule (J). One joule equals the amount of work that is done when 1 N of force moves an object over a distance of 1 m. Q: After Clarissa mows her grandmothers lawn, she volunteers to mow a neighbors lawn as well. If she pushes the mower with the same force as before and moves it over a total of 234 meters, how much work does she do mowing the neighbors lawn? A: The work Clarissa does can be calculated as: Work = 100 N  234 m = 23,400 N  m, or 23,400 J ",text,
L_0819,calculating work,T_4197,"The work equation given above can be rearranged to find force or distance if the other variables are known: Force = Work Distance Distance = Work Force After Clarissa finishes mowing both lawns, she pushes the lawn mower down the sidewalk to her own house. If she pushes the mower over a distance of 30 meters and does 2700 joules of work, how much force does she use? Substitute the known values into the equation for force: J Force = 2700 30 m = 90 N Q: When Clarissa gets back to her house, she hangs the 200-Newton lawn mower on some hooks in the garage (see the Figure 1.1). To lift the mower, she does 400 joules of work. How far does she lift the mower to hang it? A: Substitute the known values into the equation for distance: ",text,
L_0820,carbohydrate classification,T_4198,"Carbohydrates are one of four classes of biochemical compounds. The other three classes are proteins, lipids, and nucleic acids. In addition to cellulose, carbohydrates include sugars and starches. Carbohydrate molecules contain atoms of carbon, hydrogen, and oxygen. Living things use carbohydrates mainly for energy. Q: Which carbohydrates do you use for energy? A: You may eat a wide variety of carbohydratesfrom sugars in fruits to starches in potatoes. However, body cells use only sugars for energy. ",text,
L_0820,carbohydrate classification,T_4199,"Sugars are simple carbohydrates. Molecules of sugars have relatively few carbon atoms. Glucose (C6 H12 O6 ) is one of the smallest sugar molecules. Plants and some other organisms make glucose in the process of photosynthesis. Living things that cannot make glucose obtain it by consuming plants or these other organisms. In the Figure 1.1, you can see structural formulas for glucose and two other sugars, named fructose and sucrose. Fructose is a sugar that is found in fruits. It is an isomer of glucose. Isomers are compounds that have the same atoms but different arrangements of atoms. Do you see how the atoms are arranged differently in fructose than in glucose? Youre probably most familiar with the sugar sucrose, because sucrose is table sugar. Its the sugar that you spoon onto your cereal or into your iced tea. Q: Compare the structure of sucrose with the structures of glucose and fructose. How is sucrose related to the other two sugars? A: Sucrose consists of one molecule of glucose and one molecule of fructose bonded together. ",text,
L_0820,carbohydrate classification,T_4200,"Starches are complex carbohydrates. They are polymers of glucose. A polymer is a large molecule that consists of many smaller, repeating molecules, called monomers. The monomers are joined together by covalent bonds. Starches contain hundreds of glucose monomers. Plants make starches to store extra glucose. Consumers get starches by eating plants. Common sources of starches in the human diet are pictured in the Figure 1.2. Our digestive system breaks down starches to sugar, which our cells use for energy. ",text,
L_0820,carbohydrate classification,T_4201,"Cellulose is another complex carbohydrate that is a polymer of glucose. However, glucose molecules are bonded together differently in cellulose than they are in starches. Cellulose molecules bundle together to form long, tough fibers, as you can see in the Figure 1.3. Have you ever eaten raw celery? If you have, then you probably noticed that Foods that are good sources of starches. the stalks contain long, stringy fibers. The fibers are mostly cellulose. Cellulose is the most abundant biochemical compound. It makes up the cell walls of plants and gives support to stems and tree trunks. Cellulose also provides needed fiber in the human diet. We cant digest cellulose, but it helps keep food wastes moving through the digestive tract. ",text,
L_0820,carbohydrate classification,T_4201,"Cellulose is another complex carbohydrate that is a polymer of glucose. However, glucose molecules are bonded together differently in cellulose than they are in starches. Cellulose molecules bundle together to form long, tough fibers, as you can see in the Figure 1.3. Have you ever eaten raw celery? If you have, then you probably noticed that Foods that are good sources of starches. the stalks contain long, stringy fibers. The fibers are mostly cellulose. Cellulose is the most abundant biochemical compound. It makes up the cell walls of plants and gives support to stems and tree trunks. Cellulose also provides needed fiber in the human diet. We cant digest cellulose, but it helps keep food wastes moving through the digestive tract. ",text,
L_0821,carbon bonding,T_4202,"Carbon is a very common ingredient of matter because it can combine with itself and with many other elements. It can form a great diversity of compounds, ranging in size from just a few atoms to thousands of atoms. There are millions of known carbon compounds, and carbon is the only element that can form so many different compounds. ",text,
L_0821,carbon bonding,T_4203,"Carbon is a nonmetal in group 14 of the periodic table. Like other group 14 elements, carbon has four valence electrons. Valence electrons are the electrons in the outer energy level of an atom that are involved in chemical bonds. The valence electrons of carbon are shown in the electron dot diagram in the Figure 1.1. Q: How many more electrons does carbon need to have a full outer energy level? A: Carbon needs four more valence electrons, or a total of eight valence electrons, to fill its outer energy level. A full outer energy level is the most stable arrangement of electrons. Q: How can carbon achieve a full outer energy level? A: Carbon can form four covalent bonds. Covalent bonds are chemical bonds that form between nonmetals. In a covalent bond, two atoms share a pair of electrons. By forming four covalent bonds, carbon shares four pairs of electrons, thus filling its outer energy level and achieving stability. ",text,
L_0821,carbon bonding,T_4204,"A carbon atom can form covalent bonds with other carbon atoms or with the atoms of other elements. Carbon often forms bonds with hydrogen. Compounds that contain only carbon and hydrogen are called hydrocarbons. Methane (CH4 ), which is modeled in the Figure 1.2, is an example of a hydrocarbon. In methane, a single carbon atom forms covalent bonds with four hydrogen atoms. The diagram on the left in the Figure 1.2 shows all the shared valence electrons. The diagram on the right in the Figure 1.2, called a structural formula, represents each pair of shared electrons with a dash (-). Methane (CH4 ) ",text,
L_0821,carbon bonding,T_4205,"Carbon can form single, double, or even triple bonds with other carbon atoms. In a single bond, two carbon atoms share one pair of electrons. In a double bond, they share two pairs of electrons, and in a triple bond they share three pairs of electrons. Examples of compounds with these types of bonds are represented by the structural formulas in the Figure 1.3. Q: How many bonds do the carbon atoms share in each of these compounds? A: In ethane, the two carbon atoms share a single bond. In ethene they share a double bond, and in ethyne they share a triple bond. ",text,
L_0822,carbon monomers and polymers,T_4206,"Carbon has a unique ability to form covalent bonds with many other atoms. It can bond with other carbon atoms as well as with atoms of other elements. Because of this ability, carbon often forms polymers. A polymer is a large molecule that is made out of many smaller molecules that are joined together by covalent bonds. The smaller, repeating molecules are called monomers. (The prefix mono- means one and the prefix poly- means many.) Polymers may consist of just one type of monomer or of more than one type. Polymers are similar to the strings of beads pictured in the Figure 1.1. Like beads on a string, monomers in a polymer may be all the same or different from one another. ",text,
L_0822,carbon monomers and polymers,T_4207,"Many polymers of carbon occur naturally. Two examples are rubber and cellulose. Rubber is a natural polymer of the monomer named isoprene (C5 H8 ). This polymer comes from rubber trees, which grow in tropical areas. Structural formulas for rubber and isoprene are shown in the Figure 1.2. Note that just a small section of the rubber polymer is represented by the structural formula. Cellulose is a natural polymer of the monomer named glucose (C6 H12 O6 ). This polymer makes up the cell walls of plants and is the most common compound in living things. Structural formulas for cellulose and glucose are also shown in the Figure 1.2). As you can see from the structural formula for cellulose, when two glucose monomers bond together, a molecule of water (H2 O) is released. Q: How are the glucose molecules arranged in the cellulose polymer? A: The glucose molecules alternate between right-side up and upside down. ",text,
L_0822,carbon monomers and polymers,T_4207,"Many polymers of carbon occur naturally. Two examples are rubber and cellulose. Rubber is a natural polymer of the monomer named isoprene (C5 H8 ). This polymer comes from rubber trees, which grow in tropical areas. Structural formulas for rubber and isoprene are shown in the Figure 1.2. Note that just a small section of the rubber polymer is represented by the structural formula. Cellulose is a natural polymer of the monomer named glucose (C6 H12 O6 ). This polymer makes up the cell walls of plants and is the most common compound in living things. Structural formulas for cellulose and glucose are also shown in the Figure 1.2). As you can see from the structural formula for cellulose, when two glucose monomers bond together, a molecule of water (H2 O) is released. Q: How are the glucose molecules arranged in the cellulose polymer? A: The glucose molecules alternate between right-side up and upside down. ",text,
L_0822,carbon monomers and polymers,T_4208,Synthetic carbon polymers are produced in labs or factories. Plastics are common examples of synthetic carbon polymers. You are probably familiar with the plastic called polyethylene. All of the plastic items pictured in the Figure 1.3 are made of polyethylene. It consists of repeating monomers of ethylene (C2 H4 ). Structural formulas for ethylene and polyethylene are also shown in the Figure 1.4. Click image to the left or use the URL below. URL: ,text,
L_0822,carbon monomers and polymers,T_4208,Synthetic carbon polymers are produced in labs or factories. Plastics are common examples of synthetic carbon polymers. You are probably familiar with the plastic called polyethylene. All of the plastic items pictured in the Figure 1.3 are made of polyethylene. It consists of repeating monomers of ethylene (C2 H4 ). Structural formulas for ethylene and polyethylene are also shown in the Figure 1.4. Click image to the left or use the URL below. URL: ,text,
L_0823,catalysts,T_4209,"A catalyst is a substance that increases the rate of a chemical reaction. The presence of a catalyst is one of several factors that influence the rate of chemical reactions. (Other factors include the temperature, concentration, and surface area of reactants.) A catalyst isnt a reactant in the chemical reaction it speeds up. As a result, it isnt changed or used up in the reaction, so it can go on to catalyze many more reactions. Q: How is a catalyst like a tunnel through a mountain? A: Like a tunnel through a mountain, a catalyst provides a faster pathway for a chemical reaction to occur. ",text,
L_0823,catalysts,T_4210,"Catalysts interact with reactants so the reaction can occur by an alternate pathway that has a lower activation energy. Activation energy is the energy needed to start a reaction. When activation energy is lower, more reactant particles have enough energy to react so the reaction goes faster. Many catalysts work like the one in the Figure 1.1. The catalyst brings the reactants together by temporarily bonding with them. This makes it easier and quicker for the reactants to react together. Q: In the Figure 1.1, look at the energy needed in the catalytic and non-catalytic pathways of the reaction. How does the amount of energy compare? How does this affect the reaction rate along each pathway? A: The catalytic pathway of the reaction requires far less energy. Therefore, the reaction will occur faster by this pathway because more reactants will have enough energy to react. ",text,
L_0823,catalysts,T_4211,"Chemical reactions constantly occur inside living things. Many of these reactions require catalysts so they will occur quickly enough to support life. Catalysts in living things are called enzymes. Enzymes may be extremely effective. A reaction that takes a split second to occur with an enzyme might take many years without it! More than 1000 different enzymes are necessary for human life. Many enzymes are needed for the digestion of food. An example is amylase, which is found in the mouth and small intestine. Amylase catalyzes the breakdown of starch to sugar. You can see how it affects the rate of starch digestion in the Figure 1.2. A: The starches in the cracker start to break down to sugars with the help of the enzyme amylase. Try this yourself and see if you can taste the reaction. ",text,
L_0824,cellular respiration reactions,T_4212,"Cellular Respiration is the process in which the cells of living things break down the organic compound glucose with oxygen to produce carbon dioxide and water. The overall chemical equation for cellular respiration is: C6 H12 O6 + 6O2  6CO2 + 6H2 O As the Figure 1.1 shows, cellular respiration occurs in the cells of all kinds of organisms, including those that make their own food (autotrophs) as well as those that get their food by consuming other organisms (heterotrophs). Q: How is cellular respiration related to breathing? A: Breathing consists of inhaling and exhaling, and its purpose is to move gases into and out of the body. Oxygen needed for cellular respiration is brought into the body with each inhalation. Carbon dioxide and water vapor produced by cellular respiration are released from the body with each exhalation. ",text,
L_0824,cellular respiration reactions,T_4213,"The reactions of cellular respiration are catabolic reactions. In catabolic reactions, bonds are broken in larger molecules and energy is released. In cellular respiration, bonds are broken in glucose, and this releases the chemical energy that was stored in the glucose bonds. Some of this energy is converted to heat. The rest of the energy is used to form many small molecules of a compound called adenosine triphosphate, or ATP. ATP molecules contain just the right amount of stored chemical energy to power biochemical reactions inside cells. Click image to the left or use the URL below. URL: ",text,
L_0828,chemical bond,T_4220,A chemical bond is a force of attraction between atoms or ions. Bonds form when atoms share or transfer valence electrons. Valence electrons are the electrons in the outer energy level of an atom that may be involved in chemical interactions. Valence electrons are the basis of all chemical bonds. Q: Why do you think that chemical bonds form? A: Chemical bonds form because they give atoms a more stable arrangement of electrons. ,text,
L_0828,chemical bond,T_4221,"To understand why chemical bonds form, consider the common compound known as water, or H2 O. It consists of two hydrogen (H) atoms and one oxygen (O) atom. As you can see in the on the left side of the Figure 1.1, each hydrogen atom has just one electron, which is also its sole valence electron. The oxygen atom has six valence electrons. These are the electrons in the outer energy level of the oxygen atom. In the water molecule on the right in the Figure 1.1, each hydrogen atom shares a pair of electrons with the oxygen atom. By sharing electrons, each atom has electrons available to fill its sole or outer energy level. The hydrogen atoms each have a pair of shared electrons, so their first and only energy level is full. The oxygen atom has a total of eight valence electrons, so its outer energy level is full. A full outer energy level is the most stable possible arrangement of electrons. It explains why elements form chemical bonds with each other. ",text,
L_0828,chemical bond,T_4222,"Not all chemical bonds form in the same way as the bonds in water. There are actually three different types of chemical bonds, called covalent, ionic, and metallic bonds. Each type of bond is described below. Click image to the left or use the URL below. URL:  A covalent bond is the force of attraction that holds together two nonmetal atoms that share a pair of electrons. One electron is provided by each atom, and the pair of electrons is attracted to the positive nuclei of both atoms. The water molecule represented in the Figure 1.1 contains covalent bonds. An ionic bond is the force of attraction that holds together oppositely charged ions. Ionic bonds form crystals instead of molecules. Table salt contains ionic bonds. A metallic bond is the force of attraction between a positive metal ion and the valence electrons that surround itboth its own valence electrons and those of other ions of the same metal. The ions and electrons form a lattice-like structure. Only metals, such as the copper pictured in the Figure 1.2, form metallic bonds. ",text,
L_0830,chemical equations,T_4226,"A chemical equation is a shorthand way to sum up what occurs in a chemical reaction. The general form of a chemical equation is: Reactants  Products The reactants in a chemical equation are the substances that begin the reaction, and the products are the substances that are produced in the reaction. The reactants are always written on the left side of the equation and the products on the right. The arrow pointing from left to right shows that the reactants change into the products during the reaction. This happens when chemical bonds break in the reactants and new bonds form in the products. As a result, the products are different chemical substances than the reactants that started the reaction. Q: What is the general equation for the reaction in which iron rusts? A: Iron combines with oxygen to produce rust, which is the compound named iron oxide. This reaction could be represented by the general chemical equation below. Note that when there is more than one reactant, they are separated by plus signs (+). If more than one product were produced, plus signs would be used between them as well. Iron + Oxygen  Iron Oxide ",text,
L_0830,chemical equations,T_4227,"When scientists write chemical equations, they use chemical symbols and chemical formulas instead of names to represent reactants and products. Look at the chemical reaction illustrated in the Figure 1.1. In this reaction, carbon reacts with oxygen to produce carbon dioxide. Carbon is represented by the chemical symbol C. The chemical symbol for oxygen is O, but pure oxygen exists as diatomic (two-atom) molecules, represented by the chemical formula O2 . A molecule of the compound carbon dioxide consists of one atom of carbon and two atoms of oxygen, so carbon dioxide is represented by the chemical formula CO2 . Q: What is the chemical equation for this reaction? A: The chemical equation is: C + O2  CO2 Q: How have the atoms of the reactants been rearranged in the products of the reaction? What bonds have been broken, and what new bonds have formed? A: Bonds between the oxygen atoms in the oxygen molecule have been broken, and new bonds have formed between the carbon atom and the two oxygen atoms. ",text,
L_0830,chemical equations,T_4228,"All chemical equations, like equations in math, must balance. This means that there must be the same number of each type of atom on both sides of the arrow. Thats because matter is always conserved in a chemical reaction. This is the law of conservation of mass. Look at the equation above for the reaction between carbon and oxygen in the formation of carbon dioxide. Count the number of atoms of each type. Are the numbers the same on both sides of the arrow? The answer is yes, so the equation is balanced. ",text,
L_0830,chemical equations,T_4229,"Lets return to the chemical reaction in which iron (Fe) combines with oxygen (O2 ) to form rust, or iron oxide (Fe2 O3 ). The equation for this reaction is: 4Fe+ 3O2  2Fe2 O3 This equation illustrates the use of coefficients to balance chemical equations. A coefficient is a number placed in front of a chemical symbol or formula that shows how many atoms or molecules of the substance are involved in the reaction. From the equation for rusting, you can see that four atoms of iron combine with three molecules of oxygen to form two molecules of iron oxide. Q: Is the equation for the rusting reaction balanced? How can you tell? A: Yes, the equation is balanced. You can tell because there is the same number of each type of atom on both sides of the arrow. First count the iron atoms. There are four iron atoms in the reactants. There are also four iron atoms in the products (two in each of the two iron oxide molecules). Now count the oxygen atoms. There are six on each side of the arrow, confirming that the equation is balanced in terms of oxygen as well as iron. ",text,
L_0831,chemical formula,T_4230,"In a chemical formula, the elements in a compound are represented by their chemical symbols, and the ratio of different elements is represented by subscripts. Consider the compound water as an example. Each water molecule contains two hydrogen atoms and one oxygen atom. Therefore, the chemical formula for water is: H2 O The subscript 2 after the H shows that there are two atoms of hydrogen in the molecule. The O for oxygen has no subscript. When there is just one atom of an element in a molecule, no subscript is used in the chemical formula. ",text,
L_0831,chemical formula,T_4231,"The Table 1.1 shows four examples of compounds and their chemical formulas. The first two compounds are ionic compounds, and the second two are covalent compounds. Each formula shows the ratio of ions or atoms that make up the compound. Name of Compound Type of Compound Sodium chloride ionic Calcium iodide ionic Hydrogen peroxide covalent Carbon dioxide covalent Ratio of Ions or Atoms of Each Element 1 sodium ion (Na+ ) 1 chloride ion (Cl ) 1 calcium ion (Ca2+ ) 2 io- dide ions (I ) 2 hydrogen atoms (H) 2 oxygen atoms (O) 1 carbon atom (C) 2 oxy- gen atoms (O) Chemical Formulas NaCl CaI2 H2 O2 CO2 There is a different rule for writing the chemical formula for each type of compound. Ionic compounds are compounds in which positive metal ions and negative nonmetal ions are joined by ionic bonds. In these compounds, the chemical symbol for the positive metal ion is written first, followed by the symbol for the negative nonmetal ion. Click image to the left or use the URL below. URL:  Q: The ionic compound lithium fluoride consists of a ratio of one lithium ion (Li+ ) to one fluoride ion (F ). What is the chemical formula for this compound? A: The chemical formula is LiF. Covalent compounds are compounds in which nonmetals are joined by covalent bonds. In these compounds, the element that is farther to the left in the periodic table is written first, followed by the element that is farther to the right. If both elements are in the same group of the periodic table, the one with the higher period number is written first. Click image to the left or use the URL below. URL:  Q: A molecule of the covalent compound nitrogen dioxide consists of one nitrogen atom (N) and two oxygen atoms (O). What is the chemical formula for this compound? A: The chemical formula is NO2 . ",text,
L_0833,chemical reaction overview,T_4235,"A chemical reaction is a process in which some substances change into different substances. Substances that start a chemical reaction are called reactants. Substances that are produced in the reaction are called products. Reactants and products can be elements or compounds. Chemical reactions are represented by chemical equations, like the one below, in which reactants (on the left) are connected by an arrow to products (on the right). Reactants  Products Chemical reactions may occur quickly or slowly. Look at the two pictures in the Figure 1.1. Both represent chemical reactions. In the picture on the left, a reaction inside a fire extinguisher causes foam to shoot out of the extinguisher. This reaction occurs almost instantly. In the picture on the right, a reaction causes the iron tool to turn to rust. This reaction occurs very slowly. In fact, it might take many years for all of the iron in the tool to turn to rust. Q: What happens during a chemical reaction? Where do the reactants go, and where do the products come from? A: During a chemical reaction, chemical changes take place. Some chemical bonds break and new chemical bonds form. ",text,
L_0833,chemical reaction overview,T_4236,"The reactants and products in a chemical reaction contain the same atoms, but they are rearranged during the reaction. As a result, the atoms are in different combinations in the products than they were in the reactants. This happens because chemical bonds break in the reactants and new chemical bonds form in the products. Consider the chemical reaction in which water forms from oxygen and hydrogen gases. The Figure 1.2 represents this reaction. Bonds break in molecules of hydrogen and oxygen, and then new bonds form in molecules of water. In both reactants and products there are four hydrogen atoms and two oxygen atoms, but the atoms are combined differently in water. ",text,
L_0833,chemical reaction overview,T_4237,"The chemical reaction in the Figure 1.2, in which water forms from hydrogen and oxygen, is an example of a synthesis reaction. In this type of reaction, two or more reactants combine to synthesize a single product. There are several other types of chemical reactions, including decomposition, replacement, and combustion reactions. The Table 1.1 compares these four types of chemical reactions. Type of Reaction Synthesis Decomposition General Equation A+B  C AB  A + B Example 2Na + Cl2  2NaCl 2H2 O 2H2 + O2 Type of Reaction Single Replacement Double Replacement Combustion General Equation A+BC  B+ AC AB+ CD  AD + CB fuel + oxygen  carbon dioxide + water Example 2K + 2H2 O  2KOH + H2 NaCl+ AgF  NaF + AgCl CH4 + 2O2  CO2 + 2H2 O Q: The burning of wood is a chemical reaction. Which type of reaction is it? A: The burning of woodor of anything elseis a combustion reaction. In the combustion example in the table, the fuel is methane gas (CH4 ). Click image to the left or use the URL below. URL: ",text,
L_0833,chemical reaction overview,T_4238,"All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In terms of energy, there are two types of chemical reactions: endothermic reactions and exothermic reactions. In exothermic reactions, more energy is released when bonds form in products than is used to break bonds in reactants. These reactions release energy to the environment, often in the form of heat or light. In endothermic reactions, more energy is used to break bonds in reactants than is released when bonds form in products. These reactions absorb energy from the environment. Q: When it comes to energy, which type of reaction is the burning of wood? Is it an endothermic reaction or an exothermic reaction? How can you tell? A: The burning of wood is an exothermic reaction. You can tell by the heat and light energy given off by a wood fire. ",text,
L_0834,chemical reaction rate,T_4239,How fast a chemical reaction occurs is called the reaction rate. Several factors affect the rate of a given chemical reaction. They include the: temperature of reactants. concentration of reactants. surface area of reactants. presence of a catalyst. ,text,
L_0834,chemical reaction rate,T_4240,"When the temperature of reactants is higher, the rate of the reaction is faster. At higher temperatures, particles of reactants have more energy, so they move faster. As a result, they are more likely to bump into one another and to collide with greater force. For example, food spoils because of chemical reactions, and these reactions occur faster at higher temperatures (see the bread on the left in the Figure 1.1). This is why we store foods in the refrigerator or freezer (like the bread on the right in the Figure 1.1). The lower temperature slows the rate of spoilage. Left image: Bread after 1 month on a warm countertop. Right image: Bread after 1 month in a cold refrigerator. ",text,
L_0834,chemical reaction rate,T_4241,"Concentration is the number of particles of a substance in a given volume. When the concentration of reactants is higher, the reaction rate is faster. At higher concentrations, particles of reactants are crowded closer together, so they are more likely to collide and react. Did you ever see a sign like the one in the Figure 1.2? You might see it where someone is using a tank of pure oxygen for a breathing problem. Combustion, or burning, is a chemical reaction in which oxygen is a reactant. A greater concentration of oxygen in the air makes combustion more rapid if a fire starts burning. Q: It is dangerous to smoke or use open flames when oxygen is in use. Can you explain why? A: Because of the higher-than-normal concentration of oxygen, the flame of a match, lighter, or cigarette could spread quickly to other materials or even cause an explosion. ",text,
L_0834,chemical reaction rate,T_4242,"When a solid substance is involved in a chemical reaction, only the matter at the surface of the solid is exposed to other reactants. If a solid has more surface area, more of it is exposed and able to react. Therefore, increasing the surface area of solid reactants increases the reaction rate. Look at the hammer and nails pictured in the Figure 1.3. Both are made of iron and will rust when the iron combines with oxygen in the air. However, the nails have a greater surface area, so they will rust faster. ",text,
L_0834,chemical reaction rate,T_4243,"Some reactions need extra help to occur quickly. They need another substance called a catalyst. A catalyst is a substance that increases the rate of a chemical reaction. A catalyst isnt a reactant, so it isnt changed or used up in the reaction. Therefore, it can catalyze many other reactions. ",text,
L_0835,chemistry of compounds,T_4244,"A compound is a unique substance that forms when two or more elements combine chemically. Compounds form as a result of chemical reactions. The elements in compounds are held together by chemical bonds. A chemical bond is a force of attraction between atoms or ions that share or transfer valence electrons. Click image to the left or use the URL below. URL:  Water is an example of a common chemical compound. As you can see in the Figure 1.1, each water molecule consists of two atoms of hydrogen and one atom of oxygen. Water always has this 2:1 ratio of hydrogen to oxygen. Like water, all compounds consist of a fixed ratio of elements. It doesnt matter how much or how little of a compound there is. It always has the same composition. Q: Sometimes the same elements combine in different ratios. How can this happen if a compound always consists of the same elements in the same ratio? A: If the same elements combine in different ratios, they form different compounds. ",text,
L_0835,chemistry of compounds,T_4245,"Look at the Figure 1.2 of water (H2 O) and hydrogen peroxide (H2 O2 ), and read about these two compounds. Both compounds consist of hydrogen and oxygen, but they have different ratios of the two elements. As a result, water and hydrogen peroxide are different compounds with different properties. If youve ever used hydrogen peroxide to disinfect a cut, then you know that it is very different from water! Q: Read the Figure 1.3 about carbon dioxide (CO2 ) and carbon monoxide (CO). Both compounds consist of carbon and oxygen, but in different ratios. How can you tell that carbon dioxide and carbon monoxide are different compounds? Carbon Dioxide: Every time you exhale, you release carbon dioxide into the air. Its an odorless, colorless gas. Car- bon dioxide contributes to global climate change, but it isnt directly harmful to hu- man health. Carbon Monoxide: Carbon monoxide is produced when matter burns. Its a colorless, odorless gas that is very harmful to human health. In fact, it can kill people in minutes. Because you cant see or smell carbon monoxide, it must be detected with an alarm. ",text,
L_0835,chemistry of compounds,T_4245,"Look at the Figure 1.2 of water (H2 O) and hydrogen peroxide (H2 O2 ), and read about these two compounds. Both compounds consist of hydrogen and oxygen, but they have different ratios of the two elements. As a result, water and hydrogen peroxide are different compounds with different properties. If youve ever used hydrogen peroxide to disinfect a cut, then you know that it is very different from water! Q: Read the Figure 1.3 about carbon dioxide (CO2 ) and carbon monoxide (CO). Both compounds consist of carbon and oxygen, but in different ratios. How can you tell that carbon dioxide and carbon monoxide are different compounds? Carbon Dioxide: Every time you exhale, you release carbon dioxide into the air. Its an odorless, colorless gas. Car- bon dioxide contributes to global climate change, but it isnt directly harmful to hu- man health. Carbon Monoxide: Carbon monoxide is produced when matter burns. Its a colorless, odorless gas that is very harmful to human health. In fact, it can kill people in minutes. Because you cant see or smell carbon monoxide, it must be detected with an alarm. ",text,
L_0835,chemistry of compounds,T_4246,"There are two basic types of compounds that differ in the nature of the bonds that hold their atoms or ions together. They are covalent and ionic compounds. Both types are described below. Click image to the left or use the URL below. URL:  Covalent compounds consist of atoms that are held together by covalent bonds. These bonds form between nonmetals that share valence electrons. Covalent compounds exist as individual molecules. Water is an example of a covalent compound. Ionic compounds consist of ions that are held together by ionic bonds. These bonds form when metals transfer electrons to nonmetals. Ionic compounds exist as a matrix of many ions, called a crystal. Sodium chloride (table salt) is an example of an ionic compound. ",text,
L_0836,color,T_4247,"Visible light is light that has wavelengths that can be detected by the human eye. The wavelength of visible light determines the color that the light appears. As you can see in the Figure 1.1, light with the longest wavelength appears red, and light with the shortest wavelength appears violet. In between are all the other colors of light that we can see. Only seven main colors of light are actually represented in the diagram. ",text,
L_0836,color,T_4248,"A prism, like the one in the Figure 1.2, can be used to separate visible light into its different colors. A prism is a pyramid-shaped object made of transparent matter, usually clear glass or plastic. Matter that is transparent allows light to pass through it. A prism transmits light but slows it down. When light passes from air to the glass of the prism, the change in speed causes the light to change direction and bend. Different wavelengths of light bend at different angles. This makes the beam of light separate into light of different wavelengths. What we see is a rainbow of colors. Q: Look back at the rainbow that opened this article. Do you see all the different colors of light, from red at the top to violet at the bottom? What causes a rainbow to form? A: Individual raindrops act as tiny prisms. They separate sunlight into its different wavelengths and create a rainbow of colors. ",text,
L_0836,color,T_4248,"A prism, like the one in the Figure 1.2, can be used to separate visible light into its different colors. A prism is a pyramid-shaped object made of transparent matter, usually clear glass or plastic. Matter that is transparent allows light to pass through it. A prism transmits light but slows it down. When light passes from air to the glass of the prism, the change in speed causes the light to change direction and bend. Different wavelengths of light bend at different angles. This makes the beam of light separate into light of different wavelengths. What we see is a rainbow of colors. Q: Look back at the rainbow that opened this article. Do you see all the different colors of light, from red at the top to violet at the bottom? What causes a rainbow to form? A: Individual raindrops act as tiny prisms. They separate sunlight into its different wavelengths and create a rainbow of colors. ",text,
L_0836,color,T_4249,"An opaque object is one that doesnt let light pass through it. Instead, it reflects or absorbs the light that strikes it. Many objects, such as the leaves pictured in the Figure 1.3, reflect just one or a few wavelengths of visible light and absorb the rest. The wavelengths that are reflected determine the color that an object appears to the human eye. For example, the leaves appear green because they reflect green light and absorb light of other wavelengths. A transparent or translucent material, such as window glass, transmits some or all of the light that strikes it. This means that the light passes through the material rather than being reflected by it. In this case, we see the material because of the transmitted light. Therefore, the wavelength of the transmitted light determines the color that the object appears. Look at the beautiful stained glass windows in the Figure 1.4. The different colors of glass transmit The color of light that strikes an object may also affect the color that the object appears. For example, if only blue light strikes green leaves, the blue light is absorbed and no light is reflected. Q: What color do you see if an object absorbs all of the light that strikes it? A: When all of the light is absorbed, none is reflected, so the object looks black. But black isnt a color of light. Black is the absence of light. ",text,
L_0836,color,T_4249,"An opaque object is one that doesnt let light pass through it. Instead, it reflects or absorbs the light that strikes it. Many objects, such as the leaves pictured in the Figure 1.3, reflect just one or a few wavelengths of visible light and absorb the rest. The wavelengths that are reflected determine the color that an object appears to the human eye. For example, the leaves appear green because they reflect green light and absorb light of other wavelengths. A transparent or translucent material, such as window glass, transmits some or all of the light that strikes it. This means that the light passes through the material rather than being reflected by it. In this case, we see the material because of the transmitted light. Therefore, the wavelength of the transmitted light determines the color that the object appears. Look at the beautiful stained glass windows in the Figure 1.4. The different colors of glass transmit The color of light that strikes an object may also affect the color that the object appears. For example, if only blue light strikes green leaves, the blue light is absorbed and no light is reflected. Q: What color do you see if an object absorbs all of the light that strikes it? A: When all of the light is absorbed, none is reflected, so the object looks black. But black isnt a color of light. Black is the absence of light. ",text,
L_0836,color,T_4250,"The human eye can distinguish only red, green, and blue light. These three colors are called the primary colors of light. All other colors of light can be created by combining the primary colors. Look at the Venn diagram 1.5. Red and green light combine to form yellow light. Red and blue light combine to form magenta light, and blue and green light combine to form cyan light. Yellow, magenta, and cyan are called the secondary colors of light. Look at the center of the diagram, where all three primary colors of light combine. The result is white light. ",text,
L_0836,color,T_4251,"Many objects have color because they contain pigments. A pigment is a substance that colors materials by reflecting light of certain wavelengths and absorbing light of other wavelengths. A very common pigment is the dark green pigment called chlorophyll, which is found in plants. Chlorophyll absorbs all but green wavelengths of visible light. Pigments are also found in many manufactured products. They are used to color paints, inks, and dyes. Just three pigments, called primary pigments, can be combined to produce all other colors. The primary colors of pigments are the same as the secondary colors of light: cyan, magenta, and yellow. Q: A color printer needs just three colors of ink to print all of the colors that we can see. Which colors are they? A: The three colors of ink in a color printer are the three primary pigment colors: cyan, magenta, and yellow. These three colors can be combined in different ratios to produce all other colors, so they are the only colors needed for full-color printing. ",text,
L_0837,combining forces,T_4252,"You have probably heard of the famous equation E = mc2 . The ""E"" represent the amount of energy. The ""m"" represents mass. The ""c"" represent the speed of light. Writing a ""c"" is much easier than writing the actual speed of light. The speed of light is a really large number. The speed of light is about 300 million meters per second. Thats really, really fast. Light always travels at the same speed through space. In outer space, there is not any matter to get in its way. Think about riding your bicycle. When you ride on a hard surface, it is easy to pedal. You can go really fast. Imagine how your speed would change if you were riding through deep sand. You would find it hard to pedal. You would not be able to go as fast. The same is true for light. When there is no matter around, like in outer space, it can go fast. When matter gets in its way, it slows down. Light travels through some matter faster than through others. Table 1.1 gives the speed of light in six common materials. Material Air Water Glass Vegetable oil Alcohol Diamond Speed of Light (m/s) 299 million meters per second 231 million meters per second 200 million meters per second 150 million meters per second 140 million meters per second 125 million meters per second No matter how slow light travels, it still goes really, really fast. The important thing to remember is that it does travel. It is hard for us to imagine light taking time to cover a distance. Think about when you enter your science classroom. You step through the door. You tell your teacher, ""Hello."" You walk to your desk and sit down. It may take around 10 to 20 seconds to walk this distance. Imagine now your teacher turns the light off. She carries a small lamp over to the door you just entered. She asks you to watch carefully as she switches on the light. She flips the switch and you immediately see the light. The light just covered the same distance you just walked. Thats how fast light is. For us, it is hard to imagine that it moves. Now lets think about light traveling between the Sun and Earth. The Sun is 93 million miles away. What if we were able to turn off the Sun for just a second? How long would it take us to notice? Would we notice instantly like in the classroom? Remember, the Sun is a long way away. We wouldnt notice the change for a little over 8 minutes. That is because the Sun is a long way away. Even when moving as fast as light, it takes time to travel from the Sun to Earth. What do you think happens when it hits the air in our atmosphere? Air is made up of matter. When light travels through matter it slows down. How do scientists know it slows down? What evidence do scientists have? When sunlight hits Earths atmosphere it bends just a little. If sunlight goes through water droplets it bends even more. The bending of light through droplets of water is why we can see rainbows. It also explains why the straw in a glass of water appears to be broken. ",text,
L_0837,combining forces,T_4253,"When light passes from one medium (or type of matter) to another, it changes speed. You can actually see this happen. If light strikes a new substance at an angle, the light appears to bend. This is what explains the straw looking broken in the picture above. So, does light always bend as it travels into a new medium? If light travels straight into a new substance it is not bent. You may know this angle as perpendicular. The light still slows down, just does not appear to bend. Any angle other than perpendicular the light will bend as it slows down. The bending of light is called refraction. Figure 1.1 shows how refraction occurs. Notice that the angle of light changes again as it passes from the glass back to the air. In this case, the speed increases, and the ray of light resumes its initial direction. For a more detailed explanation of refraction, watch this video: Click image to the left or use the URL below. URL: ",text,
L_0838,combustion reactions,T_4254,"A combustion reaction occurs when a substance reacts quickly with oxygen (O2 ). For example, in the Figure usually referred to as fuel. The products of a complete combustion reaction include carbon dioxide (CO2 ) and water vapor (H2 O). The reaction typically gives off heat and light as well. The general equation for a complete combustion reaction is: Fuel + O2  CO2 + H2 O The burning of charcoal is a combustion reaction. ",text,
L_0838,combustion reactions,T_4255,"The fuel that burns in a combustion reaction contains compounds called hydrocarbons. Hydrocarbons are compounds that contain only carbon (C) and hydrogen (H). The charcoal pictured in the Figure 1.1 consists of hydrocarbons. So do fossil fuels such as natural gas. Natural gas is a fuel that is commonly used in home furnaces and gas stoves. The main component of natural gas is the hydrocarbon called methane (CH4 ). You can see a methane flame in the Figure 1.2. The combustion of methane is represented by the equation: CH4 + 2O2  CO2 + 2H2 O The combustion of methane gas heats a pot on a stove. Q: Sometimes the flame on a gas stove isnt just blue but has some yellow or orange in it. Why might this occur? A: If the flame isnt just blue, the methane isnt getting enough oxygen to burn completely, leaving some of the carbon unburned. The flame will also not be as hot as a completely blue flame for the same reason. ",text,
L_0840,compound machine,T_4258,"A compound machine is a machine that consists of more than one simple machine. Some compound machines consist of just two simple machines. You can read below about two examplesthe wheelbarrow and corkscrew. Other compound machines, such as bicycles, consist of many simple machines. Big compound machines such as cars may consist of hundreds or even thousands of simple machines. ",text,
L_0840,compound machine,T_4259,"Look at the wheelbarrow in the Figure 1.1. It is used to carry heavy objects. It consists of two simple machines: a lever and a wheel and axle. Effort is applied to the lever by picking up the handles of the wheelbarrow. The lever, in turn, applies upward force to the load. The force is increased by the lever, making the load easier to lift. Effort is applied to the wheel of the wheelbarrow by pushing it over the ground. The rolling wheel turns the axle and increases the force, making it easier to push the load. ",text,
L_0840,compound machine,T_4260,"The corkscrew in the Figure 1.2 is also a compound machine. It is used to pierce a cork and pull it out of the neck of a bottle. It consists of a screw and two levers. Turning the handle on top twists the screw down into the center of the cork. Then, pushing down on the two levers causes the screw to pull upward, bringing the cork with it. The levers increase the force and change its direction. ",text,
L_0840,compound machine,T_4260,"The corkscrew in the Figure 1.2 is also a compound machine. It is used to pierce a cork and pull it out of the neck of a bottle. It consists of a screw and two levers. Turning the handle on top twists the screw down into the center of the cork. Then, pushing down on the two levers causes the screw to pull upward, bringing the cork with it. The levers increase the force and change its direction. ",text,
L_0840,compound machine,T_4261,"Friction is a force that opposes motion between any surfaces that are touching. All machines have moving parts and friction, so they have to use some of the work that is applied to them to overcome friction. This makes all machines less than 100 percent efficient. Because compound machines have more moving parts than simple machines, they generally have more friction to overcome. As a result, compound machines tend to have lower efficiency than simple machines. When a compound machine consists of many simple machines, friction can become a serious problem, and it may produce a lot of heat. Lubricants such as oil or grease may be used to coat the moving parts of a machine so they slide over each other more easily. This is how friction is reduced in a car engine. ",text,
L_0840,compound machine,T_4262,"The mechanical advantage of a machine is the factor by which it changes the force applied to the machine. Many machines increase the force applied to them, and this is how they make work easier. Compound machines tend to have a greater mechanical advantage than simple machines. Thats because the mechanical advantage of a compound machine equals the product of the mechanical advantages of all its component simple machines. The greater the number of simple machines it contains, the greater its mechanical advantage tends to be. Q: Assume that the lever and the wheel and axle of a wheelbarrow each have a mechanical advantage of 2. What is the mechanical advantage of the wheelbarrow? A: The mechanical advantage of the wheelbarrow is the product of the mechanical advantage of the lever (2) and the mechanical advantage of the wheel and axle (2). Therefore, the wheelbarrow has a mechanical advantage of 4. ",text,
L_0841,compounds,T_4263,"A compound is a unique substance that forms when two or more elements combine chemically. For example, the compound carbon dioxide forms when one atom of carbon (grey in the model above) combines with two atoms of oxygen (red in the model). Another example of a compound is water. It forms when two hydrogen atoms combine with one oxygen atom. Click image to the left or use the URL below. URL:  Q: How could a water molecule be represented? A: It could be represented by a model like the one for carbon dioxide in the opening image. You can see a sample Figure 1.1. A model of water. Two things are true of all compounds: A compound always has the same elements in the same proportions. For example, carbon dioxide always has two atoms of oxygen for each atom of carbon, and water always has two atoms of hydrogen for each atom of oxygen. A compound always has the same composition throughout. For example, all the carbon dioxide in the atmosphere and all the water in the ocean have these same proportions of elements. Q: How do you think the properties of compounds compare with the properties of the elements that form them? A: You might expect the properties of a compound to be similar to the properties of the elements that make up the compound. But you would be wrong. ",text,
L_0841,compounds,T_4264,"The properties of compounds are different from the properties of the elements that form themsometimes very different. Thats because elements in a compound combine and become an entirely different substance with its own unique properties. Do you put salt on your food? Table salt is the compound sodium chloride. It contains sodium and chlorine. As shown in the Figure 1.2, sodium is a solid that reacts explosively with water, and chlorine is a poisonous gas. But together in table salt, sodium and chlorine form a harmless unreactive compound that you can safely eat. Q: The compound sodium chloride is very different from the elements sodium and chlorine that combine to form it. What are some properties of sodium chloride? A: Sodium chloride is an odorless white solid that is harmless unless consumed in large quantities. In fact, it is a necessary component of the human diet. ",text,
L_0841,compounds,T_4265,"Compounds like sodium chloride form structures called crystals. A crystal is a rigid framework of many ions locked together in a repeating pattern. Ions are electrically charged forms of atoms. You can see a crystal of sodium chloride in the Figure 1.3. It is made up of many sodium and chloride ions. Sodium and chlorine combine to form sodium chloride, or table salt. A sodium chloride crystal consists of many sodium ions (blue) and chloride ions (green) arranged in a rigid framework. Click image to the left or use the URL below. URL:  Compounds such as carbon dioxide and water form molecules instead of crystals. A molecule is the smallest particle of a compound that still has the compounds properties. It consists of two or more atoms bonded together. You saw models of carbon dioxide and water molecules above. ",text,
L_0841,compounds,T_4265,"Compounds like sodium chloride form structures called crystals. A crystal is a rigid framework of many ions locked together in a repeating pattern. Ions are electrically charged forms of atoms. You can see a crystal of sodium chloride in the Figure 1.3. It is made up of many sodium and chloride ions. Sodium and chlorine combine to form sodium chloride, or table salt. A sodium chloride crystal consists of many sodium ions (blue) and chloride ions (green) arranged in a rigid framework. Click image to the left or use the URL below. URL:  Compounds such as carbon dioxide and water form molecules instead of crystals. A molecule is the smallest particle of a compound that still has the compounds properties. It consists of two or more atoms bonded together. You saw models of carbon dioxide and water molecules above. ",text,
L_0843,conservation of energy in chemical reactions,T_4269,"All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. Like the combustion reaction in a furnace, some chemical reactions require less energy to break bonds in reactants than is released when bonds form in products. These reactions, called exothermic reactions, release energy. In other chemical reactions, it takes more energy to break bonds in reactants than is released when bonds form in products. These reactions, called endothermic reactions, absorb energy. ",text,
L_0843,conservation of energy in chemical reactions,T_4270,"Whether a chemical reaction absorbs or releases energy, there is no overall change in the amount of energy during the reaction. Thats because energy cannot be created or destroyed. This is the law of conservation of energy. Energy may change form during a chemical reactionfor example, from chemical energy to heat energy when gas burns in a furnacebut the same amount of energy remains after the reaction as before. This is true of all chemical reactions. Q: If energy cant be destroyed during a chemical reaction, what happens to the energy that is absorbed in an endothermic reaction? A: The energy is stored in the bonds of the products as chemical energy. In an endothermic reaction, the products have more stored chemical energy than the reactants. This is represented by the graph on the left in the Figure 1.1. In an exothermic reaction, the opposite is true. The products have less stored chemical energy than the reactants. You can see this in the graph on the right in the Figure 1.1. Note: H represents the change in en- ergy. Q: What happens to the excess energy in the reactants of an exothermic reaction? A: The excess energy is generally released to the surroundings when the reaction occurs. In a home heating system, for example, the energy that is released during combustion in the furnace is used to heat the home. ",text,
L_0845,conservation of mass and energy in nuclear reactions,T_4273,"Einsteins equation is possibly the best-known equation of all time. Theres reason for that. The equation is incredibly important. It changed how scientists view energy and matter, which are two of the most basic concepts in all of science. The equation shows that energy and matter are two forms of the same thing. This new idea turned science upside down when Einstein introduced it in the early 1900s. Amazingly, the idea has withstood the test of time as more and more evidence has been gathered to support it. You can listen to an explanation of Einsteins equation at URL: https://youtu.be/hW7DW9NIO9M Q: What do the letters in Einsteins equation stand for? A: E stands for energy, m stands for mass, and c stands for the speed of light. The speed of light is 300,000 kilometers (186,000 miles) per second, so c2 is a very big number. Therefore, the amount of energy in even a small mass of matter is tremendous. Suppose, for example, that you have 1 gram of matter. Thats about the mass of a paperclip. Multiplying this mass by c2 would yield enough energy to power 3,600 homes for a year! ",text,
L_0845,conservation of mass and energy in nuclear reactions,T_4274,"Einsteins equation helps scientists understand what happens in nuclear reactions and why they produce so much energy. When the nucleus of a radioisotope undergoes fission or fusion in a nuclear reaction, it loses a tiny amount of mass. What happens to the lost mass? It isnt really lost at all. It is converted to energy. How much energy? E = mc2 . The change in mass is tiny, but it results in a great deal of energy. Q: In a nuclear reaction, mass decreases and energy increases. What about the laws of conservation of mass and conservation of energy? Are mass and energy not conserved in nuclear reactions? Do we need to throw out these laws when it comes to nuclear reactions? A: No, the laws still apply. However, its more correct to say that the sum of mass and energy is always conserved in a nuclear reaction. Mass changes to energy, but the total amount of mass and energy combined remains the same. ",text,
L_0846,conservation of mass in chemical reactions,T_4275,"A chemical reaction occurs when some substances change chemically to other substances. Chemical reactions are represented by chemical equations. Consider a simple chemical reaction, the burning of methane. In this reaction, methane (CH4 ) combines with oxygen (O2 ) in the air and produces carbon dioxide (CO2 ) and water vapor (H2 O). The reaction is represented by the following chemical equation: CH4 + 2O2  CO2 + 2H2 O This equation shows that one molecule of methane combines with two molecules of oxygen to produce one molecule of carbon dioxide and two molecules of water vapor. All chemical equations must be balanced. This means that the same number of each type of atom must appear on both sides of the arrow. Q: Is the chemical equation for the burning of methane balanced? Count the atoms of each type on both sides of the arrow to find out. A: Yes, the equation is balanced. There is one carbon atom on both sides of the arrow. There are also four hydrogen atoms and four oxygen atoms on both sides of the arrow. ",text,
L_0846,conservation of mass in chemical reactions,T_4276,"Why must chemical equations be balanced? Its the law! Matter cannot be created or destroyed in chemical reactions. This is the law of conservation of mass. In every chemical reaction, the same mass of matter must end up in the products as started in the reactants. Balanced chemical equations show that mass is conserved in chemical reactions. ",text,
L_0846,conservation of mass in chemical reactions,T_4277,"How do scientists know that mass is always conserved in chemical reactions? Careful experiments in the 1700s by a French chemist named Antoine Lavoisier led to this conclusion. Lavoisier carefully measured the mass of reactants and products in many different chemical reactions. He carried out the reactions inside a sealed jar, like the one in the Figure 1.1. In every case, the total mass of the jar and its contents was the same after the reaction as it was before the reaction took place. This showed that matter was neither created nor destroyed in the reactions. Another outcome of Lavoisiers research was the discovery of oxygen. Click image to the left or use the URL below. URL:  Q: Lavoisier carried out his experiments inside a sealed glass jar. Why was sealing the jar important for his results? What might his results have been if he hadnt sealed the jar? A: Sealing the jar was important so that any gases produced in the reactions were captured and could be measured. If he hadnt sealed the jar, gases might have escaped detection. Then his results would have shown that there was less mass after the reactions than before. In other words, he would not have been able to conclude that mass is conserved in chemical reactions. ",text,
L_0847,convection,T_4278,"Convection is the transfer of thermal energy by particles moving through a fluid (either a gas or a liquid). Thermal energy is the total kinetic energy of moving particles of matter, and the transfer of thermal energy is called heat. Convection is one of three ways that thermal energy can be transferred (the other ways are conduction and thermal radiation). Thermal energy is always transferred from matter with a higher temperature to matter with a lower temperature. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0847,convection,T_4279,"The Figure 1.1 shows how convection occurs, using hot water in a pot as an example. When particles in one area of a fluid (in this case, the water at the bottom of the pot) gain thermal energy, they move more quickly, have more collisions, and spread farther apart. This decreases the density of the particles, so they rise up through the fluid. As they rise, they transfer their thermal energy to other particles of the fluid and cool off in the process. With less energy, the particles move more slowly, have fewer collisions, and move closer together. This increases their density, so they sink back down through the fluid. When they reach the bottom of the fluid, the cycle repeats. The result is a loop of moving particles called a convection current. ",text,
L_0847,convection,T_4280,"Convection currents transfer thermal energy through many fluids, not just hot water in a pot. For example, convection currents transfer thermal energy through molten rock below Earths surface, through water in the oceans, and through air in the atmosphere. Convection currents in the atmosphere create winds. You can see one way this happens in the Figure 1.2. The land heats up and cools off faster than the water because it has lower specific heat. Therefore, the land gets warmer during the day and cooler at night than the water does. During the day, warm air rises above the land and cool air from the water moves in to take its place. During the night, the opposite happens. Warm air rises above the water and cool air from the land moves out to take its place. Q: During the day, in which direction is thermal energy of the air transferred? In which direction is it transferred during the night? A: During the day, thermal energy is transferred from the air over the land to the air over the water. During the night, thermal energy is transferred in the opposite direction. ",text,
L_0848,cooling systems,T_4281,"A refrigerator is an example of a cooling system. Another example is an air conditioner. The purpose of any cooling system is to transfer thermal energy in order to keep things cool. A refrigerator, for example, transfers thermal energy from the cool air inside the refrigerator to the warm air in the kitchen. If youve ever noticed how warm the back of a running refrigerator gets, then you know that it releases a lot of thermal energy into the room. Q: Thermal energy always moves from a warmer area to a cooler area. How can thermal energy move from the cooler air inside a refrigerator to the warmer air in a room? A: The answer is work. ",text,
L_0848,cooling systems,T_4282,"A refrigerator must do work to reverse the normal direction of thermal energy flow. Work involves the use of force to move something, and doing work takes energy. In a refrigerator, the energy is usually provided by electricity. You can read in detail in the Figure 1.1 how a refrigerator does its work. ",text,
L_0848,cooling systems,T_4283,"The key to how a refrigerator or other cooling system works is the refrigerant. A refrigerant is a substance such as FreonTM that has a low boiling point and changes between liquid and gaseous states as it passes through the refrigerator. As a liquid, the refrigerant absorbs thermal energy from the cool air inside the refrigerator and changes to a gas. As a gas, it transfers thermal energy to the warm air outside the refrigerator and changes back to a liquid. Work is done by a refrigerator to move the refrigerant through the different components of the refrigerator. ",text,
L_0849,covalent bonding,T_4284,A covalent bond is the force of attraction that holds together two atoms that share a pair of valence electrons. The shared electrons are attracted to the nuclei of both atoms. This forms a molecule consisting of two or more atoms. Covalent bonds form only between atoms of nonmetals. ,text,
L_0849,covalent bonding,T_4285,"The two atoms that are held together by a covalent bond may be atoms of the same element or different elements. When atoms of different elements form covalent bonds, a new substance, called a covalent compound, results. Water is an example of a covalent compound. A water molecule is modeled in the Figure 1.1. A molecule is the smallest particle of a covalent compound that still has the properties of the compound. Q: How many valence electrons does the oxygen atom (O) share with each hydrogen atom (H)? How many covalent bonds hold the water molecule together? A: The oxygen atom shares one pair of valence electrons with each hydrogen atom. Each pair of shared electrons represents one covalent bond, so two covalent bonds hold the water molecule together. The diagram in the Figure 1.2 shows an example of covalent bonds between two atoms of the same element, in this case two atoms of oxygen. The diagram represents an oxygen molecule, so its not a new compound. Oxygen normally occurs in diatomic (two-atom) molecules. Several other elements also occur as diatomic molecules: hydrogen, nitrogen, and all but one of the halogens (fluorine, chlorine, bromine, and iodine). Q: How many electrons do these two oxygen atoms share? How many covalent bonds hold the oxygen molecule together? A: The two oxygen atoms share two pairs of electrons, so two covalent bonds hold the oxygen molecule together. ",text,
L_0849,covalent bonding,T_4285,"The two atoms that are held together by a covalent bond may be atoms of the same element or different elements. When atoms of different elements form covalent bonds, a new substance, called a covalent compound, results. Water is an example of a covalent compound. A water molecule is modeled in the Figure 1.1. A molecule is the smallest particle of a covalent compound that still has the properties of the compound. Q: How many valence electrons does the oxygen atom (O) share with each hydrogen atom (H)? How many covalent bonds hold the water molecule together? A: The oxygen atom shares one pair of valence electrons with each hydrogen atom. Each pair of shared electrons represents one covalent bond, so two covalent bonds hold the water molecule together. The diagram in the Figure 1.2 shows an example of covalent bonds between two atoms of the same element, in this case two atoms of oxygen. The diagram represents an oxygen molecule, so its not a new compound. Oxygen normally occurs in diatomic (two-atom) molecules. Several other elements also occur as diatomic molecules: hydrogen, nitrogen, and all but one of the halogens (fluorine, chlorine, bromine, and iodine). Q: How many electrons do these two oxygen atoms share? How many covalent bonds hold the oxygen molecule together? A: The two oxygen atoms share two pairs of electrons, so two covalent bonds hold the oxygen molecule together. ",text,
L_0849,covalent bonding,T_4286,"Covalent bonds form because they give atoms a more stable arrangement of electrons. Look at the oxygen atoms in the Figure 1.2. Alone, each oxygen atom has six valence electrons. By sharing two pairs of valence electrons, each oxygen atom has a total of eight valence electrons. This fills its outer energy level, giving it the most stable arrangement of electrons. The shared electrons are attracted to both oxygen nuclei, and this force of attraction holds the two atoms together in the oxygen molecule. ",text,
L_0850,crystalline carbon,T_4287,"Graphite is one of three forms of crystalline, or crystal-forming, carbon. Carbon also exists in an amorphous, or shapeless, form in substances such as coal and charcoal. Different forms of the same element are called allotropes. Besides graphite, the other allotropes of crystalline carbon are diamond and fullerenes. All three forms exist as crystals rather than molecules. In a crystal, many atoms are bonded together in a repeating pattern that may contains thousands of atoms. The arrangement of atoms in the crystal differs for each form of carbon and explains why the different forms have different properties. Click image to the left or use the URL below. URL:  Q: How do you think the properties of diamond might differ from the properties of graphite? A: Diamond is clear whereas graphite is black. Diamond is also very hard, so it doesnt break easily. Graphite, in contrast, is soft and breaks very easily. ",text,
L_0850,crystalline carbon,T_4288,"Diamond is a form of carbon in which each carbon atom is covalently bonded to four other carbon atoms. This forms a strong, rigid, three-dimensional structure (see Figure 1.1). Diamond is the hardest natural substance, and no other natural substance can scratch it. This property makes diamonds useful for cutting and grinding tools as well as for rings and other jewelry (see Figure 1.2). ",text,
L_0850,crystalline carbon,T_4288,"Diamond is a form of carbon in which each carbon atom is covalently bonded to four other carbon atoms. This forms a strong, rigid, three-dimensional structure (see Figure 1.1). Diamond is the hardest natural substance, and no other natural substance can scratch it. This property makes diamonds useful for cutting and grinding tools as well as for rings and other jewelry (see Figure 1.2). ",text,
L_0850,crystalline carbon,T_4289,"Graphite is a form of crystalline carbon in which each carbon atom is covalently bonded to three other carbon atoms. The carbon atoms are arranged in layers, with strong bonds within each layer but only weak bonds between layers (see Figure 1.3). The weak bonds between layers allow the layers to slide over one another, so graphite is relatively soft and slippery. This makes it useful as a lubricant. Q: Why do graphites properties make it useful for pencil leads? A: Being slippery, graphite slides easily over paper when you write. Being soft, it rubs off on the paper, allowing you to leave marks. Graphites softness also allows you to sharpen it easily. (Imagine trying to sharpen a diamond!) ",text,
L_0850,crystalline carbon,T_4290,"A fullerene (also called a Bucky ball) is a form of carbon in which carbon atoms are arranged in a hollow sphere resembling a soccer ball (see Figure 1.4). Each sphere contains 60 carbon atoms, and each carbon atom is bonded to three others by single covalent bonds. The bonds are relatively weak, so fullerenes can dissolve and form solutions. Fullerenes were first discovered in 1985 and have been found in soot and meteorites. Possible commercial uses of fullerenes are under investigation. Fullerene Crystal ",text,
L_0851,daltons atomic theory,T_4291,"Around 1800, the English chemist John Dalton brought back Democritus ancient idea of the atom. You can see a picture of Dalton 1.1. Dalton grew up in a working-class family. As an adult, he made a living by teaching and just did research in his spare time. Nonetheless, from his research he developed one of the most important theories in all of science. Based on his research results, he was able to demonstrate that atoms actually do exist, something that Democritus had only guessed. ",text,
L_0851,daltons atomic theory,T_4292,"Dalton did many experiments that provided evidence for the existence of atoms. For example: He investigated pressure and other properties of gases, from which he inferred that gases must consist of tiny, individual particles that are in constant, random motion. He researched the properties of compounds, which are substances that consist of more than one element. He showed that a given compound is always comprised of the same elements in the same whole-number ratio and that different compounds consist of different elements or ratios. This can happen, Dalton reasoned, only if elements are made of separate, discrete particles that cannot be subdivided. ",text,
L_0851,daltons atomic theory,T_4293,"From his research, Dalton developed a theory about atoms. Daltons atomic theory consists of three basic ideas: All substances are made of atoms. Atoms are the smallest particles of matter. They cannot be divided into smaller particles, created, or destroyed. All atoms of the same element are alike and have the same mass. Atoms of different elements are different and have different masses. Atoms join together to form compounds, and a given compound always consists of the same kinds of atoms in the same proportions. Daltons atomic theory was accepted by many scientists almost immediately. Most of it is still accepted today. However, scientists now know that atoms are not the smallest particles of matter. Atoms consist of several types of smaller particles, including protons, neutrons, and electrons. ",text,
L_0851,daltons atomic theory,T_4294,"Because Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. Three of his model atoms are pictured in the Figure and used to model compounds. Q: When scientists discovered smaller particles inside the atom, they realized that Daltons atomic models were too simple. How do modern atomic models differ from Daltons models? A: Modern atomic models, like the one pictured at the top of this article, usually represent subatomic particles, including electrons, protons, and neutrons. ",text,
L_0852,dangers and uses of radiation,T_4295,"A low level of radiation occurs naturally in the environment. This is called background radiation. One source of background radiation is rocks, which may contain small amounts of radioactive elements such as uranium. Another source is cosmic rays. These are charged particles that arrive on Earth from outer space. Background radiation is generally considered to be safe for living things. ",text,
L_0852,dangers and uses of radiation,T_4296,"Long-term or high-dose exposure to radiation can harm both living and nonliving things. Radiation knocks electrons out of atoms and changes them to ions. It also breaks bonds in DNA and other compounds in living things. One source of radiation that is especially dangerous to people is radon. Radon is a radioactive gas that forms in rocks underground. It can seep into basements and get trapped inside buildings. Then it may build up and become harmful to people who breathe it. Long-term exposure to radon can cause lung cancer. Exposure to higher levels of radiation can be very dangerous, even if the exposure is short-term. A single large dose of radiation can burn the skin and cause radiation sickness. Symptoms of this illness include extreme fatigue, destruction of blood cells, and loss of hair. Nonliving things can also be damaged by radiation. For example, high levels of radiation can weaken metals by removing electrons. This is a problem in nuclear power plants and space vehicles because they are exposed to very high levels of radiation. Q: Can you tell when you are being exposed to radiation? For example, can you sense radon in the air? A: Radiation cant be detected with the senses. This adds to its danger. However, there are other ways to detect it. ",text,
L_0852,dangers and uses of radiation,T_4297,"You generally cant see, smell, taste, hear, or feel radiation. Fortunately, there are devices such as Geiger counters that can detect radiation. A Geiger counter, like the one pictured in the Figure 1.1, contains atoms of a gas that is ionized if it encounters radiation. When this happens, the gas atoms change to ions that can carry an electric current. The current causes the Geiger counter to click. The faster the clicks occur, the higher the level of radiation. ",text,
L_0852,dangers and uses of radiation,T_4298,"Despite its dangers, radioactivity has several uses. For example, it can be used to determine the ages of ancient rocks and fossils. It can also be used as a source of power to generate electricity. Radioactivity can even be used to diagnose and treat diseases, including cancer. Cancer cells grow rapidly and take up a lot of glucose for energy. Glucose containing radioactive elements can be given to patients. Cancer cells take up more of the glucose than normal cells do and give off radiation. The radiation can be detected with special machines like the one in the Figure 1.2. The radiation may also kill cancer cells. ",text,
L_0853,decomposition reactions,T_4299,"A decomposition reaction occurs when one reactant breaks down into two or more products. It can be represented by the general equation: AB  A + B In this equation, AB represents the reactant that begins the reaction, and A and B represent the products of the reaction. The arrow shows the direction in which the reaction occurs. Q: What is the chemical equation for the decomposition of hydrogen peroxide (H2 O2 ) to water (H2 O) and oxygen (O2 )? A: The equation for this decomposition reaction is: 2 H2 O2  2 H2 O + O2 ",text,
L_0853,decomposition reactions,T_4300,"Two more examples of decomposition reactions are described below. Carbonic acid (H2 CO3 ) is an ingredient in soft drinks. A decomposition reaction takes place when carbonic acid breaks down to produce water (H2 O) and carbon dioxide (CO2 ). This occurs when you open a can of soft drink and some of the carbon dioxide fizzes out. The equation for this reaction is: H2 CO3  H2 O + CO2 Another decomposition reaction occurs when water (H2 O) breaks down to produce hydrogen (H2 ) and oxygen (O2 ) gases (see Figure 1.1). This happens when an electric current passes through the water, as illustrated below. The equation for this reaction is: 2 H2 O  2 H2 + O2 Decomposition of water. Q: What ratio of hydrogen molecules (H2 ) to oxygen molecules (O2 ) is produced in the decomposition of water? A: Two hydrogen molecules per oxygen molecule are produced because water (H2 O) has a ratio of two hydrogen atoms to one oxygen atom. ",text,
L_0854,democrituss idea of the atom,T_4301,"Democritus lived in Greece from about 460 to 370 B.C.E. Like many other ancient Greek philosophers, he spent a lot of time wondering about the natural world. Democritus wondered, for example, what would happen if you cut a chunk of mattersuch as a piece of cheese into smaller and smaller pieces. He thought that a point would be reached at which the cheese could not be cut into still smaller pieces. He called these pieces atomos, which means uncuttable in Greek. This is where the modern term atom comes from. ",text,
L_0854,democrituss idea of the atom,T_4302,"Democritus idea of the atom has been called the best guess in antiquity. Thats because it was correct in many ways, yet it was based on pure speculation. It really was just a guess. Heres what Democritus thought about the atom: How many times could you cut this piece of cheese in half? How small would the smallest pieces be? All matter consists of atoms, which cannot be further subdivided into smaller particles. Atoms are extremely smalltoo small to see. Atoms are solid particles that are indestructible. Atoms are separated from one another by emptiness, or void. Q: How are Democrituss ideas about atoms similar to modern ideas about atoms? A: Modern ideas agree that all matter is made up of extremely small building blocks called atoms. Q: How are Democrituss ideas different from modern ideas? A: Although atoms are extremely small, it is now possible to see them with very powerful microscopes. Atoms also arent the solid, uncuttable particles Democritus thought. Instead, they consist of several kinds of smaller, simpler particles as well as a lot of empty space. In addition, atoms arent really indestructible because they can be changed to other forms of matter or energy. ",text,
L_0854,democrituss idea of the atom,T_4303,"Did you ever notice dust motes moving in still air where a beam of sunlight passes through it? You can see an example in the forest scene in the Figure 1.2. This sort of observation gave Democritus the idea that atoms are in constant, random motion. If this were true, Democritus thought, then atoms must always be bumping into each other. When they do, he surmised, they either bounce apart or stick together to form clumps of atoms. Eventually, the clumps could grow big enough to be visible matter. Q: Which modern theory of matter is similar to Democritus ideas about the motion of atoms? A: The modern kinetic theory of matter is remarkably similar to Democritus ideas about the motion of atoms. According to this theory, atoms of matter are in constant random motion. This motion is greater in gases than in liquids, and it is greater in liquids than in solids. But even in solids, atoms are constantly vibrating in place. ",text,
L_0854,democrituss idea of the atom,T_4304,"Democritus thought that different kinds of matter vary because of the size, shape, and arrangement of their atoms. For example, he suggested that sweet substances are made of smooth atoms and bitter substances are made of sharp atoms. He speculated that atoms of liquids are slippery, which allows them to slide over each other and liquids to flow. Atoms of solids, in contrast, stick together, so they cannot move apart. Differences in the weight of matter, he argued, could be explained by the closeness of atoms. Atoms of lighter matter, he thought, were more spread out and separated by more empty space. Q: Democritus thought that different kinds of atoms make up different types of matter. How is this similar to modern ideas about atoms? A: The modern view is that atoms of different elements differ in their numbers of protons and electrons and this gives them different physical and chemical properties. Dust motes dance in a beam of sunlight. ",text,
L_0854,democrituss idea of the atom,T_4305,"Democritus was an important philosopher, but he was less influential than another Greek philosopher named Aristo- tle, who lived about 100 years after Democritus. Aristotle rejected Democritus idea of the atom. In fact, Aristotle thought the idea was ridiculous. Unfortunately, Aristotles opinion was accepted for more than 2000 years, and Democritus idea was more or less forgotten. However, the idea of the atom was revived around 1800 by the English scientist John Dalton. Dalton developed an entire theory about the atom, much of which is still accepted today. He based his theory on experimental evidence, not on lucky guesses. ",text,
L_0857,descriptive statistics,T_4310,"The girls in the picture above make up a small samplethere are only four of them. In scientific investigations, samples may include hundreds or even thousands of people or other objects of study. Especially when samples are very large, its important to be able to summarize their overall characteristics with a few numbers. Thats where descriptive statistics come in. Descriptive statistics are measures that show the central tendency, or center, of a sample or the variation in a sample. ",text,
L_0857,descriptive statistics,T_4311,"The central tendency of a sample can be represented by the mean, median, or mode. The mean is the average value. It is calculated by adding the individual measurements and dividing the sum by the total number of measurements. The median is the middle value. To find the median, rank all the measurements from smallest to largest and then find the measurement that is in the middle. The mode is the most common value. It is the value that occurs most often. Q: A sample of five children have the following heights: 60 cm, 58 cm, 54 cm, 62 cm, and 58 cm. What are the mean, median, and mode of this sample? A: The mean is (60 cm + 58 cm + 54 cm + 62 cm + 58 cm)  5 = 58 cm. The median and mode are both 58 cm as well. The mean, median, and mode are not always the same, as they are for this sample. In fact, sometimes these three statistics are very different from one another for the same sample. ",text,
L_0857,descriptive statistics,T_4312,Many samples have a lot of variation in measurements. Variation can be described with a statistic called the range. The range is the total spread of values in a sample. It is calculated by subtracting the smallest value from the largest value. Q: What is the range of heights in the sample of children in the previous question? A: The range is 62 cm - 54 cm = 8 cm. ,text,
L_0859,direction,T_4315,"Direction can be described in relative terms, such as up, down, in, out, left, right, forward, backward, or sideways. Direction can also be described with the cardinal directions: north, south, east, or west. On maps, cardinal directions are indicated with a compass rose. You can see one in the bottom left corner of the map in the Figure 1.1. You can use the compass rose to find directions on the map. For example, to go to the school from Jordans house, you would travel from east to west. If you wanted to go on to the post office, you would change direction at the school and then travel from south to north. ",text,
L_0859,direction,T_4316,"Look again at the map in the Figure 1.1. The distance from Jordans house to the post office is 3 km. But if Jordan told a friend how to reach the post office from his house, he couldnt just say go 3 kilometers. The friend might end up at the park instead of the post office. Jordan would have to include direction as well as distance. He could say, go west for 2 kilometers and then go north for 1 kilometer. ",text,
L_0859,direction,T_4317,"When both distance and direction are considered, motion can be represented by a vector. A vector is a measurement that has both size and direction. It may be represented by an arrow. If you are representing motion with an arrow, the length of the arrow represents distance, and the way the arrow points represents direction. The red arrows on the map in the Figure 1.1 are vectors for Jordans route from his house to the school and from the school to the post office. Q: How would you draw arrows to represent the distances and directions from the post office to the park on the map in the Figure 1.1? A: The vectors would look like this: ",text,
L_0861,distance,T_4322,"Distance is the length of the route between two points. The distance of a race, for example, is the length of the track between the starting and finishing lines. In a 100-meter sprint, that distance is 100 meters. ",text,
L_0861,distance,T_4323,"The SI unit for distance is the meter (m). Short distances may be measured in centimeters (cm), and long distances may be measured in kilometers (km). For example, you might measure the distance from the bottom to the top of a sheet of paper in centimeters and the distance from your house to your school in kilometers. ",text,
L_0861,distance,T_4324,Maps can often be used to measure distance. The map in the Figure 1.1 shows the route from Jordans house to his school. You can use the scale at the bottom of the map to measure the distance between these two points. Q: What is the distance from Jordans house to his school? A: The distance is 2 kilometers. ,text,
L_0862,doppler effect,T_4325,"The Doppler effect is a change in the frequency of sound waves that occurs when the source of the sound waves is moving relative to a stationary listener. (It can also occur when the sound source is stationary and the listener is moving.) The Figure 1.1 shows how the Doppler effect occurs. The sound waves from the police car siren travel outward in all directions. Because the car is racing forward (to the left), the sound waves get bunched up in front of the car and spread out behind it. Sound waves that are closer together have a higher frequency, and sound waves that are farther apart have a lower frequency. The frequency of sound waves, in turn, determines the pitch of the sound. Sound waves with a higher frequency produce sound with a higher pitch, and sound waves with a lower frequency produce sound with a lower pitch. ",text,
L_0862,doppler effect,T_4326,"As the car approaches listener A, the sound waves get closer together, increasing their frequency. This listener hears the pitch of the siren get higher. As the car speeds away from listener B, the sound waves get farther apart, decreasing their frequency. This listener hears the pitch of the siren get lower. Q: What will the siren sound like to listener A after the police car passes him? A: The siren will suddenly get lower in pitch because the sound waves will be much more spread out and have a lower frequency. ",text,
L_0863,earth as a magnet,T_4327,"Imagine a huge bar magnet passing through Earths axis, as in the Figure 1.1. This is a good representation of Earth as a magnet. Like a bar magnet, Earth has north and south magnetic poles. A magnetic pole is the north or south end of a magnet, where the magnet exerts the most force. ",text,
L_0863,earth as a magnet,T_4328,"Although the needle of a compass always points north, it doesnt point to Earths north geographic pole. Find the north geographic pole in the Figure 1.2. As you can see, it is located at 90 north latitude. Where does a compass Q: The north end of a compass needle points toward Earths north magnetic pole. The like poles of two magnets repel each other, and the opposite poles attract. So why doesnt the north end of a compass needle point to Earths south magnetic pole instead? A: The answer may surprise you. The compass needle actually does point to the south pole of magnet Earth. However, it is called the north magnetic pole because it is close to the north geographic pole. This naming convention was adopted a long time ago to avoid confusion. ",text,
L_0863,earth as a magnet,T_4328,"Although the needle of a compass always points north, it doesnt point to Earths north geographic pole. Find the north geographic pole in the Figure 1.2. As you can see, it is located at 90 north latitude. Where does a compass Q: The north end of a compass needle points toward Earths north magnetic pole. The like poles of two magnets repel each other, and the opposite poles attract. So why doesnt the north end of a compass needle point to Earths south magnetic pole instead? A: The answer may surprise you. The compass needle actually does point to the south pole of magnet Earth. However, it is called the north magnetic pole because it is close to the north geographic pole. This naming convention was adopted a long time ago to avoid confusion. ",text,
L_0863,earth as a magnet,T_4329,"Like all magnets, Earth has a magnetic field. Earths magnetic field is called the magnetosphere. You can see a model of the magnetosphere in the Figure 1.3. It is a huge region that extends outward from Earth in all directions. Earth exerts magnetic force over the entire field, but the force is strongest at the poles, where lines of force converge. Click image to the left or use the URL below. URL: ",text,
L_0864,efficiency,T_4330,"A dolly is a machine because it changes a force to make work easier. What is work? In physics, work is defined as the use of force to move an object over a distance. It is represented by the equation: Work = Force x Distance All machines make work easier, but they dont increase the amount of work that is done. You can never get more work out of a machine than you put into it. In fact, a machine always does less work on an object than the user does on the machine. Thats because a machine must use some of the work put into it to overcome friction. Friction is the force that opposes motion between any surfaces that are touching. All machines involve motion, so they all have friction. How much work is needed to overcome friction in a machine depends on the machines efficiency. ",text,
L_0864,efficiency,T_4331,"Efficiency is the percent of work put into a machine by the user (input work) that becomes work done by the machine (output work). The output work is always less than the input work because some of the input work is used to overcome friction. Therefore, efficiency is always less than 100 percent. The closer to 100 percent a machines efficiency is, the better it is at reducing friction. Look at the ramp in the Figure 1.1. A ramp is a type of simple machine called an inclined plane. It is easier to push the heavy piece of furniture up the ramp to the truck than to lift it straight up off the ground, but pushing the furniture over the surface of the ramp creates a lot of friction. Some of the force applied to moving the furniture must be used to overcome the friction with the ramp. Q: Why would it be more efficient to use a dolly to roll the furniture up the ramp? A: There would be less friction to overcome if you used a dolly because of the wheels. So the efficiency of the ramp would be greater with the dolly. ",text,
L_0864,efficiency,T_4332,"Efficiency can be calculated with the equation: Output work Efficiency = Input work  100% Consider a machine that puts out 6000 joules of work. To produce that much work from the machine requires the user to put in 8000 joules of work. To find the efficiency of the machine, substitute these values into the equation for efficiency: 6000 J 100% = 75% 8000 J Q: Rani puts 7500 joules of work into pushing a box up a ramp, but only 6700 joules of work actually go into moving the box. The rest of the work overcomes friction between the box and the ramp. What is the efficiency of the ramp? A: The efficiency of the ramp is: 6700 J 100% = 90% 7500 J ",text,
L_0865,einsteins concept of gravity,T_4333,"In the late 1600s, Isaac Newton introduced his law of gravity, which identifies gravity as a force of attraction between all objects with mass in the universe. The law also states that the strength of gravity between two objects depends on their mass and distance apart. Newtons law of gravity was accepted for more than two centuries. It can predict the motion of most objects and was even used by NASA to land astronauts on the moon. Its still used for most practical purposes. However, Newtons law doesnt explain why gravity occurs. It only describes how gravity seems to affect objects. There are also some cases in which Newtons law doesnt even describe what happens. Q: Newton expressed his ideas about gravity as a law. A law in science is a description of what always occurs in nature. For example, according to Newtons law, objects on Earth always fall down, not up. What is needed to explain gravity? A: A theory is needed to explain gravity. In science, a theory is a broad explanation that is supported by a great deal of evidence. ",text,
L_0865,einsteins concept of gravity,T_4334,"In the early 1900s, Albert Einstein came up with a theory of gravity that actually explains gravity rather than simply describing its effects. Einstein showed mathematically that gravity is not really a force that of attraction between all objects with mass, as Newton thought. Instead, Einstein showed that gravity is a result of the warping, or curving, of space and time, which made up the same space-time fabric. These ideas about space-time and gravity became known as Einsteins theory of general relativity. ",text,
L_0865,einsteins concept of gravity,T_4335,"Einstein derived his theory using mathematics. However, you can get a good grasp of it with the help of a simple visual analogy. Imagine a bowling ball pressing down on a trampoline. The surface of the trampoline would curve downward instead of being flat. Now imagine placing a lighter ball at the edge of the trampoline. What will happen? It will roll down toward the bowling ball. This apparent attraction to the bowling ball occurs because the trampoline curves downward, not because the two balls are actually attracted to one another by an invisible force called gravity. Einstein theorized that the sun and other very massive bodies affect space and time around them in a way that is similar to the effect of the bowling ball on the trampoline. The more massive a body is, the more it causes space-time to curve. This idea is represented by the Figure 1.1. According to Einstein, objects move toward one another because of the curves in space-time, not because they are pulling on each other with a force of attraction. Einsteins theory is supported by evidence and widely accepted today, although Newtons law is still used for many calculations. ",text,
L_0866,elastic force,T_4336,"Something that is elastic can return to its original shape after being stretched or compressed. This property is called elasticity. As you stretch or compress an elastic material like a bungee cord, it resists the change in shape. It exerts a counter force in the opposite direction. This force is called elastic force. The farther the material is stretched or compressed, the greater the elastic force becomes. As soon as the stretching or compressing force is released, elastic force causes the material to spring back to its original shape. Click image to the left or use the URL below. URL:  Q: What force stretches the bungee cord after the jumper jumps? When does the bungee cord snap back to its original shape? A: After the bungee jumper jumps, he accelerates toward the ground due to gravity. His weight stretches the bungee cord. As the bungee cord stretches, it exerts elastic force upward against the jumper, which slows his descent and brings him to a momentary stop. Then the bungee cord springs back to its original shape, and the jumper bounces upward. ",text,
L_0866,elastic force,T_4337,"Elastic force can be very useful and not just for bungee jumping. In fact, you probably use elastic force every day. A few common uses of elastic force are shown in the Figure 1.1. Do you use elastic force in any of these ways? Q: How does the resistance band work? How does it use elastic force? A: When you pull on the band, it stretches but doesnt break. The resistance you feel when you pull on it is elastic force. The farther you stretch the band, the greater the resistance is. The resistance of the band to stretching is what gives your muscles a workout. After you stop pulling on the band, it returns to its original shape, ready for the next stretch. Springs like the spring toy pictured in the Figure 1.2 also have elastic force when they are stretched or compressed. Q: Can you think of other uses of springs? A: Bedsprings provide springy support beneath a mattress. The spring in a door closer pulls the door shut. The spring in a retractable ballpoint pen retracts the point of the pen. The spring in a pogo stick bounces the rider up off the ground. ",text,
L_0866,elastic force,T_4337,"Elastic force can be very useful and not just for bungee jumping. In fact, you probably use elastic force every day. A few common uses of elastic force are shown in the Figure 1.1. Do you use elastic force in any of these ways? Q: How does the resistance band work? How does it use elastic force? A: When you pull on the band, it stretches but doesnt break. The resistance you feel when you pull on it is elastic force. The farther you stretch the band, the greater the resistance is. The resistance of the band to stretching is what gives your muscles a workout. After you stop pulling on the band, it returns to its original shape, ready for the next stretch. Springs like the spring toy pictured in the Figure 1.2 also have elastic force when they are stretched or compressed. Q: Can you think of other uses of springs? A: Bedsprings provide springy support beneath a mattress. The spring in a door closer pulls the door shut. The spring in a retractable ballpoint pen retracts the point of the pen. The spring in a pogo stick bounces the rider up off the ground. ",text,
L_0881,electromagnetic spectrum,T_4379,"Electromagnetic radiation is energy that travels in waves across space as well as through matter. Most of the electromagnetic radiation on Earth comes from the sun. Like other waves, electromagnetic waves are characterized by certain wavelengths and wave frequencies. Wavelength is the distance between two corresponding points on adjacent waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. Electromagnetic waves with shorter wavelengths have higher frequencies and more energy. ",text,
L_0881,electromagnetic spectrum,T_4380,"Visible light and infrared light are just a small part of the full range of electromagnetic radiation, which is called the electromagnetic spectrum. You can see the waves of the electromagnetic spectrum in the Figure 1.1. At the top of the diagram, the wavelengths of the waves are given. Also included are objects that are about the same size as the corresponding wavelengths. The frequencies and energy levels of the waves are shown at the bottom of the diagram. Some sources of the waves are also given. On the left side of the electromagnetic spectrum diagram are radio waves and microwaves. Radio waves have the longest wavelengths and lowest frequencies of all electromagnetic waves. They also have the least amount of energy. On the right side of the diagram are X rays and gamma rays. They have the shortest wavelengths and highest frequencies of all electromagnetic waves. They also have the most energy. Between these two extremes are waves that are commonly called light. Light includes infrared light, visible light, and ultraviolet light. The wavelengths, frequencies, and energy levels of light fall in between those of radio waves on the left and X rays and gamma rays on the right. Q: Which type of light has the longest wavelengths? A: Infrared light has the longest wavelengths. Q: What sources of infrared light are shown in the diagram? A: The sources in the diagram are people and light bulbs, but all living things and most other objects give off infrared light. ",text,
L_0882,electromagnetic waves,T_4381,"Electromagnetic waves are waves that consist of vibrating electric and magnetic fields. Like other waves, electro- magnetic waves transfer energy from one place to another. The transfer of energy by electromagnetic waves is called electromagnetic radiation. Electromagnetic waves can transfer energy through matter or across empty space. Click image to the left or use the URL below. URL:  Q: How do microwaves transfer energy inside a microwave oven? A: They transfer energy through the air inside the oven to the food. ",text,
L_0882,electromagnetic waves,T_4382,"A familiar example may help you understand the vibrating electric and magnetic fields that make up electromagnetic waves. Consider a bar magnet, like the one in the Figure 1.1. The magnet exerts magnetic force over an area all around it. This area is called a magnetic field. The field lines in the diagram represent the direction and location of the magnetic force. Because of the field surrounding a magnet, it can exert force on objects without touching them. They just have to be within its magnetic field. Q: How could you demonstrate that a magnet can exert force on objects without touching them? A: You could put small objects containing iron, such as paper clips, near a magnet and show that they move toward the magnet. An electric field is similar to a magnetic field. It is an area of electrical force surrounding a positively or negatively charged particle. You can see electric fields in the following Figure 1.2. Like a magnetic field, an electric field can exert force on objects over a distance without actually touching them. ",text,
L_0882,electromagnetic waves,T_4383,"An electromagnetic wave begins when an electrically charged particle vibrates. The Figure 1.3 shows how this happens. A vibrating charged particle causes the electric field surrounding it to vibrate as well. A vibrating electric field, in turn, creates a vibrating magnetic field. The two types of vibrating fields combine to create an electromagnetic wave. ",text,
L_0882,electromagnetic waves,T_4383,"An electromagnetic wave begins when an electrically charged particle vibrates. The Figure 1.3 shows how this happens. A vibrating charged particle causes the electric field surrounding it to vibrate as well. A vibrating electric field, in turn, creates a vibrating magnetic field. The two types of vibrating fields combine to create an electromagnetic wave. ",text,
L_0882,electromagnetic waves,T_4384,"As you can see in the Figure 1.3, the electric and magnetic fields that make up an electromagnetic wave are perpendicular (at right angles) to each other. Both fields are also perpendicular to the direction that the wave travels. Therefore, an electromagnetic wave is a transverse wave. However, unlike a mechanical transverse wave, which can only travel through matter, an electromagnetic transverse wave can travel through empty space. When waves travel through matter, they lose some energy to the matter as they pass through it. But when waves travel through space, no energy is lost. Therefore, electromagnetic waves dont get weaker as they travel. However, the energy is diluted as it travels farther from its source because it spreads out over an ever-larger area. ",text,
L_0882,electromagnetic waves,T_4385,"When electromagnetic waves strike matter, they may interact with it in the same ways that mechanical waves interact with matter. Electromagnetic waves may: reflect, or bounce back from a surface; refract, or bend when entering a new medium; diffract, or spread out around obstacles. Electromagnetic waves may also be absorbed by matter and converted to other forms of energy. Microwaves are a familiar example. When microwaves strike food in a microwave oven, they are absorbed and converted to thermal energy, which heats the food. ",text,
L_0882,electromagnetic waves,T_4386,"The most important source of electromagnetic waves on Earth is the sun. Electromagnetic waves travel from the sun to Earth across space and provide virtually all the energy that supports life on our planet. Many other sources of electromagnetic waves depend on technology. Radio waves, microwaves, and X rays are examples. We use these electromagnetic waves for communications, cooking, medicine, and many other purposes. ",text,
L_0884,electron cloud atomic model,T_4390,"Up until about 1920, scientists accepted Niels Bohrs model of the atom. In this model, negative electrons circle the positive nucleus at fixed distances from the nucleus, called energy levels. You can see the model in Figure 1.1 for an atom of the element nitrogen. Bohrs model is useful for understanding properties of elements and their chemical interactions. However, it doesnt explain certain behaviors of electrons, except for those in the simplest atom, the hydrogen atom. ",text,
L_0884,electron cloud atomic model,T_4391,"In the mid-1920s, an Austrian scientist named Erwin Schrdinger thought that the problem with Bohrs model was restricting the electrons to specific orbits. He wondered if electrons might behave like light, which scientists already knew had properties of both particles and waves. Schrdinger speculated that electrons might also travel in waves. Q: How do you pin down the location of an electron in a wave? A: You cant specify the exact location of an electron. However, Schrdinger showed that you can at least determine where an electron is most likely to be. Schrdinger developed an equation that could be used to calculate the chances of an electron being in any given place around the nucleus. Based on his calculations, he identified regions around the nucleus where electrons are most likely to be. He called these regions orbitals. As you can see in the Figure 1.2, orbitals may be shaped like spheres, dumbbells, or rings. In each case, the nucleus of the atom is at the center of the orbital. ",text,
L_0884,electron cloud atomic model,T_4391,"In the mid-1920s, an Austrian scientist named Erwin Schrdinger thought that the problem with Bohrs model was restricting the electrons to specific orbits. He wondered if electrons might behave like light, which scientists already knew had properties of both particles and waves. Schrdinger speculated that electrons might also travel in waves. Q: How do you pin down the location of an electron in a wave? A: You cant specify the exact location of an electron. However, Schrdinger showed that you can at least determine where an electron is most likely to be. Schrdinger developed an equation that could be used to calculate the chances of an electron being in any given place around the nucleus. Based on his calculations, he identified regions around the nucleus where electrons are most likely to be. He called these regions orbitals. As you can see in the Figure 1.2, orbitals may be shaped like spheres, dumbbells, or rings. In each case, the nucleus of the atom is at the center of the orbital. ",text,
L_0884,electron cloud atomic model,T_4392,"Schrdingers work on orbitals is the basis of the modern model of the atom, which scientists call the quantum mechanical model. The modern model is also commonly called the electron cloud model. Thats because each orbital around the nucleus of the atom resembles a fuzzy cloud around the nucleus, like the ones shown in the Figure 1.3 for a helium atom. The densest area of the cloud is where the electrons have the greatest chances of being. Q: In the model pictured in the Figure 1.3, where are the two helium electrons most likely to be? A: The two electrons are most likely to be inside the sphere closest to the nucleus where the cloud is darkest. ",text,
L_0888,electrons,T_4403,"Electrons are one of three main types of particles that make up atoms. The other two types are protons and neutrons. Unlike protons and neutrons, which consist of smaller, simpler particles, electrons are fundamental particles that do not consist of smaller particles. They are a type of fundamental particles called leptons. All leptons have an electric charge of -1 or 0. Click image to the left or use the URL below. URL: ",text,
L_0888,electrons,T_4404,"Electrons are extremely small. The mass of an electron is only about 1/2000 the mass of a proton or neutron, so electrons contribute virtually nothing to the total mass of an atom. Electrons have an electric charge of -1, which is equal but opposite to the charge of proton, which is +1. All atoms have the same number of electrons as protons, so the positive and negative charges cancel out, making atoms electrically neutral. ",text,
L_0888,electrons,T_4405,"Unlike protons and neutrons, which are located inside the nucleus at the center of the atom, electrons are found outside the nucleus. Because opposite electric charges attract each other, negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving through the otherwise empty space around the nucleus. The Figure shown 1.1 is a common way to represent the structure of an atom. It shows the electron as a particle orbiting the nucleus, similar to the way that planets orbit the sun. ",text,
L_0888,electrons,T_4406,"The atomic model above is useful for some purposes, but its too simple when it comes to the location of electrons. In reality, its impossible to say what path an electron will follow. Instead, its only possible to describe the chances of finding an electron in a certain region around the nucleus. The region where an electron is most likely to be is called an orbital. Each orbital can have at most two electrons. Some orbitals, called S orbitals, are shaped like spheres, with the nucleus in the center. An S orbital is pictured in Figure 1.2. Where the dots are denser, the chance of finding an electron is greater. Also pictured in Figure 1.2 is a P orbital. P orbitals are shaped like dumbbells, with the nucleus in the pinched part of the dumbbell. Click image to the left or use the URL below. URL:  Q: How many electrons can there be in each type of orbital shown above? A: There can be a maximum of two electrons in any orbital, regardless of its shape. Q: Where is the nucleus in each orbital? A: The nucleus is at the center of each orbital. It is in the middle of the sphere in the S orbital and in the pinched part of the P orbital. ",text,
L_0888,electrons,T_4407,"Electrons are located at fixed distances from the nucleus, called energy levels. You can see the first three energy levels in the Figure 1.3. The diagram also shows the maximum possible number of electrons at each energy level. Electrons at lower energy levels, which are closer to the nucleus, have less energy. At the lowest energy level, which has the least energy, there is just one orbital, so this energy level has a maximum of two electrons. Only when a lower energy level is full are electrons added to the next higher energy level. Electrons at higher energy levels, which are farther from the nucleus, have more energy. They also have more orbitals and greater possible numbers of electrons. Electrons at the outermost energy level of an atom are called valence electrons. They determine many of the properties of an element. Thats because these electrons are involved in chemical reactions with other atoms. Atoms may share or transfer valence electrons. Shared electrons bind atoms together to form chemical compounds. Q: If an atom has 12 electrons, how will they be distributed in energy levels? A: The atom will have two electrons at the first energy level, eight at the second energy level, and the remaining two at the third energy level. Q: Sometimes, an electron jumps from one energy level to another. How do you think this happens? A: To change energy levels, an electron must either gain or lose energy. Thats because electrons at higher energy levels have more energy than electrons at lower energy levels. ",text,
L_0889,elements,T_4408,"A pure substance is called an element. An element is a pure substance because it cannot be separated into any other substances. Currently, 92 different elements are known to exist in nature, although additional elements have been formed in labs. All matter consists of one or more of these elements. Some elements are very common; others are relatively rare. The most common element in the universe is hydrogen, which is part of Earths atmosphere and a component of water. The most common element in Earths atmosphere is nitrogen, and the most common element in Earths crust is oxygen. Click image to the left or use the URL below. URL: ",text,
L_0889,elements,T_4409,"Each element has a unique set of properties that is different from the set of properties of any other element. For example, the element iron is a solid that is attracted by a magnet and can be made into a magnet, like the compass needle shown in the Figure 1.1. The element neon, on the other hand, is a gas that gives off a red glow when electricity flows through it. The lighted sign in the Figure 1.2 contains neon. The needle of this compass is made of the element iron. Q: Do you know properties of any other elements? For example, what do you know about helium? A: Helium is a gas that has a lower density than air. Thats why helium balloons have to be weighted down so they wont float away. Q: Living things, like all matter, are made of elements. Do you know which element is most common in living things? A: Carbon is the most common element in living things. It has the unique property of being able to combine with many other elements as well as with itself. This allows carbon to form a huge number of different substances. ",text,
L_0889,elements,T_4410,"For thousands of years, people have wondered about the substances that make up matter. About 2500 years ago, the Greek philosopher Aristotle argued that all matter is made up of just four elements, which he identified as earth, air, water, and fire. He thought that different substances vary in their properties because they contain different proportions of these four elements. Aristotle had the right idea, but he was wrong about which substances are elements. Nonetheless, his four elements were accepted until just a few hundred years ago. Then scientists started discovering many of the elements with which we are familiar today. Eventually they discovered dozens of different elements. ",text,
L_0889,elements,T_4411,"The smallest particle of an element that still has the properties of that element is the atom. Atoms actually consist of smaller particles, including protons and electrons, but these smaller particles are the same for all elements. All the atoms of an element are like one another, and are different from the atoms of all other elements. For example, the atoms of each element have a unique number of protons. Consider carbon as an example. Carbon atoms have six protons. They also have six electrons. All carbon atoms are the same whether they are found in a lump of coal or a teaspoon of table sugar (Figure 1.3). On the other hand, carbon atoms are different from the atoms of hydrogen, which are also found in coal and sugar. Each hydrogen atom has just one proton and one electron. Carbon is the main element in coal (left). Carbon is also a major component of sugar (right). Q: Why do you think coal and sugar are so different from one another when carbon is a major component of each A: Coal and sugar differ from one another because they contain different proportions of carbon and other elements. For example, coal is about 85 percent carbon, whereas table sugar is about 42 percent carbon. Both coal and sugar also contain the elements hydrogen and oxygen but in different proportions. In addition, coal contains the elements nitrogen and sulfur. ",text,
L_0890,endothermic reactions,T_4412,"All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In some chemical reactions, called exothermic reactions, more energy is released when new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of endothermic reactions. In an endothermic reaction, it takes more energy to break bonds in the reactants than is released when new bonds form in the products. ",text,
L_0890,endothermic reactions,T_4413,"The word endothermic literally means taking in heat. A constant input of energy, often in the form of heat, is needed to keep an endothermic reaction going. This is illustrated in the Figure 1.1. Energy must be constantly added because not enough energy is released when the products form to break more bonds in the reactants. The general equation for an endothermic reaction is: Reactants + Energy  Products Note: H represents the change in en- ergy. In endothermic reactions, the temperature of the products is typically lower than the temperature of the reactants. The drop in temperature may be great enough to cause liquids to freeze. Q: Now can you guess how an instant cold pack works? A: Squeezing the cold pack breaks an inner bag of water, and the water mixes with a chemical inside the pack. The chemical and water combine in an endothermic reaction. The energy needed for the reaction to take place comes from the water, which gets colder as the reaction proceeds. ",text,
L_0890,endothermic reactions,T_4414,"One of the most important series of endothermic reactions is photosynthesis. In photosynthesis, plants make the simple sugar glucose (C6 H12 O6 ) from carbon dioxide (CO2 ) and water (H2 O). They also release oxygen (O2 ) in the process. The reactions of photosynthesis are summed up by this chemical equation: 6 CO2 + 6 H2 O  C6 H12 O6 + 6 O2 The energy for photosynthesis comes from light. Without light energy, photosynthesis cannot occur. As you can see in the Figure 1.2, plants can get the energy they need for photosynthesis from either sunlight or artificial light. ",text,
L_0891,energy,T_4415,"Energy is defined in science as the ability to move matter or change matter in some other way. Energy can also be defined as the ability to do work, which means using force to move an object over a distance. When work is done, energy is transferred from one object to another. For example, when the boy in the Figure 1.1 uses force to swing the racket, he transfers some of his energy to the racket. Q: It takes energy to play tennis. Where does this boy get his energy? A: He gets energy from the food he eats. ",text,
L_0891,energy,T_4416,"Because energy is the ability to do work, it is expressed in the same unit that is used for work. The SI unit for both work and energy is the joule (J), or Newton  meter (N  m). One joule is the amount of energy needed to apply a force of 1 Newton over a distance of 1 meter. For example, suppose the boy in the Figure 1.1 applies 20 Newtons of force to his tennis racket over a distance of 1 meter. The energy needed to do this work is 20 N m, or 20 J. ",text,
L_0891,energy,T_4417,"If you think about different sources of energysuch as batteries and the sunyou probably realize that energy can take different forms. For example, when the boy swings his tennis racket, the energy of the moving racket is an example of mechanical energy. To move his racket, the boy needs energy stored in food, which is an example of chemical energy. Other forms of energy include electrical, thermal, light, and sound energy. The different forms of energy can also be classified as either kinetic energy or potential energy. Kinetic energy is the energy of moving matter. Potential energy is energy that is stored in matter. Q: Is the chemical energy in food kinetic energy or potential energy? A: The chemical energy in food is potential energy. It is stored in the chemical bonds that make up food molecules. The stored energy is released when we digest food. Then we can use it for many purposes, such as moving (mechanical energy) or staying warm (thermal energy). Q: What is an example of kinetic energy? A: Anything that is moving has kinetic energy. An example is a moving tennis racket. ",text,
L_0892,energy conversion,T_4418,"Gravity is a force, but not like other forces you may know. Gravity is a bit special. You know that a force is a push or pull. If you push a ball, it starts to roll. If you lift a book, it moves upward. Now, imagine you drop a ball. It falls to the ground. Can you see the force pulling it down? That is what makes gravity really cool. It is invisible. Invisible means you cannot see it. But wait, it has even more surprises. Gravity holds planets in place around the Sun. Gravity keeps the Moon from flying off into space. Gravity exerts a force on objects that are not even touching. In fact, gravity can act over very large distances. However, the force does get weaker the farther apart the objects are. ",text,
L_0892,energy conversion,T_4419,"You are already very familiar with Earths gravity. It constantly pulls you toward Earths center. What might happen if there was no gravity? You know that the Earth is rotating on its axis. This motion causes our day and night cycle. The Earth also orbits the Sun. All this motion may cause you to fly off the Earth! You can thank gravity for keeping you in place. Gravity keeps us firmly down on the ground. Gravity also pulls on objects that are in the sky. It also pulls on objects that are in space. Meteors and skydivers are pulled down by gravity. Gravity also keeps the moon orbiting the Earth. Without gravity, the moon would float away. It also holds artificial satellites in their orbit. Many of these satellites help to connect the world. They allow you to pick up a phone a call in many parts of the world. You can also thank gravity for all your TV channels. Gravity keeps Earth and the other planets moving around the much more massive Sun. ",text,
L_0892,energy conversion,T_4420,"""What goes up must come down."" You have probably heard that statement before. At one time this statement was true, but no longer. Since the 1960s, we have sent many spacecraft into space. Some are still traveling away from Earth. So it is possible to overcome gravity. Do you need a giant rocket to overcome gravity? No, you actually overcome gravity every day. Think about when you climb a set of stairs. When you do, you are overcoming gravity. What if you jump on a trampoline? You are overcoming gravity for a few seconds. Everyone can overcome gravity. You just need to apply a force larger than gravity. Think about that the next time you jump into the air. You are overcoming gravity for a brief second. Enjoy it while it lasts. Eventually, gravity will win the battle. ",text,
L_0892,energy conversion,T_4421,1. What is the traditional definition of gravity? 2. Identify factors that influence the strength of gravity between two objects. ,text,
L_0892,energy conversion,T_4422,"By clicking a link below, you will leave the CK-12 site and open an external site in a new tab. This page will remain open in the original tab. ",text,
L_0893,energy level,T_4423,"Energy levels (also called electron shells) are fixed distances from the nucleus of an atom where electrons may be found. Electrons are tiny, negatively charged particles in an atom that move around the positive nucleus at the center. Energy levels are a little like the steps of a staircase. You can stand on one step or another but not in between the steps. The same goes for electrons. They can occupy one energy level or another but not the space between energy levels. The model in the Figure 1.1 shows the first four energy levels of an atom. Electrons in energy level I (also called energy level K) have the least amount of energy. As you go farther from the nucleus, electrons at higher levels have more energy, and their energy increases by a fixed, discrete amount. Electrons can jump from a lower to the next higher energy level if they absorb this amount of energy. Conversely, if electrons jump from a higher to a lower energy level, they give off energy, often in the form of light. This explains the fireworks pictured above. When the fireworks explode, electrons gain energy and jump to higher energy levels. When they jump back to their original energy levels, they release the energy as light. Different atoms have different arrangements of electrons, so they give off light of different colors. Q: In the atomic model Figure 1.1, where would you find electrons that have the most energy? A: Electrons with the most energy would be found in energy level IV. ",text,
L_0893,energy level,T_4424,"The smallest atoms are hydrogen atoms. They have just one electron orbiting the nucleus. That one electron is in the first energy level. Bigger atoms have more electrons. Electrons are always added to the lowest energy level first until it has the maximum number of electrons possible. Then electrons are added to the next higher energy level until that level is full, and so on. How many electrons can a given energy level hold? The maximum numbers of electrons possible for the first four energy levels are shown in the Figure 1.1. For example, energy level I can hold a maximum of two electrons, and energy level II can hold a maximum of eight electrons. The maximum number depends on the number of orbitals at a given energy level. An orbital is a volume of space within an atom where an electron is most likely to be found. As you can see by the images in the Figure 1.2, some orbitals are shaped like spheres (S orbitals) and some are shaped like dumbbells (P orbitals). There are other types of orbitals as well. Regardless of its shape, each orbital can hold a maximum of two electrons. Energy level I has just one orbital, so two electrons will fill this energy level. Energy level II has four orbitals, so it takes eight electrons to fill this energy level. Q: Energy level III can hold a maximum of 18 electrons. How many orbitals does this energy level have? A: At two electrons per orbital, this energy level must have nine orbitals. ",text,
L_0893,energy level,T_4425,"Electrons in the outermost energy level of an atom have a special significance. These electrons are called valence electrons, and they determine many of the properties of an atom. An atom is most stable if its outermost energy level contains as many electrons as it can hold. For example, helium has two electrons, both in the first energy level. This energy level can hold only two electrons, so heliums only energy level is full. This makes helium a very stable element. In other words, its atoms are unlikely to react with other atoms. Consider the elements fluorine and lithium, modeled in the Figure 1.3. Fluorine has seven of eight possible electrons in its outermost energy level, which is energy level II. It would be more stable if it had one more electron because this would fill its outermost energy level. Lithium, on the other hand, has just one of eight possible electrons in its outermost energy level (also energy level II). It would be more stable if it had one less electron because it would have a full outer energy level (now energy level I). Both fluorine and lithium are highly reactive elements because of their number of valence electrons. Fluorine will readily gain one electron and lithium will just as readily give up one electron to become more stable. In fact, lithium and fluorine will react together as shown in the Figure 1.4. When the two elements react, lithium transfers its one extra electron to fluorine. Q: A neon atom has ten electrons. How many electrons does it have in its outermost energy level? How stable do you think a neon atom is? A: A neon atom has two electrons in energy level I and its remaining eight electrons in energy level II, which can ",text,
L_0893,energy level,T_4425,"Electrons in the outermost energy level of an atom have a special significance. These electrons are called valence electrons, and they determine many of the properties of an atom. An atom is most stable if its outermost energy level contains as many electrons as it can hold. For example, helium has two electrons, both in the first energy level. This energy level can hold only two electrons, so heliums only energy level is full. This makes helium a very stable element. In other words, its atoms are unlikely to react with other atoms. Consider the elements fluorine and lithium, modeled in the Figure 1.3. Fluorine has seven of eight possible electrons in its outermost energy level, which is energy level II. It would be more stable if it had one more electron because this would fill its outermost energy level. Lithium, on the other hand, has just one of eight possible electrons in its outermost energy level (also energy level II). It would be more stable if it had one less electron because it would have a full outer energy level (now energy level I). Both fluorine and lithium are highly reactive elements because of their number of valence electrons. Fluorine will readily gain one electron and lithium will just as readily give up one electron to become more stable. In fact, lithium and fluorine will react together as shown in the Figure 1.4. When the two elements react, lithium transfers its one extra electron to fluorine. Q: A neon atom has ten electrons. How many electrons does it have in its outermost energy level? How stable do you think a neon atom is? A: A neon atom has two electrons in energy level I and its remaining eight electrons in energy level II, which can ",text,
L_0894,enzymes as catalysts,T_4426,"Chemical reactions constantly occur inside the cells of living things. However, under the conditions inside cells, most biochemical reactions would occur too slowly to maintain life. Thats where enzymes come in. Enzymes are catalysts in living things. Like other catalysts, they speed up chemical reactions. Enzymes are proteins that are synthesized in the cells that need them, based on instructions encoded in the cells DNA. ",text,
L_0894,enzymes as catalysts,T_4427,"Enzymes increase the rate of chemical reactions by reducing the amount of activation energy needed for reactants to start reacting. One way this can happen is modeled in the Figure 1.1. Enzymes arent changed or used up in the reactions they catalyze, so they can be used to speed up the same reaction over and over again. Each enzyme is highly specific for the particular reaction is catalyzes, so enzymes are very effective. A reaction that would take many years to occur without its enzyme might occur in a split second with the enzyme. Enzymes are also very efficient, so waste products rarely form. Q: This model of enzyme action is called the lock-and-key model. Explain why. A: The substrates (reactants) fit precisely into the active site of the enzyme like a key into a lock. Being brought together in the enzyme in this way helps the reactants react more easily. After the product is formed, it is released by the enzyme. The enzyme is now ready to pick up more reactants and catalyze another reaction. Click image to the left or use the URL below. URL: ",text,
L_0894,enzymes as catalysts,T_4428,More than 1000 different enzymes are necessary for human life. Many enzymes are needed for the digestion of food. Two examples are amylase and pepsin. Both are described in the Figure 1.2. ,text,
L_0897,exothermic reactions,T_4435,"All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In some chemical reactions, called endothermic reactions, less energy is released when new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of exothermic reactions. In an exothermic reaction, it takes less energy to break bonds in the reactants than is released when new bonds form in the products. ",text,
L_0897,exothermic reactions,T_4436,"The word exothermic means releasing heat. Energy, often in the form of heat, is released as an exothermic reaction proceeds. This is illustrated in the Figure 1.1. The general equation for an exothermic reaction is: Reactants  Products + Energy If the energy produced in an exothermic reaction is released as heat, it results in a rise in temperature. As a result, the products are likely to be warmer than the reactants. Note: H represents the change in en- ergy. Q: You turn on the hot water faucet, and hot water pours out. How does the water get hot? Do you think that an exothermic reaction might be involved? A: A hot water heater increases the temperature of water in most homes. Many hot water heaters burn a fuel such as natural gas. The burning fuel causes the water to get hot because combustion is an exothermic reaction. ",text,
L_0897,exothermic reactions,T_4437,"All combustion reactions are exothermic reactions. During a combustion reaction, a substance burns as it combines with oxygen. When substances burn, they usually give off energy as heat and light. Look at the big bonfire in the Figure 1.2. The combustion of wood is an exothermic reaction that releases a lot of energy as heat and light. You can see the light energy the fire is giving off. If you were standing near the fire, you would also feel its heat. ",text,
L_0898,external combustion engines,T_4438,A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the thermal energy to do work. There are two types of combustion engines: external and internal. A steam engine is an external combustion engine. ,text,
L_0898,external combustion engines,T_4439,"An external combustion engine burns fuel externally, or outside the engine. The burning fuel releases thermal energy, which is used to heat water and change it to steam. The pressure of the steam moves a piston back and forth inside a cylinder. The kinetic energy of the moving piston can be used to turn a vehicles wheels, a turbine, or other mechanical device. The Figure 1.1 explains in greater detail how this type of engine works. Q: What type of energy does the piston have when it moves back and forth inside the cylinder? A: Like anything else that is moving, the moving piston has kinetic energy. ",text,
L_0899,ferromagnetic material,T_4440,"Magnetism is the ability of a material to be attracted by a magnet and to act as a magnet. Magnetism is due to the movement of electrons within atoms of matter. When electrons spin around the nucleus of an atom, it causes the atom to become a tiny magnet, with north and south poles and a magnetic field. In most materials, the north and south poles of atoms point in all different directions, so overall the material is not magnetic. Examples of nonmagnetic materials include wood, glass, plastic, paper, copper, and aluminum. These materials are not attracted to magnets and cannot become magnets. In other materials, there are regions where the north and south poles of atoms are all lined up in the same direction. These regions are called magnetic domains. Generally, the magnetic domains point in different directions, so the material is still not magnetic. However, the material can be magnetized (made into a magnet) by placing it in a magnetic field. When this happens, all the magnetic domains line up, and the material becomes a magnet. You can see this in the Figure 1.1. Materials that can be magnitized are called ferromagnetic materials. They include iron, cobalt, and nickel. ",text,
L_0899,ferromagnetic material,T_4441,"Materials that have been magnetized may become temporary or permanent magnets. If you bring a bar magnet close to pile of paper clips, the paper clips will become temporarily magnetized, as all their magnetic domains line up. As a result, the paper clips will stick to the magnet and also to each other (see the Figure 1.2). However, if you remove the paper clips from the bar magnets magnetic field, their magnetic domains will no longer align. As a result, the paper clips will no longer be magnetized or stick together. If you stroke an iron nail with a bar magnet, the nail will become a permanent (or at least long-lasting) magnet. You can see how its done in the Figure 1.3. The nails magnetic domains will remain aligned even after you remove the nail from the magnetic field of the bar magnet. Q: Even permanent magnets can be demagnetized if they are dropped or heated to high temperatures. Can you explain why? ",text,
L_0899,ferromagnetic material,T_4441,"Materials that have been magnetized may become temporary or permanent magnets. If you bring a bar magnet close to pile of paper clips, the paper clips will become temporarily magnetized, as all their magnetic domains line up. As a result, the paper clips will stick to the magnet and also to each other (see the Figure 1.2). However, if you remove the paper clips from the bar magnets magnetic field, their magnetic domains will no longer align. As a result, the paper clips will no longer be magnetized or stick together. If you stroke an iron nail with a bar magnet, the nail will become a permanent (or at least long-lasting) magnet. You can see how its done in the Figure 1.3. The nails magnetic domains will remain aligned even after you remove the nail from the magnetic field of the bar magnet. Q: Even permanent magnets can be demagnetized if they are dropped or heated to high temperatures. Can you explain why? ",text,
L_0899,ferromagnetic material,T_4442,"Some materials are natural permanent magnets. The most magnetic material in nature is the mineral magnetite, also called lodestone (see Figure 1.4). The magnetic domains of magnetite naturally align with Earths axis. The picture on the left shows a chunk of magnetite attracting small bits of iron. The magnetite spoon compass shown on the right dates back about 2000 years and comes from China. The handle of the spoon always points north. Clearly, the magnetic properties of magnetite have been recognized for thousands of years. ",text,
L_0901,force,T_4445,"Force is defined as a push or pull acting on an object. There are several fundamental forces in the universe, including the force of gravity, electromagnetic force, and weak and strong nuclear forces. When it comes to the motion of everyday objects, however, the forces of interest include mainly gravity, friction, and applied force. Applied force is force that a person or thing applies to an object. Q: What forces act on Carsons scooter? A: Gravity, friction, and applied forces all act on Carsons scooter. Gravity keeps pulling both Carson and the scooter toward the ground. Friction between the wheels of the scooter and the ground prevent the scooter from sliding but also slow it down. In addition, Carson applies forces to his scooter to control its speed and direction. ",text,
L_0901,force,T_4446,"Forces cause all motions. Everytime the motion of an object changes, its because a force has been applied to it. Force can cause a stationary object to start moving or a moving object to change its speed or direction or both. A change in the speed or direction of an object is called acceleration. Look at Carsons brother Colton in the Figure starts the scooter moving in the opposite direction. The harder he pushes against the ground, the faster the scooter will go. How much an object accelerates when a force is applied to it depends not only on the strength of the force but also on the objects mass. For example, a heavier scooter would be harder to accelerate. Colton would have to push with more force to start it moving and move it faster. Q: What units do you think are used to measure force? A: The SI unit for force is the Newton (N). A Newton is the force needed to cause a mass of 1 kilogram to accelerate at 1 m/s2 , so a Newton equals 1 kg  m/s2 . The Newton was named for the scientist Sir Isaac Newton, who is famous for his laws of motion and gravity. ",text,
L_0901,force,T_4447,"Force is a vector, or a measure that has both size and direction. For example, Colton pushes on the ground in the opposite direction that the scooter moves, so thats the direction of the force he is applies. He can give the scooter a strong push or a weak push. Thats the size of the force. Like other vectors, a force can be represented with an arrow. You can see some examples in the Figure 1.2. The length of each arrow represents the strength of the force, and the way the arrow points represents the direction of the force. Q: How could you use arrows to represent the forces that start Coltons scooter moving? A: Colton pushes against the ground behind him (to the right in the Figure 1.1). The ground pushes back with equal force to the left, causing the scooter to move in that direction. Force arrows A and B in example 2 in the Figure 1.1) could represent these forces. ",text,
L_0902,forms of energy,T_4448,"Energy, or the ability to cause changes in matter, can exist in many different forms. Energy can also change from one form to another. The photo above of the guitar player represents six forms of energy: mechanical, chemical, electrical, light, thermal, and sound energy. Another form of energy is nuclear energy. Q: Can you find the six different forms of energy in the photo of the guitar player (See opening image)? A: The guitarist uses mechanical energy to pluck the strings of the guitar. He gets the energy he needs to perform from chemical energy in food he ate earlier in the day. The stage lights use electrical energy, which they change to light energy and thermal energy (commonly called heat). The guitar produces sound energy when the guitarist plucks the strings. ",text,
L_0902,forms of energy,T_4449,"The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. ",text,
L_0902,forms of energy,T_4449,"The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. ",text,
L_0902,forms of energy,T_4449,"The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. ",text,
L_0902,forms of energy,T_4449,"The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. ",text,
L_0904,frequency and pitch of sound,T_4452,"How high or low a sound seems to a listener is its pitch. Pitch, in turn, depends on the frequency of sound waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. High-pitched sounds, like the sounds of the piccolo in the Figure 1.1, have high-frequency waves. Low-pitched sounds, like the sounds of the tuba Figure 1.1, have low-frequency waves. ",text,
L_0904,frequency and pitch of sound,T_4453,"The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. Human beings can normally hear sounds with a frequency between about 20 Hz and 20,000 Hz. Sounds with frequencies below 20 hertz are called infrasound. Infrasound is too low-pitched for humans to hear. Sounds with frequencies above 20,000 hertz are called ultrasound. Ultrasound is too high-pitched for humans to hear. Some other animals can hear sounds in the ultrasound range. For example, dogs can hear sounds with frequencies as high as 50,000 Hz. You may have seen special whistles that dogsbut not peoplecan hear. The whistles produce sounds with frequencies too high for the human ear to detect. Other animals can hear even higher-frequency sounds. Bats, like the one pictured in the Figure 1.2, can hear sounds with frequencies higher than 100,000 Hz! Q: Bats use ultrasound to navigate in the dark. Can you explain how? A: Bats send out ultrasound waves, which reflect back from objects ahead of them. They sense the reflected sound waves and use the information to detect objects they cant see in the dark. This is how they avoid flying into walls and trees and also how they find flying insects to eat. ",text,
L_0904,frequency and pitch of sound,T_4453,"The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. Human beings can normally hear sounds with a frequency between about 20 Hz and 20,000 Hz. Sounds with frequencies below 20 hertz are called infrasound. Infrasound is too low-pitched for humans to hear. Sounds with frequencies above 20,000 hertz are called ultrasound. Ultrasound is too high-pitched for humans to hear. Some other animals can hear sounds in the ultrasound range. For example, dogs can hear sounds with frequencies as high as 50,000 Hz. You may have seen special whistles that dogsbut not peoplecan hear. The whistles produce sounds with frequencies too high for the human ear to detect. Other animals can hear even higher-frequency sounds. Bats, like the one pictured in the Figure 1.2, can hear sounds with frequencies higher than 100,000 Hz! Q: Bats use ultrasound to navigate in the dark. Can you explain how? A: Bats send out ultrasound waves, which reflect back from objects ahead of them. They sense the reflected sound waves and use the information to detect objects they cant see in the dark. This is how they avoid flying into walls and trees and also how they find flying insects to eat. ",text,
L_0905,friction,T_4454,"Friction is a force that opposes motion between any surfaces that are touching. Friction can work for or against us. For example, putting sand on an icy sidewalk increases friction so you are less likely to slip. On the other hand, too much friction between moving parts in a car engine can cause the parts to wear out. Other examples of friction are illustrated in the two Figures 1.1 and 1.2. ",text,
L_0905,friction,T_4455,"Friction occurs because no surface is perfectly smooth. Even surfaces that look smooth to the unaided eye make look rough or bumpy when viewed under a microscope. Look at the metal surfaces in the Figure 1.3. The aluminum foil These photos show two ways that friction is useful These photos show two ways that friction can cause problems is so smooth that its shiny. However, when highly magnified, the surface of metal appears to be very bumpy. All those mountains and valleys catch and grab the mountains and valleys of any other surface that contacts the metal. This creates friction. ",text,
L_0905,friction,T_4455,"Friction occurs because no surface is perfectly smooth. Even surfaces that look smooth to the unaided eye make look rough or bumpy when viewed under a microscope. Look at the metal surfaces in the Figure 1.3. The aluminum foil These photos show two ways that friction is useful These photos show two ways that friction can cause problems is so smooth that its shiny. However, when highly magnified, the surface of metal appears to be very bumpy. All those mountains and valleys catch and grab the mountains and valleys of any other surface that contacts the metal. This creates friction. ",text,
L_0905,friction,T_4456,"Rougher surfaces have more friction between them than smoother surfaces. Thats why we put sand on icy sidewalks and roads. You cant slide as far across ice with shoes as you can on the blades of skates (see Figure 1.4). The rougher surface of the soles of the shoes causes more friction and slows you down. Q: Heavier objects also have more friction. Can you explain why? A: Heavier objects press together with greater force, and this causes greater friction between them. Did you ever try to furniture across the floor? Its harder to overcome friction between a heavier piece of furniture and the floor than between lighter pieces and the floor. ",text,
L_0905,friction,T_4456,"Rougher surfaces have more friction between them than smoother surfaces. Thats why we put sand on icy sidewalks and roads. You cant slide as far across ice with shoes as you can on the blades of skates (see Figure 1.4). The rougher surface of the soles of the shoes causes more friction and slows you down. Q: Heavier objects also have more friction. Can you explain why? A: Heavier objects press together with greater force, and this causes greater friction between them. Did you ever try to furniture across the floor? Its harder to overcome friction between a heavier piece of furniture and the floor than between lighter pieces and the floor. ",text,
L_0905,friction,T_4457,"You know that friction produces heat. Thats why rubbing your hands together makes them warmer. But do you know why? Friction causes the molecules on rubbing surfaces to move faster, so they have more energy. This gives them a higher temperature, and they feel warmer. Heat from friction can be useful. It not only warms your hands. It also lets you light a match as shown in the Figure 1.5. On the other hand, heat from friction between moving parts inside a car engine can be a big problem. It can cause the car to overheat. Q: How is friction reduced between the moving parts inside a car engine? A: To reduce friction, oil is added to the engine. The oil coats the surfaces of the moving parts and makes them slippery. They slide over each other more easily, so there is less friction. ",text,
L_0906,fundamental particles,T_4458,"Scientists have long wanted to find the most basic building blocks of the universe. They asked, what are the fundamental particles of matter that cannot be subdivided into smaller, simpler particles, and what holds these particles together? The quest for fundamental particles began thousands of years ago. Scientists thought they had finally found them when John Dalton discovered the atom in 1803 (see the timeline in Table 1.1). The word atom means indivisible, and Dalton thought that the atom could not be divided into smaller, simpler particles. Year Discovery Year 1803 Discovery John Dalton discovers the atom. 1897 J.J. Thomson discovers the electron, the first lepton to be discovered. 1905 Albert Einstein discovers the photon, the first boson to be discovered. 1911 Ernest Rutherford discovers the proton, the first particle to be discovered in the nucleus of the atom. Year 1932 Discovery James Chadwick discovers the neutron, another particle in the nucleus. 1964 Murray Gell-Mann proposes the existence of quarks, the fundamental particles that make up protons and neutrons. 1964-present Through the research of many scientists, many other fundamental particles (except gravitons) are shown to exist. For almost 100 years after Dalton discovered atoms, they were accepted as the fundamental particles of matter. But starting in the late 1890s with the discovery of electrons, particles smaller and simpler than atoms were identified. Within a few decades, protons and neutrons were also discovered. Ultimately, hundreds of subatomic particles were found. ",text,
L_0906,fundamental particles,T_4459,"Today, scientists think that electrons truly are fundamental particles that cannot be broken down into smaller, simpler particles. They are a type of fundamental particles called leptons. Protons and neutrons, on the other hand, are no longer thought to be fundamental particles. Instead, they are now thought to consist of smaller, simpler particles of matter called quarks. Scientists theorize that leptons and quarks are held together by yet another type of fundamental particles called bosons. All three types of fundamental particlesleptons, quarks, and bosonsare described below. The following Figure 1.1 shows the variety of particles of each type. There are six types of quarks. In ordinary matter, virtually all quarks are of the types called up and down quarks. All quarks have mass, and they have an electric charge of either +2/3 or -1/3. For example, up quarks have a charge of +2/3, and down quarks have a charge of -1/3. Quarks also have a different type of charge, called color charge, although it has nothing to do with the colors that we see. Quarks are never found alone but instead always occur in groups of two or three quarks. There are also six types of leptons, including electrons. Leptons have an electric charge of either -1 or 0. Electrons, for example, have a charge of -1. Leptons have mass, although the mass of electrons is extremely small. There are four known types of bosons, which are force-carrying particles. Each of these bosons carries a different fundamental force between interacting particles. In addition, there is a particle which may exist, called the ""Higgs Boson"", which gives objects the masses they have. Some types of bosons have mass; others are massless. Bosons have an electric charge of +1, -1, or 0. Q: Protons consist of three quarks: two up quarks and one down quark. Neutrons also consist of three quarks: two down quarks and one up quark. Based on this information, what is the total electric charge of a proton? Of a neutron? A: These combinations of quarks give protons a total electric charge of +1 (2/3 + 2/3 - 1/3 = 1) and neutrons a total electric charge of 0 (2/3 - 1/3 - 1/3 = 0). ",text,
L_0906,fundamental particles,T_4460,"The interactions of matter particles are subject to four fundamental forces: gravity, electromagnetic force, weak nuclear force, and strong nuclear force. All of these forces are thought to be transmitted by bosons, the force- carrying fundamental particles. The different types of bosons and the forces they carry are shown in Table 1.2. Consider the examples of gluons, the bosons that carry the strong nuclear force. A continuous exchange of gluons between quarks binds them together in both protons and neutrons. Note that force-carrying particles for gravity (gravitons) have not yet been found. Type of Bosons Gluons Fundamental Force They Carry strong nuclear force Particles They Affect quarks Distance over Which They Carry Force only within the nucleus Type of Bosons W bosons Z bosons Photons Gravitons (hypothetical) Fundamental Force They Carry weak nuclear force Particles They Affect leptons and quarks Distance over Which They Carry Force only within the nucleus electromagnetic force force of gravity leptons and quarks leptons and quarks all distances all distances Q: Which type of boson carries force between the negative electrons and positive protons of an atom? A: Photons carry electromagnetic force. They are responsible for the force of attraction or repulsion between all electrically charged matter, including the force of attraction between negative electrons and positive protons in an atom. Q: Gravitons have not yet been discovered so they have only been hypothesized to exist. What evidence do you think leads scientists to think that these hypothetical particles affect both leptons and quarks and that they carry force over all distances? A: Gravity is known to affect all matter that has mass, and both quarks and leptons have mass. Gravity is also known to work over long as well as short distances. For example, Earths gravity keeps you firmly planted on the ground and also keeps the moon orbiting around the planet. ",text,
L_0906,fundamental particles,T_4461,"Based on their knowledge of subatomic particles, scientists have developed a theory called the standard model to explain all the matter in the universe and how it is held together. The model includes only the fundamental particles in the Table 1.2. No other particles are needed to explain all kinds of matter. According to the model, all known matter consists of quarks and leptons that interact by exchanging bosons, which transmit fundamental forces. The standard model is a good theory because all of its predictions have been verified by experimental data. However, the model doesnt explain everything, including the force of gravity and why matter has mass. Scientists continue to search for evidence that will allow them to explain these aspects of force and matter as well. ",text,
L_0907,gamma decay,T_4462,"Gamma rays are electromagnetic waves. Electromagnetic waves are waves of electric and magnetic energy that travel through space at the speed of light. The energy travels in tiny packets of energy, called photons. Photons of gamma energy are called gamma particles. Other electromagnetic waves include microwaves, light rays, and X rays. Gamma rays have the greatest amount of energy of all electromagnetic waves. Click image to the left or use the URL below. URL: ",text,
L_0907,gamma decay,T_4463,"Gamma rays are produced when radioactive elements decay. Radioactive elements are elements with unstable nuclei. To become more stable, the nuclei undergo radioactive decay. In this process, the nuclei give off energy and may also emit charged particles of matter. Types of radioactive decay include alpha, beta, and gamma decay. In alpha and beta decay, both particles and energy are emitted. In gamma decay, only energy, in the form of gamma rays, is emitted. Alpha and beta decay occur when a nucleus has too many protons or an unstable ratio of protons to neutrons. When the nucleus emits a particle, it gains or loses one or two protons, so the atom becomes a different element. Gamma decay, in contrast, occurs when a nucleus is in an excited state and has too much energy to be stable. This often happens after alpha or beta decay has occurred. Because only energy is emitted during gamma decay, the number of protons remains the same. Therefore, an atom does not become a different element during this type of decay. Q: The Figure 1.1 shows how helium-3 (He-3) decays by emitting a gamma particle. How can you tell that the atom is still the same element after gamma decay occurs? A: The nucleus of the atom has two protons (red) before the reaction occurs. After the nucleus emits the gamma particle, it still has two protons, so the atom is still the same element. ",text,
L_0907,gamma decay,T_4464,Gamma rays are the most dangerous type of radiation. They can travel farther and penetrate materials more deeply than can the charged particles emitted during alpha and beta decay. Gamma rays can be stopped only by several centimeters of lead or several meters of concrete. Its no surprise that they can penetrate and damage cells deep inside the body. ,text,
L_0908,gamma rays,T_4465,"Electromagnetic waves transfer energy across space as well as through matter. They vary in their wavelengths and frequencies, and higher-frequency waves have more energy. The full range of wavelengths of electromagnetic waves, shown in the Figure 1.1, is called the electromagnetic spectrum. ",text,
L_0908,gamma rays,T_4466,"As you can see in the Figure 1.1, gamma rays have the shortest wavelengths and highest frequencies of all electromagnetic waves. Their wavelengths are shorter than the diameter of atomic nuclei, and their frequencies are greater than 1019 hertz (Hz). Thats 10 quadrillion waves per second! Because of their high frequencies, gamma rays are also the most energetic of all electromagnetic waves. ",text,
L_0908,gamma rays,T_4467,"Gamma rays are given off by radioactive atoms and nuclear explosions. They are also given off by the sun and other stars, as well as by collapsing stars in gamma ray bursts. Fortunately, gamma rays from space are absorbed by Earths atmosphere before they can reach the surface. Q: Predict how gamma rays might affect living things on Earth if they werent absorbed by the atmosphere. A: Gamma rays would destroy most living things on Earth because they have so much energy. ",text,
L_0908,gamma rays,T_4468,"The extremely high energy of gamma rays allows them to penetrate just about anything. They can even pass through bones and teeth. This makes gamma rays very dangerous. They can destroy living cells, produce gene mutations, and cause cancer. Ironically, the deadly effects of gamma rays can be used to treat cancer. In this type of treatment, a medical device sends out focused gamma rays that target cancerous cells. The gamma rays kill the cells and destroy the cancer. ",text,
L_0910,gravity,T_4472,"Gravity has traditionally been defined as a force of attraction between things that have mass. According to this conception of gravity, anything that has mass, no matter how small, exerts gravity on other matter. Gravity can act between objects that are not even touching. In fact, gravity can act over very long distances. However, the farther two objects are from each other, the weaker is the force of gravity between them. Less massive objects also have less gravity than more massive objects. ",text,
L_0910,gravity,T_4473,"You are already very familiar with Earths gravity. It constantly pulls you toward the center of the planet. It prevents you and everything else on Earth from being flung out into space as the planet spins on its axis. It also pulls objects that are above the surfacefrom meteors to skydiversdown to the ground. Gravity between Earth and the moon and between Earth and artificial satellites keeps all these objects circling around Earth. Gravity also keeps Earth and the other planets moving around the much more massive sun. Q: There is a force of gravity between Earth and you and also between you and all the objects around you. When you drop a paper clip, why doesnt it fall toward you instead of toward Earth? A: Earth is so much more massive than you that its gravitational pull on the paper clip is immensely greater. ",text,
L_0910,gravity,T_4474,"Weight measures the force of gravity pulling downward on an object. The SI unit for weight, like other forces, is the Newton (N). On Earth, a mass of 1 kilogram has a weight of about 10 Newtons because of the pull of Earths gravity. On the moon, which has less gravity, the same mass would weigh less. Weight is measured with a scale, like the spring scale shown in the Figure 1.1. The scale measures the force with which gravity pulls an object downward. To delve a little deeper into weight and gravity, watch this video: Click image to the left or use the URL below. URL: ",text,
L_0910,gravity,T_4475,"At the following URL, read about gravity and tides. Watch the animation and look closely at the diagrams. Then answer the questions below. 1. 2. 3. 4. 5. What causes tides? Which has a greater influence on tides, the moon or the sun? Why? Why is there a tidal bulge of water on the opposite side of Earth from the moon? When are tides highest? What causes these tides to be highest? When are tides lowest? What causes these tides to be lowest? ",text,
L_0911,groups with metalloids,T_4476,"Groups 13-16 of the periodic table (orange in the Figure 1.1) are the only groups that contain elements classified as metalloids. Unlike other groups of the periodic table, which contain elements in just one class, groups 13-16 contain elements in at least two different classes. In addition to metalloids, they also contain metals, nonmetals, or both. Groups 13-16 fall between the transition metals (in groups 3-12) and the nonmetals called halogens (in group 17). ",text,
L_0911,groups with metalloids,T_4477,"Metalloids are the smallest class of elements, containing just six members: boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). Metalloids have some properties of metals (elements that can conduct electricity) and some properties of nonmetals (elements that cannot conduct electricity). For example, most metalloids can conduct electricity, but not as well as metals. Metalloids also tend to be shiny like metals, but brittle like nonmetals. Chemically, metalloids may behave like metals or nonmetals, depending on their number of valence electrons. Q: Why does the chemical behavior of an element depend on its number of valence electrons? A: Valence electrons are the electrons in an atoms outer energy level that may be involved in chemical reactions with other atoms. ",text,
L_0911,groups with metalloids,T_4478,"Group 13 of the periodic table is also called the boron group because boron (B) is the first element at the top of the group (see Figure 1.2). Boron is also the only metalloid in this group. The other four elements in the groupaluminum (Al), gallium (Ga), indium (In), and thallium (Tl)are all metals. Group 13 elements have three valence electrons and are fairly reactive. All of them are solids at room temperature. ",text,
L_0911,groups with metalloids,T_4479,"Group 14 of the periodic table is headed by the nonmetal carbon (C), so this group is also called the carbon group. Carbon is followed by silicon (Si) and germanium (Ge) (Figure 1.3), which are metalloids, and then by tin (Sn) and lead (Pb), which are metals. Group 14 elements group have four valence electrons, so they generally arent very reactive. All of them are solids at room temperature. ",text,
L_0911,groups with metalloids,T_4480,"Group 15 of the periodic table is also called the nitrogen group. The first element in the group is the nonmetal nitrogen (N), followed by phosphorus (P), another nonmetal. Arsenic (As) (Figure 1.4) and antimony (Sb) are the metalloids in this group, and bismuth (Bi) is a metal. All group 15 elements have five valence electrons, but they Germanium is a brittle, shiny, silvery- white metalloid. Along with silicon, it is used to make the tiny electric cir- cuits on computer chips. It is also used to make fiber optic cableslike the one pictured herethat carry telephone and other communication signals. vary in their reactivity. Nitrogen, for example, is not very reactive at all, whereas phosphorus is very reactive and found naturally only in combination with other substances. All group 15 elements are solids, except for nitrogen, which is a gas. ",text,
L_0911,groups with metalloids,T_4480,"Group 15 of the periodic table is also called the nitrogen group. The first element in the group is the nonmetal nitrogen (N), followed by phosphorus (P), another nonmetal. Arsenic (As) (Figure 1.4) and antimony (Sb) are the metalloids in this group, and bismuth (Bi) is a metal. All group 15 elements have five valence electrons, but they Germanium is a brittle, shiny, silvery- white metalloid. Along with silicon, it is used to make the tiny electric cir- cuits on computer chips. It is also used to make fiber optic cableslike the one pictured herethat carry telephone and other communication signals. vary in their reactivity. Nitrogen, for example, is not very reactive at all, whereas phosphorus is very reactive and found naturally only in combination with other substances. All group 15 elements are solids, except for nitrogen, which is a gas. ",text,
L_0911,groups with metalloids,T_4481,"Group 16 of the periodic table is also called the oxygen group. The first three elementsoxygen (O), sulfur (S), and selenium (Se)are nonmetals. They are followed by tellurium (Te) (Figure 1.5), a metalloid, and polonium (Po), a metal. All group 16 elements have six valence electrons and are very reactive. Oxygen is a gas at room temperature, and the other elements in the group are solids. Q: With six valence electrons, group 16 elements need to attract two electrons from another element to have a stable electron arrangement of eight valence electrons. Which group of elements in the periodic table do you think might The most common form of the metalloid arsenic is gray and shiny. Arsenic is extremely toxic, so it is used as rat poison. Surprisingly, we need it (in tiny amounts) for normal growth and a healthy nervous system. form compounds with elements in group 16? A: Group 2 elements, called the alkaline Earth metals, form compounds with elements in the oxygen group. Thats because group 2 elements have two valence electrons that they are eager to give up. An example of a group 2 and group 6 compound is calcium oxide (CaO). ",text,
L_0911,groups with metalloids,T_4481,"Group 16 of the periodic table is also called the oxygen group. The first three elementsoxygen (O), sulfur (S), and selenium (Se)are nonmetals. They are followed by tellurium (Te) (Figure 1.5), a metalloid, and polonium (Po), a metal. All group 16 elements have six valence electrons and are very reactive. Oxygen is a gas at room temperature, and the other elements in the group are solids. Q: With six valence electrons, group 16 elements need to attract two electrons from another element to have a stable electron arrangement of eight valence electrons. Which group of elements in the periodic table do you think might The most common form of the metalloid arsenic is gray and shiny. Arsenic is extremely toxic, so it is used as rat poison. Surprisingly, we need it (in tiny amounts) for normal growth and a healthy nervous system. form compounds with elements in group 16? A: Group 2 elements, called the alkaline Earth metals, form compounds with elements in the oxygen group. Thats because group 2 elements have two valence electrons that they are eager to give up. An example of a group 2 and group 6 compound is calcium oxide (CaO). ",text,
L_0912,halogens,T_4482,"Halogens are highly reactive nonmetallic elements in group 17 of the periodic table. As you can see in the periodic table 1.1, the halogens include the elements fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). All of them are relatively common on Earth except for astatine. Astatine is radioactive and rapidly decays to other, more stable elements. As a result, it is one of the least common elements on Earth. Q: Based on their position in the periodic table from the Figure 1.1, how many valence electrons do you think halogens have? A: The number of valence electrons starts at one for elements in group 1. It then increases by one from left to right across each period (row) of the periodic table for groups 1-2 and 13-18 (numbered 3-0 in the periodic table above.) Therefore, halogens have seven valence electrons. ",text,
L_0912,halogens,T_4483,"The halogens are among the most reactive of all elements, although reactivity declines from the top to the bottom of the halogen group. Because all halogens have seven valence electrons, they are eager to gain one more electron. Doing so gives them a full outer energy level, which is the most stable arrangement of electrons. Halogens often combine with alkali metals in group 1 of the periodic table. Alkali metals have just one valence electron, which they are equally eager to donate. Reactions involving halogens, especially halogens near the top of the group, may be explosive. You can see some examples in the video below. (Warning: Dont try any of these reactions at home!) Click image to the left or use the URL below. URL: ",text,
L_0912,halogens,T_4484,"The halogen group is quite diverse. It includes elements that occur in three different states of matter at room temperature. Fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. Halogens also vary in color, as you can see in the Figure 1.2. Fluorine and chlorine are green, bromine is red, and iodine and astatine are nearly black. Like other nonmetals, halogens cannot conduct electricity or heat. Compared with most other elements, halogens have relatively low melting and boiling points. ",text,
L_0912,halogens,T_4485,Most halogens have a variety of important uses. A few are described in the Figure 1.3. Q: Can you relate some of these uses of halogens to the properties of these elements? A: The ability of halogens to kill germs and bleach clothes relates to their highly reactive nature. ,text,
L_0913,hearing and the ear,T_4486,"Sound is a form of energy that travels in waves through matter. The ability to sense sound energy and perceive sound is called hearing. The organ that we use to sense sound energy is the ear. Almost all the structures in the ear are needed for this purpose. Together, they gather sound waves, amplify the waves, and change their kinetic energy to electrical signals. The electrical signals travel to the brain, which interprets them as the sounds we hear. The Figure 1.1 shows the three main parts of the ear: the outer, middle, and inner ear. It also shows the specific structures in each part of the ear. ",text,
L_0913,hearing and the ear,T_4487,"The outer ear includes the pinna, ear canal, and eardrum. The pinna is the only part of the ear that extends outward from the head. Its position and shape make it good at catching sound waves and funneling them into the ear canal. The ear canal is a tube that carries sound waves into the ear. The sound waves travel through the air inside the ear canal to the eardrum. The eardrum is like the head of a drum. It is a thin membrane stretched tight across the end of the ear canal. The eardrum vibrates when sound waves strike it, and it sends the vibrations on to the middle ear. Q: How might cupping his hands behind his ears help the boy pictured in the opening image hear better? A: His hands might help the pinna of his ears catch sound waves and direct them into the ear canal. ",text,
L_0913,hearing and the ear,T_4488,"The middle ear contains three tiny bones (ossicles) called the hammer, anvil, and stirrup. If you look at these bones in the Figure 1.1, you might notice that they resemble the objects for which they are named. The three bones transmit vibrations from the eardrum to the inner ear. The arrangement of the three bones allows them to work together as a lever that increases the amplitude of the waves as they pass to the inner ear. Q: Wave amplitude is the maximum distance particles of matter move when a wave passes through them. Why would amplifying the sound waves as they pass through the middle ear improve hearing? A: Amplified sound waves have more energy. This increases the intensity and loudness of the sounds, so they are easier to hear. ",text,
L_0913,hearing and the ear,T_4489,"The stirrup in the middle ear passes the amplified sound waves to the inner ear through the oval window. When the oval window vibrates, it causes the cochlea to vibrate as well. The cochlea is a shell-like structure that is full of fluid and lined with nerve cells called hair cells. Each hair cell has many tiny hairs, as you can see in the magnified image 1.2. When the cochlea vibrates, it causes waves in the fluid inside. The waves bend the hairs on the hair cells, and this triggers electrical impulses. The electrical impulses travel to the brain through nerves. Only after the nerve impulses reach the brain do we hear the sound. ",text,
L_0914,hearing loss,T_4490,"The ear is a complex organ that senses sound energy so we can hear. Hearing is the ability to sense sound energy and perceive sound. All of the structures of the ear that are involved in hearing must work well for a person to have normal hearing. Damage to any of the structures, through illness or injury, may cause hearing loss. Total hearing loss is called deafness. ",text,
L_0914,hearing loss,T_4491,"The most common cause of hearing loss is exposure to loud sounds. Loud sounds can damage hair cells inside the ears. Hair cells change sound waves to electrical signals that the brain can interpret as sounds. Louder sounds, which have greater intensity than softer sounds, can damage hair cells more quickly than softer sounds. You can see the relationship between sound intensity, exposure time, and hearing loss in the following Figure 1.1. The intensity of sounds is measured in decibels (dB). Q: What is the maximum amount of time you should be exposed to a sound as intense as 100 dB? What might make a sound this intense? A: You should be exposed to a 100-dB sound for no longer than 15 minutes. An example of a sound this intense is the sound of a car horn. ",text,
L_0914,hearing loss,T_4492,"Hearing loss caused by loud sounds is permanent. However, this type of hearing loss can be prevented by protecting the ears from loud sounds. People who work in jobs that expose them to loud sounds must wear hearing protectors. Examples include construction workers who work around loud machinery for many hours each day. But anyone exposed to loud sounds for longer than the permissible exposure time should wear hearing protectors. Many home and yard chores and even recreational activities are loud enough to cause hearing loss if people are exposed to them for too much time. You can see examples in the Figure 1.2. ",text,
L_0914,hearing loss,T_4493,"You can see two different types of hearing protectors in the Figure 1.3. Earplugs are simple hearing protectors that just muffle sounds by partially blocking all sound waves from entering the ears. This type of hearing protector is suitable for lower noise levels, such as the noise of a lawnmower or snowmobile. Electronic ear protectors work differently. They identify high-amplitude sound waves and send sound waves through them in the opposite direction. This causes destructive interference with the waves, which reduces their amplitude to zero or nearly zero. This changes even the loudest sounds to just a soft hiss. Sounds that people need to hear, such as the voices of co-workers, are not interfered with in this way and may be amplified instead so they can be heard more clearly. This type of hearing protector is recommended for higher noise levels and situations where its important to be able to hear lower-decibel sounds. ",text,
L_0915,heat,T_4494,"Heat is the transfer of thermal energy between substances. Thermal energy is the kinetic energy of moving particles of matter, measured by their temperature. Thermal energy always moves from matter with greater thermal energy to matter with less thermal energy, so it moves from warmer to cooler substances. You can see this in the Figure particles of the cooler substance. Thermal energy is transferred in this way until both substances have the same thermal energy and temperature. Q: How is thermal energy transferred in an oven? A: Thermal energy of the hot oven is transferred to the cooler food, raising its temperature. ",text,
L_0915,heat,T_4495,"How do you cool down a glass of room-temperature cola? You probably add ice cubes to it, as in the Figure 1.2. You might think that the ice cools down the cola, but in fact, it works the other way around. The warm cola heats up the ice. Thermal energy from the warm cola is transferred to the much colder ice, causing it to melt. The cola loses thermal energy in the process, so its temperature falls. ",text,
L_0915,heat,T_4495,"How do you cool down a glass of room-temperature cola? You probably add ice cubes to it, as in the Figure 1.2. You might think that the ice cools down the cola, but in fact, it works the other way around. The warm cola heats up the ice. Thermal energy from the warm cola is transferred to the much colder ice, causing it to melt. The cola loses thermal energy in the process, so its temperature falls. ",text,
L_0916,heat conduction,T_4496,"Conduction is the transfer of thermal energy between particles of matter that are touching. Thermal energy is the total kinetic energy of moving particles of matter, and the transfer of thermal energy is called heat. Conduction is one of three ways that thermal energy can be transferred (the other ways are convection and thermal radiation). Thermal energy is always transferred from matter with a higher temperature to matter with a lower temperature. ",text,
L_0916,heat conduction,T_4497,"To understand how conduction works, you need to think about the tiny particles that make up matter. The particles of all matter are in constant random motion, but the particles of warmer matter have more energy and move more quickly than the particles of cooler matter. When particles of warmer matter collide with particles of cooler matter, they transfer some of their thermal energy to the cooler particles. From particle to particle, like dominoes falling, thermal energy moves through matter. In the opening photo above, conduction occurs between particles of metal in the cookie sheet and anything cooler that comes into contact with ithopefully, not someones bare hands! ",text,
L_0916,heat conduction,T_4498,"The cookie sheet in the opening image transfers thermal energy to the cookies and helps them bake. There are many other common examples of conduction. The Figure 1.1 shows a few situations in which thermal energy is transferred in this way. Q: How is thermal energy transferred in each of the situations pictured in the Figure 1.1? A: Thermal energy is transferred by conduction from the hot iron to the shirt, from the hot cup to the hand holding it, from the flame of the camp stove to the bottom of the pot as well as from the bottom of the pot to the food inside, and from the feet to the snow. The shirt, hand, pot, food, and snow become warmer because of the transferred energy. Because the feet lose thermal energy, they feel colder. ",text,
L_0917,heating systems,T_4499,"Modern home heating systems keep us comfortable in cold weather. We may even depend on them for our survival. But we often take them for granted. Two common types of home heating systems are hot-water and warm-air heating systems. Both types are described below. Thermal energy is the total energy of moving particles of matter. The transfer of thermal energy is called heat. Therefore, a heating system is a system for the transfer of thermal energy. Regardless of the type of heating system in a home, the basic function is the same: to produce thermal energy and transfer it to air throughout the house. ",text,
L_0917,heating systems,T_4500,"A hot-water heating system produces thermal energy to heat water and then pumps the hot water throughout the building in a system of pipes and radiators. You can see a simple diagram of this type of heating system in the Figure 1.1. Water is heated in a boiler that burns a fuel such as natural gas or heating oil. The boiler converts the chemical energy stored in the fuel to thermal energy. The heated water is pumped from the boiler through pipes and radiators throughout the house. There is usually a radiator in each room. The radiators get warm when the hot water flows through them. The warm radiators radiate thermal energy to the air around them. The warm air then circulates throughout the rooms in convection currents. The hot water cools as it flows through the system and transfers its thermal energy. When it finally returns to the boiler, it is heated again and the cycle repeats. Q: Look closely at the hot-water heating system in the Figure 1.1. The radiator is a coiled pipe through which hot water flows. What happens to the water as it flows through the radiator? Why is each radiator connected to two pipes? Why cant water flow directly from one radiator to another through a single pipe? A: The radiator is where most of the energy transfer occurs. Water passes through such a great length of pipe in the radiator that it transfers a lot of thermal energy to the radiator. As the water transfers thermal energy, it gets cooler. The cool water flows into a return pipe rather than going directly to another radiator because the cool water no longer has enough thermal energy to heat a room. ",text,
L_0917,heating systems,T_4501,"A warm-air heating system uses thermal energy to heat air and then forces the warm air through a system of ducts and registers. You can see a this type of heating system in the Figure 1.2. The air is heated in a furnace that burns fuel such as natural gas, propane, or heating oil. After the air gets warm, a fan blows it through the ducts and out through the registers that are located in each room. Warm air blowing out of a register moves across the room, pushing cold air out of the way. The cold air enters a return register across the room and returns to the furnace with the help of another fan. In the furnace, the cold air is heated, and the cycle repeats. Q: How does a home heating system know when to run and when to stop running? A: A home heating system is turned on or off by a thermostat. ",text,
L_0917,heating systems,T_4502,"A thermostat, like the one seen in the Figure 1.3, is an important part of any home heating system. It is like the brain of the entire system. It constantly monitors the temperature in the home and tells the boiler or furnace when to turn on or off. The thermostat is set at a selected temperature, say 71  F. When the temperature in the home starts to fall below this point, the thermostat triggers the boiler or furnace to start running. When the temperature starts to rise above this point, the thermostat triggers the boiler or furnace to stop running. In this way, the thermostat maintains the homes temperature at the set point. ",text,
L_0917,heating systems,T_4502,"A thermostat, like the one seen in the Figure 1.3, is an important part of any home heating system. It is like the brain of the entire system. It constantly monitors the temperature in the home and tells the boiler or furnace when to turn on or off. The thermostat is set at a selected temperature, say 71  F. When the temperature in the home starts to fall below this point, the thermostat triggers the boiler or furnace to start running. When the temperature starts to rise above this point, the thermostat triggers the boiler or furnace to stop running. In this way, the thermostat maintains the homes temperature at the set point. ",text,
L_0919,hydrocarbons,T_4508,"Hydrocarbons are compounds that contain only carbon and hydrogen. Hydrocarbons are the simplest type of carbon-based compounds, but they can vary greatly in size. The smallest hydrocarbons have just one or two carbon atoms. The largest hydrocarbons may have thousands of carbon atoms. Q: How are hydrocarbons involved in each of the photos pictured above? A: The main ingredient of mothballs is the hydrocarbon naphthalene. The main ingredient in nail polish remover is the hydrocarbon acetone. The lawn mower runs on a mixture of hydrocarbons called gasoline, and the camp stove burns a hydrocarbon fuel named isobutane. ",text,
L_0919,hydrocarbons,T_4509,"The size of hydrocarbon molecules influences their properties, including their melting and boiling points. As a result, some hydrocarbons are gases at room temperature, while others are liquids or solids. Hydrocarbons are generally nonpolar, which means that their molecules do not have oppositely charged sides. Therefore, they do not dissolve in water, which is a polar compound. In fact, hydrocarbons tend to repel water. Thats why they are used in floor wax and similar products. ",text,
L_0919,hydrocarbons,T_4510,"Hydrocarbons are placed in two different classes: saturated hydrocarbons and unsaturated hydrocarbons. This classification is based on the number of bonds between carbon atoms. Saturated hydrocarbons have only single bonds between carbon atoms, so the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, they are saturated with hydrogen atoms. Unsaturated hydrocarbons have at least one double or triple bond between carbon atoms, so the carbon atoms are not bonded to as many hydrogen atoms as possible. In other words, they are unsaturated with hydrogen atoms. ",text,
L_0919,hydrocarbons,T_4511,"It is hard to overstate the importance of hydrocarbons to modern life. Hydrocarbons have even been called the driving force of western civilization. You saw some ways they are used in the opening image. Several other ways are pictured in the Figure 1.1. The most important use of hydrocarbons is for fuel. Gasoline, natural gas, fuel oil, diesel fuel, jet fuel, coal, kerosene, and propane are just some of the commonly used hydrocarbon fuels. Hydrocarbons are also used to make things, including plastics and synthetic fabrics such as polyester. Motor oil: Motor oil consists of several hydrocarbons. It lubricates the moving parts of car engines. Asphalt: Asphalt pavement on highways is made of hy- drocarbons found in petroleum. Candle: Many candles are made of paraffin wax, a solid mixture of hydrocarbons. Lighter: This lighter burns the hydrocarbon named butane. Rain Boots: These rain boots are made of a mixture of several hydro- carbons. Transportation: These forms of transportation are fueled by different mixtures of hydrocarbons. ",text,
L_0919,hydrocarbons,T_4512,"The main source of hydrocarbons is fossil fuelscoal, petroleum, and natural gas. Fossil fuels formed over hundreds of millions of years, as dead organisms were covered with sediments and put under great pressure. Giant ferns in ancient swamps turned into coal deposits. The Figure 1.2 shows one way that coal deposits are mined. Dead organisms in ancient seas gradually formed deposits of petroleum and natural gas. Open-Pit Coal Mine ",text,
L_0920,hydrogen and alkali metals,T_4513,"Sodium (Na) is an element in group 1 of the periodic table of the elements. This group (column) of the table is shown in Figure below. It includes the nonmetal hydrogen (H) and six metals that are called alkali metals. Elements in the same group of the periodic table have the same number of valence electrons. These are the electrons in their outer energy level that can be involved in chemical reactions. Valence electrons determine many of the properties of an element, so elements in the same group have similar properties. All the elements in group 1 have just one valence electron. This makes them very reactive. Q: Why does having just one valence electron make group 1 elements very reactive? A: With just one valence electron, group 1 elements are eager to lose that electron. Doing so allows them to achieve a full outer energy level and maximum stability. ",text,
L_0920,hydrogen and alkali metals,T_4514,"Hydrogen is a very reactive gas, and the alkali metals are even more reactive. In fact, they are the most reactive metals and, along with the elements in group 17, are the most reactive of all elements. The reactivity of alkali metals increases from the top to the bottom of the group, so lithium (Li) is the least reactive alkali metal and francium (Fr) is the most reactive. Because alkali metals are so reactive, they are found in nature only in combination with other elements. They often combine with group 17 elements, which are very eager to gain an electron. Click image to the left or use the URL below. URL: ",text,
L_0920,hydrogen and alkali metals,T_4515,"Besides being very reactive, alkali metals share a number of other properties. Alkali metals are all solids at room temperature. Alkali metals are low in density, and some of them float on water. Alkali metals are relatively soft. Some are even soft enough to cut with a knife, like the sodium pictured in the Figure 1.1. ",text,
L_0920,hydrogen and alkali metals,T_4516,"Although all group 1 elements share certain properties, such as being very reactive, they are not alike in every way. Three different group 1 elements are described in more detail below. Notice the ways in which they differ from one another. Q: Why do you think hydrogen gas usually exists as diatomic molecules? A: Each hydrogen atom has just one electron. When two hydrogen atoms bond together, they share a pair of electrons. The shared electrons fill their only energy level, giving them the most stable arrangement of electrons. Potassium is a soft, silvery metal that ignites explosively in water. It easily loses its one valence electron to form positive potassium ions (K+ ), which are needed by all living cells. Potassium is so impor- tant for plants that it is found in almost all fertilizers, like the one shown here. Potassium is abundant in Earths crust in minerals such as feldspar. Francium has one of the largest, heaviest atoms of all elements. Its one valence electron is far removed from the nucleus, as you can see in the atomic model on the right, so it is easily removed from the atom. Francium is radioactive and quickly decays to form other elements such as radium. This is why francium is extremely rare in nature. Less than an ounce of francium is present on Earth at any given time. Q: Francium decays too quickly to form compounds with other elements. Which elements to you think it would bond with if it could? A: With one valence electron, francium would bond with a halogen element in group 17, which has seven valence electrons and needs one more to fill its outer energy level. Elements in group 17 include fluorine and chlorine. ",text,
L_0920,hydrogen and alkali metals,T_4516,"Although all group 1 elements share certain properties, such as being very reactive, they are not alike in every way. Three different group 1 elements are described in more detail below. Notice the ways in which they differ from one another. Q: Why do you think hydrogen gas usually exists as diatomic molecules? A: Each hydrogen atom has just one electron. When two hydrogen atoms bond together, they share a pair of electrons. The shared electrons fill their only energy level, giving them the most stable arrangement of electrons. Potassium is a soft, silvery metal that ignites explosively in water. It easily loses its one valence electron to form positive potassium ions (K+ ), which are needed by all living cells. Potassium is so impor- tant for plants that it is found in almost all fertilizers, like the one shown here. Potassium is abundant in Earths crust in minerals such as feldspar. Francium has one of the largest, heaviest atoms of all elements. Its one valence electron is far removed from the nucleus, as you can see in the atomic model on the right, so it is easily removed from the atom. Francium is radioactive and quickly decays to form other elements such as radium. This is why francium is extremely rare in nature. Less than an ounce of francium is present on Earth at any given time. Q: Francium decays too quickly to form compounds with other elements. Which elements to you think it would bond with if it could? A: With one valence electron, francium would bond with a halogen element in group 17, which has seven valence electrons and needs one more to fill its outer energy level. Elements in group 17 include fluorine and chlorine. ",text,
L_0920,hydrogen and alkali metals,T_4516,"Although all group 1 elements share certain properties, such as being very reactive, they are not alike in every way. Three different group 1 elements are described in more detail below. Notice the ways in which they differ from one another. Q: Why do you think hydrogen gas usually exists as diatomic molecules? A: Each hydrogen atom has just one electron. When two hydrogen atoms bond together, they share a pair of electrons. The shared electrons fill their only energy level, giving them the most stable arrangement of electrons. Potassium is a soft, silvery metal that ignites explosively in water. It easily loses its one valence electron to form positive potassium ions (K+ ), which are needed by all living cells. Potassium is so impor- tant for plants that it is found in almost all fertilizers, like the one shown here. Potassium is abundant in Earths crust in minerals such as feldspar. Francium has one of the largest, heaviest atoms of all elements. Its one valence electron is far removed from the nucleus, as you can see in the atomic model on the right, so it is easily removed from the atom. Francium is radioactive and quickly decays to form other elements such as radium. This is why francium is extremely rare in nature. Less than an ounce of francium is present on Earth at any given time. Q: Francium decays too quickly to form compounds with other elements. Which elements to you think it would bond with if it could? A: With one valence electron, francium would bond with a halogen element in group 17, which has seven valence electrons and needs one more to fill its outer energy level. Elements in group 17 include fluorine and chlorine. ",text,
L_0921,hydrogen bonding,T_4517,"Polar compounds, such as water, are compounds that have a partial negative charge on one side of each molecule and a partial positive charge on the other side. All polar compounds contain polar bonds (although not all compounds that contain polar bonds are polar.) In a polar bond, two atoms share electrons unequally. One atom attracts the shared electrons more strongly, so it has a partial negative charge. The other atom attracts the shared electrons less strongly, so it is has a partial positive charge. In a water molecule, the oxygen atom attracts the shared electrons more strongly than the hydrogen atoms do. This explains why the oxygen side of the water molecule has a partial negative charge and the hydrogen side of the molecule has a partial positive charge. Q: If a molecule is polar, how might this affect its interactions with nearby molecules of the same compound? A: Opposite charges on different molecules of the same compound might cause the molecules to be attracted to each other. ",text,
L_0921,hydrogen bonding,T_4518,"Because of waters polarity, individual water molecules are attracted to one another. You can see this in the Figure of a nearby water molecule. This force of attraction is called a hydrogen bond. Hydrogen bonds are intermolecular (between-molecule) bonds, rather than intramolecular (within-molecule) bonds. They occur not only in water but in other polar molecules in which positive hydrogen atoms are attracted to negative atoms in nearby molecules. Hydrogen bonds are relatively weak as chemical bonds go. For example, they are much weaker than the bonds holding atoms together within molecules of covalent compounds. Click image to the left or use the URL below. URL: ",text,
L_0921,hydrogen bonding,T_4519,"Changes of state from solid to liquid and from liquid to gas occur when matter gains energy. The energy allows individual molecules to separate and move apart from one another. It takes more energy to bring about these changes of state for polar molecules. Although hydrogen bonds are weak, they add to the energy needed for molecules to move apart from one another, so it takes higher temperatures for these changes of state to occur in polar compounds. This explains why polar compounds have relatively high melting and boiling points. The Table 1.1 compares melting and boiling points for some polar and nonpolar covalent compounds. Name of Compound (Chemical Formula) Methane (CH4 ) Ethylene (C2 H2 ) Ammonia (NH3 ) Water (H2 O) Polar or Nonpolar? Melting Point( C) Boiling Point ( C) nonpolar nonpolar polar polar -182 -169 -78 0 -162 -104 -33 100 Q: Which compound in the Table 1.1 do you think is more polar, ammonia or water? ",text,
L_0923,inclined plane,T_4525,"An inclined plane is a simple machine that consists of a sloping surface connecting a lower elevation to a higher elevation. An inclined plane is one of six types of simple machines, and it is one of the oldest and most basic. In fact, two other simple machines, the wedge and the screw, are variations of the inclined plane. A ramp like the one in the Figure 1.1 is another example of an inclined plane. Inclined planes make it easier to move objects to a higher elevation. The sloping surface of the inclined plane supports part of the weight of the object as it moves up the slope. As a result, it takes less force to move the object uphill. The trade-off is that the object must be moved over a greater distance than if it were moved straight up to the higher elevation. ",text,
L_0923,inclined plane,T_4526,"The mechanical advantage of a simple machine is the factor by which it multiplies the force applied to the machine. It is the ratio of output force (the force put out by the machined) to input force (the force put into the machine). For an inclined plane, less force is put into moving an object up the slope than if the object were lifted straight up, so the mechanical advantage is greater than 1. The more gradual the slope of the inclined plane, the less input force is needed and the greater the mechanical advantage. Q: Which inclined plane pictured in the Figure 1.2 has a greater mechanical advantage? A: The inclined plane on the right has a more gradual slope, so it has a greater mechanical advantage. Less force is needed to move objects up the gentler slope, yet the objects attain the same elevation as they would if more force were used to push them up the steeper slope. ",text,
L_0923,inclined plane,T_4526,"The mechanical advantage of a simple machine is the factor by which it multiplies the force applied to the machine. It is the ratio of output force (the force put out by the machined) to input force (the force put into the machine). For an inclined plane, less force is put into moving an object up the slope than if the object were lifted straight up, so the mechanical advantage is greater than 1. The more gradual the slope of the inclined plane, the less input force is needed and the greater the mechanical advantage. Q: Which inclined plane pictured in the Figure 1.2 has a greater mechanical advantage? A: The inclined plane on the right has a more gradual slope, so it has a greater mechanical advantage. Less force is needed to move objects up the gentler slope, yet the objects attain the same elevation as they would if more force were used to push them up the steeper slope. ",text,
L_0924,inertia,T_4527,"Inertia is the tendency of an object to resist a change in its motion. All objects have inertia, whether they are stationary or moving. Inertia explains Newtons first law of motion, which states that an object at rest will remain at rest and an object in motion will stay in motion unless it is acted on by an unbalanced force. Thats why Newtons first law of motion is sometimes called the law of inertia. Q: You probably dont realize it, but you experience inertia all the time, and you dont have to ride a skateboard. For example, think about what happens when you are riding in a car that stops suddenly. Your body moves forward on the seat and strains against the seat belt. Why does this happen? A: The brakes stop the car but not your body, so your body keeps moving forward because of inertia. ",text,
L_0924,inertia,T_4528,"The inertia of an object depends on its mass. Objects with greater mass also have greater inertia. It would be easier for Lauren to push just one of her cousins on her skateboard than both of them. With just one twin, there would be only about half as much mass on the skateboard, so there would be less inertia to overcome. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0924,inertia,T_4529,"To change the motion of an object, inertia must be overcome by an unbalanced force acting on the object. The unbalanced force that starts Laurens cousins rolling along on the skateboard is applied by Lauren when she gives it a push. Once an object starts moving, inertia keeps it moving without any additional force being applied. In fact, it wont stop moving unless another unbalanced force opposes its motion. For example, Lauren can stop the rolling skateboard by moving to the other end and pushing in the opposite direction. Q: What if Lauren didnt stop the skateboard in this way? If it remained on a smooth, flat surface, would it just keep rolling forever? A: The inertia of the moving skateboard would keep it rolling forever if no other unbalanced force opposed its motion. However, another unbalanced force does act on the skateboard Q: What other force is acting on the skateboard? A: The other force is rolling friction between the skateboards wheels and the ground. The force of friction opposes the motion of the rolling skateboard and would eventually bring it to a stop without any help from Lauren. Friction opposes the motion of all moving objects, solike the skateboardall moving objects eventually stop moving even if no other forces oppose their motion. Later that day, Jonathan rode his skateboard and did some jumps. You can see him in the picture 1.2. When hes in the air, there is no rolling friction between his wheels and the ground, but another unbalanced force is acting on the skateboard and changing its motion. Q: What force is acting on the skateboard when it is in the air above the ground? And how will this force change the skateboards motion? A: The force of gravity is acting on the skateboard. It will pull the skateboard back down to the ground. Once its on the ground, friction will slow its motion. ",text,
L_0925,intensity and loudness of sound,T_4530,"Loudness refers to how loud or soft a sound seems to a listener. The loudness of sound is determined, in turn, by the intensity of the sound waves. Intensity is a measure of the amount of energy in sound waves. The unit of intensity is the decibel (dB). ",text,
L_0925,intensity and loudness of sound,T_4531,"The Figure 1.1 shows decibel levels of several different sounds. As decibel levels get higher, sound waves have greater intensity and sounds are louder. For every 10-decibel increase in the intensity of sound, loudness is 10 times greater. Therefore, a 30-decibel quiet room is 10 times louder than a 20-decibel whisper, and a 40-decibel light rainfall is 100 times louder than the whisper. High-decibel sounds are dangerous. They can damage the ears and cause loss of hearing. Q: How much louder than a 20-decibel whisper is the 60-decibel sound of a vacuum cleaner? A: The vacuum cleaner is 10,000 times louder than the whisper! ",text,
L_0925,intensity and loudness of sound,T_4532,"The intensity of sound waves determines the loudness of sounds, but what determines intensity? Intensity results from two factors: the amplitude of the sound waves and how far they have traveled from the source of the sound. Amplitude is a measure of the size of sound waves. It depends on the amount of energy that started the waves. Greater amplitude waves have more energy and greater intensity, so they sound louder. As sound waves travel farther from their source, the more spread out their energy becomes. You can see how this works in the Figure 1.2. As distance from the sound source increases, the area covered by the sound waves increases. The same amount of energy is spread over a greater area, so the intensity and loudness of the sound is less. This explains why even loud sounds fade away as you move farther from the source. Q: Why can low-amplitude sounds like whispers be heard only over short distances? A: The sound waves already have so little energy that spreading them out over a wider area quickly reduces their intensity below the level of hearing. ",text,
L_0926,internal combustion engines,T_4533,"A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the energy to do work. In a car, the engine does the work of providing kinetic energy that turns the wheels. The combustion engine in a car is a type of engine called an internal combustion engine. (Another type of combustion engine is an external combustion engine.) ",text,
L_0926,internal combustion engines,T_4534,"An internal combustion engine burns fuel internally, or inside the engine. This type of engine is found not only in cars but in most other motor vehicles as well. The engine works in a series of steps, which keep repeating. You can follow the steps in the Figure 1.1. 1. A mixture of fuel and air is pulled-into a cylinder through a valve, which then closes. 2. A piston inside the cylinder moves upward, compressing the fuel-air mixture in the closed cylinder. The mixture is now under a lot of pressure and very warm. 3. A spark from a spark plug ignites the fuel-air mixture, causing it to burn explosively within the confined space of the closed cylinder. 4. The pressure of the hot gases from combustion pushes the piston downward. 5. The piston moves up again, pushing exhaust gases out of the cylinder through another valve. 6. The piston moves downward again, and the cycle repeats. Q: The internal combustion engine converts thermal energy to another form of energy. Which form of energy is it? A: The engine converts thermal energy to kinetic energy, or the energy of a moving objectin this case, the moving piston. ",text,
L_0926,internal combustion engines,T_4535,"In a car, the piston in the engine is connected by the piston rod to the crankshaft. The crankshaft rotates when the piston moves up and down. The crankshaft, in turn, is connected to the driveshaft. When the crankshaft rotates, so does the driveshaft. The rotating driveshaft turns the wheels of the car. ",text,
L_0926,internal combustion engines,T_4536,"Most cars have at least four cylinders connected to the crankshaft. Their pistons move up and down in sequence, one after the other. A powerful car may have eight pistons, and some race cars may have even more. The more cylinders a car engine has, the more powerful its engine can be. ",text,
L_0927,international system of units,T_4537,"The example of the Mars Climate Orbiter shows the importance of using a standard system of measurement in science and technology. The measurement system used by most scientists and engineers is the International System of Units, or SI. There are a total of seven basic SI units, including units for length (meter) and mass (kilogram). SI units are easy to use because they are based on the number 10. Basic units are multiplied or divided by powers of ten to arrive at bigger or smaller units. Prefixes are added to the names of the units to indicate the powers of ten, as shown in the Table 1.1. Prefix kilo- (k) Multiply Basic Unit 1000 Basic Unit of Length = Meter (m) kilometer (km) = 1000 m Prefix deci- (d) centi- (c) milli- (m) micro- () nano- (n) Multiply Basic Unit 0.1 0.01 0.001 0.000001 0.000000001 Basic Unit of Length = Meter (m) decimeter (dm) = 0.1 m centimeter (cm) = 0.01 m millimeter (mm) = 0.001 m micrometer (m) = 0.000001 m nanometer (nm) = 0.000000001 m Q: What is the name of the unit that is one-hundredth (0.01) of a meter? A: The name of this unit is the centimeter. Q: What fraction of a meter is a decimeter? A: A decimeter is one-tenth (0.1) of a meter. ",text,
L_0927,international system of units,T_4538,"In the Table 1.2, two basic SI units are compared with their English system equivalents. You can use the information in the table to convert SI units to English units or vice versa. For example, from the table you know that 1 meter equals 39.37 inches. How many inches are there in 3 meters? 3 m = 3(39.37 in) = 118.11 in Measure Length Mass SI Unit meter (m) kilogram (kg) English Unit Equivalent 1 m = 39.37 in 1 kg = 2.20 lb Q: Rod needs to buy a meter of wire for a science experiment, but the wire is sold only by the yard. If he buys a yard of wire, will he have enough? (Hint: There are 36 inches in a yard.) A: Rod needs 39.37 inches (a meter) of wire, but a yard is only 36 inches, so if he buys a yard of wire he wont have enough. ",text,
L_0928,ionic bonding,T_4539,"An ionic bond is the force of attraction that holds together positive and negative ions. It forms when atoms of a metallic element give up electrons to atoms of a nonmetallic element. The Figure 1.1 shows how this happens. In row 1 of the Figure 1.1, an atom of sodium (Na) donates an electron to an atom of chlorine (Cl). By losing an electron, the sodium atom becomes a sodium ion. It now has more protons than electrons and a charge of +1. Positive ions such as sodium are given the same name as the element. The chemical symbol has a plus sign to distinguish the ion from an atom of the element. The symbol for a sodium ion is Na+ . By gaining an electron, the chlorine atom becomes a chloride ion. It now has more electrons than protons and a charge of -1. Negative ions are named by adding the suffix -ide to the first part of the element name. The symbol for chloride is Cl . Sodium and chloride ions have equal but opposite charges. Opposite electric charges attract each other, so sodium and chloride ions cling together in a strong ionic bond. You can see this in row 2 of the Figure 1.1. (Brackets separate the ions in the diagram to show that the ions in the compound do not actually share electrons.) When ionic bonds hold ions together, they form an ionic compound. The compound formed from sodium and chloride ions is named sodium chloride. It is commonly called table salt. ",text,
L_0928,ionic bonding,T_4540,"Ionic bonds form only between metals and nonmetals. Thats because metals want to give up electrons, and nonmetals want to gain electrons. Find sodium (Na) in the Figure 1.2. Sodium is an alkali metal in group 1. Like all group 1 elements, it has just one valence electron. If sodium loses that one electron, it will have a full outer energy level, which is the most stable arrangement of electrons. Now find fluorine (F) in the periodic table Figure gains one electron, it will also have a full outer energy level and the most stable arrangement of electrons. Q: Predict what other elements might form ionic bonds. A: Metals on the left and in the center of the periodic table form ionic bonds with nonmetals on the right of the periodic table. For example, alkali metals in group 1 form ionic bonds with halogen nonmetals in group 17. ",text,
L_0928,ionic bonding,T_4541,"It takes energy to remove valence electrons from an atom because the force of attraction between the negative electrons and the positive nucleus must be overcome. The amount of energy needed depends on the element. Less energy is needed to remove just one or a few valence electrons than many. This explains why sodium and other alkali metals form positive ions so easily. Less energy is also needed to remove electrons from larger atoms in the same group. For example, in group 1, it takes less energy to remove an electron from francium (Fr) at the bottom of the group than from lithium (Li) at the top of the group (see the Figure 1.2). In bigger atoms, valence electrons are farther from the nucleus. As a result, the force of attraction between the valence electrons and the nucleus is weaker. Q: What do you think happens when an atom gains an electron and becomes a negative ion? A: Energy is released when an atom gains an electron. Halogens release the most energy when they form ions. As a result, they are very reactive elements. ",text,
L_0929,ionic compounds,T_4542,"All compounds form when atoms of different elements share or transfer electrons. Compounds in which electrons are transferred from one atom to another are called ionic compounds. In this type of compound, electrons actually move between the atoms, rather than being shared between them. When atoms give up or accept electrons in this way, they become charged particles called ions. The ions are held together by ionic bonds, which form an ionic compound. Ionic compounds generally form between elements that are metals and elements that are nonmetals. For example, the metal calcium (Ca) and the nonmetal chlorine (Cl) form the ionic compound calcium chloride (CaCl2 ). In this compound, there are two negative chloride ions for each positive calcium ion. Because the positive and negative charges cancel out, an ionic compound is neutral in charge. Q: Now can you explain why calcium chloride prevents ice from forming on a snowy road? A: If calcium chloride dissolves in water, it breaks down into its ions (Ca2+ and Cl ). When water has ions dissolved in it, it has a lower freezing point. Pure water freezes at 0 C. With calcium and chloride ions dissolved in it, it wont freeze unless the temperature reaches -29 C or lower. ",text,
L_0929,ionic compounds,T_4543,"Many compounds form molecules, but ionic compounds form crystals instead. A crystal consists of many alternating positive and negative ions bonded together in a matrix. Look at the crystal of sodium chloride (NaCl) in the Figure bonds. Sodium chloride crystals are cubic in shape. Other ionic compounds may have crystals with different shapes. ",text,
L_0929,ionic compounds,T_4544,"Ionic compounds are named for their positive and negative ions. The name of the positive ion always comes first, followed by the name of the negative ion. For example, positive sodium ions and negative chloride ions form the compound named sodium chloride. Similarly, positive calcium ions and negative chloride ions form the compound named calcium chloride. Q: What is the name of the ionic compound that is composed of positive barium ions and negative iodide ions? A: The compound is named barium iodide. ",text,
L_0929,ionic compounds,T_4545,"The crystal structure of ionic compounds is strong and rigid. It takes a lot of energy to break all those ionic bonds. As a result, ionic compounds are solids with high melting and boiling points. You can see the melting and boiling points of several different ionic compounds in the Table 1.1. To appreciate how high they are, consider that the melting and boiling points of water, which is not an ionic compound, are 0 C and 100 C, respectively. Ionic Compound Sodium chloride (NaCl) Calcium chloride (CaCl2 ) Barium oxide (BaO) Iron bromide (FeBr3 ) Melting Point ( C) 801 772 1923 684 Boiling Point ( C) 1413 1935 2000 934 Solid ionic compounds are poor conductors of electricity. The strong bonds between their oppositely charged ions lock them into place in the crystal. Therefore, the charged particles cannot move freely and carry electric current, which is a flow of charge. But all that changes when ionic compounds dissolve in water. When they dissolve, they separate into individual ions. The ions can move freely, so they can carry current. Dissolved ionic compounds are called electrolytes. The rigid crystals of ionic compounds are brittle. They are more likely to break than bend when struck. As a result, ionic crystals tend to shatter easily. Try striking salt crystals with a hammer and youll find that they readily break into smaller pieces. Click image to the left or use the URL below. URL: ",text,
L_0929,ionic compounds,T_4546,Ionic compounds have many uses. Some are shown in the Figure 1.2. Many ionic compounds are used in industry. The human body needs several ions for good health. Having low levels of the ions can endanger important functions such as heartbeat. Solutions of ionic compounds can be used to restore the ions. ,text,
L_0930,ions,T_4547,"The northern lights arent caused by atoms, because atoms are not charged particles. An atom always has the same number of electrons as protons. Electrons have an electric charge of -1 and protons have an electric charge of +1. Therefore, the charges of an atoms electrons and protons cancel out. This explains why atoms are neutral in electric charge. Q: What would happen to an atoms charge if it were to gain extra electrons? A: If an atom were to gain extra electrons, it would have more electrons than protons. This would give it a negative charge, so it would no longer be neutral. ",text,
L_0930,ions,T_4548,"Atoms cannot only gain extra electrons. They can also lose electrons. In either case, they become ions. Ions are atoms that have a positive or negative charge because they have unequal numbers of protons and electrons. If atoms lose electrons, they become positive ions, or cations. If atoms gain electrons, they become negative ions, or anions. Consider the example of fluorine (see Figure 1.1). A fluorine atom has nine protons and nine electrons, so it is electrically neutral. If a fluorine atom gains an electron, it becomes a fluoride ion with an electric charge of -1. ",text,
L_0930,ions,T_4549,"Like fluoride, other negative ions usually have names ending in -ide. Positive ions, on the other hand, are just given the element name followed by the word ion. For example, when a sodium atom loses an electron, it becomes a positive sodium ion. The charge of an ion is indicated by a plus (+) or minus sign (-), which is written to the right of and just above the ions chemical symbol. For example, the fluoride ion is represented by the symbol F , and the sodium ion is represented by the symbol Na+ . If the charge is greater than one, a number is used to indicate it. For example, iron (Fe) may lose two electrons to form an ion with a charge of plus two. This ion would be represented by the symbol Fe2+ . This and some other common ions are listed with their symbols in the Table 1.1. Cations Name of Ion Calcium ion Hydrogen ion Iron(II) ion Iron(III) ion Chemical Symbol Ca2+ H+ Fe2+ Fe3+ Anions Name of Ion Chloride Fluoride Bromide Oxide Chemical Symbol Cl F Br O2 Q: How does the iron(III) ion differ from the iron(II) ion? A: The iron(III) ion has a charge of +3, so it has one less electron than the iron(II) ion, which has a charge of +2. Q: What is the charge of an oxide ion? How does its number of electrons compare to its number of protons? A: An oxide ion has a charge of -2. It has two more electrons than protons. ",text,
L_0930,ions,T_4550,"The process in which an atom becomes an ion is called ionization. It may occur when atoms are exposed to high levels of radiation. The radiation may give their outer electrons enough energy to escape from the attraction of the positive nucleus. However, most ions form when atoms transfer electrons to or from other atoms or molecules. For example, sodium atoms may transfer electrons to chlorine atoms. This forms positive sodium ions (Na+ ) and negative chloride ions (Cl ). Click image to the left or use the URL below. URL: ",text,
L_0930,ions,T_4551,"Ions are highly reactive, especially as gases. They usually react with ions of opposite charge to form neutral compounds. For example, positive sodium ions and negative chloride ions react to form the neutral compound sodium chloride, commonly known as table salt. This occurs because oppositely charged ions attract each other. Ions with the same charge, on the other hand, repel each other. Ions are also deflected by a magnetic field, as you saw in the opening image of the northern lights. ",text,
L_0931,isomers,T_4552,"Hydrocarbons are compounds that contain only carbon and hydrogen atoms. The smallest hydrocarbon, methane (CH4 ), contains just one carbon atom and four hydrogen atoms. Larger hydrocarbons contain many more. Hydro- carbons with four or more carbon atoms can have different shapes. Although they have the same chemical formula, with the same numbers of carbon and hydrogen atoms, they form different compounds, called isomers. Isomers are compounds whose properties are different because their atoms are bonded together in different arrangements. ",text,
L_0931,isomers,T_4553,"The smallest hydrocarbon that has isomers is butane, which has just four carbon atoms. In the Figure 1.1 you can see structural formulas for normal butane (or n-butane) and its only isomer, named iso-butane. Both molecules have four carbon atoms as well as ten hydrogen atoms (C4 H10 ), but the atoms are arranged differently in the two compounds. In n-butane, all four carbon atoms are lined up in a straight chain. In iso-butane, one of the carbon atoms branches off from the main chain. The next smallest hydrocarbon is pentane, which has five carbon atoms and twelve hydrogen atoms (C5 H12 ). Pentane has three isomers: n-pentane, iso-pentane, and neo-pentane. Their structural formulas are shown in the images below. Look at the carbon atoms in each isomer. In n-pentane (see Figure 1.2), the carbon atoms form a straight chain. In iso-pentane (see Figure 1.3), one carbon atom branches off from the main chain. In neo-pentane (see Figure 1.4), two carbon atoms branch off from the main chain. ",text,
L_0931,isomers,T_4554,"Butane has only two isomers and pentane has just three, but some hydrocarbons have many more isomers than these. As you increase the number of carbon atoms in a hydrocarbon, the number of isomers quickly increases. For example, heptane, with seven carbon atoms, has nine isomers; and dodecane, with twelve carbon atoms, has 355 isomers. Some hydrocarbons with many more carbon atoms have billions of isomers! Q: Why does the number of carbon atoms in a hydrocarbon determine how many isomers it has? A: The more carbon atoms there are, the greater the number of possible arrangements of carbon atoms. ",text,
L_0931,isomers,T_4554,"Butane has only two isomers and pentane has just three, but some hydrocarbons have many more isomers than these. As you increase the number of carbon atoms in a hydrocarbon, the number of isomers quickly increases. For example, heptane, with seven carbon atoms, has nine isomers; and dodecane, with twelve carbon atoms, has 355 isomers. Some hydrocarbons with many more carbon atoms have billions of isomers! Q: Why does the number of carbon atoms in a hydrocarbon determine how many isomers it has? A: The more carbon atoms there are, the greater the number of possible arrangements of carbon atoms. ",text,
L_0931,isomers,T_4554,"Butane has only two isomers and pentane has just three, but some hydrocarbons have many more isomers than these. As you increase the number of carbon atoms in a hydrocarbon, the number of isomers quickly increases. For example, heptane, with seven carbon atoms, has nine isomers; and dodecane, with twelve carbon atoms, has 355 isomers. Some hydrocarbons with many more carbon atoms have billions of isomers! Q: Why does the number of carbon atoms in a hydrocarbon determine how many isomers it has? A: The more carbon atoms there are, the greater the number of possible arrangements of carbon atoms. ",text,
L_0931,isomers,T_4554,"Butane has only two isomers and pentane has just three, but some hydrocarbons have many more isomers than these. As you increase the number of carbon atoms in a hydrocarbon, the number of isomers quickly increases. For example, heptane, with seven carbon atoms, has nine isomers; and dodecane, with twelve carbon atoms, has 355 isomers. Some hydrocarbons with many more carbon atoms have billions of isomers! Q: Why does the number of carbon atoms in a hydrocarbon determine how many isomers it has? A: The more carbon atoms there are, the greater the number of possible arrangements of carbon atoms. ",text,
L_0931,isomers,T_4555,"Because isomers are different compounds, they have different properties. Generally, branched-chain isomers have lower boiling and melting points than straight-chain isomers. For example, the boiling and melting points of iso- butane are -12  C and -160  C, respectively, compared with 0  C and -138  C for n-butane. The more branching there is, the lower the boiling and melting points are. Q: The boiling point of n-pentane is 36  C. Predict the boiling points of iso-pentane and neo-pentane. A: The boiling point of iso-pentane is 28  C, and the boiling point of neo-pentane is 10  C. ",text,
L_0932,isotopes,T_4556,"All atoms of the same element have the same number of protons, but some may have different numbers of neutrons. For example, all carbon atoms have six protons, and most have six neutrons as well. But some carbon atoms have seven or eight neutrons instead of the usual six. Atoms of the same element that differ in their numbers of neutrons are called isotopes. Many isotopes occur naturally. Usually one or two isotopes of an element are the most stable and common. Different isotopes of an element generally have the same physical and chemical properties. Thats because they have the same numbers of protons and electrons. Click image to the left or use the URL below. URL: ",text,
L_0932,isotopes,T_4557,"Hydrogen is an example of an element that has isotopes. Three isotopes of hydrogen are modeled in the Figure hydrogen. Some hydrogen atoms have one neutron as well. These atoms are the isotope named deuterium. Other hydrogen atoms have two neutrons. These atoms are the isotope named tritium. Q: The mass number of an atom is the sum of its protons and neutrons. What is the mass number of each isotope of hydrogen shown above? A: The mass numbers are: hydrogen = 1, deuterium = 2, and tritium = 3. ",text,
L_0932,isotopes,T_4558,"For most elements other than hydrogen, isotopes are named for their mass number. For example, carbon atoms with the usual 6 neutrons have a mass number of 12 (6 protons + 6 neutrons = 12), so they are called carbon-12. Carbon atoms with 7 neutrons have an atomic mass of 13 (6 protons + 7 neutrons = 13). These atoms are the isotope called carbon-13. Q: Some carbon atoms have 8 neutrons. What is the name of this isotope of carbon? A: Carbon atoms with 8 neutrons have an atomic mass of 14 (6 protons + 8 neutrons = 14), so this isotope of carbon is named carbon-14. ",text,
L_0932,isotopes,T_4559,"Atoms need a certain ratio of neutrons to protons to have a stable nucleus. Having too many or too few neutrons relative to protons results in an unstable, or radioactive, nucleus that will sooner or later break down to a more stable form. This process is called radioactive decay. Many isotopes have radioactive nuclei, and these isotopes are referred to as radioisotopes. When they decay, they release particles that may be harmful. This is why radioactive isotopes are dangerous and why working with them requires special suits for protection. The isotope of carbon known as carbon-14 is an example of a radioisotope. In contrast, the carbon isotopes called carbon-12 and carbon-13 are stable. ",text,
L_0933,kinetic energy,T_4560,"Kinetic energy is the energy of moving matter. Anything that is moving has kinetic energyfrom atoms in matter to stars in outer space. Things with kinetic energy can do work. For example, the spinning saw blade in the photo above is doing the work of cutting through a piece of metal. ",text,
L_0933,kinetic energy,T_4561,"The amount of kinetic energy in a moving object depends directly on its mass and velocity. An object with greater mass or greater velocity has more kinetic energy. You can calculate the kinetic energy of a moving object with this equation: Kinetic Energy (KE) = 12 mass  velocity2 This equation shows that an increase in velocity increases kinetic energy more than an increase in mass. If mass doubles, kinetic energy doubles as well, but if velocity doubles, kinetic energy increases by a factor of four. Thats because velocity is squared in the equation. Lets consider an example. The Figure 1.1 shows Juan running on the beach with his dad. Juan has a mass of 40 kg and is running at a velocity of 1 m/s. How much kinetic energy does he have? Substitute these values for mass and velocity into the equation for kinetic energy: m2 2 KE = 12  40 kg  (1 m s ) = 20 kg  s2 = 20 N  m, or 20 J Notice that the answer is given in joules (J), or N  m, which is the SI unit for energy. One joule is the amount of energy needed to apply a force of 1 Newton over a distance of 1 meter. What about Juans dad? His mass is 80 kg, and hes running at the same velocity as Juan (1 m/s). Because his mass is twice as great as Juans, his kinetic energy is twice as great: m2 2 KE = 12  80 kg  (1 m s ) = 40 kg  s2 = 40 N  m, or 40 J Q: What is Juans kinetic energy if he speeds up to 2 m/s from 1 m/s? A: By doubling his velocity, Juan increases his kinetic energy by a factor of four: m2 2 KE = 12  40 kg  (2 m s ) = 80 kg  s2 = 80 N  m, or 80 J ",text,
L_0934,kinetic theory of matter,T_4562,"Energy is the ability to cause changes in matter. For example, your body uses chemical energy when you lift your arm or take a step. In both cases, energy is used to move matteryou. Any matter that is moving has energy just because its moving. The energy of moving matter is called kinetic energy. Scientists think that the particles of all matter are in constant motion. In other words, the particles of matter have kinetic energy. The theory that all matter consists of constantly moving particles is called the kinetic theory of matter. ",text,
L_0934,kinetic theory of matter,T_4563,"Differences in kinetic energy explain why matter exists in different states. Particles of matter are attracted to each other, so they tend to pull together. The particles can move apart only if they have enough kinetic energy to overcome this force of attraction. Its like a tug of war between opposing sides, with the force of attraction between particles on one side and the kinetic energy of individual particles on the other side. The outcome of the war determines the state of matter. If particles do not have enough kinetic energy to overcome the force of attraction between them, matter exists as a solid. The particles are packed closely together and held rigidly in place. All they can do is vibrate. This explains why solids have a fixed volume and a fixed shape. If particles have enough kinetic energy to partly overcome the force of attraction between them, matter exists as a liquid. The particles can slide past one another but not pull apart completely. This explains why liquids can change shape but have a fixed volume. If particles have enough kinetic energy to completely overcome the force of attraction between them, matter exists as a gas. The particles can pull apart and spread out. This explains why gases have neither a fixed volume nor a fixed shape. Look at the Figure 1.1. It sums up visually the relationship between kinetic energy and state of matter. Q: How could you use a bottle of cola to demonstrate these relationships between kinetic energy and state of matter? A: You could shake a bottle of cola and then open it. Shaking causes carbon dioxide to come out of the cola solution and change to a gas. The gas fizzes out of the bottle and spreads into the surrounding air, showing that its particles have enough kinetic energy to spread apart. Then you could tilt the open bottle and pour out a small amount of the cola on a table, where it will form a puddle. This shows that particles of the liquid have enough kinetic energy to slide over each other but not enough to pull apart completely. If you do nothing to the solid glass of the cola bottle, it will remain the same size and shape. Its particles do not have enough energy to move apart or even to slide over each other. ",text,
L_0935,law of conservation of momentum,T_4564,"When skater 2 runs into skater 1, hes going faster than skater 1 so he has more momentum. Momentum is a property of a moving object that makes it hard to stop. Its a product of the objects mass and velocity. At the moment of the collision, skater 2 transfers some of his momentum to skater 1, who shoots forward when skater 2 runs into him. Whenever an action and reaction such as this occur, momentum is transferred from one object to the other. However, the combined momentum of the objects remains the same. In other words, momentum is conserved. This is the law of conservation of momentum. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_0935,law of conservation of momentum,T_4565,"The Figure 1.1 shows how momentum is conserved in the two colliding skaters. The total momentum is the same after the collision as it was before. However, after the collision, skater 1 has more momentum and skater 2 has less momentum than before. Q: What if two skaters have a head-on collision? Do you think momentum is conserved then? A: As in all actions and reactions, momentum is also conserved in a head-on collision. ",text,
L_0936,law of reflection,T_4566,"Reflection is one of several ways that light can interact with matter. Light reflects off surfaces such as mirrors that do not transmit or absorb light. When light is reflected from a smooth surface, it may form an image. An image is a copy of an object that is formed by reflected (or refracted) light. Q: Is an image an actual object? If not, what is it? A: No, an image isnt an actual object. It is focused rays of light that make a copy of an object, like a picture projected on a screen. ",text,
L_0936,law of reflection,T_4567,"If a surface is extremely smooth, as it is in a mirror, then the image formed by reflection is sharp and clear. This is called regular reflection (also called specular reflection). However, if the surface is even slightly rough or bumpy, an image may not form, or if there is an image, it is blurry or fuzzy. This is called diffuse reflection. Q: Look at the boats and their images in the Figure 1.1. Which one represents regular reflection, and which one represents diffuse reflection? A: Reflection of the boat on the left is regular reflection. The water is smooth and the image is sharp and clear. Reflection of the boat on the right is diffuse reflection. The water has ripples and the image is blurry and wavy. In the Figure 1.2, you can see how both types of reflection occur. Waves of light are represented by arrows called rays. Rays that strike the surface are referred to as incident rays, and rays that reflect off the surface are known as reflected rays. In regular reflection, all the rays are reflected in the same direction. This explains why regular reflection forms a clear image. In diffuse reflection, the rays are reflected in many different directions. This is why diffuse reflection forms, at best, a blurry image. ",text,
L_0936,law of reflection,T_4567,"If a surface is extremely smooth, as it is in a mirror, then the image formed by reflection is sharp and clear. This is called regular reflection (also called specular reflection). However, if the surface is even slightly rough or bumpy, an image may not form, or if there is an image, it is blurry or fuzzy. This is called diffuse reflection. Q: Look at the boats and their images in the Figure 1.1. Which one represents regular reflection, and which one represents diffuse reflection? A: Reflection of the boat on the left is regular reflection. The water is smooth and the image is sharp and clear. Reflection of the boat on the right is diffuse reflection. The water has ripples and the image is blurry and wavy. In the Figure 1.2, you can see how both types of reflection occur. Waves of light are represented by arrows called rays. Rays that strike the surface are referred to as incident rays, and rays that reflect off the surface are known as reflected rays. In regular reflection, all the rays are reflected in the same direction. This explains why regular reflection forms a clear image. In diffuse reflection, the rays are reflected in many different directions. This is why diffuse reflection forms, at best, a blurry image. ",text,
L_0936,law of reflection,T_4568,One thing is true of both regular and diffuse reflection. The angle at which the reflected rays leave the surface is equal to the angle at which the incident rays strike the surface. This is known as the law of reflection. The law is illustrated in the Figure 1.3. ,text,
L_0937,lens,T_4569,"A lens is a transparent object with one or two curved surfaces. It is typically made of glass (or clear plastic in the case of a contact lens). A lens refracts, or bends, light and forms an image. An image is a copy of an objected formed by the refraction (or reflection) of visible light. The more curved the surface of a lens is, the more it refracts the light that passes through it. There are two basic types of lenses: concave and convex. The two types of lenses have different shapes, so they bend light and form images in different ways. ",text,
L_0937,lens,T_4570,"A concave lens is thicker at the edges than it is in the middle. You can see the shape of a concave lens in the Figure Note that the image formed by a concave lens is on the same side of the lens as the object. It is also smaller than the object and right-side up. However, it isnt a real image. It is a virtual image. Your brain tricks you into seeing an image there. The light rays actually pass through the glass to the other side and spread out in all directions. ",text,
L_0937,lens,T_4571,"A convex lens is thicker in the middle than at the edges. You can see the shape of a convex lens in the Figure 1.2. A convex lens causes rays of light to converge, or meet, at a point called the focus (F). A convex lens forms either a real or virtual image. It depends on how close the object is to the lens relative to the focus. Q: An example of a convex lens is a hand lens. Which of the three convex lens diagrams in the Figure 1.2 shows how a hand lens makes an image? A: Youve probably looked through a hand lens before. If you have, then you know that the image it produces is right-side up. Therefore, the first diagram must show how a hand lens makes an image. Its the only one that produces a right-side up image. ",text,
L_0938,lever,T_4572,"A lever is a simple machine consisting of a bar that rotates around a fixed point. The fixed point of a lever is called the fulcrum. Like other machines, a lever makes work easier by changing the force applied to the machine or the distance over which the force is applied. How does a hammer make it easier to pull a nail out of a board? First, it changes the direction of the force applied to the hammerthe hand pushes down on the handle while the claw end of the hammer head pulls up. Often, you can push down with more force than you can push up because you can put your own weight behind it. The hammer also increases the strength of the force that is applied to it. It easily pulls the nail out of the board, which you couldnt do with your hands alone. On the other hand, the hammer decreases the distance over which the force is applied. The hand pushing down on the handle moves the handle over a distance of several inches, whereas the hammer pulls up on the nail only an inch or two. Q: Where is the fulcrum of the hammer when it is used to pull a nail out of a board? In other words, around what point does the hammer rotate? A: The fulcrum is the point where the head of the hammer rests on the surface of the board. ",text,
L_0938,lever,T_4573,"Other levers change force or distance in different ways than a hammer removing a nail. How a lever changes force or distance depends on the location of the input and output forces relative to the fulcrum. The input force is the force applied by the user to the lever. The output force is the force applied by the lever to the object. Based on the location of input and output forces, there are three basic types of levers, called first-class, second-class, and third-class levers. The Table 1.1 describes the three classes. Class of Lever Example of Lever in This Class First class Location of Input & Output Forces & Fulcrum* Ideal Mechanical Advantage Change in Direction of Force? Seesaw 1 <1 >1 yes yes yes Second class Wheelbarrow >1 no Third class Hockey stick <1 no = fulcrum I = input force O = output force The Table 1.1 includes the ideal mechanical advantage of each class of lever. The mechanical advantage is the factor by which a machine changes the input force. The ideal mechanical advantage is the increase or decrease in force that would occur if there were no friction to overcome in the use of the machine. Because all machines must overcome some friction, the ideal mechanical advantage is always somewhat greater than the actual mechanical advantage of the machine as it is used in the real world. Q: Which class of lever is a hammer when it is used to pry a nail out of a board? What is its mechanical advantage? A: To pry a nail out of a board, the fulcrum is located between the input and output forces. Therefore, when a hammer is used in this way it is a first class lever. The fulcrum is closer to the output force than the input force, so the mechanical advantage is >1. In other words, the hammer increases the force applied to it, making it easier to pry the nail out of the board. ",text,
L_0938,lever,T_4574,"All three classes of levers make work easier, but they do so in different ways. When the input and output forces are on opposite sides of the fulcrum, the lever changes the direction of the applied force. This occurs only with first-class levers. When both the input and output forces are on the same side of the fulcrum, the direction of the applied force does not change. This occurs with both second-class and third-class levers. When the input force is applied farther from the fulcrum than the output force is, the output force is greater than the input force, and the ideal mechanical advantage is greater than 1. This always occurs with second-class levers and may occur with first-class levers. When the input force is applied closer to the fulcrum than the output force is, the output force is less than the input force, and the ideal mechanical advantage is less than 1. This always occurs with third-class levers and may occur with first-class levers. When the input and output forces are the same distance from the fulcrum, the output force equals the input force, and the ideal mechanical advantage is 1. This occurs only with first some first-class levers. ",text,
L_0938,lever,T_4575,"You may be wondering why you would use a third-class lever when it doesnt change the direction or strength of the applied force. The advantage of a third-class lever is that the output force is applied over a greater distance than the input force. The output end of the lever must move faster than the input end in order to cover the greater distance. Q: A broom is a third-class lever when it is used to sweep a floor (see the Figure 1.1), so the output end of the lever moves faster than the input end. Why is this useful? A: By moving more quickly over the floor, the broom does the work faster. ",text,
L_0939,light,T_4576,"Electromagnetic waves are waves that carry energy through matter or space as vibrating electric and magnetic fields. Electromagnetic waves have a wide range of wavelengths and frequencies. Sunlight contains the complete range of wavelengths of electromagnetic waves, which is called the electromagnetic spectrum. The Figure 1.1 shows all the waves in the spectrum. ",text,
L_0939,light,T_4577,"Light includes infrared light, visible light, and ultraviolet light. As you can see from the Figure 1.1, light falls roughly in the middle of the electromagnetic spectrum. It has shorter wavelengths and higher frequencies than microwaves, but not as short and high as X rays. Q: Which type of light do you think is harmful to the skin? A: Waves of light with the highest frequencies have the most energy and are harmful to the skin. Use the electro- magnetic spectrum in the Figure 1.1 to find out which of the three types of light have the highest frequencies. ",text,
L_0939,light,T_4578,"Light with the longest wavelengths is called infrared light. The term infrared means below red. Infrared light is the range of light waves that have longer wavelengths and lower frequencies than red light in the visible range of light waves. The sun gives off infrared light as do flames and living things. You cant see infrared light waves, but you can feel them as heat. But infrared cameras and night vision goggles can detect infrared light waves and convert them to visible images. ",text,
L_0939,light,T_4579,"The only light that people can see is called visible light. This light consists of a very narrow range of wavelengths that falls between infrared light and ultraviolet light. Within the visible range, we see light of different wavelengths as different colors of light, from red light, which has the longest wavelength, to violet light, which has the shortest wavelength (see Figure 1.2). When all of the wavelengths of visible light are combined, as they are in sunlight, visible light appears white. ",text,
L_0939,light,T_4580,"Light with wavelengths shorter than visible light is called ultraviolet light. The term ultraviolet means above violet. Ultraviolet light is the range of light waves that have shorter wavelengths and higher frequencies than violet light in the visible range of light. With higher frequencies than visible light, ultraviolet light has more energy. It can be used to kill bacteria in food and to sterilize surgical instruments. The human skin also makes vitamin D when it is exposed to ultraviolet light. Vitamin D, in turn, is needed for strong bones and teeth. Too much exposure to ultraviolet light can cause sunburn and skin cancer. As the slip, slop, slap slogan suggests, you can protect your skin from ultraviolet light by wearing clothing that covers your skin, applying sunscreen to any exposed areas, and wearing a hat to protect your head from exposure. The SPF, or sun-protection factor, of sunscreen gives a rough idea of how long it protects the skin from sunburn (see Figure 1.3). A sunscreen with a higher SPF value protects the skin longer. Sunscreen must be applied liberally and often to be effective, and no sunscreen is completely waterproof. Q: You should apply sunscreen even on cloudy days. Can you explain why? A: Ultraviolet light can travel through clouds, so it can harm unprotected skin even on cloudy days. ",text,
L_0940,lipid classification,T_4581,"Lipids are one of four classes of biochemical compounds, which are compounds that make up living things and carry out life processes. (The other three classes of biochemical compounds are carbohydrates, proteins, and nucleic acids.) Living things use lipids to store energy. Lipids are also the major components of cell membranes in living things. Types of lipids include fats and oils. Fats are solid lipids that animals use to store energy. Oils are liquid lipids that plants use to store energy. Q: Can you name some lipids that are fats? What are some lipids that are oils? A: Lipids that are fats include butter and the fats in meats. Lipids that are oils include olive oil and vegetable oil. Examples of both types of lipids are pictured in the Figure 1.1. ",text,
L_0940,lipid classification,T_4582,"Lipids consist only or mainly of carbon, hydrogen, and oxygen. Both fats and oils are made up of long chains of carbon atoms that are bonded together. These chains are called fatty acids. Fatty acids may be saturated or (A) The white bands on these lamb chops are fat. (B) The yellow liquid in this bottle is olive oil. unsaturated. In the Figure 1.2 you can see structural formulas for two small fatty acids, one saturated and one unsaturated. Saturated fatty acids have only single bonds between carbon atoms. As a result, the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogens. Saturated fatty acids are found in fats. Unsaturated fatty acids have at least one double bond between carbon atoms. As a result, some carbon atoms are not bonded to as many hydrogen atoms as possible. They are unsaturated with hydrogens. Unsaturated fatty acids are found in oils. Q: Both of these fatty acid molecules have six carbon atoms and two oxygen atoms. How many hydrogen atoms does each fatty acid molecule contain? What else is different about the two molecules? A: The saturated fatty acid molecule has 12 hydrogen atoms. This is as many hydrogen atoms as can possibly be bonded to carbon atoms in this molecule. The unsaturated fatty acid molecule has 10 hydrogen atoms, or two less than the maximum possible number. The saturated fatty acid has only single bonds between its carbon atoms. The unsaturated fatty acid has a double bond between two of its carbon atoms. ",text,
L_0940,lipid classification,T_4582,"Lipids consist only or mainly of carbon, hydrogen, and oxygen. Both fats and oils are made up of long chains of carbon atoms that are bonded together. These chains are called fatty acids. Fatty acids may be saturated or (A) The white bands on these lamb chops are fat. (B) The yellow liquid in this bottle is olive oil. unsaturated. In the Figure 1.2 you can see structural formulas for two small fatty acids, one saturated and one unsaturated. Saturated fatty acids have only single bonds between carbon atoms. As a result, the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogens. Saturated fatty acids are found in fats. Unsaturated fatty acids have at least one double bond between carbon atoms. As a result, some carbon atoms are not bonded to as many hydrogen atoms as possible. They are unsaturated with hydrogens. Unsaturated fatty acids are found in oils. Q: Both of these fatty acid molecules have six carbon atoms and two oxygen atoms. How many hydrogen atoms does each fatty acid molecule contain? What else is different about the two molecules? A: The saturated fatty acid molecule has 12 hydrogen atoms. This is as many hydrogen atoms as can possibly be bonded to carbon atoms in this molecule. The unsaturated fatty acid molecule has 10 hydrogen atoms, or two less than the maximum possible number. The saturated fatty acid has only single bonds between its carbon atoms. The unsaturated fatty acid has a double bond between two of its carbon atoms. ",text,
L_0940,lipid classification,T_4583,"Some lipids contain the element phosphorus as well as carbon, hydrogen, and oxygen. These lipids are called phospholipids. Two layers of phospholipid molecules make up the cell membranes of living things. In the Figure One end of each phospholipid molecule is polar, so it has a partial electric charge. Water is also polar and has electrically charged ends, so it is attracted to the oppositely charged end of a phospholipid molecule. This end of the phospholipid molecule is described as hydrophilic, which means water loving. The other end of each phospholipid molecule is nonpolar and has no electric charge. This end of the phospho- lipid molecule repels polar water and is described as hydrophobic, or water hating. In the Figure 1.3, the hydrophilic ends of the phospholipid molecules are on the outsides of the cell membrane, and the hydrophobic ends are on the inside of the cell membrane. This arrangement of phospholipids allows some substances to pass through the cell membrane while keeping other substances out. ",text,
L_0942,longitudinal wave,T_4586,"A longitudinal wave is a type of mechanical wave. A mechanical wave is a wave that travels through matter, called the medium. In a longitudinal wave, particles of the medium vibrate in a direction that is parallel to the direction that the wave travels. You can see this in the Figure 1.1. The persons hand pushes and pulls on one end of the spring. The energy of this disturbance passes through the coils of the spring to the other end. Click image to the left or use the URL below. URL: ",text,
L_0942,longitudinal wave,T_4587,"Notice in the Figure 1.1 that the coils of the spring first crowd closer together and then spread farther apart as the wave passes through them. Places where particles of a medium crowd closer together are called compressions, and places where the particles spread farther apart are called rarefactions. The more energy the wave has, the closer together the particles are in compressions and the farther apart they are in rarefactions. ",text,
L_0942,longitudinal wave,T_4588,Earthquakes cause longitudinal waves called P waves. The disturbance that causes an earthquake sends longitudinal waves through underground rocks in all directions away from the disturbance. P waves are modeled in the Figure Q: Where are the compressions and rarefactions of the medium in this model of P waves? A: The compressions are the places where the vertical lines are closest together. The rarefactions are the places where the vertical lines are farthest apart. ,text,
L_0943,magnetic field reversal,T_4589,"Earths magnetic poles have switched places repeatedly in the past. As you can see in the Figure 1.1, each time the switch occurred, Earths magnetic field was reversed. The magnetic field is the region around a magnet over which it exerts magnetic force. We think of todays magnetic field direction as normal, but thats only because its what were used to. ",text,
L_0943,magnetic field reversal,T_4590,"Scientists dont know for certain why magnetic reversals occur, but there is hard evidence that they have for hundreds of millions of years. The evidence comes from rocks on the ocean floor. Look at Figure 1.2. They show the same ridge on the ocean floor during different periods of time. A. At the center of the ridge, hot magma pushes up through the crust and hardens into rock. Once the magma hardens, the alignment of magnetic domains in the rock is frozen in place forever. Magnetic domains are regions in the rocks where all the atoms are lined up and pointing toward Earths north magnetic pole. B. The newly hardened rock is gradually pushed away from the ridge in both directions as more magma erupts and newer rock forms. The alignment of magnetic domains in this new rock is in the opposite direction, showing that a magnetic reversal has occurred. C. A magnetic reversal occurs again. It is frozen in rock to document the change. Rock samples from many places on the ocean floor show that the north and south magnetic poles reversed hundreds of times over the last 330 million years. The last reversal was less than a million years ago. ",text,
L_0944,magnets,T_4591,"A magnet is an object that attracts certain materials such as iron. Youre probably familiar with common bar magnets, like the one shown in the Figure 1.1. Like all magnets, this bar magnet has north and south magnetic poles. The red end of the magnet is the north pole and the blue end is the south pole. The poles are regions where the magnet is strongest. The poles are called north and south because they always line up with Earths north-south axis if the magnet is allowed to move freely. (Earths axis is the imaginary line around which the planet rotates.) Q: What do you suppose would happen if you cut the bar magnet pictured in the Figure 1.1 along the line between the north and south poles? A: Both halves of the magnet would also have north and south poles. If you cut each of the halves in half, all those pieces would have north and south poles as well. Pieces of a magnet always have both north and south poles no matter how many times you cut the magnet. ",text,
L_0944,magnets,T_4592,"The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other. ",text,
L_0944,magnets,T_4592,"The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other. ",text,
L_0944,magnets,T_4592,"The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other. ",text,
L_0946,mechanical advantage,T_4596,"How much a machine changes the input force is its mechanical advantage. Mechanical advantage is the ratio of the output force to the input force, so it can be represented by the equation: Actual Mechanical Advantage = Output force Input force Note that this equation represents the actual mechanical advantage of a machine. The actual mechanical advantage takes into account the amount of the input force that is used to overcome friction. The equation yields the factor by which the machine changes the input force when the machine is actually used in the real world. ",text,
L_0946,mechanical advantage,T_4597,"It can be difficult to measure the input and output forces needed to calculate the actual mechanical advantage of a machine. Generally, an unknown amount of the input force is used to overcome friction. Its usually easier to measure the input and output distances than the input and output forces. The distance measurements can then be used to calculate the ideal mechanical advantage. The ideal mechanical advantage represents the change in input force that would be achieved by the machine if there were no friction to overcome. The ideal mechanical advantage is always greater than the actual mechanical advantage because all machines have to overcome friction. Ideal mechanical advantage can be calculated with the equation: Ideal Mechanical Advantage = Input Distance Output Distance ",text,
L_0946,mechanical advantage,T_4598,"Look at the ramp in the Figure 1.1. A ramp is a type of simple machine called an inclined plane. It can be used to raise an object off the ground. The input distance is the length of the sloped surface of the ramp. This is the distance over which the input force is applied. The output distance is the height of the ramp, or the vertical distance the object is raised. For this ramp, the input distance is 6 m and the output distance is 2 meters. Therefore, the ideal mechanical advantage of this ramp is: Input distance Ideal Mechanical Advantage = Output distance = 62 m m =3 An ideal mechanical advantage of 3 means that the ramp ideally (in the absence of friction) multiplies the input force by a factor of 3. The trade-off is that the input force must be applied over a greater distance than the object is lifted. Q: Assume that another ramp has a sloping surface of 8 m and a vertical height of 4 m. What is the ideal mechanical advantage of this ramp? A: The ramp has an ideal mechanical advantage of: Ideal Mechanical Advantage = 84 m m =2 ",text,
L_0946,mechanical advantage,T_4599,"Many machinesincluding inclined planes such as rampsincrease the strength of the force put into the machine but decrease the distance over which the force is applied. Other machines increase the distance over which the force is applied but decrease the strength of the force. Still other machines change the direction of the force, with or without also increasing its strength or distance. Which way a machine works determines its mechanical advantage, as shown in the Table 1.1. Strength of Force increases decreases stays the same (changes direction only) Distance Over Force is Applied decreases increases stays the same which Mechanical Advantage Example >1 <1 =1 ramp hammer flagpole pulley ",text,
L_0947,mechanical wave,T_4600,"The waves in the picture above are examples of mechanical waves. A mechanical wave is a disturbance in matter that transfers energy through the matter. A mechanical wave starts when matter is disturbed. A source of energy is needed to disturb matter and start a mechanical wave. Q: Where does the energy come from in the water wave pictured above? A: The energy comes from the falling droplets of water, which have kinetic energy because of their motion. ",text,
L_0947,mechanical wave,T_4601,"The energy of a mechanical wave can travel only through matter. The matter through which the wave travels is called the medium (plural, media). The medium in the water wave pictured above is water, a liquid. But the medium of a mechanical wave can be any state of matter, even a solid. Q: How do the particles of the medium move when a wave passes through them? A: The particles of the medium just vibrate in place. As they vibrate, they pass the energy of the disturbance to the particles next to them, which pass the energy to the particles next to them, and so on. Particles of the medium dont actually travel along with the wave. Only the energy of the wave travels through the medium. ",text,
L_0947,mechanical wave,T_4602,"There are three types of mechanical waves: transverse, longitudinal, and surface waves. They differ in how particles of the medium move. You can see this in the Figure 1.1. In a transverse wave, particles of the medium vibrate up and down perpendicular to the direction of the wave. In a longitudinal wave, particles of the medium vibrate back and forth parallel to the direction of the wave. In a surface wave, particles of the medium vibrate both up and down and back and forth, so they end up moving in a circle. Q: How do you think surface waves are related to transverse and longitudinal waves? A: A surface wave is combination of a transverse wave and a longitudinal wave. ",text,
L_0949,mendeleevs periodic table,T_4606,"For many years, scientists looked for a good way to organize the elements. This became increasingly important as more and more elements were discovered. An ingenious method of organizing elements was developed in 1869 by a Russian scientist named Dmitri Mendeleev, who is pictured 1.1. Mendeleevs method of organizing elements was later revised, but it served as a basis for the method that is still used today. Mendeleev was a teacher as well as a chemist. He was writing a chemistry textbook and wanted to find a way to organize the 63 known elements so it would be easier for students to learn about them. He made a set of cards of the elements, similar to a deck of playing cards. On each card, he wrote the name of a different element, its atomic mass, and other known properties. Mendeleev arranged and rearranged the cards in many different ways, looking for a pattern. He finally found it when he placed the elements in order by increasing atomic mass. Q: What is atomic mass? Why might it be a good basis for organizing elements? A: Atomic mass is the mass of one atom of an element. It is about equal to the mass of the protons plus the neutrons in an atom. It is a good basis for organizing elements because each element has a unique number of protons and atomic mass is an indirect way of organizing elements by number of protons. ",text,
L_0949,mendeleevs periodic table,T_4607,"You can see how Mendeleev organized the elements in the Figure 1.2. From left to right across each row, elements are arranged by increasing atomic mass. Mendeleev discovered that if he placed eight elements in each row and then continued on to the next row, the columns of the table would contain elements with similar properties. He called the columns groups. They are sometimes called families, because elements within a group are similar but not identical to one another, like people in a family. Mendeleevs table of the elements is called a periodic table because of its repeating pattern. Anything that keeps repeating is referred to as periodic. Other examples of things that are periodic include the monthly phases of the moon and the daily cycle of night and day. The term period refers to the interval between repetitions. For example, the moons phases repeat every four weeks. In a periodic table of the elements, the periods are the rows of the table. In Mendeleevs table, each period contains eight elements, and then the pattern repeats in the next row. ",text,
L_0949,mendeleevs periodic table,T_4608,"Did you notice the blanks in Mendeleevs table? They are spaces that Mendeleev left blank for elements that had not yet been discovered when he created his table. He predicted that these missing elements would eventually be discovered. Based on their position in the table, he even predicted their properties. For example, he predicted a missing element in row 5 of group III. He also predicted that the missing element would have an atomic mass of 68 and be a relatively soft metal like other elements in this group. Scientists searched for the missing element, and they found it just a few years later. They named the new element gallium. Scientists searched for the other missing elements in Mendeleevs table and eventually found all of them. An important measure of a good model is its ability to make accurate predictions. This makes it a useful model. Clearly, Mendeleevs periodic table was a useful model. It helped scientists discover new elements and made sense of those that were already known. ",text,
L_0950,metallic bonding,T_4609,"Metallic bonds are forces of attraction between positive metal ions and the valence electrons that are constantly moving around them (see the Figure 1.1). The valence electrons include their own and those of other, nearby ions of the same metal. The valence electrons of metals move freely in this way because metals have relatively low electronegativity, or attraction to electrons. The positive metal ions form a lattice-like structure held together by all the metallic bonds. Click image to the left or use the URL below. URL:  Q: Why do metallic bonds form only in elements that are metals? Why dont similar bonds form in elements that are nonmetals? A: Metal atoms readily give up valence electrons and become positive ions whenever they form bonds. When nonmetals bond together, the atoms share valence electrons and do not become ions. For example, when oxygen atoms bond together they form oxygen molecules in which two oxygen atoms share two pairs of valence electrons equally, so neither atom becomes charged. ",text,
L_0950,metallic bonding,T_4610,"The valence electrons surrounding metal ions are constantly moving. This makes metals good conductors of electricity. The lattice-like structure of metal ions is strong but quite flexible. This allows metals to bend without breaking. Metals are both ductile (can be shaped into wires) and malleable (can be shaped into thin sheets). Q: Look at the metalworker in the Figure 1.2. Hes hammering a piece of hot iron in order to shape it. Why doesnt the iron crack when he hits it? A: The iron ions can move within the sea of electrons around them. They can shift a little closer together or farther apart without breaking the metallic bonds between them. Therefore, the metal can bend rather than crack when the hammer hits it. ",text,
L_0950,metallic bonding,T_4610,"The valence electrons surrounding metal ions are constantly moving. This makes metals good conductors of electricity. The lattice-like structure of metal ions is strong but quite flexible. This allows metals to bend without breaking. Metals are both ductile (can be shaped into wires) and malleable (can be shaped into thin sheets). Q: Look at the metalworker in the Figure 1.2. Hes hammering a piece of hot iron in order to shape it. Why doesnt the iron crack when he hits it? A: The iron ions can move within the sea of electrons around them. They can shift a little closer together or farther apart without breaking the metallic bonds between them. Therefore, the metal can bend rather than crack when the hammer hits it. ",text,
L_0951,metalloids,T_4611,"Metalloids are the smallest class of elements. (The other two classes of elements are metals and nonmetals). There are just six metalloids. In addition to silicon, they include boron, germanium, arsenic, antimony, and tellurium. Metalloids fall between metals and nonmetals in the periodic table. They also fall between metals and nonmetals in terms of their properties. Q: How does the position of an element in the periodic table influence its properties? A: Elements are arranged in the periodic table by their atomic number, which is the number of protons in their atoms. Atoms are neutral in electric charge, so they always have the same number of electrons as protons. It is the number of electrons in the outer energy level of atoms that determines most of the properties of elements. ",text,
L_0951,metalloids,T_4612,"How metalloids behave in chemical interactions with other elements depends mainly on the number of electrons in the outer energy level of their atoms. Metalloids have from three to six electrons in their outer energy level. Boron, pictured in the Figure 1.1, is the only metalloid with just three electrons in its outer energy level. It tends to act like metals by giving up its electrons in chemical reactions. Metalloids with more than four electrons in their outer energy level (arsenic, antimony, and tellurium) tend to act like nonmetals by gaining electrons in chemical reactions. Those with exactly four electrons in their outer energy level (silicon and germanium) may act like either metals or nonmetals, depending on the other elements in the reaction. ",text,
L_0951,metalloids,T_4613,"Most metalloids have some physical properties of metals and some physical properties of nonmetals. For example, metals are good conductors of both heat and electricity, whereas nonmetals generally cannot conduct heat or electricity. And metalloids? They fall between metals and nonmetals in their ability to conduct heat, and if they can conduct electricity, they usually can do so only at higher temperatures. Metalloids that can conduct electricity at higher temperatures are called semiconductors. Silicon is an example of a semiconductor. It is used to make the tiny electric circuits in computer chips. You can see a sample of silicon and a silicon chip in the Figure 1.2. Metalloids tend to be shiny like metals but brittle like nonmetals. Because they are brittle, they may chip like glass or crumble to a powder if struck. Other physical properties of metalloids are more variable, including their boiling and melting points, although all metalloids exist as solids at room temperature. Click image to the left or use the URL below. URL: ",text,
L_0952,metals,T_4614,"Metals are elements that can conduct electricity. They are one of three classes of elements (the other two classes are nonmetals and metalloids). Metals are by far the largest of the three classes. In fact, most elements are metals. All of the elements on the left side and in the middle of the periodic table, except for hydrogen, are metals. There are several different types of metals, including alkali metals in group 1 of the periodic table, alkaline Earth metals in group 2, and transition metals in groups 3-12. The majority of metals are transition metals. ",text,
L_0952,metals,T_4615,"Elements in the same class share certain basic similarities. In addition to conducting electricity, many metals have several other shared properties, including those listed below. Metals have relatively high melting points. This explains why all metals except for mercury are solids at room temperature. Most metals are good conductors of heat. Thats why metals such as iron, copper, and aluminum are used for pots and pans. Metals are generally shiny. This is because they reflect much of the light that strikes them. The mercury pictured above is very shiny. The majority of metals are ductile. This means that they can be pulled into long, thin shapes, like the aluminum electric wires pictured in the Figure 1.1. Metals tend to be malleable. This means that they can be formed into thin sheets without breaking. An example is aluminum foil, also pictured in the Figure 1.1. Q: The defining characteristic of metals is their ability to conduct electricity. Why do you think metals have this property? A: The properties of metalsas well as of elements in the other classesdepend mainly on the number and arrangement of their electrons. ",text,
L_0952,metals,T_4616,"To understand why metals can conduct electricity, consider the metal lithium as an example. An atom of lithium is modeled below. Look at lithiums electrons. There are two electrons at the first energy level. This energy level can hold only two electrons, so it is full in lithium. The second energy level is another story. It can hold a maximum of eight electrons, but in lithium it has just one. A full outer energy level is the most stable arrangement of electrons. Lithium would need to gain seven electrons to fill its outer energy level and make it stable. Its far easier for lithium to give up its one electron in energy level 2, leaving it with a full outer energy level (now level 1). Electricity is a flow of electrons. Because lithium (like most other metals) easily gives up its extra electron, it is a good conductor of electricity. This tendency to give up electrons also explains other properties of metals such as lithium. ",text,
L_0953,microwaves,T_4617,Electromagnetic waves carry energy through matter or space as vibrating electric and magnetic fields. Electromag- netic waves have a wide range of wavelengths and frequencies. The complete range is called the electromagnetic spectrum. The Figure 1.1 shows all the waves of the spectrum. The waves used in radar guns are microwaves. ,text,
L_0953,microwaves,T_4618,"Find the microwave in the Figure 1.1. A microwave is an electromagnetic wave with a relatively long wavelength and low frequency. Microwaves are often classified as radio waves, but they have higher frequencies than other radio waves. With higher frequencies, they also have more energy. Thats why microwaves are useful for heating food in microwave ovens. Microwaves have other important uses as well, including cell phone transmissions and radar. These uses are described below. Click image to the left or use the URL below. URL: ",text,
L_0953,microwaves,T_4619,"Cell phone signals are carried through the air as microwaves. You can see how this works in the Figure 1.2. A cell phone encodes the sounds of the callers voice in microwaves by changing the frequency of the waves. This is called frequency modulation. The encoded microwaves are then sent from the phone through the air to a cell tower. From the cell tower, the waves travel to a switching center. From there they go to another cell tower and from the tower to the receiver of the person being called. The receiver changes the encoded microwaves back to sounds. Q: Cell towers reach high above the ground. Why do you think such tall towers are used? A: Microwaves can be interrupted by buildings and other obstructions, so cell towers must be placed high above the ground to prevent the interruption of cell phone signals. ",text,
L_0953,microwaves,T_4620,"Radar stands for radio detection and ranging. In police radar, a radar gun sends out short bursts of microwaves. The microwaves reflect back from oncoming vehicles and are detected by a receiver in the radar gun. The frequency of the reflected waves is used to compute the speed of the vehicles. Radar is also used for tracking storms, detecting air traffic, and other purposes. Q: How are reflected microwaves used to determine the speed of oncoming cars (see Figure 1.3)? A: As the car approaches the radar gun, the reflected microwaves get bunched up in front of the car. Therefore, the waves the receiver detects have a higher frequency than they would if they were being reflected from a stationary object. The faster the car is moving, the greater the increase in the frequency of the waves. This is an example of the Doppler effect, which can also occur with sound waves. ",text,
L_0954,mirrors,T_4621,"A mirror is typically made of glass with a shiny metal backing that reflects all the light that strikes it. When a mirror reflects light, it forms an image. An image is a copy of an object that is formed by reflection or refraction. Mirrors may have flat or curved surfaces. The shape of a mirrors surface determines the type of image it forms. For example, some mirrors form real images, and other mirrors form virtual images. Whats the difference between real and virtual images? A real image forms in front of a mirror where reflected light rays actually meet. It is a true image that could be projected on a screen. A virtual image appears to be on the other side of the mirror. Of course, reflected rays dont actually go through the mirror to the other side, so a virtual image doesnt really exist. It just appears to exist to the human brain. Q: Look back at the image of the girl pointing at her image in the mirror. Which type of image is it, real or virtual? A: The image of the girl is a virtual image. It appears to be on the other side of the mirror from the girl. ",text,
L_0954,mirrors,T_4622,"The mirror in the opening photo is a plane mirror. This is the most common type of mirror. It has a flat reflective surface and forms only virtual images. The image formed by a plane mirror is also right-side up and life sized. But something is different about the image compared with the real object in front of the mirror. Left and right are reversed. Look at the girl brushing her teeth in the Figure 1.1. She is using her left hand to brush her teeth, but her image (on the left) appears to be brushing her teeth with the right hand. All plane mirrors reverse left and right in this way. The term mirror image refers to how left and right are reversed in an image compared with the object. ",text,
L_0954,mirrors,T_4623,"Some mirrors have a curved rather than flat surface. Curved mirrors can be concave or convex. A concave mirror is shaped like the inside of a bowl. This type of mirror forms either real or virtual images, depending on where the object is placed relative to the focal point. The focal point is the point in front of the mirror where the reflected rays meet. You can see how concave mirrors form images in the Figure 1.2. Concave mirrors are used behind car headlights. They focus the light and make it brighter. Concave mirrors are also used in some telescopes. ",text,
L_0954,mirrors,T_4624,"The other type of curved mirror, a convex mirror, is shaped like the outside of a bowl. Because of its shape, it can gather and reflect light from a wide area. As you can see in the Figure 1.3, a convex mirror forms only virtual images that are right-side up and smaller than the actual object. Q: Convex mirrors are used as side mirrors on cars. You can see one in the Figure 1.4. Why is a convex mirror good for this purpose? A: Because it gathers light over a wide area, a convex mirror gives the driver a wider view of the area around the vehicle than a plane mirror would. ",text,
L_0954,mirrors,T_4624,"The other type of curved mirror, a convex mirror, is shaped like the outside of a bowl. Because of its shape, it can gather and reflect light from a wide area. As you can see in the Figure 1.3, a convex mirror forms only virtual images that are right-side up and smaller than the actual object. Q: Convex mirrors are used as side mirrors on cars. You can see one in the Figure 1.4. Why is a convex mirror good for this purpose? A: Because it gathers light over a wide area, a convex mirror gives the driver a wider view of the area around the vehicle than a plane mirror would. ",text,
L_0956,modern periodic table,T_4629,"In the 1860s, a scientist named Dmitri Mendeleev also saw the need to organize the elements. He created a table in which he arranged all of the elements by increasing atomic mass from left to right across each row. When he placed eight elements in each row and then started again in the next row, each column of the table contained elements with similar properties. He called the columns of elements groups. Mendeleevs table is called a periodic table and the rows are called periods. Thats because the table keeps repeating from row to row, and periodic means repeating. ",text,
L_0956,modern periodic table,T_4630,"A periodic table is still used today to organize the elements. You can see a simple version of the modern periodic table in the Figure 1.1. The modern table is based on Mendeleevs table, except the modern table arranges the elements by increasing atomic number instead of atomic mass. Atomic number is the number of protons in an atom, and this number is unique for each element. The modern table has more elements than Mendeleevs table because many elements have been discovered since Mendeleevs time. ",text,
L_0956,modern periodic table,T_4631,"In the Figure 1.1, each element is represented by its chemical symbol, which consists of one or two letters. The first letter of the symbol is always written in upper case, and the second letterif there is oneis always written in lower case. For example, the symbol for copper is Cu. It stands for cuprum, which is the Latin word for copper. The number above each symbol in the table is its unique atomic number. Notice how the atomic numbers increase from left to right and from top to bottom in the table. Q: Find the symbol for copper in the Figure 1.1. What is its atomic number? What does this number represent? A: The atomic number of copper is 29. This number represents the number of protons in each atom of copper. (Copper is the element that makes up the coil of wire in photo A of the opening sequence of photos.) ",text,
L_0956,modern periodic table,T_4632,"Rows of the modern periodic table are called periods, as they are in Mendeleevs table. From left to right across a period, each element has one more proton than the element before it. Some periods in the modern periodic table are longer than others. For example, period 1 contains only two elements: hydrogen (H) and helium (He). In contrast, periods 6 and 7 are so long that many of their elements are placed below the main part of the table. They are the elements starting with lanthanum (La) in period 6 and actinium (Ac) in period 7. Some elements in period 7 have not yet been named. They are represented by temporary three-letter symbols, such as Uub. The number of each period represents the number of energy levels that have electrons in them for atoms of each element in that period. Q: Find calcium (Ca) in the Figure 1.1. How many energy levels have electrons in them for atoms of calcium? A: Calcium is in period 4, so its atoms have electrons in them for the first four energy levels. ",text,
L_0956,modern periodic table,T_4633,"Columns of the modern table are called groups, as they are in Mendeleevs table. However, the modern table has many more groups18 compared with just 8 in Mendeleevs table. Elements in the same group have similar properties. For example, all elements in group 18 are colorless, odorless gases, such as neon (Ne). (Neon is the element inside the light in opening photo C.) In contrast, all elements in group 1 are very reactive solids. They react explosively with water, as you can see in the video and Figure 1.2. Click image to the left or use the URL below. URL:  The alkali metal sodium (Na) reacting with water. ",text,
L_0956,modern periodic table,T_4634,"All elements can be classified in one of three classes: metals, metalloids, or nonmetals. Elements in each class share certain basic properties. For example, elements in the metals class can conduct electricity, whereas elements in the nonmetals class generally cannot. Elements in the metalloids class fall in between the metals and nonmetals in their properties. An example of a metalloid is arsenic (As). (Arsenic is the element in opening photo B.) In the periodic table above, elements are color coded to show their class. As you move from left to right across each period of the table, the elements change from metals to metalloids to nonmetals. Q: To which class of elements does copper (Cu) belong: metal, metalloid, or nonmetal? Identify three other elements in this class. A: In the Figure 1.1, the cell for copper is colored blue. This means that copper belongs to the metals class. Other elements in the metals class include iron (Fe), sodium (Na), and gold (Au). It is apparent from the table that the majority of elements are metals. ",text,
L_0957,molecular compounds,T_4635,"Compounds that form from two or more nonmetallic elements, such as carbon and hydrogen, are called covalent compounds. In a covalent compound, atoms of the different elements are held together in molecules by covalent bonds. These are chemical bonds in which atoms share valence electrons. The force of attraction between the shared electrons and the positive nuclei of both atoms holds the atoms together in the molecule. A molecule is the smallest particle of a covalent compound that still has the properties of the compound. The largest, most complex covalent molecules have thousands of atoms. Examples include proteins and carbohy- drates, which are compounds in living things. The smallest, simplest covalent compounds have molecules with just two atoms. An example is hydrogen chloride (HCl). It consists of one hydrogen atom and one chlorine atom, as you can see in the Figure 1.1. ",text,
L_0957,molecular compounds,T_4636,"To name simple covalent compounds, follow these rules: Start with the name of the element closer to the left side of the periodic table. Follow this with the name of element closer to the right of the periodic table. Give this second name the suffix -ide. Use prefixes to represent the numbers of the different atoms in each molecule of the compound. The most commonly used prefixes are shown in the Table 1.1. Number 1 2 3 4 5 6 Prefix mono- (or none) di- tri- tetra- penta- hexa- Q: What is the name of the compound that contains three oxygen atoms and two nitrogen atoms? A: The compound is named dinitrogen trioxide. Nitrogen is named first because it is farther to the left in the periodic table than oxygen. Oxygen is given the -ide suffix because it is the second element named in the compound. The prefix di- is added to nitrogen to show that there are two atoms of nitrogen in each molecule of the compound. The prefix tri- is added to oxygen to show that there are three atoms of oxygen in each molecule. In the chemical formula for a covalent compound, the numbers of the different atoms in a molecule are represented by subscripts. For example, the formula for the compound named carbon dioxide is CO2 . Q: What is the chemical formula for dinitrogen trioxide? A: The chemical formula is N2 O3 . ",text,
L_0957,molecular compounds,T_4637,"The covalent bonds of covalent compounds are responsible for many of the properties of the compounds. Because valence electrons are shared in covalent compounds, rather than transferred between atoms as they are in ionic compounds, covalent compounds have very different properties than ionic compounds. Many covalent compounds, especially those containing carbon and hydrogen, burn easily. In contrast, many ionic compounds do not burn. Many covalent compounds do not dissolve in water, whereas most ionic compounds dissolve well in water. Unlike ionic compounds, covalent compounds do not have freely moving electrons, so they cannot conduct Name of Compound(Chemical For- mula) Sodium chloride (NaCl) Lithium fluoride (LiF) Type of Compound Boiling Point ( C) ionic ionic 1413 1676 Q: The two covalent compounds in the table are gases at room temperature, which is 20 C. For a compound to be a liquid at room temperature, what does its boiling point have to be? A: To be a liquid at room temperature, a covalent compound has to have a boiling point higher than 20 C. Water is an example of a covalent compound that is a liquid at room temperature. The boiling point of water is 100 C. ",text,
L_0958,momentum,T_4638,"Momentum is a property of a moving object that makes it hard to stop. The more mass it has or the faster its moving, the greater its momentum. Momentum equals mass times velocity and is represented by the equation: Momentum = Mass  Velocity Q: What is Codys momentum as he stands at the top of the ramp? A: Cody has no momentum as he stands there because he isnt moving. In other words, his velocity is zero. However, Cody will gain momentum as he starts moving down the ramp and picks up speed. Q: Codys older brother Jerod is pictured in the Figure 1.1. If Jerod were to travel down the ramp at the same velocity as Cody, who would have greater momentum? Who would be harder to stop? A: Jerod obviously has greater mass than Cody, so he would have greater momentum. He would also be harder to stop. ",text,
L_0958,momentum,T_4639,"To calculate momentum with the equation above, mass is measured in (kg), and velocity is measured in meters per second (m/s). For example, Cody and his skateboard have a combined mass of 40 kg. If Cody is traveling at a velocity of 1.1 m/s by the time he reaches the bottom of the ramp, then his momentum is: Momentum = 40 kg  1.1 m/s = 44 kg  m/s Note that the SI unit for momentum is kg  m/s. Q: The combined mass of Jerod and his skateboard is 68 kg. If Jerod goes down the ramp at the same velocity as Cody, what is his momentum at the bottom of the ramp? A: His momentum is: Momentum = 68 kg  1.1 m/s = 75 kg  m/s ",text,
L_0959,motion,T_4640,"In science, motion is defined as a change in position. An objects position is its location. Besides the wings of the hummingbird in the opening image, you can see other examples of motion in the Figure 1.1. In each case, the position of something is changing. Q: In each picture in the Figure 1.1, what is moving and how is its position changing? A: The train and all its passengers are speeding straight down a track to the next station. The man and his bike are racing along a curving highway. The geese are flying over their wetland environment. The meteor is shooting through the atmosphere toward Earth, burning up as it goes. ",text,
L_0959,motion,T_4641,"Theres more to motion than objects simply changing position. Youll see why when you consider the following example. Assume that the school bus pictured in the Figure 1.2 passes by you as you stand on the sidewalk. Its obvious to you that the bus is moving, but what about to the children inside the bus? The bus isnt moving relative to them, and if they look at the other children sitting on the bus, they wont appear to be moving either. If the ride is really smooth, the children may only be able to tell that the bus is moving by looking out the window and seeing you and the trees whizzing by. This example shows that how we perceive motion depends on our frame of reference. Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving. Q: What is your frame of reference if you are standing on the sidewalk and see the bus go by? How can you tell that the bus is moving? A: Your frame of reference might be the trees and other stationary objects across the street. As the bus goes by, it momentarily blocks your view of these objects, and this helps you detect the bus motion. ",text,
L_0959,motion,T_4641,"Theres more to motion than objects simply changing position. Youll see why when you consider the following example. Assume that the school bus pictured in the Figure 1.2 passes by you as you stand on the sidewalk. Its obvious to you that the bus is moving, but what about to the children inside the bus? The bus isnt moving relative to them, and if they look at the other children sitting on the bus, they wont appear to be moving either. If the ride is really smooth, the children may only be able to tell that the bus is moving by looking out the window and seeing you and the trees whizzing by. This example shows that how we perceive motion depends on our frame of reference. Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving. Q: What is your frame of reference if you are standing on the sidewalk and see the bus go by? How can you tell that the bus is moving? A: Your frame of reference might be the trees and other stationary objects across the street. As the bus goes by, it momentarily blocks your view of these objects, and this helps you detect the bus motion. ",text,
L_0960,musical instruments,T_4642,"People have been using sound to make music for thousands of years. They have invented many different kinds of musical instruments. Despite their diversity, however, musical instruments share certain similarities. All musical instruments create sound by causing matter to vibrate. The vibrations start sound waves moving through the air. Most musical instruments use resonance to amplify the sound waves and make the sounds louder. Resonance occurs when an object vibrates in response to sound waves of a certain frequency. In a musical instrument such as a drum, the whole instrument and the air inside it may vibrate when the head of the drum is struck. Most musical instruments have a way of changing the frequency of the sound waves they produce. This changes the pitch of the sounds, or how high or low the sounds seem to a listener. ",text,
L_0960,musical instruments,T_4643,"There are three basic categories of musical instruments: percussion, wind, and stringed instruments. You can read in the Figure 1.1 how instruments in each category make sound and change pitch. Q: Can you name other instruments in each of the three categories of musical instruments? A: Other percussion instruments include drums and cymbals. Other wind instruments include trumpets and flutes. Other stringed instruments include guitars and harps. ",text,
L_0962,nature of technology,T_4647,"Printers like the one that made the plastic bicycle are a new type of technology. Technology is the application of science to solve problems. Because technology finds solutions to practical problems, new technologies may have major impacts on society, science, and industry. For example, some people predict that 3-D printing will revolutionize manufacturing. Q: Making products with 3-D printers has several advantages over making them with machines in factories. What do you think some of the advantages might be? A: Making products with 3-D printers would allow anyone anywhere to make just about anything, provided they have the printer, powder, and computer program. Suppose, for example, that you live in a remote location and need a new part for your car. The solution? Just download the design on your computer and print the part on your 3-D printer. Manufacturing would no longer require specially designed machines in factories that produce pollution. Another advantage of using 3-D printers to make products is that no materials are wasted. This would lower manufacturing costs as well as save natural resources. ",text,
L_0962,nature of technology,T_4648,"New technologies such as 3-D printers often evolve slowly as new materials, designs, or processes are invented. Solar-powered cars are a good example. For several decades, researchers have been working on developing practical solar-powered cars. Why? Cars powered by sunlight have at least two important advantages over gas-powered cars. The energy they use is free and available almost everywhere, and they produce no pollution. The timeline in Table Milestone 1954: First modern solar cell 1955: First solar car 1983: First practical solar car 1987: First World Solar Challenge 2008: First Commercial solar car The first modern solar cell was invented in 1954 by a team of researchers at Bell Labs in the U.S. It could convert light energy to enough electricity to power devices. In 1955, William G. Cobb of General Motors demon- strated his 15-inch-long Sunmobile, the worlds first solar-powered automobile. Its tiny electric motor was powered by 12 solar cells on top of the car. In 1983, the first drivable solar car was created by Hans Tholstrup, a Danish inventor who was influenced by the earlier Sunmobile. Called the Quiet Achiever, Tholstrups car was driven 4000 km across Australia. However, its average speed was only 23 km/h, despite having more than 700 solar cells on its top panel. Inspired by his success with the Quiet Achiever, in 1987 Tholstrup launched the first World Solar Chal- lenge. This was the worlds first solar car race. The race is now held every other year. In that first race, the winner was General Motors Sunraycer, shown here. It had an average speed of 67 km/h. Its aerodynamic shape helped it achieve that speed. In 2008, the first commercial solar car was introduced. Called the Venturi Astrolab, it has a top speed of 120 km/h. To go this fast while using very little energy, it is built of ultra-light materials. Its oversized body protects the driver in case of collision and provides a lot of surface area for solar cells. Q: Why was the invention of the solar cell important to the evolution of solar car technology? A: The solar car could not exist without the solar cell. This invention provided a way to convert light energy to electricity that could be used to run a device such as a car. Q: The 1955 Sunmobile was just a model car. It was too small for people to drive. Why was it an important achievement in the evolution of solar car technology? A: The car wasnt practical, but it was a working solar car. It showed people that solar car technology is possible. It spurred others, including Hans Tholstrup, to work on solar cars that people could actually drive. Q: How have the World Solar Challenge races influenced the development of solar cars? A: The races have drawn a lot of attention to solar car development. The challenge of winning a race has also stimulated developers to keep improving the performance of solar cars so they can go faster and farther on solar power alone. ",text,
L_0963,neutrons,T_4649,"A neutron is one of three main particles that make up the atom. The other two particles are the proton and electron. Atoms of all elementsexcept for most atoms of hydrogenhave neutrons in their nucleus. The nucleus is the small, dense region at the center of an atom where protons are also found. Atoms generally have about the same number of neutrons as protons. For example, all carbon atoms have six protons and most also have six neutrons. A model of a carbon atom is shown in the Figure 1.1. Click image to the left or use the URL below. URL: ",text,
L_0963,neutrons,T_4650,"Unlike protons and electrons, which are electrically charged, neutrons have no charge. In other words, they are electrically neutral. Thats why the neutrons in the diagram above are labeled n0 . The zero stands for zero charge. The mass of a neutron is slightly greater than the mass of a proton, which is 1 atomic mass unit (amu). (An atomic mass unit equals about 1.67  1027 kilograms.) A neutron also has about the same diameter as a proton, or 1.7 1017 meters. ",text,
L_0963,neutrons,T_4651,"All the atoms of a given element have the same number of protons and electrons. The number of neutrons, however, may vary for atoms of the same element. For example, almost 99 percent of carbon atoms have six neutrons, but the rest have either seven or eight neutrons. Atoms of an element that differ in their numbers of neutrons are called isotopes. The nuclei of these isotopes of carbon are shown in the Figure 1.2. The isotope called carbon-14 is used to find the ages of fossils. Q: Notice the names of the carbon isotopes in the diagram. Based on this example, infer how isotopes of an element are named. A: Isotopes of an element are named for their total number of protons and neutrons. Q: The element oxygen has 8 protons. How many protons and neutrons are there in oxygen-17? A: Oxygen-17like all atoms of oxygenhas 8 protons. Its name provides the clue that it has a total of 17 protons and neutrons. Therefore, it must have 9 neutrons (8 + 9 = 17). ",text,
L_0963,neutrons,T_4652,"Neutrons consist of fundamental particles known as quarks and gluons. Each neutron contains three quarks, as shown in the diagram below. Two of the quarks are called down quarks (d) and the third quark is called an up quark (u). Gluons (represented by wavy black lines in the diagram) are fundamental particles that are given off or absorbed by quarks. They carry the strong nuclear force that holds together quarks in a neutron. ",text,
L_0964,newtons first law,T_4653,"Did you ever ride a skateboard? Even if you didnt, you probably know that to start a skateboard rolling over a level surface, you need to push off with one foot against the ground. Thats what Coreys friend Nina is doing in this picture 1.1. Do you know how to stop a skateboard once it starts rolling? Look how Ninas friend Laura does it in the Figure the skateboard. Even if Laura didnt try to stop the skateboard, it would stop sooner or later. Thats because theres also friction between the wheels and the pavement. Friction is a force that counters all kinds of motion. It occurs whenever two surfaces come into contact. ",text,
L_0964,newtons first law,T_4653,"Did you ever ride a skateboard? Even if you didnt, you probably know that to start a skateboard rolling over a level surface, you need to push off with one foot against the ground. Thats what Coreys friend Nina is doing in this picture 1.1. Do you know how to stop a skateboard once it starts rolling? Look how Ninas friend Laura does it in the Figure the skateboard. Even if Laura didnt try to stop the skateboard, it would stop sooner or later. Thats because theres also friction between the wheels and the pavement. Friction is a force that counters all kinds of motion. It occurs whenever two surfaces come into contact. ",text,
L_0964,newtons first law,T_4654,"If you understand how a skateboard starts and stops, then you already know something about Newtons first law of motion. This law was developed by English scientist Isaac Newton around 1700. Newton was one of the greatest scientists of all time. He developed three laws of motion and the law of gravity, among many other contributions. Newtons first law of motion states that an object at rest will remain at rest and an object in motion will stay in motion unless it is acted on by an unbalanced force. Without an unbalanced force, a moving object will not only keep moving, but its speed and direction will also remain the same. Newtons first law of motion is often called the law of inertia because inertia is the tendency of an object to resist a change in its motion. If an object is already at rest, inertia will keep it at rest. If an object is already in motion, inertia will keep it moving. ",text,
L_0964,newtons first law,T_4655,"Coreys friend Jerod likes to skate on the flat banks at Newtons Skate Park. Thats Jerod in the Figure 1.3. As he reaches the top of a bank, he turns his skateboard to go back down. To change direction, he presses down with his heels on one edge of the skateboard. This causes the skateboard to turn in the opposite direction. ",text,
L_0964,newtons first law,T_4656,"Q: How does Nina use Newtons first law to start her skateboard rolling? A: The skateboard wont move unless Nina pushes off from the pavement with one foot. The force she applies when she pushes off is stronger than the force of friction that opposes the skateboards motion. As a result, the force on the skateboard is unbalanced, and the skateboard moves forward. Q: How does Nina use Newtons first law to stop her skateboard? A: Once the skateboard starts moving, it would keep moving at the same speed and in the same direction if not for another unbalanced force. That force is friction between the skateboard and the pavement. The force of friction is unbalanced because Nina is no longer pushing with her foot to keep the skateboard moving. Thats why the skateboard stops. Q: How does Jerod use Newtons first law of motion to change the direction of his skateboard? A: Pressing down on just one side of a skateboard creates an unbalanced force. The unbalanced force causes the skateboard to turn toward the other side. In the picture, Jerod is pressing down with his heels, so the skateboard turns toward his toes. ",text,
L_0965,newtons law of gravity,T_4657,"Newton was the first one to suggest that gravity is universal and affects all objects in the universe. Thats why Newtons law of gravity is called the law of universal gravitation. Universal gravitation means that the force that causes an apple to fall from a tree to the ground is the same force that causes the moon to keep moving around Earth. Universal gravitation also means that while Earth exerts a pull on you, you exert a pull on Earth. In fact, there is gravity between you and every mass around youyour desk, your book, your pen. Even tiny molecules of gas are attracted to one another by the force of gravity. Q: Newtons law of universal gravitation had a huge impact on how people thought about the universe. Why do you think it was so important? A: Newtons law was the first scientific law that applied to the entire universe. It explains the motion of objects not only on Earth but in outer space as well. ",text,
L_0965,newtons law of gravity,T_4658,"Newtons law also states that the strength of gravity between any two objects depends on two factors: the masses of the objects and the distance between them. Objects with greater mass have a stronger force of gravity between them. For example, because Earth is so massive, it attracts you and your desk more strongly that you and your desk attract each other. Thats why you and the desk remain in place on the floor rather than moving toward one another. Objects that are closer together have a stronger force of gravity between them. For example, the moon is closer to Earth than it is to the more massive sun, so the force of gravity is greater between the moon and Earth than between the moon and the sun. Thats why the moon circles around Earth rather than the sun. You can see this in the Figure 1.1. ",text,
L_0966,newtons second law,T_4659,"Whenever an object speeds up, slows down, or changes direction, it accelerates. Acceleration occurs whenever an unbalanced force acts on an object. Two factors affect the acceleration of an object: the net force acting on the object and the objects mass. Newtons second law of motion describes how force and mass affect acceleration. The law states that the acceleration of an object equals the net force acting on the object divided by the objects mass. This can be represented by the equation: Acceleration = or a = Net force Mass F m Q: While Tony races along on his rollerblades, what net force is acting on the skates? A: Tony exerts a backward force against the ground, as you can see in the Figure 1.1, first with one skate and then with the other. This force pushes him forward. Although friction partly counters the forward motion of the skates, it is weaker than the force Tony exerts. Therefore, there is a net forward force on the skates. ",text,
L_0966,newtons second law,T_4660,"Newtons second law shows that there is a direct relationship between force and acceleration. The greater the force that is applied to an object of a given mass, the more the object will accelerate. For example, doubling the force on the object doubles its acceleration. The relationship between mass and acceleration is different. It is an inverse relationship. In an inverse relationship, when one variable increases, the other variable decreases. The greater the mass of an object, the less it will accelerate when a given force is applied. For example, doubling the mass of an object results in only half as much acceleration for the same amount of force. Q: Tony has greater mass than the other two boys he is racing (pictured in the opening image). How will this affect his acceleration around the track? A: Tonys greater mass will result in less acceleration for the same amount of force. ",text,
L_0967,newtons third law,T_4661,"Newtons third law of motion explains how Jerod starts his skateboard moving. This law states that every action has an equal and opposite reaction. This means that forces always act in pairs. First an action occursJerod pushes against the ground with his foot. Then a reaction occursJerod moves forward on his skateboard. The reaction is always equal in strength to the action but in the opposite direction. Q: If Jerod pushes against the ground with greater force, how will this affect his forward motion? A: His action force will be greater, so the reaction force will be greater as well. Jerod will be pushed forward with more force, and this will make him go faster and farther. ",text,
L_0967,newtons third law,T_4662,"The forces involved in actions and reactions can be represented with arrows. The way an arrow points shows the direction of the force, and the size of the arrow represents the strength of the force. Look at the skateboarders in the Figure 1.1. In the top row, the arrows represent the forces with which the skateboarders push against each other. This is the action. In the bottom row, the arrows represent the forces with which the skateboarders move apart. This is the reaction. Compare the top and bottom arrows. They point in different directions, but they are the same size. This shows that the reaction forces are equal and opposite to the action forces. ",text,
L_0967,newtons third law,T_4663,"Because action and reaction forces are equal and opposite, you might think they would cancel out, as balanced forces do. But you would be wrong. Balanced forces are equal and opposite forces that act on the same object. Thats why they cancel out. Action-reaction forces are equal and opposite forces that act on different objects, so they dont cancel out. In fact, they often result in motion. Think about Jerod again. He applies force with his foot to the ground, whereas the ground applies force to Jerod and the skateboard, causing them to move forward. Q: Actions and reactions occur all the time. Can you think of an example in your daily life? A: Heres one example. If you lean on something like a wall or your locker, you are applying force to it. The wall or locker applies an equal and opposite force to you. If it didnt, you would go right through it or else it would tip over. ",text,
L_0968,noble gases,T_4664,"Noble gases are nonreactive, nonmetallic elements in group 18 of the periodic table. As you can see in the periodic table below, noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All noble gases are colorless and odorless. They also have low boiling points, explaining why they are gases at room temperature. Radon, at the bottom of the group, is radioactive, so it constantly decays to other elements. Click image to the left or use the URL below. URL:  Q: Based on their position in the periodic table (Figure 1.1), how many valence electrons do you think noble gases have? A: The number of valence electrons starts at one for elements in group 1. It then increases by one from left to right across each period (row) of the periodic table for groups 1-2 and 13-18 (numbered 3-0 in the table above). Therefore, noble gases have eight valence electrons. ",text,
L_0968,noble gases,T_4665,"Noble gases are the least reactive of all known elements. Thats because with eight valence electrons, their outer energy levels are full. The only exception is helium, which has just two electrons. But helium also has a full outer energy level, because its only energy level (energy level 1) can hold a maximum of two electrons. A full outer energy level is the most stable arrangement of electrons. As a result, noble gases cannot become more stable by reacting with other elements and gaining or losing valence electrons. Therefore, noble gases are rarely involved in chemical reactions and almost never form compounds with other elements. ",text,
L_0968,noble gases,T_4666,"Because the noble gases are the least reactive of all elements, their eight valence electrons are used as the standard for nonreactivity and to explain how other elements interact. This is stated as the octet (group of eight) rule. According to this rule, atoms react to form compounds that allow them to have a group of eight valence electrons like the noble gases. For example, sodium (with one valence electron) reacts with chlorine (with seven valence electrons) to form the stable compound sodium chloride (table salt). In this reaction, sodium donates an electron and chlorine accepts it, giving each element an octet of valence electrons. ",text,
L_0968,noble gases,T_4667,"Did you ever get a birthday balloon like the one pictured 1.2? The balloon is filled with the noble gas helium. The gas is pumped from a tank into a Mylar balloon. Unlike a balloon filled with air, a balloon filled with helium needs to be weighted down so it wont float away. Q: Why does a helium balloon float away if its not weighted down? A: Helium atoms have just two protons, two neutrons, and two electrons, so they have less mass than any other atoms except hydrogen. As a result, helium is lighter than air, explaining why a helium balloon floats up into the air unless weighted down. Early incandescent light bulbs, like the one pictured in the Figure 1.3, didnt last very long. The filaments quickly burned out. Although air was pumped out of the bulb, it wasnt a complete vacuum. Oxygen in the small amount of air remaining inside the light bulb reacted with the metal filament. This corroded the filament and caused dark deposits on the glass. Filling a light bulb with argon gas prevents these problems. Thats why modern light bulbs are filled with argon. A: As a noble gas with eight electrons, argon doesnt react with the metal in the filament. This protects the filament and keeps the glass blub free of deposits. Noble gases are also used to fill the glass tubes of lighted signs like the one in the Figure 1.4. Although noble gases are chemically nonreactive, their electrons can be energized by sending an electric current through them. When this happens, the electrons jump to a higher energy level. When the electrons return to their original energy level, they give off energy as light. Different noble gases give off light of different colors. Neon gives off reddish-orange light, like the word Open in the sign below. Krypton gives off violet light and xenon gives off blue light. ",text,
L_0968,noble gases,T_4667,"Did you ever get a birthday balloon like the one pictured 1.2? The balloon is filled with the noble gas helium. The gas is pumped from a tank into a Mylar balloon. Unlike a balloon filled with air, a balloon filled with helium needs to be weighted down so it wont float away. Q: Why does a helium balloon float away if its not weighted down? A: Helium atoms have just two protons, two neutrons, and two electrons, so they have less mass than any other atoms except hydrogen. As a result, helium is lighter than air, explaining why a helium balloon floats up into the air unless weighted down. Early incandescent light bulbs, like the one pictured in the Figure 1.3, didnt last very long. The filaments quickly burned out. Although air was pumped out of the bulb, it wasnt a complete vacuum. Oxygen in the small amount of air remaining inside the light bulb reacted with the metal filament. This corroded the filament and caused dark deposits on the glass. Filling a light bulb with argon gas prevents these problems. Thats why modern light bulbs are filled with argon. A: As a noble gas with eight electrons, argon doesnt react with the metal in the filament. This protects the filament and keeps the glass blub free of deposits. Noble gases are also used to fill the glass tubes of lighted signs like the one in the Figure 1.4. Although noble gases are chemically nonreactive, their electrons can be energized by sending an electric current through them. When this happens, the electrons jump to a higher energy level. When the electrons return to their original energy level, they give off energy as light. Different noble gases give off light of different colors. Neon gives off reddish-orange light, like the word Open in the sign below. Krypton gives off violet light and xenon gives off blue light. ",text,
L_0969,nonmetals,T_4668,"Nonmetals are elements that generally do not conduct electricity. They are one of three classes of elements (the other two classes are metals and metalloids.) Nonmetals are the second largest of the three classes after metals. They are the elements located on the right side of the periodic table. Q: From left to right across each period (row) of the periodic table, each element has atoms with one more proton and one more electron than the element before it. How might this be related to the properties of nonmetals? A: Because nonmetals are on the right side of the periodic table, they have more electrons in their outer energy level than elements on the left side or in the middle of the periodic table. The number of electrons in the outer energy level of an atom determines many of its properties. ",text,
L_0969,nonmetals,T_4669,"As their name suggests, nonmetals generally have properties that are very different from the properties of metals. Properties of nonmetals include a relatively low boiling point, which explains why many of them are gases at room temperature. However, some nonmetals are solids at room temperature, including the three pictured above, and one nonmetalbromineis a liquid at room temperature. Other properties of nonmetals are illustrated and described in the Figure 1.1. ",text,
L_0969,nonmetals,T_4670,"Reactivity is how likely an element is to react chemically with other elements. Some nonmetals are extremely reactive, whereas others are completely nonreactive. What explains this variation in nonmetals? The answer is their number of valence electrons. These are the electrons in the outer energy level of an atom that are involved in interactions with other atoms. Lets look at two examples of nonmetals, fluorine and neon. Simple atomic models of these two elements are shown in the Figure 1.2. Q: Which element, fluorine or neon, do you predict is more reactive? A: Fluorine is more reactive than neon. Thats because it has seven of eight possible electrons in its outer energy level, whereas neon already has eight electrons in this energy level. Although neon has just one more electron than fluorine in its outer energy level, that one electron makes a huge difference. Fluorine needs one more electron to fill its outer energy level in order to have the most stable arrangement of electrons. Therefore, fluorine readily accepts an electron from any element that is equally eager to give one up, Click image to the left or use the URL below. URL: ",text,
L_0969,nonmetals,T_4670,"Reactivity is how likely an element is to react chemically with other elements. Some nonmetals are extremely reactive, whereas others are completely nonreactive. What explains this variation in nonmetals? The answer is their number of valence electrons. These are the electrons in the outer energy level of an atom that are involved in interactions with other atoms. Lets look at two examples of nonmetals, fluorine and neon. Simple atomic models of these two elements are shown in the Figure 1.2. Q: Which element, fluorine or neon, do you predict is more reactive? A: Fluorine is more reactive than neon. Thats because it has seven of eight possible electrons in its outer energy level, whereas neon already has eight electrons in this energy level. Although neon has just one more electron than fluorine in its outer energy level, that one electron makes a huge difference. Fluorine needs one more electron to fill its outer energy level in order to have the most stable arrangement of electrons. Therefore, fluorine readily accepts an electron from any element that is equally eager to give one up, Click image to the left or use the URL below. URL: ",text,
L_0969,nonmetals,T_4671,"Like most other nonmetals, fluorine cannot conduct electricity, and its electrons explain this as well. An electric current is a flow of electrons. Elements that readily give up electrons (the metals) can carry electric current because their electrons can flow freely. Elements that gain electrons instead of giving them up cannot carry electric current. They hold onto their electrons so they cannot flow. ",text,
L_0970,nuclear fission,T_4672,"Nuclear fission is the splitting of the nucleus of a radioactive atom into two smaller nuclei. This type of reaction releases a great deal of energy from a very small amount of matter. Fission of a tiny pellet of radioactive uranium- 235, like the one pictured in the Figure 1.1, releases as much energy as burning 1,000 kilograms of coal! Q: What causes the nucleus of uranium-235 atom to fission? A: Another particle collides with it. ",text,
L_0970,nuclear fission,T_4673,"The Figure 1.2 shows how nuclear fission of uranium-235 occurs. It begins when a uranium nucleus gains a neutron. This can happen naturally when a free neutron strikes it, or it can occur deliberately when a neutron is crashed into it in a nuclear power plant. In either case, the nucleus of uranium-235 becomes extremely unstable with the extra neutron. As a result, it splits into two smaller nuclei, krypton-92 and barium-141. The reaction also releases three neutrons and a great deal of energy. It can be represented by this nuclear equation: 235 U 92 141 + 1 neutron  92 36 Kr + 56 Ba + 3 neutrons + energy Note that the subscripts of the element symbols represent numbers of protons and the superscripts represent numbers of protons plus neutrons. ",text,
L_0970,nuclear fission,T_4674,"The neutrons released when uranium-235 fissions may crash into other uranium nuclei and cause them to fission as well. This can start a nuclear chain reaction. You can see how this happens in the Figure 1.3. In a chain reaction, one fission reaction leads to others, which lead to others, and so on. A nuclear chain reaction is similar to a pile of wood burning. If you start one piece of wood burning, enough heat is produced by the burning wood to start the rest of the pile burning without any further help from you. Click image to the left or use the URL below. URL: ",text,
L_0970,nuclear fission,T_4675,"If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb. However, if a nuclear chain reaction is controlled, it produces energy much more slowly. This is what occurs in a nuclear power plant. The reaction is controlled by inserting rods of nonfissioning material into the fissioning material. You can see this in the Figure 1.4. The radiation from the controlled fission is used to heat water and turn it to steam. The steam is under pressure and causes a turbine to spin. The spinning turbine runs a generator, which produces electricity. ",text,
L_0970,nuclear fission,T_4675,"If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb. However, if a nuclear chain reaction is controlled, it produces energy much more slowly. This is what occurs in a nuclear power plant. The reaction is controlled by inserting rods of nonfissioning material into the fissioning material. You can see this in the Figure 1.4. The radiation from the controlled fission is used to heat water and turn it to steam. The steam is under pressure and causes a turbine to spin. The spinning turbine runs a generator, which produces electricity. ",text,
L_0970,nuclear fission,T_4676,"In the U.S., the majority of electricity is produced by burning coal or other fossil fuels. This causes air pollution that harms the health of living things. The air pollution also causes acid rain and contributes to global warming. In addition, fossil fuels are nonrenewable resources, so if we keep using them, they will eventually run out. The main advantage of nuclear energy is that it doesnt release air pollution or cause the other environmental problems associated with the burning of fossil fuels. On the other other hand, radioactive elements are nonrenewable like fossil fuels and could eventually be used up. The main concern over the use of nuclear energy is the risk of radiation. Accidents at nuclear power plants can release harmful radiation that endangers people and other living things. Even without accidents, the used fuel that is left after nuclear fission reactions is still radioactive and very dangerous. It takes thousands of years for it to decay until it no longer releases harmful radiation. Therefore, used fuel must be stored securely to protect people and other living things. Click image to the left or use the URL below. URL: ",text,
L_0971,nuclear fusion,T_4677,"In nuclear fusion, two or more small nuclei combine to form a single, larger nucleus. You can see an example in the Figure 1.1. In this example, nuclei of two hydrogen isotopes (tritium and deuterium) fuse to form a helium nucleus. A neutron and a tremendous amount of energy are also released. ",text,
L_0971,nuclear fusion,T_4678,"Nuclear fusion of hydrogen to form helium occurs naturally in the sun and other stars. It takes place only at extremely high temperatures. Thats because a great deal of energy is needed to overcome the force of repulsion between the positively charged nuclei. The suns energy comes from fusion in its core, shown in the Figure 1.2. In the core, temperatures reach millions of degrees Kelvin. Click image to the left or use the URL below. URL:  The Sun Q: Why doesnt nuclear fusion occur naturally on Earth? A: Nuclear fusion doesnt occur naturally on Earth because it requires temperatures far higher than Earth tempera- tures. ",text,
L_0971,nuclear fusion,T_4679,"Scientists are searching for ways to create controlled nuclear fusion reactions on Earth. Their goal is develop nuclear fusion power plants, where the energy from fusion of hydrogen nuclei can be converted to electricity. You can see how this might work in the Figure 1.3. In the thermonuclear reactor, radiation from fusion is used to heat water and produce steam. The steam can then be used to turn a turbine and generate electricity. The use of nuclear fusion for energy has several pros. Unlike nuclear fission, which involves dangerous radioactive elements, nuclear fusion involves just hydrogen and helium. These elements are harmless. Hydrogen is also very plentiful. There is a huge amount of hydrogen in ocean water. The hydrogen in just a gallon of water could produce as much energy by nuclear fusion as burning 1,140 liters (300 gallons) of gasoline! The hydrogen in the oceans would generate enough energy to supply all the worlds people for a very long time. Unfortunately, using energy from nuclear fusion is far from a reality. Scientists are a long way from developing the necessary technology. One problem is raising temperatures high enough for fusion to take place. Another problem is that matter this hot exists only in the plasma state. There are no known materials that can contain plasma, although a magnet might be able to do it. Thats because plasma consists of ions and responds to magnetism. Click image to the left or use the URL below. URL: ",text,
L_0972,nucleic acid classification,T_4680,"Nucleic acids are one of four classes of biochemical compounds. (The other three classes are carbohydrates, proteins, and lipids.) Nucleic acids include RNA (ribonucleic acid) as well as DNA (deoxyribonucleic acid). Both types of nucleic acids contain the elements carbon, hydrogen, oxygen, nitrogen, and phosphorus. Q: Which of the elements in DNA is not identified with any other class of biochemical compounds? A: All biochemical compounds contain carbon, hydrogen, and oxygen; and proteins as well as nucleic acids contain nitrogen. Phosphorus is the only element that is identified with nucleic acids. ",text,
L_0972,nucleic acid classification,T_4681,"Nucleic acids consist of chains of small molecules called nucleotides, which are held together by covalent bonds. The structure of a nucleotide is shown in the Figure 1.1. Each nucleotide consists of: 1. a phosphate group, which contains phosphorus and oxygen (PO4 ). 2. a sugar, which is deoxyribose (C5 H8 O4 ) in DNA and ribose (C5 H10 O5 ) in RNA. 3. one of four nitrogen-containing bases. (A base is a compound that is not neither acidic nor neutral.) In DNA, the bases are adenine, thymine, guanine, and cytosine. RNA has the base uracil instead of thymine, but the other three bases are the same. ",text,
L_0972,nucleic acid classification,T_4682,"RNA consists of just one chain of nucleotides. DNA consists of two chains. Nitrogen bases on the two chains of DNA form hydrogen bonds with each other. Hydrogen bonds are relatively weak bonds that form between a positively charged hydrogen atom in one molecule and a negatively charged atom in another molecule. Hydrogen bonds form only between adenine and thymine, and between guanine and cytosine. These bonds hold the two chains together and give DNA is characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in the Figure 1.2. Sugars and phosphate groups form the backbone of each chain of DNA. The bonded bases are called base pairs. Determining the structure of DNA was a huge scientific breakthrough. Q: Compare the structure of DNA to a spiral staircase. What part of the molecule do the stair steps represent? A: The steps represent the base pairs. ",text,
L_0972,nucleic acid classification,T_4683,"DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in the nucleotide chains of DNA. RNA copies and interprets the genetic code in DNA and is also involved in the synthesis of proteins based on the code. Click image to the left or use the URL below. URL:  Q: DNA is found only in the nucleus of cells, but proteins are synthesized in the cytoplasm of cells, outside of the nucleus. How do you think the instructions encoded in DNA reach the cytoplasm so they can be used to make proteins? A: After RNA copies the instructions in DNA, it carries them from the nucleus to a site of protein synthesis in the cytoplasm, where the instructions are translated into a protein. ",text,
L_0976,optical instruments,T_4691,"Optics is the study of visible light and the ways it can be used to extend human vision and do other tasks. Knowledge of light was needed for the invention of optical instruments such as microscopes, telescopes, and cameras, in addition to optical fibers. These instruments use mirrors and lenses to reflect and refract light and form images. Q: What is an image? A: An image is a copy of an object created by the reflection or refraction of visible light. ",text,
L_0976,optical instruments,T_4692,"A light microscope is an instrument that uses lenses to make enlarged images of objects that are too small for the unaided eye to see. A common type of light microscope is a compound microscope, like the one shown in the Figure lenses. The objective lenses are close to the object being viewed. They form an enlarged image of the object inside the microscope. The eyepiece lenses are close to the viewers eyes. They form an enlarged image of the first image. The magnifications of all the lenses are multiplied together to yield the overall magnification of the microscope. Some light microscopes can magnify objects more than 1000 times! Q: How has the microscope advanced scientific knowledge? A: The microscope has revealed secrets of the natural world like no other single invention. The microscope let scientists see entire new worlds, leading to many discoveriesespecially in biology and medicinethat could not have been made without it. Some examples include the discovery of cells and the identification of bacteria and other single-celled organisms. With the development of more powerful microscopes, viruses were discovered and even atoms finally became visible. These discoveries changed our ideas about the human body and the nature of life itself. ",text,
L_0976,optical instruments,T_4693,"Like microscopes, telescopes use convex lenses to make enlarged images. However, telescopes make enlarged images of objectssuch as distant starsthat only appear tiny because they are very far away. There are two basic types of telescopes: reflecting telescopes and refracting telescopes. The two types are compared in the Figure 1.2. They differ in how they collect light, but both use convex lenses to form enlarged images. Click image to the left or use the URL below. URL: ",text,
L_0976,optical instruments,T_4694,"A camera is an optical instrument that forms and records an image of an object. The image may be recorded on film or it may be detected by an electronic sensor that stores the image digitally. Regardless of how the image is recorded, all cameras form images in the same basic way, as shown in the Figure 1.3. Light passes through the lens at the front of the camera and enters the camera through an opening called the aperture. As light passes through the lens, it forms a reduced real image. The image focuses on film (or a sensor) at the back of the camera. The lens may be moved back and forth to bring the image into focus. The shutter controls the amount of light that actually strikes the film (or sensor). It stays open longer in dim light to let more light in. ",text,
L_0976,optical instruments,T_4695,"Did you ever see a cat chase after a laser light, like the one in Figure 1.4? A laser is a device that produces a very focused beam of visible light of just one wavelength and color. Waves of laser light are synchronized so the crests and troughs of the waves line up. The diagram in Figure 1.4 shows why a beam of laser light is so focused compared with ordinary light from a flashlight. The following Figure 1.5 provides a closer look at the tube where laser light is created. Electrons in a material such as a ruby crystal are stimulated to radiate photons of light of one wavelength. At each end of the tube is a concave mirror. The photons of light reflect back and forth in the tube off these mirrors. This focuses the light. The mirror at one end of the tube is partly transparent. A constant stream of photons passes through the transparent part, forming the laser beam. Click image to the left or use the URL below. URL: ",text,
L_0976,optical instruments,T_4695,"Did you ever see a cat chase after a laser light, like the one in Figure 1.4? A laser is a device that produces a very focused beam of visible light of just one wavelength and color. Waves of laser light are synchronized so the crests and troughs of the waves line up. The diagram in Figure 1.4 shows why a beam of laser light is so focused compared with ordinary light from a flashlight. The following Figure 1.5 provides a closer look at the tube where laser light is created. Electrons in a material such as a ruby crystal are stimulated to radiate photons of light of one wavelength. At each end of the tube is a concave mirror. The photons of light reflect back and forth in the tube off these mirrors. This focuses the light. The mirror at one end of the tube is partly transparent. A constant stream of photons passes through the transparent part, forming the laser beam. Click image to the left or use the URL below. URL: ",text,
L_0976,optical instruments,T_4696,"Besides entertaining a cat, laser light has many other uses. One use is carrying communication signals in optical fibers. Sounds or pictures are encoded in pulses of laser light, which are then sent through an optical fiber. All of the light reflects off the inside of the fiber, so none of it escapes. As a result, the signal remains strong even over long distances. More than one signal can travel through an optical fiber at the same time, as you can see in the Figure Q: When lasers were invented in 1960, they were called ""a solution looking for a problem. Since then, they have been put to thousands of different uses. Can you name other ways that lasers are used? A: The first widespread use of lasers was the supermarket barcode scanner, introduced in 1974. The compact disc (CD) player was the first laser-equipped device commonly used by consumers, starting in 1982. The CD player was quickly followed by the laser printer. Some other uses of lasers include bloodless surgery, cutting and welding of metals, guiding missiles, thermometers, laser light shows, and acne treatments. The optical fiber in the diagram is much larger than a real optical fiber, which is only about as wide as a human hair. ",text,
L_0977,orbital motion,T_4697,"Earth and many other bodiesincluding asteroids, comets, and the other planetsmove around the sun in curved paths called orbits. Generally, the orbits are elliptical, or oval, in shape. You can see the shape of Earths orbit in the Figure 1.1. Because of the suns relatively strong gravity, Earth and the other bodies constantly fall toward the sun, but they stay far enough away from the sun because of their forward velocity to fall around the sun instead of into it. As a result, they keep orbiting the sun and never crash to its surface. The motion of Earth and the other bodies around the sun is called orbital motion. Orbital motion occurs whenever an object is moving forward and at the same time is pulled by gravity toward another object. ",text,
L_0977,orbital motion,T_4698,"Just as Earth orbits the sun, the moon also orbits Earth. The moon is affected by Earths gravity more than it is by the gravity of the sun because the moon is much closer to Earth. The gravity between Earth and the moon pulls the moon toward Earth. At the same time, the moon has forward velocity that partly counters the force of Earths gravity. So the moon orbits Earth instead of falling down to the surface of the planet. The Figure 1.2 shows the forces involved in the moons orbital motion around Earth. In the diagram, v represents the forward velocity of the moon, and a represents the acceleration due to gravity between Earth and the moon. The line encircling Earth shows the moons actual orbit, which results from the combination of v and a. ",text,
L_0977,orbital motion,T_4698,"Just as Earth orbits the sun, the moon also orbits Earth. The moon is affected by Earths gravity more than it is by the gravity of the sun because the moon is much closer to Earth. The gravity between Earth and the moon pulls the moon toward Earth. At the same time, the moon has forward velocity that partly counters the force of Earths gravity. So the moon orbits Earth instead of falling down to the surface of the planet. The Figure 1.2 shows the forces involved in the moons orbital motion around Earth. In the diagram, v represents the forward velocity of the moon, and a represents the acceleration due to gravity between Earth and the moon. The line encircling Earth shows the moons actual orbit, which results from the combination of v and a. ",text,
L_0979,ph concept,T_4703,Acids are ionic compounds that produce positively charged hydrogen ions (H+ ) when dissolved in water. Acids taste sour and react with metals. Bases are ionic compounds that produce negatively charged hydroxide ions (OH ) when dissolved in water. Bases taste bitter and do not react with metals. Examples of acids are vinegar and battery acid. The acid in vinegar is weak enough to safely eat on a salad. The acid in a car battery is strong enough to eat through skin. Examples of bases include those in antacid tablets and drain cleaner. Bases in antacid tablets are weak enough to take for an upset stomach. Bases in drain cleaner are strong enough to cause serious burns. Q: What do you think causes these differences in the strength of acids and bases? A: The strength of an acid or a base depends on how much of it breaks down into ions when it dissolves in water. ,text,
L_0979,ph concept,T_4704,"The strength of an acid depends on how many hydrogen ions it produces when it dissolves in water. A stronger acid produces more hydrogen ions than a weaker acid. For example, sulfuric acid (H2 SO4 ), which is found in car batteries, is a strong acid because nearly all of it breaks down into ions when it dissolves in water. On the other hand, acetic acid (CH3 CO2 H), which is the acid in vinegar, is a weak acid because less than 1 percent of it breaks down into ions in water. The strength of a base depends on how many hydroxide ions it produces when it dissolves in water. A stronger base produces more hydroxide ions than a weaker base. For example, sodium hydroxide (NaOH), a base in drain cleaner, is a strong base because all of it breaks down into ions when it dissolves in water. Calcium carbonate (CaCO3 ), a base in antacids, is a weak base because only a small percentage of it breaks down into ions in water. ",text,
L_0979,ph concept,T_4705,"The strength of acids and bases is measured on a scale called the pH scale, which is shown in the Figure 1.1. By definition, pH represents the acidity, or hydrogen ion (H+ ) concentration, of a solution. Pure water, which is neutral, has a pH of 7. With a higher the concentration of hydrogen ions, a solution is more acidic and has a lower pH. Acids have a pH less than 7, and the strongest acids have a pH close to zero. Bases have a pH greater than 7, and the strongest bases have a pH close to 14. Its important to realize that the pH scale is based on powers of ten. For example, a solution with a pH of 8 is 10 times more basic than a solution with a pH of 7, and a solution with a pH of 9 is 100 times more basic than a solution with a pH of 7. Q: How much more acidic is a solution with a pH of 4 than a solution with a pH of 7? A: A solution with a pH of 4 is 1000 (10  10  10, or 103 ) times more acidic than a solution with a pH of 7. Q: Which solution on the pH scale in the Figure 1.1 is the weakest acid? Which solution is the strongest base? A: The weakest acid on the scale is milk, which has a pH value between 6.5 and 6.8. The strongest base on the scale is liquid drain cleaner, which has a pH of 14. ",text,
L_0979,ph concept,T_4706,"Acidity is an important factor for living things. For example, many plants grow best in soil that has a pH between 6 and 7. Fish may also need a pH between 6 and 7. Certain air pollutants form acids when dissolved in water droplets in the air. This results in acid fog and acid rain, which may have a pH of 4 or even lower. The pH chart in the Figure lowers the pH of surface waters such as ponds and lakes. As a result, the water may become too acidic for fish and other water organisms to survive. Acid fog and acid rain killed the trees in this forest. Even normal (clean) rain is somewhat acidic. Thats because carbon dioxide (CO2 ) in the air dissolves in raindrops, producing a weak acid called carbonic acid (H2 CO3 ), which has a pH of about 5.5. When rainwater soaks into the ground, it can slowly dissolve rocks, particularly those containing calcium carbonate. This is how water forms underground caves. Q: How do you think acid rain might affect buildings and statues made of stone? A: Acid rain dissolves and damages stone buildings and statues. The Figure 1.3 shows a statue that has been damaged by acid rain. ",text,
L_0979,ph concept,T_4706,"Acidity is an important factor for living things. For example, many plants grow best in soil that has a pH between 6 and 7. Fish may also need a pH between 6 and 7. Certain air pollutants form acids when dissolved in water droplets in the air. This results in acid fog and acid rain, which may have a pH of 4 or even lower. The pH chart in the Figure lowers the pH of surface waters such as ponds and lakes. As a result, the water may become too acidic for fish and other water organisms to survive. Acid fog and acid rain killed the trees in this forest. Even normal (clean) rain is somewhat acidic. Thats because carbon dioxide (CO2 ) in the air dissolves in raindrops, producing a weak acid called carbonic acid (H2 CO3 ), which has a pH of about 5.5. When rainwater soaks into the ground, it can slowly dissolve rocks, particularly those containing calcium carbonate. This is how water forms underground caves. Q: How do you think acid rain might affect buildings and statues made of stone? A: Acid rain dissolves and damages stone buildings and statues. The Figure 1.3 shows a statue that has been damaged by acid rain. ",text,
L_0980,photosynthesis reactions,T_4707,"Most of the energy used by living things comes either directly or indirectly from the sun. Thats because sunlight provides the energy for photosynthesis. This is the process in which plants and certain other organisms synthesize glucose (C6 H12 O6 ). The process uses carbon dioxide and water and also produces oxygen. The overall chemical equation for photosynthesis is: 6CO2 + 6H2 O + Light Energy  C6 H12 O6 + 6O2 Photosynthesis changes light energy to chemical energy. The chemical energy is stored in the bonds of glucose molecules. Glucose, in turn, is used for energy by the cells of almost all living things. Photosynthetic organisms such as plants make their own glucose. Other organisms get glucose by consuming plants (or organisms that consume plants). Q: How do living things get energy from glucose? A: They break bonds in glucose and release the stored energy in the process of cellular respiration. ",text,
L_0980,photosynthesis reactions,T_4708,"The organisms pictured in the Figures 1.1, 1.2, and 1.3 all use sunlight to make glucose in the process of photo- synthesis. In addition to plants, they include bacteria and algae. All of these organisms contain the green pigment chlorophyll, which is needed to capture light energy. A tremendous amount of photosynthesis takes place in the plants of this lush tropi- cal rainforest. ",text,
L_0980,photosynthesis reactions,T_4708,"The organisms pictured in the Figures 1.1, 1.2, and 1.3 all use sunlight to make glucose in the process of photo- synthesis. In addition to plants, they include bacteria and algae. All of these organisms contain the green pigment chlorophyll, which is needed to capture light energy. A tremendous amount of photosynthesis takes place in the plants of this lush tropi- cal rainforest. ",text,
L_0985,position time graphs,T_4725,"The motion of an object can be represented by a position-time graph like Graph 1 in the Figure 1.1. In this type of graph, the y-axis represents position relative to the starting point, and the x-axis represents time. A position-time graph shows how far an object has traveled from its starting position at any given time since it started moving. Q: In the Figure 1.1, what distance has the object traveled from the starting point by the time 5 seconds have elapsed? A: The object has traveled a distance of 50 meters. ",text,
L_0985,position time graphs,T_4726,"In a position-time graph, the velocity of the moving object is represented by the slope, or steepness, of the graph line. If the graph line is horizontal, like the line after time = 5 seconds in Graph 2 in the Figure 1.2, then the slope is zero and so is the velocity. The position of the object is not changing. The steeper the line is, the greater the slope of the line is and the faster the objects motion is changing. ",text,
L_0985,position time graphs,T_4726,"In a position-time graph, the velocity of the moving object is represented by the slope, or steepness, of the graph line. If the graph line is horizontal, like the line after time = 5 seconds in Graph 2 in the Figure 1.2, then the slope is zero and so is the velocity. The position of the object is not changing. The steeper the line is, the greater the slope of the line is and the faster the objects motion is changing. ",text,
L_0985,position time graphs,T_4727,"Its easy to calculate the average velocity of a moving object from a position-time graph. Average velocity equals the change in position (represented by d) divided by the corresponding change in time (represented by t): velocity = d t For example, in Graph 2 in the Figure 1.2, the average velocity between 0 seconds and 5 seconds is: d t 25 m  0 m = 5 s0 s 25 m = 5s = 5 m/s velocity = ",text,
L_0986,potential energy,T_4728,"The diver has energy because of her position high above the pool. The type of energy she has is called potential energy. Potential energy is energy that is stored in a person or object. Often, the person or object has potential energy because of its position or shape. Q: What is it about the divers position that gives her potential energy? A: Because the diver is high above the water, she has the potential to fall toward Earth because of gravity. This gives her potential energy. ",text,
L_0986,potential energy,T_4729,"Potential energy due to the position of an object above Earths surface is called gravitational potential energy. Like the diver on the diving board, anything that is raised up above Earths surface has the potential to fall because of gravity. You can see another example of people with gravitational potential energy in the Figure 1.1. Gravitational potential energy depends on an objects weight and its height above the ground. It can be calculated with the equation: Gravitational potential energy (GPE) = weight  height Consider the little girl on the sled, pictured in the Figure 1.1. She weighs 140 Newtons, and the top of the hill is 4 meters higher than the bottom of the hill. As she sits at the top of the hill, the childs gravitational potential energy is: GPE = 140 N  4 m = 560 N  m Notice that the answer is given in Newton  meters (N  m), which is the SI unit for energy. A Newton  meter is the energy needed to move a weight of 1 Newton over a distance of 1 meter. A Newton  meter is also called a joule (J). Q: The gymnast on the balance beam pictured in the Figure 1.1 weighs 360 Newtons. If the balance beam is 1.2 meters above the ground, what is the gymnasts gravitational potential energy? A: Her gravitational potential energy is: GPE = 360 N  1.2 m = 432 N  m, or 432 J ",text,
L_0986,potential energy,T_4730,"Potential energy due to an objects shape is called elastic potential energy. This energy results when an elastic object is stretched or compressed. The farther the object is stretched or compressed, the greater its potential energy is. A point will be reached when the object cant be stretched or compressed any more. Then it will forcefully return to its original shape. Look at the pogo stick in the Figure 1.2. Its spring has elastic potential energy when it is pressed down by the boys weight. When it cant be compressed any more, it will spring back to its original shape. The energy it releases will push the pogo stickand the boyoff the ground. Q: The girl in the Figure 1.3 is giving the elastic band of her slingshot potential energy by stretching it. Shes holding a small stone against the stretched band. What will happen when she releases the band? A: The elastic band will spring back to its original shape. When that happens, watch out! Some of the bands elastic potential energy will be transferred to the stone, which will go flying through the air. ",text,
L_0986,potential energy,T_4731,"All of the examples of potential energy described above involve movement or the potential to move. The form of energy that involves movement is called mechanical energy. Other forms of energy also involve potential energy, including chemical energy and nuclear energy. Chemical energy is stored in the bonds between the atoms of compounds. For example, food and batteries both contain chemical energy. Nuclear energy is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. Nuclei of radioactive elements such as uranium are unstable, so they break apart and release the stored energy. ",text,
L_0986,potential energy,T_4731,"All of the examples of potential energy described above involve movement or the potential to move. The form of energy that involves movement is called mechanical energy. Other forms of energy also involve potential energy, including chemical energy and nuclear energy. Chemical energy is stored in the bonds between the atoms of compounds. For example, food and batteries both contain chemical energy. Nuclear energy is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. Nuclei of radioactive elements such as uranium are unstable, so they break apart and release the stored energy. ",text,
L_0987,power,T_4732,"Power is a measure of the amount of work that can be done in a given amount of time. Power can be represented by the equation: Power = Work Time In this equation, work is measured in joules (J) and time is measured in seconds (s), so power is expressed in joules per second (J/s). This is the SI unit for power, also known as the watt (W). A watt equals 1 joule of work per second. Youre probably already familiar with watts. Light bulbs and small appliances such as microwave ovens are labeled with the watts of power they provide. For example, the package of light bulbs in the Figure 1.1 is labeled 14 watts. Q: Assume you have two light bulbs of the same type, such as two compact fluorescent light bulbs like the one pictured in the Figure 1.1. If one light bulb is a 25-watt bulb and the other is a 60-watt bulb, which bulb produces brighter light? A: The 60-watt bulb is more powerful, so it produces brighter light. Compared with a less powerful device, a more powerful device can either do more work in the same time or do the same work in less time. For example, compared with a low-power microwave oven, a high-power microwave oven can cook more food in the same time or the same amount of food in less time. ",text,
L_0987,power,T_4733,"Power can be calculated using the formula above if the amount of work and time are known. For example, assume that a microwave oven does 24,000 joules of work in 30 seconds. Then the power of the microwave is: 24000 J Power = Work Time = 30 s = 800 J/s, or 800 W Q: Another microwave oven does 5,000 joules of work in 5 seconds. What is its power? A: The power of the other microwave oven is: J Power = 5000 5 s = 1000 J/s, or 1000 W Q: Which microwave oven will heat the same amount of food in less time? A: The 1000-watt microwave oven has more power, so it will heat the same amount of food in less time. ",text,
L_0987,power,T_4734,"You can also calculate work if you know power and time by rewriting the power equation above as: Work = Power  Time For example, if you use a 1000-watt microwave oven for 20 seconds, how much work does it do? First express 1000 watts in J/s and then substitute this value for power the work equation: Work = 1000 J/s  20 s = 20,000 J ",text,
L_0987,power,T_4735,"Sometimes power is measured in a unit called the horsepower. For example, the power of car engines is usually expressed in horsepowers. One horsepower is the amount of work a horse can do in 1 minute. It equals 745 watts of power. Compare the horsepowers in the Figure 1.2 to the other Figure 1.3. This team of three horses provides 3 horsepowers of power. This big tractor provides 180 horsepowers of power. Q: If the team of horses and the tractor do the same amount of work plowing a field, which will get the job done faster? A: The tractor will get the job done faster because it has more power. In fact, because the tractor has 30 times the power of the six-horse team, ideally it can do the same work 30 times faster! ",text,
L_0987,power,T_4735,"Sometimes power is measured in a unit called the horsepower. For example, the power of car engines is usually expressed in horsepowers. One horsepower is the amount of work a horse can do in 1 minute. It equals 745 watts of power. Compare the horsepowers in the Figure 1.2 to the other Figure 1.3. This team of three horses provides 3 horsepowers of power. This big tractor provides 180 horsepowers of power. Q: If the team of horses and the tractor do the same amount of work plowing a field, which will get the job done faster? A: The tractor will get the job done faster because it has more power. In fact, because the tractor has 30 times the power of the six-horse team, ideally it can do the same work 30 times faster! ",text,
L_0989,projectile motion,T_4741,"When the archer releases the bowstring, the arrow will be flung forward toward the top of the target where shes aiming. But another force will also act on the arrow in a different direction. The other force is gravity, and it will pull the arrow down toward Earth. The two forces combined will cause the arrow to move in the curved path shown in the Figure 1.1. This type of motion is called projectile motion. It occurs whenever an object curves down toward the ground because it has both a horizontal force and the downward force of gravity acting on it. Because of projectile motion, to hit the bulls eye of a target with an arrow, you actually have to aim for a spot above the bulls eye. You can see in theFigure 1.2 what happens if you aim at the bulls eye instead of above it. ",text,
L_0989,projectile motion,T_4742,"You can probably think of other examples of projectile motion. One is shown in the Figure 1.3. The cannon shoots a ball straight ahead, giving it horizontal motion. At the same time, gravity pulls the ball down toward the ground. Q: How would you show the force of gravity on the cannon ball in the Figure 1.3? A: You would add a line pointing straight down from the cannon to the ground. ",text,
L_0989,projectile motion,T_4742,"You can probably think of other examples of projectile motion. One is shown in the Figure 1.3. The cannon shoots a ball straight ahead, giving it horizontal motion. At the same time, gravity pulls the ball down toward the ground. Q: How would you show the force of gravity on the cannon ball in the Figure 1.3? A: You would add a line pointing straight down from the cannon to the ground. ",text,
L_0989,projectile motion,T_4742,"You can probably think of other examples of projectile motion. One is shown in the Figure 1.3. The cannon shoots a ball straight ahead, giving it horizontal motion. At the same time, gravity pulls the ball down toward the ground. Q: How would you show the force of gravity on the cannon ball in the Figure 1.3? A: You would add a line pointing straight down from the cannon to the ground. ",text,
L_0990,properties of acids,T_4743,"Acids are ionic compounds that produce positive hydrogen ions (H+ ) when dissolved in water. Ionic compounds are compounds that contain positive metal ions and negative nonmetal ions held together by ionic bonds. (Ions are atoms that have become charged particles by gaining or losing electrons.) An example of an acid is hydrogen chloride (HCl). When it dissolves in water, it separates into positive hydrogen ions and negative chloride ions (Cl ). This is represented by the chemical equation: H O 2 HCl H+ + Cl ",text,
L_0990,properties of acids,T_4744,"You already know that a sour taste is one property of acids. (Warning: Never taste an unknown substance to see whether it is an acid!) Acids have certain other properties as well. For example, acids can conduct electricity when dissolved in water because they consist of charged particles in solution. (Electric current is a flow of charged particles.) Acids can also react with metals, and when they do they produce hydrogen gas. An example of this type of reaction is hydrochloric acid reacting with the metal zinc (Zn). The reaction is pictured in the Figure 1.1. It can be represented by the chemical equation: Zn + 2HCl  H2 + ZnCl2 Q: What sign indicates that a gas is being produced in this reaction? A: The bubbles are hydrogen gas rising through the acid. Q: Besides hydrogen gas, what else is produced in this reaction? A: This reaction also produces zinc chloride ZnCl2 , which is a neutral ionic compound called a salt. ",text,
L_0990,properties of acids,T_4745,"Certain compounds, called indicators, change color when acids come into contact with them, so indicators can be used to detect acids. An example of an indicator is the compound called litmus. It is placed on small strips of paper that may be red or blue. If you place a few drops of acid on a strip of blue litmus paper, the paper will turn red. You can see this in the Figure 1.2. Litmus isnt the only indicator for detecting acids. Red cabbage juice also works well, as you can see in this entertaining video. Click image to the left or use the URL below. URL:  Drawing of blue litmus paper turning red in acid. ",text,
L_0990,properties of acids,T_4746,"The strength of acids is measured on a scale called the pH scale. The pH value of a solution represents its concentration of hydrogen ions. A pH value of 7 indicates a neutral solution, and a pH value less than 7 indicates an acidic solution. The lower the pH value is, the greater is the concentration of hydrogen ions and the stronger the acid. The strongest acids, such as battery acid, have pH values close to zero. ",text,
L_0990,properties of acids,T_4747,"Acids have many important uses, especially in industry. For example, sulfuric acid is used to manufacture a variety of different products, including paper, paint, and detergent. Some other uses of acids are be seen in the Figure 1.3. ",text,
L_0991,properties of bases,T_4748,"Bases are ionic compounds that produce negative hydroxide ions (OH ) when dissolved in water. An ionic com- pound contains positive metal ions and negative nonmetal ions held together by ionic bonds. (Ions are atoms that have become charged particles because they have either lost or gained electrons.) An example of a base is sodium hydroxide (NaOH). When it dissolves in water, it produces negative hydroxide ions and positive sodium ions (Na+ ). This can be represented by the equation: H O 2 NaOH OH + Na+ ",text,
L_0991,properties of bases,T_4749,"All bases share certain properties, including a bitter taste. (Warning: Never taste an unknown substance to see whether it is a base!) Bases also feel slippery. Think about how slippery soap feels. Thats because its a base. In addition, bases conduct electricity when dissolved in water because they consist of charged particles in solution. (Electric current is a flow of charged particles.) Q: Bases are closely related to compounds called acids. How are their properties similar? How are they different? A: A property that is shared by bases and acids is the ability to conduct electricity when dissolved in water. Some ways bases and acids are different is that acids taste sour whereas bases taste bitter. Also, acids but not bases react with metals. ",text,
L_0991,properties of bases,T_4750,"Certain compounds, called indicators, change color when bases come into contact with them, so they can be used to detect bases. An example of an indicator is a compound called litmus. It is placed on small strips of paper that may be red or blue. If you place a few drops of a base on a strip of red litmus paper, the paper will turn blue. You can see this in the Figure 1.1. Litmus isnt the only detector of bases. Red cabbage juice can also detect bases, as you can see in this video. Click image to the left or use the URL below. URL:  Drawing of red litmus paper turning blue in a base. ",text,
L_0991,properties of bases,T_4751,"The strength of bases is measured on a scale called the pH scale, which ranges from 0 to 14. On this scale, a pH value of 7 indicates a neutral solution, and a pH value greater than 7 indicates a basic solution. The higher the pH value is, the stronger the base. The strongest bases, such as drain cleaner, have a pH value close to 14. ",text,
L_0991,properties of bases,T_4752,"Bases are used for a variety of purposes. For example, soaps contain bases such as potassium hydroxide (KOH). Other uses of bases can be seen in the Figure 1.2. ",text,
L_0992,properties of electromagnetic waves,T_4753,"All electromagnetic waves travel at the same speed through empty space. That speed, called the speed of light, is about 300 million meters per second (3.0 x 108 m/s). Nothing else in the universe is known to travel this fast. The sun is about 150 million kilometers (93 million miles) from Earth, but it takes electromagnetic radiation only 8 minutes to reach Earth from the sun. If you could move that fast, you would be able to travel around Earth 7.5 times in just 1 second! ",text,
L_0992,properties of electromagnetic waves,T_4754,"Although all electromagnetic waves travel at the same speed across space, they may differ in their wavelengths, frequencies, and energy levels. Wavelength is the distance between corresponding points of adjacent waves (see the Figure 1.1). Wavelengths of electromagnetic waves range from longer than a soccer field to shorter than the diameter of an atom. Wave frequency is the number of waves that pass a fixed point in a given amount of time. Frequencies of electromagnetic waves range from thousands of waves per second to trillions of waves per second. The energy of electromagnetic waves depends on their frequency. Low-frequency waves have little energy and are normally harmless. High-frequency waves have a lot of energy and are potentially very harmful. Q: Which electromagnetic waves do you think have higher frequencies: visible light or X rays? A: X rays are harmful but visible light is harmless, so you can infer that X rays have higher frequencies than visible light. ",text,
L_0992,properties of electromagnetic waves,T_4755,"The speed of a wave is a product of its wavelength and frequency. Because all electromagnetic waves travel at the same speed through space, a wave with a shorter wavelength must have a higher frequency, and vice versa. This relationship is represented by the equation: Speed = Wavelength  Frequency The equation for wave speed can be rewritten as: Speed Speed Frequency = Wavelength or Wavelength = Frequency Therefore, if either wavelength or frequency is known, the missing value can be calculated. Consider an electromag- netic wave that has a wavelength of 3 meters. Its speed, like the speed of all electromagnetic waves, is 3.0  108 meters per second. Its frequency can be found by substituting these values into the frequency equation: Frequency = 3.0108 m/s 3.0 m = 1.0  108 waves/s, or 1.0  108 Hz Q: What is the wavelength of an electromagnetic wave that has a frequency of 3.0  108 hertz? A: Use the wavelength equation: Wavelength = 3.0108 m/s 3.0108 waves/s = 1.0 m ",text,
L_0994,protein classification,T_4759,"Hemoglobin is a compound in the class of compounds called proteins. Proteins are one of four classes of biochemi- cal compounds, which are compounds in living things. (The other three classes are carbohydrates, lipids, and nucleic acids.) Proteins contain carbon, hydrogen, oxygen, nitrogen, and sulfur. Protein molecules consist of one or more chains of small molecules called amino acids. ",text,
L_0994,protein classification,T_4760,"Amino acids are the building blocks of proteins. There are 20 different amino acids. The structural formula of the simplest amino acid, called glycine, is shown in the Figure 1.1. Other amino acids have slightly different structures. A protein molecule is made from one or more long chains of amino acids, each linked to its neighbors by covalent bonds. If a protein has more than one chain, the chains are held together by weaker bonds, such as hydrogen bonds. The sequence of amino acids in chains and the number of chains in a protein determine the proteins shape. The shape of a protein, in turn, determines its function. Shapes may be very complex. Click image to the left or use the URL below. URL:  Q: What do you think the ribbons in the colorful hemoglobin molecule pictured in the opening image represent? A: The ribbons represent chains of amino acids. ",text,
L_0994,protein classification,T_4761,"Proteins are the most numerous and diverse biochemical compounds, and they have many different functions. Some of their functions include: making up tissues as components of muscle. speeding up biochemical reactions as enzymes. regulating life processes as hormones. helping to defend against infections as antibodies. carrying materials around the body as transport proteins (see the example of hemoglobin in the Figure 1.2). ",text,
L_0995,protons,T_4762,"A proton is one of three main particles that make up the atom. The other two particles are the neutron and electron. Protons are found in the nucleus of the atom. This is a tiny, dense region at the center of the atom. Protons have a positive electrical charge of one (+1) and a mass of 1 atomic mass unit (amu), which is about 1.67  1027 kilograms. Together with neutrons, they make up virtually all of the mass of an atom. Click image to the left or use the URL below. URL:  Q: How do you think the sun is related to protons? A: The suns tremendous energy is the result of proton interactions. In the sun, as well as in other stars, protons from hydrogen atoms combine, or fuse, to form nuclei of helium atoms. This fusion reaction releases a huge amount of energy and takes place in nature only at the extremely high temperatures of stars such as the sun. ",text,
L_0995,protons,T_4763,"All protons are identical. For example, hydrogen protons are exactly the same as protons of helium and all other elements, or pure substances. However, atoms of different elements have different numbers of protons. In fact, atoms of any given element have a unique number of protons that is different from the numbers of protons of all other elements. For example, a hydrogen atom has just one proton, whereas a helium atom has two protons. The number of protons in an atom determines the electrical charge of the nucleus. The nucleus also contains neutrons, but they are neutral in charge. The one proton in a hydrogen nucleus, for example, gives it a charge of +1, and the two protons in a helium nucleus give it a charge of +2. ",text,
L_0995,protons,T_4764,"Protons are made of fundamental particles called quarks and gluons. As you can see in the Figure 1.1, a proton contains three quarks (colored circles) and three streams of gluons (wavy white lines). Two of the quarks are called up quarks (u), and the third quark is called a down quark (d). The gluons carry the strong nuclear force between quarks, binding them together. This force is needed to overcome the electric force of repulsion between positive protons. Although protons were discovered almost 100 years ago, the quarks and gluons inside them were discovered much more recently. Scientists are still learning more about these fundamental particles. ",text,
L_0996,pulley,T_4765,"A pulley is a simple machine that consists of a rope and grooved wheel. The rope fits into the groove in the wheel, and pulling on the rope turns the wheel. Pulleys are generally used to lift objects, especially heavy objects. The object lifted by a pulley is called the load. The force applied to the pulley is called the effort. Q: Can you guess what the pulley pictured above is used for? A: The pulley is used to lift heavy buckets full of water out of the well. ",text,
L_0996,pulley,T_4766,"Some pulleys are attached to a beam or other secure surface and remain fixed in place. They are called fixed pulleys. Other pulleys are attached to the object being moved and are moveable themselves. They are called moveable pulleys. Sometimes, fixed and moveable pulleys are used together. They make up a compound pulley. The three types of pulleys are compared in the Table 1.1. Q: Which type of pulley is the old pulley in the opening image? A: The old pulley is a single fixed pulley. It is securely attached to the beam above it. Type of Pulley How It Works Example Single fixed pul- ley Flagpole pulley No. of Rope Segments Pulling Up 1 Ideal Mechani- cal Advantage 1 Change Direction Force? yes Single moveable pulley Zip-line pulley 2 2 no Compound pulley (fixed & moveable pulleys) Crane pulley 2 2 varies in of ",text,
L_0996,pulley,T_4767,"The mechanical advantage of a simple machine such as a pulley is the factor by which the machine changes the force applied to it. The ideal mechanical advantage of a machine is its mechanical advantage in the absence of friction. All machines must overcome friction, so the ideal mechanical advantage is always somewhat greater than the actual mechanical advantage of the machine as it is used in the real world. In a pulley, the ideal mechanical advantage is equal to the number of rope segments pulling up on the object. The more rope segments that are helping to do the lifting work, the less force that is needed for the job. Look at the table of types of pulleys. It gives the ideal mechanical advantage of each type. In the single fixed pulley, only one rope segment pulls up on the load, so the ideal mechanical advantage is 1. In other words, this type of pulley doesnt increase the force that is applied to it. However, it does change the direction of the force. This allows you to use your weight to pull on one end of the rope and more easily raise the load attached to the other end. In the single moveable pulley, two rope segments pull up on the load, so the ideal mechanical advantage is 2. This type of pulley doesnt change the direction of the force applied to it, but it increases the force by a factor of 2. In a compound pulley, two or more rope segments pull up on the load, so the ideal mechanical advantage is 2 or greater than 2. This type of pulley may or may not change the direction of the force applied to itit depends on the number and arrangement of pulleysbut the increase in force may be great. Q: If a compound pulley has four rope segments pulling up on the load, by what factor does it multiply the force applied to the pulley? A: With four rope segments, the ideal mechanical advantage is 4. This means that the compound pulley multiplies the force applied to it by a factor of 4. For example if 400 Newtons of force were applied to the pulley, the pulley would apply 1600 Newtons of force to the load. ",text,
L_0997,radio waves,T_4768,"Electromagnetic waves consist of vibrating electric and magnetic fields. They transfer energy across space as well as through matter. Electromagnetic waves vary in their wavelengths and frequencies, and higher-frequency waves have more energy. The full range of wavelengths of electromagnetic waves is called the electromagnetic spectrum. It is outlined in the following Figure 1.1. ",text,
L_0997,radio waves,T_4769,"Electromagnetic waves on the left side of the Figure 1.1 are called radio waves. Radio waves are electromagnetic waves with the longest wavelengths. They may have wavelengths longer than a soccer field. They are also the electromagnetic waves with the lowest frequencies. With their low frequencies, they have the least energy of all electromagnetic waves. Nonetheless, radio waves are very useful. They are used for radio and television broadcasts and many other purposes. Click image to the left or use the URL below. URL:  Q: Based on the electromagnetic spectrum Figure 1.1, what is the range of frequencies of radio waves? A: The range of frequencies of radio waves is between 105 and 1012 Hz, or waves per second. ",text,
L_0997,radio waves,T_4770,"In radio broadcasts, sounds are encoded in radio waves, and then the waves are sent out through the atmosphere from a radio tower. A radio receiver detects the waves and changes them back to sounds. You may have listened to both AM and FM radio stations. How sounds are encoded in radio waves differs between AM and FM broadcasts. AM stands for amplitude modulation. In AM broadcasts, sound signals are encoded by changing the am- plitude, or maximum height, of radio waves. AM broadcasts use longer wavelength radio waves than FM broadcasts. Because of their longer wavelengths, AM waves reflect off a layer of the upper atmosphere called the ionosphere. You can see how this happens in the Figure 1.2. Because the waves are reflected, they can reach radio receivers that are very far away from the radio tower. FM stands for frequency modulation. In FM broadcasts, sound signals are encoded by changing the frequency of radio waves. Frequency modulation allows FM waves to encode more information than does amplitude modulation, so FM broadcasts usually produce clearer sounds than AM broadcasts. However, the relatively short wavelengths of FM waves means that they dont reflect off the ionosphere as AM waves do. Instead, FM waves pass through the ionosphere and out into space. This is also shown in the Figure 1.2. As a result, FM waves cannot reach very distant receivers. Q: The composition of the ionosphere changes somewhat from day to night. The changes make the nighttime ionosphere even better at reflecting AM radio waves. How do you think this might affect the distance AM radio waves travel at night? A: With greater reflection off the ionosphere, AM waves can travel even farther at night than they can during the day. Radio receivers can often pick up radio broadcasts at night from cities that are hundreds of miles away. ",text,
L_0997,radio waves,T_4771,"Television broadcasts also use radio waves (see Figure 1.2). For TV broadcasts, sounds are encoded with frequency modulation, and pictures are encoded with amplitude modulation. The encoded waves are broadcast from a TV tower. When the waves are received by television sets, they are decoded and changed back to sounds and pictures. ",text,
L_0998,radioactive decay,T_4772,"Radioactive decay is the process in which the nuclei of radioactive atoms emit charged particles and energy, which are called by the general term radiation. Radioactive atoms have unstable nuclei, and when the nuclei emit radiation, they become more stable. Radioactive decay is a nuclearrather than chemicalreaction because it involves only the nuclei of atoms. In a nuclear reaction, one element may change into another. Click image to the left or use the URL below. URL: ",text,
L_0998,radioactive decay,T_4773,"There are several types of radioactive decay, including alpha, beta, and gamma decay. In all three types, nuclei emit radiation, but the nature of the radiation differs. The Table 1.1 shows the radiation emitted in each type of decay. Type Alpha decay Beta decay Gamma decay Radiation Emitted alpha particle (2 protons and 2 neutrons) + energy beta particle (1 electron or 1 positron) + energy energy (gamma ray) ",text,
L_0998,radioactive decay,T_4774,"Both alpha and beta decay change the number of protons in an atoms nucleus, thereby changing the atom to a different element. In alpha decay, the nucleus loses two protons. In beta decay, the nucleus either loses a proton or gains a proton. In gamma decay, no change in proton number occurs, so the atom does not become a different element. Q: If the radioactive element polonium (Po) undergoes alpha decay, what element does it become? A: From the periodic table, the atomic number of polonium is 84, so it has 84 protons. If it loses two protons through alpha decay, it will have 82 protons. Atoms with 82 protons are the element lead (Pb). ",text,
L_0998,radioactive decay,T_4775,"The charged particles and energy emitted during radioactive decay can harm living things, but the three types of radioactive decay arent equally dangerous. Thats because they differ in how far they can travel and what they can penetrate. You can see this in the Figure 1.1. ",text,
L_0999,radioactivity,T_4776,"For an atom of one element to change into a different element, the number of protons in its nucleus must change. Thats because each element has a unique number of protons. For example, lead atoms always have 82 protons, and gold atoms always have 79 protons. Q: So how can one element change into another? A: The starting element must be radioactive, and its nuclei must gain or lose protons. ",text,
L_0999,radioactivity,T_4777,"Radioactivity is the ability of an atom to emit, or give off, charged particles and energy from its nucleus. The charged particles and energy are called by the general term radiation. Only unstable nuclei emit radiation. They are unstable because they have too much energy, too many protons, or an unstable ratio of protons to neutrons. For example, all elements with more than 83 protonssuch as uranium, radium, and poloniumhave unstable nuclei. They are called radioactive elements. The nuclei of these elements must lose protons to become more stable. When they do, they become different elements. ",text,
L_0999,radioactivity,T_4778,"Radioactivity was discovered in 1896 by a French physicist named Antoine Henri Becquerel, who is pictured 1.1. Becquerel was experimenting with uranium, which was known to glow after being exposed to sunlight. Becquerel wanted to see if the glow was caused by rays of energy, like rays of light or X-rays. He placed a bit of uranium on a photographic plate after exposing the uranium to sunlight. The plate was similar to the film that is used today to take X-rays, and Becquerel expected the uranium to leave an image on the plate. The next day, there was an image on the plate, just as Becquerel expected. This meant that uranium gives off rays after being exposed to sunlight. Becquerel was a good scientist, so he wanted to repeat his experiment to confirm his results. He placed more uranium on another photographic plate. However, the day had turned cloudy, so he tucked the plate and uranium in a drawer to try again another day. He wasnt expecting the uranium to leave an image on the plate without first being exposed to sunlight. To his surprise, there was an image on the plate in the drawer the next day. Becquerel had discovered that uranium gives off rays of energy on its own. He had discovered radioactivity, for which he received a Nobel prize. Another scientist, who worked with Becquerel, actually came up with the term radioactivity. The other scientist was the French chemist Marie Curie. She went on to discover the radioactive elements polonium and radium. She won two Nobel Prizes for her discoveries. ",text,
L_1000,radioisotopes,T_4779,"All the atoms of a given element have the same number of protons in their nucleus, but they may have different numbers of neutrons. Atoms of the same element with different numbers of neutrons are called isotopes. Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes. Their nuclei are unstable, so they break down, or decay, and emit radiation. Q: What makes the nucleus of a radioisotope unstable? A: The nucleus may be unstable because it has too many protons or an unstable ratio of protons to neutrons. For a nucleus with a small number of protons to be stable, the ratio of protons to neutrons should be 1:1. For a nucleus with a large number of protons to be stable, the ratio should be about 1:1.5. ",text,
L_1000,radioisotopes,T_4780,"Find carbon in the Figure 1.1, and youll see that its atomic number is 6. This means that all carbon atoms have 6 protons per nucleus. Almost all carbon atoms also have 6 neutrons per nucleus. These carbon atoms are called carbon-12, where 12 is the number of protons (6) plus neutrons (6). This gives carbon-12 nuclei a 1:1 ratio of protons to neutrons, so carbon-12 nuclei are stable. Some carbon atoms have more than 6 neutrons, either 7 or 8. Carbon atoms with 8 neutrons are called carbon-14 (6 protons + 8 neutrons). The nuclei of carbon-14 atoms are unstable because they have too many neutrons relative to protons, so they gradually decay. Q: What is the proton-to-neutron ratio of carbon-14 nuclei? A: With six protons and 8 neutrons, the ratio is 6:8, or 1:1.3. Q: How is carbon-14 used to estimate the ages of fossils? A: Living things take in carbon, including tiny amounts of carbon-14, throughout life. The carbon-14 constantly decays, but more carbon-14 is taken in all the time to replace it. After living things die, no new carbon-14 is taken in, and the carbon-14 they already have keeps decaying. The older a fossil is, the less carbon-14 it still has, so the remaining amount can be measured to estimate the fossils age. Click image to the left or use the URL below. URL:  Periodic Table of the Elements ",text,
L_1000,radioisotopes,T_4781,"In elements with more than 83 protons, all of the isotopes are radioactive. In the Figure 1.1, these are the elements with a yellow background. The force of repulsion among all those protons makes the nuclei unstable. Elements with more than 92 protons have such unstable nuclei that they dont even exist in nature. They have only been created in labs. ",text,
L_1002,reactants and products,T_4786,"All chemical reactionsincluding a candle burninginvolve reactants and products. Reactants are substances that start a chemical reaction. Products are substances that are produced in the reaction. When a candle burns, the reactants are fuel (the candlewick and wax) and oxygen (in the air). The products are carbon dioxide gas and water vapor. ",text,
L_1002,reactants and products,T_4787,"The relationship between reactants and products in a chemical reaction can be represented by a chemical equation that has this general form: Reactants  Products The arrow () shows the direction in which the reaction occurs. In many reactions, the reaction also occurs in the opposite direction. This is represented with another arrow pointing in the opposite direction (). Q: Write a general chemical equation for the reaction that occurs when a fuel such as candle wax burns. A: The burning of fuel is a combustion reaction. The general equation for this type of reaction is: Fuel + O2  CO2 + H2 O Q: How do the reactants in a chemical reaction turn into the products? A: Bonds break in the reactants, and new bonds form in the products. ",text,
L_1002,reactants and products,T_4788,"The reactants and products in a chemical reaction contain the same atoms, but they are rearranged during the reaction. As a result, the atoms end up in different combinations in the products. This makes the products new substances that are chemically different from the reactants. Consider the example of water forming from hydrogen and oxygen. Both hydrogen and oxygen gases exist as diatomic (two-atom) molecules. These molecules are the reactants in the reaction. The Figure 1.1 shows that bonds must break to separate the atoms in the hydrogen and oxygen molecules. Then new bonds must form between hydrogen and oxygen atoms to form water molecules. The water molecules are the products of the reaction. Q: Watch the animation of a similar chemical reaction at the following URL. Can you identify the reactants and the product in the reaction? Click image to the left or use the URL below. URL:  A: The reactants are hydrogen (H2 ) and fluorine (F2 ), and the product is hydrogen fluoride (HF). ",text,
L_1003,recognizing chemical reactions,T_4789,A change in color is just one of several potential signs that a chemical reaction has occurred. Other potential signs include: Change in temperature-Heat is released or absorbed during the reaction. Production of a gas-Gas bubbles are released during the reaction. Production of a solid-A solid settles out of a liquid solution. The solid is called a precipitate. Click image to the left or use the URL below. URL: ,text,
L_1003,recognizing chemical reactions,T_4790,"Look carefully at the Figures 1.1, 1.2, and 1.3. All of the photos demonstrate chemical reactions. For each photo, identify a sign that one or more chemical reactions have taken place. A burning campfire can warm you up on a cold day. Dissolving an antacid tablet in water produces a fizzy drink. Adding acid to milk produces solid curds of cottage cheese. Q: Did you ever make a volcano by pouring vinegar over a mountain of baking soda? If you did, you probably saw the mixture bubble up and foam over. Did a chemical reaction occur? How do you know? A: Yes, a chemical reaction occurred. You know because the bubbles are evidence that a gas has been produced and production of a gas is a sign of a chemical reaction. ",text,
L_1003,recognizing chemical reactions,T_4790,"Look carefully at the Figures 1.1, 1.2, and 1.3. All of the photos demonstrate chemical reactions. For each photo, identify a sign that one or more chemical reactions have taken place. A burning campfire can warm you up on a cold day. Dissolving an antacid tablet in water produces a fizzy drink. Adding acid to milk produces solid curds of cottage cheese. Q: Did you ever make a volcano by pouring vinegar over a mountain of baking soda? If you did, you probably saw the mixture bubble up and foam over. Did a chemical reaction occur? How do you know? A: Yes, a chemical reaction occurred. You know because the bubbles are evidence that a gas has been produced and production of a gas is a sign of a chemical reaction. ",text,
L_1003,recognizing chemical reactions,T_4790,"Look carefully at the Figures 1.1, 1.2, and 1.3. All of the photos demonstrate chemical reactions. For each photo, identify a sign that one or more chemical reactions have taken place. A burning campfire can warm you up on a cold day. Dissolving an antacid tablet in water produces a fizzy drink. Adding acid to milk produces solid curds of cottage cheese. Q: Did you ever make a volcano by pouring vinegar over a mountain of baking soda? If you did, you probably saw the mixture bubble up and foam over. Did a chemical reaction occur? How do you know? A: Yes, a chemical reaction occurred. You know because the bubbles are evidence that a gas has been produced and production of a gas is a sign of a chemical reaction. ",text,
L_1005,replacement reactions,T_4794,"A replacement reaction occurs when elements switch places in compounds. This type of reaction involves ions (electrically charged versions of atoms) and ionic compounds. These are compounds in which positive ions of a metal and negative ions of a nonmetal are held together by ionic bonds. Generally, a more reactive element replaces an element that is less reactive, and the less reactive element is set free from the compound. There are two types of replacement reactions: single and double. Both types are described below. Q: Can you predict how single and double replacement reactions differ? A: One way they differ is that a single replacement reaction involves one reactant compound, whereas a double replacement reaction involves two reactant compounds. Keep reading to learn more about these two types of reactions. ",text,
L_1005,replacement reactions,T_4795,"A single replacement reaction occurs when one element replaces another in a single compound. This type of reaction has the general equation: A + BC  B + AC In this equation, A represents a more reactive element and BC represents the original compound. During the reaction, A replaces B, forming the product compound AC and releasing the less reactive element B. An example of a single replacement reaction occurs when potassium (K) reacts with water (H2 O). A colorless solid compound named potassium hydroxide (KOH) forms, and hydrogen gas (H2 ) is set free. The equation for the reaction is: 2K + 2H2 O  2KOH + H2 In this reaction, a potassium ion replaces one of the hydrogen atoms in each molecule of water. Potassium is a highly reactive group 1 alkali metal, so its reaction with water is explosive. Q: Find potassium in the periodic table of the elements. What other element might replace hydrogen in water in a similar replacement reaction? A: Another group 1 element, such as lithium or sodium, might be involved in a similar replacement reaction with water. ",text,
L_1005,replacement reactions,T_4796,"A double replacement reaction occurs when two ionic compounds exchange ions. This produces two new ionic compounds. A double replacement reaction can be represented by the general equation: AB + CD  AD + CB AB and CD are the two reactant compounds, and AD and CB are the two product compounds that result from the reaction. During the reaction, the ions B and D change places. Q: Could the product compounds be DA and BC? A: No, they could not. In an ionic compound, the positive metal ion is always written first, followed by the negative nonmetal ion. Therefore, A and C must always come first, followed by D or B. An example of a double replacement reaction is sodium chloride (NaCl) reacting with silver fluoride (AgF). This reaction is represented by the equation: NaCl + AgF  NaF + AgCl During the reaction, chloride and fluoride ions change places, so two new compounds are formed in the products: sodium fluoride (NaF) and silver chloride (AgCl). Q: When iron sulfide (FeS) and hydrogen chloride (HCl) react together, a double replacement reaction occurs. What are the products of this reaction? What is the chemical equation for this reaction? A: The products of the reaction are iron chloride (FeCl2 ) and hydrogen sulfide (H2 S). The chemical equation for this reaction is: FeS + 2HCl  H2 S + FeCl2 ",text,
L_1007,rutherfords atomic model,T_4799,"In 1804, almost a century before the nucleus was discovered, the English scientist John Dalton provided evidence for the existence of the atom. Dalton thought that atoms were the smallest particles of matter, which couldnt be divided into smaller particles. He modeled atoms with solid wooden balls. In 1897, another English scientist, named J. J. Thomson, discovered the electron. It was first subatomic particle to be identified. Because atoms are neutral in electric charge, Thomson assumed that atoms must also contain areas of positive charge to cancel out the negatively charged electrons. He thought that an atom was like a plum pudding, consisting mostly of positively charged matter with negative electrons scattered through it. The nucleus of the atom was discovered next. It was discovered in 1911 by a scientist from New Zealand named Ernest Rutherford, who is pictured in Figure 1.1. Through his clever research, Rutherford showed that the positive charge of an atom is confined to a tiny massive region at the center of the atom, rather than being spread evenly throughout the pudding of the atom as Thomson had suggested. ",text,
L_1007,rutherfords atomic model,T_4800,"The way Rutherford discovered the atomic nucleus is a good example of the role of creativity in science. His quest actually began in 1899 when he discovered that some elements give off positively charged particles that can penetrate just about anything. He called these particles alpha () particles (we now know they were helium nuclei). Like all good scientists, Rutherford was curious. He wondered how he could use alpha particles to learn about the structure of the atom. He decided to aim a beam of alpha particles at a sheet of very thin gold foil. He chose gold because it can be pounded into sheets that are only 0.00004 cm thick. Surrounding the sheet of gold foil, he placed a screen that glowed when alpha particles struck it. It would be used to detect the alpha particles after they passed through the foil. A small slit in the screen allowed the beam of alpha particles to reach the foil from the particle emitter. You can see the setup for Rutherfords experiment in the Figure 1.2. Q: What would you expect to happen when the alpha particles strike the gold foil? A: The alpha particles would penetrate the gold foil. Alpha particles are positive, so they might be repelled by any areas of positive charge inside the gold atoms. Assuming a plum pudding model of the atom, Rutherford predicted that the areas of positive charge in the gold atoms would deflect, or bend, the path of all the alpha particles as they passed through. You can see what really happened in the Figure 1.2. Most of the alpha particles passed straight through the gold foil as though it wasnt there. The particles seemed to be passing through empty space. Only a few of the alpha particles were deflected from their straight path, as Rutherford had predicted. Surprisingly, a tiny percentage of the particles bounced back from the foil like a basketball bouncing off a backboard! Q: What can you infer from these observations? A: You can infer that most of the alpha particles were not repelled by any positive charge, whereas a few were repelled by a strong positive charge. ",text,
L_1007,rutherfords atomic model,T_4800,"The way Rutherford discovered the atomic nucleus is a good example of the role of creativity in science. His quest actually began in 1899 when he discovered that some elements give off positively charged particles that can penetrate just about anything. He called these particles alpha () particles (we now know they were helium nuclei). Like all good scientists, Rutherford was curious. He wondered how he could use alpha particles to learn about the structure of the atom. He decided to aim a beam of alpha particles at a sheet of very thin gold foil. He chose gold because it can be pounded into sheets that are only 0.00004 cm thick. Surrounding the sheet of gold foil, he placed a screen that glowed when alpha particles struck it. It would be used to detect the alpha particles after they passed through the foil. A small slit in the screen allowed the beam of alpha particles to reach the foil from the particle emitter. You can see the setup for Rutherfords experiment in the Figure 1.2. Q: What would you expect to happen when the alpha particles strike the gold foil? A: The alpha particles would penetrate the gold foil. Alpha particles are positive, so they might be repelled by any areas of positive charge inside the gold atoms. Assuming a plum pudding model of the atom, Rutherford predicted that the areas of positive charge in the gold atoms would deflect, or bend, the path of all the alpha particles as they passed through. You can see what really happened in the Figure 1.2. Most of the alpha particles passed straight through the gold foil as though it wasnt there. The particles seemed to be passing through empty space. Only a few of the alpha particles were deflected from their straight path, as Rutherford had predicted. Surprisingly, a tiny percentage of the particles bounced back from the foil like a basketball bouncing off a backboard! Q: What can you infer from these observations? A: You can infer that most of the alpha particles were not repelled by any positive charge, whereas a few were repelled by a strong positive charge. ",text,
L_1007,rutherfords atomic model,T_4801,"Rutherford made the same inferences. He concluded that all of the positive charge and virtually all of the mass of an atom are concentrated in one tiny area and the rest of the atom is mostly empty space. Rutherford called the area of concentrated positive charge the nucleus. He predictedand soon discoveredthat the nucleus contains positively charged particles, which he named protons. Rutherford also predicted the existence of neutral nuclear particles called neutrons, but he failed to find them. However, his student James Chadwick discovered them several years later. ",text,
L_1007,rutherfords atomic model,T_4802,"Rutherfords discoveries meant that Thomsons plum pudding model was incorrect. Positive charge is not spread evenly throughout an atom. Instead, it is all concentrated in the tiny nucleus. The rest of the atom is empty space except for the electrons scattered through it. In Rutherfords model of the atom, which is shown in the Figure 1.3, the electrons move around the massive nucleus like planets orbiting the sun. Thats why his model is called the planetary model. Rutherford didnt know exactly where or how electrons orbit the nucleus. That research would be undertaken by later scientists, beginning with Niels Bohr in 1913. New and improved atomic models would also be developed. Nonetheless, Rutherfords model is still often used to represent the atom. ",text,
L_1009,saturated hydrocarbons,T_4806,"Saturated hydrocarbons are hydrocarbons that contain only single bonds between carbon atoms. They are the simplest class of hydrocarbons. They are called saturated because each carbon atom is bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogen. You can see an example of a saturated hydrocarbon in the Figure 1.1. In this compound, named ethane, each carbon atom is bonded to three hydrogen atoms. In the structural formula, each dash (-) represents a single covalent bond, in which two atoms share one pair of valence electrons. Q: What is the chemical formula for ethane? A: The chemical formula is C2 H6 . ",text,
L_1009,saturated hydrocarbons,T_4807,"Saturated hydrocarbons are given the general name of alkanes. The name of specific alkanes always ends in -ane. The first part of the name indicates how many carbon atoms each molecule of the alkane has. The smallest alkane is methane. It has just one carbon atom. The next largest is ethane with two carbon atoms. The chemical formulas and properties of methane, ethane, and other small alkanes are listed in the Table 1.1. The boiling and melting points of alkanes are determined mainly by the number of carbon atoms they have. Alkanes with more carbon atoms generally boil and melt at higher temperatures. Alkane Methane Ethane Propane Butane Pentane Hexane Heptane Octane Chemical Formula CH4 C2 H6 C3 H8 C4 H10 C5 H12 C6 H14 C7 H16 C8 H18 Boiling Point( C) -162 -89 -42 0 36 69 98 126 Melting Point( C) -183 -172 -188 -138 -130 -95 -91 -57 State (at 20  C) gas gas gas gas liquid liquid liquid liquid Q: The Table 1.1 shows only alkanes that have relatively few carbon atoms. Some alkanes have many more carbon atoms. What properties might larger alkanes have? A: Alkanes with more carbon atoms have higher boiling and melting points, so some of them are solids at room temperature. ",text,
L_1009,saturated hydrocarbons,T_4808,"Structural formulas are often used to represent hydrocarbon compounds because the molecules can have different shapes and a structural formula shows how the atoms are arranged. Hydrocarbons may form straight chains, A) In a straight-chain molecule, all the carbon atoms are lined up in a row like cars of a train. The carbon atoms form the backbone of the molecule. B) In a branched-chain molecule, at least one of the carbon atoms branches off from the backbone. C) In a cyclic molecule, the chain of carbon atoms is joined at the two ends to form a ring. Each ring usually contains just five or six carbon atoms, but rings can join together to form larger molecules. A cyclic molecule generally has higher boiling and melting points than straight-chain and branched- chain molecules. ",text,
L_1012,scientific graphing,T_4814,"Graphs are very useful tools in science. They can help you visualize a set of data. With a graph, you can actually see what all the numbers in a data table mean. Three commonly used types of graphs are bar graphs, circle graphs, and line graphs. Each type of graph is suitable for showing a different type of data. ",text,
L_1012,scientific graphing,T_4815,The data in Table 1.1 shows the average number of tornadoes per year for the ten U.S. cities that have the most tornadoes. The data were averaged over the time period 1950-2007. ,text,
L_1012,scientific graphing,T_4816,"Rank City 1 2 3 4 5 6 7 8 9 10 Clearwater, FL Oklahoma City, OK Tampa-St. Petersburg, FL Houston, TX Tulsa, OK New Orleans, LA Melbourne, FL Indianapolis, IN Fort Worth, TX Lubbock, TX Average Number of Tornadoes(per 1000 Square Miles) 7.4 2.2 2.1 2.1 2.1 2.0 1.9 1.7 1.7 1.6 Bar graphs are especially useful for comparing values for different things, such as the average numbers of tornadoes for different cities. Therefore, a bar graph is a good choice for displaying the data in theTable 1.1. The bar graph below shows one way that these data could be presented. Q: What do the two axes of this bar graph represent? A: The x-axis represents cities, and the y-axis represents average numbers of tornadoes. Q: Could you switch what the axes represent? If so, how would the bar graph look? A: Yes; the x-axis could represent average numbers of tornadoes, and the y-axis could represent cities. The bars of the graph would be horizontal instead of vertical. ",text,
L_1012,scientific graphing,T_4817,"The data in Table 1.2 shows the percent of all U.S. tornadoes by tornado strength for the years 1986 to 1995. In this table, tornadoes are rated on a scale called the F scale. On this scale, F0 tornadoes are the weakest and F5 tornadoes are the strongest. Tornado Scale(F-scale rating) F0 F1 F2 F3 F4 F5 Percent of all U.S. Tornadoes 55.0% 31.6% 10.0% 2.6% 0.7% 0.1% Circle graphs are used to show percents (or fractions) of a whole, such as the percents of F0 to F5 tornadoes out of all tornadoes. Therefore, a circle graph is a good choice for the data in the table. The circle graph below displays these data. Q: What if the Table 1.2 on tornado strength listed the numbers of tornadoes rather than the percents of tornadoes? Could a circle graph be used to display these data? A: No, a circle graph can only be used to show percents (or fractions) of a whole. However, the numbers could be used to calculate percents, which could then be displayed in a circle graph. ",text,
L_1012,scientific graphing,T_4818,"Consider the data in Table 1.3. It lists the number of tornadoes in the U.S. per month, averaged over the years 2009 to 2011. Month January February March April May June July August September October November December Average Number of Tornadoes 17 33 74 371 279 251 122 57 39 65 39 34 Line graphs are especially useful for showing changes over time, or time trends in data, such as how the average number of tornadoes varies throughout the year. Therefore, a line graph would be a good choice to display the data in the Table 1.3. The line graph below shows one way this could be done. Q: Based on the line graph above, describe the trend in tornado numbers by month throughout the course of a year. A: The number of tornadoes rises rapidly from a low in January to a peak in April. This is followed by a relatively slow decline throughout the rest of the year. ",text,
L_1016,scientific modeling,T_4828,"A model is a representation of an object, system, or process. For example, a road map is a representation of an actual system of roads on the ground. Models are very useful in science. They provide a way to investigate things that are too small, large, complex, or distant to investigate directly. To be useful, a model must closely represent the real thing in important ways, but it must be simpler and easier to understand than the real thing. Q: What might be examples of things that would be modeled in physical science because they are difficult to investigate directly? A: Examples include extremely small things such as atoms, very distant objects such as stars, and complex systems such as the electric grid that carries electricity throughout the country. Q: What are ways that these things might be modeled? A: Types of models include two-dimensional diagrams, three-dimensional structures, mathematical formulas, and computer simulations. Examples of simple two-dimensional models in physical science are described below. Click image to the left or use the URL below. URL:  Click image to the left or use the URL below. URL: ",text,
L_1016,scientific modeling,T_4829,"The diagram below is a simple two-dimensional model of a water molecule. This is the smallest particle of water that still has the properties of water. The model shows that each molecule of water consists of one atom of oxygen and two atoms of hydrogen. Q: What else can you learn about water molecules from this model? A: The model shows the number of atomic particlesprotons, neutrons, and electronsin each type of atom. It also shows that each hydrogen atom in a water molecule shares its electron with the oxygen atom. Q: Do you think this water molecule model satisfies the criteria of a useful model? In other words, does it represent a real water molecule in important ways while being simpler and easier to understand than a real water molecule? A: The model shows the basic structure of a water molecule and how the atoms in the molecule share electrons. These features of the water molecule explain important properties of water. The model is also simpler and easier to understand than a real water molecule. In a real molecule, electrons spin around the nuclei at the center of the atoms in a cloud, rather than in neat, circular orbits, as shown in the model. The atoms of a real water molecule also contain even smaller particles than protons, neutrons, and electrons. For many purposes, however, its not necessary to represent these more complex features of a real water molecule. The diagram below shows another example of a simple model in physical science. This diagram is a model of an electric circuit. It represents the main parts of the circuit with simple symbols. Horizontal lines with + and - signs represent a battery. The parts labeled R1 , R2 , and R3 are devices that use electricity provided by the battery. For example, these parts might be a series of three light bulbs. Q: In the electric circuit diagram, what do the black lines connecting the battery and electric devices represent? A: The black lines represent electric wires. The wires are necessary to carry electric current from the battery to the electric devices and back to the battery again. Q: How is a circuit diagram simpler and easier to understand than an actual electric circuit? A: A circuit diagram shows only the parts of the circuit that carry electric current, and it uses simple symbols to represent them. ",text,
L_1019,scope of chemistry,T_4836,"Chemistry is the study of matter and energy and how they interact, mainly at the level of atoms and molecules. Basic concepts in chemistry include chemicals, which are specific types of matter, and chemical reactions. In a chemical reaction, atoms or molecules of certain types of matter combine chemically to form other types of matter. All chemical reactions involve energy. Q: How do you think chemistry explains why the copper on the Statue of Liberty is green instead of brownish red? A: The copper has become tarnished. The tarnishalso called patinais a compound called copper carbonate, which is green. Copper carbonate forms when copper undergoes a chemical reaction with carbon dioxide in moist air. The green patina that forms on copper actually preserves the underlying metal. Thats why its not removed from the statue. Some people also think that the patina looks attractive. ",text,
L_1019,scope of chemistry,T_4837,"Chemistry can help you understand the world around you. Everything you touch, taste, or smell is made of chemicals, and chemical reactions underlie many common changes. For example, chemistry explains how food cooks, why laundry detergent cleans your clothes, and why antacid tablets relieve an upset stomach. Other examples are illustrated in the Figure 1.1. Chemistry even explains you! Your body is made of chemicals, and chemical changes constantly take place within it. Each of these pictures represents a way that chemicals and chemical reactions af- fect our lives. ",text,
L_1021,scope of physics,T_4840,"Physics is the study of energy, matter, and their interactions. Its a very broad field because it is concerned with matter and energy at all levelsfrom the most fundamental particles of matter to the entire universe. Some people would even argue that physics is the study of everything! Important concepts in physics include motion, forces such as magnetism and gravity, and forms of energy such as light, sound, and electrical energy. Q: How do you think physics explains the distorted images formed by a funhouse mirror? A: Physics explains how energy interacts with matter. In this case, for example, physics explains how visible light reflects from mirrors to form images. Most mirrors, such as bathroom mirrors, have a flat surface. Light reflected from a flat mirror forms an image that looks the same as the object in front of it. Funhouse mirrors, like the one pictured above, are different. They have a curved surface that reflects light at different angles. This explains why the images they form are distorted. ",text,
L_1021,scope of physics,T_4841,"Physics can help you understand just about everything in the world around you. Thats because everything around you consists of matter and energy. Several examples of matter and energy interacting are pictured in the Figure 1.1. Read how physics explains each example. Examples of how matter and energy interact. Q: Based on the examples in Figure 1.1, what might be other examples of energy and matter interacting? A: Like the strings of cello, anything that vibrates produces waves of energy that travel through matter. For example, when you throw a pebble into a pond, waves of energy travel from the pebble through the water in all directions. Like an incandescent light bulb, anything that glows consists of matter that produces light energy. For example, fireflies use chemicals to produce light energy. Like a moving tennis racket, anything that moves has energy because it is moving, including your eyes as they read this sentence. ",text,
L_1022,screw,T_4842,"A screw is a simple machine that consists of an inclined plane wrapped around a central cylinder. No doubt you are familiar with screws like the wood screw in the left-hand side of the Figure 1.1. The cap of the bottle pictured on the right is another example of a screw. Screws move objects to a greater depth (or higher elevation) by increasing the force applied to the screw. Many screws are used to hold things together, such as two pieces of wood or a screw cap and bottle. When you use a screw, you apply force to turn the inclined plane. The screw, in turn, applies greater force to the object, such as the wood or bottle top. Q: Can you identify the inclined plane in each example of a screw pictured in the Figure 1.1? A: The inclined plane of the screw on the left consists of the ridges, or threads, that wrap around the central cylinder of the screw. The inclined plane of the cap on the right consists of the ridges that wrap around the inner sides of the cap. ",text,
L_1022,screw,T_4843,"The mechanical advantage of a simple machine is the factor by which it multiplies the force applied to the machine. It is the ratio of the output force to the input force. The force applied by the screw (output force) is always greater than the force applied to the screw (input force). Therefore, the mechanical advantage of a screw is always greater than 1. Look at the two screws in the Figure 1.2. In the screw on the right, the threads of the inclined plane are closer together. This screw has a greater mechanical advantage and is easier to turn than the screw on the left, so it takes less force to penetrate the wood with the right screw. The trade-off is that more turns of the screw are needed to do the job because the distance over which the input force must be applied is greater. Q: Why is it harder to turn a screw with more widely spaced threads? A: The screw moves farther with each turn when the threads are more widely space, so more force must be applied to turn the screw and cover the greater distance. ",text,
L_1024,significant figures,T_4847,"In any measurement, the number of significant figures is the number of digits thought to be correct by the person doing the measuring. It includes all digits that can be read directly from the measuring device plus one estimated digit. Look at the sketch of a beaker below. How much blue liquid does the beaker contain? The top of the liquid falls between the mark for 40 mL and 50 mL, but its closer to 50 mL. A reasonable estimate is 47 mL. In this measurement, the first digit (4) is known for certain and the second digit (7) is an estimate, so the measurement has two significant figures. Now look at the graduated cylinder sketched below. How much blue liquid does it contain? First, its important to note that you should read the amount of liquid at the bottom of its curved surface. This falls about half way between the mark for 36 mL and the mark for 37 mL, so a reasonable estimate would be 36.5 mL. Q: How many significant figures does this measurement have? A: There are three significant figures in this measurement. You know that the first two digits (3 and 6) are accurate. The third digit (5) is an estimate. ",text,
L_1024,significant figures,T_4848,"The examples above show that its easy to count the number of significant figures when you are making a measure- ment. But what if someone else has made the measurement? How do you know which digits are known for certain and which are estimated? How can you tell how many significant figures there are in the measurement? There are several rules for counting significant figures: Leading zeros are never significant. For example, in the number 006.1, only the 6 and 1 are significant. Zeros within a number between nonzero digits are always significant. For example, in the number 106.1, the zero is significant, so this number has four significant figures. Zeros that show only where the decimal point falls are not significant. For example, the number 470,000 has just two significant figures (4 and 7). The zeros just show that the 4 represents hundreds of thousands and the 7 represents tens of thousands. Therefore, these zeros are not significant. Trailing zeros that arent needed to show where the decimal point falls are significant. For example, 4.00 has three significant figures. Q: How many significant figures are there in each of these numbers: 20,080, 2.080, and 2000? A: Both 20,080 and 2.080 contain four significant figures, but 2000 has just one significant figure. ",text,
L_1024,significant figures,T_4849,"When measurements are used in a calculation, the answer cannot have more significant figures than the measurement with the fewest significant figures. This explains why the homework answer above is wrong. It has more significant figures than the measurement with the fewest significant figures. As another example, assume that you want to calculate the volume of the block of wood shown below. The volume of the block is represented by the formula: Volume = length  width  height Therefore, you would do the following calculation: Volume = 1.2 cm  1.0 cm  1 cm = 1.2 cm3 Q: Does this answer have the correct number of significant figures? A: No, it has too many significant figures. The correct answer is 1 cm3 . Thats because the height of the block has just one significant figure. Therefore, the answer can have only one significant figure. ",text,
L_1024,significant figures,T_4850,"To get the correct answer in the volume calculation above, rounding was necessary. Rounding is done when one or more ending digits are dropped to get the correct number of significant figures. In this example, the answer was rounded down to a lower number (from 1.2 to 1). Sometimes the answer is rounded up to a higher number. How do you know which way to round? Follow these simple rules: If the digit to be rounded (dropped) is less than 5, then round down. For example, when rounding 2.344 to three significant figures, round down to 2.34. If the digit to be rounded is greater than 5, then round up. For example, when rounding 2.346 to three significant figures, round up to 2.35. If the digit to be rounded is 5, round up if the digit before 5 is odd, and round down if digit before 5 is even. For example, when rounding 2.345 to three significant figures, round down to 2.34. This rule may seem arbitrary, but in a series of many calculations, any rounding errors should cancel each other out. ",text,
L_1025,simple machines,T_4851,"A machine is any device that makes work easier by changing a force. Work is done whenever a force moves an object over a distance. The amount of work done is represented by the equation: Work = Force x Distance When you use a machine, you apply force to the machine. This force is called the input force. The machine, in turn, applies force to an object. This force is called the output force. The output force may or may not be the same as the input force. The force you apply to the machine is applied over a given distance, called the input distance. The force applied by the machine to the object is also applied over a distance, called the output distance. The output distance may or may not be the same as the input distance. ",text,
L_1025,simple machines,T_4852,"Contrary to popular belief, machines do not increase the amount of work that is done. They just change how the work is done. Machines make work easier by increasing the amount of force that is applied, increasing the distance over which the force is applied, or changing the direction in which the force is applied. Q: If a machine increases the force applied, what does this tell you about the distance over which the force is applied by the machine: A: The machine must apply the force over a shorter distance. Thats because a machine doesnt change the amount of work and work equals force times distance. Therefore, if force increases, distance must decrease. For the same reason, if a machine increases the distance over which the force is applied, it must apply less force. ",text,
L_1025,simple machines,T_4853,"Examples of machines that increase force are steering wheels and pliers (see Figure 1.1). Read below to find out how both of these machines work. In each case, the machine applies more force than the user applies to the machine, but the machine applies the force over a shorter distance. ",text,
L_1025,simple machines,T_4854,"Examples of machines that increase the distance over which force is applied are leaf rakes and hammers (see Figure which the force is applied, but it reduces the strength of the force. ",text,
L_1025,simple machines,T_4855,"Some machines change the direction of the force applied by the user. They may or may not also change the strength of the force or the distance over which the force is applied. Two examples of machines that work this way are the claw ends of hammers and flagpole pulleys. You can see in the Figure 1.3 how each of these machines works. In both cases, the direction of the force applied by the user is reversed by the machine. Q: If the pulley only changes the direction of the force, how does it make the work of raising the flag easier? A: The pulley makes it easier to lift the flag because it allows a person to pull down on the rope and add his or her own weight to the effort, rather than simply lifting the load. ",text,
L_1025,simple machines,T_4856,"There are six types of simple machines that are the basis of all other machines. They are the inclined plane, lever, wedge, screw, pulley, and wheel and axle. The six types are pictured in the Figure 1.4. Youve probably used some of these simple machines yourself. Most machines are combinations of two or more simple machines. These machines are called compound machines. An example of a compound machine is a wheelbarrow (see bottom of Figure 1.4). It consists of two simple machines: a lever and a wheel and axle. Many compound machines are much more complex and consist of many simple machines. Examples include washing machines and cars. ",text,
L_1025,simple machines,T_4856,"There are six types of simple machines that are the basis of all other machines. They are the inclined plane, lever, wedge, screw, pulley, and wheel and axle. The six types are pictured in the Figure 1.4. Youve probably used some of these simple machines yourself. Most machines are combinations of two or more simple machines. These machines are called compound machines. An example of a compound machine is a wheelbarrow (see bottom of Figure 1.4). It consists of two simple machines: a lever and a wheel and axle. Many compound machines are much more complex and consist of many simple machines. Examples include washing machines and cars. ",text,
L_1025,simple machines,T_4856,"There are six types of simple machines that are the basis of all other machines. They are the inclined plane, lever, wedge, screw, pulley, and wheel and axle. The six types are pictured in the Figure 1.4. Youve probably used some of these simple machines yourself. Most machines are combinations of two or more simple machines. These machines are called compound machines. An example of a compound machine is a wheelbarrow (see bottom of Figure 1.4). It consists of two simple machines: a lever and a wheel and axle. Many compound machines are much more complex and consist of many simple machines. Examples include washing machines and cars. ",text,
L_1032,sound waves,T_4875,"In science, sound is defined as the transfer of energy from a vibrating object in waves that travel through matter. Most people commonly use the term sound to mean what they hear when sound waves enter their ears. The tree above generated sound waves when it fell to the ground, so it made sound according to the scientific definition. But the sound wasnt detected by a persons ears if there was nobody in the forest. So the answer to the riddle is both yes and no! ",text,
L_1032,sound waves,T_4876,"All sound waves begin with vibrating matter. Look at the first guitar string on the left in the Figure 1.1. Plucking the string makes it vibrate. The diagram below the figure shows the wave generated by the vibrating string. The moving string repeatedly pushes against the air particles next to it, which causes the air particles to vibrate. The vibrations spread through the air in all directions away from the guitar string as longitudinal waves. In longitudinal waves, particles of the medium vibrate back and forth parallel to the direction that the waves travel. Q: If there were no air particles to carry the vibrations away from the guitar string, how would sound reach the ear? A: It wouldnt unless the vibrations were carried by another medium. Sound waves are mechanical waves, so they can travel only though matter and not through empty space. ",text,
L_1032,sound waves,T_4877,"The fact that sound cannot travel through empty space was first demonstrated in the 1600s by a scientist named Robert Boyle. Boyle placed a ticking clock in a sealed glass jar. The clock could be heard ticking through the air and glass of the jar. Then Boyle pumped the air out of the jar. The clock was still ticking, but the ticking sound could no longer be heard. Thats because the sound couldnt travel away from the clock without air particles to pass the sound energy along. Click image to the left or use the URL below. URL: ",text,
L_1032,sound waves,T_4878,"Most of the sounds we hear reach our ears through the air, but sounds can also travel through liquids and solids. If you swim underwateror even submerge your ears in bathwaterany sounds you hear have traveled to your ears through the water. Some solids, including glass and metals, are very good at transmitting sounds. Foam rubber and heavy fabrics, on the other hand, tend to muffle sounds. They absorb rather than pass on the sound energy. Q: How can you tell that sounds travel through solids? A: One way is that you can hear loud outdoor sounds such as sirens through closed windows and doors. You can also hear sounds through the inside walls of a house. For example, if you put your ear against a wall, you may be able to eavesdrop on a conversation in the next roomnot that you would, of course. ",text,
L_1033,sources of visible light,T_4879,"Visible light includes all the wavelengths of light that the human eye can detect. It allows us to see objects in the world around us. Without visible light, we would only be able to sense most objects by sound, touch, or smell. Like humans, most other organisms also depend on visible light, either directly or indirectly. Many animalsincluding predators of jellyfishuse visible light to see. Plants and certain other organisms use visible light to make food in the process of photosynthesis. Without this food, most other organisms would not be able to survive. Q: Do you think that some animals might be able to see light that isnt visible to humans? A: Some animals can see light in the infrared or ultraviolet range of wavelengths. For example, mosquitoes can see infrared light, which is emitted by warm objects. By seeing infrared light, mosquitoes can tell where the warmest, blood-rich areas of the body are located. ",text,
L_1033,sources of visible light,T_4880,"Most of the visible light on Earth comes from the sun. The sun and other stars produce light because they are so hot. They glow with light due to their extremely high temperatures. This way of producing light is called incandescence. Incandescent light bulbs also produce light in this way. When electric current passes through a wire filament inside an incandescent bulb, the wire gets so hot that it glows. Do you see the glowing filament inside the incandescent light bulb in the Figure 1.1? Q: What are some other sources of incandescent light? A: Flames also produce incandescent light. For example, burning candles, oil lamps, and bonfires produce light in this way. ",text,
L_1033,sources of visible light,T_4881,"Some objects produce light without becoming very hot. They generate light through chemical reactions or other processes. Producing light without heat is called luminescence. Luminescence, in turn, can occur in several different ways: One type of luminescence is called fluorescence. In this process, a substance absorbs shorter-wavelength ultraviolet light and then gives off light in the visible range of wavelengths. Certain minerals produce light in this way, including gemstones such as amethyst, diamond, and emerald. Another type of luminescence is called electroluminescence. In this process, a substance gives off light when an electric current passes through it. Gases such as neon, argon, and krypton produce light by this means. The car dash lights in the Figure 1.2 are produced by electroluminescence. A third type of luminescence is called bioluminescence. This is the production of light by living things as a result of chemical reactions. The jellyfish in the opening photo above produces light by bioluminescence. So does the firefly in the Figure 1.3. Fireflies give off visible light to attract mates. ",text,
L_1033,sources of visible light,T_4882,"Many other objects appear to produce their own light, but they actually just reflect light from another source. Being lit by another source is called illumination. The moon in the Figure 1.4 is glowing so brightly that you can see shadows under the trees. It appears to glow from its own light, but its really just illuminated by light from the sun. Everything you can see that doesnt produce its own light is illuminated by light from some other source. ",text,
L_1033,sources of visible light,T_4882,"Many other objects appear to produce their own light, but they actually just reflect light from another source. Being lit by another source is called illumination. The moon in the Figure 1.4 is glowing so brightly that you can see shadows under the trees. It appears to glow from its own light, but its really just illuminated by light from the sun. Everything you can see that doesnt produce its own light is illuminated by light from some other source. ",text,
L_1035,speed,T_4885,"How fast or slow something moves is its speed. Speed determines how far something travels in a given amount of time. The SI unit for speed is meters per second (m/s). Speed may be constant, but often it varies from moment to moment. ",text,
L_1035,speed,T_4886,"Even if speed varies during the course of a trip, its easy to calculate the average speed by using this formula: speed = distance time For example, assume you go on a car trip with your family. The total distance you travel is 120 miles, and it takes 3 hours to travel that far. The average speed for the trip is: 120 mi 3h = 40 mi/h speed = Q: Terri rode her bike very slowly to the top of a big hill. Then she coasted back down the hill at a much faster speed. The distance from the bottom to the top of the hill is 3 kilometers. It took Terri 41 hour to make the round trip. What was her average speed for the entire trip? (Hint: The round-trip distance is 6 km.) A: Terris speed can be calculated as follows: 6 km 0.25 h = 24 km/h speed = ",text,
L_1035,speed,T_4887,"When you travel by car, you usually dont move at a constant speed. Instead you go faster or slower depending on speed limits, traffic lights, the number of vehicles on the road, and other factors. For example, you might travel 65 miles per hour on a highway but only 20 miles per hour on a city street (see the pictures in the Figure 1.1.) You might come to a complete stop at traffic lights, slow down as you turn corners, and speed up to pass other cars. Therefore, your speed at any given instant, or your instantaneous speed, may be very different than your speed at other times. Instantaneous speed is much more difficult to calculate than average speed. Cars race by in a blur of motion on an open highway but crawl at a snails pace when they hit city traffic. ",text,
L_1035,speed,T_4888,"If you know the average speed of a moving object, you can calculate the distance it will travel in a given period of time or the time it will take to travel a given distance. To calculate distance from speed and time, use this version of the average speed formula given above: distance = speed  time For example, if a car travels at an average speed of 60 km/h for 5 hours, then the distance it travels is: distance = 60 km/h  5 h = 300 km To calculate time from speed and distance, use this version of the formula: time = distance speed Q: If you walk 6 km at an average speed of 3 km/h, how much time does it take? A: Use the formula for time as follows: distance speed 6 km = 3 km/h =2h time = ",text,
L_1036,speed of sound,T_4889,"The speed of sound is the distance that sound waves travel in a given amount of time. Youll often see the speed of sound given as 343 meters per second. But thats just the speed of sound under a certain set of conditions, specifically, through dry air at 20  C. The speed of sound may be very different through other matter or at other temperatures. ",text,
L_1036,speed of sound,T_4890,"Sound waves are mechanical waves, and mechanical waves can only travel through matter. The matter through which the waves travel is called the medium (plural, media). The Table 1.1 gives the speed of sound in several different media. Generally, sound waves travel most quickly through solids, followed by liquids, and then by gases. Particles of matter are closest together in solids and farthest apart in gases. When particles are closer together, they can more quickly pass the energy of vibrations to nearby particles. Medium (20  C) Dry Air Speed of Sound Waves (m/s) 343 Medium (20  C) Water Wood Glass Aluminum Speed of Sound Waves (m/s) 1437 3850 4540 6320 Q: The table gives the speed of sound in dry air. Do you think that sound travels more or less quickly through air that contains water vapor? (Hint: Compare the speed of sound in water and air in the table.) A: Sound travels at a higher speed through water than air, so it travels more quickly through air that contains water vapor than it does through dry air. ",text,
L_1036,speed of sound,T_4891,"The speed of sound also depends on the temperature of the medium. For a given medium, sound has a slower speed at lower temperatures. You can compare the speed of sound in dry air at different temperatures in the following Table 1.2. At a lower temperature, particles of the medium are moving more slowly, so it takes them longer to transfer the energy of the sound waves. Temperature of Air 0 C 20  C 100  C Speed of Sound Waves (m/s) 331 343 386 Q: What do you think the speed of sound might be in dry air at a temperature of -20  C? A: For each 1 degree Celsius that temperature decreases, the speed of sound decreases by 0.6 m/s. So sound travels through dry, -20  C air at a speed of 319 m/s. ",text,
L_1038,static electricity and static discharge,T_4895,"Static electricity is a buildup of electric charges on objects. Charges build up when negative electrons are transferred from one object to another. The object that gives up electrons becomes positively charged, and the object that accepts the electrons becomes negatively charged. This can happen in several ways. One way electric charges can build up is through friction between materials that differ in their ability to give up or accept electrons. When you wipe your rubber-soled shoes on the wool mat, for example, electrons rub off the mat onto your shoes. As a result of this transfer of electrons, positive charges build up on the mat and negative charges build up on you. Once an object becomes electrically charged, it is likely to remain charged until it touches another object or at least comes very close to another object. Thats because electric charges cannot travel easily through air, especially if the air is dry. Q: Youre more likely to get a shock in the winter when the air is very dry. Can you explain why? A: When the air is very dry, electric charges are more likely to build up objects because they cannot travel easily through the dry air. This makes a shock more likely when you touch another object. ",text,
L_1038,static electricity and static discharge,T_4896,"What happens when you have become negatively charged and your hand approaches the metal doorknocker? Your negatively charged hand repels electrons in the metal, so the electrons move to the other side of the knocker. This makes the side of the knocker closest to your hand positively charged. As your negatively charged hand gets very close to the positively charged side of the metal, the air between your hand and the knocker also becomes electrically charged. This allows electrons to suddenly flow from your hand to the knocker. The sudden flow of electrons is static discharge. The discharge of electrons is the spark you see and the shock you feel. ",text,
L_1038,static electricity and static discharge,T_4897,"Another example of static discharge, but on a much larger scale, is lightning. You can see how it occurs in the following diagram (Figure 1.1). During a rainstorm, clouds develop regions of positive and negative charge due to the movement of air molecules, water drops, and ice particles. The negative charges are concentrated at the base of the clouds, and the positive charges are concentrated at the top. The negative charges repel electrons on the ground beneath them, so the ground below the clouds becomes positively charged. At first, the atmosphere prevents electrons from flowing away from areas of negative charge and toward areas of positive charge. As more charges build up, however, the air between the oppositely charged areas also becomes charged. When this happens, static electricity is discharged as bolts of lightning. ",text,
L_1040,surface wave,T_4900,"A surface wave is a wave that travels along the surface of a medium. The medium is the matter through which the wave travels. Ocean waves are the best-known examples of surface waves. They travel on the surface of the water between the ocean and the air. Q: What do you think causes ocean waves? A: Most ocean waves are caused by wind blowing across the water. Moving air molecules transfer some of their energy to molecules of ocean water. The energy travels across the surface of the water in waves. The stronger the winds are blowing, the larger the waves are and the more energy they have. ",text,
L_1040,surface wave,T_4901,"A surface wave is a combination of a transverse wave and a longitudinal wave. A transverse wave is a wave in which particles of the medium move up and down perpendicular to the direction of the wave. A longitudinal wave is a wave in which particles of the medium move parallel to the direction of the wave. In a surface wave, particles of the medium move up and down as well as back and forth. This gives them an overall circular motion. You can see how the particles move in the Figure 1.1. Click image to the left or use the URL below. URL: ",text,
L_1040,surface wave,T_4902,"In deep water, particles of water just move in circles. They dont actually move closer to shore with the energy of the waves. However, near the shore where the water is shallow, the waves behave differently. Look at the Figure 1.2. You can see how the waves start to drag on the bottom in shallow water. This creates friction that slows down the bottoms of the waves, while the tops of the waves keep moving at the same speed. The difference in speed causes the waves to get steeper until they topple over and break. The crashing waves carry water onto the shore as surf. Q: In this diagram of a wave breaking near shore, where do you think a surfer would try to catch the wave? A: The surfer would try to catch the wave where it starts to steepen and lean forward toward the shore. ",text,
L_1041,synthesis reactions,T_4903,"A synthesis reaction occurs when two or more reactants combine to form a single product. A synthesis reaction can be represented by the general equation: A+BC In this equation, the letters A and B represent the reactants that begin the reaction, and the letter C represents the product that is synthesized in the reaction. The arrow shows the direction in which the reaction occurs. Q: What is the chemical equation for the synthesis of nitrogen dioxide (NO2 ) from nitric oxide (NO) and oxygen (O2 )? A: The equation for this synthesis reaction is: 2NO + O2  2NO2 ",text,
L_1041,synthesis reactions,T_4904,"Another example of a synthesis reaction is the combination of sodium (Na) and chlorine (Cl) to produce sodium chloride (NaCl). This reaction is represented by the chemical equation: 2Na + Cl2  2NaCl Sodium is a highly reactive metal, and chlorine is a poisonous gas. Both elements are pictured in the Figure 1.1. The compound they synthesize has very different properties. Sodium chloride is commonly called table salt, which is neither reactive nor poisonous. In fact, salt is a necessary component of the human diet. ",text,
L_1042,technological design constraints,T_4905,"The development of new technologywhether its a simple kite or a complex machineis called technological design. The technological design process is a step-by-step approach to finding a solution to a problem. Often, the main challenge in technological design is finding a solution that works within the constraints, or limits, on the design. All technological designs have constraints. Q: Assume you want to design a kite. What might be some constraints on your design? A: Possible constraints might include the shape and size of the kite and the materials you use to make it. ",text,
L_1042,technological design constraints,T_4906,"Technological design constraints may be physical or social. Physical design constraints include factors such as natural laws and properties of materials. A kite, for example, will fly only if its shape allows air currents to lift it. Otherwise, gravity will keep it on the ground. Social design constraints include factors such as ease of use, safety, attractiveness, and cost. For example, a kite string should be easy to unwind as the wind carries the kite higher. ",text,
L_1042,technological design constraints,T_4907,"All technological designs have trade-offs because no design is perfect. For example, a design might be very good at solving a problem, but it might be too expensive to be practical. Or a design might be very attractive, but it might not be safe to use. Choosing the best design often involves weighing the pros and cons of different options and deciding which ones are most important. Q: What trade-offs might there be on the design of a kite? A: You might want to make a big kite, but if its too big it might be too heavy. Then it would fly only on very windy days. Or you might want to make a kite using a certain material that you really like, but the material might cost more than you can afford to spend. ",text,
L_1045,technology and society,T_4913,"Important new technologies such as the wheel have had a big impact on human society. Major advances in technol- ogy have influenced every aspect of life, including transportation, food production, manufacturing, communication, medicine, and the arts. Thats because technology has the goal of solving human problems, so new technologies usually make life better. They may make work easier, for example, or make people healthier. Sometimes, however, new technologies affect people in negative ways. For example, using a new product or process might cause human health problems or pollute the environment. Q: Can you think of a modern technology that has both positive and negative effects on people? A: Modern methods of transportation have both positive and negative effects on people. They help people and goods move quickly all over the world. However, most of them pollute the environment. For example, gasoline-powered cars and trucks add many pollutants to the atmosphere. The pollutants harm peoples health and contribute to global climate change. ",text,
L_1045,technology and society,T_4914,"Few technologies have impacted society as greatly as the powerful steam engine developed by Scottish inventor James Watt in 1775 (see Figure 1.1). Watts steam engine was soon being used to power all kinds of machines. It started a revolution in industry. For the first time in history, people did not have to rely on human or animal muscle, wind, or water for power. With the steam engine to power machines, new factories sprang up all over Britain. The Industrial Revolution began in Britain the late 1700s. It eventually spread throughout Western Europe, North America, Japan, and many other countries. It marked a major turning point in human history. Almost every aspect of daily life was influenced by it in some way. Average income and population both began to grow faster than ever before. People flocked to the new factories for jobs, and densely populated towns and cities grew up around the factories. The new towns and cities were crowded, and soot from the factories polluted the air. You can see an example of this in the Figure 1.2. This made living conditions very poor. Working conditions in the factories were also bad, with long hours and the pace set by machines. Even young children worked in the factories, damaging their health and giving them little opportunity for education or play. Q: In addition to factory machines, the steam engine was used to power farm machinery, trains, and ships. What effects might this have had on peoples lives? A: Farm machinery replaced human labor and allowed fewer people to produce more food. This is why many rural people migrated to the new towns and cities to look for work in factories. Steam-powered trains and ships made it easier for people to migrate. Food and factory goods could also be transported on steam-powered trains and ships, making them available to far more people. ",text,
L_1048,thermal conductors and insulators,T_4920,"Conduction is the transfer of thermal energy between particles of matter that are touching. Thermal conduction occurs when particles of warmer matter bump into particles of cooler matter and transfer some of their thermal energy to the cooler particles. Conduction is usually faster in certain solids and liquids than in gases. Materials that are good conductors of thermal energy are called thermal conductors. Metals are especially good thermal conductors because they have freely moving electrons that can transfer thermal energy quickly and easily. Besides the heating element inside a toaster, another example of a thermal conductor is a metal radiator, like the one in the Figure 1.1. When hot water flows through the coils of the radiator, the metal quickly heats up by conduction and then radiates thermal energy into the surrounding air. Q: Thermal conductors have many uses, but sometimes its important to prevent the transfer of thermal energy. Can you think of an example? A: One example is staying warm on a cold day. You will stay warmer if you can prevent the transfer of your own thermal energy to the outside air. ",text,
L_1048,thermal conductors and insulators,T_4921,"One way to retain your own thermal energy on a cold day is to wear clothes that trap air. Thats because air, like other gases, is a poor conductor of thermal energy. The particles of gases are relatively far apart, so they dont bump into each other or into other things as often as the more closely spaced particles of liquids or solids. Therefore, particles of gases have fewer opportunities to transfer thermal energy. Materials that are poor thermal conductors are called thermal insulators. Down-filled snowsuits, like those in the Figure 1.2, are good thermal insulators because their feather filling traps a lot of air. Another example of a thermal insulator is pictured in the Figure 1.3. The picture shows fluffy pink insulation inside the attic of a home. Like the down filling in a snowsuit, the insulation traps a lot of air. The insulation helps to prevent the transfer of thermal energy into the house on hot days and out of the house on cold days. Other materials that are thermal insulators include plastic and wood. Thats why pot handles and cooking utensils are often made of these materials. Notice that the outside of the toaster pictured in the opening image is made of plastic. The plastic casing helps prevent the transfer of thermal energy from the heating element inside to the outer surface of the toaster where it could cause burns. Q: Thermal insulators have many practical uses besides the uses mentioned above. Can you think of others? A: Thermal insulators are often used to keep food or drinks hot or cold. For example, Styrofoam coolers and thermos containers are used for these purposes. ",text,
L_1048,thermal conductors and insulators,T_4921,"One way to retain your own thermal energy on a cold day is to wear clothes that trap air. Thats because air, like other gases, is a poor conductor of thermal energy. The particles of gases are relatively far apart, so they dont bump into each other or into other things as often as the more closely spaced particles of liquids or solids. Therefore, particles of gases have fewer opportunities to transfer thermal energy. Materials that are poor thermal conductors are called thermal insulators. Down-filled snowsuits, like those in the Figure 1.2, are good thermal insulators because their feather filling traps a lot of air. Another example of a thermal insulator is pictured in the Figure 1.3. The picture shows fluffy pink insulation inside the attic of a home. Like the down filling in a snowsuit, the insulation traps a lot of air. The insulation helps to prevent the transfer of thermal energy into the house on hot days and out of the house on cold days. Other materials that are thermal insulators include plastic and wood. Thats why pot handles and cooking utensils are often made of these materials. Notice that the outside of the toaster pictured in the opening image is made of plastic. The plastic casing helps prevent the transfer of thermal energy from the heating element inside to the outer surface of the toaster where it could cause burns. Q: Thermal insulators have many practical uses besides the uses mentioned above. Can you think of others? A: Thermal insulators are often used to keep food or drinks hot or cold. For example, Styrofoam coolers and thermos containers are used for these purposes. ",text,
L_1049,thermal energy,T_4922,"Why do the air and sand of Death Valley feel so hot? Its because their particles are moving very rapidly. Anything that is moving has kinetic energy, and the faster it is moving, the more kinetic energy it has. The total kinetic energy of moving particles of matter is called thermal energy. Its not just hot things such as the air and sand of Death Valley that have thermal energy. All matter has thermal energy, even matter that feels cold. Thats because the particles of all matter are in constant motion and have kinetic energy. ",text,
L_1049,thermal energy,T_4923,"Thermal energy and temperature are closely related. Both reflect the kinetic energy of moving particles of matter. However, temperature is the average kinetic energy of particles of matter, whereas thermal energy is the total kinetic energy of particles of matter. Does this mean that matter with a lower temperature has less thermal energy than matter with a higher temperature? Not necessarily. Another factor also affects thermal energy. The other factor is mass. Q: Look at the pot of soup and the tub of water in the Figure 1.1. Which do you think has greater thermal energy? A: The soup is boiling hot and has a temperature of 100  C, whereas the water in the tub is just comfortably warm, with a temperature of about 38  C. Although the water in the tub has a much lower temperature, it has greater thermal energy. The particles of soup have greater average kinetic energy than the particles of water in the tub, explaining why the soup has a higher temperature. However, the mass of the water in the tub is much greater than the mass of the soup in the pot. This means that there are many more particles of water than soup. All those moving particles give the water in the tub greater total kinetic energy, even though their average kinetic energy is less. Therefore, the water in the tub has greater thermal energy than the soup. Q: Could a block of ice have more thermal energy than a pot of boiling water? A: Yes, the block of ice could have more thermal energy if its mass was much greater than the mass of the boiling water. ",text,
L_1050,thermal radiation,T_4924,"The bonfire from the opening image has a lot of thermal energy. Thermal energy is the total kinetic energy of moving particles of matter, and the transfer of thermal energy is called heat. Thermal energy from the bonfire is transferred to the hands by thermal radiation. Thermal radiation is the transfer of thermal energy by waves that can travel through air or even through empty space, as shown in the Figure 1.1. When the waves of thermal energy reach objects, they transfer the energy to the objects, causing them to warm up. This is how the fire warms the hands of someone sitting near the bonfire. This is also how the suns energy reaches Earth and heats its surface. Without the energy radiated from the sun, Earth would be too cold to support life as we know it. Thermal radiation is one of three ways that thermal energy can be transferred. The other two ways are conduction and convection, both of which need matter to transfer energy. Radiation is the only way of transferring thermal energy that doesnt require matter. ",text,
L_1050,thermal radiation,T_4925,"You might be surprised to learn that everything radiates thermal energy, not just really hot things such as the sun or a fire. For example, when its cold outside, a heated home radiates some of its thermal energy into the outdoor environment. A home that is poorly insulated radiates more energy than a home that is well insulated. Special cameras can be used to detect radiated heat. In the Figure 1.2, you can see an image created by one of these cameras. The areas that are yellow are the areas where the greatest amount of thermal energy is radiating from the home. Even people radiate thermal energy. In fact, when a room is full of people, it may feel noticeably warmer because of all the thermal energy the people radiate! Q: Where is thermal radiation radiating from the home in the picture? A: The greatest amount of thermal energy is radiating from the window on the upper left. A lot of thermal energy is also radiating from the edges of the windows and door. ",text,
L_1051,thomsons atomic model,T_4926,"John Dalton discovered atoms in 1804. He thought they were the smallest particles of matter, which could not be broken down into smaller particles. He envisioned them as solid, hard spheres. It wasnt until 1897 that a scientist named Joseph John (J. J.) Thomson discovered that there are smaller particles within the atom. Thomson was born in England and studied at Cambridge University, where he later became a professor. In 1906, he won the Nobel Prize in physics for his research on how gases conduct electricity. This research also led to his discovery of the electron. You can see a picture of Thomson 1.1. ",text,
L_1051,thomsons atomic model,T_4927,"In his research, Thomson passed current through a cathode ray tube, similar to the one seen in the Figure 1.2. A cathode ray tube is a glass tube from which virtually all of the air has been removed. It contains a piece of metal called an electrode at each end. One electrode is negatively charged and known as a cathode. The other electrode is positively charged and known as an anode. When high-voltage electric current is applied to the end plates, a cathode ray travels from the cathode to the anode. What is a cathode ray? Thats what Thomson wanted to know. Is it just a ray of energy that travels in waves like a ray of light? That was one popular hypothesis at the time. Or was a cathode ray a stream of moving particles? That was the other popular hypothesis. Thomson tested these ideas by placing negative and positive plates along the sides of the cathode ray tube to see how the cathode ray would be affected. The cathode ray appeared to be repelled by the negative plate and attracted by the positive plate. This meant that the ray was negative in charge and that is must consist of particles that have mass. He called the particles corpuscles, but they were later renamed electrons. Thomson also measured the mass of the particles he had identified. He did this by determining how much the cathode rays were bent when he varied the voltage. He found that the mass of the particles was 2000 times smaller than the mass of the smallest atom, the hydrogen atom. In short, Thomson had discovered the existence of particles smaller than atoms. This disproved Daltons claim that atoms are the smallest particles of matter. From his discovery, Thomson also inferred that electrons are fundamental particles within atoms. Q: Atoms are neutral in electric charge. How can they be neutral if they contain negatively charged electrons? A: Atoms also contain positively charged particles that cancel out the negative charge of the electrons. However, these positive particles werent discovered until a couple of decades after Thomson discovered electrons. ",text,
L_1051,thomsons atomic model,T_4927,"In his research, Thomson passed current through a cathode ray tube, similar to the one seen in the Figure 1.2. A cathode ray tube is a glass tube from which virtually all of the air has been removed. It contains a piece of metal called an electrode at each end. One electrode is negatively charged and known as a cathode. The other electrode is positively charged and known as an anode. When high-voltage electric current is applied to the end plates, a cathode ray travels from the cathode to the anode. What is a cathode ray? Thats what Thomson wanted to know. Is it just a ray of energy that travels in waves like a ray of light? That was one popular hypothesis at the time. Or was a cathode ray a stream of moving particles? That was the other popular hypothesis. Thomson tested these ideas by placing negative and positive plates along the sides of the cathode ray tube to see how the cathode ray would be affected. The cathode ray appeared to be repelled by the negative plate and attracted by the positive plate. This meant that the ray was negative in charge and that is must consist of particles that have mass. He called the particles corpuscles, but they were later renamed electrons. Thomson also measured the mass of the particles he had identified. He did this by determining how much the cathode rays were bent when he varied the voltage. He found that the mass of the particles was 2000 times smaller than the mass of the smallest atom, the hydrogen atom. In short, Thomson had discovered the existence of particles smaller than atoms. This disproved Daltons claim that atoms are the smallest particles of matter. From his discovery, Thomson also inferred that electrons are fundamental particles within atoms. Q: Atoms are neutral in electric charge. How can they be neutral if they contain negatively charged electrons? A: Atoms also contain positively charged particles that cancel out the negative charge of the electrons. However, these positive particles werent discovered until a couple of decades after Thomson discovered electrons. ",text,
L_1051,thomsons atomic model,T_4928,"Thomson also knew that atoms are neutral in electric charge, so he asked the same question: How can atoms contain negative particles and still be neutral? He hypothesized that the rest of the atom must be positively charged in order to cancel out the negative charge of the electrons. He envisioned the atom as being similar to a plum pudding, like the one pictured in the Figure 1.3mostly positive in charge (the pudding) with negative electrons (the plums) scattered through it. Q: How is our modern understanding of atomic structure different from Thomsons plum pudding model? A: Today we know that all of the positive charge in an atom is concentrated in a tiny central area called the nucleus, with the electrons swirling through empty space around it, as in the Figure 1.4. The nucleus was discovered just a few years after Thomson discovered the electron, so the plum pudding model was soon rejected. ",text,
L_1052,transfer of electric charge,T_4929,"The girl pictured above became negatively charged because electrons flowed from the van de Graaff generator to her. Whenever electrons are transferred between objects, neutral matter becomes charged. This occurs even with individual atoms. Atoms are neutral in electric charge because they have the same number of negative electrons as positive protons. However, if atoms lose or gain electrons, they become charged particles called ions. You can see how this happens in the Figure 1.1. When an atom loses electrons, it becomes a positively charged ion, or cation. When an atom gains electrons, it becomes a negative charged ion, or anion. ",text,
L_1052,transfer of electric charge,T_4930,"Like the formation of ions, the formation of charged matter in general depends on the transfer of electrons, either between two materials or within a material. Three ways this can occur are referred to as conduction, polarization, and friction. All three ways are described below. However, regardless of how electrons are transferred, the total charge always remains the same. Electrons move, but they arent destroyed. This is the law of conservation of charge. ",text,
L_1052,transfer of electric charge,T_4931,"The transfer of electrons from the van de Graaff generator to the man is an example of conduction. Conduction occurs when there is direct contact between materials that differ in their ability to give up or accept electrons. A van de Graff generator produces a negative charge on its dome, so it tends to give up electrons. Human hands are positively charged, so they tend to accept electrons. Therefore, electrons flow from the dome to the mans hand when they are in contact. You dont need a van de Graaff generator for conduction to take place. It may occur when you walk across a wool carpet in rubber-soled shoes. Wool tends to give up electrons and rubber tends to accept them. Therefore, the carpet transfers electrons to your shoes each time you put down your foot. The transfer of electrons results in you becoming negatively charged and the carpet becoming positively charged. ",text,
L_1052,transfer of electric charge,T_4932,"Assume that you have walked across a wool carpet in rubber-soled shoes and become negatively charged. If you then reach out to touch a metal doorknob, electrons in the neutral metal will be repelled and move away from your hand before you even touch the knob. In this way, one end of the doorknob becomes positively charged and the other end becomes negatively charged. This is called polarization. Polarization occurs whenever electrons within a neutral object move because of the electric field of a nearby charged object. It occurs without direct contact between the two objects. The Figure 1.2 models how polarization occurs. Q: What happens when the negatively charged plastic rod in the diagram is placed close to the neutral metal plate? A: Electrons in the plate are repelled by the positive charges in the rod. The electrons move away from the rod, causing one side of the plate to become positively charged and the other side to become negatively charged. ",text,
L_1052,transfer of electric charge,T_4933,"Did you ever rub an inflated balloon against your hair? You can see what happens in the Figure 1.3. Friction between the balloon and hair cause electrons from the hair to rub off on the balloon. Thats because a balloon attracts electrons more strongly than hair does. After the transfer of electrons, the balloon becomes negatively charged and the hair becomes positively charged. The individual hairs push away from each other and stand on end because like charges repel each other. The balloon and the hair attract each other because opposite charges attract. Electrons are transferred in this way whenever there is friction between materials that differ in their ability to give up or accept electrons. Q: If you rub a balloon against a wall, it may stick to the wall. Explain why. ",text,
L_1053,transition metals,T_4934,"Transition metals are all the elements in groups 3-12 of the periodic table. In the periodic table pictured in Figure known elements. In addition to copper (Cu), well known examples of transition metals include iron (Fe), zinc (Zn), silver (Ag), and gold (Au) (Copper (Cu) is pictured in its various applications in the opening image). Q: Transition metals have been called the most typical of all metals. What do you think this means? A: Unlike some other metals, transition metals have the properties that define the metals class. They are excellent conductors of electricity, for example, and they also have luster, malleability, and ductility. You can read more about these properties of transition metals below. ",text,
L_1053,transition metals,T_4935,"Transition metals are superior conductors of heat as well as electricity. They are malleable, which means they can be shaped into sheets, and ductile, which means they can be shaped into wires. They have high melting and boiling points, and all are solids at room temperature, except for mercury (Hg), which is a liquid. Transition metals are also high in density and very hard. Most of them are white or silvery in color, and they are generally lustrous, or shiny. The compounds that transition metals form with other elements are often very colorful. You can see several examples in the Figure 1.2. Some properties of transition metals set them apart from other metals. Compared with the alkali metals in group 1 and the alkaline Earth metals in group 2, the transition metals are much less reactive. They dont react quickly with water or oxygen, which explains why they resist corrosion. Q: How is the number of valence electrons typically related to the properties of elements? A: The number of valence electrons usually determines how reactive elements are as well as the ways in which they react with other elements. ",text,
L_1053,transition metals,T_4935,"Transition metals are superior conductors of heat as well as electricity. They are malleable, which means they can be shaped into sheets, and ductile, which means they can be shaped into wires. They have high melting and boiling points, and all are solids at room temperature, except for mercury (Hg), which is a liquid. Transition metals are also high in density and very hard. Most of them are white or silvery in color, and they are generally lustrous, or shiny. The compounds that transition metals form with other elements are often very colorful. You can see several examples in the Figure 1.2. Some properties of transition metals set them apart from other metals. Compared with the alkali metals in group 1 and the alkaline Earth metals in group 2, the transition metals are much less reactive. They dont react quickly with water or oxygen, which explains why they resist corrosion. Q: How is the number of valence electrons typically related to the properties of elements? A: The number of valence electrons usually determines how reactive elements are as well as the ways in which they react with other elements. ",text,
L_1053,transition metals,T_4936,"Transition metals include the elements that are most often placed below the periodic table (the pink- and purple- shaded elements in the Figure 1.1). Those that follow lanthanum (La) are called lanthanides. They are all relatively reactive for transition metals. Those that follow actinium (Ac) are called actinides. They are all radioactive. This means that they are unstable, so they decay into different, more stable elements. Many of the actinides do not occur in nature but are made in laboratories. ",text,
L_1054,transverse wave,T_4937,"A transverse wave is a wave in which particles of the medium vibrate at right angles, or perpendicular, to the direction that the wave travels. Another example of a transverse wave is the wave that passes through a rope with you shake one end of the rope up and down, as in the Figure 1.1. The direction of the wave is down the length of the rope away from the hand. The rope itself moves up and down as the wave passes through it. Click image to the left or use the URL below. URL:  Q: When a guitar string is plucked, in what direction does the wave travel? In what directions does the string vibrate? A: The wave travels down the string to the end. The string vibrates up and down at right angles to the direction of the wave. ",text,
L_1054,transverse wave,T_4938,"A transverse wave is characterized by the high and low points reached by particles of the medium as the wave passes through. The high points are called crests, and the low points are called troughs. You can see both in the Figure below. ",text,
L_1054,transverse wave,T_4939,Transverse waves called S waves occur during earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions away from the disturbance. S waves may travel for hundreds of miles. An S wave is modeled in the Figure 1.3. ,text,
L_1055,types of friction,T_4940,"Friction is the force that opposes motion between any surfaces that are in contact. There are four types of friction: static, sliding, rolling, and fluid friction. Static, sliding, and rolling friction occur between solid surfaces. Fluid friction occurs in liquids and gases. All four types of friction are described below. ",text,
L_1055,types of friction,T_4941,"Static friction acts on objects when they are resting on a surface. For example, if you are hiking in the woods, there is static friction between your shoes and the trail each time you put down your foot (see Figure 1.1). Without this static friction, your feet would slip out from under you, making it difficult to walk. In fact, thats exactly what happens if you try to walk on ice. Thats because ice is very slippery and offers very little friction. Q: Can you think of other examples of static friction? A: One example is the friction that helps the people climb the rock wall in the opening picture above. Static friction keeps their hands and feet from slipping. ",text,
L_1055,types of friction,T_4942,"Sliding friction is friction that acts on objects when they are sliding over a surface. Sliding friction is weaker than static friction. Thats why its easier to slide a piece of furniture over the floor after you start it moving than it is to get it moving in the first place. Sliding friction can be useful. For example, you use sliding friction when you write with a pencil. The pencil lead slides easily over the paper, but theres just enough friction between the pencil and paper to leave a mark. Q: How does sliding friction help you ride a bike? A: There is sliding friction between the brake pads and bike rims each time you use your bikes brakes. This friction slows the rolling wheels so you can stop. ",text,
L_1055,types of friction,T_4943,"Rolling friction is friction that acts on objects when they are rolling over a surface. Rolling friction is much weaker than sliding friction or static friction. This explains why most forms of ground transportation use wheels, including bicycles, cars, 4-wheelers, roller skates, scooters, and skateboards. Ball bearings are another use of rolling friction. You can see what they look like in the Figure 1.2. They let parts of a wheel or other machine roll rather than slide over on another. The ball bearings in this wheel reduce friction between the inner and outer cylinders when they turn. ",text,
L_1055,types of friction,T_4944,"Fluid friction is friction that acts on objects that are moving through a fluid. A fluid is a substance that can flow and take the shape of its container. Fluids include liquids and gases. If youve ever tried to push your open hand through the water in a tub or pool, then youve experienced fluid friction. You can feel the resistance of the water against your hand. Look at the skydiver in the Figure 1.3. Hes falling toward Earth with a parachute. Resistance of the air against the parachute slows his descent. The faster or larger a moving object is, the greater is the fluid friction resisting its motion. Thats why there is greater air resistance against the parachute than the skydivers body. ",text,
L_1056,ultrasound,T_4945,"Ultrasound is sound that has a wave frequency higher than the human ear can detect. It includes all sound with wave frequencies higher than 20,000 waves per second, or 20,000 hertz (Hz). Although we cant hear ultrasound, it is very useful to humans and some other animals. Uses of ultrasound include echolocation, sonar, and ultrasonography. ",text,
L_1056,ultrasound,T_4946,"Animals such as bats and dolphins send out ultrasound waves and use their echoes, or reflected waves, to identify the locations of objects they cannot see. This is called echolocation. Animals use echolocation to find prey and avoid running into objects in the dark. You can see in the Figure 1.1 how a bat uses echolocation to find insect prey. ",text,
L_1056,ultrasound,T_4947,"Sonar uses ultrasound in a way that is similar to echolocation. Sonar stands for sound navigation and ranging. It is used to locate underwater objects such as submarines. Thats how the ship pictured in the Figure 1.2 is using it. A sonar device is both a sender and a receiver. It sends out ultrasound waves and detects the waves after they reflect from underwater objects. The distance to underwater objects can be calculated from the known speed of sound in water and the time it takes for the sound waves to travel to the object. The equation for distance traveled when speed and time are known is: Distance = Speed  Time Consider the ship and submarine pictured in the Figure 1.2. If an ultrasound wave travels from the ship to the submarine and back again in 2 seconds, what is the distance from the ship to the submarine? The sound wave travels from the ship to the submarine in just 1 second, or half the time it takes to make the round trip. The speed of sound waves through ocean water is 1437 m/s. Therefore, the distance from the ship to the submarine is: Q: Now assume that the sonar device on the ship sends an ultrasound wave to the bottom of the water. If the sound wave is reflected back to the device in 4 seconds, how deep is the water? A: The time it takes the wave to reach the bottom is 2 seconds. So the distance from the ship to the bottom of the water is: Distance = 1437 m/s  2 s = 2874 m ",text,
L_1056,ultrasound,T_4947,"Sonar uses ultrasound in a way that is similar to echolocation. Sonar stands for sound navigation and ranging. It is used to locate underwater objects such as submarines. Thats how the ship pictured in the Figure 1.2 is using it. A sonar device is both a sender and a receiver. It sends out ultrasound waves and detects the waves after they reflect from underwater objects. The distance to underwater objects can be calculated from the known speed of sound in water and the time it takes for the sound waves to travel to the object. The equation for distance traveled when speed and time are known is: Distance = Speed  Time Consider the ship and submarine pictured in the Figure 1.2. If an ultrasound wave travels from the ship to the submarine and back again in 2 seconds, what is the distance from the ship to the submarine? The sound wave travels from the ship to the submarine in just 1 second, or half the time it takes to make the round trip. The speed of sound waves through ocean water is 1437 m/s. Therefore, the distance from the ship to the submarine is: Q: Now assume that the sonar device on the ship sends an ultrasound wave to the bottom of the water. If the sound wave is reflected back to the device in 4 seconds, how deep is the water? A: The time it takes the wave to reach the bottom is 2 seconds. So the distance from the ship to the bottom of the water is: Distance = 1437 m/s  2 s = 2874 m ",text,
L_1056,ultrasound,T_4948,"Another use of ultrasound is to see inside the human body. This use of ultrasound is called ultrasonography. Harmless ultrasound waves are sent inside the body, and the reflected waves are used to create an image on a screen. This technology is used to examine internal organs and unborn babies without risk to the patient. You can see a doctor using ultrasound in the Figure 1.3. ",text,
L_1057,unsaturated hydrocarbons,T_4949,"Hydrocarbons are compounds that contain only carbon and hydrogen. The carbon atoms in hydrocarbons may share single, double, or triple covalent bonds. Unsaturated hydrocarbons contain at least one double or triple bond between carbon atoms. They are classified on the basis of their bonds as alkenes, aromatic hydrocarbons, or alkynes. Q: Why do you suppose hydrocarbons with double or triple bonds are called unsaturated? A: A carbon atom always forms four covalent bonds. Carbon atoms with double or triple bonds are unable to bond with as many hydrogen atoms as they could if they were joined only by single bonds. This makes them unsaturated with hydrogen atoms. ",text,
L_1057,unsaturated hydrocarbons,T_4950,"Unsaturated hydrocarbons that contain one or more double bonds are called alkenes. The name of a specific alkene always ends in -ene and has a prefix indicating the number of carbon atoms. The structural formula in the Figure Ethene is produced by most fruits and vegetables. It speeds up ripening. The Figure 1.1 show the effects of ethene on bananas. Alkenes can have different shapes. They can form straight chains, branched chains, or rings. Alkenes with the same atoms but different shapes are called isomers. Smaller alkenes have relatively high boiling and melting points, so they are gases at room temperature. Larger alkenes have lower boiling and melting points, so they are liquids or waxy solids at room temperature. The bananas on the left were stored in a special bag that absorbs ethene. The bananas on the right were stored without a bag. ",text,
L_1057,unsaturated hydrocarbons,T_4951,"Unsaturated hydrocarbons called aromatic hydrocarbons are cyclic hydrocarbons that have double bonds. These compounds have six carbon atoms in a ring with alternating single and double bonds. The smallest aromatic hydrocarbon is benzene, which has just one ring. Its structural formula is shown in the Figure 1.2. Larger aromatic hydrocarbons consist of two or more rings, which are joined together by bonds between their carbon atoms. The name of aromatic hydrocarbons comes from their strong aroma, or scent. Thats why they are used in air fresheners and mothballs. A: Each carbon atom forms four covalent bonds. Carbon atoms always form four covalent bonds, regardless of the atoms to which it bonds. ",text,
L_1057,unsaturated hydrocarbons,T_4952,"Unsaturated hydrocarbons that contain one or more triple bonds are called alkynes. The names of specific alkynes always end in -yne and have a prefix for the number of carbon atoms. The structural formula in the Figure 1.3 represents the smallest alkyne, named ethyne, which has two carbon atoms and two hydrogen atoms (C2 H2 ). Ethyne is also called acetylene. It is burned in acetylene torches, like the one pictured in the Figure 1.4. The flame of an acetylene torch is so hot that it can melt metal. Cutting metal with an acetylene (ethyne) torch. Alkynes may form straight or branched chains. They rarely occur in ring shapes. In fact, alkynes of all shapes are relatively rare in nature. ",text,
L_1057,unsaturated hydrocarbons,T_4952,"Unsaturated hydrocarbons that contain one or more triple bonds are called alkynes. The names of specific alkynes always end in -yne and have a prefix for the number of carbon atoms. The structural formula in the Figure 1.3 represents the smallest alkyne, named ethyne, which has two carbon atoms and two hydrogen atoms (C2 H2 ). Ethyne is also called acetylene. It is burned in acetylene torches, like the one pictured in the Figure 1.4. The flame of an acetylene torch is so hot that it can melt metal. Cutting metal with an acetylene (ethyne) torch. Alkynes may form straight or branched chains. They rarely occur in ring shapes. In fact, alkynes of all shapes are relatively rare in nature. ",text,
L_1058,using earths magnetic field,T_4953,"Like a bar magnet, planet Earth has north and south magnetic poles and a magnetic field over which it exerts magnetic force. Earths magnetic field is called the magnetosphere. You can see it in the Figure 1.1. ",text,
L_1058,using earths magnetic field,T_4954,"The sun gives off radiation in solar winds. You can see solar winds in the Figure 1.1. Notice what happens to solar winds when they reach the magnetosphere. They are deflected almost completely by Earths magnetic field. Radiation in solar wind would wash over Earth and kill most living things were it not for the magnetosphere. It protects Earths organisms from radiation like an umbrella protects you from rain. Q: Now can you explain the northern lights? A: Energetic particles in solar wind collide with atoms in the atmosphere over the poles, and energy is released in the form of light. The swirling patterns of light follow lines of magnetic force in the magnetosphere. ",text,
L_1058,using earths magnetic field,T_4955,"Another benefit of Earths magnetic field is its use for navigation. People use compasses to detect Earths magnetic north pole and tell direction. Many animals have natural compasses that work just as well. For example, the loggerhead turtle in the Figure 1.2 senses the direction and strength of Earths magnetic field and uses it to navigate along migration routes. Many migratory bird species can also sense the magnetic field and use it for navigation. Recent research suggests that they may have structures in their eyes that let them see Earths magnetic field as a visual pattern. ",text,
L_1059,valence electrons,T_4956,"Valence electrons are the electrons in the outer energy level of an atom that can participate in interactions with other atoms. Valence electrons are generally the electrons that are farthest from the nucleus. As a result, they may be attracted as much or more by the nucleus of another atom than they are by their own nucleus. ",text,
L_1059,valence electrons,T_4957,"Because valence electrons are so important, atoms are often represented by simple diagrams that show only their valence electrons. These are called electron dot diagrams, and three are shown below. In this type of diagram, an elements chemical symbol is surrounded by dots that represent the valence electrons. Typically, the dots are drawn as if there is a square surrounding the element symbol with up to two dots per side. An element never has more than eight valence electrons, so there cant be more than eight dots per atom. Q: Carbon (C) has four valence electrons. What does an electron dot diagram for this element look like? A: An electron dot diagram for carbon looks like this: ",text,
L_1059,valence electrons,T_4958,"The number of valence electrons in an atom is reflected by its position in the periodic table of the elements (see the periodic table in the Figure 1.1). Across each row, or period, of the periodic table, the number of valence electrons in groups 1-2 and 13-18 increases by one from one element to the next. Within each column, or group, of the table, all the elements have the same number of valence electrons. This explains why all the elements in the same group have very similar chemical properties. For elements in groups 1-2 and 13-18, the number of valence electrons is easy to tell directly from the periodic table. This is illustrated in the simplified periodic table in the Figure 1.2. It shows just the numbers of valence electrons in each of these groups. For elements in groups 3-12, determining the number of valence electrons is more complicated. Q: Based on both periodic tables above (Figures 1.1 and 1.2), what are examples of elements that have just one valence electron? What are examples of elements that have eight valence electrons? How many valence electrons does oxygen (O) have? A: Any element in group 1 has just one valence electron. Examples include hydrogen (H), lithium (Li), and sodium (Na). Any element in group 18 has eight valence electrons (except for helium, which has a total of just two electrons). Examples include neon (Ne), argon (Ar), and krypton (Kr). Oxygen, like all the other elements in group 16, has six valence electrons. ",text,
L_1059,valence electrons,T_4959,"The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature. Instead, they undergo chemical reactions with other elements and form compounds. Table salt is the compound named sodium chloride (NaCl). It forms when an atom of sodium (Na) gives up an electron and an atom of chlorine (Cl) accepts it. When this happens, sodium becomes a positively charged ion (Na+ ), and chlorine becomes a negatively charged ion (Cl ). The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions, forming a crystal of salt. Q: Why does sodium give up an electron? A: An atom of a group 1 element such as sodium has just one valence electron. It is eager to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure 1.4. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason. Q: Why does chlorine accept the electron from sodium? A: An atom of a group 17 element such as chlorine has seven valence electrons. It is eager to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18 elements have eight valence electrons (or two in the case of helium). These elements already have a full outer energy level, so they are very stable. As a result, they rarely if ever react with other elements. Elements in other groups vary in their reactivity but are generally less reactive than elements in groups 1, 2, 16, or 17. Q: Find calcium (Ca) in the periodic table (see Figure 1.1). Based on its position in the table, how reactive do you think calcium is? Name another element with which calcium might react. A: Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in chemical reactions. It is likely to react with an element with six valence electrons that wants to gain two electrons. This would be an element in group 6, such as oxygen. Table salt (sodium chloride). ",text,
L_1059,valence electrons,T_4959,"The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature. Instead, they undergo chemical reactions with other elements and form compounds. Table salt is the compound named sodium chloride (NaCl). It forms when an atom of sodium (Na) gives up an electron and an atom of chlorine (Cl) accepts it. When this happens, sodium becomes a positively charged ion (Na+ ), and chlorine becomes a negatively charged ion (Cl ). The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions, forming a crystal of salt. Q: Why does sodium give up an electron? A: An atom of a group 1 element such as sodium has just one valence electron. It is eager to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure 1.4. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason. Q: Why does chlorine accept the electron from sodium? A: An atom of a group 17 element such as chlorine has seven valence electrons. It is eager to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18 elements have eight valence electrons (or two in the case of helium). These elements already have a full outer energy level, so they are very stable. As a result, they rarely if ever react with other elements. Elements in other groups vary in their reactivity but are generally less reactive than elements in groups 1, 2, 16, or 17. Q: Find calcium (Ca) in the periodic table (see Figure 1.1). Based on its position in the table, how reactive do you think calcium is? Name another element with which calcium might react. A: Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in chemical reactions. It is likely to react with an element with six valence electrons that wants to gain two electrons. This would be an element in group 6, such as oxygen. Table salt (sodium chloride). ",text,
L_1059,valence electrons,T_4959,"The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature. Instead, they undergo chemical reactions with other elements and form compounds. Table salt is the compound named sodium chloride (NaCl). It forms when an atom of sodium (Na) gives up an electron and an atom of chlorine (Cl) accepts it. When this happens, sodium becomes a positively charged ion (Na+ ), and chlorine becomes a negatively charged ion (Cl ). The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions, forming a crystal of salt. Q: Why does sodium give up an electron? A: An atom of a group 1 element such as sodium has just one valence electron. It is eager to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure 1.4. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason. Q: Why does chlorine accept the electron from sodium? A: An atom of a group 17 element such as chlorine has seven valence electrons. It is eager to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18 elements have eight valence electrons (or two in the case of helium). These elements already have a full outer energy level, so they are very stable. As a result, they rarely if ever react with other elements. Elements in other groups vary in their reactivity but are generally less reactive than elements in groups 1, 2, 16, or 17. Q: Find calcium (Ca) in the periodic table (see Figure 1.1). Based on its position in the table, how reactive do you think calcium is? Name another element with which calcium might react. A: Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in chemical reactions. It is likely to react with an element with six valence electrons that wants to gain two electrons. This would be an element in group 6, such as oxygen. Table salt (sodium chloride). ",text,
L_1059,valence electrons,T_4959,"The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature. Instead, they undergo chemical reactions with other elements and form compounds. Table salt is the compound named sodium chloride (NaCl). It forms when an atom of sodium (Na) gives up an electron and an atom of chlorine (Cl) accepts it. When this happens, sodium becomes a positively charged ion (Na+ ), and chlorine becomes a negatively charged ion (Cl ). The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions, forming a crystal of salt. Q: Why does sodium give up an electron? A: An atom of a group 1 element such as sodium has just one valence electron. It is eager to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure 1.4. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason. Q: Why does chlorine accept the electron from sodium? A: An atom of a group 17 element such as chlorine has seven valence electrons. It is eager to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18 elements have eight valence electrons (or two in the case of helium). These elements already have a full outer energy level, so they are very stable. As a result, they rarely if ever react with other elements. Elements in other groups vary in their reactivity but are generally less reactive than elements in groups 1, 2, 16, or 17. Q: Find calcium (Ca) in the periodic table (see Figure 1.1). Based on its position in the table, how reactive do you think calcium is? Name another element with which calcium might react. A: Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in chemical reactions. It is likely to react with an element with six valence electrons that wants to gain two electrons. This would be an element in group 6, such as oxygen. Table salt (sodium chloride). ",text,
L_1059,valence electrons,T_4960,"Valence electrons also determine how wellif at allthe atoms of an element conduct electricity. The copper wires in the cable in the Figure 1.5 are coated with plastic. Copper is an excellent conductor of electricity, so it is used for wires that carry electric current. Plastic contains mainly carbon, which cannot conduct electricity, so it is used as insulation on the wires. Q: Why do copper and carbon differ in their ability to conduct electricity? A: Atoms of metals such as copper easily give up valence electrons. Their electrons can move freely and carry electric current. Atoms of nonmetals such as the carbon, on the other hand, hold onto their electrons. Their electrons cant move freely and carry current. A few elements, called metalloids, can conduct electricity, but not as well as metals. Examples include silicon and germanium in group 14. Both become better conductors at higher temperatures. These elements are called semiconductors. Q: How many valence electrons do atoms of silicon and germanium have? What happens to their valence electrons when the atoms are exposed to an electric field? A: Atoms of these two elements have four valence electrons. When the atoms are exposed to an electric field, the valence electrons move away from the atoms and allow current to flow. ",text,
L_1060,velocity,T_4961,"Speed tells you only how fast or slow an object is moving. It doesnt tell you the direction the object is moving. The measure of both speed and direction is called velocity. Velocity is a vector. A vector is measurement that includes both size and direction. Vectors are often represented by arrows. When using an arrow to represent velocity, the length of the arrow stands for speed, and the way the arrow points indicates the direction. Click image to the left or use the URL below. URL: ",text,
L_1060,velocity,T_4962,The arrows in the Figure 1.1 represent the velocity of three different objects. Arrows A and B are the same length but point in different directions. They represent objects moving at the same speed but in different directions. Arrow C is shorter than arrow A or B but points in the same direction as arrow A. It represents an object moving at a slower speed than A or B but in the same direction as A. ,text,
L_1060,velocity,T_4963,"Objects have the same velocity only if they are moving at the same speed and in the same direction. Objects moving at different speeds, in different directions, or both have different velocities. Look again at arrows A and B from the Figure 1.1. They represent objects that have different velocities only because they are moving in different directions. A and C represent objects that have different velocities only because they are moving at different speeds. Objects represented by B and C have different velocities because they are moving in different directions and at different speeds. Q: Jerod is riding his bike at a constant speed. As he rides down his street he is moving from east to west. At the end of the block, he turns right and starts moving from south to north, but hes still traveling at the same speed. Has his velocity changed? A: Although Jerods speed hasnt changed, his velocity has changed because he is moving in a different direction. Q: How could you use vector arrows to represent Jerods velocity and how it changes? A: The arrows might look like this: ",text,
L_1060,velocity,T_4964,"You can calculate the average velocity of a moving object that is not changing direction by dividing the distance the object travels by the time it takes to travel that distance. You would use this formula: velocity = distance time This is the same formula that is used for calculating average speed. It represents velocity only if the answer also includes the direction that the object is traveling. Lets work through a sample problem. Tonis dog is racing down the sidewalk toward the east. The dog travels 36 meters in 18 seconds before it stops running. The velocity of the dog is: distance time 36 m = 18 s = 2 m/s east velocity = Note that the answer is given in the SI unit for velocity, which is m/s, and it includes the direction that the dog is traveling. Q: What would the dogs velocity be if it ran the same distance in the opposite direction but covered the distance in 24 seconds? A: In this case, the velocity would be: distance time 36 m = 24 s = 1.5 m/s west velocity = ",text,
L_1061,velocity time graphs,T_4965,"The changing velocity of the sprinteror of any other moving person or objectcan be represented by a velocity- time graph like the one in the Figure 1.1 for the sprinter. A velocity-time graph shows how velocity changes over time. The sprinters velocity increases for the first 4 seconds of the race, it remains constant for the next 3 seconds, and it decreases during the last 3 seconds after she crosses the finish line. ",text,
L_1061,velocity time graphs,T_4966,"In a velocity-time graph, acceleration is represented by the slope, or steepness, of the graph line. If the line slopes upward, like the line between 0 and 4 seconds in the Figure 1.1, velocity is increasing, so acceleration is positive. If the line is horizontal, as it is between 4 and 7 seconds, velocity is constant and acceleration is zero. If the line slopes downward, like the line between 7 and 10 seconds, velocity is decreasing and acceleration is negative. Negative acceleration is called deceleration. Q: Assume that another sprinter is running the same race. The other runner reaches a top velocity of 9 m/s by 4 seconds after the start of the race. How would the first 4 seconds of the velocity-time graph for this runner be different from the Figure 1.1? A: The graph line for this runner during seconds 0-4 would be steeper (have a greater slope). This would show that acceleration is greater during this time period for the other sprinter. ",text,
L_1062,visible light and matter,T_4967,"Reflection of light occurs when light bounces back from a surface that it cannot pass through. Reflection may be regular or diffuse. If the surface is very smooth, like a mirror, the reflected light forms a very clear image. This is called regular, or specular, reflection. In the Figure 1.1, the smooth surface of the still water in the pond on the left reflects light in this way. When light is reflected from a rough surface, the waves of light are reflected in many different directions, so a clear image does not form. This is called diffuse reflection. In the Figure 1.1, the ripples in the water in the picture on the right cause diffuse reflection of the blooming trees. ",text,
L_1062,visible light and matter,T_4968,"Transmission of light occurs when light passes through matter. As light is transmitted, it may pass straight through matter or it may be refracted or scattered as it passes through. When light is refracted, it changes direction as it passes into a new medium and changes speed. The straw in the Figure 1.2 looks bent where light travels from water to air. Light travels more quickly in air than in water and changes direction. Scattering occurs when light bumps into tiny particles of matter and spreads out in all directions. In the Figure air, giving the headlights a halo appearance. Q: What might be another example of light scattering? A: When light passes through smoky air, it is scattered by tiny particles of soot. ",text,
L_1062,visible light and matter,T_4968,"Transmission of light occurs when light passes through matter. As light is transmitted, it may pass straight through matter or it may be refracted or scattered as it passes through. When light is refracted, it changes direction as it passes into a new medium and changes speed. The straw in the Figure 1.2 looks bent where light travels from water to air. Light travels more quickly in air than in water and changes direction. Scattering occurs when light bumps into tiny particles of matter and spreads out in all directions. In the Figure air, giving the headlights a halo appearance. Q: What might be another example of light scattering? A: When light passes through smoky air, it is scattered by tiny particles of soot. ",text,
L_1062,visible light and matter,T_4969,"Light may transfer its energy to matter rather than being reflected or transmitted by matter. This is called absorption. When light is absorbed, the added energy increases the temperature of matter. If you get into a car that has been sitting in the sun all day, the seats and other parts of the cars interior may be almost too hot to touch, especially if they are black or very dark in color. Thats because dark colors absorb most of the sunlight that strikes them. Q: In hot sunny climates, people often dress in light-colored clothes. Why is this a good idea? A: Light-colored clothes absorb less light and reflect more light than dark-colored clothes, so they keep people cooler. ",text,
L_1062,visible light and matter,T_4970,"Matter can be classified on the basis of its interactions with light. Matter may be transparent, translucent, or opaque. An example of each type of matter is pictured in the Figure 1.4. Transparent matter is matter that transmits light without scattering it. Examples of transparent matter include air, pure water, and clear glass. You can see clearly through transparent objects, such as the top panes of the window 1.4, because just about all of the light that strikes them passes through to the other side. Translucent matter is matter that transmits light but scatters the light as it passes through. Light passes through translucent objects but you cannot see clearly through them because the light is scattered in all directions. The frosted glass panes at the bottom of the window 1.4 are translucent. Opaque matter is matter that does not let any light pass through it. Matter may be opaque because it absorbs light, reflects light, or does some combination of both. Examples of opaque objects are objects made of wood, like the shutters in the Figure 1.5. The shutters absorb most of the light that strikes them and reflect just a few wavelengths of visible light. The glass mirror 1.5 is also opaque. Thats because it reflects all of the light that strikes it. ",text,
L_1062,visible light and matter,T_4970,"Matter can be classified on the basis of its interactions with light. Matter may be transparent, translucent, or opaque. An example of each type of matter is pictured in the Figure 1.4. Transparent matter is matter that transmits light without scattering it. Examples of transparent matter include air, pure water, and clear glass. You can see clearly through transparent objects, such as the top panes of the window 1.4, because just about all of the light that strikes them passes through to the other side. Translucent matter is matter that transmits light but scatters the light as it passes through. Light passes through translucent objects but you cannot see clearly through them because the light is scattered in all directions. The frosted glass panes at the bottom of the window 1.4 are translucent. Opaque matter is matter that does not let any light pass through it. Matter may be opaque because it absorbs light, reflects light, or does some combination of both. Examples of opaque objects are objects made of wood, like the shutters in the Figure 1.5. The shutters absorb most of the light that strikes them and reflect just a few wavelengths of visible light. The glass mirror 1.5 is also opaque. Thats because it reflects all of the light that strikes it. ",text,
L_1063,vision and the eye,T_4971,"The human eye is an organ that is specialized to collect light and focus images. The structures of the human eye are shown in the Figure 1.1. Examine each structure in the diagram as you read about it below. The sclera, also known as the white of the eye, is an opaque outer covering that protects the eye. It keeps light out of the eye except at the center front of the eye. The cornea is a transparent outer covering of the front of the eye. It protects the eye and also acts as a convex lens. A convex lens is thicker in the middle than at the edges and makes rays of light converge, or meet at a point. The shape of the cornea helps focus light that enters the eye. The pupil is an opening in the front of the eye. It looks black because it doesnt reflect any light. All the light passes through it instead. The pupil controls the amount of light that enters the eye. It automatically gets bigger or smaller to let more or less light in as needed. The iris is the colored part of the eye. It controls the size of the pupil. The lens of the eye is a convex lens. It fine-tunes the focus so an image forms on the retina at the back of the eye. Tiny muscles control the shape of the lens to focus images of close or distant objects. The retina is a membrane lining the back of the eye. The retina has nerve cells called rods and cones that change images to electrical signals. Rods are good at sensing dim light but cant distinguish different colors of light. Cones can sense colors but not dim light. There are three different types of cones. Each type senses one of the three primary colors of light (red, green, or blue). The optic nerve carries electrical signals from the rods and cones to the brain. Q: The lens of the eye is a convex lens. How would vision be affected if the lens of the eye was concave instead of convex? A: A concave lens causes rays of light to diverge, or spread apart. It forms a virtual image on the same side of the lens at the object being viewed. Therefore, a concave lens would focus the image in front of the eye, not on the retina inside the eye. No signals would be sent to the brain so vision would not be possible. ",text,
L_1063,vision and the eye,T_4972,"The ability to see is called vision. This ability depends on more than healthy eyes. It also depends on certain parts of the brain, because the brain and eyes work together to allow us to see. The eyes collect and focus visible light. The lens and other structures of the eye work together to focus an image on the retina. The image is upside-down and reduced in size, as you can see in the Figure 1.2. Cells in the retina change the image to electrical signals that travel to the brain through the optic nerve. The brain interprets the electrical signals as shape, color, and brightness. It also interprets the image as though it were right-side up. The brain does this automatically, so what we see always appears right-side up. The brain also interprets what we are seeing. Q: The part of the brain that processes information from the eyes is the visual cortex. It is located at the back of the brain. How might an injury to the visual cortex affect vision? A: An injury to the visual cortex might cause abnormal vision or even blindness regardless of how well the eyes can gather and focus light. ",text,
L_1064,vision problems and corrective lenses,T_4973,"Many people have problems with their vision, or ability to see. Often, the problem is due to the shape of the eyes and how they focus light. Two of the most common vision problems are nearsightedness and farsightedness, which you can read about below. You may even have one of these vision problems yourself. Usually, the problems can be corrected with contact lenses or lenses in eyeglasses. In many people, they can also be corrected with laser surgery, which reshapes the outer layer of the eye. Click image to the left or use the URL below. URL: ",text,
L_1064,vision problems and corrective lenses,T_4974,"Nearsightedness, or myopia, is the condition in which nearby objects are seen clearly, but distant objects appear blurry. The Figure 1.1 shows how it occurs. The eyeball is longer (from front to back) than normal. This causes images to be focused in front of the retina instead of on the retina. Myopia can be corrected with concave lenses. The lenses focus images farther back in the eye, so they fall on the retina instead of in front of it. Q: Sometimes squinting the eyes can help someone see more clearly. Why do you think this works? A: Squinting may improve focus by slightly changing the shape of the eyes. When you squint, you tighten muscles around the eyes, putting pressure on the eyeballs. ",text,
L_1064,vision problems and corrective lenses,T_4975,"Farsightedness, or hyperopia, is the condition in which distant objects are seen clearly, but nearby objects appear blurry. It occurs when the eyeball is shorter than normal (see Figure 1.2). This causes images to be focused in a spot that would fall behind the retina (if light could pass through the retina). Hyperopia can be corrected with convex lenses. The lenses focus images farther forward in the eye, so they fall on the retina instead of behind it. Q: Joey has hyperopia. When is he more likely to need his glasses: when he reads a book or when he watches TV? A: With hyperopia, Joey is farsighted. He can probably see the TV more clearly than the words in a book because the TV is farther away. Therefore, he is more likely to need his glasses when he reads than when he watches TV. ",text,
L_1065,wave amplitude,T_4976,"Waves that travel through mattersuch as the fabric of a flagare called mechanical waves. The matter they travel through is called the medium. When the energy of a wave passes through the medium, particles of the medium move. The more energy the wave has, the farther the particles of the medium move. The distance the particles move is measured by the waves amplitude. ",text,
L_1065,wave amplitude,T_4977,"Wave amplitude is the maximum distance the particles of the medium move from their resting positions when a wave passes through. The resting position of a particle of the medium is where the particle would be in the absence of a wave. The Figure 1.1 show the amplitudes of two different types of waves: transverse and longitudinal waves. In a transverse wave, particles of the medium move up and down at right angles to the direction of the wave. Wave amplitude of a transverse wave is the difference in height between the crest and the resting position. The crest is the highest point particles of the medium reach. The higher the crests are, the greater the amplitude of the wave. In a longitudinal wave, particles of the medium move back and forth in the same direction as the wave. Wave amplitude of a longitudinal wave is the distance between particles of the medium where it is compressed by the wave. The closer together the particles are, the greater the amplitude of the wave. Q: What do you think determines a waves amplitude? A: Wave amplitude is determined by the energy of the disturbance that causes the wave. ",text,
L_1065,wave amplitude,T_4978,A wave caused by a disturbance with more energy has greater amplitude. Imagine dropping a small pebble into a pond of still water. Tiny ripples will move out from the disturbance in concentric circles. The ripples are low- amplitude waves with very little energy. Now imagine throwing a big boulder into the pond. Very large waves will be generated by the disturbance. These waves are high-amplitude waves and have a great deal of energy. ,text,
L_1066,wave frequency,T_4979,"The number of waves that pass a fixed point in a given amount of time is wave frequency. Wave frequency can be measured by counting the number of crests (high points) of waves that pass the fixed point in 1 second or some other time period. The higher the number is, the greater the frequency of the waves. The SI unit for wave frequency is the hertz (Hz), where 1 hertz equals 1 wave passing a fixed point in 1 second. The Figure 1.1 shows high-frequency and low-frequency transverse waves. Q: The wavelength of a wave is the distance between corresponding points on adjacent waves. For example, it is the distance between two adjacent crests in the transverse waves in the diagram. Infer how wave frequency is related to wavelength. ",text,
L_1066,wave frequency,T_4980,"The frequency of a wave is the same as the frequency of the vibrations that caused the wave. For example, to generate a higher-frequency wave in a rope, you must move the rope up and down more quickly. This takes more energy, so a higher-frequency wave has more energy than a lower-frequency wave with the same amplitude. You can see examples of different frequencies in the Figure 1.2 (Amplitude is the distance that particles of the medium move when the energy of a wave passes through them.) ",text,
L_1067,wave interactions,T_4981,"Atoms are the building blocks of matter. Unlike blocks that we know, these building blocks are incredibly small. In fact, they are the smallest particles of an element. Atoms still have the same properties as the elements they make up. For example, an atom of gold has the same melting point as a gold coin. If we could see it, it would have the same color. Elements are also pure substances. This means they are not mixed with anything else. Pure substances such as nickel, hydrogen, and helium make up all kinds of matter. All the atoms of a given element are identical. Atoms of different elements are not physically the same. Think of something you might have made from LEGOs. You built some shape using the many different sized and shaped blocks. This is much like how atoms combine to become everything we know. If we took only one size and shape of block and put them together, we would make a pure substance. It would be an element. If you take apart anything that you have built, those individual parts are like the atoms. With those small parts, you build bigger things. Sometimes they are all the same type of block. Other times, they may be different kinds of blocks. We use these combinations of different blocks to make more complicated things. ",text,
L_1067,wave interactions,T_4982,"Unlike LEGO bricks, atoms are extremely small. The radius of an atom is well under 1 nanometer. Thats one- billionth of a meter. Such a number is hard to imagine. Consider this: trillions of atoms would fit inside the period at the end of this sentence. In other words, atoms are way too small to be seen with the naked eye. ",text,
L_1067,wave interactions,T_4983,"Although atoms are very tiny, they consist of even smaller particles. Atoms are made of protons, neutrons, and electrons: Protons have a positive charge. Electrons have a negative charge. Neutrons are neutral in charge. ",text,
L_1067,wave interactions,T_4984,"Figure below represents a simple model of an atom. Models help scientists make sense of things. Perhaps they are either too big or too small. Maybe they are just too complicated to make sense of. This simple model helps scientists think about the atom. Is this how the atom really looks? Not exactly! Remember, a model helps us make sense of things. They may not be an exact copy of the object. You will learn about more complex models of atoms in the coming years, but this model is a good place to start. ",text,
L_1067,wave interactions,T_4985,"At the center of an atom is the nucleus (plural, nuclei). The nucleus contains most of the atoms mass. However, in size, its just a tiny part of the atom. The model in Figure above is not to scale. If an atom were the size of a football stadium, the nucleus would be only about the size of a pea. The nucleus, in turn, consists of two types of particles, called protons and neutrons. These particles are tightly packed inside the nucleus. Constantly moving about the nucleus are other particles called electrons. ",text,
L_1067,wave interactions,T_4986,"A proton is a particle inside the nucleus of an atom. It has a positive electric charge. All protons are identical. It is all about the number of protons in the atoms. The number of protons is what gives the atoms of different elements their unique properties. Atoms of each type of element have a characteristic number of protons. For example, each atom of carbon has six protons (see Figure below ). No two elements have atoms with the same number of protons. ",text,
L_1067,wave interactions,T_4987,"A neutron is a particle inside the nucleus of an atom. It has no electric charge. Atoms of an element often have the same number of neutrons as protons. For example, most carbon atoms have six neutrons as well as six protons. This is also shown in Figure below . ",text,
L_1067,wave interactions,T_4988,"An electron is a particle outside the nucleus of an atom. It has a negative electric charge. The charge of an electron is opposite but equal to the charge of a proton. Atoms have the same number of electrons as protons. As a result, the negative and positive charges ""cancel out."" This makes atoms electrically neutral. For example, a carbon atom has six electrons that ""cancel out"" its six protons. ",text,
L_1067,wave interactions,T_4989,"By clicking a link below, you will leave the CK-12 site and open an external site in a new tab. This page will remain open in the original tab. ",text,
L_1068,wave interference,T_4990,"When two or more waves meet, they interact with each other. The interaction of waves with other waves is called wave interference. Wave interference may occur when two waves that are traveling in opposite directions meet. The two waves pass through each other, and this affects their amplitude. Amplitude is the maximum distance the particles of the medium move from their resting positions when a wave passes through. How amplitude is affected by wave interference depends on the type of interference. Interference can be constructive or destructive. ",text,
L_1068,wave interference,T_4991,"Constructive interference occurs when the crests, or highest points, of one wave overlap the crests of the other wave. You can see this in the Figure 1.1. As the waves pass through each other, the crests combine to produce a wave with greater amplitude. ",text,
L_1068,wave interference,T_4992,"Destructive interference occurs when the crests of one wave overlap the troughs, or lowest points, of another wave. The Figure 1.2 shows what happens. As the waves pass through each other, the crests and troughs cancel each other out to produce a wave with zero amplitude. ",text,
L_1068,wave interference,T_4993,"Waves may reflect off an obstacle that they are unable to pass through. When waves are reflected straight back from an obstacle, the reflected waves interfere with the original waves and create standing waves. These are waves that appear to be standing still. Standing waves occur because of a combination of constructive and destructive interference. Q: How could you use a rope to produce standing waves? A: You could tie one end of the rope to a fixed object, such as doorknob, and move the other end up and down to generate waves in the rope. When the waves reach the fixed object, they are reflected back. The original waves and the reflected waves interfere to produce a standing wave. Try it yourself and see if the waves appear to stand still. ",text,
L_1069,wave particle theory,T_4994,"Electromagnetic radiation, commonly called light, is the transfer of energy by waves called electromagnetic waves. These waves consist of vibrating electric and magnetic fields. Where does electromagnetic energy come from? It is released when electrons return to lower energy levels in atoms. Electromagnetic radiation behaves like continuous waves of energy most of the time. Sometimes, however, electromagnetic radiation seems to behave like discrete, or separate, particles rather than waves. So does electromagnetic radiation consist of waves or particles? ",text,
L_1069,wave particle theory,T_4995,"This question about the nature of electromagnetic radiation was debated by scientists for more than two centuries, starting in the 1600s. Some scientists argued that electromagnetic radiation consists of particles that shoot around like tiny bullets. Other scientists argued that electromagnetic radiation consists of waves, like sound waves or water waves. Until the early 1900s, most scientists thought that electromagnetic radiation is either one or the other and that scientists on the other side of the argument were simply wrong. Q: Do you think electromagnetic radiation is a wave or a particle? A: Heres a hint: it may not be a question of either-or. Keep reading to learn more. ",text,
L_1069,wave particle theory,T_4996,"In 1905, the physicist Albert Einstein developed a new theory about electromagnetic radiation. The theory is often called the wave-particle theory. It explains how electromagnetic radiation can behave as both a wave and a particle. Einstein argued that when an electron returns to a lower energy level and gives off electromagnetic energy, the energy is released as a discrete packet of energy. We now call such a packet of energy a photon. According to Einstein, a photon resembles a particle but moves like a wave. You can see this in the Figure 1.1. The theory posits that waves of photons traveling through space or matter make up electromagnetic radiation. ",text,
L_1069,wave particle theory,T_4997,"A photon isnt a fixed amount of energy. Instead, the amount of energy in a photon depends on the frequency of the electromagnetic wave. The frequency of a wave is the number of waves that pass a fixed point in a given amount of time, such as the number of waves per second. In waves with higher frequencies, photons have more energy. ",text,
L_1069,wave particle theory,T_4998,"After Einstein proposed his theory, evidence was discovered to support it. For example, scientists shone laser light through two slits in a barrier made of a material that blocked light. You can see the setup of this type of experiment in the Figure 1.2. Using a special camera that was very sensitive to light, they took photos of the light that passed through the slits. The photos revealed tiny pinpoints of light passing through the double slits. This seemed to show that light consists of particles. However, if the camera was exposed to the light for a long time, the pinpoints accumulated in bands that resembled interfering waves. Therefore, the experiment showed that light seems to consist of particles that act like waves. ",text,
L_1070,wave speed,T_4999,"Wave speed is the distance a wave travels in a given amount of time, such as the number of meters it travels per second. Wave speed (and speed in general) can be represented by the equation: Speed = Distance Time ",text,
L_1070,wave speed,T_5000,"Wave speed is related to both wavelength and wave frequency. Wavelength is the distance between two correspond- ing points on adjacent waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. This equation shows how the three factors are related: Speed = Wavelength x Wave Frequency In this equation, wavelength is measured in meters and frequency is measured in hertz (Hz), or number of waves per second. Therefore, wave speed is given in meters per second, which is the SI unit for speed. Q: If you increase the wavelength of a wave, does the speed of the wave increase as well? A: Increasing the wavelength of a wave doesnt change its speed. Thats because when wavelength increases, wave frequency decreases. As a result, the product of wavelength and wave frequency is still the same speed. Click image to the left or use the URL below. URL: ",text,
L_1070,wave speed,T_5001,"The equation for wave speed can be used to calculate the speed of a wave when both wavelength and wave frequency are known. Consider an ocean wave with a wavelength of 3 meters and a frequency of 1 hertz. The speed of the wave is: Speed = 3 m x 1 wave/s = 3 m/s Q: Kim made a wave in a spring by pushing and pulling on one end. The wavelength is 0.1 m, and the wave frequency is 2 hertz. What is the speed of the wave? A: Substitute these values into the equation for speed: Speed = 0.1 m x 2 waves/s = 0.2 m/s ",text,
L_1070,wave speed,T_5002,"The equation for wave speed (above) can be rewritten as: Frequency = Speed Wavelength or Wavelength = Speed Frequency Therefore, if you know the speed of a wave and either the wavelength or wave frequency, you can calculate the missing value. For example, suppose that a wave is traveling at a speed of 2 meters per second and has a wavelength of 1 meter. Then the frequency of the wave is: Frequency = 2m/s 1m = 2 waves/s, or 2 Hz Q: A wave is traveling at a speed of 2 m/s and has a frequency of 2 Hz. What is its wavelength? A: Substitute these values into the equation for wavelength: Wavelength = 2m/s 2waves/s =1m ",text,
L_1070,wave speed,T_5003,"The speed of most waves depends on the medium, or the matter through which the waves are traveling. Generally, waves travel fastest through solids and slowest through gases. Thats because particles are closest together in solids and farthest apart in gases. When particles are farther apart, it takes longer for the energy of the disturbance to pass from particle to particle through the medium. Click image to the left or use the URL below. URL: ",text,
L_1071,wavelength,T_5004,"Wavelength is one way of measuring the size of waves. It is the distance between two corresponding points on adjacent waves, and it is usually measured in meters. How it is measured is a little different for transverse and longitudinal waves. In a transverse wave, particles of the medium vibrate up and down at right angles to the direction that the wave travels. The wavelength of a transverse wave can be measured as the distance between two adjacent crests, or high points, as shown in the Figure 1.1. In a longitudinal wave, particles of matter vibrate back and forth in the same direction that the wave travels. The wavelength of a longitudinal wave can be measured as the distance between two adjacent compressions, as shown in the Figure 1.2. Compressions are the places where particles of the medium crowd close together as the energy of the wave passes through. ",text,
L_1071,wavelength,T_5005,The wavelength of a wave is related to the waves energy. Short-wavelength waves have more energy than long- wavelength waves of the same amplitude. (Amplitude is a measure of how far particles of the medium move up and down or back and forth when a wave passes through them.) You can see examples of transverse waves with shorter and longer wavelengths in the Figure 1.3. A: Violet light has the greatest energy because it has the shortest wavelength. ,text,
L_1071,wavelength,T_5005,The wavelength of a wave is related to the waves energy. Short-wavelength waves have more energy than long- wavelength waves of the same amplitude. (Amplitude is a measure of how far particles of the medium move up and down or back and forth when a wave passes through them.) You can see examples of transverse waves with shorter and longer wavelengths in the Figure 1.3. A: Violet light has the greatest energy because it has the shortest wavelength. ,text,
L_1071,wavelength,T_5005,The wavelength of a wave is related to the waves energy. Short-wavelength waves have more energy than long- wavelength waves of the same amplitude. (Amplitude is a measure of how far particles of the medium move up and down or back and forth when a wave passes through them.) You can see examples of transverse waves with shorter and longer wavelengths in the Figure 1.3. A: Violet light has the greatest energy because it has the shortest wavelength. ,text,
L_1072,wedge,T_5006,"A wedge is simple machine that consists of two inclined planes, giving it a thin end and thick end, as you can see in the Figure 1.1. A wedge is used to cut or split apart objects. Force is applied to the thick end of the wedge, and the wedge, in turn, applies force to the object along both of its sloping sides. This force causes the object to split apart. A knife is another example of a wedge. In the Figure 1.2, a knife is being used to chop tough pecans. The job is easy to do with the knife because of the wedge shape of the blade. The very thin edge of the blade easily enters and cuts through the pecans. ",text,
L_1072,wedge,T_5007,"The mechanical advantage of a simple machine is the factor by which it multiplies the force applied to the machine. It is the ratio of the output force to the input force. A wedge applies more force to the object (output force) than the user applies to the wedge (input force), so the mechanical advantage of a wedge is greater than 1. A longer, thinner wedge has a greater mechanical advantage than a shorter, wider wedge. With all wedges, the trade-off is that the output force is applied over a shorter distance, so force may need to be applied to the wedge repeatedly to push it through the object. Q: Which wedge in the Figure 1.3 do you think would do the same amount of work with less input force? A: The wedge on the left has a greater mechanical advantage, so it would do the same amount of work with less input force. ",text,
L_1072,wedge,T_5007,"The mechanical advantage of a simple machine is the factor by which it multiplies the force applied to the machine. It is the ratio of the output force to the input force. A wedge applies more force to the object (output force) than the user applies to the wedge (input force), so the mechanical advantage of a wedge is greater than 1. A longer, thinner wedge has a greater mechanical advantage than a shorter, wider wedge. With all wedges, the trade-off is that the output force is applied over a shorter distance, so force may need to be applied to the wedge repeatedly to push it through the object. Q: Which wedge in the Figure 1.3 do you think would do the same amount of work with less input force? A: The wedge on the left has a greater mechanical advantage, so it would do the same amount of work with less input force. ",text,
L_1073,wheel and axle,T_5008,"A wheel and axle is a simple machine that consists of two connected rings or cylinders, one inside the other. Both rings or cylinders turn in the same direction around a single center point. The inner ring or cylinder is called the axle, and the outer one is called the wheel. Besides the Ferris wheel, the doorknob in the Figure 1.1 is another example of a wheel and axle. In a wheel and axle, force may be applied either to the wheel or to the axle. This force is called the input force. A wheel and axle does not change the direction of the input force. However, the force put out by the machine, called the output force, is either greater than the input force or else applied over a greater distance. A: In a Ferris wheel, the force is applied to the axle by the Ferris wheels motor. In a doorknob, the force is applied to the wheel by a persons hand. ",text,
L_1073,wheel and axle,T_5009,"The mechanical advantage of a machine is the factor by which the machine changes the input force. It equals the ratio of the output force to the input force. A wheel and axle may either increase or decrease the input force, depending on whether the input force is applied to the axle or the wheel. When the input force is applied to the axle, as it is with a Ferris wheel, the wheel turns with less force. Because the output force is less than the input force, the mechanical advantage is less than 1. However, the wheel turns over a greater distance, so it turns faster than the axle. The speed of the wheel is one reason that the Ferris wheel ride is so exciting. When the input force is applied to the wheel, as it is with a doorknob, the axle turns over a shorter distance but with greater force, so the mechanical advantage is greater than 1. This allows you to turn the doorknob with relatively little effort, while the axle of the doorknob applies enough force to slide the bar into or out of the doorframe. ",text,
L_1074,why earth is a magnet,T_5010,"Like the real Earth, the globe pictured above is a magnet. A magnet is an object that has north and south magnetic poles and a magnetic field. The magnetic globe is a modern device, but the idea that Earth is a magnet is far from new. It was first proposed in 1600 by a British physician named William Gilbert. He used a spherical magnet to represent Earth. With a compass, he demonstrated that it the spherical magnet causes a compass needle to behave the same way that Earth causes a compass needle to behave. This showed that a spherical magnet is a good model for Earth and therefore that Earth is a magnet. Q: Can you describe Earths magnetic poles and magnetic field? A: Earth has north and south magnetic poles. The North Pole is located at about 80 degrees north latitude. The magnetic field is an area around Earth that is affected by its magnetic field. The field is strongest at the poles, and lines of magnetic force move from the north to the south magnetic pole. ",text,
L_1074,why earth is a magnet,T_5011,"Although the idea that Earth is a magnet is centuries old, the discovery of why Earth is a magnet is a relatively new. In the early 1900s, scientists started using seismographic data to learn about Earths inner structure. A seismograph detects and measure earthquake waves. Evidence from earthquakes showed that Earth has a solid inner core and a liquid outer core (see the Figure 1.1). The outer core consists of molten metals, mainly iron and nickel. Scientists think that Earths magnetic field is generated by the movement of charged particles through these molten metals in the outer core. The particles move as Earth spins on its axis. ",text,
L_1076,work,T_5014,"Work is defined differently in physics than in everyday language. In physics, work means the use of force to move an object. The teens who are playing basketball in the picture above are using force to move their bodies and the basketball, so they are doing work. The teen who is studying isnt moving anything, so she isnt doing work. Not all force that is used to move an object does work. For work to be done, the force must be applied in the same direction that the object moves. If a force is applied in a different direction than the object moves, no work is done. The Figure 1.1 illustrates this point. Q: If the box the man is carrying is very heavy, does he do any work as he walks across the room with it? A: Regardless of the weight of the box, the man does no work on it as he holds it while walking across the room. However, he does more work when he first lifts a heavier box to chest height. ",text,
L_1076,work,T_5015,"Work is directly related to both the force applied to an object and the distance the object moves. It can be represented by the equation: Work = Force  Distance This equation shows that the greater the force that is used to move an object or the farther the object is moved, the more work that is done. To see the effects of force and distance on work, compare the weight lifters in the Figure 1.2. The two weight lifters on the left are lifting the same amount of weight, but the one on the bottom is lifting the weight a greater distance. Therefore, this weight lifter is doing more work. The two weight lifters on the bottom right are both lifting the weight the same distance, but the weight lifter on the left is lifting a heavier weight, so she is doing more work. ",text,
L_0002,earth science and its branches,T_0016,FIGURE 1.11 (A) Mineralogists focus on all kinds of minerals. (B) Seismographs are used to measure earthquakes and pinpoint their origins.,image,textbook_images/earth_science_and_its_branches_20011.png
L_0002,earth science and its branches,T_0017,FIGURE 1.12 These folded rock layers have bent over time. Studying rock layers helps scientists to explain these layers and the geologic history of the area.,image,textbook_images/earth_science_and_its_branches_20012.png
L_0002,earth science and its branches,T_0017,FIGURE 1.13 This research vessel is specially designed to explore the seas around Antarctica.,image,textbook_images/earth_science_and_its_branches_20013.png
L_0002,earth science and its branches,T_0018,FIGURE 1.14 Meteorologists can help us to prepare for major storms or know if today is a good day for a picnic.,image,textbook_images/earth_science_and_its_branches_20014.png
L_0002,earth science and its branches,T_0018,FIGURE 1.15 Carbon dioxide released into the atmo- sphere is causing global warming.,image,textbook_images/earth_science_and_its_branches_20015.png
L_0002,earth science and its branches,T_0019,"FIGURE 1.16 In a marine ecosystem, coral, fish, and other sea life depend on each other for survival.",image,textbook_images/earth_science_and_its_branches_20016.png
L_0003,erosion and deposition by flowing water,T_0021,FIGURE 10.1 Flowing water erodes or deposits parti- cles depending on how fast the water is moving and how big the particles are.,image,textbook_images/erosion_and_deposition_by_flowing_water_20018.png
L_0003,erosion and deposition by flowing water,T_0023,FIGURE 10.2 How Flowing Water Moves Particles. How particles are moved by flowing water de- pends on their size.,image,textbook_images/erosion_and_deposition_by_flowing_water_20019.png
L_0003,erosion and deposition by flowing water,T_0027,FIGURE 10.3 Erosion by Runoff. Runoff has eroded small channels through this bare field.,image,textbook_images/erosion_and_deposition_by_flowing_water_20020.png
L_0003,erosion and deposition by flowing water,T_0027,FIGURE 10.4 Mountain Stream. This mountain stream races down a steep slope.,image,textbook_images/erosion_and_deposition_by_flowing_water_20021.png
L_0003,erosion and deposition by flowing water,T_0029,FIGURE 10.5 How a Waterfall Forms and Moves. Why does a waterfall keep moving upstream?,image,textbook_images/erosion_and_deposition_by_flowing_water_20022.png
L_0003,erosion and deposition by flowing water,T_0029,"FIGURE 10.6 Meanders form because water erodes the outside of curves and deposits eroded material on the inside. Over time, the curves shift position.",image,textbook_images/erosion_and_deposition_by_flowing_water_20023.png
L_0003,erosion and deposition by flowing water,T_0030,"FIGURE 10.7 An alluvial fan in Death Valley, California (left), Nile River Delta in Egypt (right).",image,textbook_images/erosion_and_deposition_by_flowing_water_20024.png
L_0003,erosion and deposition by flowing water,T_0032,FIGURE 10.8 This diagram shows how a river builds natural levees along its banks.,image,textbook_images/erosion_and_deposition_by_flowing_water_20025.png
L_0003,erosion and deposition by flowing water,T_0033,FIGURE 10.9 This cave has both stalactites and stalag- mites.,image,textbook_images/erosion_and_deposition_by_flowing_water_20026.png
L_0003,erosion and deposition by flowing water,T_0034,FIGURE 10.10 A sinkhole.,image,textbook_images/erosion_and_deposition_by_flowing_water_20027.png
L_0004,erosion and deposition by waves,T_0035,FIGURE 10.11 Ocean waves transfer energy from the wind through the water. This gives waves the energy to erode the shore.,image,textbook_images/erosion_and_deposition_by_waves_20028.png
L_0004,erosion and deposition by waves,T_0037,"FIGURE 10.12 Over millions of years, wave erosion can create wave-cut cliffs (A), sea arches (B), or sea stacks (C).",image,textbook_images/erosion_and_deposition_by_waves_20029.png
L_0004,erosion and deposition by waves,T_0039,FIGURE 10.13 Sand deposited along a shoreline creates a beach.,image,textbook_images/erosion_and_deposition_by_waves_20030.png
L_0004,erosion and deposition by waves,T_0039,FIGURE 10.14 Beach deposits usually consist of small pieces of rock and shell in addition to sand.,image,textbook_images/erosion_and_deposition_by_waves_20031.png
L_0004,erosion and deposition by waves,T_0040,FIGURE 10.15 Longshore drift carries particles of sand and rock down a coastline.,image,textbook_images/erosion_and_deposition_by_waves_20032.png
L_0004,erosion and deposition by waves,T_0041,FIGURE 10.16 Spit from Space. Farewell Spit in New Zealand is clearly visible from space. This photo was taken by an astronaut orbiting Earth.,image,textbook_images/erosion_and_deposition_by_waves_20033.png
L_0004,erosion and deposition by waves,T_0042,"FIGURE 10.17 Wave-Deposited Landforms. These land- forms were deposited by waves. (A) Sandbars connect the small islands on this beach on Thailand. (B) A barrier island is a long, narrow island. It forms when sand is deposited by waves parallel to a coast. It develops from a sandbar that has built up enough to break through the waters surface. A barrier island helps protect the coast from wave erosion.",image,textbook_images/erosion_and_deposition_by_waves_20034.png
L_0004,erosion and deposition by waves,T_0043,FIGURE 10.18 A breakwater is an artificial barrier island. How does it help protect the shoreline?,image,textbook_images/erosion_and_deposition_by_waves_20035.png
L_0004,erosion and deposition by waves,T_0044,FIGURE 10.19 A groin is built perpendicular to the shore- line. Sand collects on the upcurrent side.,image,textbook_images/erosion_and_deposition_by_waves_20036.png
L_0006,erosion and deposition by glaciers,T_0054,FIGURE 10.27 (A) The continent of Antarctica is covered with a continental glacier. (B) A valley glacier in the Canadian Rockies. (C) The surface of a valley glacier.,image,textbook_images/erosion_and_deposition_by_glaciers_20044.png
L_0006,erosion and deposition by glaciers,T_0056,FIGURE 10.28 Features Eroded by Valley Glaciers. Ero- sion by valley glaciers forms the unique features shown here.,image,textbook_images/erosion_and_deposition_by_glaciers_20045.png
L_0008,fossils,T_0066,"FIGURE 11.1 A variety of fossil types are pictured here. Preserved Remains: (A) teeth of a cow, (B) nearly complete dinosaur skeleton embedded in rock, (C) sea shell pre- served in a rock. Preserved Traces: (D) dinosaur tracks in mud, (E) fossil animal burrow in rock, (F) fossil feces from a meat-eating dinosaur in Canada.",image,textbook_images/fossils_20051.png
L_0008,fossils,T_0066,FIGURE 11.2 Fossilization. This flowchart shows how most fossils form.,image,textbook_images/fossils_20052.png
L_0008,fossils,T_0067,FIGURE 11.3 Ways Fossils Form. (A) Complete Preser- vation. This spider looks the same as it did the day it died millions of years ago! (B) Molds and Casts. A mold is a hole left in rock after an organisms remains break. A cast forms from the minerals that fill that hole and solidify. (C) Compression. A dark stain is left on a rock that was compressed. These ferns were fossilized by compression.,image,textbook_images/fossils_20053.png
L_0008,fossils,T_0070,FIGURE 11.4 What can we learn from fossil clues like this fish fossil found in the Wyoming desert?,image,textbook_images/fossils_20054.png
L_0008,fossils,T_0071,FIGURE 11.5 Trilobites are good index fossils. Why are trilobite fossils useful as index fossils?,image,textbook_images/fossils_20055.png
L_0009,relative ages of rocks,T_0073,"FIGURE 11.6 Laws of Stratigraphy. This diagram illus- trates the laws of stratigraphy. A = Law of Superposition, B = Law of Lateral Conti- nuity, C = Law of Original Horizontality, D = Law of Cross-Cutting Relationships",image,textbook_images/relative_ages_of_rocks_20056.png
L_0009,relative ages of rocks,T_0073,FIGURE 11.7 Superposition. The rock layers at the bottom of this cliff are much older than those at the top. What force eroded the rocks and exposed the layers?,image,textbook_images/relative_ages_of_rocks_20057.png
L_0009,relative ages of rocks,T_0074,FIGURE 11.8 Lateral Continuity. Layers of the same rock type are found across canyons at the Grand Canyon.,image,textbook_images/relative_ages_of_rocks_20058.png
L_0009,relative ages of rocks,T_0077,FIGURE 11.9 Cross-cutting relationships in rock layers. Rock D is a dike that cuts across all the other rocks. Is it older or younger than the other rocks?,image,textbook_images/relative_ages_of_rocks_20060.png
L_0009,relative ages of rocks,T_0077,"FIGURE 11.10 Huttons unconformity, in Scotland.",image,textbook_images/relative_ages_of_rocks_20059.png
L_0009,relative ages of rocks,T_0079,"FIGURE 11.11 Chalk Cliffs. (A) Matching chalk cliffs in Denmark and (B) in Dover, U.K.",image,textbook_images/relative_ages_of_rocks_20061.png
L_0009,relative ages of rocks,T_0081,FIGURE 11.12 Using Index Fossils to Match Rock Lay- ers. Rock layers with the same index fossils must have formed at about the same time. The presence of more than one type of index fossil provides stronger evidence that rock layers are the same age.,image,textbook_images/relative_ages_of_rocks_20062.png
L_0009,relative ages of rocks,T_0085,FIGURE 11.13 The Geologic Time Scale.,image,textbook_images/relative_ages_of_rocks_20063.png
L_0009,relative ages of rocks,T_0086,FIGURE 11.14 The evolution of life is shown on this spi- ral.,image,textbook_images/relative_ages_of_rocks_20064.png
L_0010,absolute ages of rocks,T_0089,"FIGURE 11.15 Isotopes are named for their number of protons plus neutrons. If a carbon atom had 7 neutrons, what would it be named?",image,textbook_images/absolute_ages_of_rocks_20065.png
L_0010,absolute ages of rocks,T_0089,FIGURE 11.16 Carbon-14 forms in the atmosphere. It combines with oxygen and forms carbon dioxide. How does carbon-14 end up in fossils?,image,textbook_images/absolute_ages_of_rocks_20066.png
L_0010,absolute ages of rocks,T_0090,"FIGURE 11.17 Unstable isotopes, such as carbon-14, decay by losing atomic particles. They form different, stable elements when they decay. In this case, the daughter is nitrogen-14.",image,textbook_images/absolute_ages_of_rocks_20067.png
L_0010,absolute ages of rocks,T_0092,FIGURE 11.18 The rate of decay of carbon-14 is stable over time.,image,textbook_images/absolute_ages_of_rocks_20068.png
L_0011,the origin of earth,T_0096,FIGURE 12.1 The Orion Nebula is the birthplace of new stars.,image,textbook_images/the_origin_of_earth_20069.png
L_0011,the origin of earth,T_0096,FIGURE 12.2 The Inner Planets.,image,textbook_images/the_origin_of_earth_20070.png
L_0011,the origin of earth,T_0096,"FIGURE 12.3 The Kuiper Belt, a ring of icy debris in our solar system just beyond Neptune, contains many solar system bodies.",image,textbook_images/the_origin_of_earth_20071.png
L_0011,the origin of earth,T_0098,FIGURE 12.4 Earths layers.,image,textbook_images/the_origin_of_earth_20072.png
L_0011,the origin of earth,T_0101,FIGURE 12.5 Gases from Earths interior came through volcanoes and into the atmosphere.,image,textbook_images/the_origin_of_earth_20073.png
L_0012,early earth,T_0108,FIGURE 12.6 E. coli (Escherichia coli) is a primitive prokaryote that may resemble the earliest cells. genetic instructions to the next generation.,image,textbook_images/early_earth_20074.png
L_0012,early earth,T_0110,"FIGURE 12.7 These rocks in Glacier National Park, Montana may contain some of the oldest fossil microbes on Earth.",image,textbook_images/early_earth_20075.png
L_0012,early earth,T_0112,FIGURE 12.8 This fossil is from the Ediacara Fauna. Nothing alive today seems to have evolved from the Ediacara organisms.,image,textbook_images/early_earth_20076.png
L_0014,water on earth,T_0132,FIGURE 13.1 Take a look at this image. Do you think that Earth deserves the name water planet?,image,textbook_images/water_on_earth_20085.png
L_0014,water on earth,T_0132,"FIGURE 13.2 What percentage of Earths surface fresh- water is water vapor in the air? Only a tiny fraction of Earths freshwater is in the liquid state. Most liquid freshwater is under the ground in layers of rock. Of freshwater on the surface, the majority occurs in lakes and soil. What percentage of freshwater on the surface is found in living things?",image,textbook_images/water_on_earth_20086.png
L_0014,water on earth,T_0134,FIGURE 13.3 The water cycle has no beginning or end. Water just keeps moving along.,image,textbook_images/water_on_earth_20087.png
L_0015,surface water,T_0137,FIGURE 13.4 All these forms of flowing water are streams.,image,textbook_images/surface_water_20088.png
L_0015,surface water,T_0139,FIGURE 13.5 Water in a stream flows along the ground from higher to lower elevation. What force causes the water to keep flowing?,image,textbook_images/surface_water_20089.png
L_0015,surface water,T_0139,FIGURE 13.6 River basins in the U.S.,image,textbook_images/surface_water_20090.png
L_0015,surface water,T_0140,FIGURE 13.7 The Great Lakes of North America get their name from their great size.,image,textbook_images/surface_water_20091.png
L_0015,surface water,T_0143,FIGURE 13.8 Craters and rifts become lakes when they fill with water. Where does the water come from?,image,textbook_images/surface_water_20092.png
L_0015,surface water,T_0145,FIGURE 13.9 These are just three of many types of wetlands.,image,textbook_images/surface_water_20093.png
L_0015,surface water,T_0146,FIGURE 13.10 A river in Indiana floods after very heavy rains. Some areas received almost a foot of rain in less than 24 hours!,image,textbook_images/surface_water_20094.png
L_0016,groundwater,T_0148,FIGURE 13.11 Water seeps into the ground through permeable material and stops when it reaches an impermeable rock. Predict the purpose of the well in the diagram.,image,textbook_images/groundwater_20095.png
L_0016,groundwater,T_0151,"FIGURE 13.12 An aquifer is a layer of saturated porous rock. It lies below the water table. An impermeable layer, such as clay, is below the aquifer.",image,textbook_images/groundwater_20096.png
L_0016,groundwater,T_0152,"FIGURE 13.13 In this map, the area over the Ogallala aquifer is shaded in blue.",image,textbook_images/groundwater_20097.png
L_0016,groundwater,T_0153,"FIGURE 13.14 Big Spring is named for its large size. It releases more than 12,000 liters of water per second!",image,textbook_images/groundwater_20098.png
L_0016,groundwater,T_0153,FIGURE 13.15 Lake George gets its water from a number of springs.,image,textbook_images/groundwater_20099.png
L_0016,groundwater,T_0154,FIGURE 13.16 Grand Prismatic Spring in the Yellowstone National Park is the largest hot spring in the U.S. How can you tell from the photo that the water in this spring is hot?,image,textbook_images/groundwater_20100.png
L_0016,groundwater,T_0155,FIGURE 13.17 Old Faithful in Yellowstone National Park is a geyser named for its regular cycle of eruptions.,image,textbook_images/groundwater_20101.png
L_0016,groundwater,T_0156,FIGURE 13.18 A well runs from the surface to a point below the water table. Why must a well go lower than the water table?,image,textbook_images/groundwater_20102.png
L_0017,introduction to the oceans,T_0158,FIGURE 14.1 Volcanoes were one source of water va- por on ancient Earth. What were other sources?,image,textbook_images/introduction_to_the_oceans_20104.png
L_0017,introduction to the oceans,T_0159,"FIGURE 14.2 At the time shown, there was one vast ocean and two smaller ones. How many oceans are there today? Thats why some people refer to the oceans together as the World Ocean.",image,textbook_images/introduction_to_the_oceans_20105.png
L_0017,introduction to the oceans,T_0161,FIGURE 14.3 The oceans and atmosphere exchange gases. Why does water vapor enter the atmosphere from the water?,image,textbook_images/introduction_to_the_oceans_20106.png
L_0017,introduction to the oceans,T_0163,FIGURE 14.4 Coral reefs teem with life.,image,textbook_images/introduction_to_the_oceans_20107.png
L_0017,introduction to the oceans,T_0166,FIGURE 14.5 What percentage of the salts in ocean water is sodium chloride?,image,textbook_images/introduction_to_the_oceans_20108.png
L_0017,introduction to the oceans,T_0168,FIGURE 14.6 Distance from shore and depth of water define ocean zones. Which zone is on the ocean floor?,image,textbook_images/introduction_to_the_oceans_20109.png
L_0018,ocean movements,T_0170,FIGURE 14.8 Waves cause the rippled surface of the ocean.,image,textbook_images/ocean_movements_20111.png
L_0018,ocean movements,T_0170,FIGURE 14.9 A wave travels through the water. How would you describe the movement of wa- ter molecules as a wave passes through?,image,textbook_images/ocean_movements_20112.png
L_0018,ocean movements,T_0172,FIGURE 14.10 Waves break when they reach the shore.,image,textbook_images/ocean_movements_20113.png
L_0018,ocean movements,T_0173,FIGURE 14.11 A 2004 tsunami caused damage like this all along the coast of the Indian Ocean. Many lives were lost.,image,textbook_images/ocean_movements_20114.png
L_0018,ocean movements,T_0174,FIGURE 14.12 Where is the intertidal zone in this pic- ture?,image,textbook_images/ocean_movements_20115.png
L_0018,ocean movements,T_0176,FIGURE 14.13 High and low tides are due mainly to the pull of the Moons gravity.,image,textbook_images/ocean_movements_20116.png
L_0018,ocean movements,T_0176,FIGURE 14.14 The Sun and Moon both affect Earths tides.,image,textbook_images/ocean_movements_20117.png
L_0018,ocean movements,T_0177,FIGURE 14.15 Earths surface currents flow in the pat- terns shown here.,image,textbook_images/ocean_movements_20118.png
L_0018,ocean movements,T_0180,"FIGURE 14.16 In this satellite photo, different colors indicate the temperatures of water and land. The warm Gulf Stream can be seen snaking up eastern North America.",image,textbook_images/ocean_movements_20119.png
L_0018,ocean movements,T_0180,FIGURE 14.17 Deep currents flow because of differences in density of ocean water.,image,textbook_images/ocean_movements_20120.png
L_0018,ocean movements,T_0181,FIGURE 14.18 An upwelling occurs when deep ocean water rises to the surface.,image,textbook_images/ocean_movements_20121.png
L_0019,the ocean floor,T_0183,"FIGURE 14.19 Sound waves travel through ocean water, but they bounce off the ocean floor. They move through ocean water at a known speed. Can you use these facts to explain how sonar works?",image,textbook_images/the_ocean_floor_20122.png
L_0019,the ocean floor,T_0183,"FIGURE 14.20 A map of a 10,000 foot-high undersea volcano in Indonesia made by multibeam solar.",image,textbook_images/the_ocean_floor_20123.png
L_0019,the ocean floor,T_0184,FIGURE 14.21 Vehicles for Underwater Exploration. These special vehicles have been used to study the ocean floor.,image,textbook_images/the_ocean_floor_20124.png
L_0019,the ocean floor,T_0185,FIGURE 14.22 The features of the ocean floor. This dia- gram has a lot of vertical exaggeration.,image,textbook_images/the_ocean_floor_20125.png
L_0019,the ocean floor,T_0188,"FIGURE 14.23 Metals from the ocean crust are brought by hot water onto the seafloor to create chimneys, as shown in this photo.",image,textbook_images/the_ocean_floor_20126.png
L_0020,ocean life,T_0190,FIGURE 14.24 Living things in the oceans are placed in these three groups.,image,textbook_images/ocean_life_20127.png
L_0020,ocean life,T_0190,"FIGURE 14.25 The phytoplankton (left) and zooplankton (right) shown here have been magnified. Otherwise, they would be too small for you to see.",image,textbook_images/ocean_life_20128.png
L_0020,ocean life,T_0191,FIGURE 14.26 Nekton swim through ocean water.,image,textbook_images/ocean_life_20129.png
L_0020,ocean life,T_0192,FIGURE 14.27 These animals live on the ocean floor.,image,textbook_images/ocean_life_20130.png
L_0020,ocean life,T_0192,FIGURE 14.28 Tubeworms live near hot water vents on the deep ocean floor.,image,textbook_images/ocean_life_20131.png
L_0020,ocean life,T_0193,FIGURE 14.29 Many marine food chains look like this example.,image,textbook_images/ocean_life_20132.png
L_0022,energy in the atmosphere,T_0211,FIGURE 15.6 These campers can feel and see the en- ergy of their campfire.,image,textbook_images/energy_in_the_atmosphere_20138.png
L_0022,energy in the atmosphere,T_0215,"FIGURE 15.7 This curve models a wave. Based on this figure, how would you define wave- length?",image,textbook_images/energy_in_the_atmosphere_20139.png
L_0022,energy in the atmosphere,T_0215,FIGURE 15.8 Compare the wavelengths of radio waves and gamma rays. Which type of wave has more energy?,image,textbook_images/energy_in_the_atmosphere_20140.png
L_0022,energy in the atmosphere,T_0219,FIGURE 15.9 Convection currents are the main way that heat moves through the atmosphere. Why does warm air rise?,image,textbook_images/energy_in_the_atmosphere_20141.png
L_0022,energy in the atmosphere,T_0220,"FIGURE 15.10 The lowest latitudes get the most energy from the Sun. The highest latitudes get the least. How do the differences in energy striking different latitudes affect Earth? The planet is much warmer at the equator than at the poles. In the atmosphere, the differences in heat energy cause winds and weather. On the surface, the differences cause ocean currents. Can you explain how?",image,textbook_images/energy_in_the_atmosphere_20142.png
L_0022,energy in the atmosphere,T_0221,FIGURE 15.11 Human actions have increased the natu- ral greenhouse effect.,image,textbook_images/energy_in_the_atmosphere_20143.png
L_0023,layers of the atmosphere,T_0223,FIGURE 15.12 How does air temperature change in the layer closest to Earth?,image,textbook_images/layers_of_the_atmosphere_20144.png
L_0023,layers of the atmosphere,T_0226,FIGURE 15.13 Temperature Inversion and Air Pollution. How does a temperature inversion affect air quality?,image,textbook_images/layers_of_the_atmosphere_20145.png
L_0023,layers of the atmosphere,T_0230,FIGURE 15.14 How does the ozone layer protect Earths surface from UV light?,image,textbook_images/layers_of_the_atmosphere_20146.png
L_0023,layers of the atmosphere,T_0234,FIGURE 15.15 Friction with gas molecules causes mete- ors to burn up in the mesosphere.,image,textbook_images/layers_of_the_atmosphere_20147.png
L_0023,layers of the atmosphere,T_0238,FIGURE 15.16 The International Space Station orbits in the thermosphere.,image,textbook_images/layers_of_the_atmosphere_20148.png
L_0023,layers of the atmosphere,T_0238,FIGURE 15.17 Glowing ions in the thermosphere light up the night sky.,image,textbook_images/layers_of_the_atmosphere_20149.png
L_0030,world climates,T_0304,FIGURE 17.9 Find where you live on the map. What type of climate do you have?,image,textbook_images/world_climates_20190.png
L_0030,world climates,T_0306,FIGURE 17.10 Africa is famous for its grasslands and their wildlife.,image,textbook_images/world_climates_20191.png
L_0030,world climates,T_0306,"FIGURE 17.11 Dry climates may be deserts or steppes. Sonoran Desert in Arizona (22 north latitude), Utah Steppe (40 north latitude).",image,textbook_images/world_climates_20192.png
L_0030,world climates,T_0307,FIGURE 17.12 How do these climates differ from each other?,image,textbook_images/world_climates_20193.png
L_0030,world climates,T_0308,FIGURE 17.13 Conifer forests are typical of the subarctic.,image,textbook_images/world_climates_20194.png
L_0030,world climates,T_0309,"FIGURE 17.14 Polar climates include polar and alpine tundra. Polar Tundra in Northern Alaska (70 N latitude), Alpine Tundra in the Colorado Rockies (40 N latitude).",image,textbook_images/world_climates_20195.png
L_0031,climate change,T_0313,FIGURE 17.17 Pleistocene glaciers covered an enormous land area. Chicago is just one city that couldnt have existed during the Pleistocene.,image,textbook_images/climate_change_20198.png
L_0031,climate change,T_0314,FIGURE 17.18 Earths temperature. Different sets of data all show an increase in temperature since about 1880 (the Industrial Revolution).,image,textbook_images/climate_change_20199.png
L_0031,climate change,T_0314,FIGURE 17.19 Earths temperature (18502007). Earth has really heated up over the last 150 years. Do you know why?,image,textbook_images/climate_change_20200.png
L_0031,climate change,T_0317,FIGURE 17.20 How much more carbon dioxide was in the air in 2005 than in 1960?,image,textbook_images/climate_change_20201.png
L_0031,climate change,T_0318,"FIGURE 17.21 How much did sea level rise between 1880 and 2000? Other effects of global warming include more extreme weather. Earth now has more severe storms, floods, heat waves, and droughts than it did just a few decades ago. Many living things cannot adjust to the changing climate. For example, coral reefs are dying out in all the worlds oceans.",image,textbook_images/climate_change_20202.png
L_0031,climate change,T_0319,FIGURE 17.22 The Arctic will experience the greatest temperature changes.,image,textbook_images/climate_change_20203.png
L_0031,climate change,T_0321,"FIGURE 17.23 In the 2050s, there may be only half as much sea ice as there was in the 1950s.",image,textbook_images/climate_change_20204.png
L_0031,climate change,T_0321,FIGURE 17.24 This diagram represents the Pacific Ocean in a normal year. North and South America are the brown shapes on the right.,image,textbook_images/climate_change_20205.png
L_0031,climate change,T_0322,FIGURE 17.25 How do you think El Nio affects climate on the western coast of South America?,image,textbook_images/climate_change_20206.png
L_0031,climate change,T_0322,FIGURE 17.26 How do you think La Nia affects climate on the western coast of South America?,image,textbook_images/climate_change_20207.png
L_0033,cycles of matter,T_0337,FIGURE 18.10 This piece of carbon looks like a lump of coal. Coal is mostly carbon. hydrogen. Then it forms compounds such as sugars and proteins. How do living things get the carbon they need? Carbon moves through ecosystems in the carbon cycle.,image,textbook_images/cycles_of_matter_20217.png
L_0033,cycles of matter,T_0338,FIGURE 18.11 Carbon changes form as it moves through its cycle. Follow carbon through the dia- gram as you read about the cycle below.,image,textbook_images/cycles_of_matter_20218.png
L_0033,cycles of matter,T_0341,FIGURE 18.12 Large parts of this Amazon rainforest have been cleared to grow crops. How does this affect the carbon cycle?,image,textbook_images/cycles_of_matter_20219.png
L_0033,cycles of matter,T_0344,"FIGURE 18.13 The nitrogen cycle includes air, soil, and living things.",image,textbook_images/cycles_of_matter_20220.png
L_0034,the human population,T_0347,FIGURE 18.16 A population cant get much larger than the carrying capacity. What might happen if it did?,image,textbook_images/the_human_population_20223.png
L_0034,the human population,T_0348,"FIGURE 18.17 Growth of the human population. Until recently, the human population grew very slowly.",image,textbook_images/the_human_population_20224.png
L_0034,the human population,T_0349,"FIGURE 18.18 Digging a London sewer (1840s). Before 1800, human wastes were thrown into the streets of cities such as London. In the early 1800s, sewers were dug to carry away the wastes.",image,textbook_images/the_human_population_20225.png
L_0034,the human population,T_0350,"FIGURE 18.19 This child is getting a polio vaccine. He will never get sick with polio, which could save his live or keep him from becoming crippled.",image,textbook_images/the_human_population_20226.png
L_0034,the human population,T_0350,FIGURE 18.20 World population growth rates. Is the population growing faster in the wealthiest countries or the poorest countries?,image,textbook_images/the_human_population_20227.png
L_0034,the human population,T_0352,FIGURE 18.21 Compare this graph with the graph of the carrying capacity. What do you think is the carrying capacity of the human popu- lation?,image,textbook_images/the_human_population_20228.png
L_0034,the human population,T_0352,"FIGURE 18.22 In the mid 1900s, Australian tree snakes invaded Guam and other islands in the Pacific. The snakes stowed away on boats and planes. Tree snakes had no natural enemies on the islands. Their populations exploded and they drove sev- eral island species extinct. the threat of hunger. Many also do not have safe, clean water. Some people live in crowded, run-down housing or something that is barely considered housing.",image,textbook_images/the_human_population_20229.png
L_0036,pollution of the land,T_0363,FIGURE 19.9 What can we learn from the story of Love Canal?,image,textbook_images/pollution_of_the_land_20238.png
L_0036,pollution of the land,T_0368,FIGURE 19.10 This agricultural worker is wearing the proper safety gear to handle a chemical pesticide.,image,textbook_images/pollution_of_the_land_20239.png
L_0036,pollution of the land,T_0368,"FIGURE 19.11 Avoid putting hazardous waste in the household trash. Instead, take it to a hazardous waste collection center.",image,textbook_images/pollution_of_the_land_20240.png
L_0037,introduction to earths surface,T_0370,FIGURE 2.1 (A) A compass is a device that is used to determine direction. The needle points to Earths magnetic north pole. (B) A com- pass rose shows the four major directions plus intermediates between them.,image,textbook_images/introduction_to_earths_surface_20241.png
L_0037,introduction to earths surface,T_0371,FIGURE 2.2 Earths magnetic north pole is about 11 degrees offset from its geographic north pole.,image,textbook_images/introduction_to_earths_surface_20242.png
L_0037,introduction to earths surface,T_0371,FIGURE 2.3 Nautical maps include a double compass rose that shows both magnetic directions (inner circle) and geographic compass di- rections (outer circle).,image,textbook_images/introduction_to_earths_surface_20243.png
L_0037,introduction to earths surface,T_0371,FIGURE 2.4 Topography of Earth showing North America and South America.,image,textbook_images/introduction_to_earths_surface_20244.png
L_0037,introduction to earths surface,T_0371,FIGURE 2.5 This image was made from data of the Landsat satellite. It shows the topography of the San Francisco Peaks and surround- ing areas.,image,textbook_images/introduction_to_earths_surface_20245.png
L_0037,introduction to earths surface,T_0372,FIGURE 2.6 This image shows Earth with water removed. The red areas are high elevations (mountains). Yellow and green areas are lower elevations. Blue areas are the lowest on the ocean floor.,image,textbook_images/introduction_to_earths_surface_20246.png
L_0037,introduction to earths surface,T_0372,"FIGURE 2.7 Features of continents include mountain ranges, plateaus, and plains. destructive forces. The bits and pieces of rock carried by rivers are deposited where rivers meet the oceans. These can form deltas, like the Mississippi River delta. They can also form barrier islands, like Padre Island in Texas. Rivers bring sand to the shore, which forms our beaches. These are constructive forces.",image,textbook_images/introduction_to_earths_surface_20247.png
L_0037,introduction to earths surface,T_0372,FIGURE 2.8 Summary of major landforms on conti- nents and features of coastlines.,image,textbook_images/introduction_to_earths_surface_20248.png
L_0037,introduction to earths surface,T_0373,"FIGURE 2.9 The continental shelf and slope of the southeastern United States goes down to the ocean floor. ocean floor. Much of the ocean floor is called the abyssal plain. The ocean floor is not totally flat. In many places, small hills rise above the ocean floor. These hills are undersea volcanoes, called seamounts (Figure 2.10). Some rise more than 1000 m above the seafloor.",image,textbook_images/introduction_to_earths_surface_20249.png
L_0037,introduction to earths surface,T_0373,"FIGURE 2.10 A chain of seamounts off the coast of New England (left). Oceanographers mapped one of these seamounts, called Bear Seamount, in great detail (right).",image,textbook_images/introduction_to_earths_surface_20250.png
L_0037,introduction to earths surface,T_0373,FIGURE 2.11 Map of the mid-ocean ridge system (yellow-green) in Earths oceans.,image,textbook_images/introduction_to_earths_surface_20251.png
L_0038,modeling earths surface,T_0375,FIGURE 2.13 A road map of the state of Florida. What information can you get from this map?,image,textbook_images/modeling_earths_surface_20253.png
L_0038,modeling earths surface,T_0377,FIGURE 2.14 A map projection translates Earths curved surface onto two dimensions.,image,textbook_images/modeling_earths_surface_20254.png
L_0038,modeling earths surface,T_0378,"FIGURE 2.15 Gerardus Mercator developed a map projection used often today, known as the Mercator projection.",image,textbook_images/modeling_earths_surface_20255.png
L_0038,modeling earths surface,T_0378,FIGURE 2.16 A Mercator projection translates the curved surface of Earth onto a cylinder.,image,textbook_images/modeling_earths_surface_20256.png
L_0038,modeling earths surface,T_0380,FIGURE 2.17 A conic map projection wraps Earth with a cone shape rather than a cylinder.,image,textbook_images/modeling_earths_surface_20257.png
L_0038,modeling earths surface,T_0380,FIGURE 2.18 A gnomonic projection places a flat piece of paper on a point somewhere on Earth and projects an image from that point.,image,textbook_images/modeling_earths_surface_20258.png
L_0038,modeling earths surface,T_0381,FIGURE 2.19 A Robinson projection better represents the true shapes and sizes of land areas.,image,textbook_images/modeling_earths_surface_20259.png
L_0038,modeling earths surface,T_0382,FIGURE 2.20 Lines of latitude start with the equator. Lines of longitude begin at the prime meridian.,image,textbook_images/modeling_earths_surface_20260.png
L_0038,modeling earths surface,T_0384,FIGURE 2.21 Lines of latitude and longitude form convenient reference points on a map.,image,textbook_images/modeling_earths_surface_20261.png
L_0038,modeling earths surface,T_0386,FIGURE 2.22 A topographic map like one that you might use for the sport of orienteering.,image,textbook_images/modeling_earths_surface_20262.png
L_0038,modeling earths surface,T_0387,FIGURE 2.23 A globe is the most accurate way to represent Earths curved surface.,image,textbook_images/modeling_earths_surface_20263.png
L_0039,topographic maps,T_0388,FIGURE 2.25 View of Swamp Canyon in Bryce Canyon National Park.,image,textbook_images/topographic_maps_20265.png
L_0039,topographic maps,T_0388,FIGURE 2.26 A map of a portion of Bryce Canyon National Park road map showing Swamp Canyon Loop.,image,textbook_images/topographic_maps_20266.png
L_0039,topographic maps,T_0389,FIGURE 2.27 Topographic map of Swamp Canyon Trail portion of Bryce Canyon National Park.,image,textbook_images/topographic_maps_20267.png
L_0039,topographic maps,T_0391,"FIGURE 2.28 Portion of a USGS topographic map of Stowe, VT.",image,textbook_images/topographic_maps_20268.png
L_0039,topographic maps,T_0391,"FIGURE 2.29 Portion of a USGS topographic map of Stowe, VT. Cady Hill (elevation 1122 ft) is shown by concentric circles in the lower left portion of the map. Another hill (eleva- tion ~ 960 ft) is on the upper right portion of the map.",image,textbook_images/topographic_maps_20269.png
L_0039,topographic maps,T_0391,"FIGURE 2.30 On a contour map, a circle with inward hatches indicates a depression.",image,textbook_images/topographic_maps_20270.png
L_0039,topographic maps,T_0391,"FIGURE 2.31 Illustrations of three-dimensional ground configurations (top) and corre- sponding topographic map (bottom). Note that the V-shaped markings on the topographic maps correspond to drainage channels. Also, the closely- spaced contour lines denote the rapid rising cliff face on the left side.",image,textbook_images/topographic_maps_20271.png
L_0039,topographic maps,T_0394,"FIGURE 2.32 Bathymetric map of Bear Lake, Utah.",image,textbook_images/topographic_maps_20272.png
L_0039,topographic maps,T_0395,"FIGURE 2.33 A portion of the geologic map of the Grand Canyon, Arizona.",image,textbook_images/topographic_maps_20273.png
L_0040,using satellites and computers,T_0396,"FIGURE 2.34 Left: Track of hurricane that hit Galveston, Texas on Sept. 8, 1900. Right: Galveston in the aftermath.",image,textbook_images/using_satellites_and_computers_20274.png
L_0040,using satellites and computers,T_0400,FIGURE 2.35 Satellite in a polar orbit.,image,textbook_images/using_satellites_and_computers_20275.png
L_0040,using satellites and computers,T_0400,FIGURE 2.36 NASAs fleet of satellites to study the Earth.,image,textbook_images/using_satellites_and_computers_20276.png
L_0040,using satellites and computers,T_0400,"FIGURE 2.37 Various satellite images: (a) water vapor in atmosphere, (b) ocean surface temperatures, (c) global vegetation.",image,textbook_images/using_satellites_and_computers_20277.png
L_0040,using satellites and computers,T_0401,"FIGURE 2.38 (a) You need a GPS receiver to use the GPS system. (b) It takes signals from 4 GPS satellites to find your location pre- cisely on the surface GPS receiver detects radio signals from nearby GPS satellites. There are precise clocks on each satellite and in the receiver. The receiver measures the time for radio signals from satellite to reach it. The receiver uses the time and the speed of radio signals to calculate the distance between the receiver and the satellite. The receiver does this with at least four different satellites to locate its position on the Earths surface (Figure 2.38). GPS receivers are now being built into many items, such as cell phones and cars.",image,textbook_images/using_satellites_and_computers_20278.png
L_0040,using satellites and computers,T_0402,FIGURE 2.39 This three-dimensional image of Mars north pole was made from satellite im- ages and computers.,image,textbook_images/using_satellites_and_computers_20279.png
L_0040,using satellites and computers,T_0402,FIGURE 2.40 Map of insurance filings for crop damage in 2008.,image,textbook_images/using_satellites_and_computers_20280.png
L_0041,use and conservation of resources,T_0405,FIGURE 20.1 Forests should be renewable resources. The forest on the left is healthy and is used for recreation. The forest on the right was killed by acid rain.,image,textbook_images/use_and_conservation_of_resources_20281.png
L_0041,use and conservation of resources,T_0407,FIGURE 20.2 This oil rig was pumping oil from below the ocean floor when it exploded.,image,textbook_images/use_and_conservation_of_resources_20282.png
L_0041,use and conservation of resources,T_0410,FIGURE 20.3 The U.S. uses more than its share of oil. What if everyone used resources this way? (Note: Per capita means per person.),image,textbook_images/use_and_conservation_of_resources_20283.png
L_0041,use and conservation of resources,T_0411,FIGURE 20.4 Bulldozers crushes a mountain of trash.,image,textbook_images/use_and_conservation_of_resources_20284.png
L_0041,use and conservation of resources,T_0411,FIGURE 20.5 Buying locally grown produce at a farmers market saves resources.,image,textbook_images/use_and_conservation_of_resources_20285.png
L_0041,use and conservation of resources,T_0413,FIGURE 20.6 These types of packaging are hard to recycle. Could you reuse any of them?,image,textbook_images/use_and_conservation_of_resources_20286.png
L_0042,use and conservation of energy,T_0417,FIGURE 20.10 What percent of energy in the U.S. is used for transportation and in homes?,image,textbook_images/use_and_conservation_of_energy_20290.png
L_0042,use and conservation of energy,T_0418,FIGURE 20.11 The U.S. gets 85 percent of its energy from fossil fuels. Where does the other 15 percent come from?,image,textbook_images/use_and_conservation_of_energy_20291.png
L_0042,use and conservation of energy,T_0418,FIGURE 20.12 Energy is used to build and operate an oil well. What happens to the oil after its pumped out of the well?,image,textbook_images/use_and_conservation_of_energy_20292.png
L_0042,use and conservation of energy,T_0418,FIGURE 20.13 Solar panels collect sunlight on the roof of this house. The energy can be used to run the household.,image,textbook_images/use_and_conservation_of_energy_20293.png
L_0042,use and conservation of energy,T_0420,FIGURE 20.14 The Energy Star logo shows that an appliance uses energy efficiently.,image,textbook_images/use_and_conservation_of_energy_20294.png
L_0043,humans and the water supply,T_0422,"FIGURE 21.1 In this global water use chart, see how much is used for agriculture. Why do you think so much water is used in agricul- ture?",image,textbook_images/humans_and_the_water_supply_20295.png
L_0043,humans and the water supply,T_0422,FIGURE 21.2 Overhead irrigation systems like this one are widely used to irrigate crops on big farms. What are some drawbacks of irrigation?,image,textbook_images/humans_and_the_water_supply_20296.png
L_0043,humans and the water supply,T_0424,FIGURE 21.3 What will happen to the water that runs off the van? Where will it go?,image,textbook_images/humans_and_the_water_supply_20297.png
L_0043,humans and the water supply,T_0425,FIGURE 21.4 Sunshine brings golfers to the desert but a lot of water is needed to make the desert green enough to play.,image,textbook_images/humans_and_the_water_supply_20298.png
L_0043,humans and the water supply,T_0427,"FIGURE 21.5 This glacier in Patagonia, Argentina stores a lot of frozen freshwater.",image,textbook_images/humans_and_the_water_supply_20299.png
L_0043,humans and the water supply,T_0429,"FIGURE 21.6 Water is a luxury in Africa, and many people have to carry water home. How would you use water differently if you had to get your water this way?",image,textbook_images/humans_and_the_water_supply_20300.png
L_0044,water pollution,T_0433,FIGURE 21.9 Pollution from a factory enters a stream at a single point.,image,textbook_images/water_pollution_20303.png
L_0044,water pollution,T_0434,"FIGURE 21.10 This vehicle is spreading fertilizer on a field before planting. millions of fish. In Wisconsin, cow manure leaked into a citys water supply. Almost half a million people got sick. More than 100 people died.",image,textbook_images/water_pollution_20304.png
L_0044,water pollution,T_0434,"FIGURE 21.11 From the air, this looks like a pond of water. Its really a pond of hog manure. To get an idea of how big the lagoon is, check out the vehicles at the bottom of the picture.",image,textbook_images/water_pollution_20305.png
L_0044,water pollution,T_0438,FIGURE 21.12 This coastal ocean water is full of trash and sewage.,image,textbook_images/water_pollution_20306.png
L_0044,water pollution,T_0439,"FIGURE 21.13 After an oil rig explosion, hundreds of miles of beaches looked like this one. Cleaning them up was a huge task.",image,textbook_images/water_pollution_20307.png
L_0044,water pollution,T_0440,"FIGURE 21.14 Nuclear power plants need huge amounts of water for cooling, so they are built close to water. The water thats returned to the lake may be warm enough to kill fish.",image,textbook_images/water_pollution_20308.png
L_0045,protecting the water supply,T_0441,"FIGURE 21.16 Left: The Cuyahoga River flows through Cleveland, Ohio. In the mid 1900s, there was a lot of industry in this part of Ohio. The river became very polluted. Right: Today, the river is much cleaner.",image,textbook_images/protecting_the_water_supply_20310.png
L_0045,protecting the water supply,T_0443,FIGURE 21.17 Why should people always clean up after their pets?,image,textbook_images/protecting_the_water_supply_20311.png
L_0045,protecting the water supply,T_0444,FIGURE 21.18 Four processes are used to treat water to make it safe for drinking.,image,textbook_images/protecting_the_water_supply_20312.png
L_0045,protecting the water supply,T_0446,FIGURE 21.19 This is a drip irrigation system. Look at the soil in the photo. Its damp around each plant but dry everywhere else.,image,textbook_images/protecting_the_water_supply_20313.png
L_0045,protecting the water supply,T_0448,FIGURE 21.20 This beautiful garden contains only plants that need very little water.,image,textbook_images/protecting_the_water_supply_20314.png
L_0047,air pollution,T_0458,"FIGURE 22.1 Black particulates coming out of a factory smokestack. Many particulates are too small to see, but they can still be dangerous.",image,textbook_images/air_pollution_20319.png
L_0047,air pollution,T_0459,FIGURE 22.2 Photochemical smog is common in the air over many California cities.,image,textbook_images/air_pollution_20320.png
L_0047,air pollution,T_0460,FIGURE 22.3 Ozone forms near the ground as a sec- ondary pollutant.,image,textbook_images/air_pollution_20321.png
L_0047,air pollution,T_0463,FIGURE 22.4 Cutting and burning trees to clear land for farming is called slash-and-burn agri- culture. How does this affect the atmo- sphere?,image,textbook_images/air_pollution_20322.png
L_0048,effects of air pollution,T_0466,FIGURE 22.5 Ozone damaged snap bean plants are shown on the left. Healthy snap bean plants are shown on the right.,image,textbook_images/effects_of_air_pollution_20323.png
L_0048,effects of air pollution,T_0466,FIGURE 22.6 The ozone air quality index gives the parts of ozone per million parts of air. How many parts of ozone are unhealthy for everyone?,image,textbook_images/effects_of_air_pollution_20324.png
L_0048,effects of air pollution,T_0469,FIGURE 22.7 This carbon monoxide detector will sound an alarm if the gas rises above a safe level.,image,textbook_images/effects_of_air_pollution_20325.png
L_0048,effects of air pollution,T_0469,FIGURE 22.8 This diagram shows how mercury bioac- cumulates. Compare the parts per million (ppm) of mercury in phytoplankton and gull eggs. Can you explain the differ- ence?,image,textbook_images/effects_of_air_pollution_20326.png
L_0048,effects of air pollution,T_0471,FIGURE 22.9 This pH scale includes both normal and acid rain. At what pH do fish have prob- lems reproducing?,image,textbook_images/effects_of_air_pollution_20327.png
L_0048,effects of air pollution,T_0472,FIGURE 22.10 Nitrogen and sulfur oxides combine with rain to form acid rain.,image,textbook_images/effects_of_air_pollution_20328.png
L_0048,effects of air pollution,T_0473,"FIGURE 22.11 This photo shows a gargoyle that is being dissolved by acid rain on Notre Dame cathedral in Paris, France.",image,textbook_images/effects_of_air_pollution_20329.png
L_0048,effects of air pollution,T_0476,FIGURE 22.12 CFCs break down ozone in the strato- sphere.,image,textbook_images/effects_of_air_pollution_20330.png
L_0048,effects of air pollution,T_0476,FIGURE 22.13 The hole in the ozone layer occurs over Antarctica. How do you think the hole in the ozone layer could affect life on Earth?,image,textbook_images/effects_of_air_pollution_20331.png
L_0049,reducing air pollution,T_0479,FIGURE 22.14 This is a model of a hydrogen car. A major problem with hydrogen cars is the lack of hydrogen fuel.,image,textbook_images/reducing_air_pollution_20332.png
L_0049,reducing air pollution,T_0480,FIGURE 22.15 How a Scrubber Works. Some scrubbers use steam to remove pollutants from exhaust.,image,textbook_images/reducing_air_pollution_20333.png
L_0049,reducing air pollution,T_0483,"FIGURE 22.16 This diagram shows how a cap-and-trade system works. meeting their goals. Most scientists also think the Kyoto Protocol did not go far enough to limit greenhouse gases. A stricter agreement must be reached very soon. Unfortunately, efforts to limit greenhouse gas emissions are mired in politics. Meanwhile, crucial time is being lost.",image,textbook_images/reducing_air_pollution_20334.png
L_0050,telescopes,T_0488,FIGURE 23.1 The Andromeda Galaxy as it appeared 2.5 million years ago. How would you find out how it looks right now?,image,textbook_images/telescopes_20335.png
L_0050,telescopes,T_0488,FIGURE 23.2 An electromagnetic wave has oscillating electric and magnetic fields.,image,textbook_images/telescopes_20336.png
L_0050,telescopes,T_0489,FIGURE 23.3 The electromagnetic spectrum from radio waves to gamma rays.,image,textbook_images/telescopes_20337.png
L_0050,telescopes,T_0492,FIGURE 23.4 Refracting telescopes can be very large.,image,textbook_images/telescopes_20338.png
L_0050,telescopes,T_0492,FIGURE 23.5 Newtonian reflector telescopes are fairly easy to make. These telescopes can be built by school students.,image,textbook_images/telescopes_20339.png
L_0050,telescopes,T_0492,FIGURE 23.6 The radio telescope at the Arecibo Obser- vatory in Puerto Rico.,image,textbook_images/telescopes_20340.png
L_0050,telescopes,T_0492,FIGURE 23.7 The Very Large Array in New Mexico con- sists of 27 radio telescopes.,image,textbook_images/telescopes_20341.png
L_0050,telescopes,T_0493,FIGURE 23.8 The Hubble Space Telescope has opened up the universe to human observation.,image,textbook_images/telescopes_20342.png
L_0050,telescopes,T_0493,FIGURE 23.9 Stars in the star cluster appear as points of light. Observations like these must be made with a space telescope.,image,textbook_images/telescopes_20343.png
L_0050,telescopes,T_0496,FIGURE 23.10 Galileo made the drawing on the left in 1610. On the right is a modern photo- graph of the Moon.,image,textbook_images/telescopes_20344.png
L_0050,telescopes,T_0498,FIGURE 23.11 The dark lines indicate the elements that this star contains.,image,textbook_images/telescopes_20345.png
L_0051,early space exploration,T_0500,FIGURE 23.12 A rocket pushes in one direction so that it moves in the opposite direction.,image,textbook_images/early_space_exploration_20346.png
L_0051,early space exploration,T_0502,FIGURE 23.13 This missile is pushed upwards into the sky by its thrust.,image,textbook_images/early_space_exploration_20347.png
L_0051,early space exploration,T_0502,FIGURE 23.14 Robert Goddard with the first American rocket to use liquid fuel. This rocket was launched in 1926.,image,textbook_images/early_space_exploration_20348.png
L_0051,early space exploration,T_0502,FIGURE 23.15 A captured German V2 rocket was launched in New Mexico after the war.,image,textbook_images/early_space_exploration_20349.png
L_0051,early space exploration,T_0502,FIGURE 23.16 This Saturn V rocket took the first men to the Moon during Apollo 11.,image,textbook_images/early_space_exploration_20350.png
L_0051,early space exploration,T_0503,FIGURE 23.17 Isaac Newton explained how a cannonball fired from a high point with enough speed could orbit Earth.,image,textbook_images/early_space_exploration_20351.png
L_0051,early space exploration,T_0506,FIGURE 23.18 Communications satellites carry solar panels to provide energy for their mis- sions.,image,textbook_images/early_space_exploration_20352.png
L_0051,early space exploration,T_0509,FIGURE 23.19 Satellites detect different wavelengths of energy. This means that they can find different types of objects.,image,textbook_images/early_space_exploration_20353.png
L_0051,early space exploration,T_0510,"FIGURE 23.20 Laika went into orbit on the Soviet space- craft, Sputnik 2.",image,textbook_images/early_space_exploration_20354.png
L_0051,early space exploration,T_0510,FIGURE 23.21 Apollo 11 astronaut Buzz Aldrin with the Lunar Module Eagle and the American flag in the background. The photo was taken by Commander Neil Armstrong. nations working together.,image,textbook_images/early_space_exploration_20355.png
L_0052,recent space exploration,T_0514,FIGURE 23.22 Salyut 7 with a docked spacecraft to bring crew on and off.,image,textbook_images/recent_space_exploration_20356.png
L_0052,recent space exploration,T_0514,"FIGURE 23.23 Mir, with an American space shuttle at- tached.",image,textbook_images/recent_space_exploration_20357.png
L_0052,recent space exploration,T_0515,"FIGURE 23.24 The International Space Station, as pho- tographed from the Space Shuttle Atlantis in May 2010.",image,textbook_images/recent_space_exploration_20358.png
L_0052,recent space exploration,T_0516,"FIGURE 23.25 The space shuttle Atlantis rides a special- ized Boeing 747 from its landing site in California back to Florida. an airplane. The shuttle is launched from Kennedy Space Center in Cape Canaveral, Florida. During launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large booster rockets. Figure 23.26 shows the stages of a normal space shuttle mission. Once in space, the orbiter can deliver equipment or supplies to the International Space Station. Astronauts can to repair orbiting equipment such as the Hubble Space Telescope. They may also do experiments directly on board the orbiter.",image,textbook_images/recent_space_exploration_20359.png
L_0052,recent space exploration,T_0516,FIGURE 23.26 The stages of a shuttle mission. The orbiter takes off like a rocket and lands like an airplane.,image,textbook_images/recent_space_exploration_20360.png
L_0052,recent space exploration,T_0517,FIGURE 23.27 The disasters on the Challenger space shuttle mission showed just how danger- ous space travel can be.,image,textbook_images/recent_space_exploration_20361.png
L_0052,recent space exploration,T_0520,FIGURE 23.28 The Cone Nebula is a star-forming pillar of gas and dust.,image,textbook_images/recent_space_exploration_20362.png
L_0052,recent space exploration,T_0520,"FIGURE 23.29 This artists painting of one of the two Mars rovers shows the six wheels, as well as a set of instruments being extended forward by a robotic arm. The Cassini mission has been studying Saturn, including its rings and moons, since 2004. The Huygens probe is studying Saturns moon Titan. Titan has some of the conditions that are needed to support life. Some missions visit the smaller objects in our solar system. The Deep Impact Probe collided with a comet in 2005. The probe sent back data from the impact. The Stardust mission visited another comet. There it collected tiny dust particles. Missions are underway to study some asteroids and Pluto. Small objects in our solar system may help us to understand how the solar system formed.",image,textbook_images/recent_space_exploration_20363.png
L_0053,planet earth,T_0523,FIGURE 24.1 This is how the Earth looks from space - like a blue and white marble.,image,textbook_images/planet_earth_20364.png
L_0053,planet earth,T_0523,"FIGURE 24.2 Compare the Sun with the other planets and see how the Sun is much bigger than all the other planets. Atmosphere: the thin layer of air, mostly nitrogen and oxygen, that surrounds the Earth. Hydrosphere: all the water on Earth. Biosphere: all the living organisms on Earth. Lithosphere: the solid rock part of Earth, including mountains, valleys, continents, and all of the rock beneath the oceans.",image,textbook_images/planet_earth_20365.png
L_0053,planet earth,T_0523,"FIGURE 24.3 Earth has four layers: atmosphere, hydro- sphere, biosphere, and lithosphere.",image,textbook_images/planet_earth_20366.png
L_0053,planet earth,T_0525,"FIGURE 24.4 The Moon orbits the Earth, and the Earth- Moon system orbits the Sun.",image,textbook_images/planet_earth_20367.png
L_0053,planet earth,T_0525,FIGURE 24.5 The strength of the force of gravity be- tween objects A and B depends on the mass of the objects and the distance (u) between them.,image,textbook_images/planet_earth_20368.png
L_0053,planet earth,T_0525,FIGURE 24.6 Earths space. magnetic field extends into,image,textbook_images/planet_earth_20369.png
L_0053,planet earth,T_0525,FIGURE 24.7 Earths magnetic field protects the planet from harmful radiation.,image,textbook_images/planet_earth_20370.png
L_0053,planet earth,T_0525,"FIGURE 24.8 The needle of a compass will align with Earths magnetic field, making the com- pass a useful device for navigation.",image,textbook_images/planet_earth_20371.png
L_0053,planet earth,T_0527,"FIGURE 24.9 Imagine a pendulum at the North Pole. The pendulum always swings in the same direction. But because of Earths rotation, its direction appears to change to observers on Earth.",image,textbook_images/planet_earth_20372.png
L_0053,planet earth,T_0529,FIGURE 24.10 The Earth tilts on its axis.,image,textbook_images/planet_earth_20373.png
L_0053,planet earth,T_0529,FIGURE 24.11 Earths tilt changes the length of the days and nights during different seasons.,image,textbook_images/planet_earth_20374.png
L_0053,planet earth,T_0530,"FIGURE 24.12 Earth and the other planets in the solar system make elliptical orbits around the Sun. The distance between the Earth and the Sun is about 150 million kilometers. Earth revolves around the Sun at an average speed of about 27 kilometers (17 miles) per second. Mercury and Venus are closer to the Sun, so they take shorter times to make one orbit. Mercury takes only about 88 Earth days to make one trip around the Sun. All of the other planets take longer amounts of time. The exact amount depends on the planets distance from the Sun. Saturn takes more than 29 Earth years to make one revolution around the Sun.",image,textbook_images/planet_earth_20375.png
L_0054,earths moon,T_0531,"FIGURE 24.13 The Mare Moscoviense is one of the few maria, or dark, flat areas, on the far side.",image,textbook_images/earths_moon_20376.png
L_0054,earths moon,T_0534,"FIGURE 24.14 Craters, like the one shown in this image, are found on the surface of the Moon.",image,textbook_images/earths_moon_20377.png
L_0054,earths moon,T_0534,FIGURE 24.15 Maria (the dark areas) and terrae (the light areas) cover the Moon.,image,textbook_images/earths_moon_20378.png
L_0055,the sun,T_0538,"FIGURE 24.16 The sizes of the planets relative to the Sun, if the Sun was the size of a basketball.",image,textbook_images/the_sun_20379.png
L_0055,the sun,T_0542,"FIGURE 24.17 The Suns atmosphere contains the pho- tosphere, the chromosphere, and the corona. This image was taken by NASAs Spacelab 2 instruments.",image,textbook_images/the_sun_20380.png
L_0055,the sun,T_0546,FIGURE 24.18 The darker regions in this image are sunspots.,image,textbook_images/the_sun_20381.png
L_0055,the sun,T_0547,FIGURE 24.19 This image is actually made up of two suc- cessive images and shows how a solar flare develops.,image,textbook_images/the_sun_20382.png
L_0056,the sun and the earthmoon system,T_0549,"FIGURE 24.20 During a solar eclipse, the Moon casts a shadow on the Earth. The shadow is made up of two parts: the darker umbra and the lighter penumbra.",image,textbook_images/the_sun_and_the_earthmoon_system_20383.png
L_0056,the sun and the earthmoon system,T_0549,FIGURE 24.21 A photo of a total solar eclipse.,image,textbook_images/the_sun_and_the_earthmoon_system_20384.png
L_0056,the sun and the earthmoon system,T_0550,FIGURE 24.22 A lunar eclipse is shown in a series of pictures.,image,textbook_images/the_sun_and_the_earthmoon_system_20385.png
L_0057,introduction to the solar system,T_0554,FIGURE 25.1 On left is a line art drawing of the Ptole- maic system with Earth at the center. On the right is a drawing of the Ptolemaic system from 1568 by a Portuguese as- tronomer.,image,textbook_images/introduction_to_the_solar_system_20386.png
L_0057,introduction to the solar system,T_0555,"FIGURE 25.2 Copernicus proposed a different idea that had the Sun at the center of the universe model more seriously. Through his telescope, Galileo saw moons orbiting Jupiter. He proposed that this was like the planets orbiting the Sun.",image,textbook_images/introduction_to_the_solar_system_20387.png
L_0057,introduction to the solar system,T_0556,"FIGURE 25.3 This artistic composition shows the eight planets, a comet, and an asteroid. Object Mass (Relative to Earth) Diameter of Planet (Relative to Earth) 3.81 Earths diameter",image,textbook_images/introduction_to_the_solar_system_20388.png
L_0057,introduction to the solar system,T_0558,FIGURE 25.4 The Sun and planets with the correct sizes. The distances between them are not correct. Figure 25.5 shows those distances correctly. In the upper left are the orbits of the inner planets and the asteroid belt. The asteroid belt is a collection of many small objects between the orbits of Mars and Jupiter. In the upper right are the orbits of the outer planets and the Kuiper belt. The Kuiper belt is a group of objects beyond the orbit of Neptune.,image,textbook_images/introduction_to_the_solar_system_20389.png
L_0057,introduction to the solar system,T_0558,"FIGURE 25.5 In this image, distances are shown to scale.",image,textbook_images/introduction_to_the_solar_system_20390.png
L_0057,introduction to the solar system,T_0562,FIGURE 25.6 The nebula was drawn together by gravity.,image,textbook_images/introduction_to_the_solar_system_20391.png
L_0058,inner planets,T_0564,FIGURE 25.7 Tiny Mercury is the small black dot in the lower center of this picture of the Sun. The larger dark area near the left edge is a sunspot.,image,textbook_images/inner_planets_20392.png
L_0058,inner planets,T_0564,"FIGURE 25.8 The surface of Mercury is covered with craters, like Earths Moon.",image,textbook_images/inner_planets_20393.png
L_0058,inner planets,T_0565,FIGURE 25.9,image,textbook_images/inner_planets_20394.png
L_0058,inner planets,T_0568,"FIGURE 25.10 Mercury is one of the most dense planets, with a very large core.",image,textbook_images/inner_planets_20395.png
L_0058,inner planets,T_0570,FIGURE 25.11 Venus in real color. The planet is covered by a thick layer of clouds.,image,textbook_images/inner_planets_20396.png
L_0058,inner planets,T_0570,FIGURE 25.12 A topographical image of Venus produced by the Magellan probe using radar. Color differences enhance small scale struc- ture. reddish-brown.,image,textbook_images/inner_planets_20397.png
L_0058,inner planets,T_0570,"FIGURE 25.13 Maat Mons volcano on Venus, with lava beds in the foreground.",image,textbook_images/inner_planets_20398.png
L_0058,inner planets,T_0573,FIGURE 25.14 Earth from space.,image,textbook_images/inner_planets_20399.png
L_0058,inner planets,T_0576,FIGURE 25.15 Mars is Earths second nearest neighbor planet.,image,textbook_images/inner_planets_20400.png
L_0058,inner planets,T_0578,"FIGURE 25.16 The largest volcano in the solar system, Olympus Mons.",image,textbook_images/inner_planets_20401.png
L_0058,inner planets,T_0578,"FIGURE 25.17 The largest canyon in the solar system, Valles Marineris.",image,textbook_images/inner_planets_20402.png
L_0058,inner planets,T_0580,FIGURE 25.18 Phobos is Mars larger moon. It has a 6.9 mile (11.1 km) radius.,image,textbook_images/inner_planets_20403.png
L_0059,outer planets,T_0581,FIGURE 25.19 Jupiter is the largest planet in our solar system.,image,textbook_images/outer_planets_20404.png
L_0059,outer planets,T_0584,FIGURE 25.20 The Great Red Spot has been on Jupiter since weve had telescopes powerful enough to see it.,image,textbook_images/outer_planets_20405.png
L_0059,outer planets,T_0584,"FIGURE 25.21 The Galilean moons are as large as small planets. showed that Jupiter has a ring system. This ring system is very faint, so it is very difficult to observe from Earth.",image,textbook_images/outer_planets_20406.png
L_0059,outer planets,T_0585,FIGURE 25.22 Saturn is the least dense planet in our solar system.,image,textbook_images/outer_planets_20407.png
L_0059,outer planets,T_0587,FIGURE 25.23 Cassini scientists waited years for the right conditions to produce the first movie that shows lightning on another planet - Saturn.,image,textbook_images/outer_planets_20408.png
L_0059,outer planets,T_0587,FIGURE 25.24 This hexagon has been visible for nearly 30 years.,image,textbook_images/outer_planets_20409.png
L_0059,outer planets,T_0588,FIGURE 25.25 Titan has an atmosphere like Earths first atmosphere.,image,textbook_images/outer_planets_20410.png
L_0059,outer planets,T_0589,FIGURE 25.26 Uranus is the 7th planet out from the Sun.,image,textbook_images/outer_planets_20411.png
L_0059,outer planets,T_0592,FIGURE 25.27 Uranus rings are almost perpendicular to the planets orbit.,image,textbook_images/outer_planets_20412.png
L_0059,outer planets,T_0592,"FIGURE 25.28 The five biggest moons of Uranus: Miranda, Ariel, Umbriel, Titania, and Oberon.",image,textbook_images/outer_planets_20413.png
L_0059,outer planets,T_0593,FIGURE 25.29 Neptune has a great dark spot at the center left and a small dark spot at the bottom center.,image,textbook_images/outer_planets_20414.png
L_0059,outer planets,T_0595,FIGURE 25.30 Neptunes moon Triton.,image,textbook_images/outer_planets_20415.png
L_0060,other objects in the solar system,T_0598,FIGURE 25.31 Asteroid Ida with its tiny moon Dactyl. The asteroids mean radius is 15.7 km.,image,textbook_images/other_objects_in_the_solar_system_20416.png
L_0060,other objects in the solar system,T_0598,FIGURE 25.32 The asteroid belt is between Mars and Jupiter.,image,textbook_images/other_objects_in_the_solar_system_20417.png
L_0060,other objects in the solar system,T_0601,FIGURE 25.33 Meteors burning up as they fall through Earths atmosphere.,image,textbook_images/other_objects_in_the_solar_system_20418.png
L_0060,other objects in the solar system,T_0603,"FIGURE 25.34 The Mars Rover, Opportunity, found a metal meteorite on the Red Planet.",image,textbook_images/other_objects_in_the_solar_system_20419.png
L_0060,other objects in the solar system,T_0604,FIGURE 25.35 Comet Hale-Bopp lit up the night sky in 1997.,image,textbook_images/other_objects_in_the_solar_system_20420.png
L_0060,other objects in the solar system,T_0607,FIGURE 25.36 Ceres is a large spherical object in the asteroid belt.,image,textbook_images/other_objects_in_the_solar_system_20421.png
L_0060,other objects in the solar system,T_0607,"FIGURE 25.37 Pluto with its moons: Charon, Nix and Hydra.",image,textbook_images/other_objects_in_the_solar_system_20422.png
L_0060,other objects in the solar system,T_0608,FIGURE 25.38 An artists drawing of what Haumea and its moons might look like. The moons are drawn closer to Haumea than their actual orbits.,image,textbook_images/other_objects_in_the_solar_system_20423.png
L_0060,other objects in the solar system,T_0609,FIGURE 25.39 Makemake is a dwarf planet.,image,textbook_images/other_objects_in_the_solar_system_20424.png
L_0060,other objects in the solar system,T_0610,"FIGURE 25.40 Eris is the largest known dwarf planet, but its so far from the Sun that it wasnt discovered until 2005.",image,textbook_images/other_objects_in_the_solar_system_20425.png
L_0061,stars,T_0611,FIGURE 26.1 Orion has three stars that make up his belt. Orions belt is fairly easy to see in the night sky.,image,textbook_images/stars_20426.png
L_0061,stars,T_0619,FIGURE 26.2 Stars form in a nebula like this one in Orions sword.,image,textbook_images/stars_20427.png
L_0061,stars,T_0622,"FIGURE 26.3 A supernova, as seen by the Hubble Space Telescope.",image,textbook_images/stars_20428.png
L_0061,stars,T_0623,FIGURE 26.4 An artists depiction of a neutron star.,image,textbook_images/stars_20429.png
L_0062,galaxies,T_0626,FIGURE 26.6 These hot blue stars are in an open clus- ter known as the Jewel Box. The red star is a young red supergiant.,image,textbook_images/galaxies_20431.png
L_0062,galaxies,T_0626,"FIGURE 26.7 The globular cluster, M13, contains red and blue giant stars.",image,textbook_images/galaxies_20432.png
L_0062,galaxies,T_0628,FIGURE 26.8 The Andromeda Galaxy is the closest ma- jor galaxy to our own.,image,textbook_images/galaxies_20433.png
L_0062,galaxies,T_0628,FIGURE 26.9 The Pinwheel Galaxy is a spiral galaxy displaying prominent arms.,image,textbook_images/galaxies_20434.png
L_0062,galaxies,T_0629,FIGURE 26.10 M87 is an elliptical galaxy in the lower left of this image. How many elliptical galaxies do you see? Are there other types of galaxies displayed?,image,textbook_images/galaxies_20435.png
L_0062,galaxies,T_0632,"FIGURE 26.11 This irregular galaxy, NGC 55, is neither spiral nor elliptical.",image,textbook_images/galaxies_20436.png
L_0062,galaxies,T_0632,FIGURE 26.12 The Milky Way Galaxy in the night sky above Death Valley.,image,textbook_images/galaxies_20437.png
L_0068,types of rocks,T_0685,FIGURE 4.1 The rock cycle.,image,textbook_images/types_of_rocks_20468.png
L_0068,types of rocks,T_0685,FIGURE 4.2 Rocks contain many clues about the conditions in which they formed. The minerals contained within the rocks also contain geological information.,image,textbook_images/types_of_rocks_20469.png
L_0068,types of rocks,T_0686,FIGURE 4.3 Lava is molten rock. This lava will harden into an igneous rock.,image,textbook_images/types_of_rocks_20470.png
L_0068,types of rocks,T_0686,FIGURE 4.4 This sandstone is an example of a sedi- mentary rock. It formed when many small pieces of sand were cemented together to form a rock.,image,textbook_images/types_of_rocks_20471.png
L_0068,types of rocks,T_0687,FIGURE 4.5 This mica schist is a metamorphic rock. It was changed from a sedimentary rock like shale.,image,textbook_images/types_of_rocks_20472.png
L_0069,igneous rocks,T_0688,FIGURE 4.7 The Sierra Nevada of California are com- posed mainly of granite. These rocks are beautifully exposed in the Yosemite Valley.,image,textbook_images/igneous_rocks_20474.png
L_0069,igneous rocks,T_0688,"FIGURE 4.8 (A) This granite has more plagioclase feldspar than many granites. (B) Dior- ite has more dark-colored minerals than granite. (C) Gabbro. (D) Peridotite is an intrusive igneous rock with olivine and other mafic minerals. rapid cooling time does not allow time for large crystals to form. Some extrusive igneous rocks cool so rapidly that crystals do not develop at all. These form a glass, such as obsidian. Others, such as pumice, contain holes where gas bubbles were trapped in the lava. The holes make pumice so light that it actually floats in water. The most common extrusive igneous rock is basalt. It is the rock that makes up the ocean floor. Figure 4.10 shows four types of extrusive igneous rocks.",image,textbook_images/igneous_rocks_20475.png
L_0069,igneous rocks,T_0688,FIGURE 4.9 (A) Lava cools to form extrusive igneous rock. The rocks here are basalts. (B) The strange rock formations of Chiricahua National Monument in Arizona are formed of the extrusive igneous rock rhyolite.,image,textbook_images/igneous_rocks_20477.png
L_0069,igneous rocks,T_0688,"FIGURE 4.10 (A) This rhyolite is light colored. Few minerals are visible to the naked eye. (B) Andesite is darker than rhyolite. (C) Since basalt crystals are too small to see, the rock looks dark all over. (D) Komatiite is a very rare ultramafic rock. This rock is derived from the mantle.",image,textbook_images/igneous_rocks_20476.png
L_0069,igneous rocks,T_0689,"FIGURE 4.11 This sarcophagus is housed at the Vat- ican Museum. The rock is the igneous extrusive rock porphyry. Porphyry has large crystals because the magma began to cool slowly, then erupted.",image,textbook_images/igneous_rocks_20478.png
L_0070,sedimentary rocks,T_0690,"FIGURE 4.13 Cobbles, pebbles, and sands are the sediments that are seen on this beach.",image,textbook_images/sedimentary_rocks_20480.png
L_0071,metamorphic rocks,T_0694,FIGURE 4.14 (A) Hornfels is a rock that is created by contact metamorphism. (B) Hornfels is so hard that it can create peaks like the Matterhorn.,image,textbook_images/metamorphic_rocks_20481.png
L_0071,metamorphic rocks,T_0694,FIGURE 4.15 (A) Regional metamorphic rocks often display layering called foliation. (B) Re- gional metamorphism with high pressures and low temperatures can result in blue schist.,image,textbook_images/metamorphic_rocks_20482.png
L_0071,metamorphic rocks,T_0695,FIGURE 4.16 (A) Marble is a beautiful rock that is com- monly used for buildings. (B) Many of the great statues of the Renaissance were carved from marble. Michelangelo cre- ated this Moses between 1513 and 1515.,image,textbook_images/metamorphic_rocks_20483.png
L_0072,earths energy,T_0702,FIGURE 5.1 Kicking a soccer ball takes energy from your food and gives it to the soccer ball.,image,textbook_images/earths_energy_20484.png
L_0072,earths energy,T_0704,FIGURE 5.2 Rechargeable batteries are renewable because they can be refilled with energy. Is the energy they are refilled with always renewable?,image,textbook_images/earths_energy_20485.png
L_0073,nonrenewable energy resources,T_0712,FIGURE 5.3 Coal is a solid hydrocarbon formed from decaying plant material over millions of years.,image,textbook_images/nonrenewable_energy_resources_20486.png
L_0073,nonrenewable energy resources,T_0717,"FIGURE 5.4 This oil refinery processes crude oil into usable energy sources, such as gasoline.",image,textbook_images/nonrenewable_energy_resources_20487.png
L_0073,nonrenewable energy resources,T_0725,FIGURE 5.5 Burning fossil fuels releases pollutants into the air.,image,textbook_images/nonrenewable_energy_resources_20488.png
L_0073,nonrenewable energy resources,T_0728,FIGURE 5.6 Nuclear power plants like this one provide France with almost 80% of its electricity.,image,textbook_images/nonrenewable_energy_resources_20489.png
L_0074,renewable energy resources,T_0731,FIGURE 5.7 Solar energy is clean and renewable. So- lar panels are needed to collect the sun- light for use.,image,textbook_images/renewable_energy_resources_20490.png
L_0074,renewable energy resources,T_0735,FIGURE 5.8 A solar power tower is used to concen- trate the solar energy collected by many solar panels.,image,textbook_images/renewable_energy_resources_20491.png
L_0074,renewable energy resources,T_0735,FIGURE 5.9 Solar panels on top of a car could power the car. This technology is a long way from being practical.,image,textbook_images/renewable_energy_resources_20492.png
L_0074,renewable energy resources,T_0736,FIGURE 5.10 Glen Canyon Dam harnesses the power of flowing water to generate electricity.,image,textbook_images/renewable_energy_resources_20493.png
L_0074,renewable energy resources,T_0741,FIGURE 5.11 Winds are funneled through passes in mountain ranges. Altamont Pass in Cal- ifornia is the site of many wind turbines.,image,textbook_images/renewable_energy_resources_20494.png
L_0076,continental drift,T_0762,"FIGURE 6.7 Wegener used fossil evidence to sup- port his continental drift hypothesis. The fossils of these organisms are found on lands that are now far apart. Wegener suggested that when the organisms were alive, the lands were joined and the or- ganisms were living side-by-side.",image,textbook_images/continental_drift_20501.png
L_0076,continental drift,T_0763,"FIGURE 6.8 Earths magnetic field is like a magnet with its north pole near the geographic north pole and the south pole near the geographic south pole. Anywhere lavas have cooled, these magnetite crystals point to the magnetic poles. The little magnets point to where the north pole was when the lava cooled. Scientists can use this to figure out where the continents were at that time. This evidence clearly shows that the continents have moved. During Wegeners life, scientists did not know how the continents could move. Wegeners idea was nearly forgotten. But as more evidence mounted, new ideas came about.",image,textbook_images/continental_drift_20502.png
L_0079,stress in earths crust,T_0793,FIGURE 7.1 Stress caused these rocks to fracture.,image,textbook_images/stress_in_earths_crust_20523.png
L_0079,stress in earths crust,T_0794,FIGURE 7.2 This rock has undergone shearing. The pencil is pointing to a line. Stresses forced rock on either side of that line to go in opposite directions.,image,textbook_images/stress_in_earths_crust_20524.png
L_0079,stress in earths crust,T_0794,"FIGURE 7.3 With increasing stress, the rock deforms and may eventually fracture.",image,textbook_images/stress_in_earths_crust_20525.png
L_0079,stress in earths crust,T_0795,FIGURE 7.4 Layers of different types of rocks are ex- posed in this photo from Grand Staircase- Escalante National Monument. White lay- ers of limestone are hard and form cliffs. Red layers of shale are flakier and form slopes.,image,textbook_images/stress_in_earths_crust_20526.png
L_0079,stress in earths crust,T_0795,"FIGURE 7.5 Joints in this granite created a zone of weakness. The rock below the joints fell, leaving scars in this hillside.",image,textbook_images/stress_in_earths_crust_20527.png
L_0079,stress in earths crust,T_0796,"FIGURE 7.6 This is a geologic cross section of the Grand Staircase in Utah. A small fold, called an syncline, is revealed at the left of the diagram.",image,textbook_images/stress_in_earths_crust_20528.png
L_0079,stress in earths crust,T_0796,"FIGURE 7.7 The rock layers in the center right are tilted in one direction, forming a mono- cline.",image,textbook_images/stress_in_earths_crust_20529.png
L_0079,stress in earths crust,T_0796,"FIGURE 7.8 An anticline is a convex upward fold, as shown in (A). An anticline is well displayed in (B), which was taken at Calico Ghost Town, California.",image,textbook_images/stress_in_earths_crust_20530.png
L_0079,stress in earths crust,T_0796,"FIGURE 7.9 (A) A syncline is a concave downward fold. (B) This syncline is seen at Calico Ghost Town near Barstow, California.",image,textbook_images/stress_in_earths_crust_20533.png
L_0079,stress in earths crust,T_0796,FIGURE 7.10 Joints in boulders in the Arizona desert. The rock on either side of the joints has not moved.,image,textbook_images/stress_in_earths_crust_20531.png
L_0079,stress in earths crust,T_0796,"FIGURE 7.11 (A) This image shows a small fault. The black rock layer is not a line because a fault has broken it. Rock on each side of the fault has moved. (B) A large fault runs between the lighter colored rock on the left and the darker colored rock on the right. There has been so much movement along the fault that the darker rock doesnt resemble anything around it. the faults dip. If the fault dips at an angle, the fault is a dip-slip fault. Imagine you are standing on a road looking at the fault. The hanging wall is the rock that overlies the fault, while the footwall is beneath the fault. If you are walking along a fault, the hanging wall is above you and the footwall is where your feet would be. Miners often extract mineral resources along faults. They used to hang their lanterns above their heads. That is why these layers were called the hanging wall. In normal faults, the hanging wall drops down relative to the footwall. Normal faults are caused by tension that pulls the crust apart, causing the hanging wall to slide down. Normal faults can build huge mountain ranges in regions experiencing tension (Figure 7.12).",image,textbook_images/stress_in_earths_crust_20532.png
L_0079,stress in earths crust,T_0796,FIGURE 7.12 The Teton Range in Wyoming rose up along a normal fault.,image,textbook_images/stress_in_earths_crust_20534.png
L_0079,stress in earths crust,T_0798,"FIGURE 7.13 In this thrust fault, the rock on the left is thrust over the rock on the right.",image,textbook_images/stress_in_earths_crust_20535.png
L_0079,stress in earths crust,T_0798,FIGURE 7.14 Diagram of strike-slip faults.,image,textbook_images/stress_in_earths_crust_20536.png
L_0079,stress in earths crust,T_0798,FIGURE 7.15 The San Andreas Fault is visible from the air in some locations. This transform fault separates the Pacific plate on the west and the North American plate on the east.,image,textbook_images/stress_in_earths_crust_20537.png
L_0079,stress in earths crust,T_0800,"FIGURE 7.16 As India rams into Eurasia, the Himalaya Mountains rise.",image,textbook_images/stress_in_earths_crust_20538.png
L_0079,stress in earths crust,T_0802,FIGURE 7.17 The Himalayas.,image,textbook_images/stress_in_earths_crust_20539.png
L_0079,stress in earths crust,T_0802,"FIGURE 7.18 Cotopaxi is in the Andes Mountains of Ecuador. The 19,300 foot tall mountain is the highest active volcano in the world.",image,textbook_images/stress_in_earths_crust_20540.png
L_0079,stress in earths crust,T_0802,FIGURE 7.19 This diagram shows how a basin-and- range forms.,image,textbook_images/stress_in_earths_crust_20541.png
L_0086,igneous landforms and geothermal activ,T_0865,FIGURE 8.20 The Mono Craters in California are lava domes.,image,textbook_images/igneous_landforms_and_geothermal_activ_20584.png
L_0086,igneous landforms and geothermal activ,T_0866,"FIGURE 8.21 Lava erupts into the Pacific Ocean in Hawaii, creating new land.",image,textbook_images/igneous_landforms_and_geothermal_activ_20585.png
L_0086,igneous landforms and geothermal activ,T_0867,FIGURE 8.22 The granite intrusions that form the Sierra Nevada in California are well exposed.,image,textbook_images/igneous_landforms_and_geothermal_activ_20586.png
L_0087,weathering,T_0872,FIGURE 9.1 A hard winter has damaged this road.,image,textbook_images/weathering_20588.png
L_0087,weathering,T_0873,"FIGURE 9.2 Diagram showing ice wedging. Ice wedging happens because water expands as it goes from liquid to solid. When the temperature is warm, water works its way into cracks in rock. When the temperature cools below freezing, the water turns to ice and expands. The ice takes up more space. Over time, this wedges the rock apart. Ice wedging is very effective at weathering. You can find large piles of broken rock at the base of a slope. These rocks were broken up by ice wedging. Once loose, they tumbled down the slope.",image,textbook_images/weathering_20589.png
L_0087,weathering,T_0874,FIGURE 9.3 Rocks on a beach are worn down by abrasion as passing waves cause them to strike each other.,image,textbook_images/weathering_20590.png
L_0087,weathering,T_0881,FIGURE 9.4 Iron ore oxidizes readily.,image,textbook_images/weathering_20591.png
L_0087,weathering,T_0881,FIGURE 9.5 Devils Tower shows differential weather- ing. Hard rock from inside a volcano makes up the tower.,image,textbook_images/weathering_20592.png
L_0089,acid rain,T_0901,"FIGURE 1.1 Tall smokestacks allow the emissions to rise high into the atmosphere and travel up to 1,000 km (600 miles) downwind.",image,textbook_images/acid_rain_20602.png
L_0089,acid rain,T_0901,FIGURE 1.2 Pollutants are deposited dry or in precipi- tation.,image,textbook_images/acid_rain_20603.png
L_0089,acid rain,T_0901,FIGURE 1.3,image,textbook_images/acid_rain_20604.png
L_0089,acid rain,T_0902,FIGURE 1.4,image,textbook_images/acid_rain_20605.png
L_0090,adaptation and evolution of populations,T_0905,FIGURE 1.1 Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/186577,image,textbook_images/adaptation_and_evolution_of_populations_20606.png
L_0092,agriculture and human population growth,T_0909,"FIGURE 1.1 In a hunter-gatherer society, people relied on the resources they could find where they lived.",image,textbook_images/agriculture_and_human_population_growth_20607.png
L_0092,agriculture and human population growth,T_0910,FIGURE 1.2,image,textbook_images/agriculture_and_human_population_growth_20608.png
L_0092,agriculture and human population growth,T_0910,FIGURE 1.3 Farming has increasingly depended on machines. Such advanced farming prac- tices allow one farmer to feed many more people than in the past.,image,textbook_images/agriculture_and_human_population_growth_20609.png
L_0092,agriculture and human population growth,T_0911,"FIGURE 1.4 Early in the Industrial Revolution, large numbers of people who had been freed from food production were available to work in factories.",image,textbook_images/agriculture_and_human_population_growth_20610.png
L_0092,agriculture and human population growth,T_0912,FIGURE 1.5,image,textbook_images/agriculture_and_human_population_growth_20611.png
L_0094,air quality,T_0921,FIGURE 1.1,image,textbook_images/air_quality_20614.png
L_0094,air quality,T_0922,FIGURE 1.2,image,textbook_images/air_quality_20615.png
L_0095,asteroids,T_0926,FIGURE 1.1,image,textbook_images/asteroids_20616.png
L_0095,asteroids,T_0926,FIGURE 1.2,image,textbook_images/asteroids_20617.png
L_0095,asteroids,T_0927,FIGURE 1.3,image,textbook_images/asteroids_20618.png
L_0095,asteroids,T_0928,FIGURE 1.4,image,textbook_images/asteroids_20619.png
L_0096,availability of natural resources,T_0932,FIGURE 1.1,image,textbook_images/availability_of_natural_resources_20620.png
L_0096,availability of natural resources,T_0934,FIGURE 1.2,image,textbook_images/availability_of_natural_resources_20621.png
L_0096,availability of natural resources,T_0934,FIGURE 1.3,image,textbook_images/availability_of_natural_resources_20622.png
L_0098,bathymetric evidence for seafloor spreading,T_0939,FIGURE 1.1,image,textbook_images/bathymetric_evidence_for_seafloor_spreading_20626.png
L_0098,bathymetric evidence for seafloor spreading,T_0941,FIGURE 1.2,image,textbook_images/bathymetric_evidence_for_seafloor_spreading_20627.png
L_0099,big bang,T_0943,FIGURE 1.1,image,textbook_images/big_bang_20629.png
L_0099,big bang,T_0945,FIGURE 1.2,image,textbook_images/big_bang_20630.png
L_0103,carbon cycle and climate,T_0961,"FIGURE 1.1 The carbon cycle shows where a carbon atom might be found. The black num- bers indicate how much carbon is stored in various reservoirs, in billions of tons (""GtC"" stands for gigatons of carbon). The purple numbers indicate how much carbon moves between reservoirs each year. The sediments, as defined in this diagram, do not include the ~70 million GtC of carbonate rock and kerogen.",image,textbook_images/carbon_cycle_and_climate_20641.png
L_0103,carbon cycle and climate,T_0964,FIGURE 1.2,image,textbook_images/carbon_cycle_and_climate_20642.png
L_0103,carbon cycle and climate,T_0965,FIGURE 1.3,image,textbook_images/carbon_cycle_and_climate_20643.png
L_0104,causes of air pollution,T_0968,FIGURE 1.1,image,textbook_images/causes_of_air_pollution_20644.png
L_0104,causes of air pollution,T_0970,FIGURE 1.2,image,textbook_images/causes_of_air_pollution_20645.png
L_0104,causes of air pollution,T_0970,FIGURE 1.3,image,textbook_images/causes_of_air_pollution_20646.png
L_0106,characteristics and origins of life,T_0979,FIGURE 1.1,image,textbook_images/characteristics_and_origins_of_life_20649.png
L_0106,characteristics and origins of life,T_0979,FIGURE 1.2,image,textbook_images/characteristics_and_origins_of_life_20650.png
L_0107,chemical bonding,T_0980,FIGURE 1.1,image,textbook_images/chemical_bonding_20651.png
L_0107,chemical bonding,T_0980,FIGURE 1.2,image,textbook_images/chemical_bonding_20652.png
L_0107,chemical bonding,T_0980,FIGURE 1.3,image,textbook_images/chemical_bonding_20653.png
L_0107,chemical bonding,T_0980,"FIGURE 1.4 Water is a polar molecule. Because the oxygen atom has the electrons most of the time, the hydrogen side (blue) of the molecule has a slightly positive charge while the oxygen side (red) has a slightly negative charge.",image,textbook_images/chemical_bonding_20654.png
L_0109,cleaning up groundwater,T_0992,FIGURE 1.1 Test wells are drilled to monitor groundwater pollution.,image,textbook_images/cleaning_up_groundwater_20660.png
L_0110,climate change in earth history,T_0995,FIGURE 1.1,image,textbook_images/climate_change_in_earth_history_20661.png
L_0110,climate change in earth history,T_0995,FIGURE 1.2,image,textbook_images/climate_change_in_earth_history_20662.png
L_0111,climate zones and biomes,T_0999,FIGURE 1.1,image,textbook_images/climate_zones_and_biomes_20663.png
L_0113,coal power,T_1012,FIGURE 1.1 Bituminous coal is a sedimentary rock.,image,textbook_images/coal_power_20667.png
L_0113,coal power,T_1015,FIGURE 1.2,image,textbook_images/coal_power_20668.png
L_0114,coastal pollution,T_1016,FIGURE 1.1,image,textbook_images/coastal_pollution_20671.png
L_0116,comets,T_1025,FIGURE 1.1,image,textbook_images/comets_20676.png
L_0118,conserving water,T_1033,FIGURE 1.1,image,textbook_images/conserving_water_20679.png
L_0119,continental drift,T_1035,FIGURE 1.1,image,textbook_images/continental_drift_20680.png
L_0119,continental drift,T_1035,FIGURE 1.2,image,textbook_images/continental_drift_20681.png
L_0120,coriolis effect,T_1036,FIGURE 1.1,image,textbook_images/coriolis_effect_20682.png
L_0121,correlation using relative ages,T_1039,FIGURE 1.1,image,textbook_images/correlation_using_relative_ages_20683.png
L_0121,correlation using relative ages,T_1040,FIGURE 1.2 The white clay is a key bed that marks the Cretaceous-Tertiary Boundary.,image,textbook_images/correlation_using_relative_ages_20684.png
L_0123,deep ocean currents,T_1045,FIGURE 1.1,image,textbook_images/deep_ocean_currents_20687.png
L_0123,deep ocean currents,T_1046,FIGURE 1.2,image,textbook_images/deep_ocean_currents_20688.png
L_0124,determining relative ages,T_1047,FIGURE 1.1,image,textbook_images/determining_relative_ages_20689.png
L_0127,distance between stars,T_1054,FIGURE 1.1 Parallax is used to measure the distance to stars that are relatively nearby.,image,textbook_images/distance_between_stars_20691.png
L_0128,distribution of water on earth,T_1056,FIGURE 1.1,image,textbook_images/distribution_of_water_on_earth_20692.png
L_0131,dwarf planets,T_1064,"FIGURE 1.1 In 1992, Plutos orbit was recognized to be part of the Kuiper belt. With more than 200 million Kuiper belt objects, Pluto has failed the test of clearing other bodies out its orbit.",image,textbook_images/dwarf_planets_20696.png
L_0131,dwarf planets,T_1065,FIGURE 1.2 This composite image compares the size of the dwarf planet Ceres to Earth and the Moon.,image,textbook_images/dwarf_planets_20697.png
L_0131,dwarf planets,T_1066,FIGURE 1.3,image,textbook_images/dwarf_planets_20698.png
L_0132,early atmosphere and oceans,T_1068,FIGURE 1.1 The gases that create a comets tail can become part of the atmosphere of a planet.,image,textbook_images/early_atmosphere_and_oceans_20699.png
L_0132,early atmosphere and oceans,T_1073,FIGURE 1.2,image,textbook_images/early_atmosphere_and_oceans_20700.png
L_0140,earths core,T_1099,FIGURE 1.1 An iron meteorite is the closest thing to the Earths core that we can hold in our hands.,image,textbook_images/earths_core_20715.png
L_0144,earths magnetic field,T_1115,FIGURE 1.1,image,textbook_images/earths_magnetic_field_20720.png
L_0148,eclipses,T_1123,"FIGURE 1.1 A solar eclipse, not to scale.",image,textbook_images/eclipses_20727.png
L_0148,eclipses,T_1123,FIGURE 1.2,image,textbook_images/eclipses_20728.png
L_0148,eclipses,T_1124,FIGURE 1.3 The Moons shadow in a solar eclipse covers a very small area.,image,textbook_images/eclipses_20729.png
L_0148,eclipses,T_1124,FIGURE 1.4 A lunar eclipse.,image,textbook_images/eclipses_20730.png
L_0150,effect of latitude on climate,T_1128,FIGURE 1.1,image,textbook_images/effect_of_latitude_on_climate_20733.png
L_0151,effects of air pollution on human health,T_1131,FIGURE 1.1 A lung tumor is highlighted in this illustra- tion.,image,textbook_images/effects_of_air_pollution_on_human_health_20734.png
L_0154,electromagnetic energy in the atmosphere,T_1139,FIGURE 1.1 The electromagnetic spectrum; short wavelengths are the fastest with the high- est energy.,image,textbook_images/electromagnetic_energy_in_the_atmosphere_20740.png
L_0154,electromagnetic energy in the atmosphere,T_1139,FIGURE 1.2 A prism breaks apart white light.,image,textbook_images/electromagnetic_energy_in_the_atmosphere_20741.png
L_0155,energy conservation,T_1141,FIGURE 1.1,image,textbook_images/energy_conservation_20742.png
L_0155,energy conservation,T_1142,FIGURE 1.2 A: One way is to look for this ENERGY STAR logo (Figure 1.3).,image,textbook_images/energy_conservation_20743.png
L_0155,energy conservation,T_1142,FIGURE 1.3,image,textbook_images/energy_conservation_20744.png
L_0156,energy from biomass,T_1143,FIGURE 1.1,image,textbook_images/energy_from_biomass_20745.png
L_0157,energy use,T_1147,FIGURE 1.1,image,textbook_images/energy_use_20746.png
L_0157,energy use,T_1147,FIGURE 1.2,image,textbook_images/energy_use_20747.png
L_0158,environmental impacts of mining,T_1148,FIGURE 1.1,image,textbook_images/environmental_impacts_of_mining_20748.png
L_0161,exoplanets,T_1158,"FIGURE 1.1 The extrasolar planet Fomalhaut is sur- rounded by a large disk of gas. The disk is not centered on the planet, suggesting that another planet may be pulling on the gas as well.",image,textbook_images/exoplanets_20755.png
L_0162,expansion of the universe,T_1160,FIGURE 1.1,image,textbook_images/expansion_of_the_universe_20756.png
L_0162,expansion of the universe,T_1161,FIGURE 1.2,image,textbook_images/expansion_of_the_universe_20757.png
L_0165,faults,T_1170,"FIGURE 1.1 Joints in rocks at Joshua Tree National Park, in California.",image,textbook_images/faults_20764.png
L_0165,faults,T_1171,FIGURE 1.2 Faults are easy to recognize as they cut across bedded rocks.,image,textbook_images/faults_20765.png
L_0165,faults,T_1172,FIGURE 1.3,image,textbook_images/faults_20766.png
L_0165,faults,T_1172,FIGURE 1.4,image,textbook_images/faults_20767.png
L_0165,faults,T_1173,FIGURE 1.5,image,textbook_images/faults_20768.png
L_0167,flooding,T_1179,FIGURE 1.1,image,textbook_images/flooding_20774.png
L_0167,flooding,T_1179,FIGURE 1.2,image,textbook_images/flooding_20775.png
L_0167,flooding,T_1180,FIGURE 1.3,image,textbook_images/flooding_20776.png
L_0167,flooding,T_1183,FIGURE 1.4,image,textbook_images/flooding_20777.png
L_0169,folds,T_1187,FIGURE 1.1,image,textbook_images/folds_20779.png
L_0169,folds,T_1189,FIGURE 1.2,image,textbook_images/folds_20780.png
L_0169,folds,T_1189,FIGURE 1.3,image,textbook_images/folds_20781.png
L_0169,folds,T_1189,"FIGURE 1.4 Basins can be enormous. This is a ge- ologic map of the Michigan Basin, which is centered in the state of Michigan but extends into four other states and a Cana- dian province.",image,textbook_images/folds_20782.png
L_0169,folds,T_1189,FIGURE 1.5,image,textbook_images/folds_20783.png
L_0170,formation of earth,T_1193,"FIGURE 1.1 Earths interior: Inner core, outer core, mantle, and crust.",image,textbook_images/formation_of_earth_20784.png
L_0170,formation of earth,T_1195,FIGURE 1.2 The Allende Meteorite is a carbona- ceous chondrite that struck Earth in 1969. The calcium-aluminum-rich inclusions are fragments of the earliest solar system.,image,textbook_images/formation_of_earth_20785.png
L_0171,formation of the moon,T_1198,FIGURE 1.1,image,textbook_images/formation_of_the_moon_20786.png
L_0172,formation of the sun and planets,T_1201,FIGURE 1.1,image,textbook_images/formation_of_the_sun_and_planets_20787.png
L_0173,fossil fuel formation,T_1202,FIGURE 1.1 This wetland may look something like an ancient coal-forming swamp.,image,textbook_images/fossil_fuel_formation_20788.png
L_0173,fossil fuel formation,T_1202,FIGURE 1.2,image,textbook_images/fossil_fuel_formation_20789.png
L_0174,fossil fuel reserves,T_1204,FIGURE 1.1 Worldwide oil reserves.,image,textbook_images/fossil_fuel_reserves_20790.png
L_0174,fossil fuel reserves,T_1204,FIGURE 1.2,image,textbook_images/fossil_fuel_reserves_20791.png
L_0175,fresh water ecosystems,T_1206,FIGURE 1.1,image,textbook_images/fresh_water_ecosystems_20792.png
L_0175,fresh water ecosystems,T_1208,FIGURE 1.2,image,textbook_images/fresh_water_ecosystems_20793.png
L_0175,fresh water ecosystems,T_1210,FIGURE 1.3 A swamp is characterized by trees in still water.,image,textbook_images/fresh_water_ecosystems_20794.png
L_0176,galaxies,T_1212,FIGURE 1.1,image,textbook_images/galaxies_20795.png
L_0176,galaxies,T_1212,FIGURE 1.2,image,textbook_images/galaxies_20796.png
L_0176,galaxies,T_1213,"FIGURE 1.3 The large, reddish-yellow object in the middle of this figure is a typical elliptical galaxy. What other types of galaxies can you find in the figure?",image,textbook_images/galaxies_20797.png
L_0176,galaxies,T_1213,FIGURE 1.4 Astronomers believe that these dusty el- liptical galaxies form when two galaxies of similar size collide.,image,textbook_images/galaxies_20798.png
L_0176,galaxies,T_1214,FIGURE 1.5,image,textbook_images/galaxies_20799.png
L_0177,geologic time scale,T_1216,FIGURE 1.1 The geologic time scale is based on rela- tive ages. No actual ages were placed on the original time scale. Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/186648,image,textbook_images/geologic_time_scale_20800.png
L_0178,geological stresses,T_1218,FIGURE 1.1,image,textbook_images/geological_stresses_20801.png
L_0178,geological stresses,T_1218,FIGURE 1.2,image,textbook_images/geological_stresses_20802.png
L_0178,geological stresses,T_1219,"FIGURE 1.3 With increasing stress, the rock under- goes: (1) elastic deformation, (2) plastic deformation, and (3) fracture.",image,textbook_images/geological_stresses_20803.png
L_0179,geothermal power,T_1220,FIGURE 1.1 A geothermal energy plant in Iceland. Ice- land gets about one fourth of its electricity from geothermal sources.,image,textbook_images/geothermal_power_20804.png
L_0180,glaciers,T_1222,FIGURE 1.1,image,textbook_images/glaciers_20805.png
L_0180,glaciers,T_1225,FIGURE 1.2,image,textbook_images/glaciers_20806.png
L_0180,glaciers,T_1227,FIGURE 1.3,image,textbook_images/glaciers_20807.png
L_0181,global warming,T_1230,FIGURE 1.1 Recent temperature increases show how much temperature has risen since the Industrial Revolution began.,image,textbook_images/global_warming_20808.png
L_0181,global warming,T_1232,FIGURE 1.2,image,textbook_images/global_warming_20809.png
L_0181,global warming,T_1232,FIGURE 1.3,image,textbook_images/global_warming_20810.png
L_0181,global warming,T_1232,FIGURE 1.4,image,textbook_images/global_warming_20811.png
L_0183,gravity in the solar system,T_1238,FIGURE 1.1,image,textbook_images/gravity_in_the_solar_system_20814.png
L_0184,greenhouse effect,T_1240,FIGURE 1.1 The Earths heat budget shows the amount of energy coming into and going out of the Earths system and the im- portance of the greenhouse effect. The numbers are the amount of energy that is found in one square meter of that location.,image,textbook_images/greenhouse_effect_20815.png
L_0185,groundwater aquifers,T_1242,FIGURE 1.1,image,textbook_images/groundwater_aquifers_20816.png
L_0185,groundwater aquifers,T_1245,FIGURE 1.2,image,textbook_images/groundwater_aquifers_20817.png
L_0185,groundwater aquifers,T_1245,FIGURE 1.3,image,textbook_images/groundwater_aquifers_20818.png
L_0185,groundwater aquifers,T_1245,FIGURE 1.4,image,textbook_images/groundwater_aquifers_20819.png
L_0186,groundwater depletion,T_1247,FIGURE 1.1,image,textbook_images/groundwater_depletion_20820.png
L_0187,groundwater pollution,T_1251,FIGURE 1.1 Tanks may break and leak whatever tox- ins they contain into the ground.,image,textbook_images/groundwater_pollution_20824.png
L_0188,growth of human populations,T_1254,FIGURE 1.1,image,textbook_images/growth_of_human_populations_20825.png
L_0188,growth of human populations,T_1254,FIGURE 1.2 Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/186839,image,textbook_images/growth_of_human_populations_20826.png
L_0191,heat transfer in the atmosphere,T_1258,FIGURE 1.1 Thermal convection where the heat source is at the bottom and there is a ceiling at the top.,image,textbook_images/heat_transfer_in_the_atmosphere_20827.png
L_0192,heat waves and droughts,T_1261,FIGURE 1.1,image,textbook_images/heat_waves_and_droughts_20828.png
L_0196,hot springs and geysers,T_1278,"FIGURE 1.1 Even in winter, the water in this hot spring in Yellowstone doesnt freeze.",image,textbook_images/hot_springs_and_geysers_20837.png
L_0196,hot springs and geysers,T_1279,FIGURE 1.2,image,textbook_images/hot_springs_and_geysers_20838.png
L_0197,how fossilization creates fossils,T_1280,FIGURE 1.1,image,textbook_images/how_fossilization_creates_fossils_20839.png
L_0197,how fossilization creates fossils,T_1282,FIGURE 1.2 Hyenas eating an antelope. Will the ante- lope in this photo become a fossil?,image,textbook_images/how_fossilization_creates_fossils_20840.png
L_0197,how fossilization creates fossils,T_1282,FIGURE 1.3 Fossil shell that has been attacked by a boring sponge.,image,textbook_images/how_fossilization_creates_fossils_20841.png
L_0197,how fossilization creates fossils,T_1283,FIGURE 1.4,image,textbook_images/how_fossilization_creates_fossils_20842.png
L_0197,how fossilization creates fossils,T_1285,"FIGURE 1.5 organisms can be buried by mudslides, volcanic ash, or covered by sand in a sandstorm (Figure 1.6). Skeletons can be covered by mud in lakes, swamps, or bogs.",image,textbook_images/how_fossilization_creates_fossils_20843.png
L_0197,how fossilization creates fossils,T_1285,FIGURE 1.6,image,textbook_images/how_fossilization_creates_fossils_20844.png
L_0197,how fossilization creates fossils,T_1286,FIGURE 1.7 of past climates and geological conditions as well.,image,textbook_images/how_fossilization_creates_fossils_20845.png
L_0197,how fossilization creates fossils,T_1287,FIGURE 1.8,image,textbook_images/how_fossilization_creates_fossils_20846.png
L_0198,how ocean currents moderate climate,T_1288,"FIGURE 1.1 London, England in winter.",image,textbook_images/how_ocean_currents_moderate_climate_20847.png
L_0198,how ocean currents moderate climate,T_1288,FIGURE 1.2,image,textbook_images/how_ocean_currents_moderate_climate_20848.png
L_0199,human evolution,T_1291,FIGURE 1.1,image,textbook_images/human_evolution_20849.png
L_0199,human evolution,T_1291,FIGURE 1.2,image,textbook_images/human_evolution_20850.png
L_0201,igneous rocks,T_1301,FIGURE 1.1,image,textbook_images/igneous_rocks_20853.png
L_0202,impact of continued global warming,T_1303,FIGURE 1.1,image,textbook_images/impact_of_continued_global_warming_20854.png
L_0202,impact of continued global warming,T_1304,FIGURE 1.2 Temperature changes over Antarctica.,image,textbook_images/impact_of_continued_global_warming_20855.png
L_0202,impact of continued global warming,T_1304,"FIGURE 1.3 Although scientists do not all agree, hurricanes are likely to become more severe and possibly more frequent. Tropical and subtropical insects will expand their ranges, resulting in the spread of tropical diseases such as malaria, encephalitis, yellow fever, and dengue fever.",image,textbook_images/impact_of_continued_global_warming_20856.png
L_0203,impacts of hazardous waste,T_1305,FIGURE 1.1,image,textbook_images/impacts_of_hazardous_waste_20857.png
L_0203,impacts of hazardous waste,T_1309,FIGURE 1.2,image,textbook_images/impacts_of_hazardous_waste_20858.png
L_0204,importance of the atmosphere,T_1311,FIGURE 1.1,image,textbook_images/importance_of_the_atmosphere_20859.png
L_0204,importance of the atmosphere,T_1314,FIGURE 1.2,image,textbook_images/importance_of_the_atmosphere_20860.png
L_0205,importance of the oceans,T_1320,FIGURE 1.1,image,textbook_images/importance_of_the_oceans_20861.png
L_0206,influences on weathering,T_1321,FIGURE 1.1,image,textbook_images/influences_on_weathering_20862.png
L_0206,influences on weathering,T_1323,"FIGURE 1.2 Wet, warm tropical areas have the most weathering.",image,textbook_images/influences_on_weathering_20863.png
L_0207,inner vs. outer planets,T_1324,FIGURE 1.1,image,textbook_images/inner_vs._outer_planets_20864.png
L_0207,inner vs. outer planets,T_1325,FIGURE 1.2,image,textbook_images/inner_vs._outer_planets_20865.png
L_0211,introduction to groundwater,T_1341,FIGURE 1.1,image,textbook_images/introduction_to_groundwater_20870.png
L_0212,intrusive and extrusive igneous rocks,T_1343,FIGURE 1.1,image,textbook_images/intrusive_and_extrusive_igneous_rocks_20871.png
L_0212,intrusive and extrusive igneous rocks,T_1343,FIGURE 1.2,image,textbook_images/intrusive_and_extrusive_igneous_rocks_20872.png
L_0212,intrusive and extrusive igneous rocks,T_1344,FIGURE 1.3,image,textbook_images/intrusive_and_extrusive_igneous_rocks_20873.png
L_0212,intrusive and extrusive igneous rocks,T_1344,"FIGURE 1.4 case, the magma cooled enough to form some crystals before erupting. Once erupted, the rest of the lava cooled rapidly. This is called porphyritic texture.",image,textbook_images/intrusive_and_extrusive_igneous_rocks_20874.png
L_0212,intrusive and extrusive igneous rocks,T_1344,FIGURE 1.5,image,textbook_images/intrusive_and_extrusive_igneous_rocks_20875.png
L_0213,jupiter,T_1346,FIGURE 1.1,image,textbook_images/jupiter_20876.png
L_0213,jupiter,T_1346,FIGURE 1.2 Jupiters structure.,image,textbook_images/jupiter_20877.png
L_0213,jupiter,T_1347,FIGURE 1.3,image,textbook_images/jupiter_20878.png
L_0213,jupiter,T_1348,FIGURE 1.4,image,textbook_images/jupiter_20879.png
L_0215,landforms from glacial erosion and deposition,T_1360,FIGURE 1.1,image,textbook_images/landforms_from_glacial_erosion_and_deposition_20887.png
L_0215,landforms from glacial erosion and deposition,T_1360,FIGURE 1.2,image,textbook_images/landforms_from_glacial_erosion_and_deposition_20888.png
L_0215,landforms from glacial erosion and deposition,T_1360,FIGURE 1.3,image,textbook_images/landforms_from_glacial_erosion_and_deposition_20889.png
L_0215,landforms from glacial erosion and deposition,T_1360,FIGURE 1.4,image,textbook_images/landforms_from_glacial_erosion_and_deposition_20890.png
L_0215,landforms from glacial erosion and deposition,T_1360,FIGURE 1.5,image,textbook_images/landforms_from_glacial_erosion_and_deposition_20891.png
L_0215,landforms from glacial erosion and deposition,T_1362,FIGURE 1.6 A large boulder dropped by a glacier is a glacial erratic.,image,textbook_images/landforms_from_glacial_erosion_and_deposition_20892.png
L_0215,landforms from glacial erosion and deposition,T_1363,"FIGURE 1.7 The long, dark lines on a glacier in Alaska are medial and lateral moraines.",image,textbook_images/landforms_from_glacial_erosion_and_deposition_20893.png
L_0215,landforms from glacial erosion and deposition,T_1364,FIGURE 1.8,image,textbook_images/landforms_from_glacial_erosion_and_deposition_20894.png
L_0216,landforms from groundwater erosion and deposition,T_1367,"FIGURE 1.1 When water sinks into the ground, it be- comes groundwater.",image,textbook_images/landforms_from_groundwater_erosion_and_deposition_20895.png
L_0216,landforms from groundwater erosion and deposition,T_1367,FIGURE 1.2,image,textbook_images/landforms_from_groundwater_erosion_and_deposition_20896.png
L_0216,landforms from groundwater erosion and deposition,T_1368,FIGURE 1.3,image,textbook_images/landforms_from_groundwater_erosion_and_deposition_20897.png
L_0216,landforms from groundwater erosion and deposition,T_1368,FIGURE 1.4,image,textbook_images/landforms_from_groundwater_erosion_and_deposition_20898.png
L_0217,lithification of sedimentary rocks,T_1369,FIGURE 1.1,image,textbook_images/lithification_of_sedimentary_rocks_20899.png
L_0221,location and direction,T_1381,FIGURE 1.1,image,textbook_images/location_and_direction_20907.png
L_0221,location and direction,T_1386,FIGURE 1.2,image,textbook_images/location_and_direction_20908.png
L_0222,long term climate change,T_1388,FIGURE 1.1,image,textbook_images/long_term_climate_change_20909.png
L_0222,long term climate change,T_1390,FIGURE 1.2,image,textbook_images/long_term_climate_change_20910.png
L_0222,long term climate change,T_1391,FIGURE 1.3,image,textbook_images/long_term_climate_change_20911.png
L_0224,magnetic evidence for seafloor spreading,T_1393,FIGURE 1.1 Magnetic polarity is normal at the ridge crest but reversed in symmetrical patterns away from the ridge center. This normal and reversed pattern continues across the seafloor.,image,textbook_images/magnetic_evidence_for_seafloor_spreading_20912.png
L_0224,magnetic evidence for seafloor spreading,T_1394,FIGURE 1.2,image,textbook_images/magnetic_evidence_for_seafloor_spreading_20913.png
L_0225,magnetic polarity evidence for continental drift,T_1395,FIGURE 1.1 Magnetite crystals.,image,textbook_images/magnetic_polarity_evidence_for_continental_drift_20914.png
L_0225,magnetic polarity evidence for continental drift,T_1396,FIGURE 1.2 Earths current north magnetic pole is in northern Canada.,image,textbook_images/magnetic_polarity_evidence_for_continental_drift_20915.png
L_0225,magnetic polarity evidence for continental drift,T_1396,FIGURE 1.3,image,textbook_images/magnetic_polarity_evidence_for_continental_drift_20916.png
L_0225,magnetic polarity evidence for continental drift,T_1398,FIGURE 1.4 Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/186134,image,textbook_images/magnetic_polarity_evidence_for_continental_drift_20917.png
L_0226,maps,T_1399,FIGURE 1.1,image,textbook_images/maps_20918.png
L_0226,maps,T_1400,FIGURE 1.2,image,textbook_images/maps_20919.png
L_0226,maps,T_1400,FIGURE 1.3,image,textbook_images/maps_20920.png
L_0227,mars,T_1402,FIGURE 1.1,image,textbook_images/mars_20921.png
L_0227,mars,T_1405,FIGURE 1.2,image,textbook_images/mars_20922.png
L_0227,mars,T_1405,FIGURE 1.3,image,textbook_images/mars_20923.png
L_0227,mars,T_1405,FIGURE 1.4 The north polar ice cap on Mars.,image,textbook_images/mars_20924.png
L_0227,mars,T_1406,"FIGURE 1.5 The Mars Science Laboratory was launched on November 26, 2011 and will search for any evidence that the Red Planet was once capable of supporting life. Curiosity is a car-sized rover that will scour the red planet for clues after it lands in August 2012.",image,textbook_images/mars_20925.png
L_0229,measuring earthquake magnitude,T_1409,FIGURE 1.1,image,textbook_images/measuring_earthquake_magnitude_20926.png
L_0230,mechanical weathering,T_1411,FIGURE 1.1 Ice wedging.,image,textbook_images/mechanical_weathering_20927.png
L_0230,mechanical weathering,T_1412,FIGURE 1.2 Rocks on a beach are worn down by abrasion as passing waves cause them to strike each other.,image,textbook_images/mechanical_weathering_20928.png
L_0230,mechanical weathering,T_1414,FIGURE 1.3,image,textbook_images/mechanical_weathering_20929.png
L_0231,mercury,T_1415,FIGURE 1.1,image,textbook_images/mercury_20930.png
L_0231,mercury,T_1417,FIGURE 1.2,image,textbook_images/mercury_20931.png
L_0231,mercury,T_1418,"FIGURE 1.3 Mercury contains a thin crust, a mantle, and a large, liquid core that is rich in iron. Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/186936",image,textbook_images/mercury_20932.png
L_0232,mercury pollution,T_1420,FIGURE 1.1,image,textbook_images/mercury_pollution_20933.png
L_0232,mercury pollution,T_1421,FIGURE 1.2 Methyl mercury bioaccumulates up the food chain.,image,textbook_images/mercury_pollution_20934.png
L_0233,mesosphere,T_1423,"FIGURE 1.1 Although the mesosphere has extremely low pressure, it occasionally has clouds. The clouds in the photo are mesopheric clouds called noctilucent clouds.",image,textbook_images/mesosphere_20936.png
L_0237,metamorphic rocks,T_1432,FIGURE 1.1,image,textbook_images/metamorphic_rocks_20939.png
L_0238,meteors,T_1435,FIGURE 1.1 A meteor streaks across the sky.,image,textbook_images/meteors_20940.png
L_0238,meteors,T_1435,FIGURE 1.2 A lunar meteorite originates on the Moon and strikes Earth. Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/186958,image,textbook_images/meteors_20941.png
L_0240,milky way,T_1439,FIGURE 1.1,image,textbook_images/milky_way_20944.png
L_0240,milky way,T_1439,FIGURE 1.2,image,textbook_images/milky_way_20945.png
L_0246,moon,T_1473,FIGURE 1.1,image,textbook_images/moon_20973.png
L_0246,moon,T_1474,FIGURE 1.2,image,textbook_images/moon_20974.png
L_0246,moon,T_1475,FIGURE 1.3,image,textbook_images/moon_20975.png
L_0246,moon,T_1475,"FIGURE 1.4 The Moons internal structure shows a small metallic core (yellow), a primi- tive mantle (orange), a depleted mantle (blue), and a crust (gray). The crust is composed of igneous rock rich in the elements oxygen, silicon, magnesium, and aluminum. The crust is about 60 km thick on the near side of the Moon and about 100 km thick on the far side.",image,textbook_images/moon_20976.png
L_0248,natural gas power,T_1481,FIGURE 1.1,image,textbook_images/natural_gas_power_20980.png
L_0248,natural gas power,T_1483,FIGURE 1.2 A natural gas drill rig in Texas.,image,textbook_images/natural_gas_power_20981.png
L_0249,natural resource conservation,T_1484,FIGURE 1.1 Recycling can help conserve natural re- sources.,image,textbook_images/natural_resource_conservation_20982.png
L_0250,neptune,T_1485,FIGURE 1.1,image,textbook_images/neptune_20983.png
L_0250,neptune,T_1486,FIGURE 1.2,image,textbook_images/neptune_20984.png
L_0250,neptune,T_1487,FIGURE 1.3 Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/186951,image,textbook_images/neptune_20985.png
L_0251,nitrogen cycle in ecosystems,T_1489,FIGURE 1.1,image,textbook_images/nitrogen_cycle_in_ecosystems_20986.png
L_0251,nitrogen cycle in ecosystems,T_1489,"FIGURE 1.2 The nitrogen cycle. Nitrogen-fixing bacteria either live free or in a symbiotic relationship with leguminous plants (peas, beans, peanuts). The symbiotic bacteria use carbohydrates from the plant to produce ammonia that is useful to the plant. Plants use this fixed nitrogen to build amino acids, nucleic acids (DNA, RNA), and chlorophyll. When these legumes die, the fixed nitrogen they contain fertilizes the soil.",image,textbook_images/nitrogen_cycle_in_ecosystems_20987.png
L_0252,non renewable energy resources,T_1492,FIGURE 1.1,image,textbook_images/non_renewable_energy_resources_20988.png
L_0252,non renewable energy resources,T_1495,FIGURE 1.2,image,textbook_images/non_renewable_energy_resources_20989.png
L_0253,nuclear power,T_1497,"FIGURE 1.1 When struck by a tiny particle, Uranium-235 breaks apart and releases energy.",image,textbook_images/nuclear_power_20990.png
L_0253,nuclear power,T_1497,FIGURE 1.2 Nuclear power plants like this one provide France with almost 80% of its electricity.,image,textbook_images/nuclear_power_20991.png
L_0253,nuclear power,T_1498,"FIGURE 1.3 Uranium mine in Kakadu National Park, Australia.",image,textbook_images/nuclear_power_20992.png
L_0253,nuclear power,T_1498,FIGURE 1.4,image,textbook_images/nuclear_power_20993.png
L_0255,obtaining energy resources,T_1503,FIGURE 1.1,image,textbook_images/obtaining_energy_resources_20996.png
L_0255,obtaining energy resources,T_1504,FIGURE 1.2 Less energy is being wasted. Non-renewable resources will last longer. The cost is kept lower.,image,textbook_images/obtaining_energy_resources_20997.png
L_0256,ocean ecosystems,T_1505,FIGURE 1.1,image,textbook_images/ocean_ecosystems_20998.png
L_0256,ocean ecosystems,T_1507,FIGURE 1.2,image,textbook_images/ocean_ecosystems_20999.png
L_0256,ocean ecosystems,T_1507,FIGURE 1.3,image,textbook_images/ocean_ecosystems_21000.png
L_0256,ocean ecosystems,T_1507,FIGURE 1.4,image,textbook_images/ocean_ecosystems_21001.png
L_0256,ocean ecosystems,T_1508,FIGURE 1.5,image,textbook_images/ocean_ecosystems_21002.png
L_0257,ocean garbage patch,T_1510,FIGURE 1.1 Trash has washed up on this beach.,image,textbook_images/ocean_garbage_patch_21003.png
L_0257,ocean garbage patch,T_1513,FIGURE 1.2,image,textbook_images/ocean_garbage_patch_21004.png
L_0257,ocean garbage patch,T_1513,FIGURE 1.3 Plastic bags in the ocean can be mis- taken for food by an unsuspecting marine predator.,image,textbook_images/ocean_garbage_patch_21005.png
L_0258,ocean zones,T_1516,FIGURE 1.1 Vertical and horizontal ocean zones.,image,textbook_images/ocean_zones_21006.png
L_0259,oil spills,T_1520,FIGURE 1.1,image,textbook_images/oil_spills_21007.png
L_0259,oil spills,T_1522,FIGURE 1.2,image,textbook_images/oil_spills_21008.png
L_0259,oil spills,T_1522,FIGURE 1.3 Burning the oil can reduce the amount in the water.,image,textbook_images/oil_spills_21009.png
L_0259,oil spills,T_1522,"FIGURE 1.4 A containment boom holds back oil, but it is only effective in calm water.",image,textbook_images/oil_spills_21010.png
L_0259,oil spills,T_1524,"FIGURE 1.5 The toll on wildlife is felt throughout the Gulf. Plankton, which form the base of the food chain, are killed by the oil, leaving other organisms without food. Islands and marshlands around the Gulf have many species that are already at risk, including four endangered species of sea turtles. With such low numbers, rebuilding their populations after the spill will be difficult.",image,textbook_images/oil_spills_21011.png
L_0260,overpopulation and over consumption,T_1528,FIGURE 1.1 Pesticides are hazardous in large quanti- ties and some are toxic in small quantities.,image,textbook_images/overpopulation_and_over_consumption_21012.png
L_0260,overpopulation and over consumption,T_1530,FIGURE 1.2,image,textbook_images/overpopulation_and_over_consumption_21013.png
L_0261,ozone depletion,T_1532,FIGURE 1.1,image,textbook_images/ozone_depletion_21015.png
L_0261,ozone depletion,T_1532,FIGURE 1.2,image,textbook_images/ozone_depletion_21016.png
L_0261,ozone depletion,T_1533,FIGURE 1.3,image,textbook_images/ozone_depletion_21017.png
L_0262,paleozoic and mesozoic seas,T_1536,FIGURE 1.1,image,textbook_images/paleozoic_and_mesozoic_seas_21018.png
L_0263,paleozoic plate tectonics,T_1540,FIGURE 1.1,image,textbook_images/paleozoic_plate_tectonics_21019.png
L_0264,petroleum power,T_1544,FIGURE 1.1,image,textbook_images/petroleum_power_21021.png
L_0264,petroleum power,T_1545,FIGURE 1.2,image,textbook_images/petroleum_power_21022.png
L_0264,petroleum power,T_1546,FIGURE 1.3,image,textbook_images/petroleum_power_21023.png
L_0264,petroleum power,T_1546,FIGURE 1.4,image,textbook_images/petroleum_power_21024.png
L_0265,planet orbits in the solar system,T_1547,FIGURE 1.1,image,textbook_images/planet_orbits_in_the_solar_system_21026.png
L_0268,ponds and lakes,T_1553,FIGURE 1.1,image,textbook_images/ponds_and_lakes_21029.png
L_0268,ponds and lakes,T_1553,FIGURE 1.2,image,textbook_images/ponds_and_lakes_21030.png
L_0268,ponds and lakes,T_1553,FIGURE 1.3 The Badwater Basin in Death Valley con- tains water in wet years. The lake basin is a remnant from when the region was much wetter just after the Ice Ages.,image,textbook_images/ponds_and_lakes_21031.png
L_0269,population size,T_1556,"FIGURE 1.1 In a desert such as this, what is the limiting factor on plant populations? What would make the population increase? What would make the population de- crease?",image,textbook_images/population_size_21032.png
L_0269,population size,T_1556,FIGURE 1.2,image,textbook_images/population_size_21033.png
L_0270,precambrian continents,T_1558,FIGURE 1.1,image,textbook_images/precambrian_continents_21034.png
L_0270,precambrian continents,T_1559,FIGURE 1.2,image,textbook_images/precambrian_continents_21035.png
L_0270,precambrian continents,T_1560,FIGURE 1.3 The Precambrian craton is exposed in the Grand Canyon where the Colorado River has cut through the younger sedimentary rocks.,image,textbook_images/precambrian_continents_21036.png
L_0271,precambrian plate tectonics,T_1562,FIGURE 1.1 Rodinia as it came together about 1.1 billion years ago.,image,textbook_images/precambrian_plate_tectonics_21037.png
L_0277,preventing hazardous waste problems,T_1581,FIGURE 1.1 Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/186861,image,textbook_images/preventing_hazardous_waste_problems_21048.png
L_0278,principle of horizontality,T_1583,FIGURE 1.1,image,textbook_images/principle_of_horizontality_21049.png
L_0279,principle of uniformitarianism,T_1585,FIGURE 1.1,image,textbook_images/principle_of_uniformitarianism_21050.png
L_0279,principle of uniformitarianism,T_1586,"FIGURE 1.2 The Mesquite sand dune in Death Valley National Park, California. This doesnt look exactly like the outcrop of Navajo sandstone, but if you could cut a cross-section into the face of the dune it would look very similar.",image,textbook_images/principle_of_uniformitarianism_21051.png
L_0280,principles of relative dating,T_1588,FIGURE 1.1,image,textbook_images/principles_of_relative_dating_21052.png
L_0280,principles of relative dating,T_1589,FIGURE 1.2,image,textbook_images/principles_of_relative_dating_21053.png
L_0281,processes of the water cycle,T_1593,"FIGURE 1.1 Because it is a cycle, the water cycle has no beginning and no end.",image,textbook_images/processes_of_the_water_cycle_21055.png
L_0281,processes of the water cycle,T_1596,FIGURE 1.2,image,textbook_images/processes_of_the_water_cycle_21056.png
L_0281,processes of the water cycle,T_1599,FIGURE 1.3,image,textbook_images/processes_of_the_water_cycle_21057.png
L_0281,processes of the water cycle,T_1599,FIGURE 1.4,image,textbook_images/processes_of_the_water_cycle_21058.png
L_0282,protecting water from pollution,T_1601,FIGURE 1.1,image,textbook_images/protecting_water_from_pollution_21059.png
L_0283,radioactive decay as a measure of age,T_1605,FIGURE 1.1 A parent emits an alpha particle to create a daughter.,image,textbook_images/radioactive_decay_as_a_measure_of_age_21060.png
L_0283,radioactive decay as a measure of age,T_1606,FIGURE 1.2,image,textbook_images/radioactive_decay_as_a_measure_of_age_21061.png
L_0284,radiometric dating,T_1608,FIGURE 1.1,image,textbook_images/radiometric_dating_21062.png
L_0284,radiometric dating,T_1610,FIGURE 1.2 Zircon crystal.,image,textbook_images/radiometric_dating_21063.png
L_0285,reducing air pollution,T_1614,FIGURE 1.1,image,textbook_images/reducing_air_pollution_21064.png
L_0285,reducing air pollution,T_1615,FIGURE 1.2,image,textbook_images/reducing_air_pollution_21065.png
L_0285,reducing air pollution,T_1615,FIGURE 1.3,image,textbook_images/reducing_air_pollution_21066.png
L_0286,reducing ozone destruction,T_1619,FIGURE 1.1,image,textbook_images/reducing_ozone_destruction_21067.png
L_0287,revolutions of earth,T_1621,"FIGURE 1.1 According to Ptolemy, a planet moves on a small circle (epicycle) that in turn moves on a larger circle (deferent) around Earth.",image,textbook_images/revolutions_of_earth_21068.png
L_0287,revolutions of earth,T_1622,FIGURE 1.2,image,textbook_images/revolutions_of_earth_21069.png
L_0287,revolutions of earth,T_1622,FIGURE 1.3,image,textbook_images/revolutions_of_earth_21070.png
L_0287,revolutions of earth,T_1623,FIGURE 1.4,image,textbook_images/revolutions_of_earth_21071.png
L_0288,rocks,T_1624,FIGURE 1.1,image,textbook_images/rocks_21072.png
L_0288,rocks,T_1624,FIGURE 1.2,image,textbook_images/rocks_21073.png
L_0288,rocks,T_1624,"FIGURE 1.3 Rock samples. Sample Sample 1 Minerals plagioclase, quartz, hornblende, pyrox- ene plagioclase, hornblende, pyroxene Texture Crystals, visible to naked eye Formation Magma cooled slowly Rock type Diorite",image,textbook_images/rocks_21074.png
L_0289,rocks and processes of the rock cycle,T_1626,FIGURE 1.1,image,textbook_images/rocks_and_processes_of_the_rock_cycle_21075.png
L_0291,rotation of earth,T_1635,"FIGURE 1.1 Foucaults Pendulum is at the Pantheon in Paris, France.",image,textbook_images/rotation_of_earth_21079.png
L_0292,safety of water,T_1640,"FIGURE 1.1 Dracunculiasis, commonly known as Guinea Worm, is contracted when a per- son drinks the guinea worm larvae.",image,textbook_images/safety_of_water_21080.png
L_0293,satellites shuttles and space stations,T_1641,"FIGURE 1.1 The space shuttle Atlantis being launched into orbit by a rocket on Cape Canaveral, Florida.",image,textbook_images/satellites_shuttles_and_space_stations_21081.png
L_0293,satellites shuttles and space stations,T_1644,FIGURE 1.2,image,textbook_images/satellites_shuttles_and_space_stations_21082.png
L_0293,satellites shuttles and space stations,T_1644,FIGURE 1.3,image,textbook_images/satellites_shuttles_and_space_stations_21083.png
L_0293,satellites shuttles and space stations,T_1644,FIGURE 1.4,image,textbook_images/satellites_shuttles_and_space_stations_21084.png
L_0293,satellites shuttles and space stations,T_1644,FIGURE 1.5 The space shuttle orbiter Atlantis touches down at the Kennedy Space Center in Florida.,image,textbook_images/satellites_shuttles_and_space_stations_21085.png
L_0294,saturn,T_1645,FIGURE 1.1,image,textbook_images/saturn_21086.png
L_0294,saturn,T_1647,FIGURE 1.2,image,textbook_images/saturn_21087.png
L_0294,saturn,T_1647,"FIGURE 1.3 primitive life may exist on Titan, the extreme cold and lack of carbon dioxide make it unlikely (Figure 1.4).",image,textbook_images/saturn_21088.png
L_0294,saturn,T_1647,FIGURE 1.4,image,textbook_images/saturn_21089.png
L_0300,seafloor spreading hypothesis,T_1667,"FIGURE 1.1 Magma at the mid-ocean ridge creates new seafloor. Since new oceanic crust is created at the mid-ocean ridges, either Earth is getting bigger (which it is not) or oceanic crust must be destroyed somewhere. Since the oldest oceanic crust was found at the edges of the trenches, Hess hypothesized that the seafloor subducts into Earths interior at the trenches to be recycled in the mantle.",image,textbook_images/seafloor_spreading_hypothesis_21094.png
L_0301,seasons,T_1670,FIGURE 1.1 The Earths tilt on its axis leads to one hemisphere facing the Sun more than the other hemisphere and gives rise to sea- sons.,image,textbook_images/seasons_21095.png
L_0301,seasons,T_1673,FIGURE 1.2,image,textbook_images/seasons_21096.png
L_0302,seawater chemistry,T_1675,FIGURE 1.1,image,textbook_images/seawater_chemistry_21099.png
L_0302,seawater chemistry,T_1675,FIGURE 1.2,image,textbook_images/seawater_chemistry_21100.png
L_0303,sedimentary rock classification,T_1677,FIGURE 1.1,image,textbook_images/sedimentary_rock_classification_21101.png
L_0303,sedimentary rock classification,T_1677,"FIGURE 1.2 Fossils in a biochemical rock, limestone, in the Carmel Formation in Utah. Picture Rock Name Conglomerate Type of Sedimentary Rock Clastic (fragments of non-organic sediments) Picture Rock Name Rock Gypsum Type of Sedimentary Rock Chemical precipitate",image,textbook_images/sedimentary_rock_classification_21102.png
L_0304,sedimentary rocks,T_1678,FIGURE 1.1,image,textbook_images/sedimentary_rocks_21103.png
L_0304,sedimentary rocks,T_1678,FIGURE 1.2 A river dumps sediments along its bed and on its banks.,image,textbook_images/sedimentary_rocks_21104.png
L_0305,seismic waves,T_1679,"FIGURE 1.1 The crest, trough, and amplitude are illus- trated in this diagram.",image,textbook_images/seismic_waves_21105.png
L_0305,seismic waves,T_1681,"FIGURE 1.2 unsqueezing Earth materials as they travel. This produces a change in volume for the material. P-waves bend slightly when they travel from one layer into another. Seismic waves move faster through denser or more rigid material. As P-waves encounter the liquid outer core, which is less rigid than the mantle, they slow down. This makes the P-waves arrive later and further away than would be expected. The result is a P-wave shadow zone. No P-waves are picked up at seismographs 104o to 140o from the earthquakes focus.",image,textbook_images/seismic_waves_21106.png
L_0305,seismic waves,T_1681,FIGURE 1.3 How P-waves travel through Earths interior.,image,textbook_images/seismic_waves_21107.png
L_0306,short term climate change,T_1686,"FIGURE 1.1 Under normal conditions, low pressure and warm water (shown in red) build up in the western Pacific Ocean. Notice that continents are shown in brown in the image. North and South America are on the right in this image.",image,textbook_images/short_term_climate_change_21109.png
L_0306,short term climate change,T_1686,"FIGURE 1.2 In El Nio conditions, the trade winds weaken or reverse directions. Warm wa- ter moves eastward across the Pacific Ocean and piles up against South Amer- ica.",image,textbook_images/short_term_climate_change_21110.png
L_0306,short term climate change,T_1687,FIGURE 1.3 A La Nia year is like a normal year but the circulation patterns are more extreme.,image,textbook_images/short_term_climate_change_21111.png
L_0311,solar energy on earth,T_1710,FIGURE 1.1,image,textbook_images/solar_energy_on_earth_21126.png
L_0311,solar energy on earth,T_1710,FIGURE 1.2,image,textbook_images/solar_energy_on_earth_21127.png
L_0312,solar power,T_1712,FIGURE 1.1,image,textbook_images/solar_power_21128.png
L_0312,solar power,T_1712,FIGURE 1.2,image,textbook_images/solar_power_21129.png
L_0312,solar power,T_1713,FIGURE 1.3,image,textbook_images/solar_power_21130.png
L_0313,star classification,T_1714,FIGURE 1.1 A Hertzsprung-Russell diagram shows the brightness and color of main se- quence stars. The brightness is indicated by luminosity and is higher up the y- axis. The temperature is given in degrees Kelvin and is higher on the left side of the x-axis. How does our Sun fare in terms of brightness and color compared with other stars?,image,textbook_images/star_classification_21131.png
L_0314,star constellations,T_1717,"FIGURE 1.1 In this image the Big Dipper is outlined and shown next to the Aurora borealis near Fairbanks, Alaska.",image,textbook_images/star_constellations_21132.png
L_0315,star power,T_1721,FIGURE 1.1 A thermonuclear bomb is an uncon- trolled fusion reaction in which enormous amounts of energy are released.,image,textbook_images/star_power_21133.png
L_0315,star power,T_1722,FIGURE 1.2,image,textbook_images/star_power_21134.png
L_0315,star power,T_1722,FIGURE 1.3,image,textbook_images/star_power_21135.png
L_0316,states of water,T_1724,"FIGURE 1.1 A water molecule. The hydrogen atoms have a slightly positive charge, and the oxygen atom has a slightly negative charge.",image,textbook_images/states_of_water_21136.png
L_0316,states of water,T_1724,FIGURE 1.2,image,textbook_images/states_of_water_21137.png
L_0319,streams and rivers,T_1733,FIGURE 1.1,image,textbook_images/streams_and_rivers_21138.png
L_0319,streams and rivers,T_1733,FIGURE 1.2,image,textbook_images/streams_and_rivers_21139.png
L_0319,streams and rivers,T_1734,FIGURE 1.3,image,textbook_images/streams_and_rivers_21140.png
L_0319,streams and rivers,T_1734,"FIGURE 1.4 The East River meanders through Crested Butte, Colorado.",image,textbook_images/streams_and_rivers_21141.png
L_0319,streams and rivers,T_1735,FIGURE 1.5,image,textbook_images/streams_and_rivers_21142.png
L_0319,streams and rivers,T_1735,FIGURE 1.6,image,textbook_images/streams_and_rivers_21143.png
L_0320,supervolcanoes,T_1737,FIGURE 1.1,image,textbook_images/supervolcanoes_21144.png
L_0320,supervolcanoes,T_1738,FIGURE 1.2,image,textbook_images/supervolcanoes_21145.png
L_0321,surface features of the sun,T_1742,FIGURE 1.1,image,textbook_images/surface_features_of_the_sun_21146.png
L_0321,surface features of the sun,T_1742,FIGURE 1.2 Magnetic activity leads up to a small solar flare.,image,textbook_images/surface_features_of_the_sun_21147.png
L_0321,surface features of the sun,T_1743,FIGURE 1.3 A solar prominence.,image,textbook_images/surface_features_of_the_sun_21148.png
L_0323,sustainable development,T_1750,"FIGURE 1.1 One of the most important steps to achieving a more sustainable future is to reduce human population growth. This has been happening in recent years. Studies have shown that the birth rate decreases as women become educated, because educated women tend to have fewer, and healthier, children.",image,textbook_images/sustainable_development_21152.png
L_0326,testing hypotheses,T_1758,FIGURE 1.1 Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/185963,image,textbook_images/testing_hypotheses_21155.png
L_0329,thermosphere and beyond,T_1769,FIGURE 1.1,image,textbook_images/thermosphere_and_beyond_21156.png
L_0331,tides,T_1779,FIGURE 1.1,image,textbook_images/tides_21162.png
L_0331,tides,T_1781,FIGURE 1.2,image,textbook_images/tides_21163.png
L_0331,tides,T_1781,"FIGURE 1.3 A spring tide occurs when the gravita- tional pull of both Moon and the Sun is in the same direction, making high tides higher and low tides lower and creating a large tidal range.",image,textbook_images/tides_21164.png
L_0331,tides,T_1781,"FIGURE 1.4 A neap tide occurs when the high tide of the Sun adds to the low tide of the Moon and vice versa, so the tidal range is relatively small.",image,textbook_images/tides_21165.png
L_0334,tree rings ice cores and varves,T_1789,FIGURE 1.1,image,textbook_images/tree_rings_ice_cores_and_varves_21172.png
L_0334,tree rings ice cores and varves,T_1790,FIGURE 1.2 Ice core section showing annual layers.,image,textbook_images/tree_rings_ice_cores_and_varves_21173.png
L_0334,tree rings ice cores and varves,T_1791,FIGURE 1.3 Ancient varve sediments in a rock out- crop.,image,textbook_images/tree_rings_ice_cores_and_varves_21174.png
L_0335,troposphere,T_1793,FIGURE 1.1,image,textbook_images/troposphere_21175.png
L_0337,types of air pollution,T_1798,FIGURE 1.1,image,textbook_images/types_of_air_pollution_21176.png
L_0337,types of air pollution,T_1798,"FIGURE 1.2 Volatile organic compounds (VOCs) are mostly hydrocarbons. Important VOCs include methane (a naturally occurring greenhouse gas that is increasing because of human activities), chlorofluorocarbons (human-made compounds that are being phased out because of their effect on the ozone layer), and dioxin (a byproduct of chemical production that serves no useful purpose, but is harmful to humans and other organisms).",image,textbook_images/types_of_air_pollution_21177.png
L_0337,types of air pollution,T_1799,FIGURE 1.3,image,textbook_images/types_of_air_pollution_21178.png
L_0338,types of fossilization,T_1802,FIGURE 1.1,image,textbook_images/types_of_fossilization_21179.png
L_0338,types of fossilization,T_1802,FIGURE 1.2 Trilobite.,image,textbook_images/types_of_fossilization_21180.png
L_0342,universe,T_1826,FIGURE 1.1,image,textbook_images/universe_21198.png
L_0343,uranus,T_1830,FIGURE 1.1,image,textbook_images/uranus_21199.png
L_0343,uranus,T_1830,FIGURE 1.2,image,textbook_images/uranus_21200.png
L_0344,uses of water,T_1833,FIGURE 1.1,image,textbook_images/uses_of_water_21201.png
L_0344,uses of water,T_1836,FIGURE 1.2 Drip irrigation delivers water to the base of each plant so little is lost to evaporation and runoff.,image,textbook_images/uses_of_water_21202.png
L_0344,uses of water,T_1837,FIGURE 1.3,image,textbook_images/uses_of_water_21203.png
L_0344,uses of water,T_1838,FIGURE 1.4,image,textbook_images/uses_of_water_21204.png
L_0344,uses of water,T_1842,FIGURE 1.5 Wetlands and other environments depend on clean water to survive.,image,textbook_images/uses_of_water_21205.png
L_0345,venus,T_1844,FIGURE 1.1,image,textbook_images/venus_21206.png
L_0345,venus,T_1845,"FIGURE 1.2 with a bit of sulfur dioxide. They also contain corrosive sulfuric acid. Because carbon dioxide is a greenhouse gas, the atmosphere traps heat from the Sun and creates a powerful greenhouse effect. Even though Venus is further from the Sun than Mercury, the greenhouse effect makes Venus the hottest planet. Temperatures at the surface reach 465 C (860 F). Thats hot enough to melt lead.",image,textbook_images/venus_21207.png
L_0345,venus,T_1846,"FIGURE 1.3 Orbiting spacecraft have used radar to reveal mountains, valleys, and canyons. Most of the surface has large areas of volcanoes surrounded by plains of lava. In fact, Venus has many more volcanoes than any other planet in the solar system, and some of those volcanoes are very large.",image,textbook_images/venus_21208.png
L_0345,venus,T_1846,FIGURE 1.4,image,textbook_images/venus_21209.png
L_0350,water distribution,T_1868,FIGURE 1.1,image,textbook_images/water_distribution_21225.png
L_0350,water distribution,T_1869,FIGURE 1.2,image,textbook_images/water_distribution_21226.png
L_0350,water distribution,T_1872,FIGURE 1.3,image,textbook_images/water_distribution_21227.png
L_0351,water pollution,T_1874,FIGURE 1.1 Municipal and agricultural pollution.,image,textbook_images/water_pollution_21228.png
L_0351,water pollution,T_1876,FIGURE 1.2 Industrial Waste Water: Polluted water coming from a factory in Mexico. The different colors of foam indicate various chemicals in the water and industrial pol- lution.,image,textbook_images/water_pollution_21229.png
L_0351,water pollution,T_1876,FIGURE 1.3,image,textbook_images/water_pollution_21230.png
L_0355,weathering and erosion,T_1886,FIGURE 1.1,image,textbook_images/weathering_and_erosion_21242.png
L_0356,wegener and the continental drift hypothesis,T_1888,FIGURE 1.1,image,textbook_images/wegener_and_the_continental_drift_hypothesis_21243.png
L_0356,wegener and the continental drift hypothesis,T_1888,FIGURE 1.2,image,textbook_images/wegener_and_the_continental_drift_hypothesis_21244.png
L_0356,wegener and the continental drift hypothesis,T_1889,"FIGURE 1.3 Thermal convection occurs as hot rock in the deep mantle rises towards the Earths surface. This rock then spreads out and cools, sinking back towards the core, where it can be heated again. This circulation of rock through the mantle cre- ates convection cells.",image,textbook_images/wegener_and_the_continental_drift_hypothesis_21245.png
L_0358,wind waves,T_1895,FIGURE 1.1,image,textbook_images/wind_waves_21248.png
L_0362,the microscope,T_1911,FIGURE 1.10 The head of ant as seen with an electron microscope,image,textbook_images/the_microscope_21258.png
L_0362,the microscope,T_1914,FIGURE 1.11 Cells in cork,image,textbook_images/the_microscope_21259.png
L_0362,the microscope,T_1915,FIGURE 1.12 Van Leeuwenhoeks drawings of animal- cules as they appeared under his micro- scope,image,textbook_images/the_microscope_21260.png
L_0370,flatworms and roundworms,T_1997,FIGURE 12.12 Tapeworm life cycle.,image,textbook_images/flatworms_and_roundworms_21316.png
L_0370,flatworms and roundworms,T_1997,FIGURE 12.13 This roundworm named ascaris is the largest and most common parasitic worm in humans.,image,textbook_images/flatworms_and_roundworms_21317.png
L_0370,flatworms and roundworms,T_2000,FIGURE 12.14 Hooks on the mouth end of a hookworm,image,textbook_images/flatworms_and_roundworms_21318.png
L_0371,mollusks and annelids,T_2002,FIGURE 12.15 Example of a mollusk: clam,image,textbook_images/mollusks_and_annelids_21319.png
L_0371,mollusks and annelids,T_2002,FIGURE 12.16 Garden snail,image,textbook_images/mollusks_and_annelids_21320.png
L_0371,mollusks and annelids,T_2002,FIGURE 12.17 Radula of a sea slug,image,textbook_images/mollusks_and_annelids_21321.png
L_0371,mollusks and annelids,T_2006,FIGURE 12.18 Segmented earthworm,image,textbook_images/mollusks_and_annelids_21322.png
L_0371,mollusks and annelids,T_2009,FIGURE 12.19 Polychaete worm: feather duster,image,textbook_images/mollusks_and_annelids_21323.png
L_0374,introduction to vertebrates,T_2028,"FIGURE 13.1 Examples of Vertebrates: (left to right) Fish, Amphibian, Reptile, Bird, and Mammal.",image,textbook_images/introduction_to_vertebrates_21336.png
L_0374,introduction to vertebrates,T_2029,FIGURE 13.2 This sketch of the vertebral column of a goat shows the groups of vertebrae into which the vertebral column is commonly divided.,image,textbook_images/introduction_to_vertebrates_21337.png
L_0374,introduction to vertebrates,T_2030,FIGURE 13.3 Human endoskeleton,image,textbook_images/introduction_to_vertebrates_21338.png
L_0374,introduction to vertebrates,T_2035,FIGURE 13.4 Phylogenetic Tree of Vertebrate Evolution. The earliest vertebrates evolved almost 550 million years ago. Which class of vertebrates evolved last?,image,textbook_images/introduction_to_vertebrates_21339.png
L_0374,introduction to vertebrates,T_2038,FIGURE 13.5 A water snake climbs onto a rock to bask and warm up in the sun. MEDIA Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/137118,image,textbook_images/introduction_to_vertebrates_21340.png
L_0375,fish,T_2040,FIGURE 13.6 Anglerfish,image,textbook_images/fish_21341.png
L_0375,fish,T_2041,FIGURE 13.7 Aquatic adaptations in fish: gill cover; scales; fins,image,textbook_images/fish_21342.png
L_0375,fish,T_2043,FIGURE 13.8 Adult salmon gather near the water sur- face to spawn. hatch. This is called mouth brooding.,image,textbook_images/fish_21343.png
L_0375,fish,T_2044,"FIGURE 13.9 Salmon larvae, each with a yolk sac at- tached to it.",image,textbook_images/fish_21344.png
L_0375,fish,T_2046,FIGURE 13.10 Butterfly fish like this one have fake eyespots. The eyespots may confuse larger predators long enough for the butterfly fish to escape.,image,textbook_images/fish_21345.png
L_0383,introduction to the human body,T_2122,FIGURE 16.1 Different types of cells in the human body are specialized for specific jobs.,image,textbook_images/introduction_to_the_human_body_21395.png
L_0383,introduction to the human body,T_2124,FIGURE 16.2 The human body consists of these four tissue types.,image,textbook_images/introduction_to_the_human_body_21396.png
L_0383,introduction to the human body,T_2124,FIGURE 16.3 Tissues in the heart work together to pump blood.,image,textbook_images/introduction_to_the_human_body_21397.png
L_0383,introduction to the human body,T_2125,FIGURE 16.4 Six human organ systems,image,textbook_images/introduction_to_the_human_body_21398.png
L_0384,the integumentary system,T_2127,FIGURE 16.5 The skin is much more complex that it appears from the outside.,image,textbook_images/the_integumentary_system_21399.png
L_0384,the integumentary system,T_2127,FIGURE 16.6 Layers and structures of the skin,image,textbook_images/the_integumentary_system_21400.png
L_0384,the integumentary system,T_2128,FIGURE 16.7 Melanocytes are located at the bottom of the epidermis.,image,textbook_images/the_integumentary_system_21401.png
L_0384,the integumentary system,T_2129,"FIGURE 16.8 Structures in the dermis include hair follicles and sebaceous glands, which produce sebum.",image,textbook_images/the_integumentary_system_21402.png
L_0384,the integumentary system,T_2131,FIGURE 16.9 Acne on a teenaged boys forehead,image,textbook_images/the_integumentary_system_21403.png
L_0385,the skeletal system,T_2138,FIGURE 16.10 The human skeleton includes bones and cartilage.,image,textbook_images/the_skeletal_system_21404.png
L_0385,the skeletal system,T_2139,FIGURE 16.11 Types of tissues in bone,image,textbook_images/the_skeletal_system_21405.png
L_0385,the skeletal system,T_2140,FIGURE 16.12 Example of immovable joint: skull,image,textbook_images/the_skeletal_system_21406.png
L_0385,the skeletal system,T_2140,"FIGURE 16.13 Examples of movable joints: shoulder, elbow, and knee",image,textbook_images/the_skeletal_system_21407.png
L_0385,the skeletal system,T_2143,"FIGURE 16.14 Bone mass declines with age, leading to osteoporosis in many people by old age.",image,textbook_images/the_skeletal_system_21408.png
L_0386,the muscular system,T_2145,FIGURE 16.15 A soldier prepares for a fitness challenge by doing one-arm pushups.,image,textbook_images/the_muscular_system_21409.png
L_0386,the muscular system,T_2145,FIGURE 16.16 A muscle fiber is a single cell that can con- tract. Each muscle fiber contains many myofibrils.,image,textbook_images/the_muscular_system_21410.png
L_0386,the muscular system,T_2147,FIGURE 16.17 Three types of human muscle tissue,image,textbook_images/the_muscular_system_21411.png
L_0386,the muscular system,T_2149,FIGURE 16.18 Human Skeletal Muscles. Skeletal mus- cles enable the body to move.,image,textbook_images/the_muscular_system_21412.png
L_0386,the muscular system,T_2149,FIGURE 16.19 Skeletal muscles are attached to bones by tendons.,image,textbook_images/the_muscular_system_21413.png
L_0386,the muscular system,T_2150,FIGURE 16.20 Bicep and triceps muscles let you bend and straighten your arm at the elbow.,image,textbook_images/the_muscular_system_21414.png
L_0386,the muscular system,T_2153,FIGURE 16.21 Exercising muscles makes them stronger and increases their endurance.,image,textbook_images/the_muscular_system_21415.png
L_0386,the muscular system,T_2153,FIGURE 16.22 Snowshoeing,image,textbook_images/the_muscular_system_21416.png
L_0387,food and nutrients,T_2157,FIGURE 17.2 Good sources of carbohydrates,image,textbook_images/food_and_nutrients_21418.png
L_0387,food and nutrients,T_2159,"FIGURE 17.3 Good sources of protein include whole grains, vegetables, and beans.",image,textbook_images/food_and_nutrients_21419.png
L_0387,food and nutrients,T_2159,"FIGURE 17.4 Good sources of lipids include fish, nuts, and seeds.",image,textbook_images/food_and_nutrients_21420.png
L_0387,food and nutrients,T_2160,"FIGURE 17.5 When you are active outside on a warm day, its important to drink plenty of water. You need to replace the water you lose in sweat.",image,textbook_images/food_and_nutrients_21421.png
L_0389,the digestive system,T_2171,FIGURE 17.10 Major organs of the digestive system make up the GI tract.,image,textbook_images/the_digestive_system_21426.png
L_0389,the digestive system,T_2172,FIGURE 17.11 Peristalsis,image,textbook_images/the_digestive_system_21427.png
L_0389,the digestive system,T_2176,FIGURE 17.12 Digestive system organs and glands,image,textbook_images/the_digestive_system_21428.png
L_0389,the digestive system,T_2178,FIGURE 17.13 Teeth are important for mechanical diges- tion.,image,textbook_images/the_digestive_system_21429.png
L_0389,the digestive system,T_2181,FIGURE 17.14 This diagram shows whats inside each of the millions of villi that line the jejunum and ileum of the small intestine. The villus is drawn greatly enlarged.,image,textbook_images/the_digestive_system_21430.png
L_0389,the digestive system,T_2187,FIGURE 17.15 Picnic food is a potential cause of food- borne illness.,image,textbook_images/the_digestive_system_21431.png
L_0390,overview of the cardiovascular system,T_2189,FIGURE 18.1 The cardiovascular system transports many substances to and from cells throughout the body.,image,textbook_images/overview_of_the_cardiovascular_system_21432.png
L_0390,overview of the cardiovascular system,T_2190,FIGURE 18.2 Pulmonary and systemic circulation,image,textbook_images/overview_of_the_cardiovascular_system_21433.png
L_0391,heart and blood vessels,T_2194,FIGURE 18.3 Parts of the heart,image,textbook_images/heart_and_blood_vessels_21434.png
L_0391,heart and blood vessels,T_2195,"FIGURE 18.4 Blood flows through the heart along two different paths, shown here by blue and red arrows. Notice where valves open and close to keep the blood moving in just one direction along each path.",image,textbook_images/heart_and_blood_vessels_21435.png
L_0391,heart and blood vessels,T_2198,"FIGURE 18.5 Arteries, veins and capillaries",image,textbook_images/heart_and_blood_vessels_21436.png
L_0391,heart and blood vessels,T_2201,FIGURE 18.6 Plaque buildup in an artery reduces blood flow through the vessel.,image,textbook_images/heart_and_blood_vessels_21437.png
L_0392,blood,T_2203,FIGURE 18.7 Blood donation,image,textbook_images/blood_21438.png
L_0392,blood,T_2205,"FIGURE 18.8 Blood cells include disk-shaped red blood cells (left), spherical white blood cells (right), and small cell fragments called platelets (center).",image,textbook_images/blood_21439.png
L_0392,blood,T_2206,FIGURE 18.9 Normal and agglutinated blood: normal blood smear (left) and agglutinated blood smear (right). MEDIA Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/137144,image,textbook_images/blood_21440.png
L_0392,blood,T_2213,FIGURE 18.10 Comparison of sickle-shaped and normal red blood cells,image,textbook_images/blood_21441.png
L_0393,the respiratory system,T_2215,FIGURE 19.1 Structures of the respiratory system,image,textbook_images/the_respiratory_system_21442.png
L_0393,the respiratory system,T_2217,FIGURE 19.2 How the diaphragm controls breathing,image,textbook_images/the_respiratory_system_21443.png
L_0393,the respiratory system,T_2218,FIGURE 19.3 How gases are exchanged in alveoli,image,textbook_images/the_respiratory_system_21444.png
L_0393,the respiratory system,T_2222,"FIGURE 19.4 Changes in the lungs due to asthma (top), pneumonia (bottom left), and emphysema (right)",image,textbook_images/the_respiratory_system_21445.png
L_0394,the excretory system,T_2224,FIGURE 19.5 Water lost in sweat must be balanced in some way for the body to maintain home- ostasis.,image,textbook_images/the_excretory_system_21446.png
L_0394,the excretory system,T_2226,FIGURE 19.6 The kidneys are the main organs of the urinary system.,image,textbook_images/the_excretory_system_21447.png
L_0394,the excretory system,T_2226,FIGURE 19.7 Structures in the kidney,image,textbook_images/the_excretory_system_21448.png
L_0396,chemistry of living things,T_2239,FIGURE 2.6 Model of an atom,image,textbook_images/chemistry_of_living_things_21456.png
L_0396,chemistry of living things,T_2239,FIGURE 2.7 Model of a water molecule,image,textbook_images/chemistry_of_living_things_21457.png
L_0396,chemistry of living things,T_2243,FIGURE 2.8 Starchy foods,image,textbook_images/chemistry_of_living_things_21458.png
L_0396,chemistry of living things,T_2244,FIGURE 2.9 Hemoglobin is an example of a transport protein in the blood. You can see how it works in the Figure 2.9. The heme parts of a hemoglobin molecule bind with oxygen. Each red blood cell has hundreds of hemoglobin molecules and each hemoglobin molecule can carry up to four oxygen molecules. This is how oxygen is carried in the blood to cells throughout the body.,image,textbook_images/chemistry_of_living_things_21459.png
L_0396,chemistry of living things,T_2245,"FIGURE 2.10 Saturated and unsaturated fatty acids In saturated fatty acids, carbon atoms are bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogen. Saturated fatty acids are found in fats. In unsaturated fatty acids, some carbon atoms are not bonded to as many hydrogen atoms as possible. Instead, they share double bonds with other carbon atoms. Unsaturated fatty acids are found in oils.",image,textbook_images/chemistry_of_living_things_21460.png
L_0396,chemistry of living things,T_2246,FIGURE 2.11 A nucleotide,image,textbook_images/chemistry_of_living_things_21461.png
L_0396,chemistry of living things,T_2246,FIGURE 2.12 DNA molecule,image,textbook_images/chemistry_of_living_things_21462.png
L_0396,chemistry of living things,T_2247,FIGURE 2.13 This student athlete is using energy to run a race.,image,textbook_images/chemistry_of_living_things_21463.png
L_0396,chemistry of living things,T_2250,FIGURE 2.14 The products of photosynthesis are oxy- gen (O2 ) and glucose. These two sub- stances are also the reactants of cellular respiration. The products of cellular respi- ration are carbon dioxide (CO2 ) and water (H2 O). These two substances are also the reactants of photosynthesis.,image,textbook_images/chemistry_of_living_things_21464.png
L_0398,the nervous system,T_2259,FIGURE 20.2 Parts of a neuron,image,textbook_images/the_nervous_system_21468.png
L_0398,the nervous system,T_2261,"FIGURE 20.3 This diagram shows a synapse between neurons. When a nerve impulse arrives at the end of the axon, neurotransmitters are released and travel to the dendrite of an- other neuron, carrying the nerve impulse from one neuron to the next.",image,textbook_images/the_nervous_system_21469.png
L_0398,the nervous system,T_2263,FIGURE 20.4 The brain and spinal cord make up the central nervous system.,image,textbook_images/the_nervous_system_21470.png
L_0398,the nervous system,T_2264,FIGURE 20.5 Three major parts of the brain,image,textbook_images/the_nervous_system_21471.png
L_0398,the nervous system,T_2265,FIGURE 20.6 The four lobes of the left hemisphere are color coded in this illustration.,image,textbook_images/the_nervous_system_21472.png
L_0398,the nervous system,T_2268,"FIGURE 20.7 The central nervous system interprets messages from sense organs and inter- nal organs and the motor division sends messages to internal organs, glands, and muscles.",image,textbook_images/the_nervous_system_21473.png
L_0398,the nervous system,T_2271,FIGURE 20.8 Children as young as 2 years of age can be vaccinated against viral meningitis.,image,textbook_images/the_nervous_system_21474.png
L_0398,the nervous system,T_2275,FIGURE 20.9 Wearing the right type of helmet can re- duce the risk of a brain injury when riding a bike.,image,textbook_images/the_nervous_system_21475.png
L_0399,the senses,T_2279,FIGURE 20.10 You have to keep your eyes on the ball to hit a volleyball.,image,textbook_images/the_senses_21476.png
L_0399,the senses,T_2280,FIGURE 20.11 3-D glasses make movies look three-dimensional.,image,textbook_images/the_senses_21477.png
L_0399,the senses,T_2281,FIGURE 20.12 Parts of the eye,image,textbook_images/the_senses_21478.png
L_0399,the senses,T_2282,FIGURE 20.13 How eye shape affects vision,image,textbook_images/the_senses_21479.png
L_0399,the senses,T_2283,"FIGURE 20.14 This outdoor fruit market stimulates all the senses sight, sound, smell, taste, and touch.",image,textbook_images/the_senses_21480.png
L_0399,the senses,T_2284,FIGURE 20.15 How the ears sense sounds,image,textbook_images/the_senses_21481.png
L_0399,the senses,T_2286,FIGURE 20.16 The tiny red bumps on this tongue are taste buds.,image,textbook_images/the_senses_21482.png
L_0400,the endocrine system,T_2288,FIGURE 20.17 Endocrine system glands,image,textbook_images/the_endocrine_system_21483.png
L_0400,the endocrine system,T_2294,FIGURE 20.18 The thyroid gland is controlled by a negative feedback loop that includes the hypothalamus and pituitary gland.,image,textbook_images/the_endocrine_system_21484.png
L_0401,infectious diseases,T_2297,FIGURE 21.1 Types of pathogens that cause human diseases,image,textbook_images/infectious_diseases_21485.png
L_0401,infectious diseases,T_2298,FIGURE 21.2 Sneezing sends thousands of tiny droplets into the air unless the mouth and nose are covered. Each droplet may carry thousands of bacteria or viruses.,image,textbook_images/infectious_diseases_21486.png
L_0401,infectious diseases,T_2299,FIGURE 21.3 The proper way to wash your hands,image,textbook_images/infectious_diseases_21487.png
L_0402,noninfectious diseases,T_2300,"FIGURE 21.4 In panel A, an abnormal cell (2) is prevented from dividing, and the abnormal cell dies (1). In panel B, an abnormal cell is not prevented from dividing. Instead, it divides uncontrollably, leading to the formation of a tumor.",image,textbook_images/noninfectious_diseases_21488.png
L_0402,noninfectious diseases,T_2301,FIGURE 21.5 Chemicals in cigarettes,image,textbook_images/noninfectious_diseases_21489.png
L_0402,noninfectious diseases,T_2304,FIGURE 21.6 This young woman is applying sunscreen to reduce her exposure to cancer-causing UV radiation.,image,textbook_images/noninfectious_diseases_21490.png
L_0402,noninfectious diseases,T_2308,FIGURE 21.7 An insulin pump monitors blood glucose levels and injects the needed amount of insulin to keep glucose levels within the normal range.,image,textbook_images/noninfectious_diseases_21491.png
L_0402,noninfectious diseases,T_2310,FIGURE 21.8 Pollen from ragweed blossoms like these cause allergic reactions in many people.,image,textbook_images/noninfectious_diseases_21492.png
L_0405,male reproductive system,T_2328,"FIGURE 22.1 Male reproductive system as viewed from the side The epididymis is a tube that is about 6 meters (20 feet) long in adults. It is tightly coiled, so it fits inside the scrotum on top of the testes. The epididymis is where sperm mature. It stores the sperm until they leave the body. The vas deferens is a tube that carries sperm from the epididymis to the urethra. The prostate gland secretes a fluid that mixes with sperm to help form semen. Semen is a whitish liquid that contains sperm. It passes through the urethra and out of the body.",image,textbook_images/male_reproductive_system_21502.png
L_0405,male reproductive system,T_2330,FIGURE 22.2 Structure of sperm,image,textbook_images/male_reproductive_system_21503.png
L_0406,female reproductive system,T_2333,"FIGURE 22.3 Female reproductive system as viewed from the side fallopian tube. During birth, a baby passes from the uterus through the vagina to leave the body.",image,textbook_images/female_reproductive_system_21504.png
L_0406,female reproductive system,T_2337,FIGURE 22.4 How an egg and its follicle develop in an ovary: (1) undeveloped eggs; (2) and (3) egg and follicle developing; (4) ovulation; (5) and (6) follicle (now called corpus lu- teum) breaking down,image,textbook_images/female_reproductive_system_21505.png
L_0407,reproduction and life stages,T_2339,FIGURE 22.5 Blastocyst stage,image,textbook_images/reproduction_and_life_stages_21506.png
L_0407,reproduction and life stages,T_2341,"FIGURE 22.6 Embryonic Development (Weeks 48). Most organs develop in the embryo during weeks 4 through 8. If the embryo is exposed to toxins during this period, the effects are likely to be very damaging. Can you explain why? (Note: the draw- ings of the embryos are not to scale.)",image,textbook_images/reproduction_and_life_stages_21507.png
L_0407,reproduction and life stages,T_2343,FIGURE 22.7 Developments in the fetus,image,textbook_images/reproduction_and_life_stages_21508.png
L_0407,reproduction and life stages,T_2345,FIGURE 22.8 Placenta and umbilical cord,image,textbook_images/reproduction_and_life_stages_21509.png
L_0407,reproduction and life stages,T_2347,FIGURE 22.9 A pregnant woman needs to pay special attention to her diet and eat a variety of healthy foods.,image,textbook_images/reproduction_and_life_stages_21510.png
L_0407,reproduction and life stages,T_2348,FIGURE 22.10 Smiling is an early milestone in infant development.,image,textbook_images/reproduction_and_life_stages_21511.png
L_0407,reproduction and life stages,T_2350,FIGURE 22.11 Learning how to write is a major accom- plishment of childhood.,image,textbook_images/reproduction_and_life_stages_21512.png
L_0407,reproduction and life stages,T_2351,"FIGURE 22.12 A teenage boy develops a bump in his throat called an Adams apple because of an increase in the size of the larynx, or voice box.",image,textbook_images/reproduction_and_life_stages_21513.png
L_0407,reproduction and life stages,T_2351,FIGURE 22.13 Teen friends enjoying card games and each others company,image,textbook_images/reproduction_and_life_stages_21514.png
L_0407,reproduction and life stages,T_2355,"FIGURE 22.14 This elderly man not only plays the guitar. He built the guitar that hes playing in the photo. to be one of them? If so, adopt a healthy lifestyle now and follow it for life. Doing so will increase your chances of staying fit and active in old age.",image,textbook_images/reproduction_and_life_stages_21515.png
L_0408,reproductive system health,T_2359,"FIGURE 22.15 HPV, the virus that causes genital warts, may also cause cancer.",image,textbook_images/reproductive_system_health_21516.png
L_0409,what is ecology,T_2364,"FIGURE 23.1 Organisms show tremendous diversity. Some of the smallest and largest living or- ganisms are pictured here: billions of mi- croorganisms that thrive in this hot spring give it its striking colors (left); blue whales are the largest living organisms (right). Organisms depend on their environment to meet their needs, so they are greatly influenced by it. There are many factors in the environment that affect organisms. The factors can be classified as either biotic or abiotic.",image,textbook_images/what_is_ecology_21518.png
L_0409,what is ecology,T_2365,"FIGURE 23.2 From individuals to the biosphere, ecol- ogy can be studied at several different levels. An ecosystem consists of all the biotic and abiotic factors in an area. It includes a community, the abiotic factors in the environment, and all their interactions. A biome is a group of similar ecosystems with the same general abiotic factors and primary producers. Biomes may be terrestrial (land-based) or aquatic (water-based). The biosphere consists of all the parts of Earth where life can be found. This is the highest level of organization in ecology. It includes all of the other levels below it. The biosphere consists of all the worlds biomes, both terrestrial and aquatic.",image,textbook_images/what_is_ecology_21519.png
L_0410,populations,T_2367,"FIGURE 23.3 Patterns of population distribution include clumped, random, and uniform distribu- tions. Each pattern is associated with dif- ferent types of species or environments.",image,textbook_images/populations_21520.png
L_0410,populations,T_2368,FIGURE 23.4 Curve A represents exponential popula- tion growth. Curve B represents logistic population growth.,image,textbook_images/populations_21521.png
L_0410,populations,T_2370,FIGURE 23.5 A population pyramid shows the age-sex structure of a population. This population pyramid represents the human population of the African country of Angola in 2005.,image,textbook_images/populations_21522.png
L_0410,populations,T_2370,FIGURE 23.6 Growth of the Human Population.,image,textbook_images/populations_21523.png
L_0410,populations,T_2372,FIGURE 23.7 The demographic transition occurred in the stages shown in this graph.,image,textbook_images/populations_21524.png
L_0413,biomes,T_2389,FIGURE 23.18 Major terrestrial biomes,image,textbook_images/biomes_21535.png
L_0413,biomes,T_2391,"FIGURE 23.19 Terrestrial biomes include tropical rainfor- est, temperate grassland, and tundra.",image,textbook_images/biomes_21536.png
L_0413,biomes,T_2395,FIGURE 23.20 Plants and algae are producers in the littoral zone along the shore of this lake in Iceland.,image,textbook_images/biomes_21537.png
L_0413,biomes,T_2396,"FIGURE 23.21 Intertidal zone along the North Sea in the Netherlands Below 200 meters is the aphotic zone. There are no primary producers here because there isnt enough sunlight for photosynthesis. However, the water may be rich in nutrients because of dead organisms drifting down from above. Organisms that live here may include bacteria, sponges, sea anemones, worms, sea stars, and fish. The bottom of the ocean is called the benthic zone. It includes the sediments on the bottom of the ocean and the water just above it. Organisms living in this zone include clams and crabs. They may be few in number due to relatively scarce nutrients in this zone. There are many more organisms around deep-sea vents. Microorganisms use chemicals that pour out of the vents to make food by chemosynthesis. These producers support large numbers of other organisms, including crustaceans and red tubeworms like those pictured in Figure 23.22.",image,textbook_images/biomes_21538.png
L_0413,biomes,T_2396,FIGURE 23.22 Ocean vent biome,image,textbook_images/biomes_21539.png
L_0415,cycles of matter,T_2408,FIGURE 24.7 The water cycle has no beginning or end. It just keeps repeating.,image,textbook_images/cycles_of_matter_21546.png
L_0415,cycles of matter,T_2410,"FIGURE 24.8 The thorny devil lizard lives in such a dry environment in Australia that it has a unique specialization for obtaining water. The scales on its body collect dew and channel it to the corners of the mouth, so the lizard can drink it.",image,textbook_images/cycles_of_matter_21547.png
L_0415,cycles of matter,T_2412,FIGURE 24.9 The Carbon Cycle.,image,textbook_images/cycles_of_matter_21548.png
L_0415,cycles of matter,T_2415,FIGURE 24.10 The nitrogen cycle,image,textbook_images/cycles_of_matter_21549.png
L_0417,air pollution,T_2423,FIGURE 25.1 This stone statue has been dissolved by acid rain.,image,textbook_images/air_pollution_21553.png
L_0417,air pollution,T_2424,FIGURE 25.2 Earths atmosphere creates a natural greenhouse effect that moderates Earths temperature.,image,textbook_images/air_pollution_21554.png
L_0417,air pollution,T_2424,FIGURE 25.3 Shrinking of the Arctic ice cap due to global warming contributes to rising sea levels.,image,textbook_images/air_pollution_21555.png
L_0417,air pollution,T_2427,FIGURE 25.4 Carbon monoxide alarm,image,textbook_images/air_pollution_21556.png
L_0418,water pollution,T_2429,FIGURE 25.5 Algal bloom,image,textbook_images/water_pollution_21557.png
L_0418,water pollution,T_2430,FIGURE 25.6 Hypoxic dead zone in the Gulf of Mexico,image,textbook_images/water_pollution_21558.png
L_0418,water pollution,T_2435,FIGURE 25.7 Plastic debris in the ocean washes up on shore in the Hawaiian Islands,image,textbook_images/water_pollution_21559.png
L_0419,natural resources,T_2438,FIGURE 25.8 This photo shows a huge coal field in the Philippines as it appears from space. Coal is a fossil fuel and a nonrenewable natural resource.,image,textbook_images/natural_resources_21560.png
L_0419,natural resources,T_2439,"FIGURE 25.9 Bare soil is easily washed away by heavy rains or winds, but it takes millions of years to replace. Ruts in soil washed away by runoff are evident in this photo.",image,textbook_images/natural_resources_21561.png
L_0419,natural resources,T_2441,FIGURE 25.10 Worldwide energy use in 2010,image,textbook_images/natural_resources_21562.png
L_0419,natural resources,T_2442,"FIGURE 25.11 Sunlight, wind, and living things can all be used as energy resources.",image,textbook_images/natural_resources_21563.png
L_0419,natural resources,T_2444,"FIGURE 25.12 If you use air conditioning in hot weather, set the thermostat above normal room temperature to save energy resources.",image,textbook_images/natural_resources_21564.png
L_0419,natural resources,T_2446,FIGURE 25.13 Kitchen and garden wastes can be recycled by composting them.,image,textbook_images/natural_resources_21565.png
L_0424,photosynthesis,T_2494,"FIGURE 4.7 Photosynthetic organisms include plants, algae, and some bacteria.",image,textbook_images/photosynthesis_21589.png
L_0424,photosynthesis,T_2495,"FIGURE 4.8 The small green, circular structures in the plant cells pictured here are chloroplasts.",image,textbook_images/photosynthesis_21590.png
L_0424,photosynthesis,T_2498,FIGURE 4.9 Chloroplast,image,textbook_images/photosynthesis_21591.png
L_0425,cellular respiration,T_2501,FIGURE 4.11 Astronaut Chris Hadfield eats a banana aboard the International Space Station.,image,textbook_images/cellular_respiration_21593.png
L_0425,cellular respiration,T_2505,FIGURE 4.12 Cut-away view of a mitochondrion,image,textbook_images/cellular_respiration_21594.png
L_0425,cellular respiration,T_2505,FIGURE 4.13,image,textbook_images/cellular_respiration_21595.png
L_0425,cellular respiration,T_2508,FIGURE 4.14 How photosynthesis and cellular respira- tion are related,image,textbook_images/cellular_respiration_21596.png
L_0425,cellular respiration,T_2510,FIGURE 4.15 The muscles of these hurdlers are work- ing too hard for aerobic respiration to keep them supplied with energy.,image,textbook_images/cellular_respiration_21597.png
L_0425,cellular respiration,T_2512,FIGURE 4.16 Bread has little holes in it from carbon dioxide produced by yeast.,image,textbook_images/cellular_respiration_21598.png
L_0428,protein synthesis,T_2538,FIGURE 5.15 Blueprints for a house,image,textbook_images/protein_synthesis_21613.png
L_0428,protein synthesis,T_2538,FIGURE 5.16 Comparison of RNA and DNA,image,textbook_images/protein_synthesis_21614.png
L_0428,protein synthesis,T_2540,"FIGURE 5.17 Translating the genetic code of RNA. The codons are read in sequence until a stop codon is reached. UAG, UGA, and UAA are all stop codons. They dont code for any amino acids.",image,textbook_images/protein_synthesis_21615.png
L_0428,protein synthesis,T_2540,FIGURE 5.18 How the genetic code is read,image,textbook_images/protein_synthesis_21616.png
L_0428,protein synthesis,T_2543,FIGURE 5.19 Transcription step of protein synthesis,image,textbook_images/protein_synthesis_21617.png
L_0428,protein synthesis,T_2544,FIGURE 5.20 Translation step of protein synthesis,image,textbook_images/protein_synthesis_21618.png
L_0428,protein synthesis,T_2544,FIGURE 5.21 Examples of mutagens,image,textbook_images/protein_synthesis_21619.png
L_0432,darwins theory of evolution,T_2584,FIGURE 7.1 Charles Darwin as a young man in the 1830s,image,textbook_images/darwins_theory_of_evolution_21637.png
L_0432,darwins theory of evolution,T_2585,FIGURE 7.2 Route of the Beagle,image,textbook_images/darwins_theory_of_evolution_21638.png
L_0432,darwins theory of evolution,T_2585,"FIGURE 7.3 Giant tortoises on the Galpagos Islands varied in shell shape, depending on which island they inhabited.",image,textbook_images/darwins_theory_of_evolution_21639.png
L_0432,darwins theory of evolution,T_2586,FIGURE 7.4 Variation in beak size and shape in Gal- pagos finches,image,textbook_images/darwins_theory_of_evolution_21640.png
L_0432,darwins theory of evolution,T_2589,FIGURE 7.5 Variation in pigeons as a result of artificial selection,image,textbook_images/darwins_theory_of_evolution_21641.png
L_0433,evidence for evolution,T_2594,FIGURE 7.6 Most of what we know about dinosaurs is based on fossils such as this one.,image,textbook_images/evidence_for_evolution_21642.png
L_0433,evidence for evolution,T_2595,FIGURE 7.7 Fossil footprint of a three-toed dinosaur,image,textbook_images/evidence_for_evolution_21643.png
L_0433,evidence for evolution,T_2595,FIGURE 7.8 Wasp encased in amber,image,textbook_images/evidence_for_evolution_21644.png
L_0433,evidence for evolution,T_2596,FIGURE 7.9 Fossils found in lower rock layers are generally older than fossils found in rock layers closer to the surface.,image,textbook_images/evidence_for_evolution_21645.png
L_0433,evidence for evolution,T_2596,"FIGURE 7.10 This whale ancestor, called Ambulocetus, lived about 48 million years ago.",image,textbook_images/evidence_for_evolution_21646.png
L_0433,evidence for evolution,T_2598,FIGURE 7.11 Front limb bones of different mammals,image,textbook_images/evidence_for_evolution_21647.png
L_0433,evidence for evolution,T_2600,"FIGURE 7.12 From left to right, embryos of a chicken, turtle, pig, and human being",image,textbook_images/evidence_for_evolution_21648.png
L_0434,the scale of evolution,T_2603,FIGURE 7.13 Fossils show how horses evolved over the past 50 million of years. Horses in- creased in size. Their teeth and feet also changed.,image,textbook_images/the_scale_of_evolution_21649.png
L_0434,the scale of evolution,T_2607,FIGURE 7.14 Darwins finches evolved new traits by natural selection.,image,textbook_images/the_scale_of_evolution_21650.png
L_0434,the scale of evolution,T_2609,FIGURE 7.15 This male anole lizard is puffing out a flap of yellow skin to attract a mate.,image,textbook_images/the_scale_of_evolution_21651.png
L_0434,the scale of evolution,T_2610,FIGURE 7.16 Coevolution of a hummingbird and flower- ing plant,image,textbook_images/the_scale_of_evolution_21652.png
L_0435,history of life on earth,T_2613,FIGURE 7.17 Earths history in a day,image,textbook_images/history_of_life_on_earth_21653.png
L_0435,history of life on earth,T_2615,FIGURE 7.18 Geologic time scale,image,textbook_images/history_of_life_on_earth_21654.png
L_0435,history of life on earth,T_2617,FIGURE 7.19 Model of the earliest cell,image,textbook_images/history_of_life_on_earth_21655.png
L_0435,history of life on earth,T_2619,FIGURE 7.20 How eukaryotic cells may have evolved,image,textbook_images/history_of_life_on_earth_21656.png
L_0435,history of life on earth,T_2621,FIGURE 7.21 Sponges (left) and trilobite fossil (right) from the Cambrian Period,image,textbook_images/history_of_life_on_earth_21657.png
L_0435,history of life on earth,T_2625,FIGURE 7.22 Forest of the Carboniferous Period,image,textbook_images/history_of_life_on_earth_21658.png
L_0435,history of life on earth,T_2626,FIGURE 7.23 The supercontinent Pangaea formed dur- ing the Permian Period.,image,textbook_images/history_of_life_on_earth_21659.png
L_0435,history of life on earth,T_2630,FIGURE 7.24 Tyrannosaurus rex skeleton on display in a museum,image,textbook_images/history_of_life_on_earth_21660.png
L_0435,history of life on earth,T_2633,FIGURE 7.25 Woolly mammoths lived during the last ice age.,image,textbook_images/history_of_life_on_earth_21661.png
L_0437,bacteria,T_2650,FIGURE 8.9 Salmonella bacteria,image,textbook_images/bacteria_21670.png
L_0437,bacteria,T_2652,FIGURE 8.10 Bacteria classified by shape,image,textbook_images/bacteria_21671.png
L_0437,bacteria,T_2652,FIGURE 8.11 Gram-positive (left) and gram-negative (right) bacteria,image,textbook_images/bacteria_21672.png
L_0437,bacteria,T_2654,FIGURE 8.12 Bacteria are used to make fermented foods such as these.,image,textbook_images/bacteria_21673.png
L_0437,bacteria,T_2655,FIGURE 8.13 Deer ticks are vectors for the bacteria that cause Lyme disease. The ticks are actu- ally very small and may go unnoticed.,image,textbook_images/bacteria_21674.png
L_0442,adulthood and aging,T_2693,FIGURE 1.1,image,textbook_images/adulthood_and_aging_21696.png
L_0449,aquatic biomes,T_2717,FIGURE 1.1,image,textbook_images/aquatic_biomes_21707.png
L_0449,aquatic biomes,T_2718,FIGURE 1.2,image,textbook_images/aquatic_biomes_21708.png
L_0454,autoimmune diseases,T_2735,FIGURE 1.1,image,textbook_images/autoimmune_diseases_21717.png
L_0457,bacteria in the digestive system,T_2745,FIGURE 1.1,image,textbook_images/bacteria_in_the_digestive_system_21724.png
L_0458,bacteria nutrition,T_2750,FIGURE 1.1 These mutualistic bacteria-containing nodules on a soybean root help provide the plant with nitrogen.,image,textbook_images/bacteria_nutrition_21725.png
L_0460,barriers to pathogens,T_2756,FIGURE 1.1 This drawing shows that the skin has many layers. The outer layer is so tough that it keeps out most pathogens.,image,textbook_images/barriers_to_pathogens_21727.png
L_0460,barriers to pathogens,T_2757,FIGURE 1.2,image,textbook_images/barriers_to_pathogens_21728.png
L_0467,blood types,T_2774,FIGURE 1.1,image,textbook_images/blood_types_21741.png
L_0468,blood vessels,T_2777,FIGURE 1.1,image,textbook_images/blood_vessels_21742.png
L_0469,bony fish,T_2781,FIGURE 1.1,image,textbook_images/bony_fish_21743.png
L_0469,bony fish,T_2785,FIGURE 1.2,image,textbook_images/bony_fish_21744.png
L_0470,cancer,T_2788,"FIGURE 1.1 The mutations that cause cancer may occur when people are exposed to pathogens, such as the human papilloma virus (HPV), which is shown here.",image,textbook_images/cancer_21745.png
L_0470,cancer,T_2788,"FIGURE 1.2 The mutations that cause cancer may oc- cur when people are exposed to chemical carcinogens, such as those in cigarettes. It can be argued that tobacco smoke is the main source of chemical carcinogens.",image,textbook_images/cancer_21746.png
L_0470,cancer,T_2790,"FIGURE 1.3 The mutations that cause cancer may oc- cur when people are exposed to radiation, including the radiation from sunlight.",image,textbook_images/cancer_21747.png
L_0471,cardiovascular diseases,T_2792,FIGURE 1.1,image,textbook_images/cardiovascular_diseases_21748.png
L_0472,cardiovascular system,T_2795,FIGURE 1.1 The cardiovascular system moves nutri- ents and other substances throughout the body.,image,textbook_images/cardiovascular_system_21750.png
L_0473,cardiovascular system health,T_2796,FIGURE 1.1,image,textbook_images/cardiovascular_system_health_21751.png
L_0473,cardiovascular system health,T_2797,FIGURE 1.2,image,textbook_images/cardiovascular_system_health_21752.png
L_0481,cellular respiration,T_2818,FIGURE 1.1,image,textbook_images/cellular_respiration_21763.png
L_0483,central nervous system,T_2826,FIGURE 1.1 The brain and spinal cord make up the central nervous system.,image,textbook_images/central_nervous_system_21765.png
L_0483,central nervous system,T_2826,FIGURE 1.2,image,textbook_images/central_nervous_system_21766.png
L_0485,chemistry of life,T_2835,FIGURE 1.1,image,textbook_images/chemistry_of_life_21772.png
L_0485,chemistry of life,T_2837,"FIGURE 1.2 The periodic table groups the elements based on their properties. The table begins with Hydrogen, atomic number 1.",image,textbook_images/chemistry_of_life_21773.png
L_0488,chromosomal disorders,T_2849,FIGURE 1.1 A child with Down syndrome.,image,textbook_images/chromosomal_disorders_21780.png
L_0488,chromosomal disorders,T_2849,"FIGURE 1.2 Outside of chromosome 21 and the sex chromosomes, most embryos with extra chromosomes do not usually survive. Because chromosomes carry many, many genes, a disruption of a chromosome can cause severe problems with the development of a fetus. Individuals with one (or more) fewer chromosome usually dont survive either. Can you explain why?",image,textbook_images/chromosomal_disorders_21781.png
L_0489,circulation and the lymphatic system,T_2851,FIGURE 1.1,image,textbook_images/circulation_and_the_lymphatic_system_21782.png
L_0489,circulation and the lymphatic system,T_2852,FIGURE 1.2,image,textbook_images/circulation_and_the_lymphatic_system_21783.png
L_0494,connecting cellular respiration and photosynthesis,T_2865,FIGURE 1.1,image,textbook_images/connecting_cellular_respiration_and_photosynthesis_21791.png
L_0499,diabetes,T_2880,FIGURE 1.1,image,textbook_images/diabetes_21799.png
L_0501,digestive system organs,T_2887,"FIGURE 1.1 This drawing shows the liver, gallbladder, and pancreas. These organs are part of the digestive system. Food does not pass through them, but they secrete sub- stances needed for chemical digestion.",image,textbook_images/digestive_system_organs_21802.png
L_0501,digestive system organs,T_2888,FIGURE 1.2,image,textbook_images/digestive_system_organs_21803.png
L_0501,digestive system organs,T_2889,FIGURE 1.3 This is what the villi lining the intestine looks like when magnified. Each one is actually only about 1 millimeter long. Villi are just barely visible with the unaided eye.,image,textbook_images/digestive_system_organs_21804.png
L_0502,diseases of the nervous system,T_2893,FIGURE 1.1 This scan shows a person with encephali- tis.,image,textbook_images/diseases_of_the_nervous_system_21805.png
L_0502,diseases of the nervous system,T_2894,"FIGURE 1.2 These bacteria, shown at more than 1,000 times their actual size, are the cause of bacterial meningitis. Despite their tiny size, they can cause very serious illness.",image,textbook_images/diseases_of_the_nervous_system_21806.png
L_0502,diseases of the nervous system,T_2895,FIGURE 1.3,image,textbook_images/diseases_of_the_nervous_system_21807.png
L_0502,diseases of the nervous system,T_2896,"FIGURE 1.4 Disease Huntingtons disease Cause An inherited gene codes for an ab- normal protein that causes the death of neurons. An abnormally low level of a neu- rotransmitter affects the part of the brain that controls movement. Abnormal changes in the brain cause the gradual loss of most nor- mal brain functions. Symptoms Uncontrolled jerky movements, loss of muscle control, problems with memory and learning Uncontrolled shaking, slowed movements, problems with speaking Memory loss, confusion, mood swings, gradual loss of control over mental and physical abilities",image,textbook_images/diseases_of_the_nervous_system_21808.png
L_0505,dna the genetic material,T_2903,FIGURE 1.1 DNAs three-dimensional structure is a double helix. The hydrogen bonds be- tween the bases at the center of the helix hold the helix together.,image,textbook_images/dna_the_genetic_material_21812.png
L_0505,dna the genetic material,T_2904,FIGURE 1.2,image,textbook_images/dna_the_genetic_material_21813.png
L_0507,echinoderms,T_2909,FIGURE 1.1,image,textbook_images/echinoderms_21816.png
L_0507,echinoderms,T_2909,FIGURE 1.2,image,textbook_images/echinoderms_21817.png
L_0509,effects of water pollution,T_2914,"FIGURE 1.1 Lake Valencia, Venezuela, showing green algal blooms. How did the algal bloom form? What will it do to the lake over time?",image,textbook_images/effects_of_water_pollution_21819.png
L_0509,effects of water pollution,T_2916,FIGURE 1.2,image,textbook_images/effects_of_water_pollution_21820.png
L_0510,energy pyramids,T_2918,"FIGURE 1.1 As illustrated by this ecological pyramid, it takes a lot of phytoplankton to support the carnivores of the oceans. This energy pyramid has four trophic levels, which sig- nify the organisms place in the food chain from the original source of energy.",image,textbook_images/energy_pyramids_21821.png
L_0511,enzymes in the digestive system,T_2919,"FIGURE 1.1 Bile is made in the liver, stored in the gallbladder, and then secreted into the intestine. It helps break down fats.",image,textbook_images/enzymes_in_the_digestive_system_21822.png
L_0512,evolution acts on the phenotype,T_2922,FIGURE 1.1,image,textbook_images/evolution_acts_on_the_phenotype_21823.png
L_0514,excretory system problems,T_2925,FIGURE 1.1,image,textbook_images/excretory_system_problems_21824.png
L_0514,excretory system problems,T_2926,"FIGURE 1.2 During dialysis, a patients blood is sent through a filter that removes waste prod- ucts. The clean blood is returned to the body.",image,textbook_images/excretory_system_problems_21825.png
L_0515,features of populations,T_2928,FIGURE 1.1,image,textbook_images/features_of_populations_21826.png
L_0515,features of populations,T_2928,FIGURE 1.2,image,textbook_images/features_of_populations_21827.png
L_0516,female reproductive structures,T_2929,FIGURE 1.1,image,textbook_images/female_reproductive_structures_21828.png
L_0517,female reproductive system,T_2930,"FIGURE 1.1 This represents a human egg, which is the gamete, or reproductive cell, in fe- males. Notice that is does not have a distinct shape, like a sperm cell has. The egg is a round cell with a haploid nucleus in the center. The egg contains most of the cytoplasm and organelles present in the first cell of a new organism.",image,textbook_images/female_reproductive_system_21829.png
L_0518,fermentation,T_2931,FIGURE 1.1,image,textbook_images/fermentation_21830.png
L_0521,fish,T_2936,"FIGURE 1.1 The humphead or Napoleon wrasse shows some of the general traits of fish, including scales, fins, and a streamlined body.",image,textbook_images/fish_21834.png
L_0521,fish,T_2937,FIGURE 1.2,image,textbook_images/fish_21835.png
L_0521,fish,T_2939,FIGURE 1.3 Whale sharks are the largest cartilagi- nous fish.,image,textbook_images/fish_21836.png
L_0522,flatworms,T_2943,FIGURE 1.1,image,textbook_images/flatworms_21839.png
L_0523,food and nutrients,T_2945,FIGURE 1.1,image,textbook_images/food_and_nutrients_21841.png
L_0525,fossils,T_2948,FIGURE 1.1,image,textbook_images/fossils_21844.png
L_0525,fossils,T_2948,"FIGURE 1.2 About 25 to 40 million years ago these insects were trapped in a gooey substance, called resin, that comes from trees. The fossils in the movie Jurassic Park were trapped in resin.",image,textbook_images/fossils_21845.png
L_0525,fossils,T_2948,"FIGURE 1.3 This device, called a spectrophotometer, can be used to measure the level of radioactive decay of certain elements in rocks and fossils to determine their age.",image,textbook_images/fossils_21846.png
L_0538,harmful bacteria,T_2987,"FIGURE 1.1 The Black Death, which killed at least one third of Europes population in the 1300s, is believed to have been caused by the bacterium Yersinia pestis.",image,textbook_images/harmful_bacteria_21872.png
L_0539,health hazards of air pollution,T_2992,FIGURE 1.1,image,textbook_images/health_hazards_of_air_pollution_21873.png
L_0540,health of the digestive system,T_2996,FIGURE 1.1,image,textbook_images/health_of_the_digestive_system_21874.png
L_0541,hearing and balance,T_2999,FIGURE 1.1,image,textbook_images/hearing_and_balance_21875.png
L_0541,hearing and balance,T_2999,FIGURE 1.2 nerve). The brain reads the sound and tells you what you are hearing.,image,textbook_images/hearing_and_balance_21876.png
L_0541,hearing and balance,T_3000,"FIGURE 1.3 This gymnast is using the semicircular canals in her ears, along with the cerebel- lum in her brain, to help keep her balance on the balance beam.",image,textbook_images/hearing_and_balance_21877.png
L_0542,heart,T_3001,FIGURE 1.1 The atria receive blood and the ventricles pump blood out of the heart.,image,textbook_images/heart_21879.png
L_0543,helpful bacteria,T_3004,FIGURE 1.1,image,textbook_images/helpful_bacteria_21881.png
L_0544,hiv and aids,T_3010,"FIGURE 1.1 In this picture, the large structure on the bottom is a human immune cell. It is infected with HIV. A new HIV particle is shown budding out of the immune cell.",image,textbook_images/hiv_and_aids_21882.png
L_0545,homeostasis,T_3013,FIGURE 1.1,image,textbook_images/homeostasis_21883.png
L_0546,how the eye works,T_3015,FIGURE 1.1,image,textbook_images/how_the_eye_works_21884.png
L_0547,human causes of extinction,T_3019,FIGURE 1.1,image,textbook_images/human_causes_of_extinction_21886.png
L_0548,human digestive system,T_3021,FIGURE 1.1,image,textbook_images/human_digestive_system_21888.png
L_0550,human genome project,T_3025,FIGURE 1.1,image,textbook_images/human_genome_project_21890.png
L_0551,human population,T_3026,FIGURE 1.1,image,textbook_images/human_population_21891.png
L_0552,human skeletal system,T_3030,"FIGURE 1.1 Storage. Bones store calcium. They contain more calcium than any other organ. Calcium is released by the bones when blood levels of calcium drop too low. The mineral, phosphorus is also stored in bones.",image,textbook_images/human_skeletal_system_21892.png
L_0552,human skeletal system,T_3031,FIGURE 1.2,image,textbook_images/human_skeletal_system_21893.png
L_0568,indoor air pollution,T_3086,FIGURE 1.1,image,textbook_images/indoor_air_pollution_21918.png
L_0569,infancy and childhood,T_3088,FIGURE 1.1 This babys teeth have started to come in. Babies often chew on toys or other objects when they are getting new teeth. They may even chew on their toes.,image,textbook_images/infancy_and_childhood_21919.png
L_0569,infancy and childhood,T_3089,FIGURE 1.2,image,textbook_images/infancy_and_childhood_21920.png
L_0571,influences on darwin,T_3093,FIGURE 1.1,image,textbook_images/influences_on_darwin_21922.png
L_0572,injuries of the nervous system,T_3096,FIGURE 1.1,image,textbook_images/injuries_of_the_nervous_system_21923.png
L_0579,jawless fish,T_3113,FIGURE 1.1,image,textbook_images/jawless_fish_21937.png
L_0580,keeping bones and joints healthy,T_3115,FIGURE 1.1,image,textbook_images/keeping_bones_and_joints_healthy_21938.png
L_0580,keeping bones and joints healthy,T_3116,FIGURE 1.2,image,textbook_images/keeping_bones_and_joints_healthy_21939.png
L_0581,keeping skin healthy,T_3121,FIGURE 1.1,image,textbook_images/keeping_skin_healthy_21940.png
L_0582,keeping the nervous system healthy,T_3124,"FIGURE 1.1 Wear safety goggles or sunglasses to protect your eyes from injury. Wear hearing protectors, such as ear plugs to protect your ears from loud sounds. Wear a safety helmet for activities like bike riding and skating ( Figure 1.2). Wear a safety belt every time you ride in a motor vehicle. Avoid unnecessary risks, such as performing dangerous stunts on your bike. Never dive into water that is not approved for diving. If the water is too shallow, you could seriously injure your brain or spinal cord. A few minutes of fun could turn into a lifetime in a wheelchair.",image,textbook_images/keeping_the_nervous_system_healthy_21941.png
L_0582,keeping the nervous system healthy,T_3124,FIGURE 1.2,image,textbook_images/keeping_the_nervous_system_healthy_21942.png
L_0583,kidneys,T_3125,FIGURE 1.1,image,textbook_images/kidneys_21943.png
L_0583,kidneys,T_3126,FIGURE 1.2,image,textbook_images/kidneys_21944.png
L_0586,light reactions of photosynthesis,T_3136,FIGURE 1.1,image,textbook_images/light_reactions_of_photosynthesis_21952.png
L_0586,light reactions of photosynthesis,T_3139,FIGURE 1.2,image,textbook_images/light_reactions_of_photosynthesis_21953.png
L_0586,light reactions of photosynthesis,T_3141,"FIGURE 1.3 Photosynthesis is a two stage process. As is depicted here, the energy from sun- light is needed to start photosynthesis. The initial stage is called the light reac- tions as they occur only in the presence of light. During these initial reactions, water is used and oxygen is released. The energy from sunlight is converted into a small amount of ATP and an en- ergy carrier called NADPH. Together with carbon dioxide, these are used to make glucose (sugar) through a process called the Calvin Cycle. NADP+ and ADP (and Pi, inorganic phosphate) are regenerated to complete the process.",image,textbook_images/light_reactions_of_photosynthesis_21954.png
L_0587,limiting factors to population growth,T_3142,FIGURE 1.1,image,textbook_images/limiting_factors_to_population_growth_21955.png
L_0590,male reproductive structures,T_3156,FIGURE 1.1,image,textbook_images/male_reproductive_structures_21965.png
L_0591,male reproductive system,T_3157,"FIGURE 1.1 Testosterone, the main sex hormone in males, allows men to build larger muscles than women.",image,textbook_images/male_reproductive_system_21966.png
L_0599,menstrual cycle,T_3172,FIGURE 1.1,image,textbook_images/menstrual_cycle_21984.png
L_0601,microscopes,T_3177,FIGURE 1.1 Basic light microscopes opened up a new world to curious people.,image,textbook_images/microscopes_21986.png
L_0601,microscopes,T_3177,FIGURE 1.2,image,textbook_images/microscopes_21987.png
L_0601,microscopes,T_3178,FIGURE 1.3 A scanning electron microscope.,image,textbook_images/microscopes_21988.png
L_0606,mollusks,T_3189,FIGURE 1.1,image,textbook_images/mollusks_21996.png
L_0606,mollusks,T_3189,FIGURE 1.2,image,textbook_images/mollusks_21997.png
L_0607,muscles and exercise,T_3192,FIGURE 1.1 Anaerobic exercises involve the muscles working against resistance. In this case the resistance is the weight of a barbell.,image,textbook_images/muscles_and_exercise_21998.png
L_0607,muscles and exercise,T_3193,"FIGURE 1.2 When done regularly, aerobic activities, such as cycling, make the heart stronger. Other aerobic activities include mowing lawn, shoveling snow and cross country skiing.",image,textbook_images/muscles_and_exercise_21999.png
L_0607,muscles and exercise,T_3194,FIGURE 1.3,image,textbook_images/muscles_and_exercise_22000.png
L_0608,muscles bones and movement,T_3195,"FIGURE 1.1 The biceps and triceps act against one another to bend and straighten the elbow joint. To bend the elbow, the biceps contracts and the triceps relaxes. To straighten the elbow, the triceps contract and the biceps relax.",image,textbook_images/muscles_bones_and_movement_22001.png
L_0610,nails and hair,T_3203,FIGURE 1.1,image,textbook_images/nails_and_hair_22003.png
L_0613,nervous system,T_3210,FIGURE 1.1,image,textbook_images/nervous_system_22008.png
L_0614,non infectious reproductive system disorders,T_3213,FIGURE 1.1,image,textbook_images/non_infectious_reproductive_system_disorders_22009.png
L_0616,nonrenewable resources,T_3217,FIGURE 1.1,image,textbook_images/nonrenewable_resources_22013.png
L_0616,nonrenewable resources,T_3217,FIGURE 1.2,image,textbook_images/nonrenewable_resources_22014.png
L_0619,organic compounds,T_3224,FIGURE 1.1,image,textbook_images/organic_compounds_22019.png
L_0619,organic compounds,T_3225,FIGURE 1.2,image,textbook_images/organic_compounds_22020.png
L_0619,organic compounds,T_3225,"FIGURE 1.3 Amino acids connect together like beads on a necklace. MET, ASN, TRP, and GLN refer to four different amino acids.",image,textbook_images/organic_compounds_22021.png
L_0619,organic compounds,T_3225,FIGURE 1.4,image,textbook_images/organic_compounds_22022.png
L_0619,organic compounds,T_3226,"FIGURE 1.5 Phospholipids in a membrane, shown as two layers (a bilayer) of phospholipids fac- ing each other.",image,textbook_images/organic_compounds_22023.png
L_0619,organic compounds,T_3227,"FIGURE 1.6 A model representing DNA, a nucleic acid.",image,textbook_images/organic_compounds_22024.png
L_0621,organization of the human body,T_3232,FIGURE 1.1,image,textbook_images/organization_of_the_human_body_22029.png
L_0621,organization of the human body,T_3233,FIGURE 1.2,image,textbook_images/organization_of_the_human_body_22030.png
L_0623,origins of life,T_3242,FIGURE 1.1,image,textbook_images/origins_of_life_22034.png
L_0623,origins of life,T_3242,FIGURE 1.2,image,textbook_images/origins_of_life_22035.png
L_0624,outdoor air pollution,T_3243,FIGURE 1.1,image,textbook_images/outdoor_air_pollution_22036.png
L_0624,outdoor air pollution,T_3243,FIGURE 1.2,image,textbook_images/outdoor_air_pollution_22037.png
L_0624,outdoor air pollution,T_3245,FIGURE 1.3,image,textbook_images/outdoor_air_pollution_22038.png
L_0626,pathogens,T_3251,FIGURE 1.1,image,textbook_images/pathogens_22041.png
L_0626,pathogens,T_3251,FIGURE 1.2,image,textbook_images/pathogens_22042.png
L_0626,pathogens,T_3251,FIGURE 1.3,image,textbook_images/pathogens_22043.png
L_0626,pathogens,T_3251,"FIGURE 1.4 The Herpes simplex virus, which is rep- resented here, causes cold sores on the lips. Viruses are extremely small parti- cles. This illustration is greatly magnified.",image,textbook_images/pathogens_22044.png
L_0626,pathogens,T_3252,FIGURE 1.5,image,textbook_images/pathogens_22045.png
L_0627,pedigree analysis,T_3255,"FIGURE 1.1 In a pedigree, squares symbolize males, and circles represent females. A horizon- tal line joining a male and female indicates that the couple had offspring. Vertical lines indicate offspring which are listed left to right, in order of birth. Shading of the circle or square indicates an individual who has the trait being traced. In this pedigree, the inheritance of the recessive trait is being traced. A is the dominant allele, and a is the recessive allele.",image,textbook_images/pedigree_analysis_22047.png
L_0628,peripheral nervous system,T_3256,"FIGURE 1.1 The blue lines in this drawing represent nerves of the peripheral nervous system. Every peripheral nerve is connected di- rectly or indirectly to the spinal cord. No- tice the thick sciatic nerve. It is the longest (and thickest) nerve in the body, running from the lower region of the spinal cord to just above the knee.",image,textbook_images/peripheral_nervous_system_22048.png
L_0628,peripheral nervous system,T_3257,"FIGURE 1.2 The sensory division interprets messages from sense organs and internal organs, and the motor division sends messages to internal organs, glands, and muscles.",image,textbook_images/peripheral_nervous_system_22049.png
L_0628,peripheral nervous system,T_3257,FIGURE 1.3,image,textbook_images/peripheral_nervous_system_22050.png
L_0628,peripheral nervous system,T_3258,"FIGURE 1.4 These womens central nervous systems are controlling the movements of their hands and arms as they play the violin. Their brains send commands to their so- matic nervous system, which controls the muscles of their hands and arms.",image,textbook_images/peripheral_nervous_system_22051.png
L_0628,peripheral nervous system,T_3258,"FIGURE 1.5 The woman pictured here is just pretend- ing to be frightened, but assuming that she really was scared, think of which di- vision of the autonomic nervous system would prepare her body for an emergency. your heart rate. The fact that this happened in the blink of an eye shows how amazing the nervous system is.",image,textbook_images/peripheral_nervous_system_22052.png
L_0637,polygenic traits,T_3277,"FIGURE 1.1 Polygenic traits tend to result in a distribu- tion that resembles a bell-shaped curve, with few at the extremes and most in the middle. There may be 4 or 6 or more alleles involved in the phenotype. At the left extreme, individuals are com- pletely dominant for all alleles, and at the right extreme, individuals are completely recessive for all alleles. Individuals in the middle have various combinations of recessive and dominant alleles.",image,textbook_images/polygenic_traits_22067.png
L_0638,population growth patterns,T_3279,FIGURE 1.1,image,textbook_images/population_growth_patterns_22068.png
L_0638,population growth patterns,T_3280,FIGURE 1.2,image,textbook_images/population_growth_patterns_22069.png
L_0638,population growth patterns,T_3281,"FIGURE 1.3 Usually, populations first grow exponentially while resources are abundant. But as populations increase and re- sources become less available, rates of growth slow down and slowly level off, reaching the carrying capacity. The carrying capacity is the upper limit to the population size that the environment can support. This type of growth is shown as an ""S-shaped"" curve below ( Figure 1.3) and is called logistic growth. Why do you think occurs?",image,textbook_images/population_growth_patterns_22070.png
L_0640,pregnancy and childbirth,T_3284,FIGURE 1.1,image,textbook_images/pregnancy_and_childbirth_22074.png
L_0640,pregnancy and childbirth,T_3286,FIGURE 1.2,image,textbook_images/pregnancy_and_childbirth_22075.png
L_0641,preserving water sources,T_3289,FIGURE 1.1,image,textbook_images/preserving_water_sources_22076.png
L_0642,preventing infectious diseases,T_3292,"FIGURE 1.1 This picture shows the proper way to wash your hands. Frequent hand washing helps prevent the spread of pathogens. and wash your hands often to avoid spreading pathogens to other people. Dont go to work or school if youre vomiting, have diarrhea or are running a fever (and if you are, drink plenty of fluids). Also, to avoid infectious diseases, dont share personal items; use your own toothbrush, comb, and razor. And avoid sharing drinking glasses or dining utensils.",image,textbook_images/preventing_infectious_diseases_22078.png
L_0643,preventing noninfectious diseases,T_3293,FIGURE 1.1,image,textbook_images/preventing_noninfectious_diseases_22079.png
L_0645,process of cellular respiration,T_3298,FIGURE 1.1,image,textbook_images/process_of_cellular_respiration_22084.png
L_0646,processes of breathing,T_3305,FIGURE 1.1,image,textbook_images/processes_of_breathing_22085.png
L_0647,producers,T_3306,FIGURE 1.1,image,textbook_images/producers_22086.png
L_0654,recombinant dna,T_3321,FIGURE 1.1,image,textbook_images/recombinant_dna_22095.png
L_0655,reduce reuse and recycle,T_3323,FIGURE 1.1,image,textbook_images/reduce_reuse_and_recycle_22096.png
L_0655,reduce reuse and recycle,T_3325,"FIGURE 1.2 These aluminum cans are packed to- gether in a recycling plant to be reused. If you have recycling in your community, make sure you separate aluminum, plastics, glass, and paper products. See if your school recycles. If not, you and some friends could start a recycling club, or organize efforts to better recycling goals.",image,textbook_images/reduce_reuse_and_recycle_22097.png
L_0656,renewable resources and alternative energy sources,T_3327,"FIGURE 1.1 Wind power, a renewable resource, shown here in a modern wind energy farm. The wind is used to turn turbines that generate electricity.",image,textbook_images/renewable_resources_and_alternative_energy_sources_22098.png
L_0656,renewable resources and alternative energy sources,T_3327,FIGURE 1.2 These solar panels convert sunlight into electricity.,image,textbook_images/renewable_resources_and_alternative_energy_sources_22099.png
L_0656,renewable resources and alternative energy sources,T_3327,FIGURE 1.3 Hydropower plant.,image,textbook_images/renewable_resources_and_alternative_energy_sources_22100.png
L_0656,renewable resources and alternative energy sources,T_3327,FIGURE 1.4,image,textbook_images/renewable_resources_and_alternative_energy_sources_22101.png
L_0661,respiration,T_3340,"FIGURE 1.1 Being able to control breathing is impor- tant for many activities, such as swim- ming. The woman in the photograph is exhaling as she exits the water.",image,textbook_images/respiration_22107.png
L_0661,respiration,T_3340,"FIGURE 1.2 During respiration, oxygen gets pulled into the lungs and enters the blood by passing across the thin alveoli mem- branes and into the capillaries. The alve- oli are at the end of the long air passages.",image,textbook_images/respiration_22108.png
L_0662,respiratory system diseases,T_3342,FIGURE 1.1,image,textbook_images/respiratory_system_diseases_22109.png
L_0662,respiratory system diseases,T_3345,FIGURE 1.2 Asthma occurs when the bronchioles swell and the muscles around the bronchioles contract.,image,textbook_images/respiratory_system_diseases_22110.png
L_0662,respiratory system diseases,T_3346,FIGURE 1.3,image,textbook_images/respiratory_system_diseases_22111.png
L_0662,respiratory system diseases,T_3347,FIGURE 1.4,image,textbook_images/respiratory_system_diseases_22112.png
L_0662,respiratory system diseases,T_3349,FIGURE 1.5,image,textbook_images/respiratory_system_diseases_22113.png
L_0662,respiratory system diseases,T_3349,FIGURE 1.6,image,textbook_images/respiratory_system_diseases_22114.png
L_0664,respiratory system organs,T_3356,FIGURE 1.1,image,textbook_images/respiratory_system_organs_22115.png
L_0664,respiratory system organs,T_3356,FIGURE 1.2,image,textbook_images/respiratory_system_organs_22116.png
L_0665,rna,T_3357,FIGURE 1.1,image,textbook_images/rna_22117.png
L_0667,roundworms,T_3362,FIGURE 1.1,image,textbook_images/roundworms_22120.png
L_0675,segmented worms,T_3389,FIGURE 1.1 Leeches are parasitic worms. Notice the presence of segments.,image,textbook_images/segmented_worms_22135.png
L_0676,sex linked inheritance,T_3391,FIGURE 1.1 A person with red-green colorblindness would not be able to see the number.,image,textbook_images/sex_linked_inheritance_22136.png
L_0677,sexually transmitted infections,T_3393,FIGURE 1.1 This graph shows data on the number of cases of chlamydia in U.S. males and females in 2009. Which two age groups had the highest rates of chlamydia? Why do you think rates were highest in these age groups?,image,textbook_images/sexually_transmitted_infections_22137.png
L_0677,sexually transmitted infections,T_3394,"FIGURE 1.2 This lip blister, or cold sore, is caused by a herpes virus. The virus is closely related to the virus that causes genital herpes. The genital herpes virus causes similar blisters on the genitals. If youve ever had a cold sore, you know how painful they can be. Genital herpes blisters are also painful.",image,textbook_images/sexually_transmitted_infections_22138.png
L_0678,skeletal system joints,T_3395,FIGURE 1.1,image,textbook_images/skeletal_system_joints_22139.png
L_0678,skeletal system joints,T_3395,FIGURE 1.2 The joints between your vertebrae are partially movable.,image,textbook_images/skeletal_system_joints_22140.png
L_0678,skeletal system joints,T_3396,FIGURE 1.3 Your hip joint is a ball-and-socket joint. The ball end of one bone fits into the socket of another bone. These joints can move in many different directions.,image,textbook_images/skeletal_system_joints_22141.png
L_0678,skeletal system joints,T_3396,"FIGURE 1.4 Hinge Joint. The knee joint is a hinge joint. Like a door hinge, a hinge joint allows backward and forward movement.",image,textbook_images/skeletal_system_joints_22142.png
L_0678,skeletal system joints,T_3396,FIGURE 1.5 Pivot Joint. The joint at which the radius and ulna meet is a pivot joint. Movement at this joint allows you to flip your palm over without moving your elbow joint.,image,textbook_images/skeletal_system_joints_22143.png
L_0679,skin,T_3397,FIGURE 1.1,image,textbook_images/skin_22144.png
L_0679,skin,T_3400,FIGURE 1.2,image,textbook_images/skin_22145.png
L_0679,skin,T_3402,FIGURE 1.3,image,textbook_images/skin_22146.png
L_0680,smooth skeletal and cardiac muscles,T_3403,FIGURE 1.1,image,textbook_images/smooth_skeletal_and_cardiac_muscles_22147.png
L_0682,sources of water pollution,T_3407,FIGURE 1.1,image,textbook_images/sources_of_water_pollution_22152.png
L_0691,the carbon cycle,T_3428,FIGURE 1.1,image,textbook_images/the_carbon_cycle_22166.png
L_0694,timeline of evolution,T_3437,FIGURE 1.1 The geologic time scale is used to de- scribe events that occurred millions and billions of years ago. The geologic time scale of Earths past is organized ac- cording to events that took place during different periods on the time scale. Ge- ologic time is the same as the age of the Earth: between 4.404 and 4.57 billion years. Look closely for such events as the extinction of dinosaurs and many marine animals.,image,textbook_images/timeline_of_evolution_22170.png
L_0695,touch,T_3439,FIGURE 1.1 The spines on this cactus are like needles; they help keep away animals that might want to eat the cactus.,image,textbook_images/touch_22171.png
L_0697,transcription of dna to rna,T_3444,FIGURE 1.1,image,textbook_images/transcription_of_dna_to_rna_22174.png
L_0697,transcription of dna to rna,T_3444,FIGURE 1.2,image,textbook_images/transcription_of_dna_to_rna_22175.png
L_0698,translation of rna to protein,T_3445,FIGURE 1.1,image,textbook_images/translation_of_rna_to_protein_22176.png
L_0698,translation of rna to protein,T_3445,FIGURE 1.2,image,textbook_images/translation_of_rna_to_protein_22177.png
L_0698,translation of rna to protein,T_3445,"FIGURE 1.3 This chart shows the genetic code used by all organisms. For example, an RNA codon reading GUU would encode for a valine (Val) according to this chart. Start at the center for the first base of the three base codon, and work your way out. Notice that more than one codon may encode for a single amino acid. For example, glycine (Gly) is encoded by a GGG, GGA, GGC, and GGU. Notice there are 64 codons. Of the 64 codons, three are stop codons.",image,textbook_images/translation_of_rna_to_protein_22178.png
L_0702,types of echinoderms,T_3459,"FIGURE 1.1 The giant red brittle star, an ophiuroid echinoderm.",image,textbook_images/types_of_echinoderms_22187.png
L_0704,types of nutrients,T_3469,FIGURE 1.1,image,textbook_images/types_of_nutrients_22189.png
L_0704,types of nutrients,T_3471,FIGURE 1.2,image,textbook_images/types_of_nutrients_22190.png
L_0704,types of nutrients,T_3472,"FIGURE 1.3 can lead to heart disease. 2. Unsaturated fats are found mainly in plant foods, such as vegetable oil, olive oil, and nuts. Unsaturated lipids are also found in fish, such as salmon. Unsaturated lipids are needed in small amounts for good health. Most lipids in your diet should be unsaturated.",image,textbook_images/types_of_nutrients_22191.png
L_0705,urinary system,T_3474,FIGURE 1.1,image,textbook_images/urinary_system_22192.png
L_0709,vision correction,T_3489,FIGURE 1.1,image,textbook_images/vision_correction_22201.png
L_0709,vision correction,T_3489,FIGURE 1.2,image,textbook_images/vision_correction_22202.png
L_0716,acids and bases,T_3519,FIGURE 10.6 Blue litmus paper turns red when placed in an acidic solution.,image,textbook_images/acids_and_bases_22216.png
L_0716,acids and bases,T_3520,FIGURE 10.7 Acids are used widely for many purposes.,image,textbook_images/acids_and_bases_22217.png
L_0716,acids and bases,T_3523,FIGURE 10.8 Red litmus paper turns blue when placed in a basic solution.,image,textbook_images/acids_and_bases_22218.png
L_0716,acids and bases,T_3524,FIGURE 10.9 Bases are used in many products.,image,textbook_images/acids_and_bases_22219.png
L_0716,acids and bases,T_3529,FIGURE 10.10 This pH scale shows the acidity of several common acids and bases. Which substance on this scale is the weakest acid? Which substance is the strongest base?,image,textbook_images/acids_and_bases_22220.png
L_0716,acids and bases,T_3529,FIGURE 10.11 Acid fog and acid rain killed the trees in this forest.,image,textbook_images/acids_and_bases_22221.png
L_0716,acids and bases,T_3529,FIGURE 10.12 What neutral products are produced when antacid tablets react with hydrochloric acid in the stomach?,image,textbook_images/acids_and_bases_22222.png
L_0717,radioactivity,T_3531,"FIGURE 11.1 X-rays are a form of energy that can pass through skin and muscle but not bone. Thats why bones show up clearly in an X-ray, while the rest of the body is barely visible.",image,textbook_images/radioactivity_22223.png
L_0717,radioactivity,T_3533,FIGURE 11.2 This periodic table highlights elements that have only radioactive isotopes.,image,textbook_images/radioactivity_22224.png
L_0717,radioactivity,T_3534,FIGURE 11.3 This sign is used to warn people of dan- gerous radiation.,image,textbook_images/radioactivity_22225.png
L_0717,radioactivity,T_3535,FIGURE 11.4 A Geiger counter detects radiation.,image,textbook_images/radioactivity_22226.png
L_0717,radioactivity,T_3536,FIGURE 11.5 This machine scans a patients body and detects radiation.,image,textbook_images/radioactivity_22227.png
L_0718,radioactive decay,T_3538,FIGURE 11.6 Alpha decay results in the loss of two protons and two neutrons from a nucleus.,image,textbook_images/radioactive_decay_22228.png
L_0718,radioactive decay,T_3539,"FIGURE 11.7 In beta decay, an electron and a proton form from a neutron (another unusual particle, called an antineutrino, is also produced). Only the electron is emitted from the nucleus. How does this change the atomic number and atomic mass of the atom?",image,textbook_images/radioactive_decay_22229.png
L_0718,radioactive decay,T_3541,"FIGURE 11.8 Its easy to stop alpha particles and even beta particles. However, its very difficult to stop gamma rays.",image,textbook_images/radioactive_decay_22230.png
L_0718,radioactive decay,T_3542,FIGURE 11.9 This diagram models the rate of decay of phosphorus-32 to sulfur-32.,image,textbook_images/radioactive_decay_22231.png
L_0718,radioactive decay,T_3544,"FIGURE 11.10 After organisms die, the carbon-14 they contain is lost at a constant rate.",image,textbook_images/radioactive_decay_22232.png
L_0719,nuclear energy,T_3547,FIGURE 11.11 This pellet of uranium-235 can release a huge amount of energy if it undergoes nuclear fission.,image,textbook_images/nuclear_energy_22233.png
L_0719,nuclear energy,T_3547,FIGURE 11.12 The fissioning of a nucleus of uranium-235 begins when it captures a neutron. MEDIA Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/5018,image,textbook_images/nuclear_energy_22234.png
L_0719,nuclear energy,T_3547,"FIGURE 11.13 In a nuclear chain reaction, each nuclear reaction leads to more nuclear reactions.",image,textbook_images/nuclear_energy_22235.png
L_0719,nuclear energy,T_3548,FIGURE 11.14 This diagram shows the main parts of a nuclear power plant.,image,textbook_images/nuclear_energy_22236.png
L_0719,nuclear energy,T_3550,"FIGURE 11.15 In this nuclear fusion reaction, nuclei of two hydrogen isotopes (tritium and deu- terium) fuse together. They form a helium nucleus, a neutron, and energy.",image,textbook_images/nuclear_energy_22237.png
L_0719,nuclear energy,T_3552,FIGURE 11.16 The extremely hot core of the sun radiates energy from nuclear fusion.,image,textbook_images/nuclear_energy_22238.png
L_0719,nuclear energy,T_3552,"FIGURE 11.17 In the thermonuclear reactor modeled here, radiation from fusion is used to heat water and form steam. The steam can then be used to turn a turbine and gen- erate electricity.",image,textbook_images/nuclear_energy_22239.png
L_0719,nuclear energy,T_3553,FIGURE 11.18 Albert Einstein is considered by many to be the greatest physicist of all time.,image,textbook_images/nuclear_energy_22240.png
L_0720,distance and direction,T_3556,"FIGURE 12.1 These are just a few examples of people or things in motion. If you look around, youre likely to see many more.",image,textbook_images/distance_and_direction_22241.png
L_0720,distance and direction,T_3556,"FIGURE 12.2 To a person outside the bus, the buss motion is obvious. To children riding the bus, its motion may not be as obvious.",image,textbook_images/distance_and_direction_22242.png
L_0720,distance and direction,T_3557,FIGURE 12.3 These students are running a 100-meter sprint.,image,textbook_images/distance_and_direction_22243.png
L_0720,distance and direction,T_3560,"FIGURE 12.4 This map shows the routes from Mias house to the school, post office, and park.",image,textbook_images/distance_and_direction_22244.png
L_0721,speed and velocity,T_3561,FIGURE 12.6 Speed limit signs like this one warn drivers to reduce their speed on dangerous roads.,image,textbook_images/speed_and_velocity_22246.png
L_0721,speed and velocity,T_3562,FIGURE 12.7 Cars race by in a blur of motion on an open highway but crawl at a snails pace when they hit city traffic.,image,textbook_images/speed_and_velocity_22247.png
L_0721,speed and velocity,T_3564,FIGURE 12.8 This graph shows how far a bike rider is from her starting point at 7:30 AM until she returned at 12:30 PM.,image,textbook_images/speed_and_velocity_22248.png
L_0721,speed and velocity,T_3566,FIGURE 12.9 These vectors show both the speed and direction of motion.,image,textbook_images/speed_and_velocity_22249.png
L_0722,acceleration,T_3567,"FIGURE 12.11 How is velocity changing in each of these pictures? sudden. You feel yourself thrust forward. If the car turns right, you feel as though you are being pushed to the left. With a left turn, you feel a push to the right. The next time you ride in a car, notice how it feels as the car accelerates in each of these ways. For an interactive simulation about acceleration, go to this URL: http://phet.colorado.edu/en/",image,textbook_images/acceleration_22251.png
L_0722,acceleration,T_3568,FIGURE 12.12 Gravity helps this cyclist increase his downhill velocity.,image,textbook_images/acceleration_22252.png
L_0722,acceleration,T_3569,FIGURE 12.13 This graph shows how the velocity of a runner changes during a 10-second sprint.,image,textbook_images/acceleration_22253.png
L_0723,what is force,T_3571,"FIGURE 13.1 When this girl pushes the swing away from her, it causes the swing to move in that direction.",image,textbook_images/what_is_force_22254.png
L_0723,what is force,T_3571,FIGURE 13.2 Forces can vary in both strength and direction.,image,textbook_images/what_is_force_22255.png
L_0723,what is force,T_3573,FIGURE 13.3 A book resting on a table is acted on by two opposing forces.,image,textbook_images/what_is_force_22256.png
L_0723,what is force,T_3575,"FIGURE 13.4 When unbalanced forces are applied to an object in opposite directions, the smaller force is subtracted from the larger force to yield the net force.",image,textbook_images/what_is_force_22257.png
L_0723,what is force,T_3575,"FIGURE 13.5 When two forces are applied to an object in the same direction, the two forces are added to yield the net force. If you need more practice calculating net force, go to this URL: http://www.physicsclassroom.com/class/newtlaws/U",image,textbook_images/what_is_force_22258.png
L_0724,friction,T_3576,FIGURE 13.7 Sometimes friction is useful. Sometimes its not.,image,textbook_images/friction_22260.png
L_0724,friction,T_3577,FIGURE 13.8 The surface of metal looks very smooth unless you look at it under a high-powered microscope.,image,textbook_images/friction_22261.png
L_0724,friction,T_3578,FIGURE 13.9 The knife-like blades of speed skates min- imize friction with the ice.,image,textbook_images/friction_22262.png
L_0724,friction,T_3579,"FIGURE 13.10 When you rub the surface of a match head across the rough striking surface on the matchbox, the friction produces enough heat to ignite the match.",image,textbook_images/friction_22263.png
L_0724,friction,T_3580,FIGURE 13.11 A dolly with wheels lets you easily roll boxes across the floor.,image,textbook_images/friction_22264.png
L_0724,friction,T_3581,FIGURE 13.12 Static friction between shoes and the sidewalk makes it possible to walk without slipping.,image,textbook_images/friction_22265.png
L_0724,friction,T_3584,FIGURE 13.13 The ball bearings in this wheel reduce fric- tion between the inner and outer cylinders when they turn.,image,textbook_images/friction_22266.png
L_0725,gravity,T_3587,FIGURE 13.16 A scale measures the pull of gravity on an object.,image,textbook_images/gravity_22269.png
L_0725,gravity,T_3588,FIGURE 13.17 Sir Isaac Newton discovered that gravity is universal.,image,textbook_images/gravity_22270.png
L_0725,gravity,T_3591,FIGURE 13.18 The moon keeps moving around Earth rather than the sun because it is much closer to Earth.,image,textbook_images/gravity_22271.png
L_0725,gravity,T_3591,FIGURE 13.19 Einstein thought that gravity is the effect of curves in space and time around mas- sive objects such as Earth. He proposed that the curves in space and time cause nearby objects to follow a curved path. How does this differ from Newtons idea of gravity?,image,textbook_images/gravity_22272.png
L_0725,gravity,T_3593,"FIGURE 13.20 A boy drops an object at time t = 0 s. At time t = 1 s, the object is falling at a velocity of 9.8 m/s. What is its velocity by time t = 5 ?",image,textbook_images/gravity_22273.png
L_0725,gravity,T_3594,FIGURE 13.21 The cannon ball moves in a curved path because of the combined horizontal and downward forces.,image,textbook_images/gravity_22274.png
L_0725,gravity,T_3595,FIGURE 13.22 Aiming at the center of a target is likely to result in a hit below the bulls eye.,image,textbook_images/gravity_22275.png
L_0725,gravity,T_3595,"FIGURE 13.23 In this diagram, ""v"" represents the forward velocity of the moon, and ""a"" represents the acceleration due to gravity. The line encircling Earth shows the moons actual orbit, which results from the combination of ""v"" and ""a.""",image,textbook_images/gravity_22276.png
L_0727,newtons first law,T_3598,"FIGURE 14.2 Pool balls remain at rest until an unbal- anced force is applied to them. After they are in motion, they stay in motion until another force opposes their motion.",image,textbook_images/newtons_first_law_22281.png
L_0727,newtons first law,T_3600,FIGURE 14.3 The tendency of an object to resist a change in its motion depends on its mass. Which box has greater inertia?,image,textbook_images/newtons_first_law_22282.png
L_0727,newtons first law,T_3601,"FIGURE 14.4 Force must be applied to overcome the inertia of a soccer ball at rest. Once objects start moving, inertia keeps them moving without any additional force being applied. In fact, they wont stop moving unless another unbalanced force opposes their motion. What if the rolling soccer ball is not kicked by another player or stopped by a fence or other object? Will it just keep rolling forever? It would if another unbalanced force did not oppose its motion. Friction in this case rolling friction with the ground will oppose the motion of the rolling soccer ball. As a result, the ball will eventually come to rest. Friction opposes the motion of all moving objects, so, like the soccer ball, all moving objects eventually come to a stop even if no other forces oppose their motion.",image,textbook_images/newtons_first_law_22283.png
L_0728,newtons second law,T_3603,FIGURE 14.6 Hitting a baseball with greater force gives it greater acceleration. Hitting a softball with the same amount of force results in less acceleration. Can you explain why?,image,textbook_images/newtons_second_law_22285.png
L_0728,newtons second law,T_3604,"FIGURE 14.7 This empty trunk has a mass of 10 kilo- grams. The weights also have a mass of 10 kilograms. If the weights are placed in the trunk, what will be its mass? How will this affect its acceleration?",image,textbook_images/newtons_second_law_22286.png
L_0729,newtons third law,T_3606,FIGURE 14.9 Each example shown here includes an action and reaction.,image,textbook_images/newtons_third_law_22288.png
L_0729,newtons third law,T_3607,FIGURE 14.10 A bowling ball and a softball differ in mass. How does this affect their momen- tum?,image,textbook_images/newtons_third_law_22289.png
L_0729,newtons third law,T_3609,FIGURE 14.11 How can you tell momentum has been conserved in this collision?,image,textbook_images/newtons_third_law_22290.png
L_0731,buoyancy of fluids,T_3624,"FIGURE 15.12 Fluid pressure exerts force on all sides of this object, but the force is greater at the bottom of the object where the fluid is deeper.",image,textbook_images/buoyancy_of_fluids_22302.png
L_0731,buoyancy of fluids,T_3626,FIGURE 15.13 Whether an object sinks or floats depends on its weight and the strength of the buoyant force acting on it.,image,textbook_images/buoyancy_of_fluids_22303.png
L_0731,buoyancy of fluids,T_3627,FIGURE 15.14 The substances pictured here float in a fluid because they are less dense than the fluid.,image,textbook_images/buoyancy_of_fluids_22304.png
L_0732,work,T_3628,FIGURE 16.2 Carrying a box while walking does not result in work being done. Work is done only when the box is first lifted up from the ground. Can you explain why?,image,textbook_images/work_22307.png
L_0732,work,T_3630,FIGURE 16.3 Weight lifters do more work when they move weights a longer distance or move heavier weights.,image,textbook_images/work_22308.png
L_0732,work,T_3632,FIGURE 16.4 Which way of removing leaves would take less effort on your part?,image,textbook_images/work_22309.png
L_0732,work,T_3632,FIGURE 16.5 Hair dryers vary in power. How do you think this affects drying time?,image,textbook_images/work_22310.png
L_0732,work,T_3634,FIGURE 16.6 The horses and the tractor are both pulling a plow. The horses provide less horsepower than the tractor. Which do you think will get the job done faster?,image,textbook_images/work_22311.png
L_0733,machines,T_3636,"FIGURE 16.8 Both of these machines increase the force applied by the user, while reducing the distance over which the force is applied.",image,textbook_images/machines_22313.png
L_0733,machines,T_3637,"FIGURE 16.9 Both of these machines increase the dis- tance over which force applied, while re- ducing the strength of the force.",image,textbook_images/machines_22314.png
L_0733,machines,T_3638,FIGURE 16.10 Both of these machines change the direction over which force is applied. The claw hammer also increases the strength of the force.,image,textbook_images/machines_22315.png
L_0733,machines,T_3642,FIGURE 16.11 A ramp is a machine because it makes work easier by changing a force. How does it change force?,image,textbook_images/machines_22316.png
L_0733,machines,T_3644,FIGURE 16.12 The input force is applied along the length of the sloping ramp surface. The output force is applied along the height of the ramp. The input distance is greater than the output distance. This means that the input force is less than the output force.,image,textbook_images/machines_22317.png
L_0734,simple machines,T_3646,FIGURE 16.14 An inclined plane makes it easier to move objects to a higher elevation.,image,textbook_images/simple_machines_22319.png
L_0734,simple machines,T_3648,FIGURE 16.15 The thin edge of a knife or chisel enters an object and forces it apart.,image,textbook_images/simple_machines_22320.png
L_0734,simple machines,T_3649,FIGURE 16.16 All of these examples are screws. Can you identify the inclined plane in each example?,image,textbook_images/simple_machines_22321.png
L_0734,simple machines,T_3649,FIGURE 16.17 The threads of a screw or bolt may be closer together or farther apart. How does this affect its ideal mechanical ad- vantage?,image,textbook_images/simple_machines_22322.png
L_0734,simple machines,T_3650,FIGURE 16.18 Using a hammer to remove a nail changes both the direction and strength of the applied force. Where is the fulcrum of the hammer when it is used in this way?,image,textbook_images/simple_machines_22323.png
L_0734,simple machines,T_3651,"FIGURE 16.19 Which class of lever would you use to carry a heavy load, sweep a floor, or pry open a can of paint?",image,textbook_images/simple_machines_22324.png
L_0734,simple machines,T_3653,FIGURE 16.20 Both a Ferris wheel and a car steering wheel have an outer wheel and an inner axle.,image,textbook_images/simple_machines_22325.png
L_0734,simple machines,T_3654,"FIGURE 16.21 In both of these examples, pulling the rope turns the wheel of the pulley.",image,textbook_images/simple_machines_22326.png
L_0735,compound machines,T_3656,FIGURE 16.24 A pair of scissors is a compound machine consisting of levers and wedges.,image,textbook_images/compound_machines_22329.png
L_0735,compound machines,T_3658,"FIGURE 16.25 As a third-class lever, how does a fishing rod change the force applied to the rod? How does the reel help land the fish?",image,textbook_images/compound_machines_22330.png
L_0736,types of energy,T_3660,FIGURE 17.2 It takes energy to swing a bat. Where does the batter get her energy?,image,textbook_images/types_of_energy_22332.png
L_0736,types of energy,T_3661,FIGURE 17.3 All of these photos show things that have kinetic energy because they are moving.,image,textbook_images/types_of_energy_22333.png
L_0736,types of energy,T_3662,"FIGURE 17.4 Before leaves fall from trees in autumn, they have potential energy. Why do they have the potential to fall?",image,textbook_images/types_of_energy_22334.png
L_0736,types of energy,T_3663,FIGURE 17.5 All three of these people have gravita- tional potential energy. Can you think of other examples? You Try It! Problem: Kris is holding a 2-kg book 1.5 m above the floor. What is the gravitational potential energy of the book?,image,textbook_images/types_of_energy_22335.png
L_0736,types of energy,T_3664,FIGURE 17.6 Changing the shape of an elastic material gives it potential energy.,image,textbook_images/types_of_energy_22336.png
L_0736,types of energy,T_3667,FIGURE 17.7 Energy continuously changes back and forth between potential and kinetic energy on a swing or trampoline.,image,textbook_images/types_of_energy_22337.png
L_0737,forms of energy,T_3670,FIGURE 17.9 Kinetic and potential energy add up to mechanical energy.,image,textbook_images/forms_of_energy_22339.png
L_0737,forms of energy,T_3671,FIGURE 17.10 Chemical energy is stored in wood and released when the wood burns.,image,textbook_images/forms_of_energy_22340.png
L_0737,forms of energy,T_3672,FIGURE 17.11 A lightning bolt is a powerful discharge of electrical energy. A battery contains stored chemical energy and converts it to electrical energy.,image,textbook_images/forms_of_energy_22341.png
L_0737,forms of energy,T_3674,"FIGURE 17.12 In the sun, hydrogen nuclei fuse to form helium nuclei. This releases a huge amount of energy, some of which reaches Earth.",image,textbook_images/forms_of_energy_22342.png
L_0737,forms of energy,T_3674,"FIGURE 17.13 Atoms are moving at the same speed in the soup on the spoon as they are in the soup in the pot. However, there are more atoms of soup in the pot, so it has more thermal energy.",image,textbook_images/forms_of_energy_22343.png
L_0737,forms of energy,T_3675,"FIGURE 17.14 Radio waves, microwaves, and X rays are examples of electromagnetic energy.",image,textbook_images/forms_of_energy_22344.png
L_0737,forms of energy,T_3676,FIGURE 17.15 Vibrating objects such as drumheads pro- duce sound energy.,image,textbook_images/forms_of_energy_22345.png
L_0737,forms of energy,T_3677,FIGURE 17.16 Energy is constantly changing form. Can you think of other examples of energy conversions?,image,textbook_images/forms_of_energy_22346.png
L_0738,energy resources,T_3678,FIGURE 17.18 Whitewater rafting is an exciting sport.,image,textbook_images/energy_resources_22348.png
L_0738,energy resources,T_3679,"FIGURE 17.19 Do you use any of these fossil fuels? How do you use them? sunlight to stored chemical energy in food, which was eaten by other organisms. After the plants and other organisms died, their remains gradually changed to fossil fuels as they were pressed beneath layers of sediments. Petroleum and natural gas formed from marine organisms and are often found together. Coal formed from giant tree ferns and other swamp plants. When fossil fuels burn, they release thermal energy, water vapor, and carbon dioxide. Carbon dioxide produced by fossil fuel use is a major cause of global warming. The burning of fossil fuels also releases many pollutants into the air. Pollutants such as sulfur dioxide form acid rain, which kills living things and damages metals, stonework, and other materials. Pollutants such as nitrogen oxides cause smog, which is harmful to human health. Tiny particles, or particulates, released when fossil fuels burn also harm human health. Natural gas releases the least pollution; coal releases the most (see Figure 17.20). Petroleum has the additional risk of oil spills, which may seriously damage ecosystems.",image,textbook_images/energy_resources_22349.png
L_0738,energy resources,T_3679,"FIGURE 17.20 This table compares the levels of several air pollutants released by the burning of natural gas, oil, and coal.",image,textbook_images/energy_resources_22350.png
L_0738,energy resources,T_3680,FIGURE 17.21 Do you remember Japans 2011 nuclear disaster? (Note: the map on the right is not to scale.),image,textbook_images/energy_resources_22351.png
L_0738,energy resources,T_3688,FIGURE 17.22 Which of the energy resources in this circle graph are renewable?,image,textbook_images/energy_resources_22352.png
L_0738,energy resources,T_3688,"FIGURE 17.23 The U.S. uses far more oil than any other country in the world. It is even far ahead of the next largest oil user, which is China. The differences in use per person in these countries are even greater.",image,textbook_images/energy_resources_22353.png
L_0738,energy resources,T_3688,FIGURE 17.24 Small savings in energy really add up when everybody conserves energy.,image,textbook_images/energy_resources_22354.png
L_0739,temperature and heat,T_3692,FIGURE 18.1 The cocoa is scalding hot. The bath water is comfortably warm. Why does the bath water have more thermal energy than the cocoa?,image,textbook_images/temperature_and_heat_22355.png
L_0739,temperature and heat,T_3694,FIGURE 18.2 The red liquid in this thermometer is alcohol. Alcohol expands uniformly over a wide range of temperatures. This makes it ideal for use in thermometers.,image,textbook_images/temperature_and_heat_22356.png
L_0739,temperature and heat,T_3695,FIGURE 18.3 A cool spoon gets warmer when it is placed in a hot liquid. Can you explain why?,image,textbook_images/temperature_and_heat_22357.png
L_0739,temperature and heat,T_3696,FIGURE 18.4 Sand on a beach heats up quickly in the sun because sand has a relatively low specific heat.,image,textbook_images/temperature_and_heat_22358.png
L_0740,transfer of thermal energy,T_3698,FIGURE 18.6 How is thermal energy transferred in each of these examples?,image,textbook_images/transfer_of_thermal_energy_22360.png
L_0740,transfer of thermal energy,T_3701,FIGURE 18.7 Thermal insulators have many practical uses. Can you think of others?,image,textbook_images/transfer_of_thermal_energy_22361.png
L_0740,transfer of thermal energy,T_3702,FIGURE 18.8 Convection currents carry thermal energy throughout the soup in the pot.,image,textbook_images/transfer_of_thermal_energy_22362.png
L_0740,transfer of thermal energy,T_3702,"FIGURE 18.9 A sea breeze blows toward land during the day, and a land breeze blows toward water at night. Why does the wind change direction after the sun goes down?",image,textbook_images/transfer_of_thermal_energy_22363.png
L_0740,transfer of thermal energy,T_3703,"FIGURE 18.10 Earth is warmed by energy that radiates from the sun. Earth radiates some of the energy back into space. Green- house gases (GHGs) trap much of the re- radiated energy, causing an increase in the temperature of the atmosphere close to the surface.",image,textbook_images/transfer_of_thermal_energy_22364.png
L_0741,using thermal energy,T_3705,"FIGURE 18.12 When water is heated in the boiler, it expands. It might burst the pipes of the system if it werent for the expansion tank. This tank holds excess water after it ex- pands.",image,textbook_images/using_thermal_energy_22366.png
L_0741,using thermal energy,T_3706,"FIGURE 18.13 The warm-air vent is placed near the floor of the room. Warm air is less dense than cold air so it rises. If the warm-air vent were placed near the ceiling instead, how would this affect the transfer of thermal energy throughout the room?",image,textbook_images/using_thermal_energy_22367.png
L_0741,using thermal energy,T_3708,FIGURE 18.14 A refrigerator must do work to reverse the normal direction of heat flow.,image,textbook_images/using_thermal_energy_22368.png
L_0741,using thermal energy,T_3710,"FIGURE 18.15 Thermal energy is converted to the kinetic energy of the moving piston inside the cylinder. The moving piston, in turn, can be used to turn a turbine or do other useful work.",image,textbook_images/using_thermal_energy_22369.png
L_0742,characteristics of waves,T_3712,FIGURE 19.1 A drop of water causes a disturbance that travels through the pond as a wave.,image,textbook_images/characteristics_of_waves_22371.png
L_0742,characteristics of waves,T_3716,"FIGURE 19.2 In a transverse wave, the medium moves at right angles to the direction of the wave.",image,textbook_images/characteristics_of_waves_22372.png
L_0742,characteristics of waves,T_3716,FIGURE 19.3 Crests and troughs are the high and low points of a transverse wave.,image,textbook_images/characteristics_of_waves_22373.png
L_0742,characteristics of waves,T_3716,FIGURE 19.4 An S wave is a transverse wave that trav- els through rocks under Earths surface.,image,textbook_images/characteristics_of_waves_22374.png
L_0742,characteristics of waves,T_3717,"FIGURE 19.5 In a longitudinal wave, the medium moves back and forth in the same direction as the wave.",image,textbook_images/characteristics_of_waves_22375.png
L_0742,characteristics of waves,T_3719,FIGURE 19.6 The compressions and rarefactions of a longitudinal wave are like the crests and troughs of a transverse wave.,image,textbook_images/characteristics_of_waves_22376.png
L_0742,characteristics of waves,T_3719,FIGURE 19.7 P waves are longitudinal waves that travel through rocks under Earths surface.,image,textbook_images/characteristics_of_waves_22377.png
L_0742,characteristics of waves,T_3720,FIGURE 19.8 Surface waves are both transverse and longitudinal waves.,image,textbook_images/characteristics_of_waves_22378.png
L_0743,measuring waves,T_3721,FIGURE 19.11 Wave amplitude and wavelength are two important measures of wave size.,image,textbook_images/measuring_waves_22381.png
L_0743,measuring waves,T_3723,"FIGURE 19.12 Both of these waves have the same ampli- tude, but they differ in wavelength. Which wave has more energy?",image,textbook_images/measuring_waves_22382.png
L_0743,measuring waves,T_3725,FIGURE 19.13 A transverse wave with a higher fre- quency has crests that are closer to- gether.,image,textbook_images/measuring_waves_22383.png
L_0744,wave interactions and interference,T_3730,FIGURE 19.14 This man is sending sound waves toward a rock wall so he can hear an echo.,image,textbook_images/wave_interactions_and_interference_22384.png
L_0744,wave interactions and interference,T_3730,FIGURE 19.15 Ocean waves are reflected by rocks on shore.,image,textbook_images/wave_interactions_and_interference_22385.png
L_0744,wave interactions and interference,T_3731,"FIGURE 19.16 Waves strike a wall at an angle, called the angle of incidence. The waves are re- flected at the same angle, called the angle of reflection, but in a different direction. Both angles are measured relative to a line that is perpendicular to the wall.",image,textbook_images/wave_interactions_and_interference_22386.png
L_0744,wave interactions and interference,T_3731,FIGURE 19.17 This pencil looks broken where it enters the water because of refraction of light waves.,image,textbook_images/wave_interactions_and_interference_22387.png
L_0744,wave interactions and interference,T_3732,FIGURE 19.18 The person can hear the radio around the corner of the building because of the diffraction of sound waves.,image,textbook_images/wave_interactions_and_interference_22388.png
L_0744,wave interactions and interference,T_3732,FIGURE 19.19 An obstacle or opening that is shorter than the wavelength causes greater diffraction of waves.,image,textbook_images/wave_interactions_and_interference_22389.png
L_0744,wave interactions and interference,T_3734,FIGURE 19.20 Constructive interference increases wave amplitude.,image,textbook_images/wave_interactions_and_interference_22390.png
L_0744,wave interactions and interference,T_3736,FIGURE 19.21 Destructive interference decreases wave amplitude.,image,textbook_images/wave_interactions_and_interference_22391.png
L_0748,characteristics of sound,T_3770,FIGURE 20.1 This tree cracked and fell to the ground in a storm. Can you imagine what it sounded like when it came crashing down?,image,textbook_images/characteristics_of_sound_22407.png
L_0748,characteristics of sound,T_3771,FIGURE 20.2 Plucking a guitar string makes it vibrate. The vibrating string sends sound waves through the air in all directions.,image,textbook_images/characteristics_of_sound_22408.png
L_0748,characteristics of sound,T_3775,FIGURE 20.3 High-decibel sounds can damage the ears and cause loss of hearing. Which sounds in the graph are dangerously loud?,image,textbook_images/characteristics_of_sound_22409.png
L_0748,characteristics of sound,T_3775,"FIGURE 20.4 The energy of sound waves spreads out over a greater area as the waves travel farther from the sound source. This di- agram represents just a small section of the total area of sound waves spreading out from the source. Sound waves ac- tually travel away from the source in all directions. As distance from the source increases, the area covered by the sound waves increases, lessening their inten- sity.",image,textbook_images/characteristics_of_sound_22410.png
L_0748,characteristics of sound,T_3776,FIGURE 20.5 A piccolo and a tuba sound very differ- ent. One difference is the pitch of their sounds.,image,textbook_images/characteristics_of_sound_22411.png
L_0748,characteristics of sound,T_3777,FIGURE 20.6 The sirens pitch changes as the police car zooms by. Can you explain why?,image,textbook_images/characteristics_of_sound_22412.png
L_0749,hearing sound,T_3779,FIGURE 20.7 The three main parts of the ear have different functions in hearing.,image,textbook_images/hearing_sound_22413.png
L_0749,hearing sound,T_3782,"FIGURE 20.8 This highly magnified image of a hair cell shows the tiny hair-like structures on its surface. What function do the ""hairs"" play in hearing?",image,textbook_images/hearing_sound_22414.png
L_0749,hearing sound,T_3782,"FIGURE 20.9 The louder the sounds are, the less time you should be exposed to them for the sake of your hearing.",image,textbook_images/hearing_sound_22415.png
L_0750,using sound,T_3786,"FIGURE 20.12 A drum, saxophone, and violin represent the three basic categories of musical in- struments. Can you name other instru- ments in each category?",image,textbook_images/using_sound_22418.png
L_0750,using sound,T_3789,FIGURE 20.13 Bats use ultrasound to find prey.,image,textbook_images/using_sound_22419.png
L_0750,using sound,T_3790,FIGURE 20.14 Sonar works on the same principle as echolocation.,image,textbook_images/using_sound_22420.png
L_0750,using sound,T_3791,FIGURE 20.15 This ultrasound image shows an unborn baby inside its mothers body. Do you see the babys face?,image,textbook_images/using_sound_22421.png
L_0751,electromagnetic waves,T_3793,FIGURE 21.1 Magnetic and electric fields are invisible areas of force surrounding magnets and charged particles. The field lines in the diagrams represent the direction and location of the force.,image,textbook_images/electromagnetic_waves_22422.png
L_0751,electromagnetic waves,T_3794,FIGURE 21.2 An electromagnetic wave starts with a vibrating charged particle.,image,textbook_images/electromagnetic_waves_22423.png
L_0751,electromagnetic waves,T_3798,FIGURE 21.3 A photon of light energy is given off when an electron returns to a lower energy level.,image,textbook_images/electromagnetic_waves_22424.png
L_0752,properties of electromagnetic waves,T_3800,"FIGURE 21.4 Light slows down when it enters water from the air. This causes the wave to refract, or bend.",image,textbook_images/properties_of_electromagnetic_waves_22425.png
L_0752,properties of electromagnetic waves,T_3802,FIGURE 21.5 Wavelength and frequency of electromagnetic waves.,image,textbook_images/properties_of_electromagnetic_waves_22426.png
L_0753,the electromagnetic spectrum,T_3804,"FIGURE 21.6 Electromagnetic radiation from the sun reaches Earth across space. It strikes everything on Earths surface, including these volleyball players.",image,textbook_images/the_electromagnetic_spectrum_22427.png
L_0753,the electromagnetic spectrum,T_3804,FIGURE 21.7 How do the wavelength and frequency of waves change across the electromagnetic spectrum?,image,textbook_images/the_electromagnetic_spectrum_22428.png
L_0753,the electromagnetic spectrum,T_3806,FIGURE 21.8 AM radio waves reflect off the ionosphere and travel back to Earth. Radio waves used for FM radio and television pass through the ionosphere and do not reflect back.,image,textbook_images/the_electromagnetic_spectrum_22429.png
L_0753,the electromagnetic spectrum,T_3807,FIGURE 21.9 This television tower broadcasts signals using radio waves.,image,textbook_images/the_electromagnetic_spectrum_22430.png
L_0753,the electromagnetic spectrum,T_3810,FIGURE 21.10 Microwaves are used for cell phones and radar. MEDIA Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/5050,image,textbook_images/the_electromagnetic_spectrum_22431.png
L_0753,the electromagnetic spectrum,T_3810,"FIGURE 21.11 Red light (right) has the longest wave- length, and violet light (left) has the short- est wavelength.",image,textbook_images/the_electromagnetic_spectrum_22432.png
L_0753,the electromagnetic spectrum,T_3812,FIGURE 21.12 This sterilizer for laboratory equipment uses ultraviolet light to kill bacteria.,image,textbook_images/the_electromagnetic_spectrum_22433.png
L_0753,the electromagnetic spectrum,T_3813,"FIGURE 21.13 If your skin normally burns in 10 minutes of sun exposure, using sunscreen with an SPF of 30 means that, ideally, your skin will burn only after 30 times 10 minutes, or 300 minutes, of sun exposure. How long does sunscreen with an SPF of 50 protect skin from sunburn?",image,textbook_images/the_electromagnetic_spectrum_22434.png
L_0753,the electromagnetic spectrum,T_3814,FIGURE 21.14 Two common uses of X rays are illustrated here.,image,textbook_images/the_electromagnetic_spectrum_22435.png
L_0754,the light we see,T_3817,FIGURE 22.1 This classroom has two obvious sources of visible light. Can you identify all of them?,image,textbook_images/the_light_we_see_22436.png
L_0754,the light we see,T_3818,FIGURE 22.2 Bioluminescent organisms include jelly- fish and fireflies. Jellyfish give off visible light to startle predators. Fireflies give off visible light to attract mates.,image,textbook_images/the_light_we_see_22437.png
L_0754,the light we see,T_3825,FIGURE 22.3 The objects pictured here differ in the way light interacts with them.,image,textbook_images/the_light_we_see_22438.png
L_0754,the light we see,T_3826,FIGURE 22.4 The color of light depends on its wave- length.,image,textbook_images/the_light_we_see_22439.png
L_0754,the light we see,T_3826,FIGURE 22.5 A prism separates visible light into its different wavelengths.,image,textbook_images/the_light_we_see_22440.png
L_0754,the light we see,T_3826,FIGURE 22.6 The color that objects appear depends on the wavelengths of light they reflect or transmit.,image,textbook_images/the_light_we_see_22441.png
L_0754,the light we see,T_3826,"FIGURE 22.7 The three primary colors of lightred, green, and bluecombine to form white light in the center of the figure. What are the secondary colors of light? Can you find them in the diagram?",image,textbook_images/the_light_we_see_22442.png
L_0754,the light we see,T_3827,"FIGURE 22.8 Printer ink comes in three primary pig- ment colors: cyan, magenta, and yellow.",image,textbook_images/the_light_we_see_22443.png
L_0755,optics,T_3829,FIGURE 22.9 Still waters of a lake create a mirror image of the surrounding scenery.,image,textbook_images/optics_22444.png
L_0755,optics,T_3830,FIGURE 22.10 Whether reflection is regular or diffuse de- pends on the smoothness of the reflective surface.,image,textbook_images/optics_22445.png
L_0755,optics,T_3831,"FIGURE 22.11 According to the law of reflection, the an- gle of reflection always equals the angle of incidence. The angles of both reflected and incident light are measured relative to an imaginary line, called normal, that is perpendicular (at right angles) to the reflective surface.",image,textbook_images/optics_22446.png
L_0755,optics,T_3834,FIGURE 22.12 The term mirror image refers to how left and right are reversed in the image compared with the real object.,image,textbook_images/optics_22447.png
L_0755,optics,T_3834,FIGURE 22.13 The image created by a concave mirror depends on how far the object is from the mirror.,image,textbook_images/optics_22448.png
L_0755,optics,T_3836,FIGURE 22.14 A convex mirror forms a virtual image that appears to be on the opposite side of the mirror from the object. How is the image different from the object?,image,textbook_images/optics_22449.png
L_0755,optics,T_3836,FIGURE 22.15 Light refracts when it passes from one medium to another at an angle other than 90 . Can you explain why?,image,textbook_images/optics_22450.png
L_0755,optics,T_3838,FIGURE 22.16 The image formed by a concave lens is a virtual image.,image,textbook_images/optics_22451.png
L_0755,optics,T_3841,FIGURE 22.17 The type of image made by a convex lens depends on how close the object is to the lens. Which diagram shows how a hand lens makes an image?,image,textbook_images/optics_22452.png
L_0755,optics,T_3841,FIGURE 22.18 A compound microscope uses convex lenses to make enlarged images of tiny objects.,image,textbook_images/optics_22453.png
L_0755,optics,T_3843,"FIGURE 22.19 These telescopes differ in how they collect light, but both use convex lenses to enlarge the image.",image,textbook_images/optics_22454.png
L_0755,optics,T_3843,FIGURE 22.20 A camera uses a convex lens to form an image on film or a sensor.,image,textbook_images/optics_22455.png
L_0755,optics,T_3844,FIGURE 22.21 A very focused beam of bright laser light moves around the room for the cat to chase. The diagram shows why the beam of laser light is so focused compared with ordinary light from a flashlight.,image,textbook_images/optics_22456.png
L_0755,optics,T_3844,FIGURE 22.22 A laser light uses two concave mirrors to focus photons of colored light.,image,textbook_images/optics_22457.png
L_0756,vision,T_3845,FIGURE 22.24 The human eye is the organ specialized to collect light and focus images. Structures of the Eye,image,textbook_images/vision_22459.png
L_0756,vision,T_3846,FIGURE 22.25 The brain and eyes work together to allow us to see.,image,textbook_images/vision_22460.png
L_0756,vision,T_3847,FIGURE 22.26 Myopia and hyperopia can be corrected with lenses.,image,textbook_images/vision_22461.png
L_0761,magnets and magnetism,T_3883,FIGURE 24.2 The north and south poles of a bar magnet attract paper clips.,image,textbook_images/magnets_and_magnetism_22485.png
L_0761,magnets and magnetism,T_3886,FIGURE 24.3 Lines of magnetic force are revealed by the iron filings attracted to this magnet.,image,textbook_images/magnets_and_magnetism_22486.png
L_0761,magnets and magnetism,T_3887,"FIGURE 24.4 When it come to magnets, there is a force of attraction between opposite poles and a force of repulsion between like poles.",image,textbook_images/magnets_and_magnetism_22487.png
L_0761,magnets and magnetism,T_3887,FIGURE 24.5 Refrigerator magnets stick to a refrigerator door because it contains iron. Why wont the magnets stick to wooden cabinet doors?,image,textbook_images/magnets_and_magnetism_22488.png
L_0761,magnets and magnetism,T_3888,FIGURE 24.6 Magnetic domains must be aligned by an outside magnetic field for most ferromagnetic materials to become magnets.,image,textbook_images/magnets_and_magnetism_22489.png
L_0761,magnets and magnetism,T_3889,"FIGURE 24.7 Paper clips become temporary magnets when placed in a magnetic field. An iron nail becomes a permanent magnet when stroked with a bar magnet. Some materials are natural permanent magnets. The most magnetic material in nature is the mineral magnetite, also called lodestone. The magnetic domains of magnetite naturally align with Earths axis. Figure 24.8 shows a chunk of magnetite attracting iron nails and iron filings. The magnetic properties of magnetite have been recognized for thousands of years. The earliest compasses used magnetite pointers to show direction. The magnetite spoon compass in Figure 24.8 dates back about 2000 years and comes from China.",image,textbook_images/magnets_and_magnetism_22490.png
L_0761,magnets and magnetism,T_3889,FIGURE 24.8 Magnetite naturally attracts iron nails and filings. Its natural magnetism was discovered thousands of years ago.,image,textbook_images/magnets_and_magnetism_22491.png
L_0762,earth as a magnet,T_3890,FIGURE 24.10 Earth is like a giant bar magnet.,image,textbook_images/earth_as_a_magnet_22493.png
L_0762,earth as a magnet,T_3892,FIGURE 24.11 Earths magnetic north pole is close to the geographic north pole.,image,textbook_images/earth_as_a_magnet_22494.png
L_0762,earth as a magnet,T_3892,FIGURE 24.12 The magnetosphere extends outward from Earth in all directions.,image,textbook_images/earth_as_a_magnet_22495.png
L_0762,earth as a magnet,T_3893,"FIGURE 24.13 We think of todays magnetic pole orientation as ""normal"" only because thats what we are used to.",image,textbook_images/earth_as_a_magnet_22496.png
L_0762,earth as a magnet,T_3894,FIGURE 24.14 The alignment of magnetic domains in rocks on the ocean floor provide evidence for Earths magnetic reversals.,image,textbook_images/earth_as_a_magnet_22497.png
L_0762,earth as a magnet,T_3894,"FIGURE 24.15 Charged particles flow through Earths liquid outer core, making Earth a giant magnet.",image,textbook_images/earth_as_a_magnet_22498.png
L_0762,earth as a magnet,T_3895,"FIGURE 24.16 The garden warbler flies from Europe to central Africa in the fall and returns to Eu- rope in the spring. Its internal ""compass"" helps it find the way.",image,textbook_images/earth_as_a_magnet_22499.png
L_0767,types of matter,T_3921,FIGURE 3.7 Each of the elements described here has different uses because of its properties.,image,textbook_images/types_of_matter_22521.png
L_0767,types of matter,T_3924,FIGURE 3.8 Gold is gold no matter where it is found because all gold atoms are alike.,image,textbook_images/types_of_matter_22522.png
L_0767,types of matter,T_3926,FIGURE 3.9 Table salt is much different than its com- ponents. What are some of its proper- ties?,image,textbook_images/types_of_matter_22523.png
L_0767,types of matter,T_3927,FIGURE 3.10 Water is a compound that forms molecules. Each water molecule consists of two atoms of hydrogen (white) and one atom of oxygen (red).,image,textbook_images/types_of_matter_22524.png
L_0767,types of matter,T_3927,"FIGURE 3.11 A crystal of table salt has a regular, repeating pattern of ions.",image,textbook_images/types_of_matter_22525.png
L_0767,types of matter,T_3928,FIGURE 3.12 All these substances are mixtures. How do they differ from compounds?,image,textbook_images/types_of_matter_22526.png
L_0767,types of matter,T_3930,FIGURE 3.13 These three mixtures differ in the size of their particles. Which mixture has the largest particles? Which has the smallest particles?,image,textbook_images/types_of_matter_22527.png
L_0767,types of matter,T_3931,FIGURE 3.14 Separating the components of a mixture depends on their physical properties. Which physical property is used in each example shown here?,image,textbook_images/types_of_matter_22528.png
L_0772,inside the atom,T_3963,FIGURE 5.1 This simple atomic model shows the par- ticles inside the atom.,image,textbook_images/inside_the_atom_22558.png
L_0772,inside the atom,T_3967,FIGURE 5.2 This model shows the particles that make up a carbon atom.,image,textbook_images/inside_the_atom_22559.png
L_0772,inside the atom,T_3968,FIGURE 5.3 The strong force is effective only between particles that are very close together in the nucleus.,image,textbook_images/inside_the_atom_22560.png
L_0772,inside the atom,T_3969,FIGURE 5.4 The symbol He stands for the element helium. Can you infer how many electrons a helium atom has?,image,textbook_images/inside_the_atom_22561.png
L_0772,inside the atom,T_3971,"FIGURE 5.5 When a fluorine atom gains an electron, it becomes a negative fluoride ion.",image,textbook_images/inside_the_atom_22562.png
L_0772,inside the atom,T_3974,"FIGURE 5.6 All isotopes of a given element have the same number of protons (P), but they differ in the number of neutrons (N). What is the mass number of each isotope shown here?",image,textbook_images/inside_the_atom_22563.png
L_0773,history of the atom,T_3979,"FIGURE 5.7 Democritus first introduced the idea of the atom almost 2500 years ago. the idea of atoms was ridiculous. Unfortunately, Aristotles ideas were accepted for more than 2000 years. During that time, Democrituss ideas were more or less forgotten.",image,textbook_images/history_of_the_atom_22564.png
L_0773,history of the atom,T_3980,FIGURE 5.8 John Dalton used evidence from experiments to show that atoms exist.,image,textbook_images/history_of_the_atom_22565.png
L_0773,history of the atom,T_3983,"FIGURE 5.9 Daltons model atoms were hard, solid balls. How do they differ from the atomic models you saw in the lesson ""Inside the Atom"" from earlier in the chapter?",image,textbook_images/history_of_the_atom_22566.png
L_0773,history of the atom,T_3985,FIGURE 5.10 This sketch shows the basic set up of Thomsons experiments. The vacuum tube is a glass tube that contains very little air. It has metal plates at each end and along the sides.,image,textbook_images/history_of_the_atom_22567.png
L_0773,history of the atom,T_3987,"FIGURE 5.11 Thomsons atomic model includes neg- ative electrons in a ""sea"" of positive charge.",image,textbook_images/history_of_the_atom_22568.png
L_0773,history of the atom,T_3990,FIGURE 5.12 Rutherford shot a beam of positive alpha particles at thin gold foil.,image,textbook_images/history_of_the_atom_22569.png
L_0773,history of the atom,T_3990,FIGURE 5.13 This model shows Rutherfords idea of the atom. How does it compare with Thomsons plum pudding model?,image,textbook_images/history_of_the_atom_22570.png
L_0774,modern atomic theory,T_3992,"FIGURE 5.14 In Bohrs atomic model, electrons orbit at fixed distances from the nucleus. These distances are called energy levels.",image,textbook_images/modern_atomic_theory_22571.png
L_0774,modern atomic theory,T_3992,FIGURE 5.15 This model of an atom contains six energy levels (n = 1 to 6). Atoms absorb or emit energy when some of their electrons jump to a different energy level.,image,textbook_images/modern_atomic_theory_22572.png
L_0774,modern atomic theory,T_3993,FIGURE 5.16 Atoms in fireworks give off light when their electrons jump back to a lower energy level.,image,textbook_images/modern_atomic_theory_22573.png
L_0774,modern atomic theory,T_3996,FIGURE 5.17 This sketch represents the electron cloud model for helium. What does the electron cloud represent?,image,textbook_images/modern_atomic_theory_22574.png
L_0774,modern atomic theory,T_3996,FIGURE 5.18 This model represents an atom of the element magnesium (Mg). How many electrons does the atom have at each en- ergy level? What is the maximum number it could have at each level?,image,textbook_images/modern_atomic_theory_22575.png
L_0775,how elements are organized,T_3998,FIGURE 6.2 Mendeleevs table of the elements organizes the elements by atomic mass. The table has a repeating pattern.,image,textbook_images/how_elements_are_organized_22577.png
L_0775,how elements are organized,T_4003,FIGURE 6.3 The modern periodic table of the elements is a lot like Mendeleevs table. But the modern table is based on atomic number instead of atomic mass. It also has more than 110 elements. Mendeleevs table only had about 65 elements.,image,textbook_images/how_elements_are_organized_22578.png
L_0776,classes of elements,T_4005,FIGURE 6.5 The three properties described here characterize most metals.,image,textbook_images/classes_of_elements_22580.png
L_0776,classes of elements,T_4006,"FIGURE 6.6 Unlike metals, solid nonmetals are dull and brittle.",image,textbook_images/classes_of_elements_22581.png
L_0776,classes of elements,T_4009,FIGURE 6.7 Metalloids share properties with both metals and nonmetals.,image,textbook_images/classes_of_elements_22582.png
L_0776,classes of elements,T_4010,"FIGURE 6.8 The number of electrons increases from left to right across each period in the periodic table. In period 2, lithium (Li) has the fewest electrons and neon (Ne) has the most. How do the numbers of electrons in their outer energy levels compare?",image,textbook_images/classes_of_elements_22583.png
L_0777,groups of elements,T_4011,"FIGURE 6.9 In group 1 of the periodic table, all the elements except hydrogen (H) are alkali metals.",image,textbook_images/groups_of_elements_22584.png
L_0777,groups of elements,T_4013,FIGURE 6.10 The alkaline Earth metals make up group 2 of the periodic table.,image,textbook_images/groups_of_elements_22585.png
L_0777,groups of elements,T_4013,FIGURE 6.11 All the elements in groups 3-12 are transition metals.,image,textbook_images/groups_of_elements_22586.png
L_0777,groups of elements,T_4014,"FIGURE 6.12 These groups each contain one or more metalloids. reactive. Oxygen (O), for example, readily reacts with metals to form compounds such as rust. Oxygen is a gas at room temperature. The other four elements in group 16 are solids.",image,textbook_images/groups_of_elements_22587.png
L_0778,introduction to chemical bonds,T_4017,"FIGURE 7.1 These diagrams show the valence elec- trons of hydrogen and water atoms and a water molecule. The diagrams represent electrons with dots, so they are called electron dot diagrams.",image,textbook_images/introduction_to_chemical_bonds_22590.png
L_0778,introduction to chemical bonds,T_4021,FIGURE 7.2 Different compounds may contain the same elements in different ratios. How does this affect their properties?,image,textbook_images/introduction_to_chemical_bonds_22591.png
L_0779,ionic bonds,T_4023,FIGURE 7.3 An ionic bond forms when the metal sodium gives up an electron to the non- metal chlorine.,image,textbook_images/ionic_bonds_22592.png
L_0779,ionic bonds,T_4024,FIGURE 7.4 Sodium and chlorine are on opposite sides of the periodic table. How is this related to their numbers of valence elec- trons?,image,textbook_images/ionic_bonds_22593.png
L_0779,ionic bonds,T_4026,"FIGURE 7.5 Sodium chloride crystals are cubic in shape. Other ionic compounds may have crystals with different shapes. ion always comes first. For example, sodium and chloride ions form the compound named sodium chloride. You Try It! Problem: What is the name of the ionic compound composed of positive barium ions and negative iodide ions?",image,textbook_images/ionic_bonds_22594.png
L_0780,covalent bonds,T_4029,FIGURE 7.7 This figure shows three ways of representing a covalent bond. A dash (-) between two atoms represents one pair of shared electrons.,image,textbook_images/covalent_bonds_22596.png
L_0780,covalent bonds,T_4030,FIGURE 7.8 An oxygen atom has a more stable arrangement of electrons when it forms covalent bonds with two hydrogen atoms.,image,textbook_images/covalent_bonds_22597.png
L_0780,covalent bonds,T_4031,FIGURE 7.9 A water molecule has two polar bonds.,image,textbook_images/covalent_bonds_22599.png
L_0780,covalent bonds,T_4031,FIGURE 7.10 An oxygen molecule has two nonpolar bonds. This is called a double bond. The two oxygen atoms attract equally the four shared electrons.,image,textbook_images/covalent_bonds_22598.png
L_0780,covalent bonds,T_4034,"FIGURE 7.11 Covalent compounds may be polar or nonpolar, as these two examples show. In both molecules, the oxygen atoms attract electrons more strongly than the carbon or hydrogen atoms do.",image,textbook_images/covalent_bonds_22600.png
L_0780,covalent bonds,T_4034,"FIGURE 7.12 Water is a polar compound, so its molecules are attracted to each other and form hydrogen bonds.",image,textbook_images/covalent_bonds_22601.png
L_0781,metallic bonds,T_4035,FIGURE 7.13 Positive metal ions and their shared electrons form metallic bonds.,image,textbook_images/metallic_bonds_22602.png
L_0781,metallic bonds,T_4037,FIGURE 7.14 A blacksmith shapes a piece of iron.,image,textbook_images/metallic_bonds_22603.png
L_0781,metallic bonds,T_4037,FIGURE 7.15 The girders of this bridge are made of steel.,image,textbook_images/metallic_bonds_22604.png
L_0782,introduction to chemical reactions,T_4038,FIGURE 8.1 Each of these pictures shows a chemical change taking place.,image,textbook_images/introduction_to_chemical_reactions_22606.png
L_0782,introduction to chemical reactions,T_4040,FIGURE 8.2 A chemical reaction changes hydrogen and oxygen to water.,image,textbook_images/introduction_to_chemical_reactions_22607.png
L_0783,chemical equations,T_4042,FIGURE 8.4 This figure shows a common chemical reaction. The drawing below the equation shows how the atoms are rearranged in the reaction. What chemical bonds are broken and what new chemical bonds are formed in this reaction?,image,textbook_images/chemical_equations_22609.png
L_0783,chemical equations,T_4046,FIGURE 8.5 Lavoisier carried out several experiments inside a sealed glass jar. Why was sealing the jar important for his results?,image,textbook_images/chemical_equations_22610.png
L_0784,types of chemical reactions,T_4048,FIGURE 8.6 Sodium and chlorine combine to synthesize table salt.,image,textbook_images/types_of_chemical_reactions_22611.png
L_0784,types of chemical reactions,T_4049,"FIGURE 8.7 In this photo, the air over Los Angeles, California is brown with smog.",image,textbook_images/types_of_chemical_reactions_22612.png
L_0784,types of chemical reactions,T_4051,"FIGURE 8.8 As carbon dioxide increases in the atmo- sphere, more carbon dioxide dissolves in ocean water.",image,textbook_images/types_of_chemical_reactions_22613.png
L_0784,types of chemical reactions,T_4054,FIGURE 8.9 A decomposition reaction occurs when an electric current passes through water.,image,textbook_images/types_of_chemical_reactions_22614.png
L_0784,types of chemical reactions,T_4056,FIGURE 8.10 The burning of charcoal is an example of a combustion reaction.,image,textbook_images/types_of_chemical_reactions_22615.png
L_0784,types of chemical reactions,T_4058,FIGURE 8.11 The blue flame on this gas stove is pro- duced when natural gas burns.,image,textbook_images/types_of_chemical_reactions_22616.png
L_0785,chemical reactions and energy,T_4059,FIGURE 8.12 Plants can get the energy they need for photosynthesis from either sunlight or ar- tificial light.,image,textbook_images/chemical_reactions_and_energy_22617.png
L_0785,chemical reactions and energy,T_4061,FIGURE 8.13 The combustion of wood is an exothermic reaction that releases energy as heat and light.,image,textbook_images/chemical_reactions_and_energy_22618.png
L_0785,chemical reactions and energy,T_4061,FIGURE 8.14 These graphs compare the energy changes in endothermic and exothermic reactions. What happens to the energy that is absorbed in an endothermic reaction?,image,textbook_images/chemical_reactions_and_energy_22619.png
L_0785,chemical reactions and energy,T_4062,FIGURE 8.15 Even exothermic reactions need activation energy to get started.,image,textbook_images/chemical_reactions_and_energy_22620.png
L_0785,chemical reactions and energy,T_4064,FIGURE 8.16 The chemical reactions that spoil food occur faster at higher temperatures.,image,textbook_images/chemical_reactions_and_energy_22621.png
L_0785,chemical reactions and energy,T_4065,FIGURE 8.17 Its dangerous to smoke or use open flames when oxygen is in use. Can you explain why?,image,textbook_images/chemical_reactions_and_energy_22622.png
L_0785,chemical reactions and energy,T_4066,FIGURE 8.18 The nails have more surface area ex- posed to the air than the head of the hammer. How does this affect the rate at which they rust?,image,textbook_images/chemical_reactions_and_energy_22623.png
L_0786,properties of carbon,T_4068,FIGURE 9.1 The dots in this diagram represent the four valence electrons of carbon.,image,textbook_images/properties_of_carbon_22624.png
L_0786,properties of carbon,T_4069,"FIGURE 9.2 Methane is one of the simplest carbon compounds. At room temperature, it exists as a gas. It is a component of natural gas. These diagrams show two ways of representing the covalent bonds in methane.",image,textbook_images/properties_of_carbon_22625.png
L_0786,properties of carbon,T_4070,"FIGURE 9.3 Carbon atoms can form single, double, or triple bonds with each other. How many bonds do the carbon atoms share in each compound shown here?",image,textbook_images/properties_of_carbon_22626.png
L_0786,properties of carbon,T_4071,"FIGURE 9.4 A string of beads serves as a simple model of a polymer. Like monomers mak- ing up a polymer, the beads in a string may be all the same or different from one another. MEDIA Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/5089",image,textbook_images/properties_of_carbon_22627.png
L_0786,properties of carbon,T_4071,FIGURE 9.5 Many common products are made of the plastic known as polyethylene.,image,textbook_images/properties_of_carbon_22628.png
L_0787,hydrocarbons,T_4074,FIGURE 9.6 Each of these pictures shows a use of hydrocarbons.,image,textbook_images/hydrocarbons_22629.png
L_0787,hydrocarbons,T_4075,FIGURE 9.7 Ethane is a saturated hydrocarbon. What is its chemical formula?,image,textbook_images/hydrocarbons_22630.png
L_0787,hydrocarbons,T_4076,FIGURE 9.8 Alkanes may have any of these three shapes.,image,textbook_images/hydrocarbons_22631.png
L_0787,hydrocarbons,T_4077,"FIGURE 9.9 Butane and isobutane have the same atoms but different shapes. Isomers usually have somewhat different properties. For example, straight-chain molecules generally have higher boiling and melting points than their branched-chain isomers. The boiling and melting points of iso-butane are -12C and -160C, respectively. Compare these values with the boiling and melting points of butane in Table 9.2. Do these two compounds follow the general trend?",image,textbook_images/hydrocarbons_22632.png
L_0787,hydrocarbons,T_4080,FIGURE 9.10 Ethene is the smallest alkene.,image,textbook_images/hydrocarbons_22633.png
L_0787,hydrocarbons,T_4081,FIGURE 9.11 These two bunches of bananas were stored in different ways. The bananas on the right were stored in the open air. The bananas on the left were stored in a special bag that absorbs the ethene they release. The bananas in the bag have not yet turned brown because they were not exposed to ethene.,image,textbook_images/hydrocarbons_22634.png
L_0787,hydrocarbons,T_4081,FIGURE 9.12 Ethyne is the smallest alkyne.,image,textbook_images/hydrocarbons_22635.png
L_0787,hydrocarbons,T_4081,FIGURE 9.13 This acetylene torch is being used to cut metal.,image,textbook_images/hydrocarbons_22636.png
L_0787,hydrocarbons,T_4082,FIGURE 9.14 Benzene is an aromatic hydrocarbon. Does each carbon atom in benzene have a total of four bonds? Count them to find out.,image,textbook_images/hydrocarbons_22637.png
L_0787,hydrocarbons,T_4083,FIGURE 9.15 These photos show just a few of the many uses of hydrocarbons.,image,textbook_images/hydrocarbons_22638.png
L_0788,carbon and living things,T_4087,FIGURE 9.16 Glucose and fructose are isomers. Su- crose contains a molecule of each.,image,textbook_images/carbon_and_living_things_22639.png
L_0788,carbon and living things,T_4087,FIGURE 9.17 These foods are all good sources of starch.,image,textbook_images/carbon_and_living_things_22640.png
L_0788,carbon and living things,T_4088,FIGURE 9.18 Cellulose molecules form large cellulose fibers.,image,textbook_images/carbon_and_living_things_22641.png
L_0788,carbon and living things,T_4090,FIGURE 9.19 Glycine is one of 20 common amino acids that make up the proteins of living things.,image,textbook_images/carbon_and_living_things_22642.png
L_0788,carbon and living things,T_4091,FIGURE 9.20 The blood protein hemoglobin binds with oxygen and carries it from the lungs to cells throughout the body. Heme is a small molecule containing iron that is part of the larger hemoglobin molecule. Oxy- gen binds to the iron in heme.,image,textbook_images/carbon_and_living_things_22643.png
L_0788,carbon and living things,T_4093,FIGURE 9.21 Both of these fatty acid molecules have six carbon atoms and two oxygen atoms. How many hydrogen atoms does each fatty acid have?,image,textbook_images/carbon_and_living_things_22644.png
L_0788,carbon and living things,T_4095,FIGURE 9.22 The arrangement of phospholipid molecules in a cell membrane allows the membrane to control what enters and leaves the cell.,image,textbook_images/carbon_and_living_things_22645.png
L_0788,carbon and living things,T_4096,FIGURE 9.23 Each nucleotide contains these three components.,image,textbook_images/carbon_and_living_things_22646.png
L_0788,carbon and living things,T_4096,FIGURE 9.24 DNA has the shape of a double helix because of hydrogen bonds between ni- trogen bases.,image,textbook_images/carbon_and_living_things_22647.png
L_0789,biochemical reactions,T_4098,FIGURE 9.25 Photosynthesis and cellular respiration are closely related. What are the products and reactants of each process?,image,textbook_images/biochemical_reactions_22648.png
L_0789,biochemical reactions,T_4098,"FIGURE 9.26 These organisms use sunlight to make glucose in the process of photosynthesis. All of them contain the green pigment chlorophyll, which is needed to capture light energy.",image,textbook_images/biochemical_reactions_22649.png
L_0790,acceleration,T_4102,FIGURE 1.1,image,textbook_images/acceleration_22651.png
L_0791,acceleration due to gravity,T_4105,FIGURE 1.1,image,textbook_images/acceleration_due_to_gravity_22652.png
L_0793,acid base neutralization,T_4109,FIGURE 1.1 These antacid tablets contain the base calcium carbonate (CaCO3 ). The base reacts with hydrochloric acid (HCl) in the stomach. The reaction neutralizes the acid to relieve acid indigestion.,image,textbook_images/acid_base_neutralization_22654.png
L_0794,activation energy,T_4111,FIGURE 1.1,image,textbook_images/activation_energy_22655.png
L_0797,alloys,T_4120,FIGURE 1.1,image,textbook_images/alloys_22661.png
L_0798,alpha decay,T_4123,FIGURE 1.1,image,textbook_images/alpha_decay_22662.png
L_0800,archimedes law,T_4130,FIGURE 1.1,image,textbook_images/archimedes_law_22664.png
L_0801,artificial light,T_4133,FIGURE 1.1,image,textbook_images/artificial_light_22665.png
L_0801,artificial light,T_4133,FIGURE 1.2,image,textbook_images/artificial_light_22666.png
L_0801,artificial light,T_4134,FIGURE 1.3,image,textbook_images/artificial_light_22667.png
L_0801,artificial light,T_4135,FIGURE 1.4,image,textbook_images/artificial_light_22668.png
L_0802,atomic forces,T_4137,FIGURE 1.1,image,textbook_images/atomic_forces_22670.png
L_0802,atomic forces,T_4138,FIGURE 1.2,image,textbook_images/atomic_forces_22671.png
L_0802,atomic forces,T_4139,FIGURE 1.3,image,textbook_images/atomic_forces_22672.png
L_0803,atomic nucleus,T_4141,FIGURE 1.1,image,textbook_images/atomic_nucleus_22673.png
L_0804,atomic number,T_4143,FIGURE 1.1,image,textbook_images/atomic_number_22674.png
L_0804,atomic number,T_4144,FIGURE 1.2,image,textbook_images/atomic_number_22675.png
L_0808,beta decay,T_4159,FIGURE 1.1,image,textbook_images/beta_decay_22678.png
L_0809,biochemical compound classification,T_4162,FIGURE 1.1,image,textbook_images/biochemical_compound_classification_22679.png
L_0810,biochemical reaction chemistry,T_4169,FIGURE 1.1 Q: What are the reactants and products in photosynthesis and cellular respiration?,image,textbook_images/biochemical_reaction_chemistry_22680.png
L_0811,bohrs atomic model,T_4170,FIGURE 1.1,image,textbook_images/bohrs_atomic_model_22681.png
L_0811,bohrs atomic model,T_4172,FIGURE 1.2,image,textbook_images/bohrs_atomic_model_22682.png
L_0813,bond polarity,T_4176,FIGURE 1.1,image,textbook_images/bond_polarity_22683.png
L_0813,bond polarity,T_4176,FIGURE 1.2,image,textbook_images/bond_polarity_22684.png
L_0813,bond polarity,T_4177,FIGURE 1.3,image,textbook_images/bond_polarity_22685.png
L_0815,buoyancy,T_4183,FIGURE 1.1,image,textbook_images/buoyancy_22689.png
L_0815,buoyancy,T_4183,"FIGURE 1.2 Because of buoyant force, objects seem lighter in water. You may have noticed this when you went swimming and could easily pick up a friend or sibling under the water. Some of the persons weight was countered by the buoyant force of the water.",image,textbook_images/buoyancy_22690.png
L_0815,buoyancy,T_4184,FIGURE 1.3,image,textbook_images/buoyancy_22691.png
L_0816,calculating acceleration from force and mass,T_4187,FIGURE 1.1 A: It would take only 32 N of force (40 kg  0.8 m/s2 ).,image,textbook_images/calculating_acceleration_from_force_and_mass_22692.png
L_0817,calculating acceleration from velocity and time,T_4189,FIGURE 1.1,image,textbook_images/calculating_acceleration_from_velocity_and_time_22694.png
L_0819,calculating work,T_4197,FIGURE 1.1,image,textbook_images/calculating_work_22695.png
L_0820,carbohydrate classification,T_4199,FIGURE 1.1 Note: Each unlettered point where lines intersect represents a carbon atom.,image,textbook_images/carbohydrate_classification_22696.png
L_0820,carbohydrate classification,T_4201,FIGURE 1.2,image,textbook_images/carbohydrate_classification_22697.png
L_0820,carbohydrate classification,T_4201,FIGURE 1.3,image,textbook_images/carbohydrate_classification_22698.png
L_0821,carbon bonding,T_4203,FIGURE 1.1,image,textbook_images/carbon_bonding_22699.png
L_0821,carbon bonding,T_4204,FIGURE 1.2,image,textbook_images/carbon_bonding_22700.png
L_0821,carbon bonding,T_4205,FIGURE 1.3,image,textbook_images/carbon_bonding_22701.png
L_0822,carbon monomers and polymers,T_4207,FIGURE 1.1,image,textbook_images/carbon_monomers_and_polymers_22702.png
L_0822,carbon monomers and polymers,T_4207,FIGURE 1.2,image,textbook_images/carbon_monomers_and_polymers_22703.png
L_0822,carbon monomers and polymers,T_4208,FIGURE 1.3,image,textbook_images/carbon_monomers_and_polymers_22704.png
L_0822,carbon monomers and polymers,T_4208,FIGURE 1.4,image,textbook_images/carbon_monomers_and_polymers_22705.png
L_0823,catalysts,T_4210,FIGURE 1.1,image,textbook_images/catalysts_22706.png
L_0823,catalysts,T_4211,"FIGURE 1.2 Q: If you chew a starchy food such as a soda cracker for a couple of minutes, you may notice that it starts to taste slightly sweet. Why does this happen?",image,textbook_images/catalysts_22707.png
L_0824,cellular respiration reactions,T_4212,FIGURE 1.1,image,textbook_images/cellular_respiration_reactions_22708.png
L_0828,chemical bond,T_4221,FIGURE 1.1,image,textbook_images/chemical_bond_22714.png
L_0830,chemical equations,T_4227,FIGURE 1.1,image,textbook_images/chemical_equations_22717.png
L_0833,chemical reaction overview,T_4235,FIGURE 1.1,image,textbook_images/chemical_reaction_overview_22719.png
L_0833,chemical reaction overview,T_4236,FIGURE 1.2,image,textbook_images/chemical_reaction_overview_22720.png
L_0834,chemical reaction rate,T_4240,FIGURE 1.1,image,textbook_images/chemical_reaction_rate_22721.png
L_0834,chemical reaction rate,T_4241,FIGURE 1.2,image,textbook_images/chemical_reaction_rate_22722.png
L_0834,chemical reaction rate,T_4242,FIGURE 1.3,image,textbook_images/chemical_reaction_rate_22723.png
L_0835,chemistry of compounds,T_4244,FIGURE 1.1 All water molecules have two hydrogen atoms (gray) and one oxygen atom (blue).,image,textbook_images/chemistry_of_compounds_22724.png
L_0835,chemistry of compounds,T_4245,"FIGURE 1.2 Water: Water is odorless and colorless. We drink it, bathe in it, and use it to wash our clothes. In fact, we cant live without it. Hydrogen Peroxide: Hydrogen peroxide is also odorless and colorless. Its used as an antiseptic to kill germs on cuts. Its also used as bleach to remove color form hair. A: You can tell that they are different compounds from their very different properties. Carbon dioxide is a harmless gas that living things add to the atmosphere during respiration. Carbon monoxide is a deadly gas that can quickly kill people if it becomes too concentrated in the air.",image,textbook_images/chemistry_of_compounds_22725.png
L_0835,chemistry of compounds,T_4245,FIGURE 1.3,image,textbook_images/chemistry_of_compounds_22726.png
L_0836,color,T_4248,FIGURE 1.1,image,textbook_images/color_22727.png
L_0836,color,T_4248,FIGURE 1.2,image,textbook_images/color_22728.png
L_0836,color,T_4249,FIGURE 1.3 light of different colors.,image,textbook_images/color_22729.png
L_0836,color,T_4249,FIGURE 1.4,image,textbook_images/color_22730.png
L_0836,color,T_4250,FIGURE 1.5,image,textbook_images/color_22731.png
L_0837,combining forces,T_4253,FIGURE 1.1,image,textbook_images/combining_forces_22733.png
L_0838,combustion reactions,T_4254,FIGURE 1.1,image,textbook_images/combustion_reactions_22734.png
L_0838,combustion reactions,T_4255,FIGURE 1.2,image,textbook_images/combustion_reactions_22735.png
L_0840,compound machine,T_4260,FIGURE 1.1,image,textbook_images/compound_machine_22737.png
L_0840,compound machine,T_4260,FIGURE 1.2,image,textbook_images/compound_machine_22738.png
L_0841,compounds,T_4263,FIGURE 1.1,image,textbook_images/compounds_22740.png
L_0841,compounds,T_4265,FIGURE 1.2,image,textbook_images/compounds_22741.png
L_0841,compounds,T_4265,FIGURE 1.3,image,textbook_images/compounds_22742.png
L_0843,conservation of energy in chemical reactions,T_4270,FIGURE 1.1,image,textbook_images/conservation_of_energy_in_chemical_reactions_22746.png
L_0846,conservation of mass in chemical reactions,T_4277,FIGURE 1.1 Antoine Lavoisier.,image,textbook_images/conservation_of_mass_in_chemical_reactions_22748.png
L_0847,convection,T_4279,FIGURE 1.1,image,textbook_images/convection_22749.png
L_0847,convection,T_4280,FIGURE 1.2,image,textbook_images/convection_22750.png
L_0848,cooling systems,T_4283,FIGURE 1.1,image,textbook_images/cooling_systems_22751.png
L_0849,covalent bonding,T_4285,FIGURE 1.1,image,textbook_images/covalent_bonding_22752.png
L_0849,covalent bonding,T_4285,FIGURE 1.2,image,textbook_images/covalent_bonding_22753.png
L_0850,crystalline carbon,T_4288,FIGURE 1.1,image,textbook_images/crystalline_carbon_22754.png
L_0850,crystalline carbon,T_4288,FIGURE 1.2,image,textbook_images/crystalline_carbon_22755.png
L_0850,crystalline carbon,T_4289,FIGURE 1.3,image,textbook_images/crystalline_carbon_22756.png
L_0850,crystalline carbon,T_4290,FIGURE 1.4,image,textbook_images/crystalline_carbon_22757.png
L_0851,daltons atomic theory,T_4292,FIGURE 1.1,image,textbook_images/daltons_atomic_theory_22758.png
L_0851,daltons atomic theory,T_4294,FIGURE 1.2,image,textbook_images/daltons_atomic_theory_22759.png
L_0852,dangers and uses of radiation,T_4297,FIGURE 1.1,image,textbook_images/dangers_and_uses_of_radiation_22760.png
L_0853,decomposition reactions,T_4300,FIGURE 1.1,image,textbook_images/decomposition_reactions_22762.png
L_0854,democrituss idea of the atom,T_4302,FIGURE 1.1,image,textbook_images/democrituss_idea_of_the_atom_22763.png
L_0854,democrituss idea of the atom,T_4304,FIGURE 1.2,image,textbook_images/democrituss_idea_of_the_atom_22764.png
L_0859,direction,T_4316,FIGURE 1.1,image,textbook_images/direction_22769.png
L_0861,distance,T_4324,FIGURE 1.1,image,textbook_images/distance_22772.png
L_0862,doppler effect,T_4326,FIGURE 1.1,image,textbook_images/doppler_effect_22773.png
L_0863,earth as a magnet,T_4328,FIGURE 1.1,image,textbook_images/earth_as_a_magnet_22774.png
L_0863,earth as a magnet,T_4328,"FIGURE 1.2 needle point instead? It points to Earths north magnetic pole, which is located at about 80 north latitude. Earth also has two south poles: a south geographic pole and a south magnetic pole.",image,textbook_images/earth_as_a_magnet_22775.png
L_0863,earth as a magnet,T_4329,FIGURE 1.3,image,textbook_images/earth_as_a_magnet_22776.png
L_0864,efficiency,T_4331,FIGURE 1.1,image,textbook_images/efficiency_22777.png
L_0865,einsteins concept of gravity,T_4335,"FIGURE 1.1 This diagram shows how Earths mass bends the fabric of space and time around it, causing smaller objects such as satellites to move toward Earth.",image,textbook_images/einsteins_concept_of_gravity_22778.png
L_0866,elastic force,T_4337,"FIGURE 1.1 And like stretchy materials, they return to their original shape when the stretching or compressing force is released. Springs are used in scales to measure weight. They also cushion the ride in a car.",image,textbook_images/elastic_force_22779.png
L_0866,elastic force,T_4337,FIGURE 1.2,image,textbook_images/elastic_force_22780.png
L_0881,electromagnetic spectrum,T_4380,FIGURE 1.1,image,textbook_images/electromagnetic_spectrum_22802.png
L_0882,electromagnetic waves,T_4382,FIGURE 1.1,image,textbook_images/electromagnetic_waves_22803.png
L_0882,electromagnetic waves,T_4383,FIGURE 1.2,image,textbook_images/electromagnetic_waves_22804.png
L_0882,electromagnetic waves,T_4383,FIGURE 1.3,image,textbook_images/electromagnetic_waves_22805.png
L_0884,electron cloud atomic model,T_4391,FIGURE 1.1,image,textbook_images/electron_cloud_atomic_model_22807.png
L_0884,electron cloud atomic model,T_4391,FIGURE 1.2,image,textbook_images/electron_cloud_atomic_model_22808.png
L_0884,electron cloud atomic model,T_4392,FIGURE 1.3,image,textbook_images/electron_cloud_atomic_model_22809.png
L_0888,electrons,T_4405,FIGURE 1.1,image,textbook_images/electrons_22817.png
L_0888,electrons,T_4406,FIGURE 1.2,image,textbook_images/electrons_22818.png
L_0888,electrons,T_4407,FIGURE 1.3,image,textbook_images/electrons_22819.png
L_0889,elements,T_4409,FIGURE 1.1,image,textbook_images/elements_22820.png
L_0889,elements,T_4410,FIGURE 1.2 The red lights in this sign contain the element neon.,image,textbook_images/elements_22821.png
L_0889,elements,T_4411,FIGURE 1.3 substance?,image,textbook_images/elements_22822.png
L_0890,endothermic reactions,T_4413,FIGURE 1.1,image,textbook_images/endothermic_reactions_22823.png
L_0891,energy,T_4416,FIGURE 1.1,image,textbook_images/energy_22825.png
L_0893,energy level,T_4423,FIGURE 1.1,image,textbook_images/energy_level_22826.png
L_0893,energy level,T_4424,FIGURE 1.2,image,textbook_images/energy_level_22827.png
L_0893,energy level,T_4425,FIGURE 1.3,image,textbook_images/energy_level_22828.png
L_0893,energy level,T_4425,"FIGURE 1.4 hold only eight electrons. This means that is outermost energy level is full. Therefore, a neon atom is very stable.",image,textbook_images/energy_level_22829.png
L_0894,enzymes as catalysts,T_4427,FIGURE 1.1,image,textbook_images/enzymes_as_catalysts_22830.png
L_0894,enzymes as catalysts,T_4428,FIGURE 1.2,image,textbook_images/enzymes_as_catalysts_22831.png
L_0897,exothermic reactions,T_4436,FIGURE 1.1,image,textbook_images/exothermic_reactions_22835.png
L_0898,external combustion engines,T_4439,FIGURE 1.1,image,textbook_images/external_combustion_engines_22837.png
L_0899,ferromagnetic material,T_4440,FIGURE 1.1 Magnetic domains must be lined up by an outside magnetic field for most ferromag- netic materials to become magnets.,image,textbook_images/ferromagnetic_material_22838.png
L_0899,ferromagnetic material,T_4441,FIGURE 1.2,image,textbook_images/ferromagnetic_material_22839.png
L_0899,ferromagnetic material,T_4441,"FIGURE 1.3 A: Jarring or heating a magnet moves the magnetic domains out of alignment. When the magnetic domains no longer line up in the same direction, the material is no longer magnetic.",image,textbook_images/ferromagnetic_material_22840.png
L_0899,ferromagnetic material,T_4442,FIGURE 1.4,image,textbook_images/ferromagnetic_material_22841.png
L_0901,force,T_4446,FIGURE 1.1,image,textbook_images/force_22842.png
L_0901,force,T_4447,FIGURE 1.2,image,textbook_images/force_22843.png
L_0902,forms of energy,T_4449,"FIGURE 1.1 This drummer has mechanical energy as he moves the drumsticks to hit the drums and cymbals. The moving drumsticks also have mechanical energy, but they would have mechanical energy even if they werent moving. Thats because they have the potential to fall when the drum- mer is holding them above the floor. This potential energy is due to gravity.",image,textbook_images/forms_of_energy_22844.png
L_0902,forms of energy,T_4449,FIGURE 1.2,image,textbook_images/forms_of_energy_22845.png
L_0902,forms of energy,T_4449,FIGURE 1.3 The bright lights on this stage use elec- trical energy. They are wired into the electrical system of the of the hall. The guitars and microphone also use electri- cal energy. You can see the electrical cords running from them to the outlet on the floor below the musicians.,image,textbook_images/forms_of_energy_22846.png
L_0902,forms of energy,T_4449,"FIGURE 1.4 starts with vibrations of his vocal cords, which are folds of tissue in his throat. The vibrations pass to surrounding particles of matter and then from one particle to another in waves. Sound waves can travel through air, water, and other substances, but not through empty space.",image,textbook_images/forms_of_energy_22847.png
L_0904,frequency and pitch of sound,T_4453,FIGURE 1.1,image,textbook_images/frequency_and_pitch_of_sound_22850.png
L_0904,frequency and pitch of sound,T_4453,FIGURE 1.2,image,textbook_images/frequency_and_pitch_of_sound_22851.png
L_0905,friction,T_4455,FIGURE 1.1,image,textbook_images/friction_22852.png
L_0905,friction,T_4455,FIGURE 1.2,image,textbook_images/friction_22853.png
L_0905,friction,T_4456,FIGURE 1.3,image,textbook_images/friction_22854.png
L_0905,friction,T_4456,FIGURE 1.4,image,textbook_images/friction_22855.png
L_0906,fundamental particles,T_4459,FIGURE 1.1,image,textbook_images/fundamental_particles_22857.png
L_0907,gamma decay,T_4463,FIGURE 1.1,image,textbook_images/gamma_decay_22858.png
L_0908,gamma rays,T_4467,FIGURE 1.1,image,textbook_images/gamma_rays_22859.png
L_0910,gravity,T_4474,FIGURE 1.1,image,textbook_images/gravity_22864.png
L_0911,groups with metalloids,T_4477,FIGURE 1.1,image,textbook_images/groups_with_metalloids_22865.png
L_0911,groups with metalloids,T_4480,"FIGURE 1.2 Boron is a very hard, black metalloid with a high melting point. In the mineral called borax, it is used to wash clothes. In boric acid, it is used as an eyewash and insecticide.",image,textbook_images/groups_with_metalloids_22866.png
L_0911,groups with metalloids,T_4480,FIGURE 1.3,image,textbook_images/groups_with_metalloids_22867.png
L_0911,groups with metalloids,T_4481,FIGURE 1.4,image,textbook_images/groups_with_metalloids_22868.png
L_0911,groups with metalloids,T_4481,"FIGURE 1.5 Tellurium is a silvery white, brittle met- alloid. It is toxic and may cause birth defects. Tellurium can conduct electricity when exposed to light, so it is used to make solar panels. It has several other uses as well. For example, it makes steel and copper easier to work with and lends color to ceramics.",image,textbook_images/groups_with_metalloids_22869.png
L_0912,halogens,T_4483,FIGURE 1.1,image,textbook_images/halogens_22870.png
L_0912,halogens,T_4484,FIGURE 1.2,image,textbook_images/halogens_22871.png
L_0913,hearing and the ear,T_4487,FIGURE 1.1,image,textbook_images/hearing_and_the_ear_22873.png
L_0914,hearing loss,T_4491,FIGURE 1.1,image,textbook_images/hearing_loss_22875.png
L_0915,heat,T_4495,FIGURE 1.1,image,textbook_images/heat_22878.png
L_0915,heat,T_4495,FIGURE 1.2,image,textbook_images/heat_22879.png
L_0916,heat conduction,T_4498,FIGURE 1.1 Hot Iron: A hot iron removes the wrinkles in a shirt. Hot Cocoa: Holding a cup of hot cocoa feels good when you have cold hands. Camp Stove: This camp stove can be used to cook food in a small pot. Snow: Ouch! Can you imagine how cold this snow must feel on bare feet?,image,textbook_images/heat_conduction_22880.png
L_0917,heating systems,T_4500,FIGURE 1.1,image,textbook_images/heating_systems_22881.png
L_0917,heating systems,T_4502,FIGURE 1.2 Warm-air heating system.,image,textbook_images/heating_systems_22882.png
L_0917,heating systems,T_4502,FIGURE 1.3,image,textbook_images/heating_systems_22883.png
L_0919,hydrocarbons,T_4511,FIGURE 1.1,image,textbook_images/hydrocarbons_22886.png
L_0919,hydrocarbons,T_4512,FIGURE 1.2,image,textbook_images/hydrocarbons_22887.png
L_0920,hydrogen and alkali metals,T_4515,FIGURE 1.1,image,textbook_images/hydrogen_and_alkali_metals_22888.png
L_0920,hydrogen and alkali metals,T_4516,"FIGURE 1.2 Hydrogen has the smallest, lightest atoms of all elements. Pure hydrogen is a colorless, odorless, tasteless gas that is nontoxic but highly flammable. Hydrogen gas exists mainly as diatomic (two-atom) molecules (H2 ), as shown in the diagram on the right. Hydrogen is the most abun- dant element in the universe and the third most abundant element on Earth, occur- ring mainly in compounds such as water.",image,textbook_images/hydrogen_and_alkali_metals_22889.png
L_0920,hydrogen and alkali metals,T_4516,FIGURE 1.3,image,textbook_images/hydrogen_and_alkali_metals_22890.png
L_0920,hydrogen and alkali metals,T_4516,FIGURE 1.4,image,textbook_images/hydrogen_and_alkali_metals_22891.png
L_0921,hydrogen bonding,T_4518,FIGURE 1.1,image,textbook_images/hydrogen_bonding_22892.png
L_0923,inclined plane,T_4526,FIGURE 1.1,image,textbook_images/inclined_plane_22894.png
L_0923,inclined plane,T_4526,FIGURE 1.2,image,textbook_images/inclined_plane_22895.png
L_0924,inertia,T_4527,FIGURE 1.1 Inertia explains why its important to always wear a seat belt.,image,textbook_images/inertia_22896.png
L_0924,inertia,T_4529,FIGURE 1.2,image,textbook_images/inertia_22897.png
L_0925,intensity and loudness of sound,T_4531,FIGURE 1.1,image,textbook_images/intensity_and_loudness_of_sound_22899.png
L_0926,internal combustion engines,T_4534,FIGURE 1.1,image,textbook_images/internal_combustion_engines_22901.png
L_0928,ionic bonding,T_4539,FIGURE 1.1,image,textbook_images/ionic_bonding_22902.png
L_0928,ionic bonding,T_4540,FIGURE 1.2,image,textbook_images/ionic_bonding_22903.png
L_0929,ionic compounds,T_4543,FIGURE 1.1,image,textbook_images/ionic_compounds_22904.png
L_0930,ions,T_4548,FIGURE 1.1,image,textbook_images/ions_22906.png
L_0931,isomers,T_4554,FIGURE 1.1,image,textbook_images/isomers_22907.png
L_0931,isomers,T_4554,FIGURE 1.2,image,textbook_images/isomers_22908.png
L_0931,isomers,T_4554,FIGURE 1.3,image,textbook_images/isomers_22909.png
L_0931,isomers,T_4554,FIGURE 1.4,image,textbook_images/isomers_22910.png
L_0932,isotopes,T_4558,FIGURE 1.1,image,textbook_images/isotopes_22911.png
L_0933,kinetic energy,T_4561,FIGURE 1.1,image,textbook_images/kinetic_energy_22912.png
L_0934,kinetic theory of matter,T_4563,FIGURE 1.1,image,textbook_images/kinetic_theory_of_matter_22914.png
L_0936,law of reflection,T_4567,FIGURE 1.1,image,textbook_images/law_of_reflection_22916.png
L_0936,law of reflection,T_4567,FIGURE 1.2,image,textbook_images/law_of_reflection_22917.png
L_0937,lens,T_4570,FIGURE 1.1,image,textbook_images/lens_22920.png
L_0938,lever,T_4575,FIGURE 1.1,image,textbook_images/lever_22921.png
L_0939,light,T_4577,FIGURE 1.1,image,textbook_images/light_22922.png
L_0939,light,T_4579,FIGURE 1.2 Visible light spectrum.,image,textbook_images/light_22923.png
L_0939,light,T_4580,FIGURE 1.3,image,textbook_images/light_22924.png
L_0940,lipid classification,T_4582,FIGURE 1.1,image,textbook_images/lipid_classification_22925.png
L_0940,lipid classification,T_4582,FIGURE 1.2,image,textbook_images/lipid_classification_22926.png
L_0940,lipid classification,T_4583,FIGURE 1.3,image,textbook_images/lipid_classification_22927.png
L_0942,longitudinal wave,T_4586,FIGURE 1.1,image,textbook_images/longitudinal_wave_22932.png
L_0942,longitudinal wave,T_4588,FIGURE 1.2,image,textbook_images/longitudinal_wave_22933.png
L_0943,magnetic field reversal,T_4589,FIGURE 1.1,image,textbook_images/magnetic_field_reversal_22934.png
L_0943,magnetic field reversal,T_4590,FIGURE 1.2,image,textbook_images/magnetic_field_reversal_22935.png
L_0944,magnets,T_4592,FIGURE 1.1,image,textbook_images/magnets_22936.png
L_0944,magnets,T_4592,FIGURE 1.2,image,textbook_images/magnets_22937.png
L_0944,magnets,T_4592,FIGURE 1.3,image,textbook_images/magnets_22938.png
L_0946,mechanical advantage,T_4598,FIGURE 1.1,image,textbook_images/mechanical_advantage_22939.png
L_0947,mechanical wave,T_4602,FIGURE 1.1,image,textbook_images/mechanical_wave_22940.png
L_0949,mendeleevs periodic table,T_4606,FIGURE 1.1,image,textbook_images/mendeleevs_periodic_table_22942.png
L_0949,mendeleevs periodic table,T_4607,FIGURE 1.2,image,textbook_images/mendeleevs_periodic_table_22943.png
L_0950,metallic bonding,T_4610,FIGURE 1.1 Metallic bonds.,image,textbook_images/metallic_bonding_22944.png
L_0950,metallic bonding,T_4610,FIGURE 1.2 Metal worker shaping iron metal.,image,textbook_images/metallic_bonding_22945.png
L_0951,metalloids,T_4612,FIGURE 1.1,image,textbook_images/metalloids_22946.png
L_0951,metalloids,T_4613,FIGURE 1.2,image,textbook_images/metalloids_22947.png
L_0952,metals,T_4615,FIGURE 1.1,image,textbook_images/metals_22948.png
L_0953,microwaves,T_4617,FIGURE 1.1,image,textbook_images/microwaves_22949.png
L_0953,microwaves,T_4619,FIGURE 1.2,image,textbook_images/microwaves_22950.png
L_0953,microwaves,T_4620,FIGURE 1.3,image,textbook_images/microwaves_22951.png
L_0954,mirrors,T_4622,FIGURE 1.1,image,textbook_images/mirrors_22952.png
L_0954,mirrors,T_4623,FIGURE 1.2,image,textbook_images/mirrors_22953.png
L_0954,mirrors,T_4624,FIGURE 1.3,image,textbook_images/mirrors_22954.png
L_0954,mirrors,T_4624,FIGURE 1.4,image,textbook_images/mirrors_22955.png
L_0956,modern periodic table,T_4630,FIGURE 1.1,image,textbook_images/modern_periodic_table_22959.png
L_0956,modern periodic table,T_4633,FIGURE 1.2,image,textbook_images/modern_periodic_table_22960.png
L_0957,molecular compounds,T_4636,FIGURE 1.1,image,textbook_images/molecular_compounds_22961.png
L_0958,momentum,T_4638,FIGURE 1.1,image,textbook_images/momentum_22962.png
L_0959,motion,T_4641,FIGURE 1.1,image,textbook_images/motion_22963.png
L_0959,motion,T_4641,FIGURE 1.2 Click image to the left or use the URL below. URL: https://www.ck12.org/flx/render/embeddedobject/5019,image,textbook_images/motion_22964.png
L_0960,musical instruments,T_4643,FIGURE 1.1,image,textbook_images/musical_instruments_22965.png
L_0963,neutrons,T_4649,FIGURE 1.1,image,textbook_images/neutrons_22969.png
L_0963,neutrons,T_4651,FIGURE 1.2,image,textbook_images/neutrons_22970.png
L_0964,newtons first law,T_4653,FIGURE 1.1,image,textbook_images/newtons_first_law_22971.png
L_0964,newtons first law,T_4653,FIGURE 1.2,image,textbook_images/newtons_first_law_22972.png
L_0964,newtons first law,T_4655,FIGURE 1.3,image,textbook_images/newtons_first_law_22973.png
L_0965,newtons law of gravity,T_4658,FIGURE 1.1,image,textbook_images/newtons_law_of_gravity_22975.png
L_0966,newtons second law,T_4659,FIGURE 1.1,image,textbook_images/newtons_second_law_22976.png
L_0967,newtons third law,T_4662,FIGURE 1.1,image,textbook_images/newtons_third_law_22977.png
L_0968,noble gases,T_4664,FIGURE 1.1,image,textbook_images/noble_gases_22978.png
L_0968,noble gases,T_4667,FIGURE 1.2 Q: How does argon prevent the problems of early light bulbs?,image,textbook_images/noble_gases_22979.png
L_0968,noble gases,T_4667,FIGURE 1.3,image,textbook_images/noble_gases_22980.png
L_0969,nonmetals,T_4670,FIGURE 1.1,image,textbook_images/nonmetals_22982.png
L_0969,nonmetals,T_4670,"FIGURE 1.2 such as the metal lithium or sodium. As a result, fluorine is highly reactive. In fact, reactions with fluorine are often explosive. Neon, on the other hand, already has a full outer energy level. It is already very stable and never reacts with other elements. It neither accepts nor gives up electrons. Neon doesnt even react with fluorine, which reacts with all other elements except helium.",image,textbook_images/nonmetals_22983.png
L_0970,nuclear fission,T_4672,FIGURE 1.1,image,textbook_images/nuclear_fission_22984.png
L_0970,nuclear fission,T_4673,FIGURE 1.2,image,textbook_images/nuclear_fission_22985.png
L_0970,nuclear fission,T_4675,FIGURE 1.3,image,textbook_images/nuclear_fission_22986.png
L_0970,nuclear fission,T_4675,FIGURE 1.4,image,textbook_images/nuclear_fission_22987.png
L_0971,nuclear fusion,T_4677,FIGURE 1.1 Nuclear Fusion,image,textbook_images/nuclear_fusion_22988.png
L_0971,nuclear fusion,T_4678,FIGURE 1.2,image,textbook_images/nuclear_fusion_22989.png
L_0971,nuclear fusion,T_4679,FIGURE 1.3,image,textbook_images/nuclear_fusion_22990.png
L_0972,nucleic acid classification,T_4681,FIGURE 1.1,image,textbook_images/nucleic_acid_classification_22991.png
L_0972,nucleic acid classification,T_4683,FIGURE 1.2,image,textbook_images/nucleic_acid_classification_22992.png
L_0976,optical instruments,T_4692,FIGURE 1.1,image,textbook_images/optical_instruments_22996.png
L_0976,optical instruments,T_4693,FIGURE 1.2,image,textbook_images/optical_instruments_22997.png
L_0976,optical instruments,T_4694,FIGURE 1.3,image,textbook_images/optical_instruments_22998.png
L_0976,optical instruments,T_4695,FIGURE 1.4,image,textbook_images/optical_instruments_22999.png
L_0976,optical instruments,T_4695,FIGURE 1.5,image,textbook_images/optical_instruments_23000.png
L_0976,optical instruments,T_4696,FIGURE 1.6,image,textbook_images/optical_instruments_23001.png
L_0977,orbital motion,T_4698,FIGURE 1.1,image,textbook_images/orbital_motion_23002.png
L_0977,orbital motion,T_4698,FIGURE 1.2,image,textbook_images/orbital_motion_23003.png
L_0979,ph concept,T_4705,FIGURE 1.1,image,textbook_images/ph_concept_23007.png
L_0979,ph concept,T_4706,FIGURE 1.2,image,textbook_images/ph_concept_23008.png
L_0979,ph concept,T_4706,FIGURE 1.3,image,textbook_images/ph_concept_23009.png
L_0980,photosynthesis reactions,T_4708,FIGURE 1.1,image,textbook_images/photosynthesis_reactions_23010.png
L_0980,photosynthesis reactions,T_4708,FIGURE 1.2 The green streaks on this very blue lake are photosynthetic bacteria called cyanobacteria.,image,textbook_images/photosynthesis_reactions_23011.png
L_0985,position time graphs,T_4726,FIGURE 1.1,image,textbook_images/position_time_graphs_23020.png
L_0985,position time graphs,T_4726,FIGURE 1.2,image,textbook_images/position_time_graphs_23021.png
L_0986,potential energy,T_4729,FIGURE 1.1,image,textbook_images/potential_energy_23022.png
L_0986,potential energy,T_4731,FIGURE 1.2,image,textbook_images/potential_energy_23023.png
L_0986,potential energy,T_4731,FIGURE 1.3,image,textbook_images/potential_energy_23024.png
L_0987,power,T_4732,FIGURE 1.1,image,textbook_images/power_23025.png
L_0987,power,T_4735,FIGURE 1.2,image,textbook_images/power_23026.png
L_0987,power,T_4735,FIGURE 1.3,image,textbook_images/power_23027.png
L_0989,projectile motion,T_4742,FIGURE 1.1,image,textbook_images/projectile_motion_23031.png
L_0989,projectile motion,T_4742,FIGURE 1.2,image,textbook_images/projectile_motion_23032.png
L_0989,projectile motion,T_4742,FIGURE 1.3,image,textbook_images/projectile_motion_23033.png
L_0990,properties of acids,T_4744,FIGURE 1.1 Hydrochloric acid reacting with the metal zinc.,image,textbook_images/properties_of_acids_23034.png
L_0990,properties of acids,T_4745,FIGURE 1.2,image,textbook_images/properties_of_acids_23035.png
L_0990,properties of acids,T_4747,"FIGURE 1.3 Nitric acid and Phosphoric acid: Both nitric acid and phosphoric acid are used to make fertilizer. Hydrochloric acid: Hy- drochloric acid is used to clean swimming pools, bricks, and concrete. Sulfuric acid: Sulfuric Acid is an important component of car batteries.",image,textbook_images/properties_of_acids_23036.png
L_0991,properties of bases,T_4750,FIGURE 1.1,image,textbook_images/properties_of_bases_23037.png
L_0991,properties of bases,T_4752,FIGURE 1.2,image,textbook_images/properties_of_bases_23038.png
L_0992,properties of electromagnetic waves,T_4754,FIGURE 1.1,image,textbook_images/properties_of_electromagnetic_waves_23039.png
L_0994,protein classification,T_4760,FIGURE 1.1,image,textbook_images/protein_classification_23042.png
L_0994,protein classification,T_4761,FIGURE 1.2 The blood protein hemoglobin binds with oxygen and carries it from the lungs to all the bodys cells. Heme is a small molecule containing iron that is part of the larger hemoglobin molecule. Oxygen binds to the iron in heme.,image,textbook_images/protein_classification_23043.png
L_0997,radio waves,T_4769,FIGURE 1.1,image,textbook_images/radio_waves_23045.png
L_0997,radio waves,T_4770,FIGURE 1.2,image,textbook_images/radio_waves_23046.png
L_0999,radioactivity,T_4778,FIGURE 1.1,image,textbook_images/radioactivity_23048.png
L_1000,radioisotopes,T_4780,FIGURE 1.1,image,textbook_images/radioisotopes_23049.png
L_1002,reactants and products,T_4788,FIGURE 1.1,image,textbook_images/reactants_and_products_23051.png
L_1003,recognizing chemical reactions,T_4790,FIGURE 1.1,image,textbook_images/recognizing_chemical_reactions_23052.png
L_1003,recognizing chemical reactions,T_4790,FIGURE 1.2,image,textbook_images/recognizing_chemical_reactions_23053.png
L_1003,recognizing chemical reactions,T_4790,FIGURE 1.3,image,textbook_images/recognizing_chemical_reactions_23054.png
L_1007,rutherfords atomic model,T_4800,FIGURE 1.1,image,textbook_images/rutherfords_atomic_model_23057.png
L_1007,rutherfords atomic model,T_4800,FIGURE 1.2,image,textbook_images/rutherfords_atomic_model_23058.png
L_1007,rutherfords atomic model,T_4802,FIGURE 1.3,image,textbook_images/rutherfords_atomic_model_23059.png
L_1009,saturated hydrocarbons,T_4807,FIGURE 1.1,image,textbook_images/saturated_hydrocarbons_23060.png
L_1009,saturated hydrocarbons,T_4808,"FIGURE 1.2 4. Compare and contrast straight-chain, branched-chain, and cyclic alkanes.",image,textbook_images/saturated_hydrocarbons_23061.png
L_1019,scope of chemistry,T_4837,FIGURE 1.1,image,textbook_images/scope_of_chemistry_23071.png
L_1021,scope of physics,T_4841,FIGURE 1.1,image,textbook_images/scope_of_physics_23073.png
L_1022,screw,T_4842,FIGURE 1.1,image,textbook_images/screw_23074.png
L_1022,screw,T_4843,FIGURE 1.2,image,textbook_images/screw_23075.png
L_1025,simple machines,T_4853,FIGURE 1.1,image,textbook_images/simple_machines_23076.png
L_1025,simple machines,T_4856,FIGURE 1.2,image,textbook_images/simple_machines_23077.png
L_1025,simple machines,T_4856,FIGURE 1.3,image,textbook_images/simple_machines_23078.png
L_1025,simple machines,T_4856,FIGURE 1.4,image,textbook_images/simple_machines_23079.png
L_1032,sound waves,T_4876,FIGURE 1.1,image,textbook_images/sound_waves_23092.png
L_1033,sources of visible light,T_4880,FIGURE 1.1,image,textbook_images/sources_of_visible_light_23094.png
L_1033,sources of visible light,T_4882,FIGURE 1.2,image,textbook_images/sources_of_visible_light_23095.png
L_1033,sources of visible light,T_4882,FIGURE 1.3,image,textbook_images/sources_of_visible_light_23096.png
L_1035,speed,T_4887,FIGURE 1.1,image,textbook_images/speed_23098.png
L_1038,static electricity and static discharge,T_4897,FIGURE 1.1,image,textbook_images/static_electricity_and_static_discharge_23101.png
L_1040,surface wave,T_4901,FIGURE 1.1,image,textbook_images/surface_wave_23103.png
L_1041,synthesis reactions,T_4904,FIGURE 1.1,image,textbook_images/synthesis_reactions_23105.png
L_1045,technology and society,T_4914,FIGURE 1.1 This is a museum model similar to the steam engine invented by James Watt.,image,textbook_images/technology_and_society_23110.png
L_1048,thermal conductors and insulators,T_4920,FIGURE 1.1,image,textbook_images/thermal_conductors_and_insulators_23114.png
L_1048,thermal conductors and insulators,T_4921,FIGURE 1.2,image,textbook_images/thermal_conductors_and_insulators_23115.png
L_1048,thermal conductors and insulators,T_4921,FIGURE 1.3,image,textbook_images/thermal_conductors_and_insulators_23116.png
L_1049,thermal energy,T_4923,FIGURE 1.1,image,textbook_images/thermal_energy_23117.png
L_1050,thermal radiation,T_4925,FIGURE 1.1,image,textbook_images/thermal_radiation_23118.png
L_1051,thomsons atomic model,T_4927,FIGURE 1.1,image,textbook_images/thomsons_atomic_model_23120.png
L_1051,thomsons atomic model,T_4927,FIGURE 1.2,image,textbook_images/thomsons_atomic_model_23121.png
L_1051,thomsons atomic model,T_4928,FIGURE 1.3,image,textbook_images/thomsons_atomic_model_23122.png
L_1052,transfer of electric charge,T_4929,FIGURE 1.1,image,textbook_images/transfer_of_electric_charge_23124.png
L_1052,transfer of electric charge,T_4932,FIGURE 1.2,image,textbook_images/transfer_of_electric_charge_23125.png
L_1052,transfer of electric charge,T_4933,"FIGURE 1.3 A: Electrons are transferred from the wall to the balloon, making the balloon negatively charged and the wall positively charged. The balloon sticks to the wall because opposite charges attract.",image,textbook_images/transfer_of_electric_charge_23126.png
L_1053,transition metals,T_4935,FIGURE 1.1,image,textbook_images/transition_metals_23127.png
L_1053,transition metals,T_4935,"FIGURE 1.2 Other properties of the transition metals are unique. They are the only elements that may use electrons in the next to highestas well as the highestenergy level as valence electrons. Valence electrons are the electrons that form bonds with other elements in compounds and that generally determine the properties of elements. Transition metals are unusual in having very similar properties even with different numbers of valence electrons. The transition metals also include the only elements that produce a magnetic field. Three of them have this property: iron (Fe), cobalt (Co), and nickel (Ni).",image,textbook_images/transition_metals_23128.png
L_1054,transverse wave,T_4937,FIGURE 1.1,image,textbook_images/transverse_wave_23129.png
L_1054,transverse wave,T_4938,FIGURE 1.2,image,textbook_images/transverse_wave_23130.png
L_1054,transverse wave,T_4939,FIGURE 1.3,image,textbook_images/transverse_wave_23131.png
L_1055,types of friction,T_4941,FIGURE 1.1,image,textbook_images/types_of_friction_23132.png
L_1055,types of friction,T_4943,FIGURE 1.2,image,textbook_images/types_of_friction_23133.png
L_1055,types of friction,T_4944,FIGURE 1.3,image,textbook_images/types_of_friction_23134.png
L_1056,ultrasound,T_4947,FIGURE 1.1,image,textbook_images/ultrasound_23136.png
L_1056,ultrasound,T_4947,FIGURE 1.2 Distance = 1437 m/s  1 s = 1437 m,image,textbook_images/ultrasound_23137.png
L_1056,ultrasound,T_4948,FIGURE 1.3,image,textbook_images/ultrasound_23138.png
L_1057,unsaturated hydrocarbons,T_4950,FIGURE 1.1,image,textbook_images/unsaturated_hydrocarbons_23139.png
L_1057,unsaturated hydrocarbons,T_4951,FIGURE 1.2 Q: How many bonds does each carbon atom in benzene form?,image,textbook_images/unsaturated_hydrocarbons_23140.png
L_1057,unsaturated hydrocarbons,T_4952,FIGURE 1.3,image,textbook_images/unsaturated_hydrocarbons_23141.png
L_1057,unsaturated hydrocarbons,T_4952,FIGURE 1.4,image,textbook_images/unsaturated_hydrocarbons_23142.png
L_1058,using earths magnetic field,T_4954,FIGURE 1.1,image,textbook_images/using_earths_magnetic_field_23143.png
L_1058,using earths magnetic field,T_4955,FIGURE 1.2,image,textbook_images/using_earths_magnetic_field_23144.png
L_1059,valence electrons,T_4959,FIGURE 1.1,image,textbook_images/valence_electrons_23145.png
L_1059,valence electrons,T_4959,FIGURE 1.2,image,textbook_images/valence_electrons_23146.png
L_1059,valence electrons,T_4959,FIGURE 1.3,image,textbook_images/valence_electrons_23147.png
L_1059,valence electrons,T_4959,FIGURE 1.4,image,textbook_images/valence_electrons_23148.png
L_1059,valence electrons,T_4960,FIGURE 1.5,image,textbook_images/valence_electrons_23149.png
L_1060,velocity,T_4962,FIGURE 1.1,image,textbook_images/velocity_23150.png
L_1061,velocity time graphs,T_4966,FIGURE 1.1,image,textbook_images/velocity_time_graphs_23151.png
L_1062,visible light and matter,T_4967,FIGURE 1.1,image,textbook_images/visible_light_and_matter_23152.png
L_1062,visible light and matter,T_4968,FIGURE 1.2,image,textbook_images/visible_light_and_matter_23153.png
L_1062,visible light and matter,T_4968,FIGURE 1.3,image,textbook_images/visible_light_and_matter_23154.png
L_1062,visible light and matter,T_4970,FIGURE 1.4,image,textbook_images/visible_light_and_matter_23155.png
L_1062,visible light and matter,T_4970,FIGURE 1.5,image,textbook_images/visible_light_and_matter_23156.png
L_1063,vision and the eye,T_4971,FIGURE 1.1,image,textbook_images/vision_and_the_eye_23157.png
L_1063,vision and the eye,T_4972,FIGURE 1.2,image,textbook_images/vision_and_the_eye_23158.png
L_1064,vision problems and corrective lenses,T_4974,FIGURE 1.1,image,textbook_images/vision_problems_and_corrective_lenses_23159.png
L_1064,vision problems and corrective lenses,T_4975,FIGURE 1.2,image,textbook_images/vision_problems_and_corrective_lenses_23160.png
L_1065,wave amplitude,T_4977,FIGURE 1.1,image,textbook_images/wave_amplitude_23161.png
L_1066,wave frequency,T_4979,"FIGURE 1.1 A: Waves with a higher frequency have crests that are closer together, so higher frequency waves have shorter wavelengths.",image,textbook_images/wave_frequency_23164.png
L_1066,wave frequency,T_4980,FIGURE 1.2,image,textbook_images/wave_frequency_23165.png
L_1067,wave interactions,T_4984,FIGURE 1.1,image,textbook_images/wave_interactions_23166.png
L_1067,wave interactions,T_4987,FIGURE 1.2,image,textbook_images/wave_interactions_23167.png
L_1068,wave interference,T_4991,FIGURE 1.1,image,textbook_images/wave_interference_23168.png
L_1068,wave interference,T_4993,FIGURE 1.2,image,textbook_images/wave_interference_23169.png
L_1069,wave particle theory,T_4996,FIGURE 1.1,image,textbook_images/wave_particle_theory_23170.png
L_1071,wavelength,T_5005,FIGURE 1.1,image,textbook_images/wavelength_23172.png
L_1071,wavelength,T_5005,FIGURE 1.2,image,textbook_images/wavelength_23173.png
L_1071,wavelength,T_5005,"FIGURE 1.3 Q: Of all the colors of visible light, red light has the longest wavelength and violet light has the shortest wavelength. Which color of light has the greatest energy?",image,textbook_images/wavelength_23174.png
L_1072,wedge,T_5007,FIGURE 1.1,image,textbook_images/wedge_23175.png
L_1072,wedge,T_5007,FIGURE 1.2,image,textbook_images/wedge_23176.png
L_1073,wheel and axle,T_5008,FIGURE 1.1 Q: Where is the force applied in a Ferris wheel and a doorknob? Is it applied to the wheel or to the axle?,image,textbook_images/wheel_and_axle_23178.png
L_1074,why earth is a magnet,T_5011,FIGURE 1.1,image,textbook_images/why_earth_is_a_magnet_23179.png
L_1076,work,T_5014,FIGURE 1.1,image,textbook_images/work_23180.png
L_1076,work,T_5015,FIGURE 1.2,image,textbook_images/work_23181.png
L_0003,erosion and deposition by flowing water,DD_0001,"The diagram represents the coastal Erosion of a headland. A headland is an area of hard rock which sticks out into the sea. Headlands form in areas of alternating hard and soft rock. Where the soft rock erodes, bays are formed on either side of the headland. As the headland becomes more exposed to the wind and waves the rate of its erosion increases. When headlands erode they create distinct features such as caves, arches, stacks and stumps. The sequence in the erosion of a headland is as follows: 1. Waves attack a weakness in the headland. 2. A cave is formed. 3. Eventually the cave erodes through the headland to form an arch. 4. The roof of the arch collapses leaving a column of rock called a stack. 5. The stack collapses leaving a stump.",image,teaching_images/erosion_6859.png
L_0003,erosion and deposition by flowing water,DD_0002,"The diagram shows how a waterfall is formed by erosion. Waterfalls begin with mountain streams that begin high up in mountains. These streams flow down very quickly because of the steep slope, and flowing water, especially fast-moving water, erodes soil and rocks. Soft rock erodes more quickly than hard rock. When soft rock erodes, the stream bed can collapse, causing an abrupt drop in the stream. This sudden drop is what creates a waterfall. In the diagram, the overhang is where the stream bed collapsed to create the waterfall. Because of the flowing water, the soft rock at the side of the waterfall will continue to erode. This continued erosion will cause more of the stream bed to collapse. The waterfall overhang will then retreat upstream and create a higher waterfall.",image,teaching_images/erosion_8064.png
L_0006,erosion and deposition by glaciers,DD_0003,"This diagram shows about Erosion and Deposition by Glaciers. Glaciers are made up of fallen snow that, over many years, compresses into large, thickened ice masses. Glaciers form when snow remains in one location long enough to transform into ice. What makes glaciers unique is their ability to move. Due to sheer mass, glaciers flow like very slow rivers. Some glaciers are as small as football fields, while others grow to be dozens or even hundreds of kilometers long. Presently, glaciers occupy about 10 percent of the world's total land area, with most located in polar regions like Antarctica, Greenland, and the Canadian Arctic. Most glaciers lie within mountain ranges. Glaciers cause erosion by plucking and abrasion. Glaciers deposit their sediment when they melt. Landforms deposited by glaciers include drumlins, kettle lakes, and eskers. A ground moraine is a thick layer of sediments left behind by a retreating glacier. A drumlin is a long, low hill of sediments deposited by a glacier. Drumlins often occur in groups called drumlin fields. An esker is a winding ridge of sand deposited by a stream of meltwater. A kettle lake occurs where a chunk of ice was left behind in the sediments of a retreating glacier. When the ice melted, it left a depression. The meltwater filled it to form a lake.",image,teaching_images/glaciers_6926.png
L_0006,erosion and deposition by glaciers,DD_0004,"The diagram shows several features of an alpine glacier. Glaciers are masses of flowing ice that are formed when more snow falls than melts each year. Snow falls in the accumulation zone, usually the part of the glacier with the highest elevation. Further down the glacier, usually at a lower altitude, is the ablation area, where most of the melting and evaporation occur. At locations where a glacier flows rapidly, friction creates giant cracks called crevasse. Moraines are created when the glacier pushes or carries rocky debris as it moves. Medial moraines run down the middle of a glacier, lateral moraines along the sides, and terminal moraines are found at the terminus of a glacier. Glaciers cause erosion by plucking and abrasion. Valley glaciers form several unique features through erosion, including cirques and artes. Glaciers deposit their sediment when they melt. Landforms deposited by glaciers include drumlins, kettle lakes, and eskers.",image,teaching_images/glaciers_6936.png
L_0008,fossils,DD_0005,"The diagram here shows us the stages of fossil creation. The first picture shows a living dinosaur that may have existed a thousand years ago. The second picture shows us dinosaur bones beneath waterbed. The third picture shows the bones separated and within the earth's rocks. And finally the fourth picture shows a man excavating and discovering the dinosaur bones, also known as fossils. Now what exactly are fossils? Fossils are nothing but the remains or impression of a prehistoric plant or animal embedded in rock and preserved in petrified form. The process by which remains or traces of living things become fossils is called fossilization. Most fossils are preserved in sedimentary rocks. Fossils are our best clues about the history of life on Earth.",image,teaching_images/fossils_9105.png
L_0008,fossils,DD_0006,The diagram shows one way that fossils can form. There are 4 main stages. We see it begins when plants and animals die. They sink to the bottom of the sea. The dead animals become covered by sediment. Over time the pressure from the sediment compresses the dead animals into oil. Oil eventually moves up thru rocks. It then forms a reservoir and the process is complete.,image,teaching_images/fossils_6897.png
L_0009,relative ages of rocks,DD_0007,"This diagram represents the cross-cutting relationships of rocks. Layer 1, as shown, is the oldest layer because it is the layer that is the deepest. This is the law of superposition. In the diagram below, “dike” is the youngest rock layer. This is figured by the law of cross-cutting relationships. The layers are always older than the rock that cuts across them. In the diagram below, dike cuts through all four layers. Therefore, layer 1 is the oldest, layer 2 is the second oldest, layer 3 is the third oldest, layer 4 is the fourth oldest, and dike is the youngest layer of rock.",image,teaching_images/stratigraphy_9259.png
L_0009,relative ages of rocks,DD_0008,"The study of rock strata is called stratigraphy. This Diagram is all about the Laws of Stratigraphy. The laws of stratigraphy can help scientists understand Earths past. The relative ages of rocks are important for understanding Earths history. The diagram refers to the position of rock layers and their relative ages, which is called Superposition. New rock layers are always deposited on top of existing rock layers. Therefore, deeper layers must be older than layers closer to the surface. A is the area covered by Law of Cross-Cutting relationships, B is the unconformities, C is the law of Original Horizontality, D is the Law of Conti-unity, E is the law of Superposition. Some rock layers extend over a very wide area. They may be found on more than one continent or in more than one country.",image,teaching_images/stratigraphy_9262.png
L_0016,groundwater,DD_0009,"The picture shows the groundwater and how it moves. Rivers and lakes hold a lot of Earths liquid freshwater. Twenty times more of Earths liquid freshwater is found below the surface than on the surface. Groundwater (or ground water) is the water present beneath Earth's surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from, and eventually flows to, the surface naturally. Natural discharge often occurs at springs and seeps, and can form oases or wetlands. Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.",image,teaching_images/aquifers_6510.png
L_0016,groundwater,DD_0010,"This diagram depicts how the groundwater is formed. WIth the diagram, we can understand how the groundwater is formed. First, the water is poured down from the cloud to the earth's surface. The water is recharged to the top layer of the earth called piezometric surface. Below the piezometric surface, the layer containing water is called unconfined aquifer. The top level of the unconfined aquifer is called water table level. Under the unconfined aquifer, there is a layer that the water cannot penetrate. We call the layer as impermeable layer. Under the impermeable layer, a thick layer containing water is called confide aquifer. The earth region that supports the confined aquifer is called confining bed. The hole to obtain water in the unconfined aquifer is called artesian bore.",image,teaching_images/aquifers_6524.png
L_0016,groundwater,DD_0011,"This diagram shows the structure of groundwater storage in the earth. The top layer of the earth is call unsaturated zone and does not have water stored. The below the unsaturated zone, there is an unconfined aquifer which contains the water closest to the earth surface. The boundary between the unsaturated zone and unconfined aquifer is called water table. The unconfined water layer absorbers the water from the surface and provide the water to the river or to the ground by a pump. The water circulation period in the unconfined aquifer is from days to years. Under the unconfined aquifer, there is a confining bed. Under the confining bed, there is confined aquifer. This is deeper layer than unconfined aquifer and the water returning cycle to the ground is century long. Under the confined aquifer, there is another confining bed. Below the confined aquifer, there is another confined aquifer. The water returning cycle to the ground is millennium long.",image,teaching_images/aquifers_6953.png
L_0017,introduction to the oceans,DD_0012,"This diagram represents the layers of the ocean. The oceans are divided into two broad realms; the pelagic and the benthic. Pelagic refers to the open water in which swimming and floating organisms live. Organisms living there are called the pelagos. From the shallowest to the deepest, biologists divide the pelagic into the epipelagic the mesopelagic the bathypelagic the abyssopelagic and the deepest, the hadopelagic. The last three zones have no sunlight at all. The Habitat zone is formed by 5 mini zones: Abbysal, Bathyal, Hadal, Neritic, and Oceanic. One-third of the Earth is made up of the Abbysal zone. It is very cold and dark in this zone. In the Bathyal zone, the food and temperature easily fall into the deepest zones of the ocean. The Hadal zone is the deepest zone in the ocean. It has high-pressure conditions and it's really cold. The Neritic zone is rich in plants, animals, and nutrients that are carried by currents of land. In the Oceanic zone, there is an abundant life of plankton.",image,teaching_images/ocean_zones_7130.png
L_0017,introduction to the oceans,DD_0013,"This diagram shows the ocean floor. Like land terrains, the ocean floor also has ridges, valleys, plains and volcanoes. The seabed (also known as the seafloor, sea floor, or ocean floor) is the bottom of the ocean. The oceanic zone begins in the area off shore where the water measures 200 meters (656 feet) deep or deeper. It is the region of open sea beyond the edge of the continental shelf and includes 65% of the ocean's completely open water. The photic zone or sunlight zone is the depth of the water in a lake or ocean that is exposed to such intensity of sunlight which designates compensation point. The aphotic zone is the portion of a lake or ocean where there is little or no sunlight. It is formally defined as the depths beyond which less than 1% of sunlight penetrates. The abyssal zone is the layer of the pelagic zone of the ocean. At depths of 4,000 to 6,000 metres (13,123 to 19,685 feet), this zone remains in perpetual darkness and never receives daylight. The continental shelf is the area of the seabed around a large landmass where the sea is relatively shallow compared with the open ocean. This is geologically part of the continental crust. Studying the ocean floor is difficult because the environment is so hostile but scientists have discovered good ways to study the ocean floor through the years. Some ways are by using a sonar and special vehicles (some of which can even be done remotely).",image,teaching_images/ocean_zones_8125.png
L_0018,ocean movements,DD_0014,"The diagram shows the relationship between the moon and tides around Earth. Tides are daily changes in the level of ocean water. They occur all around the globe. High tides occur when the water reaches its highest level in a day. Low tides occur when the water reaches its lowest level in a day. Tides keep cycling from high to low and back again. The main cause of tides is the pull of the Moons gravity on Earth. The pull is the greatest on whatever is closest to the Moon. Although the gravity pulls the land, only the water can move. As a result, a tidal bulge (high tide) is formed due to gravity. Earth itself is pulled harder by the Moons gravity than is the ocean on the side of Earth opposite the Moon. As a result, there is a tidal bulge of water on the opposite side of Earth due to inertia. This creates another high tide. With water bulging on two sides of Earth, there's less water left in between. This creates low tides on the other two sides of the planet.",image,teaching_images/tides_133.png
L_0018,ocean movements,DD_0015,"This diagram illustrates the components and behavior of a wave propagating through water. The highest point in a wave is called the Crest, whereas the lowest point is called the Trough. Waves are periodic, meaning they maintain the same pattern as they propagate. The distance from one crest to another is called the Wavelength. The wavelength can also be measured from any point in the wave to the next point at the same elevation. Beneath the wave crests, water molecules tend to move in an orbital path. Two important properties of a wave are its Frequency and Period. The frequency of a wave is related to how fast the wave is moving. Frequency is defined as the number of times a particular point in a wave, say a crest, passes by a given point each second. Period is defined as the time it takes for a wave to move through one wavelength or cycle.",image,teaching_images/ocean_waves_7117.png
L_0018,ocean movements,DD_0016,"This diagram represents the different positions of the Sun and moon in relation to the Earth, with two different types of tides. The positions of the Sun and moon affect tides, because the Sun's gravity determines how much influence the moon has on tides. Spring tides occur during new moon and full moon, because the Sun and moon are in a straight line, and their combined gravity causes extreme tides on Earth (high or low). Neap tides happen when the moon is in 1st quarter or third quarter, because since the Sun and moon are not in line here, the gravity is weaker and the tides do not have as great of a range. So, spring tides and neap tides are essentially opposite concepts. As you can see in Diagram A, the light blue area around the Earth represents the amount of tide, and there are extreme highs and lows. In Diagram B, the light blue area is more averaged out around the globe.",image,teaching_images/tides_151.png
L_0018,ocean movements,DD_0017,"This is a diagram showing how a mechanical wave moves. The wave travels in the direction from A to B. The number of waves that pass point A in one second is called wave frequency. The time is takes for a wave crest to pass point A and reach point B is called the wave period. The distance from point A to point B is a wavelength, which measures the crest of the first wave to the crest of the second. The trough is the low point of the wave, and the crest is the high point. There are three types of mechanical waves that move through a medium: transverse, longitudinal, and surface.",image,teaching_images/ocean_waves_9152.png
L_0018,ocean movements,DD_0018,"This image shows how spring tide occurs, a tide just after a new or full moon, when there is the greatest difference between high and low water. The times and amplitude of tides at a locale are influenced by the alignment of the Sun and Moon. Approximately twice a month, around new moon and full moon when the Sun, Moon, and Earth from a line, the tidal force due to the sun reinforces that due to the Moon. The tide's range is then at its maximum; this is called the spring tide.",image,teaching_images/tides_2614.png
L_0019,the ocean floor,DD_0019,"This diagram shows an abbreviated version of underwater landscape. The ground under an ocean gets slowly deeper shortly after passing the beach, which is called the continental shelf. After this it slopes down steadily in the continental slope. After the slop is an abyssal plain, which is significantly deeper but not as deep as a trench-here, there is no sunlight. A volcanic arc comes before an underwater volcano, which forms a volcanic island that may or may not be dormant. A continental slope can also be considered a continental rise if it is seen from the opposite direction.",image,teaching_images/parts_ocean_floor_9206.png
L_0019,the ocean floor,DD_0020,"The following diagram is that of an ocean floor. The major features on the ocean floor are continental shelf, continental slope, continental rise and the coast. The continental shelf in the ocean floor is nearest to the edges of continents. It has a gentle slope. The continental slope lies between the continental shelf and the abyssal plain. It has a steep slope with a sharp drop to the deep ocean floor. The abyssal plain forms much of the floor under the open ocean. Magma erupts through the ocean floor to make new seafloor. The magma hardens to create the ridge.",image,teaching_images/parts_ocean_floor_7237.png
L_0023,layers of the atmosphere,DD_0021,"The Earth has five different layers in its atmosphere. The atmosphere layers vary by temperature. As the altitude in the atmosphere increases, the air temperature changes. The lowest layer is the troposphere, it gets some of its heat from the sun. However, it gets most of its heat from the Earth's surface. The troposphere is also the shortest layer of the atmosphere. It holds 75 percent of all the gas molecules in the atmosphere. The air is densest in this layer.",image,teaching_images/layers_of_atmosphere_7066.png
L_0023,layers of the atmosphere,DD_0022,The diagram shows the 5 layers of Earth's atmosphere and their relative distance from the Earth's surface. Troposphere is the shortest layer closest to Earth's surface at about 15km away from the surface. The stratosphere is the layer above the troposphere and rises to about 50 kilometers above the surface. The mesosphere is the layer above the stratosphere and rises to about 80 kilometers above the surface. Temperature decreases with altitude in this layer. The thermosphere is the layer above the mesosphere and rises to 500 kilometers above the surface. The International Space Station orbits Earth in this layer. The exosphere is the layer above the thermosphere. This is the top of the atmosphere.,image,teaching_images/layers_of_atmosphere_8102.png
L_0033,cycles of matter,DD_0025,"This is a diagram of the nitrogen cycle. Nitrogen is present in the earth's soil, atmoshpere, and biosphere. The amount of nitrogen on the earth is fixed, and it can't be created or destroyed. It can only change the forms it takes in chemical compounds. Nitrogen gas in the atmosphere enters the soil and ocean through t the action of nitrogen fixing bacteria. These bacterial convert nitrogen gas to ammonium, nitrites, and then to nitrates. Once in the soil, these nitrates can enter the terrestrial food web, or return to the atmosphere by the action of denitrifying bacteria. Nitrates in the ocean can the marine ecosystem, or can be converted back to nitrogen gas by denitrifying bacteria. Humans add nitrogen to the soil when they use fertiizers. These fertilizers can enter the marine food web as runoff.",image,teaching_images/cycle_nitrogen_6718.png
L_0033,cycles of matter,DD_0026,"The element carbon is the basis of all life on Earth. Biochemical compounds consist of chains of carbon atoms and just a few other elements. Like water, carbon is constantly recycled through the biotic and abiotic factors of ecosystems. The carbon cycle includes carbon in sedimentary rocks and fossil fuels under the ground, the ocean, the atmosphere, and living things. The diagram represents the carbon cycle. It shows some ways that carbon moves between the different parts of the cycle.",image,teaching_images/cycle_carbon_63.png
L_0033,cycles of matter,DD_0027,"This is a diagram of the carbon cycle. Carbon is found in all living things on Earth. Carbon is cycled between the living (biotic) and nonliving (abiotic) parts of the ecosystem. Carbon is found in sedimentary rocks and fossil fuels, the atmosphere and in living things. Animals and plants release carbon in the form of carbon dioxide during the process of respiration. Carbon dioxide in the air is taken up by plants during photosynthesis. Photosynthesis produces glucose, a carbohydrate. Glucose is broken down by animals for energy.",image,teaching_images/cycle_carbon_70.png
L_0033,cycles of matter,DD_0028,"This diagram shows the carbon cycle. Here are examples of how carbon moves through human, animal, and plant activity. All living things contain carbon, as do the ocean, air, rocks, and underground fossil fuels, which are made in a process that takes millions of years. Plants take in sunlight and carbon dioxide, and create energy through photosynthesis. When they decay, and are buried underground, plants and other organisms turn into fossil fuel. When we burn fossil fuels, carbon dioxide is quickly released into the air. Plants can also release carbon dioxide just like animals do, through respiration.",image,teaching_images/cycle_carbon_5008.png
L_0033,cycles of matter,DD_0029,"This is an illustration of the nitrogen cycle. Nitrogen exists in several forms in the earth's soil, atmoshpere, and organisms. The earth has a fixed amount of nitrogen, and is endlessly cycled through these forms in the nitrogen cycle. Animals get their nitrogen directly by eating plants, or indirectly by eating organisms that have eaten plants. Plants can't use the form of nitrogen gas in the air. Plants can only use nitrogen in chemical compounds called nitrates. Plants absorb nitrates from the soil through their roots in a process called assimilation. Most plants use nitrates that are produced by bacteria that live in soil. A certain type of plants called legumes have nitrogen-fixing bacterial living in their roots, and don't need the bacteria in the soil. Bacteria that can change nitrogen gas in the atmosphere to nitrates are called Nitrogen-fixing bacteria. The nitrates in the detritus of organisms have their nitrogen returned to the soil as ammonium by the decomposition action of detrivores. Nitrifying bacteria change some ammonium in the soil into nitrates that can be used by plants. The rest of the ammonium is changed into nitrogen gas by denitrifying bacteria. Denitrifying bacteria convert ammonium to nitrogen gas that is released into the atmoshpere.",image,teaching_images/cycle_nitrogen_6719.png
L_0047,air pollution,DD_0030,"This diagram shows the natural ozone destruction. It consists in 3 steps, the first one occurs when the uv radiation shocks the ozone molecule and this one gets divided into the oxygen molecule and the oxygen atom. Then, the ozone molecule is added to the oxygen atom getting as result those oxygen molecules.",image,teaching_images/ozone_formation_7149.png
L_0048,effects of air pollution,DD_0031,"This diagram depicts how the acid rain forms. There are factories, vegetation, houses, river and ocean in the picture. Houses and venation is on the earth's surface. First, the acidic gases are emitted from the factories. Those acid gases include sulphur dioxide and nitrogen oxides. The acid gases are included in cloud forming process by wind. The clouds containing acid gases dissolve in rainwater to form the acid rain. The acid rain poured to the earth's surface. The acid rain is absorbed to the earth and is flowing to the river. Now, the river contains the acid rain. The river flows to the ocean. The river of acid rain kills plantlife, pollutes rivers and streams, and erodes stonework. This process continues as long as the factories emit the acid gases.",image,teaching_images/acid_rain_formation_6507.png
L_0048,effects of air pollution,DD_0032,This diagram shows how acid rain is caused by air pollution. Acid rain is mainly caused when air pollutants such as sulphur and nitrogen oxides mix with water vapor in the atmosphere. Nitrogen and sulphur oxides are generated on the earth's surface by man-made sources such as factories. A natural source of nitrogen oxides are volcanoes. These air pollutants generated then move upwards into the earth's atmosphere and get deposited back on the earth as dry or wet deposits. Wet deposits happen when gases and particulate matter mixes with water vapor which causes acid-rain/precipitation. Dry deposits come back to earth in the form of acidic gases and particulate matter.,image,teaching_images/acid_rain_formation_8000.png
L_0055,the sun,DD_0033,"This diagram shows the internal structure of the sun. The atmosphere lies on top and has the following layers. The corona is the outermost layer. Then lies the chromosphere, a reddish gaseous layer immediately above the photosphere of the sun or another star which, together with the corona, constitutes its outer atmosphere. The photosphere is about 300 km thick. Most of the Sun's visible light that we see originates from this region. Then lies the convection zone and the radiation zone. Then is the core which is made up of a very hot and dense mass of atomic nuclei and electrons.",image,teaching_images/sun_layers_6305.png
L_0055,the sun,DD_0034,"The diagram represents the various parts of the sun. There are three main parts to the Sun's interior: the core, the radiative zone, and the convective zone. The core is at the center. It is the hottest region, where the nuclear fusion reactions that power the Sun occur. Moving outward, next comes the radiative (or radiation) zone. Its name is derived from the way energy is carried outward through this layer, carried by photons as thermal radiation. The third and final region of the solar interior is named the convective (or convection) zone. It is also named after the dominant mode of energy flow in this layer; heat moves upward via roiling convection, much like the bubbling motion in a pot of boiling oatmeal. The boundary between the Sun's interior and the solar atmosphere is called the photosphere. It is what we see as the visible “surface” of the Sun. The photosphere is not like the surface of a planet; even if you could tolerate the heat you couldn't stand on it. The sun has its own atmosphere. The lower region of the solar atmosphere is called the chromosphere. A thin transition region, where temperatures rise sharply, separates the chromosphere from the vast corona above. The uppermost portion of the Sun's atmosphere is called the corona, and is surprisingly much hotter than the Sun's surface (photosphere).",image,teaching_images/sun_layers_6304.png
L_0056,the sun and the earthmoon system,DD_0035,"The diagram shows the phases of the moon as it moves in orbit around the earth. Although we can see the moon in the night sky, it does not actually produce its own light. Instead, it reflects the light of the sun onto the earth, much like a mirror would. When the moon is fully lit by the sun, we can see the entire face of the moon. This is called a full moon. However, as the moon moves around its orbit, we see less reflected light due to its changing position. The moon is waning when the reflected surface of the moon is becoming smaller. When we can see only half of the waning moon, we call this the last quarter. When the moon reaches the other side of the earth, it becomes completely dark because the earth blocks the suns light. However, as the moon continues to move around the earth, the suns light will gradually reach the moon again, and the moon reappears in the night sky. The moon is waxing when the reflected surface of the moon is becoming bigger. When we can see half of the waxing moon, we call this the first quarter. The moon will continue to grow until it again becomes a full moon. A full lunar cycle takes about 29.5 days.",image,teaching_images/earth_moon_phases_6008.png
L_0056,the sun and the earthmoon system,DD_0036,"This diagram shows 8 phases of the moon. When the side of the moon facing the earth is not illuminated by the Sun the moon phase is called New Moon. When the side of the moon facing the earth is fully lit by the sun, the moon phase is known as Full Moon. The first quarter and last quarter are phases when exactly half of the moon is lit by the sun. The intermediate stages are known as Crescent and Gibbous.",image,teaching_images/earth_moon_phases_2534.png
L_0056,the sun and the earthmoon system,DD_0037,"The diagram shows the different phases of moon. The moon does not produce any light of its own. It only reflects light from the sun. As the moon moves around the earth, we see different parts of the moon lit up by the sun. This causes the phases of the moon. A full moon occurs when the whole side facing earth is lit. This happens when earth is between the moon and the sun. About one week later, the moon enters the quarter-moon phase. Only half of the moon's lit surface is visible from earth, so it appears as a half circle. When the moon moves between earth and the sun, the side facing earth is completely dark. This is called the new moon phase. Sometimes you can just barely make out the outline of the new moon in the sky. This is because some sunlight reflects off the earth and hits the moon. Before and after the quarter-moon phases are the gibbous and crescent phases. During the crescent moon phase, the moon is less than half lit. It is seen as only a sliver or crescent shape. During the gibbous moon phase, the moon is more than half lit. It is not full. The moon undergoes a complete cycle of phases about every 29.5 days.",image,teaching_images/earth_moon_phases_2549.png
L_0056,the sun and the earthmoon system,DD_0038,"This image shows the different phases of moon. The phases of the Moon are the different ways the Moon looks from Earth over about a month. As the Moon orbits around the Earth, the half of the Moon that faces the Sun will be lit up. The different shapes of the lit portion of the Moon that can be seen from Earth are known as phases of the Moon. A new moon is when the Moon cannot be seen because we are looking at the unlit half of the Moon. A waxing crescent moon is when the Moon looks like crescent and the crescent increases (“waxes”) in size from one day to the next. The first quarter moon (or a half moon) is when half of the lit portion of the Moon is visible after the waxing crescent phase. A waxing gibbous moon occurs when more than half of the lit portion of the Moon can be seen and the shape increases (“waxes”) in size from one day to the next. A full moon is when we can see the entire lit portion of the Moon. A waning gibbous moon occurs when more than half of the lit portion of the Moon can be seen and the shape decreases (“wanes”) in size from one day to the next. The last quarter moon (or a half moon) is when half of the lit portion of the Moon is visible after the waning gibbous phase. A waning crescent moon is when the Moon looks like the crescent and the crescent decreases (“wanes”) in size from one day to the next.",image,teaching_images/earth_moon_phases_139.png
L_0056,the sun and the earthmoon system,DD_0039,"Illustrated in the diagram are the 8 different phases of the moon. The moon does not produce its own light. However, the moon becomes visible to us due to its capability to reflect light from the sun. As it moves around the Earth, we see these phases that result from the different angles the moon makes with the sun. A New Moon occurs when the side of the moon facing the earth is not illuminated by the sun. After a few days, a thin crescent shape of the moon becomes visible in the night sky. The crescent moon waxes, or appears to grow fatter, each night. When half of the moon is illuminated, it is called a First Quarter moon. The moon continues to wax, forms a gibbous shape, until it eventually becomes a Full Moon. This now means that the moon has completed one half of a month. During the second half, the shape of the moon starts to wane, growing thinner every night. Once the moon reaches the Third Quarter, it shows the other half of its disc that is illuminated by the sun. It continues to wane while nearing its approach to the New Moon Phase. The Moon undergoes a complete cycle of phases about every 29.5 days.",image,teaching_images/earth_moon_phases_2736.png
L_0057,introduction to the solar system,DD_0040,"The diagram shows the Solar System. The Sun and all the objects held by its gravity make up the solar system. There are eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, and Neptune. Pluto, Eris, Ceres, Make and Haumea are dwarf planets. The ancient Greeks believed Earth was at the center of the universe and everything else orbited Earth. Copernicus proposed that the Sun at the center of the universe and the planets and stars orbit the Sun. Planets are held by the force of gravity in elliptical orbits around the Sun. The solar system formed from a giant cloud of gas and dust about 4.6 billion years ago. This model explains why the planets all lie in one plane and orbit in the same direction around the Sun.",image,teaching_images/solar_system_1428.png
L_0057,introduction to the solar system,DD_0041,"This diagram shows our Solar system. Our solar system consists of an average star we call the Sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes: the satellites of the planets; numerous comets, asteroids, and meteoroids; and the interplanetary medium. Jupiter is the largest planet and Saturn and Neptune have rings around them. Earth lies after Mercury and Venus. All the planets revolve around the sun. Pluto is the farthest and Mercury is nearest to the sun.",image,teaching_images/solar_system_6293.png
L_0057,introduction to the solar system,DD_0042,"There are eight planets in the Solar System. From closest to farthest from the Sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The first four planets are called terrestrial planets. They are mostly made of rock and metal, and they are mostly solid. The last four planets are called gas giants. This is because they are large planets that are mostly made of gas. Even though they are made of gas, they have much more mass than the terrestrial planets. Pluto had been called a planet since it was discovered in 1930, but in 2006 astronomers meeting at the International Astronomical Union decided on the definition of a planet, and Pluto did not fit. Instead they defined a new category of dwarf planet, into which Pluto did fit, along with some others. These small planets are sometimes called plutinos.",image,teaching_images/solar_system_1435.png
L_0057,introduction to the solar system,DD_0043,"This diagram shows a few of the objects in our solar system. The first object shown in the upper row is the sun which is a star and is at the center of our solar system. The next three objects are the planets mercury, venus, earth. The objects in the second row are the moon which is the Earth's moon followed by the planets mars, jupiter and saturn. Jupiter is the largest planet. The planet saturn contains rings around it. Mercury is the planet closest to the sun in our solar system. Earth is the planet that we live on. The two planets not shown in this diagram are neptune and pluto.",image,teaching_images/solar_system_6303.png
L_0068,types of rocks,DD_0044,"This diagram shows how rocks can change from one type to another when they undergo certain processes. For magma, when it solidifies, it becomes an igneous rock. Igneous rocks can then turn into metamorphic rocks when they undergo metamorphism. They can also turn back into magma when they undergo melting. Otherwise, when igneous rocks go through erosion, they become sediment. Sediment can also be obtained from metamorphic and sedimentary rocks when they undergo erosion, too. Sediments can then undergo lithification to become sedimentary rocks. Sedimentary rocks can also become metamorphic rocks when they undergo metamorphism. And finally, metamorphic rocks can turn into magma when they undergo melting.",image,teaching_images/cycle_rock_6744.png
L_0068,types of rocks,DD_0045,"The diagram shows types of rocks and rock formation cycles. There are three major rock types. Rock of these three rock types can become rock of one of the other rock types. All rocks on Earth change, but these changes usually happen very slowly. Some changes happen below Earths surface. Some changes happen above ground. Any type of rock can change and become a new type of rock. Magma can cool and crystallize. Existing rocks can be weathered and eroded to form sediments. Rock can change by heat or pressure deep in Earths crust. There are three main processes that can change rock: Cooling and forming crystals. Deep within the Earth, temperatures can get hot enough to melt rock. This molten material is called magma. As it cools, crystals grow, forming an igneous rock. The crystals will grow larger if the magma cools slowly, as it does if it remains deep within the Earth. If the magma cools quickly, the crystals will be very small. Weathering and erosion. Water, wind, ice, and even plants and animals all act to wear down rocks. Over time they can break larger rocks into smaller pieces called sediments.",image,teaching_images/cycle_rock_6723.png
L_0068,types of rocks,DD_0046,"The Rock Cycle illustrates how rocks continually change form. There are three basic types of rocks: igneous, sedimentary and metamorphic, and each of these rocks can be changed into any one of the other types. The names of the rock types refer to the way the rocks are formed. Arrows in the diagram display how one type of rock may change to another type of rock. All igneous rocks start out as melted rock(magma) and then crystallize, or freeze. When an igneous rock is exposed on the surface, it goes through the process of weathering and erosion that breaks the rock down into smaller pieces. Wind and water carry the smaller pieces of igneous rock into piles called sediment. Through the process of compaction and cementation, the sediment gets buried and the pieces of rock become cemented together to form a new type of rock called a sedimentary rock. If a sedimentary rock is exposed at the surface, it can be eroded away and eventually changed into a new sedimentary rock. However, if a sedimentary(or an igneous) rock gets buried deep in the Earth, heat and pressure will cause profound physical and/or chemical change. This process is called metamorphosis, and the new rock is called a metamorphic rock. Metamorphic rock can also be weathered and eroded and eventually changed into a sedimentary rock. Or, if a metamorphic rock is forced deeper into the Earth, the rock can melt and become magma. Igneous rock and sedimentary rock can also be forced deep into the Earth and melt into magma. Once magma cools, it forms igneous rocks again.",image,teaching_images/cycle_rock_6748.png
L_0076,continental drift,DD_0054,"The diagram shows the changes of Pangaea, which is a supercontinent of continents on the earth. The left upper sub figure shows the configuration of Pangaea in 200 million years ago. The right upper sub figure shows the configuration of Pangaea in 180 million years ago. The left lower sub figure shows the configuration of Pangaea in 65 million years ago. The right lower sub figure shows the current configuration of Pangea.",image,teaching_images/continental_drift_8043.png
L_0076,continental drift,DD_0055,This diagram shows one of the pillars of Wegener's theory of the previous existence of Pangaea: the localization of fossils. Fossils are the remains or impression of prehistoric animals. Many fossils of the same organisms have been found on widely separated places. Wegener thought the existence of Pangaea allowed movement to said organisms that would be impossible nowadays. The diagram shows the area where some species had lived and the suspected routes allowed by the existence of the supercontinent.,image,teaching_images/continental_drift_8044.png
L_0076,continental drift,DD_0056,"The diagram shows how the earth looked according to the continental drift hypothesis. All the continents were fused together as one big land mass called pangaea. Panthalassa was the vast global ocean that surrounded the supercontinent Pangaea. Gondwana is the part of Pangaea that lay in the Southern Hemisphere. Gondwana included most of the landmasses in today's Southern Hemisphere- South America, Africa, India, Australia, and Antarctica. The part of Pangaea that lay in the Northern Hemisphere was called Laurasia. It included most of the present-day North America, Greenland, Europe, and Asia. Tethys Sea was an ocean that existed between the continents of Gondwana and Laurasia.",image,teaching_images/continental_drift_9081.png
L_0079,stress in earths crust,DD_0063,"Rocks are present all over earth and sometimes stress causes damage to them. Stress can occur to rocks when force is applied to them. There are four types of rock stresses. They are: confining stress, compression stress, tension stress and shear stress. Confining stress occurs when other rocks push down on a rock below them. Compression stress occurs when rocks are pressed together. Tension stress occurs when rocks are forced apart. Shear stress occurs when two or more rocks are forced in opposite directions.",image,teaching_images/faults_1737.png
L_0079,stress in earths crust,DD_0064,"The diagram shows different types of geological faults. Reverse fault is the geologic fault in which the hanging wall has moved upward relative to the footwall. Hanging wall is the block of rock that lies above an inclined fault while footwall is the block of rock that lies on the underside of an inclined fault. Reverse faults occur where two blocks of rock are forced together by compression. Normal fault is the geologic fault in which the hanging wall has moved downward relative to the footwall. Normal faults occur where two blocks of rock are pulled apart, as by tension. Strike-slip fault is the geologic fault in which the blocks of rock on either side of the fault slide horizontally in opposite directions along the line of the fault plane.",image,teaching_images/faults_186.png
L_0079,stress in earths crust,DD_0065,"The image below shows different types of faults. A fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement as a result of rock mass movement. Large faults within the Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes. In strike-slip faults the fault surface is usually near vertical and the footwall moves either left or right or laterally with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults. In a normal fault, the block above the fault moves down relative to the block below the fault. This fault motion is caused by tensional forces and results in extension.",image,teaching_images/faults_1747.png
L_0111,climate zones and biomes,DD_0073,"The diagram shows a biome pyramid. It consists of four regions: Arctic region, Subarctic region, Temperate region and Tropical region. The Arctic region consists of Tundra. The Subarctic region consists of Boreal forest. The Temperate region consists of Temperate forest, Grassland, Chapparal, and Desert. The Tropical region consists of Tropical forest, Grassland, and Desert. The temperature and the dryness of a place decide its region. As the temperature increases, there is a change in the different regions. The hottest and driest region is the Desert. The coldest and the driest region is the Tundra. The coldest and the least dry region is the Tropical forest.",image,teaching_images/biomes_6557.png
L_0111,climate zones and biomes,DD_0074,"This is a map showing ten different biomes and where they can be found in on a world map. A biome is a group of similar ecosystems with the same general abiotic factors and primary producers. The oceans on the map are all classified as marine biomes, while the rivers and lakes are freshwater biomes. The northernmost parts of North America, Europe, and Asia are ice, tundra, and taiga biomes. The central parts of North America, Europe, and Asia are classified as grassland and temperate forest. The southern parts of North America, Europe, and Asia, as well as the northern parts of Africa, are classified as savana, desert, and temperate forest. South America and the south eastern part of Africa are classified as tropical rainforest, desert, and savana. Australia is made up mostly of desert and grassland. Antarctica is entirely iced.",image,teaching_images/biomes_8018.png
L_0111,climate zones and biomes,DD_0075,"This is a map showing where different biomes are found around the world. A biome can be defined a group of similar ecosystems with sharing abiotic factors and primary producers. In this map we can see bands of color stretching East to West, showing how similar latitudes often share similar biomes. Near the equator we see deserts and rainforests. In the North we see tundra and taiga. Most of central Europe is temperate broadleaf forest. In USA we see mostly temperate forest in the East, temperate steppe in the middle, and in the West there is a lot of montane forest as well as arid desert.",image,teaching_images/biomes_6562.png
L_0148,eclipses,DD_0078,"This diagram shows a lunar eclipse. In a lunar eclipse, the earth lies in between the sun and the moon. The shadow of the Earth can be divided into two distinctive parts: the umbra and penumbra. There is no direct solar radiation within the umbra. However solar illumination is only partially blocked in the outer portion of the Earth's shadow, called the penumbra. This is because of the Sun's large angular size. In this diagram, the moon lies in the umbra of the earth. This leads to a total lunar eclipse.",image,teaching_images/earth_eclipses_1631.png
L_0148,eclipses,DD_0079,"This image shows the types of solar eclipses. When a new moon passes directly between the Earth and the Sun, it causes a solar eclipse. When the sun, moon and Earth are lined up, the Moon casts a shadow on the Earth and blocks our view of the Sun. When the Moons shadow completely blocks the Sun, it is a total solar eclipse. If only part of the Sun is out of view, it is a partial solar eclipse. An anular eclipse occurs when the edge of the sun remains visible as a bright ring around the moon.",image,teaching_images/earth_eclipses_4570.png
L_0148,eclipses,DD_0080,"The diagram shows the lunar eclipse. The lunar eclipse occurs when the moon passes behind the earth into its umbra region. During the total lunar eclipse, moon travels completely inside the earth's umbra. But in partial lunar eclipse, only a portion of the moon passes through earth's umbra region. When moon passes through earth's penumbra region, it is penumbral eclipsed. Since earth's shadow is large lunar eclipse lasts for hours and anyone with the view of moon can see the eclipse. Partial lunar eclipse occurs at least twice a year but total lunar eclipse is rear. The moon glows with dull red coloring during total lunar eclipse.",image,teaching_images/earth_eclipses_1671.png
L_0148,eclipses,DD_0081,"This diagram shows solar eclipse. Moon rotates around the earth on an orbit that is shown in the picture. During solar eclipse, the moon lies between sun and earth so there will be a shadow on earth. Certain regions of earth will be dark due to the shadow of the moon since sun rays do not reach those regions. Moon is smaller than earth so the shadow covers a small region of the earth. The areas marked by Penumbera experience a partial eclipse, while Umbra areas experience full eclipse.",image,teaching_images/earth_eclipses_1654.png
L_0184,greenhouse effect,DD_0082,"This diagram illustrates the basic processes behind the greenhouse effect. The greenhouse effect is a natural process that warms the Earth, and, in fact, is quite necessary for our survival. In the shown diagram, arrows display how the greenhouse effect works. Electromagnetic radiation from the Sun passes through the Earths atmosphere. The Earth absorbs these short wavelengths and warms up. Heat is then radiated from the Earth as longer wavelength infrared radiation. Some of this infrared radiation is absorbed by greenhouse gases in the atmosphere. Absorption of heat causes the atmosphere to warm and emit its own infrared radiation. The Earths surface and lower atmosphere warm until they reach a temperature where the infrared radiation emitted back into space, plus the directly reflected solar radiation, balance the absorbed energy coming in from the Sun. The equilibrium of incoming and outgoing radiation is what keeps the Earth warm and habitable.",image,teaching_images/greenhouse_effect_6945.png
L_0184,greenhouse effect,DD_0083,"When sunlight heats Earth's surface, some heat radiates back into the atmosphere. Some of this heat is absorbed by gases in the atmosphere. This is the greenhouse effect, and it helps to keep Earth warm. The greenhouse effect also allows Earth to have temperatures that can support life. Gases that absorb heat in the atmosphere are called greenhouse gases. They include carbon dioxide and water vapor mainly and a small amount of methane and ozone as well. Human actions have increased the levels of greenhouse gases in the atmosphere. The diagram here illustrates exactly what is written above. Apart from Earth, in the Solar System, there also greenhouse effects on Mars, Venus, and Titan. Thus, if it were not for greenhouse gases trapping heat in the atmosphere, the Earth would be a very cold place.",image,teaching_images/greenhouse_effect_6940.png
L_0283,radioactive decay as a measure of age,DD_0084,"The following diagram provides an example of Alpha Decay, where a Radium atom transforms or decays into a radon atom. Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into an atom with a mass number that is reduced by four and an atomic number that is reduced by two. Alpha decay only occurs in very heavy elements such as uranium, thorium and radium. The nuclei of these atoms are very neutron rich (i.e. have a lot more neutrons in their nucleus than they do protons) which makes emission of the alpha particle possible. After an atom ejects an alpha particle, a new parent atom is formed which has two fewer neutrons and two fewer protons. Thus, when Radium-226 decays by alpha emission, Radon-222 is created.",image,teaching_images/radioactive_decay_8173.png
L_0283,radioactive decay as a measure of age,DD_0085,"Gamma decay is the process by which the nucleus of an atom emits a high energy photon, that is, extremely short-wavelength electromagnetic radiation. It is one of three major types of radioactivity (the other two being alpha decay and beta decay). Gamma decay is similar to the emission of light (usually visible light) by decay in the orbits of the electrons surrounding the nucleus. In each case the energy states, and the wavelengths of the emitted radiation, are governed by the law of quantum mechanics. But while the electron orbits have relatively low energy, the nuclear states have much higher energy. Gamma decay is a process of emission of gamma rays that accompanies other forms of radioactive decay, such as alpha and beta decay. Nuclei are not normally in excited states, so gamma radiation is typically incidental to alpha or beta decay the alpha or beta decay leaves the nucleus in an excited state, and gamma decay happens soon afterwards. Gamma radiation is the most penetrating of the three kinds. Gamma ray photons can travel through several centimeters of aluminum.",image,teaching_images/radioactive_decay_7517.png
L_0283,radioactive decay as a measure of age,DD_0086,"The diagram below shows the beta decay of carbon 14. The carbon-14 nucleus has a neutron within it change into a proton Then we see both a beta minus particle (an electron with high kinetic energy) and an antineutrino ejected from the nucleus. Carbon 14 has two extra neutrons in its nucleus and that is a higher energy configuration and is a bit unstable, so it can release an electron and have a neutron turn into a proton-forming Nitrogen 14 instead, which is more stable.",image,teaching_images/radioactive_decay_8168.png
L_0287,revolutions of earth,DD_0087,The diagram shows different imaginary lines around the earth. At the very north is the north pole and at the very south is the south pole of the earth. An imaginary line around the earth near the north pole is the arctic circle. It is located at 66.5 north of equator. An imaginary line around the earth near the south pole is the Antarctic circle. It is located at 66.5 south of equator. Equator is an imaginary line that goes round the Earth and divides it into two halves. The northern half is called northern hemisphere and the southern half is called southern hemisphere. Tropic of cancer and tropic of Capricorn are the two imaginary lines around the Earth on either side of the equator. The Tropic of Cancer is 23 26 north of it and the Tropic of Capricorn is 23 26 south of it.,image,teaching_images/earth_poles_8061.png
L_0287,revolutions of earth,DD_0088,"This Diagram shows the Earth's rotation. Which is the amount of time that it takes to rotate once on its axis. This is, apparently, accomplished once a day every 24 hours. However, there are actually two different kinds of rotation that need to be considered here. For one, there's the amount of time it takes for the Earth to turn once on its axis so that it returns to the same orientation compared to the rest of the Universe. Then there's how long it takes for the Earth to turn so that the Sun returns to the same spot in the sky. Earth's rotation is slowing slightly with time; thus, a day was shorter in the past. This is due to the tidal effects the Moon has on Earth's rotation. Atomic clocks show that a modern-day is longer by about 1.7 milliseconds than a century ago, slowly increasing the rate at which UTC is adjusted by leap seconds.",image,teaching_images/earth_poles_163.png
L_0291,rotation of earth,DD_0089,"The diagram shows the rotation of the Earth on its axis and how the Sun illuminates its surface. It helps us understand how day and night work. One rotation takes 24 hours, exactly the length of a day. Dividing the Earth into two parts along the Greenwich meridian, the part facing the Sun is illuminated by the daylight, whereas the other part is in the dark. By rotating, the part of the Earth in the dark ends up receiving the daylight and vice versa. When we say the Sun rises in the east it means that the east is facing the Sun. In the same way the west, which is the part in the dark, is where the Sun sets and the Moon and the stars appear. The changing of day and night is the result of the Earth rotating.",image,teaching_images/earth_day_night_86.png
L_0291,rotation of earth,DD_0090,"This diagram shows the earth rotating around its axis and the sun's rays hitting the earth. The side of the earth facing the sun has daylight. The side of the earth facing away from the sun is dark and has night. The earth rotates around its axis, once every 24 hours. Hence every part of the earth experiences day and night every 24 hours. There are 5 major circles of latitude that mark the diagram of the earth. There are the Arctic Circles, Tropic of Cancer, Equator, Tropic of Capricorn and the Antarctic Circle. The arctic circle is the northern most circle and the Antarctic circle is the southern most circle. The equator is the latitude in the middle that divides the earth into the northern and southern hemispheres. The tropic of cancer lies between the Arctic circle and the equator. The tropic of capricorn lies between the Antarctic circle and the equator.",image,teaching_images/earth_day_night_2744.png
L_0301,seasons,DD_0091,"The diagram below shows the earth's seasons. During part of the year, Earth is closer to the sun than at other times. However, in the Northern Hemisphere, we are having winter when Earth is closest to the sun and summer when it is the farthest away! Compared with how far away the sun is, this change in Earth's distance throughout the year does not make much difference to our weather's Earth orbits the sun, its tilted axis always points in the same direction. So, throughout the year, different parts of Earth get the suns direct rays.",image,teaching_images/seasons_6279.png
L_0301,seasons,DD_0092,"The earth revolves around the sun. Its takes one year to make one full revolution. This diagram shows different configurations of the earth and the sun over the course of one year that lead to the four prominent seasons: spring, summer, fall and winter. Since the earth is inclined at an angle of 23.5 degrees, at certain times of the year, the northern hemisphere gets longer days and shorter nights, which causes the season of summer. At the same time the southern hemisphere gets shorter days and longer nights, which leads to winter. June 21 is the longest day of the year in the Northern hemisphere, and is known as the Summer Solstice in the Northern Hemisphere. December 22 is the shortest day of the year in the Northern Hemisphere and is known as the Winter Solstice in the Northern Hemisphere.",image,teaching_images/seasons_6281.png
L_0301,seasons,DD_0093,"The diagram below shows the earth's seasons. During part of the year, Earth is closer to the sun than at other times. However, in the Northern Hemisphere, we are having winter when Earth is closest to the sun and summer when it is the farthest away! Compared with how far away the sun is, this change in Earth's distance throughout the year does not make much difference to our weather. Earth's axis is an imaginary pole going right through the center of Earth from “top” to “bottom.” Earth spins around this pole, making one complete turn each day. That is why we have day and night, and why every part of Earth's surface gets some of each.",image,teaching_images/seasons_647.png
L_0301,seasons,DD_0094,"The diagram shows the earth's equinox phenomenon. An equinox is an astronomical event in which the plane of Earth's equator passes through the center of the Sun which occurs twice each year during spring and autumn as shown below. On an equinox, day and night are of “approximately” equal duration all over the planet. The equinoxes, along with solstices, are directly related to the seasons of the year. In the northern hemisphere, the vernal equinox (March) conventionally marks the beginning of spring and is considered the New Year in the Persian calendar or Iranian calendars as Nouroz (means new day). On the other hand, the autumnal equinox (September) marks the beginning of autumn. In the southern hemisphere, the vernal equinox occurs in September and the autumnal equinox in March.",image,teaching_images/seasons_672.png
L_0362,the microscope,DD_0097,"The image below shows the different parts of an Optical microscope. The Optical microscope is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were possibly invented in their present compound form in the 17th century. Basic optical microscopes can be very simple, although there are many complex designs which aim to improve resolution and sample contrast. All modern optical microscopes designed for viewing samples by transmitted light share the same basic components of the light path. In addition, the vast majority of microscopes have the same 'structural' components. The eyepiece, or ocular lens, is a cylinder containing two or more lenses; its function is to bring the image into focus for the eye. The eyepiece is inserted into the top end of the body tube. Eyepieces are interchangeable and many eyepieces can be inserted with different degrees of magnification.",image,teaching_images/parts_microscope_7187.png
L_0362,the microscope,DD_0098,"This diagram shows the parts of a compound light microscope. The eyepiece is used to view a microscopic item placed on the stage. It can be used to view cells, bacteria, and small objects like insect wings. When holding a microscope, always use the arm and the base. Handle it carefully, as these are expensive and fragile objects. Use the condenser focus and objective lenses to make the object being viewed clearer. The course focus and fine focus can be used to adjust how close the lenses are to the stage. These focus pieces also make the image clearer.",image,teaching_images/parts_microscope_7193.png
L_0362,the microscope,DD_0099,"The diagram shows the anatomy of a microscope. There are two optical systems in a compound microscope: The Ocular Lens and the Objective Lens. Eyepiece or Ocular is what you look through at the top of the microscope. Eyepiece Tube holds the eyepieces in place above the objective lens. Objective Lenses are the primary optical lenses on a microscope. They range from 4x-100x and typically, include, three, four or five on lens on most microscopes. Objectives can be forward or rear-facing. Nosepiece houses the objectives. The objectives are exposed and are mounted on a rotating turret so that different objectives can be conveniently selected. Coarse and Fine Focus knobs are used to focus the microscope. Stage is where the specimen to be viewed is placed. Stage Clips are used when there is no mechanical stage. Aperture is the hole in the stage through which the base (transmitted) light reaches the stage. Illuminator is the light source for a microscope, typically located in the base of the microscope. Condenser is used to collect and focus the light from the illuminator on to the specimen. Iris Diaphragm controls the amount of light reaching the specimen. It is located above the condenser and below the stage. Condenser Focus Knob moves the condenser up or down to control the lighting focus on the specimen.",image,teaching_images/parts_microscope_7174.png
L_0370,flatworms and roundworms,DD_0117,"This diagram shows the earthworm anatomy. The segmented body parts provide important structural functions. Segmentation can help the earthworm move. Each segment or section has muscles and bristles called setae. The bristles or setae help anchor and control the worm when moving through soil. The bristles hold a section of the worm firmly into the ground while the other part of the body protrudes forward. The earthworm uses segments to either contract or relax independently to cause the body to lengthen in one area or contract in other areas. Segmentation helps the worm to be flexible and strong in its movement. If each segment moved together without being independent, the earthworm would be stationary.",image,teaching_images/parts_worm_7295.png
L_0370,flatworms and roundworms,DD_0118,"Flatworms are invertebrates. They belong to Phylum Platyhelminthes. There are over 25,000 species of flatworms in the world. Not all flatworms are as long as tapeworms. Some are actually only around a millimeter in length. Flatworms reproduce sexually, in most species the individual able to provide both egg and sperm for reproduction. Flatworms go from egg, to larva to adulthood. Flatworm adaptations include mesoderm, muscle tissues, a head region, and bilateral symmetry. Flatworms are free-living heterotrophs or parasites. Roundworms are invertebrates in Phylum Nematoda. Roundworms have a pseudocoelom and complete digestive system. They are free-living heterotrophs or parasites.",image,teaching_images/parts_worm_7321.png
L_0370,flatworms and roundworms,DD_0119,"The diagram shows the earthworm's internal anatomy with its key parts and definitions. An earthworm is a tube-shaped, segmented worm found in the phylum Annelida. The body of the earthworm is segmented which looks like many little rings joined or fused together. Segmentation helps the worm to be flexible and strong in its movement. An earthworm's digestive system runs through the length of its body. The digestive system consists of the mouth, the crop, the gut and the gizzard. Earthworms are hermaphrodites where each earthworm contains both male and female sex organs. Some other key features of the earthworm include its brain, which consists of a large cluster of nerve cells connected to a ventral nerve cord which runs the length of the body, and its heart, which is a set of typically five muscular swellings that pump blood through their bodies.",image,teaching_images/parts_worm_7310.png
L_0375,fish,DD_0127,"This diagram depicts the anatomy of a fish. Several parts of the fish such as the cheek, gills, fins and guts are shown in the diagram. The gills are present towards the front of the fish and are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. There are several types of fins on a fish. The tail fin is located at the end of the fish and is used for propulsion. The pectoral fins are located at the sides of the fish. The pelvic fins are located below the pectoral fins. The dorsal fins are located at the back of the fish whereas the anal fin is located behind the anus, towards the back of the fish.",image,teaching_images/parts_fish_2842.png
L_0375,fish,DD_0128,"Here is a diagram of the external parts of a fish. The caudal fin is used for steering. The adipose, anal, and dorsal fins are used for swimming and balance. The pelvic fin helps fish move up and down. The pectoral fin works like a brake, and also helps fish to move left and right. The lateral line is used to detect movement and vibration in the surrounding water. The gill plate/operculum is a flexible bony plate that covers the gills. The preopercle is part of the operculum. The maxillary holds the upper teeth.",image,teaching_images/parts_fish_2913.png
L_0384,the integumentary system,DD_0129,"This picture shows the layers and structure of the skin. The skin is made up of two distinct layers called the epidermis and dermis. The upper layer of the skin is called the epidermis. It is thick and tough and forms a protective layer. The epidermis consists of cells that contain a lot of keratin. The cells of the epidermis also contains cells that produce melanin which is the pigment that gives the skin much of its color. Below the epidermis, is the dermis. It is made of tough connective tissue. The dermis contains the hair follicles and sebaceous glands. Hair follicles are structures where hairs originate. Each hair grows out of a follicle, passes up through the epidermis, and extends above the skin surface. Sebaceous glands are commonly called oil glands. They produce an oily substance called sebum. Sebum is secreted into hair follicles. Then it makes its way along the hair shaft to the surface of the skin. Sebum waterproofs the hair and skin and helps prevent them from drying out. The red string like object in the diagram is the arrector pili muscle. It is a small muscle connecting a hair follicle to the dermis that contracts to make the hair stand erect in response to cold or fear.",image,teaching_images/hair_follicles_6986.png
L_0384,the integumentary system,DD_0130,"This is the diagram of an active hair follicle. A hair follicle is a mammalian skin organ that produces hair. Hair production occurs in phases, including growth (anagen), cessation (catagen), and rest (telogen) phases. Stem cells are responsible for hair production. The shape of the hair follicle has an effect on the hair shape and texture of the individual's hair. The papilla is a large structure at the base of the hair follicle. The dermal papilla is made up mainly of connective tissue and a capillary loop. Cell division in the papilla is either rare or non-existent. Around the papilla is the germinal matrix. The root sheath is composed of an external and internal root sheath. Other structures associated with the hair follicle include the cup in which the follicle grows known as the sebaceous glands. Hair follicle receptors sense the position of the hair.",image,teaching_images/hair_follicles_6985.png
L_0384,the integumentary system,DD_0131,"The image below shows the Layers and structures of the skin. Skin has three layers: The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone. Below the dermis lies a layer of fat that helps insulate the body from heat and cold, provides protective padding, and serves as an energy storage area. The fat is contained in living cells, called fat cells, held together by fibrous tissue.",image,teaching_images/skin_cross_section_7574.png
L_0384,the integumentary system,DD_0132,"The diagram shows the layers and structures of the skin. Skin, glands, hair and nails belong to the Integumentary System. This system serves as a protective barrier that prevents internal body parts from exposure to harmful elements like ultraviolet light, extreme temperature and toxins. The skin covers the entire external surface of the human body and thus, it is the major organ of the Integumentary System. Skin has three main layers: epidermis, dermis and hypodermis. The outermost layer of the skin is the epidermis. There are no blood vessels, nerve endings, or glands in this skin layer. Nonetheless, this layer of skin is very active. It contains melanocytes that produce melanin, a brown pigment which gives the skin its color. Attached under the epidermis is the more complex structure called the dermis. This layer contains nerve endings, blood vessels and two types of glands, the sebaceous and sweat glands. The sweat produced by these glands travels out of the body through a pore on the surface of the skin. Sebaceous glands produce sebum which waterproofs the hair. Hair follicles, where hairs originate, are also found in the dermis. Each hair grows out of a follicle, passes up through the epidermis, and extends above the skin surface. Lastly, the hypodermis is the deepest layer of the skin which contains cells that serve as fat and energy storage for the body's use.",image,teaching_images/skin_cross_section_7589.png
L_0385,the skeletal system,DD_0133,"This diagram depicts the human skeleton. The axial skeleton includes the skull, vertebral column, and thoracic cage. The skull consists of 28 bones: 8 cranial vault bones, 14 facial bones, and 6 auditory ossicles. From a lateral view, the parietal, temporal, and sphenoid bones can be seen. From a frontal view, the orbits and nasal cavity can be seen, as well as associated bones and structures, such as the frontal bone, zygomatic bone, maxilla, and mandible. The interior of the cranial vault contains three fossae with several foramina. Seen from below, the base of the skull reveals numerous foramina and other structures, such as processes for muscle attachment. The vertebral column contains 7 cervical, 12 thoracic, and 5 lumbar vertebrae, plus 1 sacral and 1 coccygeal bone. Each vertebra consists of a body, an arch, and processes. Regional differences in vertebrae are as follows: cervical vertebrae have transverse foramina; thoracic vertebrae have long spinous processes and attachment sites for the ribs; lumbar vertebrae have rectangular transverse and spinous processes, and the position of their facets limit rotation; the sacrum is a single, fused bone; the coccyx is four or fewer fused vertebrae. The thoracic cage consists of thoracic vertebrae, ribs, and sternum. There are 12 pairs of ribs: 7 true and 5 false (two of the false ribs are also called floating ribs). The sternum consists of the manubrium, body, and xiphoid process. The appendicular skeleton consists of the bones of the upper and lower limbs and their girdles. The pectoral girdle includes the scapula and clavicle. The upper limb consists of the arm (humerus), forearm (ulna and radius), wrist (eight carpal bones), and hand (five metacarpals, three phalanges in each finger, and two phalanges in the thumb). The pelvic girdle is made up of the sacrum and two coxae. Each coxa consists of an ilium, ischium, and pubis. The lower limb includes the thigh (femur), leg (tibia and fibula), ankle (seven tarsals), and foot (metatarsals and phalanges, similar to the bones in the hand).",image,teaching_images/parts_skeleton_7256.png
L_0385,the skeletal system,DD_0134,"The image below shows the Human Skeleton. The human skeleton is the internal framework of the body. It is composed of around 300 bones at birth, this total decreases to 206 bones by adulthood after some bones have fused together. The human skeleton performs six major functions; support, movement, protection, production of blood cells, storage of minerals and endocrine regulation. Bones are the main organs of the skeletal system. Some people think bones are like chalk: dead, dry, and brittle. In reality, bones are very much alive. They consist of living tissues and are supplied with blood and nerves.",image,teaching_images/parts_skeleton_7266.png
L_0385,the skeletal system,DD_0135,"This diagram shows some major bones of the human skeletal system. There are 206 bones in a normal human body. The hands and feet contain many those bones--the hand bones are called carpals, metacarpals, and phalanges. The foot bones are called tarsals, metatarsals, and phalanges. The skeletal system has several functions for humans. It gives the body structure and shape. It gives protection to vital organs--for example the skull protects the brain and the ribcage protects the heart and lungs. It helps with movement--muscles attach to the bones and together they help us move. The final function is blood production. Red and white blood cells are made in the bone marrow of the long bones.",image,teaching_images/parts_skeleton_7270.png
L_0386,the muscular system,DD_0136,"The diagram shows the huma's body muscular system. Most muscles are attached to bones with tendons. Many muscles derive their name from their anatomical region. For example, the Rectus Abdominis is found in the abdominal region. Other muscles, like the Tibialis Anterior are named after the bone they are attached to, in this case the tibia. Other muscles are classified by form. The Deltoid have a delta or a triangular shape.",image,teaching_images/human_system_muscular_6165.png
L_0386,the muscular system,DD_0137,"This diagram shows the structure of human back. The human back is the large posterior area of the human body, rising from the top of the buttocks to the back of the neck and the shoulders. It is the surface opposite to the chest, its height being defined by the vertebral column (commonly referred to as the spine or backbone) and its breadth being supported by the ribcage and shoulders. The spinal canal runs through the spine and provides nerves to the rest of the body. Trapezius is either of a pair of large triangular muscles extending over the back of the neck and shoulders and moving the head and shoulder blade. The triceps brachii muscle is the large muscle on the back of the upper limb of many vertebrates. The latissimus dorsi of the back is the larger, flat, dorso-lateral muscle on the trunk, posterior to the arm. Gluteus is any of three muscles in each buttock which move the thigh, the largest of which is the gluteus maximus.",image,teaching_images/human_system_muscular_6166.png
L_0386,the muscular system,DD_0138,"The diagram shows the entire muscular system of the human body. Muscles are the main organs of the muscular system. Their main function is movement of the body. Muscles are the only tissue in our bodies that can contract and therefore move the other parts of the body. They are composed primarily of muscle fibers. Many muscles derive their name from their anatomical region. The rectus abdominis, for example, is found in the abdominal region. A function of the muscular system is to produce body heat. As a result of contraction, our muscular system produces waste heat.",image,teaching_images/human_system_muscular_6159.png
L_0386,the muscular system,DD_0139,"This diagram depicts the structure of muscle cells. Muscle cells are also known as muscle fibers. The diagram illustrates components such as striated myofibrils, which is exclusive to that kind of cell. Myofibrils consist of filaments. There are thin filaments and thick filaments. Each cell is covered by a plasma membrane sheath which is called the sarcolemma. Tunnel-like extensions from the sarcolemma pass through the muscle fibre from one side of it to the other in transverse sections through the diameter of the fibre. The cell contains sarcoplasm, which is the cytoplasm of muscle cells.",image,teaching_images/muscle_fiber_7082.png
L_0386,the muscular system,DD_0140,"This diagram represents the structure of a skeletal muscle. Each skeletal muscle fiber is a single cylindrical muscle cell. Each muscle is surrounded by a connective tissue sheath called the epimysium. Fascia, connective tissue outside the epimysium, surrounds and separates the muscles. Portions of the epimysium project inward to divide the muscle into compartments. Each compartment contains a bundle of muscle fibers. Each bundle of muscle fiber is called a fasciculus and is surrounded by a layer of connective tissue called the perimysium. Within the fasciculus, each individual muscle cell, called a muscle fiber, is surrounded by connective tissue called the endomysium. The connective tissue covering furnish support and protection for the delicate cells and allow them to withstand the forces of contraction. The coverings also provide pathways for the passage of blood vessels and nerves. Commonly, the epimysium, perimysium, and endomysium extend beyond the fleshy part of the muscle, the belly or gaster, to form a thick ropelike tendon or a broad, flat sheet-like aponeurosis. The tendon and aponeurosis form indirect attachments from muscles to the periosteum of bones or to the connective tissue of other muscles.",image,teaching_images/muscle_fiber_7083.png
L_0389,the digestive system,DD_0141,"Below is a diagram of the digestive system. The digestive system, as you can see, is made up of several organs and parts of the body. The digestive system breaks down food and absorbs nutrients into your body. The mouth is the first digestive organ that food enters, and the saliva starts the digestion of the food. The esophagus is the long narrow tube that carries food from the oral cavity to the stomach. The stomach stores the food until the small intestine is empty. The liver and gallbladder produce and store other secretions from the food. For instance, the liver produces bile secretions. The large intestine is where the food enters after it leaves the small intestine, and the large intestine is connected to the anus. The anus is where the body releases the food as waste (feces.)",image,teaching_images/human_system_digestive_3675.png
L_0389,the digestive system,DD_0142,"This diagram shows major organs and general functions of the digestive system. The digestive system is the body system that breaks down food and absorbs nutrients. It also eliminates solid food wastes that remain after food is digested. It has several organs such as the liver, stomach, pancreas, colon and intestines. Food enters the digestive system through the mouth and exits the system through the anus. In the stomach, chemicals called enzymes change the food into smaller molecules that the body can use. The pancreas is the part of the digestive system that produces important enzymes and hormones that help break down foods. It is located in the abdominal cavity behind the stomach. In the small intestine, our bodies absorb the nutrients from our food. Finally, colon mixes the solid waste material with water so we can easily eliminate it from our bodies through the anus.",image,teaching_images/human_system_digestive_6091.png
L_0389,the digestive system,DD_0143,"This diagram shows the digestive system in humans. Each part of the system plays an important role--although some organs such as the gallbladder can be removed without causing any long term effects on the person. The mouth is the beginning of the digestive process. This is where mechanical breakdown occurs--the teeth, tongue, and saliva break down the food so it can travel down the esophagus more easily. The purpose of the esophagus is to move the food down the digestive tract. The stomach mixes the food with enzymes and continues the breakdown. The intestines continue the breakdown and move the food to the rectum. The duodenum is the first part of the small intestine. It is also the shortest part. This is where most chemical digestion takes place. It then moves to the large intestine and then finally the rectum. The rectum is where the remaining food waste leaves the body.",image,teaching_images/human_system_digestive_3678.png
L_0389,the digestive system,DD_0144,"The diagram shows the human digestive system. It has several organs such as the liver, stomach, pancreas and intestines. Food enters the digestive system through the mouth and exits the system through the anus. The esophagus is a long tube that connects the mouth and the stomach. In the stomach, chemicals called enzymes change the food into smaller molecules that the body can use. The pancreas is the part of the digestive system that produces important enzymes and hormones that help break down foods. It is located in the abdominal cavity behind the stomach. In the small intestine, our bodies absorb the nutrients from our food. Finally, the large intestine mixes the solid waste material with water so we can easily eliminate it from our bodies through the anus. Overall, there are 9 main organs in the Digestive system.",image,teaching_images/human_system_digestive_3679.png
L_0390,overview of the cardiovascular system,DD_0145,"This diagram shows the cross-section of the human heart. The human heart is divided into the left and right halves. The heart has an upper chamber called the atrium and a lower chamber called the ventricle in each half. The red arrows show oxygenated blood coming from the lungs into the left atrium which then flows into the left ventricle and leaves the heart through the aorta. The blue arrows show deoxygenated blood coming to the heart from the through the anterior and posterior vena cava, flows through the right atrium, right ventricle and enters into the lungs.",image,teaching_images/human_system_circulatory_3648.png
L_0390,overview of the cardiovascular system,DD_0146,"The diagram shows the different components that make up the heart. The heart is the key organ in the circulatory system. As a hollow, muscular pump, its main function is to propel blood throughout the body. The septum is the wall of muscle divides it down the middle, into a left half and a right half. There are 4 chambers in the heart: top chamber is called atrium; bottom chambers are called ventricles. Blood can flow from the atrium to ventricle because of openings called valves. Valves open in one direction like trapdoors to let the blood pass through, then they close, so the blood cannot flow backwards into the atria. There are also valves at the bottom of the large arteries that carry blood away from the heart: the aorta and the pulmonary artery. These valves keep the blood from flowing backward into the heart once it has been pumped out. Blood vessels of the body carry blood in a circle: moving away from the heart in arteries, traveling to various parts of the body in capillaries, and going back to the heart in veins. All the blood from the body is eventually collected into the two largest veins: the superior vena cava, which receives blood from the upper body, and the inferior vena cava, which receives blood from the lower body region.",image,teaching_images/human_system_circulatory_6068.png
L_0390,overview of the cardiovascular system,DD_0147,"The diagram shows the circulatory system. It is the system that circulates blood and lymph through the body consisting of the heart, blood vessels, blood, lymph, and the lymphatic vessels and glands. Arterial circulation is the part of your circulatory system that involves arteries, like the aorta and pulmonary arteries. Arteries are blood vessels that carry blood away from your heart. (The exception is the coronary arteries, which supply your heart muscle with oxygen-rich blood.) Venous circulation is the part of your circulatory system that involves veins, like the vena cavae and pulmonary veins. Veins are blood vessels that carry blood to your heart. Veins have thinner walls than arteries.",image,teaching_images/human_system_circulatory_1379.png
L_0393,the respiratory system,DD_0148,"The diagram shows the structures of the respiratory system. They include the nose, trachea, lungs, and diaphragm. The diaphragm is a large, sheet-like muscle below the lungs. When you inhale, air enters the respiratory system through your nose and ends up in your lungs, where gas exchange with the blood takes place. In the nose, mucus and hairs trap any dust or other particles in the air. The air is also warmed and moistened so it wont harm delicate tissues of the lungs. Next, air passes through the pharynx, a passageway that is shared with the digestive system. From the pharynx, the air passes next through the larynx, or voice box. After the larynx, air moves into the trachea, or wind pipe. This is a long tube that leads down to the lungs in the chest. In the chest, the trachea divides as it enters the lungs to form the right and left bronchi (bronchus, singular). These passages are covered with mucus and tiny hairs called cilia. The mucus traps any remaining particles in the air. The cilia move and sweep the particles and mucus toward the throat so they can be expelled from the body. Air passes from the bronchi into smaller passages called bronchioles. The bronchioles end in clusters of tiny air sacs called alveoli (alveolus, singular). The alveoli in the lungs are where gas exchange between the air and blood takes place. Shown also is the rib (or ribs) the protect the lungs and other vital organs within the chest.",image,teaching_images/human_system_respiratory_6195.png
L_0393,the respiratory system,DD_0149,"The diagram shows the structures of the human respiratory system which is a series of organs responsible for taking in oxygen and expelling carbon dioxide. There are 3 major parts of the respiratory system: the airway, the lungs, and the muscles of respiration. The airway includes the nose, mouth, pharynx, larynx, trachea, bronchi, and bronchioles. In this diagram, we focus on the functions of the nose, mouth, trachea, lungs, and diaphragm. The nose is the primary opening for the respiratory system, made of bone, muscle, and cartilage. The nasal cavity is a cavity within your nose filled with mucus membranes and hairs. Also called the oral cavity, the mouth is the secondary exterior opening for the respiratory system. Most commonly, the majority of respiration is achieved via the nose and nasal cavity, but the mouth can be used if needed. Also known as the wind pipe, the trachea is a tube made of cartilage rings that are lined with pseudo-stratified ciliated columnar epithelium. The lungs work together with the other parts of the respiratory system to allow oxygen in the air to be taken into the body while also enabling the body to get rid of carbon dioxide in the air breathed out. The diaphragm is an important muscle of respiration which is situated beneath the lungs. It contracts to expand the space inside the thoracic cavity, whilst moving a few inches inferiorly into the abdominal cavity.",image,teaching_images/human_system_respiratory_3749.png
L_0393,the respiratory system,DD_0150,"This image shows the parts of the human respiratory system. Respiration involves taking in air filled with oxygen into the human body or lungs and releasing carbon dioxide from the body. Respiration involves breathing through the nose/nasal cavity. The air then travels down into the lungs through the pharynx, followed by the larynx and finally through the trachea. The lungs are located in the chest cavity or thoracic cavity along with the heart. The chest cavity are covered by ribs on the outside. The pleura lines the thoracic cavity and envelopes the lungs. The trachea is subdivided into two bronchi before it enters the lungs. The bronchi are further divided into tiny bronchioles inside the lungs. The bronchioles have a tree like structure. The lungs are separated from the abdominal cavity by the diaphragm. The diaphragm contracts while breathing in and relaxes when breathing outs. The process of respiration is controlled by the respiratory centers located in the brain.",image,teaching_images/human_system_respiratory_1327.png
L_0393,the respiratory system,DD_0151,"The diagram shows the parts of the respiratory system. The human respiratory system is a series of organs responsible for taking in oxygen and expelling carbon dioxide. As we breathe, oxygen enters the nose or mouth and passes the sinuses, which are hollow spaces in the skull. Sinuses help regulate the temperature and humidity of the air we breathe. The trachea, also called the windpipe, filters the air that is inhaled, according to the American Lung Association. It branches into the bronchi, which are two tubes that carry air into each lung. The bronchial tubes are lined with tiny hairs called cilia. Cilia move back and forth, carrying mucus up and out. Mucus, a sticky fluid, collects dust, germs and other matter that has invaded the lungs. We expel mucus when we sneeze, cough, spit or swallow.",image,teaching_images/human_system_respiratory_3601.png
L_0398,the nervous system,DD_0152,This diagram depicts the parts of a neuron. A neuron is a basic building block of the nervous system that is responsible for receiving and transmitting information. Dendrites are treelike extensions at the beginning of a neuron that help increase the surface area of the cell body. The cell body is where the signals from the dendrites are joined and passed on. The nucleus is present within the cell body. It produces RNA that supports important cell functions. The axon is the elongated fiber that connects the cell body to the axon endings and transmits the neural signal. The axon is often covered with a fatty substance called the myelin sheath that acts as an insulator.,image,teaching_images/parts_neuron_7232.png
L_0398,the nervous system,DD_0153,"The diagram below shows the human nervous system. The nervous system conducts stimuli from sensory receptors to the brain and spinal cord and that conducts impulses back to other parts of the body. As with other higher vertebrates, the human nervous system has two main parts: the central nervous system (the brain and spinal cord) and the peripheral nervous system (the nerves that carry impulses to and from the central nervous system). The nervous system consists of the brain, spinal cord, sensory organs, and all the nerves that connect these organs with the rest of the body. Together, these organs are responsible for the control of the body and communication among its parts. The brain and spinal cord from the control center known as the central nervous system.",image,teaching_images/human_system_nervous_6184.png
L_0398,the nervous system,DD_0154,"This diagram shows the structure of a cell. It has the cell body, dived into the dendrite, nucleus, and also the axon. Other parts of the cell are the myelin sheath, node of Ranvier and lastly the synaptic know",image,teaching_images/parts_neuron_7206.png
L_0398,the nervous system,DD_0155,"This is a diagram of the anatomy of a brain. The brain is made up of several parts, as you can see in the picture. The brain has four lobes. The frontal lobe is used for the basic purpose of reasoning. The parietal lobe is used for the sense, touch. The temporal lobe is used for hearing. The occipital lobe is used for sight. The cerebellum is the next largest part of the brain. It controls body position, coordination, and balance.",image,teaching_images/human_system_nervous_6178.png
L_0398,the nervous system,DD_0156,"The diagram shows the anatomy of a multipolar neutron. A multipolar neuron (or multipolar neurone) is a type of neuron that possesses a single (usually long) axon and many dendrites, allowing for the integration of a great deal of information from other neurons. These dendritic branches can also emerge from the nerve cell body. Multipolar neurons constitute the majority of neurons in the brain and include motor neurons and interneurons. It is found majority in the cerebral cortex. The nerve endings of an axon don't actually touch the dendrites of other neurons. The messages must cross a tiny gap between the two neurons, called the synapse. There are two types of synaptic cells: presynaptic and postsynaptic. The presynaptic cell is the neuron sending the signal. The postsynaptic cell is the structure receiving the signal.",image,teaching_images/parts_neuron_7230.png
L_0398,the nervous system,DD_0157,"The diagram shows the various parts of the human brain. The three main parts of the brain are the cerebrum, cerebellum and medula. The cerebrum is divided down the middle from the front to the back of the head. The two halves of the cerebrum are called the right and left hemispheres. Each hemisphere is further subdivided into lobes which are shown in this diagram. The lobes shown are frontal lobe, parietal lobe, temporal lobe and occipital lobe. The cerebrum is the largest part of the brain, the next largest part is the cerebellum. The spinal cord is a long, tube-shaped bundle of neurons. Cererbum controls conscious functions, such as thinking, sensing, speaking, and voluntary muscle movements. Cerebellum controls body position, coordination, and balance. The main function of the spinal cord is to carry nerve impulses back and forth between the body and brain.",image,teaching_images/human_system_nervous_2864.png
L_0399,the senses,DD_0158,"Below is a diagram of the ear. The ear is made up of several parts, as shown in the diagram. Sound waves travel through the ear. Sound waves enter the auditory canal. Then they travel to the ear drum where it sends the vibrations from the sound waves to the inner ear. The sound waves then liquify and go into the cochlea. They then travel through the ear nerves, and is sent to the brain.",image,teaching_images/human_system_ear_2866.png
L_0399,the senses,DD_0159,"This diagram shows the anatomy of the human ear. The human ear is divided into the outer ear which contains the auricle and the earlobe. The outer ear is followed by the middle ear that contains eardrum and tympanic cavity and the ossicles. Lastly, the inner ear followed the middle ear and it contains the semicircular canals, vestibule, cochlea portions. The auditory canonical connects the outer ear to the middle ear. The eardrum and the tympanic cavity are at the end of the auditory canal. The vestibular nerve, semicircular ducts and cochlea are after the tympanic cavity. Ossicles are tiny bones in the middle ear that transmit sound from the eardrum to the cochlea. Sound waves travel through the outer ear, are modulated by the middle ear, and are transmitted to the inner ear.",image,teaching_images/human_system_ear_6103.png
L_0405,male reproductive system,DD_0164,"This image shows the posterior view of female reproductive system. The female reproductive system (or female genital system) is made up of the internal and external sex organs that function in human reproduction. The female reproductive system is immature at birth and develops to maturity at puberty to be able to produce gametes, and to carry a fetus to full term. The internal sex organs are the uterus and Fallopian tubes, and the ovaries. The uterus or womb accommodates the embryo which develops into the fetus. The uterus also produces vaginal and uterine secretions which help the transit of sperm to the Fallopian tubes. The ovaries produce the ova (egg cells). The external sex organs are also known as the genitals and these are the organs of the vulva including the labia, clitoris and vaginal opening. The vagina is connected to the uterus at the cervix.",image,teaching_images/human_system_reproductory_7014.png
L_0405,male reproductive system,DD_0165,"The diagram shows the parts and organs of the male reproductive system. The male reproductive organs include the penis, testes, epididymis, Ductus (vas) deferens, and prostate gland. The penis is an external, cylinder-shaped organ that contains the urethra. The urethra is the tube that carries urine out of the body. It also carries sperm out of the body. The testis (testis, singular) are oval organs that produce sperm and secrete testosterone. They are located inside a sac called the scrotum that hangs down outside the body. The scrotum also contains the epididymis. The epididymis is a tube that is about 6 meters (20 feet) long in adults. It is tightly coiled, so it fits inside the scrotum on top of the testes. The epididymis is where sperm mature. It stores the sperm until they leave the body. The vas deferens is a tube that carries sperm from the epididymis to the urethra. The prostate gland secretes a fluid that mixes with sperm to help form semen. Semen is a whitish liquid that contains sperm. It passes through the urethra and out of the body. Also shown are some parts of the digestive system like the rectum and anus.",image,teaching_images/human_system_reproductory_7036.png
L_0405,male reproductive system,DD_0166,"The diagram below shows the female reproductive system. The female reproductive system is made up of the internal and external sex organs that function in human reproduction. The internal sex organs are the uterus and Fallopian tubes, and the ovaries. The uterus or womb accommodates the embryo which develops into the fetus. The uterus also produces vaginal and uterine secretions which help the transit of sperm to the Fallopian tubes. The ovaries produce the ova (egg cells). The external sex organs are also known as the genitals and these are the organs of the vulva including the labia, clitoris and vaginal opening. The vagina is connected to the uterus at the cervix. The uterus or womb is the major female reproductive organ.",image,teaching_images/human_system_reproductory_7039.png
L_0407,reproduction and life stages,DD_0167,"This diagram shows a blastocyst, which is a small, fluid-filled ball of cells that travels through the fallopian tube until it implants on the wall of the uterus and continues to develop as an embryo. The blastocyst is composed of an outer, circular layer and an internal mass. The outside is known as the trophoblast and looks like a single layer of cells. It will eventually develop into structures that support the developing fetus. The internal mass is called the inner cell mass, also known as the embryoblast. It will eventually develop into a fetus.",image,teaching_images/blastocyst_9028.png
L_0407,reproduction and life stages,DD_0168,"This diagram shows the six stages of development of a human embryo, in two rows that are arranged left to right. The first stage, at the top left, is a fertilized egg, which is a single cell. After fertilization, the egg undergoes mitosis, which replicates the cells so that the embryo can grow. The 2-, 4-, 8-, and 16-cell stages each show a progressively larger number of cells, seemingly arranged at random. The final stage is the blastocyst, where the cells appear to form a ball. After this, the embryo will implant on the wall of the uterus and be known as a fetus.",image,teaching_images/blastocyst_9024.png
L_0407,reproduction and life stages,DD_0169,"This diagram shows the blastocyst stage in the process of fertilization. The blastocyst has an inner and outer layer of cells. The inner layer is called the embryoblast, will develop into the new human being. The outer layer is called the trophoblast, will develop into other structures needed to support the new organism. This layer surrounds the inner cell mass or the embryoblast and a fluid-filled cavity known as the blastocoele. When the outer cells of the blastocyst embeds itself in the uterine lining or the endometrium. This process is called implantation. It generally occurs about a week after fertilization.",image,teaching_images/blastocyst_9033.png
L_0415,cycles of matter,DD_0175,"This diagram depicts the water cycle, which is an important part of the ecosystem. The water in the water cycle exists in three different phases, liquid, solid (ice) and gas (water vapor). Water from lakes and oceans evaporates and is carried by rising air currents in the atmosphere. In the atmosphere the water vapor condenses and forms tiny droplets of water that form clouds. When the droplets get big enough the water comes back to earth in the form of precipitation. Precipitation can be in the form of rain, snow, sleet, or hail. Eventually the water evaporates again and the cycle starts over. Water can also enter the atmosphere through trees and plants from a process called transpiration.",image,teaching_images/cycle_water_1490.png
L_0415,cycles of matter,DD_0176,"This diagram shows the processes of the water cycle. It takes place on, above, and below Earths surface. During the water cycle, water occurs in three different states: gas (water vapor), liquid (water), and solid (ice). Many processes are involved as water changes state to move through the cycle. One of the processes is called Evaporation. It takes place when water on Earths surface changes to water vapor. The sun heats the water and turns it into water vapor which escapes up into the atmosphere. Most evaporation occurs from the surface of the ocean. Sublimation is another process takes place when snow and ice on Earths surface change directly to water vapor without first melting to form liquid water. This also happens because of heat from the sun. Transpiration is yet another process that takes place when plants release water vapor through pores in their leaves called stomata. As the water vapor rises up into the earth's atmosphere, it cools and condenses. Condensation is the process of converting water vapor into water droplets. If the droplets get big enough, they fall as precipitation. Precipitation is any form of water that falls from the atmosphere. Precipitation that falls on land may flow over the surface of the ground. This water is called runoff. The runoff may reach a water body such as an ocean or get soaked into the ground.",image,teaching_images/cycle_water_1503.png
L_0415,cycles of matter,DD_0177,"This diagram shows the water cycle. Water from lakes, streams, rivers, and other bodies of water evaporates and turns into clouds. This leads to condensation which leads to precipitation in the form of rain and snow. Some precipitation adds to the bodies of water and some goes into the ground. The water that goes into the ground is called ground water--some of it eventually makes its way to bodies of water. Water also can come down from mountains and end up in bodies of water--this is called runoff.",image,teaching_images/cycle_water_4953.png
L_0424,photosynthesis,DD_0183,This diagram depicts photosynthesis. Photosynthesis is the process in which plants synthesize glucose. The process uses carbon dioxide and water and also produces oxygen. The plant gets energy from sunlight using a green pigment called chlorophyll. Photosynthesis changes light energy to chemical energy. The chemical energy is stored in the bonds of glucose molecules. Glucose is used for energy by the cells of almost all living things. Plants make their own glucose.,image,teaching_images/photosynthesis_1262.png
L_0424,photosynthesis,DD_0184,"This diagram shows the process of photosynthesis, the process of how plants convert sunlight into energy. The plant uses sunlight and water to make glucose and creates oxygen as a waste product. Chemical energy is stored in the bonds of glucose molecules.",image,teaching_images/photosynthesis_4103.png
L_0424,photosynthesis,DD_0185,"This diagram represents photosynthesis. Photosynthesis the process in which plants synthesizes glucose. During photosynthesis, it gets its energy from the sun (light energy.) Photosynthesis changes light energy (the energy the plant receives from the sun) to chemical energy. This process uses carbon dioxide and water. In return, it produces oxygen and carbohydrates. It does this by the energy it receives from the sun. The equation for photosynthesis is 6CO2 + 6H2 O + Light Energy C6 H12 O6 + 6O2.",image,teaching_images/photosynthesis_4126.png
L_0435,history of life on earth,DD_0192,"The diagram is a representation of the major division of earths history. The geological timescale is a representation of time elapsed after the formation of earth, divided into slices, each differentiated by a geological event whose record is held in rock samples. Geological time is primarily divided into eons, which are divided into eras, which are further divided into periods. The periods are further divided into epochs, and epochs into ages, while eons are grouped into super-eons. The lengths of these eras are often measured by the term “mya,” which represents “millions of years ago. The first three eons are grouped under the Precambrian super-eon. The fourth eon, called the Phanerozoic, is ongoing. Although the first three eons together account for most of Earthas history, stretching out for nearly four billion years, there was little of note in terms of biological activity or geological diversity. So, in representations such as the table above, they are usually collectively called the Precambrian. It contains the Hadeon eon, when Earth was forming and the Late Heavy Bombardment took place; the Archeon eon, when water first showed up and the first lifeforms evolved; the Proterozoic eon, when the first multicellular organisms appeared and Earthas atmosphere received oxygen for the first time as a result of the proliferation of cyanobacteria.",image,teaching_images/geologic_time_6924.png
L_0435,history of life on earth,DD_0193,"The diagram shows an example of geologic time scale, which is a tool that scientists and historians used to describe and understand the different time frames of the Earths existence. This geologic time scale shows a timeline of events beginning from the late Proterozoic Era, approximately 650 million years ago. It is divided into eras and periods, and lists the major events that occurred in Earths history each period. From the geologic time scale, we can tell when different creatures evolved and first appeared on Earth. We know that the first amphibians appeared during the Devonian Period in the Paleozoic Era, approximately 400 million years ago. The first dinosaurs appeared during the Triassic Period of the Mesozoic Era, about 250 million years ago. Humans like us only appeared on Earth approximately 2.6 million years ago, during the Quaternary Period of the Cenozoic Era. The human race is very young, considering the Earth is approximately 4.6 billion years old!",image,teaching_images/geologic_time_6918.png
L_0513,excretion,DD_0201,"This is the diagram representing the human excretory system. The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, to help maintain internal chemical homeostasis and prevent damage to the body. It has following parts: The aorta begins at the top of the left ventricle, the heart's muscular pumping chamber. The inferior vena cava is a large vein that carries deoxygenated blood from the lower and middle body into the right atrium of the heart. The kidneys are bean-shaped organs which are present on each side of the vertebral column in the abdominal cavity. The kidney's primary function is the elimination of waste from the bloodstream by production of urine. The ureters are muscular ducts that propel urine from the kidneys to the urinary bladder. The urinary bladder is the organ that collects waste excreted by the kidneys prior to disposal by urination. Urethra is a tube which connects the urinary bladder to the outside of the body.",image,teaching_images/human_system_excretory_6107.png
L_0513,excretion,DD_0202,"This is a diagram of the major organs of the excretory system. The kidneys, ureter, bladder, and urethra all play important roles in this system. The kidneys filter blood and produce urine. The kidneys are shaped like beans and are located on each side of the body. After the kidneys, urine enters into the ureter. Then the urine moves into the bladder. When the bladder is about half full, it then releases into the urethra. This is how urine is filtered out of the body.",image,teaching_images/human_system_excretory_6117.png
L_0513,excretion,DD_0203,"The diagram shows the human urinary system. It includes two kidneys, two ureters and a urinary bladder. Blood is filtered by the kidneys to remove waste. Excess water and waste leaves the kidneys in the form of urine through the ureters to the bladder. Contractions of muscles in the ureters move the urine down into the bladder. Urine is excreted from the bladder through the urethra by the process of urination.",image,teaching_images/human_system_excretory_6115.png
L_0719,nuclear energy,DD_0204,"This Diagram shows how a Nuclear plant Work. Heat is used to boil water into steam and drive a turbine which turns a generator, making electricity. There are two separate water systems involved. One pumps fluid around the core of the reactor, absorbing the heat and keeping the pile from going into a meltdown. This liquid is kept separate because it's highly radioactive. It's pumped through carefully sealed pipes that go through a second water tank. The heat from the irradiated water heats these pipes, and then the pipes heat the second water tank, turning that water into steam. The steam is used to spin turbines, which are kind of like an RC car's motor except kind of opposite like, this generate electricity. The turbine water is clean and relatively safe, because it's not in direct contact with the irradiated systems.",image,teaching_images/nuclear_energy_7093.png
L_0719,nuclear energy,DD_0205,"Nuclear energy is the energy released in nuclear reactions. Two types of reactions that release huge amounts of energy are nuclear fission and nuclear fusion. The diagram demonstrates Nuclear Fusion. Nuclear fusion is a nuclear reaction in which two or more atomic nuclei come close enough to form one or more different atomic nuclei and subatomic particles (neutrons and/or protons). In the diagram, there are two hydrogen isotopes, Deuterium and Tritium. These combine to form a single, larger nucleus. They form a helium nucleus and a neutron. A great deal of energy is also released.",image,teaching_images/nuclear_energy_8115.png
L_0719,nuclear energy,DD_0206,"The diagram illustrates the process of Nuclear fission. Nuclear fission is the splitting of the nucleus of an atom into two smaller nuclei. This type of reaction releases a great deal of energy like heat and radiation from a very small amount of matter. Illustrated in the diagram is a neutron colliding with a uranium nucleus causing it to split into two smaller daughter nuclei. This process releases a large amount of energy and also releases three more fast neutrons. This type of reaction is used to create a chain reaction. If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb. If a nuclear chain reaction is controlled, it produces energy more slowly. This is what occurs in a nuclear power plant. The radiation from the controlled fission is used to heat water and turn it to steam. The steam is under pressure and causes a turbine to spin. The spinning turbine runs a generator, which produces electricity.",image,teaching_images/nuclear_energy_8118.png
L_0719,nuclear energy,DD_0207,This is how we get electricity from nuclear power. The water near the cooling towers is through the reservoir and then back up to a filter. The water then goes through the reactor core and turns into steam. The steam from the reactor then travels into the condenser and turbines were it then goes through the generator and produces electricity.,image,teaching_images/nuclear_energy_7101.png
L_0722,acceleration,DD_0208,"As time increases, distance increases as well. Over time, there is a steady speed and then a straight line indicates a stationary moment in time. It then returns to the start.",image,teaching_images/velocity_time_graphs_8216.png
L_0722,acceleration,DD_0209,"Figure 1 presents different velocity-time graphs. A velocity-time graph shows how an object's velocity or speed changes over time. The y axis represents velocity (v), while the x axis represents time (t). In the graph for constant velocity, the line remains horizontal, showing that the velocity of the object does not change over time. In the graph for constant acceleration, the line slopes upwards, showing that the velocity of the object increases over time. This increase in velocity is called acceleration. In the graph for constant retardation, the line slopes downwards, which means that velocity decreases over time. This decrease is called retardation. Retardation can also be called negative acceleration or deceleration. A moving object can both accelerate and decelerate. In the graph for irregular motion, the line moves up and down. This means that the velocity of object increases and decreases several times.",image,teaching_images/velocity_time_graphs_8213.png
L_0722,acceleration,DD_0210,"This Diagram shows a Velocity-time that is used for determine the acceleration of an object. The vertical axis of a velocity-time graph is the velocity of the object and the horizontal axis is the time taken from the start. When an object is moving with a constant velocity, the line on the graph is horizontal. When an object is moving with a steadily increasing velocity, or a steadily decreasing velocity, the line on the graph is straight, but sloped. The diagram shows some typical lines on a velocity-time graph. The steeper the line, the more rapidly the velocity of the object is changing. The blue line is steeper than the red line because it represents an object that is increasing in velocity much more quickly than the one represented by the red line.",image,teaching_images/velocity_time_graphs_8220.png
L_0734,simple machines,DD_0211,"Shown in the diagram are the six types of simple machines. A simple machine is a mechanical device that makes work easier. It includes the inclined plane, wedge, lever, wheel and axle, screw and pulley. An inclined plane is a flat surface that is slanted, or inclined, so it can help move objects across distances. A common inclined plane is a ramp used to lift heavy objects in a back of a truck. Instead of using the smooth side of the inclined plane to make work easier, you can also use the pointed edges to do other kinds of work. When you use the edge to push things apart, this movable inclined plane is called a wedge. An ax blade is one example of a wedge. Any tool that pries something loose is a lever. Levers can also lift objects. A lever is an arm that turns against a fulcrum (the point or support on which a lever pivots). Think of the claw end of a hammer that you used to pry nails loose; it's a lever. The Wheel and Axle makes work easier by moving objects across distances. The wheel (or round end) turns with the axle (or cylindrical post) causing movement. On a wagon, for example, a container rests on top of the axle to help transport heavy objects. A Screw helps you do work is that it can be easily turned to move itself through a solid space like turning a jar cover to keep it the jar air tight. Instead of an axle, a wheel could also rotate a rope, cord, or belt. This variation of the wheel and axle is the pulley. In a pulley, a cord wraps around a wheel. Instead of an axle, you can use the wheels rotation to raise and lower objects, making work easier. On a flagpole, for example, a rope is attached to a pulley to raise and lower the flag more easily.",image,teaching_images/simple_machines_9246.png
L_0740,transfer of thermal energy,DD_0212,"This diagram shows convection currents. Convection is the transfer of heat from one place to another by the movement of fluids. The heat source lies at the bottom of the diagram. The heat generated by this source causes the air next to it, to warm up. Warm air is lighter than cool air, and hence it rises up. As it rises up, it moves away from the heat source and cools down. As it cools down, it gets heavier and sinks towards the heat source. This cycle continues and causes a convection current.",image,teaching_images/convection_of_air_8050.png
L_0740,transfer of thermal energy,DD_0213,"This diagram shows the phenomena of the transfer of thermal energy. It happens by the convection of hot and cold air. The sun heats up the air, making it warm and less dense. Less dense air tends to go up, cooling down as doing it. Cool air becomes more dense and tends to sink, and wind does the job of making the air travel through different places, warming or cooling as he goes.",image,teaching_images/convection_of_air_6657.png
L_0743,measuring waves,DD_0214,"The figure shows a transverse wave. In a transverse wave, wave amplitude is the height of each crest above the resting position. The higher the crests are, the greater the amplitude. Another important measure of wave size is wavelength. Wave amplitude is the maximum distance the particles of a medium move from their resting position when a wave passes through. The resting position (dotted line in the middle of the wave) is where the particles would be in the absence of a wave. Wavelength can be measured as the distance between two adjacent crests of a transverse wave. It is usually measured in meters. Wavelength is related to the energy of a wave. Short-wavelength waves have more energy than long-wavelength waves of the same amplitude.",image,teaching_images/waves_9296.png
L_0743,measuring waves,DD_0215,"This diagram represents a sound wave and its characteristics. The peak of a wave is called compression or crest. The valley of a wave is called rarefaction or trough. Wave length is the length between two consecutive peaks, i.e. crest or two consecutive valleys, i.e. trough of a wave. Louder sound has shorter wavelength and softer sound has longer wavelength. Magnitude of maximum disturbance on either side of the normal position or mean value in a medium is called amplitude. In other words, amplitude is the distance from normal to the crest or trough. Time required to produce one complete wave is called time period or time taken to complete on oscillation is called the time period of the sound wave. The number of sound waves produced in unit time is called the frequency of sound waves. Frequency is the reciprocal of the time period of wave. Distance covered by sound wave in unit time is called the velocity of sound wave.",image,teaching_images/waves_7678.png
L_0753,the electromagnetic spectrum,DD_0216,"This diagram shows light waves of varying lengths, and some of their characteristics. The red line illustrates the wavelengths. Above that is a bar showing which light waves penetrate the Earth's atmosphere. Below the red line are the names of the different types of light, with their wavelength measured in (m). The illustrations of physical objects are to show scale. Below that is a diagram of the different light frequencies, measured in Hertz. Below that is a measure of the temperatures at which these light waves are most commonly emitted.",image,teaching_images/em_spectrum_6818.png
L_0753,the electromagnetic spectrum,DD_0217,"The diagram shows different kinds of waves. Visible light is the part of the electromagnetic spectrum that humans can see. Visible light includes all the colors of the rainbow. Each color is determined by its wavelength. Visible light ranges from violet wavelengths of 400 nanometers (nm) through red at 700 nm. There are parts of the electromagnetic spectrum that humans cannot see. This radiation exists all around you. You just can't see it! Every star, including our Sun, emits radiation of many wavelengths. Astronomers can learn a lot from studying the details of the spectrum of radiation from a star. Many extremely interesting objects can't be seen with the unaided eye.",image,teaching_images/em_spectrum_9095.png
L_0755,optics,DD_0218,"This diagram explains the concept of refraction. Light travels at a constant speed in vaccuum but travels at different speends in different media. When light travels from one medium to another, the speed of light changes causing it to appear to bend. This bending of light is called refraction. Refraction occurs when the angle of incidence (i) is not 90 degrees. In this diagram (r) is the angle of refraction. The angle of refraction is dependent on the angle o incidence as well as the speed of light in the medium through which it is travelling. XY is the boundary between the media through which light is travelling. At the point of incidence where the ray strikes the boundary XY, a line can be drawn perpendicular to XY. This line is known as a normal line (labeled NN' in the diagram).",image,teaching_images/optics_refraction_9190.png
L_0755,optics,DD_0219,"This diagram shows the setup of an amateur reflecting telescope. The telescope tube sits on a movable mount that allows it to point at and track objects in the sky. The mount shown is equitorial, meaning that it can be aligned to the north star for easier tracking of other stars and planets as they move ac cross the sky. The mount has a counterweight to help balance the weight of the telescope tube. The entire assembly sits on the three legs of a tripod. When pointed at the sky, light enters the optical tube through its aperture. The aperture is the circular end of the tube that allows light to enter when uncovered. Once light has entered the telescope, it is gathered and directed to the eyepiece by mirrors. The lenses in the eyepiece take this light and bring an image to focus for a human to see. The finderscope is a second smaller telescope attached the optical tube. It has lower magnification than the telescope, and this makes finding objects and pointing the telescope easier.",image,teaching_images/parts_telescope_8149.png
L_0755,optics,DD_0220,"This diagram explains the law of reflection and shows how light gets reflected from a surface. The law of reflection states that the angle of incidence (i) is always equal to the angle of reflection (r). The angles of both reflected and incident ray are measured relative to the imaginary dotted-line, called normal, that is perpendicular (at right angles) to the mirror (reflective surface). On the other hand, Refraction is caused by the change in speed experienced by a wave when it changes medium. The refracted ray is a ray (drawn perpendicular to the wave fronts) that shows the direction that light travels after it has crossed over the boundary. The angle that the incident ray makes with the normal line is referred to as the angle of incidence. Similarly, the angle that the refracted ray makes with the normal line is referred to as the angle of refraction. Thus, this is what the following diagram is all about.",image,teaching_images/optics_refraction_9200.png
L_0755,optics,DD_0221,"The diagram below is about two different types of lens. A lens is a transparent piece of glass or plastic with at least one curved surface. A lens works by refraction: it bends light rays as they pass through it so they change direction. In a convex lens (sometimes called a positive lens), the glass (or plastic) surfaces bulge outwards in the center giving the classic lentil-like shape. A convex lens is also called a converging lens because it makes parallel light rays passing through it bend inward and meet (converge) at a spot just beyond the lens known as the focal point Convex lenses are used in things like telescopes and binoculars to bring distant light rays to a focus in your eyes. A concave lens is exactly the opposite with the outer surfaces curving inward, so it makes parallel light rays curve outward or diverge. That's why concave lenses are sometimes called diverging lenses. (One easy way to remember the difference between concave and convex lenses is to think of concave lenses caving inwards). Concave lenses are used in things like TV projectors to make light rays spread out into the distance.",image,teaching_images/optics_lense_types_9163.png
L_0755,optics,DD_0222,"This diagram shows the arrangement of optics found in a refracting telescope. Llight entering the telescope first encounters the large objective lens placed a telescopes aperture the optical tube through its aperture, a circular opening at the forward end of the tube. The objective lens is convex, and it causes rays of light entered the telescope parallel to one another to converge. The eyepiece lens is located in the path of these converging rays, and brings an image to focus for the human eye.",image,teaching_images/parts_telescope_8156.png
L_0755,optics,DD_0223,"This Diagrams shows the different types of lenses. A lens is a clear (transparent) object (like glass, plastic or even a drop of water) that changes the way things look by bending the light that goes through it. They may make things appear larger, smaller, or upside-down. Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus. It is this type of lens that is most commonly used in corrective lenses. If the lens is biconvex or plano-convex, a collimated beam of light passing through the lens converges to a spot (a focus) behind the lens. In this case, the lens is called a positive or converging lens.",image,teaching_images/optics_lense_types_9159.png
L_0755,optics,DD_0224,"This diagram shows the arrangement of optics found in a reflecting telescope. Light enters the optical tube through its aperture, a circular opening at the forward end of the tube. When light enters the telescope, it encounters a concave reflecting mirror at the back of telescope tube. This large reflecting mirror is called the objective. Light reflected from the objective converges on a small right angle mirror at the center of the optical tube. This mirror reflects the gathered light to the eyepiece. The lenses in the eyepiece take this light and bring an image to focus for a human to see.",image,teaching_images/parts_telescope_8153.png
L_0762,earth as a magnet,DD_0230,This Diagram shows the Earth's Magnetic Field. Our planets magnetic field is believed to be generated deep down in the Earths core. And is created by the rotation of the Earth and Earth's core. It shields the Earth against harmful particles in space. The field is unstable and has changed often in the history of the Earth. The magnetic field creates magnetic poles that are near the geographical poles. A compass uses the geomagnetic field to find directions. Many migratory animals also use the field when they travel long distances each spring and fall. The magnetic poles will trade places during a magnetic reversal.,image,teaching_images/earth_magnetic_field_6775.png
L_0762,earth as a magnet,DD_0231,"This Diagram Shows the earth and how it acts as a magnet. It clearly depicts the geographic north pole and the magnetic north pole. Like all magnets, Earth has a magnetic field. Earths magnetic field is called the magnetosphere. It is a huge region that extends outward from Earth for several thousand kilometers but is strongest at the poles. Evidence in rocks shows that Earths magnetic poles switched positions hundreds of times in the past. Scien- tists think that Earths magnetic field is caused by the movement of charged particles through molten metals in the outer core. Earths magnetic field helps protect Earths surface and its organisms from harmful solar particles by pulling most of the particles toward the magnetic poles. Earths magnetic field is also used for navigation by humans and many other",image,teaching_images/earth_magnetic_field_6788.png
L_0772,inside the atom,DD_0241,"This diagram shows the makings of an atom. The nucleus contains protons and neutrons, which are represented as green and orange spheres. Protons have positive charges and neutrons have no charge. The rings outside the nucleus contain electrons, which have negative charges. The electrons are represented by purple spheres. The atom's mass is made up of the protons and neutrons. The outermost ring of electrons is called the valence ring, which contains one valence electron in this diagram.",image,teaching_images/atomic_structure_9020.png
L_0772,inside the atom,DD_0242,"Carbon has three isotopes which are shown in this diagram. Carbon always has six protons, but the number of neutrons it has can vary. The number of positively charged protons in an isotope is called the atomic number. The mass number of an isotope is equal to the number of its positively charged protons plus the number it's of neutrally charged neutrons. A Carbon-12 atom has six protons and six neutrons in its nucleus. A Carbon-13 isotope has six protons and seven neutrons in its nucleus, giving it a mass number of thirteen. Tritium has a proton and two neutrons in its nucleus, giving it a mass number of three. All three have a single electron. Another isotope of carbon, Carbon-14 has six protons and eight neutrons in its nucleus, giving it a mass number of fourteen.",image,teaching_images/isotopes_9127.png
L_0772,inside the atom,DD_0243,"Three isotopes of hydrogen are shown here. The number of protons in an atom determines the element, but the number of neutrons the atom of an element has can vary. The number of positively charged protons in an isotope is called the atomic number. This will also equal the number of electrons in a neutrally charged atom. The mass number of an isotope is equal to its atomic number plus the number of neutrally charged neutrons it has. A hydrogen atom has one proton and zero neutrons in its nucleus. Hyrogen has two isotopes called deuterium and tritium. Deuterim has a proton and a neutron in its nucleus, giving it a mass number of two. Tritium has a proton and two neutrons in its nucleus, giving it a mass number of three. All three have a single electron.",image,teaching_images/isotopes_7057.png
L_0772,inside the atom,DD_0244,"The figure shows the nuclear symbol for the chemical element Boron. There are two important numbers in a nuclear symbol. In the lower left part, there is the atomic number. The atomic number shows the number of protons. In the upper left part, there is the mass number. The mass number is the sum of the number of protons and neutrons. In addition, if the element is an ion, the charge is shown in the upper right part of the symbol.",image,teaching_images/atomic_mass_number_9001.png
L_0772,inside the atom,DD_0245,The diagram shows how elements are written in relation to the mass and atomic number. The symbol X stands for the chemical symbol of the element. Two numbers are commonly used to distinguish atoms: atomic number and mass number. The symbol A at the top right of the element symbol refers to the mass number. Mass number is the number of protons plus the number of neutrons in an atom. The symbol Z at the bottom right of the element symbol refers to the atomic number. The atomic number is the number of protons in an atom. This number is unique for atoms of each kind of element.,image,teaching_images/atomic_mass_number_9009.png
L_0772,inside the atom,DD_0246,"The figure shows a diagrammatic representation of a Helium-4 atom. We see how the atom has a nucleus surrounded by shells of electrons. In this case, the atom has two protons and two neutrons in the central nucleus. Two electrons orbit around the nucleus. The electrons are both in the first shell. The protons have a positive charge. The electrons have a negative charge. The neutrons do not have a charge.",image,teaching_images/atomic_mass_number_9006.png
L_0772,inside the atom,DD_0247,This diagram shows a simple model of an atom. At the center of the atom is the nucleus. The nucleus contains neutrons and protons. A proton is a particle with a positive electric charge. The neutron is a particle with no electric charge. Electrons are particles with negative charges. They revolve around the nucleus in orbits. An atom typically has the same number of protons and electrons. Hence the positive and negative charges cancel each other out.,image,teaching_images/atomic_structure_6540.png
L_0772,inside the atom,atomic_structure_9018,"This image shows the electron shells of a Germanium atom. There are a totals of 32 orbiting electrons in four distinct shells. The inner shell has two electrons. The second shell has 8 electrons. The third shell has 18 electrons. The fourth, outer shell has 4 electrons. The electrons in the outer shell are called valence electrons. In the center of the atom sits the nucleus. The nucleus has a positive charge.",image,teaching_images/atomic_structure_9018.png
L_0775,how elements are organized,DD_0249,Pictured below is a diagram of the periodic table. The periodic table is used today to classify elements. The elements in a periodic table are organized by the atomic number. The number of protons in an atom is what the atomic number represents on the chart. Rows on the periodic table are called periods. The columns in the periodic table are called groups. The modern periodic table have 18 groups. The elements are arranged in the periodic table by the atomic number from left to right from the lowest atomic numbers to highest.,image,teaching_images/periodic_table_8162.png
L_0775,how elements are organized,DD_0250,"This image shows the Periodic table. It is a table of the chemical elements arranged in order of atomic number, usually in rows, so that elements with similar atomic structure (and hence similar chemical properties) appear in vertical columns. This ordering shows periodic trends, such as elements with similar behaviour in the same column. It also shows four rectangular blocks with some approximately similar chemical properties. In general, within one row (period) the elements are metals on the left, and non-metals on the right. The rows of the table are called periods; the columns are called groups. The periodic table provides a useful framework for analyzing chemical behaviour, and is widely used in chemistry and other sciences.",image,teaching_images/periodic_table_8157.png
L_0775,how elements are organized,DD_0251,"The following image shows the Periodic Table of Elements. This is a list of known atoms. In the table, the elements are placed in the order of their atomic numbers starting with the lowest number. The atomic number of an element is the same as the number of protons in that particular atom. In the periodic table the elements are arranged into periods and groups. A row of elements across the table is called a period. Each period has a number: from 1 to 7. Period 1 has only 2 elements in it: hydrogen and helium. Period 2 and Period 3 both have 8 elements. Other periods are longer. The periodic table can be used by chemists to observe patterns, and relationships between the elements.",image,teaching_images/periodic_table_7388.png
L_0778,introduction to chemical bonds,DD_0252,"Water is a transparent common substance that makes up the earth's oceans, lakes, seas, rivers, streams and more. Water is essential for every living thing to replenish and hydrate. The chemical formula for water contains one oxygen atom to two hydrogen atoms. Everything from the earth's crust to the human brain contain great amounts of water. Water on earth is continually being used and then goes through the water cycle to become new and usable again. The water cycle involves evaporation, transpiration, condensation, precipitation and runoff. Even though water does not have any calories or nutritional benefit it is essential to all living forms on earth. Fishing which occurs in salt and fresh type waters yields much food for the world's people. Water even involves exercise for those who like to swim and engage in other sports like water skiing, wakeboarding and so on.",image,teaching_images/lewis_dot_diagrams_9146.png
L_0778,introduction to chemical bonds,DD_0253,"This image shows the chemical structure of Acetylene. Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. As an alkyne, acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond. The carboncarbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180.",image,teaching_images/lewis_dot_diagrams_9130.png
L_0778,introduction to chemical bonds,DD_0254,"The diagram shows the Lewis Dot Structure of Carbon. Lewis Structures are visual representations of the bonds between atoms and illustrate the lone pairs of electrons in molecules. The electrons in the outermost electron shell are called valence electrons. These electrons have an essential role in chemical bonding. Lewis Structures can also be called Lewis dot diagrams and are used as a simple way to show the configuration of atoms within a molecule. In constructing a Lewis Structure, an element is represented by a Lewis symbol (e.g. C for Carbon). It is surrounded by dots that are used to represent the valence electrons of the element. Lewis symbols differ slightly for ions. When forming a Lewis symbol for an ion, the chemical symbol is surrounded by dots that are used to represent valence electrons, and the whole structure is placed in square brackets with superscript representing the charge of the ion.",image,teaching_images/lewis_dot_diagrams_9140.png
L_0779,ionic bonds,DD_0255,"This diagram shows the ionic bonds in lithium fluoride molecule. An ionic bond is the force of attraction that holds together positive and negative ions. The lithium fluorine molecule consists of one lithium atom and one fluorine atom with the chemical formula of LiF. The lithium ion has one more protons than the number of electron thus has the charge of +1. The fluorine ion has one more electron than the number of protons thus has the charge of -1. The lithium ion and fluorine ion have equal but opposite charges so they attract each other. By the attracting force, they form a lithium fluoride molecule.",image,teaching_images/chemical_bonding_ionic_9071.png
L_0779,ionic bonds,DD_0256,"The diagram shows an example of ionic bonding. Ionic bonding is a type of chemical bond that occurs between a metallic atom and a nonmetallic atom that join together to form an ionic compound. In the figure, the metallic atom is the sodium atom and the nonmetallic atom is the chlorine atom. During iconic bonding, the metallic atom gives up an electron to the nonmetallic atom. The sodium atom therefore loses an electron while the chlorine atom gains an electron. Because of the electron transfer, each atom now has an unequal number of electrons and protons, thereby becoming an electrically charged ion. An atom that has lost an electron becomes an ion with a positive charge. A positive ion is called a cation. An atom that has gained an electron becomes an ion with a negative charge. A negative ion is called an anion. In short, the sodium atom becomes a sodium cation, whereas the chlorine atom becomes a chloride anion. (Chlorine becomes chloride when it gains an electrical charge.) Because the two ions have opposite electrical charges, they become attracted to each other and bond together, forming the ionic compound sodium chloride.",image,teaching_images/chemical_bonding_ionic_9066.png
L_0780,covalent bonds,DD_0257,"This diagram depicts covalent bonds in the ammonia compound. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It has 3 hydrogen atoms and 1 nitrogen atom. The nitrogen atom has 5 outer electrons, and the hydrogen atom has 1 electron. The nitrogen atom shares 2 electrons with each hydrogen atom, one provided by the nitrogen atom and the other provided by the hydrogen atom.",image,teaching_images/chemical_bonding_covalent_9051.png
L_0780,covalent bonds,DD_0258,"This diagram shows the covalent bonds in water molecule. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The water molecule consists of two hydrogen atoms and one oxygen atom with the chemical formula of H2O. The oxygen atom has 6 electrons and each hydrogen atom has one electron. The oxygen atom shares 2 electrons with two electrons from two hydrogen atoms. So, it completes the outer most shell of oxygen atom with 8 total electrons.",image,teaching_images/chemical_bonding_covalent_9053.png
L_0780,covalent bonds,DD_0259,"This diagram shows the covalent bonds in carbon dioxide molecule. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The carbon dioxide molecule consists of two oxygen atoms and one carbon atom with the chemical formula of CO2. At the outer most shell of carbon atom, there are 4 electrons. Each oxygen atoms shares 2 electrons with carbon atom. So, it completes the outer most shell of carbon atom with 8 total electrons.",image,teaching_images/chemical_bonding_covalent_9063.png
L_0787,hydrocarbons,DD_0260,"The diagram shows the chemical composition of four saturated hydrocarbons. It shows the chemical structure of four alkanes namely ethane, propane, butane and pentane with 2,3,4 and 5 carbon atoms respectively. All the above mentioned alkanes are straight chain compounds with 6,8,10 and 12 hydrogen atoms respectively.",image,teaching_images/hydrocarbons_7051.png
L_0787,hydrocarbons,DD_0261,"The diagram shows the molecular structure of Butane. Butane molecules have four carbon atoms and ten hydrogen atoms (C4 H10). Butane is classified as compounds that contain only carbon and hydrogen molecules, called Hydrocarbons. Saturated Hydrocarbons are the simplest Hydrocarbons. They are called saturated because each carbon atom is bonded to as many hydrogen atoms as possible and single bonds between carbon atoms. In other words, the carbon atoms are saturated with hydrogen. The diagram shows 3 carbon-carbon bonds and 10 carbon-hydrogen bonds. Their most important use is as fuels. Hydrocarbons are also used to manufacture many products, including plastics and synthetic fabrics such as polyester.",image,teaching_images/hydrocarbons_9121.png
L_0787,hydrocarbons,DD_0262,"The diagram shows the molecular structure of Hydrocarbons. Hydrocarbons can be classified into Saturated and Unsaturated Hydrocarbons. Saturated Hydrocarbons are the simplest Hydrocarbons. They are called saturated because each carbon atom is bonded to as many hydrogen atoms as possible and single bond between carbon atoms. In other words, the carbon atoms are saturated with hydrogen. As shown in the diagram, each carbon atoms are bonded to 3 hydrogen atoms and only one carbon atoms. In unsaturated hydrocarbons, The carbon atoms may have more than one bond to other carbon atoms and only 2 hydrogen atoms. Hydrocarbons are used to manufacture many products, including plastics and synthetic fabrics such as polyester. They are also used as fuels like Butane.",image,teaching_images/hydrocarbons_9118.png
L_0789,biochemical reactions,DD_0263,"The diagram depicts the process of cellular respiration. There are three steps in this process. The first step is Glycolysis. In Glycolysis, glucose in the cytoplasm is broken into two molecules of pyruvic acid and two molecules of ATP by direct synthesis. Then pyruvate from Glycolysis is actively pumped into mitochondria. One carbon dioxide molecule and one hydrogen molecule are removed from the pyruvate (called oxidative decarboxylation) to produce an acetyl group, which joins to an enzyme called CoA to form acetyl CoA. This is essential for the Krebs cycle.2 Acetyl CoA gives 2 NADH molecules and acetyl-CoA enters the Citric Acid Cycle, which is also known as Kreb's cycle. This happens inside the mitochondria. The citric acid cycle is an 8-step process involving different enzymes and co-enzymes. During the cycle, acetyl-CoA (2 carbons) + oxaloacetate (4 carbons) yields citrate (6 carbons), which is rearranged to a more reactive form called isocitrate (6 carbons). Isocitrate is modified to become -ketoglutarate (5 carbons), succinyl-CoA, succinate, fumarate, malate, and, finally, oxaloacetate. The total yield from 1 glucose molecule (2 pyruvate molecules) is 6 NADH, 2 FADH2, and 2 ATP. All the hydrogen molecules which have been removed in the steps before (Krebs cycle, Link reaction) are pumped inside the mitochondria using energy that electrons release. Eventually, the electrons powering the pumping of hydrogen into the mitochondria mix with some hydrogen and oxygen to form water and the hydrogen molecules stop being pumped. Eventually, the hydrogen flows back into the cytoplasm of the mitochondria through protein channels. As the hydrogen flows, ATP is made from ADP and phosphate ions. The Electron transport Chain gives about 34 ATP by ATP synthase. The maximum energy generated per glucose molecule is 38 ATP.",image,teaching_images/cellular_respiration_9048.png
L_0789,biochemical reactions,DD_0264,"This diagram shows the biochemical reaction cycles. Since all energy source of the biological objects on the earth is the sun, the cycle starts from the sun. Sun gives light to plants. The plants produce Glucose or sugar and oxygen by the process called photosynthesis with carbon dioxide and water produced by other plants and animals. Specifically, the Chloroplasts in the plants produces the Glucose. The Glucose and the sugar and oxygen are consumed by other plants and animals by cellular respiration in mitochondria. By the cellular respiration, plants and animals produce ATP which is a source of energy. Comsuming the Glucose and oxygen, the plants and animals also produce water and carbon dioxide. The water and carbon dioxide provides the ingredient for photosynthesis of plants. With the water and carbon dioxide, the plants produces glucose and oxygen with sunlight which completes the cycle.",image,teaching_images/cellular_respiration_8026.png
L_0789,biochemical reactions,DD_0265,"The diagram depicts the Oxygen Cycle. This is the cycle that maintains the levels of oxygen in the atmosphere. Oxygen from the atmosphere is used up in two processes, namely combustion, respiration and in the formation of oxides of nitrogen. Oxygen is returned to the atmosphere in only one major process, that is, photosynthesis. Carbon dioxide and water are taken up by plants in the presence of sunlight and chlorophyll to give glucose and oxygen. This glucose and oxygen are converted into carbon dioxide and water during respiration. Respiration also gives energy for work in the form of ATP.",image,teaching_images/cellular_respiration_9045.png
L_0936,law of reflection,DD_0266,"This diagram shows Ray (optics). In optics, a ray is an idealized model of light, obtained by choosing a line that is perpendicular to the wave fronts of the actual light, and that points in the direction of energy flow. Rays are used to model the propagation of light through an optical system by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of ray tracing. This allows even very complex optical systems to be analyzed mathematically or simulated by computer. All three rays should meet at the same point. The Principal Ray or Chief Ray (sometimes known as the b ray) in an optical system is the meridional ray that starts at the edge of the object and passes through the center of the aperture stop. This ray crosses the optical axis at the locations of the pupils. As such, chief rays are equivalent to the rays in a pinhole camera. The Central Ray is perpendicular to Infrared Radiation. The third one, called the Focal Ray, is a mirror image of the parallel ray. The focal ray is drawn from the tip of the object through (or towards) the focal point, reflecting off the mirror parallel to the principal axis.",image,teaching_images/optics_ray_diagrams_9167.png
L_0936,law of reflection,DD_0267,"This diagram explains the law of reflection and shows how light gets reflected from a surface. The law of reflection states that the angle of incidence (i) is always equal to the angle of reflection (r). The angles of both reflected and incident ray are measured relative to the imaginary dotted-line, called normal, that is perpendicular (at right angles) to the mirror (reflective surface).",image,teaching_images/optics_reflection_9179.png
L_0936,law of reflection,DD_0268,The reflection of a tree shines in to the lake. When the human eye sees the reflection from the tree on the water it looks the right direction. The image of the tree is upside down. The water reflection on the lake makes things upright to the human eye.,image,teaching_images/optics_ray_diagrams_9168.png
L_0936,law of reflection,DD_0269,This diagram depicts how light rays can reflect off various surfaces. Incident rays will reflect back at a specific angle if the surface is smooth. A rough or broken surface will have reflected rays with a wide variety of reflected angles. The left part of the diagram shows why your reflection in a mirror is smooth and natural looking.,image,teaching_images/optics_reflection_9183.png
L_0972,nucleic acid classification,DD_0270,"The diagram shows the structure of deoxyribonucleic acid (DNA) which carries the genetic information of organisms. DNA is made up of a double helix of two complementary strands. The strands of the double helix are anti-parallel with one being 5' to 3', and the opposite strand 3' to 5'. Each single strand of DNA is a chain of four types of nucleotides. The four types of nucleotide correspond to the four nucleobases adenine, cytosine, guanine, and thymine, commonly abbreviated as A, C, G and T. Adenine pairs with thymine (two hydrogen bonds), and guanine pairs with cytosine (three hydrogen bonds). During DNA replication, the parent DNA unwinds and each parental strand serves as a template for replication of new strands. Nucleobases are matched to synthesize the new daughter strands.",image,teaching_images/dna_6763.png
L_0972,nucleic acid classification,DD_0271,"This diagram shows the structure of a DNA or deoxyribonucleic acid. Deoxyribonucleic acid is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. Most DNA molecules consist of two strands coiled around each other to form a double helix. The two DNA strands are composed of simpler units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing compounds either cytosine (C), guanine (G), adenine (A), or thymine (T). The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone.",image,teaching_images/dna_8052.png
L_1063,vision and the eye,DD_0272,"The ability to see is called vision. The eyes sense light and form images which The brain then interprets. The images are formed by the eyes and the brain tells us what we are looking at. All creatures have different types of eyes, some are great at seeing vast distances such as the eagle or owl and some are able to pick up light in dark settings in order to see better at night, such as cats. Many people have issues with their vision but we have been able to correct this with lenses which come in the form of glasses or contact lenses. The eyes are made up of several parts the pupil, cornea, iris, lens, retina and the optic nerve which carries the images the eyes sees and takes the images to brain for it to interpret.",image,teaching_images/human_system_eye_2857.png
L_1063,vision and the eye,DD_0273,"Below is a diagram of the structure of the eyeball. As you can see below, the eyeball is made up of various parts. One of the major parts is the cornea. The cornea of the eyeball is a clear covering that protects the eyeball. The light first comes through the cornea then goes through the pupil. The pupil is the opening in the center of the eyeball. The pupil is the dark part in the center of the iris, which is the colored part of the eye. The light then goes through the lens and reaches the retina. The retina is the part where the image first occurs. Then the optic nerves carries the impulses to the brain.",image,teaching_images/human_system_eye_6138.png
L_1063,vision and the eye,DD_0274,This picture shows the parts of the eye. The light enters the eye through the pupil. The cornea covers the eye and protects it from damage. The iris controls the size of the pupil. The size of the pupil changes based on the amount of light that enters the eye. The lens projects the image onto retina. The retina has nerve cells which transmit color and other information to the brain. The space between the lens and Retina is filled by a transparent liquid called Viterous gel. Fovea has the highest concentration of cone cells. Cone cells are responsible for seeing color and function best in bright light.,image,teaching_images/human_system_eye_2876.png
L_1068,wave interference,DD_0275,"This diagram shows the result of constructive wave interference. The highest point of a waves amplitude is called a crest. The lowest point in amplitude is called a trough. Constructive interference occurs when two waves meet and overlap so that their crests and troughs align. In this image, the crests and troughs of Wave 1 and Wave 2 synchronize. This causes an increase in amplitude. The result is the wave on the right, which has a greater amplitude than Wave 1 and Wave 2.",image,teaching_images/waves_interactions_interference_7681.png
L_1068,wave interference,DD_0276,"This diagram shows the results of constructive interference and destructive interference in sound waves. Wave interference is when two waves meet while traveling in opposite directions. The highest point of a waves amplitude is called a crest. The lowest point in amplitude is called a trough. In the example of constructive interference, the crests and troughs of the two waves align. This causes increased wave amplitude when the two waves overlap. In the example of destructive interference, the highest point of amplitude of one wave occurs at the lowest point of the other and cancel each other out. This causes decreased wave amplitude when the two waves overlap.",image,teaching_images/waves_interactions_interference_9298.png