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L_0296 | scientific community | T_1654 | A hypothesis will not be fully accepted unless it is supported by the work of many scientists. Although a study may take place in a single laboratory, a scientist must present her work to the community of scientists in her field. Initially, she may present her data and conclusions at a scientific conference where she will talk with many other scientists. Later, she will write a paper to be published in a scientific journal. After she submits the paper, several scientists will review the paper - a process called peer review - to suggest further investigations or changes in interpretation to make the paper stronger. The scientists will then recommend or deny the paper for publication. Once it is published, other scientists incorporate the results into their own research. If they cannot replicate her results, her work will be thrown out! Scientific ideas are advanced after many papers on a topic are published. | text | null |
L_0296 | scientific community | T_1655 | There scientific community controls the quality and type of research that is done by project funding. Most scientific research is expensive, so scientists must write a proposal to a funding agency, such as the National Science Foun- dation or the National Aeronautics and Space Administration (NASA), to pay for equipment, supplies, and salaries. Scientific proposals are reviewed by other scientists in the field and are evaluated for funding. In many fields, the funding rate is low and the money goes only to the most worthy research projects. The scientific community monitors scientific integrity. During their training, students learn how to conduct good scientific experiments. They learn not to fake, hide, or selectively report data, and they learn how to fairly evaluate data and the work of other scientists. Scientists who do not have scientific integrity are strongly condemned by the scientific community. Nothing is perfect, but considering all the scientific research that is done, there are few incidences of scientific dishonesty. Yet when they do occur, they are often reported with great vehemence by the media. Often this causes the public to mistrust scientists in ways that are unwarranted. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0297 | scientific explanations and interpretations | T_1656 | Scientists usually begin an investigation with facts. A fact is a bit of information that is true. Facts come from data collected from observations or from experiments that have already been run. Data is factual information that is not subject to opinion or bias. What is a fact? Look at the following list and identify if the statement is a fact (from observation or prior experi- ments), an opinion, or a combination. Can you be sure from the photo that Susan has a cold? 1. 2. 3. 4. 5. 6. 7. Susan has long hair. Susan is sneezing and has itchy eyes. She is not well. She has a cold. Colds are caused by viruses. Echinacea is an herb that prevents colds. Bill Gates is the smartest man in the United States. People born under the astrological sign Leo are fiery, self-assured, and charming. Average global temperature has been rising at least since 1960. | text | null |
L_0297 | scientific explanations and interpretations | T_1657 | The following is an analysis of the statements above: 1. This is a fact made from observation. 2. The first part is from observations. The second is a fact drawn from the prior observations. The third is an opinion, since she might actually have allergies or the flu. Tests could be done to see what is causing her illness. 3. This is a fact. Many, many scientific experiments have shown that colds are caused by viruses. 4. While that sounds like a fact, the scientific evidence is mixed. One reputable study published in 2007 showed a decrease of 58%, but several other studies have shown no beneficial effect. 5. Bill Gates is the wealthiest man in the United States; thats a fact. But theres no evidence that hes also the smartest man, and chances are hes not. This is an opinion. 6. This sounds like a fact, but it is not. It is easy to test. Gather together a large number of subjects, each with a friend. Have the friends fill out a questionnaire describing the subject. Match the traits against the persons astrological sign to see if the astrological predictions fit. Are Leos actually more fiery, self assured, and charming? Tests like this have not supported the claims of astrologers, yet astrologers have not modified their opinions. 7. This is a fact. The Figure 1.2 shows the temperature anomaly since 1880. Theres no doubt that temperature has risen overall since 1880 and especially since the late 1970s. Global Average Annual Temperatures are Rising. This graph shows temperature anomaly relative to the 1951-1980 aver- age (the average is made to be 0). The green bars show uncertainty. | text | null |
L_0298 | scientific method | T_1658 | The goal of science is to answer questions about the natural world. Scientific questions must be testable. Which of these two questions is a good scientific question and which is not? What is the age of our planet Earth? How many angels can dance on the head of a pin? The first is a good scientific question that can be answered by radiometrically dating rocks among other techniques. The second cannot be answered using data, so it is not a scientific question. | text | null |
L_0298 | scientific method | T_1659 | Scientists use the scientific method to answer questions. The scientific method is a series of steps that help to investigate a question. Often, students learn that the scientific method is a linear process that goes like this: Ask a question. The question is based on one or more observations or on data from a previous experiment. Do some background research. Create a hypothesis. Do experiments or make observations to test the hypothesis. Gather the data. Formulate a conclusion. The process doesnt always go in a straight line. A scientist might ask a question, then do some background research and discover that the question needed to be asked a different way, or that a different question should be asked. Click image to the left or use the URL below. URL: | text | null |
L_0298 | scientific method | T_1660 | Now, lets ask a scientific question. Remember that it must be testable. We learned above that average global temperature has been rising since record keeping began in 1880. We know that carbon dioxide is a greenhouse gas. Greenhouse gases trap heat in the atmosphere. This leads us to a question: Question: Is the amount of carbon dioxide in Earths atmosphere changing? This is a good scientific question because it is testable. How has carbon dioxide in the atmosphere changed over those 50-plus years (see Figure 1.1)? About how much has atmospheric CO2 risen between 1958 and 2011 in parts per million? | text | null |
L_0298 | scientific method | T_1661 | So weve answered the question using data from research that has already been done. If scientists had not been monitoring CO2 levels over the years, wed have had to start these measurements now. Because this question can be answered with data, it is testable. Click image to the left or use the URL below. URL: | text | null |
L_0325 | temperature of the atmosphere | T_1753 | The atmosphere is layered, corresponding with how the atmospheres temperature changes with altitude. By under- standing the way temperature changes with altitude, we can learn a lot about how the atmosphere works. | text | null |
L_0325 | temperature of the atmosphere | T_1754 | Why does warm air rise (Figure 1.1)? Gas molecules are able to move freely, and if they are uncontained, as they are in the atmosphere, they can take up more or less space. When gas molecules are cool, they are sluggish and do not take up as much space. With the same number of molecules in less space, both air density and air pressure are higher. When gas molecules are warm, they move vigorously and take up more space. Air density and air pressure are lower. Warmer, lighter air is more buoyant than the cooler air above it, so it rises. The cooler air then sinks down, because it is denser than the air beneath it. This is convection, which was described in the chapter Plate Tectonics. | text | null |
L_0325 | temperature of the atmosphere | T_1755 | The property that changes most strikingly with altitude is air temperature. Unlike the change in pressure and density, which decrease with altitude, changes in air temperature are not regular. A change in temperature with distance is called a temperature gradient. | text | null |
L_0325 | temperature of the atmosphere | T_1756 | The atmosphere is divided into layers based on how the temperature in that layer changes with altitude, the layers temperature gradient (Figure 1.2). The temperature gradient of each layer is different. In some layers, temperature increases with altitude and in others it decreases. The temperature gradient in each layer is determined by the heat source of the layer (See opening image). The four main layers of the atmosphere have different temperature gradients, cre- ating the thermal structure of the atmo- sphere. This video is very thorough in its discussion of the layers of the atmosphere. Remember that the chemical composi- tion of each layer is nearly the same except for the ozone layer that is found in the stratosphere. Click image to the left or use the URL below. URL: | text | null |
L_0332 | tornadoes | T_1782 | Tornadoes, also called twisters, are fierce products of severe thunderstorms (Figure 1.1). As air in a thunderstorm rises, the surrounding air races in to fill the gap. This forms a tornado, a funnel-shaped, whirling column of air extending downward from a cumulonimbus cloud. A tornado lasts from a few seconds to several hours. The average wind speed is about 177 kph (110 mph), but some winds are much faster. A tornado travels over the ground at about 45 km per hour (28 miles per hour) and goes about 25 km (16 miles) before losing energy and disappearing (Figure 1.2). The formation of this tornado outside Dimmit, Texas, in 1995 was well studied. This tornado struck Seymour, Texas, in 1979. | text | null |
L_0332 | tornadoes | T_1782 | Tornadoes, also called twisters, are fierce products of severe thunderstorms (Figure 1.1). As air in a thunderstorm rises, the surrounding air races in to fill the gap. This forms a tornado, a funnel-shaped, whirling column of air extending downward from a cumulonimbus cloud. A tornado lasts from a few seconds to several hours. The average wind speed is about 177 kph (110 mph), but some winds are much faster. A tornado travels over the ground at about 45 km per hour (28 miles per hour) and goes about 25 km (16 miles) before losing energy and disappearing (Figure 1.2). The formation of this tornado outside Dimmit, Texas, in 1995 was well studied. This tornado struck Seymour, Texas, in 1979. | text | null |
L_0332 | tornadoes | T_1783 | An individual tornado strikes a small area, but it can destroy everything in its path. Most injuries and deaths from tornadoes are caused by flying debris (Figure 1.3). In the United States an average of 90 people are killed by tornadoes each year. The most violent two percent of tornadoes account for 70% of the deaths by tornadoes. | text | null |
L_0332 | tornadoes | T_1784 | Tornadoes form at the front of severe thunderstorms. Lines of these thunderstorms form in the spring where where maritime tropical (mT) and continental polar (cP) air masses meet. Although there is an average of 770 tornadoes annually, the number of tornadoes each year varies greatly (Figure 1.4). | text | null |
L_0332 | tornadoes | T_1785 | In late April 2011, severe thunderstorms pictured in the satellite image spawned the deadliest set of tornadoes in more than 25 years. In addition to the meeting of cP and mT mentioned above, the jet stream was blowing strongly Tornado damage at Ringgold, Georgia in April 2011. The frequency of F3, F4, and F5 torna- does in the United States. The red region that starts in Texas and covers Oklahoma, Nebraska, and South Dakota is called Tornado Alley because it is where most of the violent tornadoes occur. in from the west. The result was more than 150 tornadoes reported throughout the day (Figure 1.5). The entire region was alerted to the possibility of tornadoes in those late April days. But meteorologists can only predict tornado danger over a very wide region. No one can tell exactly where and when a tornado will touch down. Once a tornado is sighted on radar, its path is predicted and a warning is issued to people in that area. The exact path is unknown because tornado movement is not very predictable. | text | null |
L_0332 | tornadoes | T_1785 | In late April 2011, severe thunderstorms pictured in the satellite image spawned the deadliest set of tornadoes in more than 25 years. In addition to the meeting of cP and mT mentioned above, the jet stream was blowing strongly Tornado damage at Ringgold, Georgia in April 2011. The frequency of F3, F4, and F5 torna- does in the United States. The red region that starts in Texas and covers Oklahoma, Nebraska, and South Dakota is called Tornado Alley because it is where most of the violent tornadoes occur. in from the west. The result was more than 150 tornadoes reported throughout the day (Figure 1.5). The entire region was alerted to the possibility of tornadoes in those late April days. But meteorologists can only predict tornado danger over a very wide region. No one can tell exactly where and when a tornado will touch down. Once a tornado is sighted on radar, its path is predicted and a warning is issued to people in that area. The exact path is unknown because tornado movement is not very predictable. | text | null |
L_0332 | tornadoes | T_1786 | The intensity of tornadoes is measured on the Fujita Scale (see Table 1.1), which assigns a value based on wind speed and damage. F Scale F0 (km/hr) 64-116 (mph) 40-72 F1 117-180 73-112 F2 181-253 113-157 F3 254-333 158-206 F4 333-419 207-260 F5 420-512 261-318 F6 >512 >318 Damage Light - tree branches fall and chimneys may col- lapse Moderate - mobile homes, autos pushed aside Considerable - roofs torn off houses, large trees up- rooted Severe - houses torn apart, trees uprooted, cars lifted Devastating - houses lev- eled, cars thrown Incredible - structures fly, cars become missiles Maximum tornado wind speed Click image to the left or use the URL below. URL: | text | null |
L_0339 | types of marine organisms | T_1806 | The smallest and largest animals on Earth live in the oceans. Why do you think the oceans can support large animals? Marine animals breathe air or extract oxygen from the water. Some float on the surface and others dive into the oceans depths. There are animals that eat other animals, and plants generate food from sunlight. A few bizarre creatures break down chemicals to make food! The following section divides ocean life into seven basic groups. | text | null |
L_0339 | types of marine organisms | T_1807 | Plankton are organisms that cannot swim but that float along with the current. The word "plankton" comes from the Greek for wanderer. Most plankton are microscopic, but some are visible to the naked eye (Figure 1.1). Phytoplankton are tiny plants that make food by photosynthesis. Because they need sunlight, phytoplankton live in the photic zone. Phytoplankton are responsible for about half of the total primary productivity (food energy) on Earth. Like other plants, phytoplankton release oxygen as a waste product. Microscopic diatoms are a type of phyto- plankton. Zooplankton, or animal plankton, eat phytoplankton as their source of food (Figure 1.2). Some zooplankton live as plankton all their lives and others are juvenile forms of animals that will attach to the bottom as adults. Some small invertebrates live as zooplankton. Copepods are abundant and so are an important food source for larger animals. | text | null |
L_0339 | types of marine organisms | T_1807 | Plankton are organisms that cannot swim but that float along with the current. The word "plankton" comes from the Greek for wanderer. Most plankton are microscopic, but some are visible to the naked eye (Figure 1.1). Phytoplankton are tiny plants that make food by photosynthesis. Because they need sunlight, phytoplankton live in the photic zone. Phytoplankton are responsible for about half of the total primary productivity (food energy) on Earth. Like other plants, phytoplankton release oxygen as a waste product. Microscopic diatoms are a type of phyto- plankton. Zooplankton, or animal plankton, eat phytoplankton as their source of food (Figure 1.2). Some zooplankton live as plankton all their lives and others are juvenile forms of animals that will attach to the bottom as adults. Some small invertebrates live as zooplankton. Copepods are abundant and so are an important food source for larger animals. | text | null |
L_0339 | types of marine organisms | T_1808 | The few true plants found in the oceans include salt marsh grasses and mangrove trees. Although they are not true plants, large algae, which are called seaweed, also use photosynthesis to make food. Plants and seaweeds are found in the neritic zone, where the light they need penetrates so that they can photosynthesize (Figure 1.3). Kelp grows in forests in the neritic zone. Otters and other organisms depend on the kelp-forest ecosystem. | text | null |
L_0339 | types of marine organisms | T_1809 | The variety and number of invertebrates, animals without a backbone, is truly remarkable (Figure 1.4). Marine invertebrates include sea slugs, sea anemones, starfish, octopuses, clams, sponges, sea worms, crabs, and lobsters. Most of these animals are found close to the shore, but they can be found throughout the ocean. Jellies are otherworldly creatures that glow in the dark, without brains or bones, some more than 100 feet long. Along with many other ocean areas, they live just off Californias coast. Click image to the left or use the URL below. URL: | text | null |
L_0339 | types of marine organisms | T_1810 | Fish are vertebrates; they have a backbone. What are some of the features fish have that allows them to live in the oceans? All fish have most or all of these traits: Fins with which to move and steer. Scales for protection. Gills for extracting oxygen from the water. A swim bladder that lets them rise and sink to different depths. (a) Mussels; (b) Crown of thorns sea star; (c) Moon jelly; (d) A squid. Ectothermy (cold-bloodedness), so that their bodies are the same temperature as the surrounding water. Bioluminescence, or light created from a chemical reaction that can attract prey or mates in the dark ocean. Included among the fish are sardines, salmon, and eels, as well as the sharks and rays (which lack swim bladders) (Figure 1.5). | text | null |
L_0339 | types of marine organisms | T_1811 | Only a few types of reptiles live in the oceans and they live in warm water. Why are reptiles so restricted in their ability to live in the sea? Sea turtles, sea snakes, saltwater crocodiles, and marine iguana that are found only at the Galapagos Islands sum up the marine reptile groups (Figure 1.6). Sea snakes bear live young in the ocean, but turtles, crocodiles, and marine iguanas all lay their eggs on land. The Great White Shark is a fish that preys on other fish and marine mammals. Sea turtles are found all over the oceans, but their numbers are diminishing. | text | null |
L_0339 | types of marine organisms | T_1811 | Only a few types of reptiles live in the oceans and they live in warm water. Why are reptiles so restricted in their ability to live in the sea? Sea turtles, sea snakes, saltwater crocodiles, and marine iguana that are found only at the Galapagos Islands sum up the marine reptile groups (Figure 1.6). Sea snakes bear live young in the ocean, but turtles, crocodiles, and marine iguanas all lay their eggs on land. The Great White Shark is a fish that preys on other fish and marine mammals. Sea turtles are found all over the oceans, but their numbers are diminishing. | text | null |
L_0339 | types of marine organisms | T_1812 | Many types of birds are adapted to living in the sea or on the shore. With their long legs for wading and long bills for digging in sand for food, shorebirds are well adapted for the intertidal zone. Many seabirds live on land but go to sea to fish, such as gulls, pelicans, and frigate birds. Some birds, like albatross, spend months at sea and only come on shore to raise chicks (Figure 1.7). | text | null |
L_0339 | types of marine organisms | T_1813 | What are the common traits of mammals? Mammals are endothermic (warm-blooded) vertebrates that give birth to live young, feed them with milk, and have hair, ears, and a jaw bone with teeth. What traits might mammals have to be adapted to life in the ocean? (a) Shorebirds; (b) Seabirds; (c) Albatross. For swimming: streamlined bodies, slippery skin or hair, fins. For warmth: fur, fat, high metabolic rate, small surface area to volume, specialized blood system. For salinity: kidneys that excrete salt, impervious skin. The five types of marine mammals are pictured here: (Figure 1.8). (a) Cetaceans: whales, dolphins, and porpoises. (b) Sirenians: manatee and the dugong. (c) Mustelids: Sea otters (terrestrial members are skunks, badgers and weasels). (d) Pinnipeds: Seals, sea lions, and walruses. (e) Polar bear. | text | null |
L_0339 | types of marine organisms | T_1813 | What are the common traits of mammals? Mammals are endothermic (warm-blooded) vertebrates that give birth to live young, feed them with milk, and have hair, ears, and a jaw bone with teeth. What traits might mammals have to be adapted to life in the ocean? (a) Shorebirds; (b) Seabirds; (c) Albatross. For swimming: streamlined bodies, slippery skin or hair, fins. For warmth: fur, fat, high metabolic rate, small surface area to volume, specialized blood system. For salinity: kidneys that excrete salt, impervious skin. The five types of marine mammals are pictured here: (Figure 1.8). (a) Cetaceans: whales, dolphins, and porpoises. (b) Sirenians: manatee and the dugong. (c) Mustelids: Sea otters (terrestrial members are skunks, badgers and weasels). (d) Pinnipeds: Seals, sea lions, and walruses. (e) Polar bear. | text | null |
L_0352 | weather fronts | T_1877 | Two air masses meet at a front. At a front, the two air masses have different densities and do not easily mix. One air mass is lifted above the other, creating a low pressure zone. If the lifted air is moist, there will be condensation and precipitation. Winds are common at a front. The greater the temperature difference between the two air masses, the stronger the winds will be. Fronts are the main cause of stormy weather. There are four types of fronts, three moving and one stationary. With cold fronts and warm fronts, the air mass at the leading edge of the front gives the front its name. In other words, a cold front is right at the leading edge of moving cold air and a warm front marks the leading edge of moving warm air. | text | null |
L_0352 | weather fronts | T_1878 | At a stationary front the air masses do not move (Figure 1.1). A front may become stationary if an air mass is stopped by a barrier, such as a mountain range. A stationary front may bring days of rain, drizzle, and fog. Winds usually blow parallel to the front, but in opposite directions. After several days, the front will likely break apart. | text | null |
L_0352 | weather fronts | T_1879 | When a cold air mass takes the place of a warm air mass, there is a cold front (Figure 1.2). The map symbol for a stationary front has red domes for the warm air mass and blue triangles for the cold air mass. Imagine that you are standing in one spot as a cold front approaches. Along the cold front, the denser, cold air pushes up the warm air, causing the air pressure to decrease (Figure 1.2). If the humidity is high enough, some types of cumulus clouds will grow. High in the atmosphere, winds blow ice crystals from the tops of these clouds to create cirrostratus and cirrus clouds. At the front, there will be a line of rain showers, snow showers, or thunderstorms with blustery winds (Figure 1.3). A squall line is a line of severe thunderstorms that forms along a cold front. Behind the front is the cold air mass. This mass is drier, so precipitation stops. The weather may be cold and clear or only partly cloudy. Winds may continue to blow into the low pressure zone at the front. The weather at a cold front varies with the season. Spring and summer: the air is unstable so thunderstorms or tornadoes may form. Spring: if the temperature gradient is high, strong winds blow. Autumn: strong rains fall over a large area. Winter: the cold air mass is likely to have formed in the frigid arctic, so there are frigid temperatures and heavy snows. | text | null |
L_0352 | weather fronts | T_1879 | When a cold air mass takes the place of a warm air mass, there is a cold front (Figure 1.2). The map symbol for a stationary front has red domes for the warm air mass and blue triangles for the cold air mass. Imagine that you are standing in one spot as a cold front approaches. Along the cold front, the denser, cold air pushes up the warm air, causing the air pressure to decrease (Figure 1.2). If the humidity is high enough, some types of cumulus clouds will grow. High in the atmosphere, winds blow ice crystals from the tops of these clouds to create cirrostratus and cirrus clouds. At the front, there will be a line of rain showers, snow showers, or thunderstorms with blustery winds (Figure 1.3). A squall line is a line of severe thunderstorms that forms along a cold front. Behind the front is the cold air mass. This mass is drier, so precipitation stops. The weather may be cold and clear or only partly cloudy. Winds may continue to blow into the low pressure zone at the front. The weather at a cold front varies with the season. Spring and summer: the air is unstable so thunderstorms or tornadoes may form. Spring: if the temperature gradient is high, strong winds blow. Autumn: strong rains fall over a large area. Winter: the cold air mass is likely to have formed in the frigid arctic, so there are frigid temperatures and heavy snows. | text | null |
L_0352 | weather fronts | T_1880 | At a warm front, a warm air mass slides over a cold air mass (Figure 1.4). When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable. Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching. The transition from cold air to warm air takes place over a long distance, so the first signs of changing weather appear long before the front is actually over you. Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. High cirrus clouds mark the transition from one air mass to the other. Warm air moves forward to take over the position of colder air. Over time, cirrus clouds become thicker and cirrostratus clouds form. As the front approaches, altocumulus and altostratus clouds appear and the sky turns gray. Since it is winter, snowflakes fall. The clouds thicken and nimbostratus clouds form. Snowfall increases. Winds grow stronger as the low pressure approaches. As the front gets closer, the cold air mass is just above you but the warm air mass is not too far above that. The weather worsens. As the warm air mass approaches, temperatures rise and snow turns to sleet and freezing rain. Warm and cold air mix at the front, leading to the formation of stratus clouds and fog (Figure 1.5). Cumulus clouds build at a warm front. | text | null |
L_0352 | weather fronts | T_1880 | At a warm front, a warm air mass slides over a cold air mass (Figure 1.4). When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable. Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching. The transition from cold air to warm air takes place over a long distance, so the first signs of changing weather appear long before the front is actually over you. Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. High cirrus clouds mark the transition from one air mass to the other. Warm air moves forward to take over the position of colder air. Over time, cirrus clouds become thicker and cirrostratus clouds form. As the front approaches, altocumulus and altostratus clouds appear and the sky turns gray. Since it is winter, snowflakes fall. The clouds thicken and nimbostratus clouds form. Snowfall increases. Winds grow stronger as the low pressure approaches. As the front gets closer, the cold air mass is just above you but the warm air mass is not too far above that. The weather worsens. As the warm air mass approaches, temperatures rise and snow turns to sleet and freezing rain. Warm and cold air mix at the front, leading to the formation of stratus clouds and fog (Figure 1.5). Cumulus clouds build at a warm front. | text | null |
L_0352 | weather fronts | T_1880 | At a warm front, a warm air mass slides over a cold air mass (Figure 1.4). When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable. Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching. The transition from cold air to warm air takes place over a long distance, so the first signs of changing weather appear long before the front is actually over you. Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. High cirrus clouds mark the transition from one air mass to the other. Warm air moves forward to take over the position of colder air. Over time, cirrus clouds become thicker and cirrostratus clouds form. As the front approaches, altocumulus and altostratus clouds appear and the sky turns gray. Since it is winter, snowflakes fall. The clouds thicken and nimbostratus clouds form. Snowfall increases. Winds grow stronger as the low pressure approaches. As the front gets closer, the cold air mass is just above you but the warm air mass is not too far above that. The weather worsens. As the warm air mass approaches, temperatures rise and snow turns to sleet and freezing rain. Warm and cold air mix at the front, leading to the formation of stratus clouds and fog (Figure 1.5). Cumulus clouds build at a warm front. | text | null |
L_0352 | weather fronts | T_1881 | An occluded front usually forms around a low pressure system (Figure 1.6). The occlusion starts when a cold front catches up to a warm front. The air masses, in order from front to back, are cold, warm, and then cold again. The map symbol for an occluded front is mixed cold front triangles and warm front domes. Coriolis effect curves the boundary where the two fronts meet towards the pole. If the air mass that arrives third is colder than either of the first two air masses, that air mass slip beneath them both. This is called a cold occlusion. If the air mass that arrives third is warm, that air mass rides over the other air mass. This is called a warm occlusion (Figure 1.7). The weather at an occluded front is especially fierce right at the occlusion. Precipitation and shifting winds are typical. The Pacific Coast has frequent occluded fronts. An occluded front with the air masses from front to rear in order as cold, warm, cold. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0352 | weather fronts | T_1881 | An occluded front usually forms around a low pressure system (Figure 1.6). The occlusion starts when a cold front catches up to a warm front. The air masses, in order from front to back, are cold, warm, and then cold again. The map symbol for an occluded front is mixed cold front triangles and warm front domes. Coriolis effect curves the boundary where the two fronts meet towards the pole. If the air mass that arrives third is colder than either of the first two air masses, that air mass slip beneath them both. This is called a cold occlusion. If the air mass that arrives third is warm, that air mass rides over the other air mass. This is called a warm occlusion (Figure 1.7). The weather at an occluded front is especially fierce right at the occlusion. Precipitation and shifting winds are typical. The Pacific Coast has frequent occluded fronts. An occluded front with the air masses from front to rear in order as cold, warm, cold. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0353 | weather maps | T_1882 | Weather maps simply and graphically depict meteorological conditions in the atmosphere. Weather maps may display only one feature of the atmosphere or multiple features. They can depict information from computer models or from human observations. On a weather map, important meteorological conditions are plotted for each weather station. Meteorologists use many different symbols as a quick and easy way to display information on the map (Figure 1.1). Once conditions have been plotted, points of equal value can be connected by isolines. Weather maps can have many types of connecting lines. For example: Explanation of some symbols that may appear on a weather map. Lines of equal temperature are called isotherms. Isotherms show temperature gradients and can indicate the location of a front. In terms of precipitation, what does the 0o C (32o F) isotherm show? Isobars are lines of equal average air pressure at sea level (Figure 1.2). Closed isobars represent the locations of high and low pressure cells. Isotachs are lines of constant wind speed. Where the minimum values occur high in the atmosphere, tropical cyclones may develop. The highest wind speeds can be used to locate the jet stream. Surface weather analysis maps are weather maps that only show conditions on the ground (Figure 1.3). Surface analysis maps may show sea level mean pressure, temperature, and amount of cloud cover. Click image to the left or use the URL below. URL: | text | null |
L_0353 | weather maps | T_1882 | Weather maps simply and graphically depict meteorological conditions in the atmosphere. Weather maps may display only one feature of the atmosphere or multiple features. They can depict information from computer models or from human observations. On a weather map, important meteorological conditions are plotted for each weather station. Meteorologists use many different symbols as a quick and easy way to display information on the map (Figure 1.1). Once conditions have been plotted, points of equal value can be connected by isolines. Weather maps can have many types of connecting lines. For example: Explanation of some symbols that may appear on a weather map. Lines of equal temperature are called isotherms. Isotherms show temperature gradients and can indicate the location of a front. In terms of precipitation, what does the 0o C (32o F) isotherm show? Isobars are lines of equal average air pressure at sea level (Figure 1.2). Closed isobars represent the locations of high and low pressure cells. Isotachs are lines of constant wind speed. Where the minimum values occur high in the atmosphere, tropical cyclones may develop. The highest wind speeds can be used to locate the jet stream. Surface weather analysis maps are weather maps that only show conditions on the ground (Figure 1.3). Surface analysis maps may show sea level mean pressure, temperature, and amount of cloud cover. Click image to the left or use the URL below. URL: | text | null |
L_0353 | weather maps | T_1882 | Weather maps simply and graphically depict meteorological conditions in the atmosphere. Weather maps may display only one feature of the atmosphere or multiple features. They can depict information from computer models or from human observations. On a weather map, important meteorological conditions are plotted for each weather station. Meteorologists use many different symbols as a quick and easy way to display information on the map (Figure 1.1). Once conditions have been plotted, points of equal value can be connected by isolines. Weather maps can have many types of connecting lines. For example: Explanation of some symbols that may appear on a weather map. Lines of equal temperature are called isotherms. Isotherms show temperature gradients and can indicate the location of a front. In terms of precipitation, what does the 0o C (32o F) isotherm show? Isobars are lines of equal average air pressure at sea level (Figure 1.2). Closed isobars represent the locations of high and low pressure cells. Isotachs are lines of constant wind speed. Where the minimum values occur high in the atmosphere, tropical cyclones may develop. The highest wind speeds can be used to locate the jet stream. Surface weather analysis maps are weather maps that only show conditions on the ground (Figure 1.3). Surface analysis maps may show sea level mean pressure, temperature, and amount of cloud cover. Click image to the left or use the URL below. URL: | text | null |
L_0354 | weather versus climate | T_1883 | All weather takes place in the atmosphere, virtually all of it in the lower atmosphere. Weather describes what the atmosphere is like at a specific time and place. A locations weather depends on: air temperature air pressure fog humidity cloud cover precipitation wind speed and direction All of these characteristics are directly related to the amount of energy that is in the system and where that energy is. The ultimate source of this energy is the Sun. Weather is the change we experience from day to day. Weather can change rapidly. | text | null |
L_0354 | weather versus climate | T_1884 | Although almost anything can happen with the weather, climate is more predictable. The weather on a particular winter day in San Diego may be colder than on the same day in Lake Tahoe, but, on average, Tahoes winter climate is significantly colder than San Diegos (Figure 1.1). Climate is the long-term average of weather in a particular spot. Good climate is why we choose to vacation in Hawaii in February, even though the weather is not guaranteed to be good! A locations climate can be described by its air temperature, humidity, wind speed and direction, and the type, quantity, and frequency of precipitation. The climate for a particular place is steady, and changes only very slowly. Climate is determined by many factors, including the angle of the Sun, the likelihood of cloud cover, and the air pressure. All of these factors are related to the amount of energy that is found in that location over time. The climate of a region depends on its position relative to many things. These factors are described in the next sections. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0357 | wind power | T_1890 | Energy from the Sun also creates wind, which can be used as wind power. The Sun heats different locations on Earth by different amounts. Air that becomes warm rises and then sucks cooler air into that spot. The movement of air from one spot to another along the ground creates wind. Since wind is moving, it has kinetic energy. Wind power is the fastest growing renewable energy source in the world. Windmills are now seen in many locations, either individually or, more commonly, in large fields. | text | null |
L_0357 | wind power | T_1891 | Wind is the source of energy for wind power. Wind has been used for power for centuries. For example, windmills were used to grind grain and pump water. Sailing ships traveled by wind power long before ships were powered by fossil fuels. Wind can be used to generate electricity, as the moving air spins a turbine to create electricity (Figure Click image to the left or use the URL below. URL: | text | null |
L_0357 | wind power | T_1892 | Wind power has many advantages. It does not burn, so it does not release pollution or carbon dioxide. Also, wind is plentiful in many places. Wind, however, does not blow all of the time, even though power is needed all of the time. Just as with solar power, engineers are working on technologies that can store wind power for later use. Windmills are expensive and wear out quickly. A lot of windmills are needed to power a region, so nearby residents may complain about the loss of a nice view if a wind farm is built. Coastlines typically receive a lot of wind, but wind farms built near beaches may cause unhappiness for local residents and tourists. The Cape Wind project off of Cape Cod, Massachusetts has been approved but is generating much controversy. Opponents are in favor of green power but not at that location. Proponents say that clean energy is needed and the project would supply 75% of the electricity needed for Cape Cod and nearby islands (Figure 1.2). California was an early adopter of wind power. Windmills are found in mountain passes, where the cooler Pacific Ocean air is sucked through on its way to warmer inland valleys. Large fields of windmills can be seen at Altamont Pass in the eastern San Francisco Bay Area, San Gorgonio Pass east of Los Angeles, and Tehachapi Pass at the southern end of the San Joaquin Valley. | text | null |
L_0359 | scientific ways of thinking | T_1898 | Most people think of science as a collection of facts or a body of knowledge. For example, you may have memorized the processes of the water cycle. As shown in Figure 1.1, the processes include evaporation and precipitation. Such knowledge of the natural world is only part of what science is. Science is as much about doing as knowing. Science is a way of learning about the natural world that depends on evidence, reasoning, and repeated testing. Scientists explain the world based on their observations. If they develop new ideas about the way the world works, they set up ways to test these new ideas. Scientific knowledge keeps changing because scientists are always doing science. | text | null |
L_0359 | scientific ways of thinking | T_1899 | When Miranda and Jeanny wondered whether bacteria might decompose plastic, they were thinking like a scientist. What does it mean to think like a scientist? A scientist is observant. Miranda and Jeanny observed all the plastic trash when they visited a landfill. They also saw a lot of plastic trash along a local river. A scientist wonders and asks questions. Miranda and Jeanny wondered if any bacteria could help break down plastic. They asked: Can some bacteria consume chemicals in plastic for food? A scientist tries to find answers using evidence and logic. Often, a scientist does experiments to gather more evidence and test ideas. Miranda and Jeanny did a lot of online research to find out what other scientists had already learned. Then they did their own experiments. They gathered and tested bacteria. For example, they grew bacteria on gel like the red gel in Figure 1.2. You can learn the details of their research and their amazing results by watching this video: A scientist is skeptical. Claims must be backed by adequate evidence. Miranda and Jeanny repeated their experiments so they were confident in their results. Only then did they draw conclusions. A scientist has an open mind. Scientific knowledge is always evolving as new evidence comes in. Miranda and Jeanny made an important contribution with the evidence they gathered. They discovered two species of bacteria that could consume a harmful chemical in plastic. | text | null |
L_0359 | scientific ways of thinking | T_1900 | Some knowledge in science gains the status of a theory. Scientists use the term theory differently than it is used in everyday language. You might say, I think my dad is late because he got stuck in traffic, but its just a theory. In other words, its just one of many possible explanations for why hes late. In science, a theory is much more than that. A scientific theory is a broad explanation that is widely accepted because it is supported by a great deal of evidence. Scientific theories are tested and confirmed repeatedly. Because theories are broad explanations, they generally help explain many different observations. An example in life science is the theory of evolution by natural selection. It explains how living things change through time as they adapt to their environment. This theory is supported by a huge amount of evidence. The evidence ranges from DNA to fossils like the ones in Figure 1.3. Another sort of scientific knowledge is called a law. A scientific law is a description of what always occurs under certain conditions in nature. In other words, it describes many observations but doesnt explain them. Examples of scientific laws in life science include Mendels laws of inheritance. These laws describe how traits are passed from parents to their offspring. | text | null |
L_0359 | scientific ways of thinking | T_1900 | Some knowledge in science gains the status of a theory. Scientists use the term theory differently than it is used in everyday language. You might say, I think my dad is late because he got stuck in traffic, but its just a theory. In other words, its just one of many possible explanations for why hes late. In science, a theory is much more than that. A scientific theory is a broad explanation that is widely accepted because it is supported by a great deal of evidence. Scientific theories are tested and confirmed repeatedly. Because theories are broad explanations, they generally help explain many different observations. An example in life science is the theory of evolution by natural selection. It explains how living things change through time as they adapt to their environment. This theory is supported by a huge amount of evidence. The evidence ranges from DNA to fossils like the ones in Figure 1.3. Another sort of scientific knowledge is called a law. A scientific law is a description of what always occurs under certain conditions in nature. In other words, it describes many observations but doesnt explain them. Examples of scientific laws in life science include Mendels laws of inheritance. These laws describe how traits are passed from parents to their offspring. | text | null |
L_0360 | what is life science | T_1901 | Life is complex, and there are millions of species alive today. Many millions more lived in the past and then went extinct. Organisms include microscopic, single-celled organisms. They also include complex, multicellular animals such as you. Clearly, life science is a huge science. Thats why a life scientist usually specializes in just one field within life science. Dr. Smith, for example, specializes in ecology. You can see the focus of ecology and several other life science fields in Table 1.1. Click on the links provided if you want to learn about careers in these fields. Field Ecology Focus of Study interactions of organisms with each other and their environment Botany Zoology plants animals Microbiology microorganisms such as bacteria Entomology insects Cell biology cells of living things Physiology tissues and organs and how they function genes, traits, and inheritance Genetics Epidemiology Paleontology causes of diseases and how they spread fossils and evolution Learn about a Career in this Field | text | null |
L_0360 | what is life science | T_1902 | Each field of life science has its own specific body of knowledge and relevant theories. However, two theories are basic to all of the life sciences. They form the foundation of every life science field. They are the cell theory and the theory of evolution by natural selection. Both theories have been tested repeatedly. Both are supported by a great deal of evidence. | text | null |
L_0360 | what is life science | T_1903 | According to the cell theory, all organisms are made up of one or more cells. Cells are the sites where all life processes take place. Cells come only from pre-existing cells. New cells forms when existing cells divide. Most cells are too small to see without a microscope. If you were to look at a drop of your blood under a microscope, Figure 1.5 shows two types of cells you might see. You can learn more about cells and the cell theory in the chapter Cells and Their Structures. | text | null |
L_0360 | what is life science | T_1904 | The theory of evolution by natural selection explains how populations of organisms can change over time. As environments change, so must the traits of organisms if they are to survive in the new conditions. Evolution by natural selection explains how this happens. It also explains why there are so many different species of organisms on Earth today. You can see examples of the incredible diversity of living animals in Figure 1.6. You can read more about the theory of evolution in the chapter Evolution. | text | null |
L_0360 | what is life science | T_1905 | Most scientific theories were developed by scientists doing basic scientific research. Like other sciences, life science may be either basic or applied science. | text | null |
L_0360 | what is life science | T_1906 | The aim of basic science is to discover new knowledge. It leads to a better understanding of the natural world. It doesnt necessarily have any practical use. An example of basic research in life science is studying how yeast cells grow and divide. Yeasts are single-celled organisms that are easy to study. By studying yeast cells, life scientists discovered the series of events called the cell cycle. The cell cycle works not only in yeasts but in all other organisms with similar cells. Therefore, this basic research made a major contribution to our understanding of living things. Watch the following animation to learn more about the basic yeast research and the cell cycle. You can also see yeast cells dividing. | text | null |
L_0360 | what is life science | T_1907 | Knowledge gained by this basic research on yeast cells has been applied to practical problems. Scientists have developed drugs to treat cancer based on knowledge of the cell cycle. Cancer is a disease in which cells divide out of control. The new drugs interfere with the cell cycle of cancer cells, so the cells stop dividing. This is an example of applied science. The aim of applied science is to find solutions to practical problems. Applied science generally rests on knowledge gained by basic science. | text | null |
L_0361 | the scientific method | T_1908 | A life scientist would carry out a scientific investigation to try to answer this question. A scientific investigation follows a general plan called the scientific method. The scientific method is a series of logical steps for testing a possible answer to a question. The steps are shown in the flow chart in Figure 1.8. | text | null |
L_0361 | the scientific method | T_1909 | The steps of the scientific method are described in greater detail below. Note that these steps are meant as a guide, not a rigid sequence. Steps may be followed in a somewhat different order, for example, or steps may be repeated or skipped. 1. Make observations. Observations refer to anything detected with one or more senses. The senses include sight, hearing, touch, smell, and taste. 2. Ask a question raised by the observations. 3. Form a hypothesis. A hypothesis is a potential, testable answer to a scientific question. Testable means that if the hypothesis is false, its possible to find evidence showing that its false. This step usually requires some research. You have to find out what other investigators have already learned about the observations. For example, has anyone already tried to answer the question? What other hypotheses have been proposed? 4. Test the hypothesis. Make predictions based on the hypothesis and then determine if they are correct. This may involve carrying out an experiment. An experiment is a controlled scientific test that often takes place in a lab. It investigates the effects of one factor, called the independent variable, on another factor, called the dependent variable. Experimental controls are other factors that might affect the dependent variable. Controls are kept constant so they will not affect the results of the experiment. 5. Analyze the results of the test and draw a conclusion. Do the results agree with the predictions? If so, they provide support for the hypothesis. If not, they disprove the hypothesis. 6. Communicate results. One way is by presenting a poster at a scientific conference, like the scientists in Figure are communicated, scientists should describe their hypothesis and how it was tested in addition to the results of the test. This allows other scientists to repeat the investigation to see whether they get the same results. This is called replication. Replication is important because it adds weight to the findings. The results are more likely to be reliable if they can be repeated. | text | null |
L_0361 | the scientific method | T_1910 | You can apply the scientific method to the question that was raised above about athletic ability. Assume you are a life scientist. You observe variation in athletic abilities. Some athletes tend to build more muscle mass. Others tend to develop greater endurance. You ask, Is there a gene that might explain these differences? You research the problem on the Internet. You learn about a gene named ACE that might affect how people respond to athletic training. Based on all of your research, you develop a hypothesis. You hypothesize that people with different versions (D or I) of the ACE gene will respond differently to the same athletic training program. People with D genes will increase their muscle mass but not their endurance. People with I genes will increase their endurance but not their muscle mass. How can you test your hypothesis? You can see how actual life science researchers did it by watching this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0363 | safety in life science research | T_1916 | A science lab has many potential dangers. Thats why lab procedures and equipment are often labeled with safety symbols, like the ones in Figure 1.14. These symbols warn of specific hazards, such as flames or broken glass. Learn the symbols so you can recognize the dangers. Then learn how to avoid them. The best way to avoid lab dangers is to follow the lab safety rules listed below. Following the rules can help prevent accidents. Watch this funny student video to see just how important some of these rules are: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0363 | safety in life science research | T_1917 | Wear long sleeves and shoes that completely cover your feet. If your hair is long, tie it back or cover it with a hair net. Protect your eyes, skin, and clothing by wearing safety goggles, an apron, and gloves. Use hot mitts to handle hot objects. Never work alone in the lab. Never engage in horseplay in the lab. Never eat or drink in the lab. Never do experiments without your teachers approval. Always add acid to water, never the other way around. Add the acid slowly to avoid splashing. Take care to avoid knocking over Bunsen burners. Keep them away from flammable materials such as paper. Use your hand to fan vapors toward your nose rather than smelling substances directly. Never point the open end of a test tube toward anyoneincluding you! Clean up any spills immediately. Dispose of lab wastes according to your teachers instructions. Wash glassware and counters when you finish your work. Wash your hands with soap and water before leaving the lab. | text | null |
L_0363 | safety in life science research | T_1918 | Many of the lab safety rules are common-sense precautions. Common-sense should also prevail in the field. Be aware, however, that field research may have its own unique dangers. Therefore, other safety rules may apply when you work in the field. The rules will depend on the particular field setting and its specific risks. Consider the field botanist in Figure 1.13. There may be microorganisms in the water that could make her sick. She might come into contact with plants that cause an allergic reaction. The water or shore might be strewn with dangerous objects such as broken glass that could cause serious injury. To stay safe in the field, she needs to be aware of these risks and take steps to avoid them. If you work in the field or take a science fieldtrip, you should do the sameand always follow your teachers instructions. | text | null |
L_0363 | safety in life science research | T_1919 | Even when you follow the rules, accidents can happen. Immediately alert your teacher if an accident occurs. Report all accidents, whether or not you think they are serious. | text | null |
L_0364 | introduction to plants | T_1920 | Plants are multicellular eukaryotes that are placed in the Plant Kingdom. Plant cells have cell walls that are made of cellulose. Plant cells also have chloroplasts. They allow plants to make food by photosynthesis. In addition, plants have specialized reproductive organs that produce gametes. Male reproductive organs produce sperm. Female reproductive organs produce eggs. Male and female reproductive organs may be on the same plant or on different plants. | text | null |
L_0364 | introduction to plants | T_1921 | Plants are somewhat limited by temperature in terms of where they can grow. They need temperatures above freezing while they are actively growing. They also need light, carbon dioxide, and water. These substances are required for photosynthesis. Like most other living things, plants need oxygen. Oxygen is required for cellular respiration. In addition, plants need minerals. The minerals are required to make proteins and other organic molecules. | text | null |
L_0364 | introduction to plants | T_1922 | Life as we know it would not be possible without plants. Why are plants so important? Plants supply food to nearly all land organisms, including people. We mainly eat either plants or other living things that eat plants. Plants produce oxygen during photosynthesis. Oxygen is needed by all aerobic organisms. Plants absorb carbon dioxide during photosynthesis. This helps control the greenhouse effect and global warming. Plants recycle matter in ecosystems. For example, they are an important part of the water cycle. They take up liquid water from the soil through their roots. They release water vapor to the air from their leaves. This is called transpiration. Plants provide many products for human use. They include timber, medicines, dyes, oils, and rubber. Plants provide homes for many other living things. For example, a single tree may provide food and shelter to many species of animals, like the birds in Figure 10.2. | text | null |
L_0364 | introduction to plants | T_1923 | A tissue is a group of specialized cells of the same kind that perform the same function. Modern plants have three major types of tissues. Theyre called dermal, ground, and vascular tissues. | text | null |
L_0364 | introduction to plants | T_1924 | Dermal tissue covers the outside of a plant. Its like the plants skin. Cells of dermal tissue secrete a waxy substance called cuticle. Cuticle helps prevent water loss and damage to the plant. | text | null |
L_0364 | introduction to plants | T_1925 | Ground tissue makes up much of the inside of a plant. The cells of ground tissue carry out basic metabolic functions and other biochemical reactions. Ground tissue may also store food or water. | text | null |
L_0364 | introduction to plants | T_1926 | Vascular tissue runs through the ground tissue inside a plant. It transports fluids throughout the plant. Vascular tissue actually consists of two types of tissues, called xylem and phloem. The two types of vascular tissue are packaged together in bundles. You can see them in the celery in Figure 10.3. Xylem carries water and dissolved minerals from the roots upward to the leaves. Phloem carries water and dissolved sugar from the leaves to other parts of the plant. | text | null |
L_0364 | introduction to plants | T_1927 | An organ is a structure composed of two or more types of tissues that work together to do a specific task. Most modern plants have several organs that help them survive and reproduce in a variety of habitats. Major organs of most plants include roots, stems, and leaves. These and other plant organs generally contain all three major tissue types. | text | null |
L_0364 | introduction to plants | T_1928 | Roots are important organs in most modern plants. There are two types of roots: primary roots, which grow downward; and secondary roots, which branch out to the sides. Together, all the roots of a plant make up the plants root system. Figure 10.4 shows two different types of plant root systems. A taproot system has a very long primary root, called a taproot. A fibrous root system has many smaller roots and no large, primary root. The roots of plants have three major jobs: absorbing water and minerals, anchoring and supporting the plant, and storing food. Roots are covered with thin-walled dermal cells and tiny root hairs. These features are well suited to absorb water and dissolved minerals from the soil. Root systems help anchor plants to the ground. They allow plants to grow tall without toppling over. A tough covering may replace the dermal cells in older roots. This makes them ropelike and even stronger. In many plants, ground tissue in roots stores food produced by the leaves during photosynthesis. | text | null |
L_0364 | introduction to plants | T_1929 | Stems are organs that hold plants upright. They allow plants to get the sunlight and air they need. Stems also bear leaves, flowers, cones, and smaller stems. These structures grow at points called nodes. The stem between nodes is called an internode. (See Figure 10.5.) Stems are needed for transport and storage. Their vascular tissue carries water and minerals from roots to leaves. It carries dissolved sugar from the leaves to the rest of the plant. Without this connection between roots and leaves, plants could not survive high above the ground in the air. In many plants, ground tissue in stems also stores food or water during cold or dry seasons. | text | null |
L_0364 | introduction to plants | T_1930 | Leaves are the keys not only to plant life but to virtually all life on land. The primary role of leaves is to collect sunlight and make food by photosynthesis. Leaves vary in size, shape, and how they are arranged on stems. You can see examples of different types of leaves in Figure 10.6. Each type of leaf is well suited for the plants environment. It maximizes light exposure while conserving water, reducing wind resistance, or benefiting the plant in some other way in its particular habitat. For example, some leaves are divided into many smaller leaflets. This reduces wind resistance and water loss. Leaves are basically factories for photosynthesis. A factory has specialized machines to produce a product. In a leaf, the "machines" are the chloroplasts. A factory is connected to a transportation system that supplies it with raw materials and carries away the finished product. In a leaf, transport is carried out by veins containing vascular tissue. Veins carry water and minerals to the cells of leaves. They carry away dissolved sugar. A factory has bricks, siding, or other external protection. A leaf is covered with dermal cells. They secrete waxy cuticle to prevent evaporation of water from the leaf. A factory has doors and windows to let some materials enter and leave. The surface of the leaf has tiny pores called stomata (stoma, singular). They can open and close to control the movement of gases between the leaves and the air. You can see a close-up of a stoma in Figure 10.7. | text | null |
L_0364 | introduction to plants | T_1931 | Most plants continue to grow throughout their lives. Like other multicellular organisms, plants grow through a combination of cell growth and cell division. Cell growth increases cell size. Cell division increases the number of cells. As plant cells grow, they also become specialized into different cell types. Once cells become specialized, they can no longer divide. So how do plants grow after that? The key to continued growth is meristem. Meristem is a type of plant tissue consisting of undifferentiated cells that can continue to divide. Meristem at the tips of roots and stems allows them to grow in length. This is called primary growth. The stem (trunk) of the giant sequoia tree in Figure 10.8 has achieved amazing growth in length during its many years of life. Meristem within and around vascular tissues allows growth in width. This is called secondary growth. The rings in the tree stump in Figure 10.8 show secondary growth in a tree. Each ring represents one year of growth. | text | null |
L_0364 | introduction to plants | T_1931 | Most plants continue to grow throughout their lives. Like other multicellular organisms, plants grow through a combination of cell growth and cell division. Cell growth increases cell size. Cell division increases the number of cells. As plant cells grow, they also become specialized into different cell types. Once cells become specialized, they can no longer divide. So how do plants grow after that? The key to continued growth is meristem. Meristem is a type of plant tissue consisting of undifferentiated cells that can continue to divide. Meristem at the tips of roots and stems allows them to grow in length. This is called primary growth. The stem (trunk) of the giant sequoia tree in Figure 10.8 has achieved amazing growth in length during its many years of life. Meristem within and around vascular tissues allows growth in width. This is called secondary growth. The rings in the tree stump in Figure 10.8 show secondary growth in a tree. Each ring represents one year of growth. | text | null |
L_0364 | introduction to plants | T_1931 | Most plants continue to grow throughout their lives. Like other multicellular organisms, plants grow through a combination of cell growth and cell division. Cell growth increases cell size. Cell division increases the number of cells. As plant cells grow, they also become specialized into different cell types. Once cells become specialized, they can no longer divide. So how do plants grow after that? The key to continued growth is meristem. Meristem is a type of plant tissue consisting of undifferentiated cells that can continue to divide. Meristem at the tips of roots and stems allows them to grow in length. This is called primary growth. The stem (trunk) of the giant sequoia tree in Figure 10.8 has achieved amazing growth in length during its many years of life. Meristem within and around vascular tissues allows growth in width. This is called secondary growth. The rings in the tree stump in Figure 10.8 show secondary growth in a tree. Each ring represents one year of growth. | text | null |
L_0364 | introduction to plants | T_1932 | All plants have a life cycle that includes alternation of generations. You can see a general plant life cycle in Figure MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0364 | introduction to plants | T_1933 | Plants alternate between haploid and diploid generations. Haploid cells have one of each pair of chromosomes. Diploid cells have two of each pair. Plants in the haploid generation are called gametophytes. They form from haploid spores. They have male and/or female reproductive organs and reproduce sexually. They produce haploid gametes by mitosis. Fertilization of gametes produces diploid zygotes. Zygotes develop into the diploid generation. Plants in the diploid generation are called sporophytes. They form from the fertilization of gametes. They reproduce asexually. They have a structure called a sporangium that produces haploid spores by meiosis. Spores develop into the haploid generation. Then the cycle repeats. | text | null |
L_0364 | introduction to plants | T_1934 | One of the two generations of a plants life cycle is usually dominant. Individuals in the dominant generation generally live longer and grow larger. They are the organisms that you would recognize as a fern, tree, or other plant. Individuals in the nondominant generation tend to be smaller and shorter-lived. They often live in or on the dominant plant. They may go unnoticed. Early plants spent most of their life cycle as gametophytes. Some modern plants such as mosses still have this type of life cycle. However, almost all modern plants spend most of their life cycle as sporophytes. | text | null |
L_0365 | evolution and classification of plants | T_1935 | The first plants were probably similar to the stoneworts in Figure 10.11. Stoneworts are green algae. Like stoneworts, the first plants were aquatic. They may have had stalks but not stems. They also may have had hair-like structures called rhizoids but not roots. The first plants probably had male and female reproductive organs and needed water to reproduce. In stoneworts, sperm need at least a thin film of moisture to swim to eggs. | text | null |
L_0365 | evolution and classification of plants | T_1936 | By the time the earliest plants evolved, animals were already the dominant living things in the water. Plants were also limited to the upper layer of water. Only near the top of the water column is there enough sunlight for photosynthesis. So plants never became dominant aquatic organisms. | text | null |
L_0365 | evolution and classification of plants | T_1937 | All that changed when plants moved from water to land. This may have happened by 500 million years ago or even earlier. On land, everything was wide open. There were no other living things. Without plants, there was nothing for other organisms to eat. Land could not be colonized by other organisms until land plants became established. The earliest land plants may have resembled the modern liverworts in Figure 10.12. | text | null |
L_0365 | evolution and classification of plants | T_1938 | Moving to the land was a huge step in plant evolution. Until then, virtually all life had evolved in water. Dry land was a very different kind of place. The biggest problem was the dryness. Simply absorbing enough water to stay alive was a huge challenge. It kept early plants small and low to the ground. Water was also needed for sexual reproduction, so sperm could swim to eggs. There were other hardships on land besides dryness. For example, sunlight on land was strong and dangerous. Solar radiation put land organisms at high risk of mutations. | text | null |
L_0365 | evolution and classification of plants | T_1939 | After they left the water, plants evolved adaptations that helped them withstand the harsh conditions on land. One of the earliest and most important adaptations to evolve was vascular tissue. For a fast-paced introduction to vascular plants and their successes, watch this video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0365 | evolution and classification of plants | T_1940 | Vascular tissue forms a plants "plumbing system." It carries water and dissolved minerals from the soil to all the other cells of the plant. It also carries food (sugar dissolved in water) from photosynthetic cells to other cells in the plant for growth or storage. The evolution of vascular tissue revolutionized the plant kingdom. Vascular tissue greatly improved the ability of plants to absorb and transfer water. This allowed plants to grow larger and taller. They could also liver in drier habitats and survive periods of drought. Early vascular plants probably resembled the fern in Figure 10.13. | text | null |
L_0365 | evolution and classification of plants | T_1941 | Other early adaptations to life on land included the evolution of true leaves and roots. Leaves allowed plants to take better advantage of sunlight for photosynthesis. Roots helped plants absorb water and minerals from soil. Early land plants also evolved a dominant sporophyte generation. Sporophytes are diploid, so they have two copies of each gene. This gives them a "back-up" copy in case of mutation. This was important for coping with the strong solar radiation and higher risk of mutations on land. | text | null |
L_0365 | evolution and classification of plants | T_1942 | With all these adaptations, its easy to see why vascular plants were very successful. They spread quickly and widely on land. As vascular plants spread, many nonvascular plants went extinct. Vascular plants became and remain the dominant land plants on Earth. | text | null |
L_0365 | evolution and classification of plants | T_1943 | Early vascular plants still needed moisture. They needed it in order to reproduce. Sperm had to swim from male to female reproductive organs for fertilization. Even spores needed some water to grow and often to disperse as well. In addition, dryness and other harsh conditions made it very difficult for tiny new offspring plants to survive. With the evolution of seeds in vascular plants, all that changed. Seed plants evolved a number of adaptations that made it possible to reproduce without water. Seeds also nourished and protected tiny new offspring. As a result, seed plants were wildly successful. They exploded into virtually all of Earths habitats. | text | null |
L_0365 | evolution and classification of plants | T_1944 | A seed is a reproductive structure that contains an embryo and a food supply, called endosperm. Both the embryo and endosperm are enclosed within a tough outer coating, called a hull (or shell). You can see these parts of a seed in Figure 10.14. An embryo is a zygote that has already started to develop and grow. Early growth and development of a plant embryo inside a seed is called germination. The seed protects and nourishes the embryo and gives it a huge head start in the "race" of life. Both a parent plant and its offspring are better off if they dont grow too closely together. That way, they will not need to compete for resources. Many seeds have structures that help them travel away from the parent plant. You can see some examples in Figure 10.15. Some seeds can also wait to germinate until conditions are favorable for growth. This increases the offsprings chances of surviving even more. | text | null |
L_0365 | evolution and classification of plants | T_1945 | Seed plants also evolved other reproductive structures. These included ovules, pollen, and pollen tubes. An ovule is a female reproductive structure in seed plants. It contains a tiny female gametophyte. The gametophyte produces an egg cell. After the egg is fertilized by sperm, the ovule develops into a seed. Pollen is a tiny male gametophyte enclosed in a tough capsule. Pollen carries sperm to an ovule while preventing the sperm from drying out. Pollen grains cant swim, but they are very light, so the wind can carry them. Therefore, they can travel through air instead of water. Pollen also evolved the ability to grow a tube, called a pollen tube. Sperm could be transferred through the tube directly from the pollen grain to the egg. This allowed sperm to reach an egg without swimming through a film of water. It finally freed plants from depending on moisture to reproduce. | text | null |
L_0365 | evolution and classification of plants | T_1946 | The first seed plants formed seeds in cones, like the cone in Figure 10.16. Cones are reproductive structures made of overlapping scales. Scales are modified leaves. Male cones contain pollen. Female cones contain eggs. They are also where seeds develop. The seeds in cones are "naked." They arent protected inside an ovary, which was a later adaptation of seed plants. | text | null |
L_0365 | evolution and classification of plants | T_1946 | The first seed plants formed seeds in cones, like the cone in Figure 10.16. Cones are reproductive structures made of overlapping scales. Scales are modified leaves. Male cones contain pollen. Female cones contain eggs. They are also where seeds develop. The seeds in cones are "naked." They arent protected inside an ovary, which was a later adaptation of seed plants. | text | null |
L_0365 | evolution and classification of plants | T_1947 | Some seed plants evolved another major adaptation. This was the formation of seeds in flowers. Flowers are plant structures that contain male and/or female reproductive organs. | text | null |
L_0365 | evolution and classification of plants | T_1948 | You can see the parts of a typical flower in Figure 10.17. The male reproductive organ in a flower is the stamen. It has a stalk-like filament that ends in an anther. The anther is where pollen forms. The female reproductive organ in a flower is the pistil. It consists of a stigma, style, and ovary. The stigma is the top of the pistil. It is sticky to help it "catch" pollen. The style connects the stigma to the ovary. The ovary is where eggs form and seeds develop. As seeds develop, the ovary turns into a fruit. The fruit protects the seeds. It also attracts animals that may eat the fruit and help disperse the seeds. Petals are usually the most visible parts of a flower. They may be large and showy and are often brightly colored. Leaf-like green sepals protect the flower while it is still a bud. | text | null |
L_0365 | evolution and classification of plants | T_1949 | The showy petals of flowers evolved to help attract pollinators. Wind-blown pollen might land just anywhere and be wasted. A pollinator is an animal that picks up pollen on its body and carries it directly to another flower of the same species. This helps ensure that pollination occurs. Pollinators are usually small animals such as bees, butterflies, and bats. You can see an example in Figure 10.18. | text | null |
L_0365 | evolution and classification of plants | T_1950 | The most basic division of modern plants is between nonvascular and vascular plants. Vascular plants are further divided into those that reproduce without seeds and those that reproduce with seeds. Seed plants, in turn, are divided into those that produce naked seeds in cones and those that produce seeds in the ovaries of flowers. | text | null |
L_0365 | evolution and classification of plants | T_1951 | Modern nonvascular plants are called bryophytes. There are about 17,000 bryophyte species. They include liver- worts, hornworts, and mosses. Mosses are the most numerous group of bryophytes. You can see an example of moss in Figure 10.19. Like the moss in the figure, most bryophytes are small. They lack not only vascular tissues. They also lack true roots, leaves, seeds, and flowers. Bryophytes live in moist habitats. Without the adaptations of vascular plants, bryophytes are not very good at absorbing water. They also need water to reproduce. | text | null |
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