Ecology
N Torres Dana Desonie, Ph.D. Douglas Wilkin, Ph.D. Jean Brainard, Ph.D.
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AUTHORS N Torres Dana Desonie, Ph.D. Douglas Wilkin, Ph.D. Jean Brainard, Ph.D.
CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2014 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: March 8, 2014
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Contents
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Contents 1
Introduction to Ecology
1
2
What are Biomes?
4
3
Flow of Energy in Ecosystems
7
4
Food Webs
12
5
Energy Pyramids
15
6
Symbiosis
18
7
Processes of the Water Cycle
21
8
Photosynthesis
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9
Carbon Cycle
30
10 Nitrogen Cycle in Ecosystems
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11 Nitrogen Cycle in Ecosystems
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12 Tropisms
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C HAPTER
Chapter 1. Introduction to Ecology
1
Introduction to Ecology
• Define ecology. • Distinguish between abiotic and biotic factors.
Do organisms live in isolation? No, organisms are not separated from their environment or from other organisms. They interact in many ways with their surroundings. For example, these deer may be drinking from this stream or eating nearby plants. Ecology is the study of these interactions. Introduction to Ecology
Life Science can be studied at many different levels. You can study small things like cells. Or you can study big things like a group of animals. You can also study the biosphere, which is any area in which organisms live. The study of the biosphere is part of ecology, the study of how living organisms interact with each other and with their environment. Research in Ecology
Ecology involves many different fields, including geology, soil science, geography, meteorology, genetics, chemistry, and physics. You can also divide ecology into the study of different organisms, such as animal ecology, plant ecology, insect ecology, and so on. Ecologists also study biomes. A biome is a large community of plants and animals that live in the same place. For example, ecologists can study the biomes as diverse as the Arctic, the tropics, or the desert ( Figure 1.1). They may want to know why different species live in different biomes. They may want to know what would make a particular biome or ecosystem stable. Can you think of other aspects of a biome or ecosystem that ecologists could study? Ecologists do two types of research: 1
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FIGURE 1.1 An example of a biome, the Atacama Desert, in Chile.
1. Field studies. 2. Laboratory studies. Field studies involve collecting data outside in the natural world. An ecologist who completes a field study may travel to a tropical rainforest to study, count, and classify all of the insects that live in a certain area. Laboratory studies involve working inside, usually in a controlled environment. Sometimes, ecologists collect data from the field, and then they analyze that data in the lab. Also, they use computer programs to predict what will happen to organisms that live in a specific area. For example, they may make predictions about what happens to insects in the rainforest after a fire. Organisms and Environments
All organisms have the ability to grow and reproduce. To grow and reproduce, organisms must get materials and energy from the environment. Plants obtain their energy from the sun through photosynthesis, whereas animals obtain their energy from other organisms. Either way, these plants and animals, as well as the bacteria and fungi, are constantly interacting with other species as well as the non-living parts of their ecosystem. An organism’s environment includes two types of factors: 1. Abiotic factors are the parts of the environment that are not living, such as sunlight, climate, soil, water, and air. 2. Biotic factors are the parts of the environment that are alive, or were alive and then died, such as plants, animals, and their remains. Biotic factors also include bacteria, fungi and protists. Ecology studies the interactions between biotic factors, such as organisms like plants and animals, and abiotic factors. For example, all animals (biotic factors) breathe in oxygen (abiotic factor). All plants (biotic factor) absorb carbon dioxide (abiotic factor) and need water (abiotic factor) to survive. Can you think of another way that abiotic and biotic factors interact with each other? Vocabulary
• abiotic factor: Aspect of the environment that is not a living organism, such as soil, water or air. 2
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Chapter 1. Introduction to Ecology
• biome: Large community of plants and animals distinguished by the dominant forms of animal and plant life and the climate. • biotic factor: Components of the environment that are living, or were alive and then died, such as plants or animals. • biosphere: Part of the planet and atmosphere with living organisms. • ecology: Study of how living organisms interact with each other and with their environment. • photosynthesis: Process by which specific organisms (including all plants) use the sun’s energy to make their own food from carbon dioxide and water; process that converts the energy of the sun, or solar energy, into carbohydrates, a type of chemical energy. Summary
• Ecology is the study of how living organisms interact with each other and with their environment. • Abiotic factors are the parts of the environment that have never been alive, while biotic factors are the parts of the environment that are alive, or were alive and then died. Practice
Use the resource below to answer the questions that follow. • A Study in Stream Ecology at USGS http://gallery.usgs.gov/videos/449#.UKWeJId9KSo (6:57)
MEDIA Click image to the left for more content.
1. What are some of the abiotic factors that scientists monitor when dealing with stream ecosystems? 2. What are some of the biotic factors that scientists monitor when dealing with stream ecosystems? 3. Remembering what you’ve learned about the scientific process, why is it valuable for scientists to use the same procedures and gather the same information across different streams and a wide ranging geography? What does this allow them to do? How does this affect the strength and applicability of their research? 4. What is a "benchmark" in ecology? Why are they essential? 5. Why is it important to have a reference stream if you want to gauge the effects of Homo sapiens on streams? What characteristics should this reference stream have? 6. How does water pollution seem to be affecting diversity in some streams? What data would be necessary to prove the pollution is the causative agent affecting stream biodiversity? Review
1. What do ecologists study? 2. In a forest, what are some biotic factors present? Abiotic factors?
References 1. Courtesy of NASA. . Public Domain 3
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C HAPTER
2
What are Biomes?
• Define biome and describe how they are classified.
Where was this picture taken? This scene is from Anza-Borrago California Desert Park. However, deserts exist around the globe. You might find a similar picture of a desert in Africa. The desert is one type of biome. What are Biomes?
Tropical rainforests and deserts are two familiar types of biomes. A biome is an area with similar populations of organisms. This can easily be seen with a community of plants and animals. Remember that a community is all of the populations of different species that live in the same area and interact with one another. Different biomes, such as a forest ( Figure 2.1) or a desert, obviously have different communities of plants and animals. How are the plants and animals different in the rainforest than those in the desert? Why do you think they are so different? The differences in the biomes are due to differences in the abiotic factors, especially climate. Climate is the typical weather in an area over a long period of time. The climate includes the amount of rainfall and the average temperature in the region. Obviously, the climate in the desert is much different than the climate in the rainforest. As a result, different types of plants and animals live in each biome. There are into two major groups of biomes: 1. Terrestrial biomes, which are land-based, such as deserts and forests. 2. Aquatic biomes, which are water-based, such as ponds and lakes. The abiotic factors, such as the amount of rainfall and the temperature, are going to influence other abiotic factors, such as the quality of the soil. This, in turn, is going to influence the plants that migrate into the ecosystem and thrive in that biome. Recall that migration is the movement of an organism into or out of a population. It can also refer to 4
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Chapter 2. What are Biomes?
FIGURE 2.1 Tropical rainforest landscape in Hawaii. Notice how the plants are different from those in the desert.
a whole new species moving into a habitat. The type of plants that live in a biome are going to attract a certain type of animal to that habitat. It is the interaction of the abiotic and biotic factors that describe a biome and ecosystem. In aquatic biomes, abiotic factors such as salt, sunlight and temperature play significant roles. For example, a hot dry biome is going to be completely different from a moderate wet biome. The soil quality will be different. Together, these will result in different plants being able to occupy each biome. Different plants will attract different animals (herbivores) to eat these plants. These animals, in turn, will attract different (carnivores) animals to eat the herbivores. So it is the abiotic factors that determine the biotic factors of an ecosystem, and together these define the biome. Vocabulary
• • • • • • • •
abiotic factor: Nonliving aspect of the environment. aquatic biome: Biome that is based in the water, such as ponds, lakes, streams, or oceans. biome: Area with similar climate that includes similar communities of plants and animals. biotic factor: Living aspects of the environment. climate: Typical weather in an area over a long period of time. habitat: Ecological or environmental area in which a particular species live. migration: Movement of individual organisms into, or out of, a population. terrestrial biome: Biome that is based on land, such as a desert or rainforest.
Summary
• A biome is an area with similar climate that includes similar communities of plants and animals. • Climate influences the types of plants and animals that inhabit a specific biome. Practice
Use the resources below to answer the questions that follow. • Biomes at http://www.youtube.com/watch?v=ag5ATGEplbU (7:50)
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MEDIA Click image to the left for more content.
1. Where do tundra biomes primarily occur? How much precipitation do these areas see annually? 2. What areas are best known for having Taiga biomes? What is the temperature range this biome experiences? 3. What is a behavioral adaptation that animals in desert biomes display? • Earth’s Biomes at http://www.forgefx.com/casestudies/prenticehall/ph/biomes/biomes.htm 1. How many months a year is the temperature in La Paz, Bolivia above 15C? How many months a year is it below 5C? What kind of biome is it located in? 2. How many months a year is the temperature in Quebec, Canada above 15C? How many months a year is it below 5C? What kind of biome is it located in? 3. How many months a year does Quillayute, WA, USA receive more than 30cm of precipitation? How many months a year does it receive less than 5cm of precipitation? What kind of biome is it located in? 4. How many months a year does Cairo, Egypt receive more than 30cm of precipitation? How many months a year does it receive less than 5cm of precipitation? What kind of biome is it located in? 5. How many months a year does Jakarta, Indonesia receive more than 30cm of precipitation? How many months a year does it receive less than 5cm of precipitation? What kind of biome is it located in? Review
1. What is a biome? 2. Give two examples of terrestrial biomes.
References 1. daveynin. . CC BY 2.0
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C HAPTER
Chapter 3. Flow of Energy in Ecosystems
3
Flow of Energy in Ecosystems
• Define trophic levels. • Compare and contrast food chains and webs. • Explain how energy flows through ecosystems.
What is the source of energy for almost all ecosystems? The Sun supports most of Earth’s ecosystems. Plants create chemical energy from abiotic factors that include solar energy. Chemosynthesizing bacteria create usable chemical energy from unusable chemical energy. The food energy created by producers is passed to consumers, scavengers, and decomposers. Trophic Levels
Energy flows through an ecosystem in only one direction. Energy is passed from organisms at one trophic level or energy level to organisms in the next trophic level. Which organisms do you think are at the first trophic level ( Figure 3.1)? Most of the energy at a trophic level –about 90% –is used at that trophic level. Organisms need it for locomotion, heating themselves, and reproduction. So animals at the second trophic level have only about 10% as much energy available to them as do organisms at the first trophic level. Animals at the third level have only 10% as much available to them as those at the second level. Food Chains
The set of organisms that pass energy from one trophic level to the next is described as the food chain ( Figure 3.2). In this simple depiction, all organisms eat at only one trophic level ( Figure 3.3). What are the consequences of the loss of energy at each trophic level? Each trophic level can support fewer organisms. 7
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FIGURE 3.1 Producers are always the first trophic level, herbivores the second, the carnivores that eat herbivores the third, and so on.
FIGURE 3.2 A simple food chain in a lake. The producers, algae, are not shown. For the predatory bird at the top, how much of the original energy is left?
What does this mean for the range of the osprey (or lion, or other top predator)? A top predator must have a very large range in which to hunt so that it can get enough energy to live. Why do most food chains have only four or five trophic levels? There is not enough energy to support organisms in a sixth trophic level. Food chains of ocean animals are longer than those of land-based animals because ocean conditions are more stable. Why do organisms at higher trophic levels tend to be larger than those at lower levels? The reason for this is simple: a large fish must be able to eat a small fish, but the small fish does not have to be able to eat the large fish ( Figure 3.4). 8
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Chapter 3. Flow of Energy in Ecosystems
FIGURE 3.3 How many osprey are there relative to the number of shrimp?
FIGURE 3.4 In this image the predators (wolves) are smaller than the prey (bison), which goes against the rule placed above. How does this relationship work? Many wolves are acting together to take down the bison.
Food Webs
What is a more accurate way to depict the passage of energy in an ecosystem? A food web ( Figure 3.5) recognizes that many organisms eat at multiple trophic levels. Even food webs are interconnected. All organisms depend on two global food webs. The base of one is phytoplankton and the other is land plants. How are these two webs interconnected? Birds or bears that live on land may eat fish, which connects the two food webs. 9
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FIGURE 3.5 A food web includes the relationships between producers, consumers, and decomposers.
Humans are an important part of both of these food webs; we are at the top of a food web, since nothing eats us. That means that we are top predators. Summary
• A food chain describes the passage of energy between trophic levels. • A food web is a set of interconnected and overlapping food chains. • Food webs are interconnected, such as nearby land and a marine food webs. Making Connections
MEDIA Click image to the left for more content.
Practice
Use this resource to answer the questions that follow. http://www.youtube.com/watch?v=o_RBHfjZsUQ
MEDIA Click image to the left for more content.
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Chapter 3. Flow of Energy in Ecosystems
1. What do all organisms require? 2. What provides the energy required by the ecosystem? 3. How is energy transferred from one organism to another? 4. How is some of the energy lost? 5. How do nutrients move through and ecosystem? Review
1. What does a food chain depict? Why do scientists usually use a food web instead of a food chain? 2. Start with the Sun and describe what happens to energy through the trophic levels. Why does this not go on forever (with many more trophic levels)? 3. What trophic level do you inhabit? Do all humans inhabit the same trophic level?
References 1. Images of lion and landscape copyright by Eric Isselée, 2010; image of giraffe copyright Kletr, 2010; composite created by CK-12 Foundation. . Used under licenses from Shutterstock.com 2. Images from Nordisk familjebok, modified by CK-12 Foundation. . Public Domain 3. LeoNomis. . Public Domain 4. Courtesy of Doug Smith, National Park Service. . Public Domain 5. Fox and rat images copyright Shutterstock.com, 2010; Puffin image copyright Tomica Ristic, 2010; Salmon image copyright Shutterstock.com; Cephalopod image copyright kittasgraphics, 2010; Auklet image copyright Rozhkovs, 2010; Gull image copyright Potapov Alexander, 2010; Background and sun image copyright mirabile, 2010. . Images used under licenses from Shutterstock.com
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C HAPTER
4
Food Webs
• Define a food web. • Be able to draw and interpret a food web.
How do the grasshopper and the grass interact? Grasshoppers don’t just hop on the grass. They also eat the grass. Other organisms also eat the grass, and some animals even eat the grasshopper. These interactions can be visualized by drawing a food web. Food Webs
Energy must constantly flow through an ecosystem for the system to remain stable. What exactly does this mean? Essentially, it means that organisms must eat other organisms. Food chains ( Figure 4.1) show the eating patterns in an ecosystem. Food energy flows from one organism to another. Arrows are used to show the feeding relationship between the animals. The arrow points from the organism being eaten to the organism that eats it. For example, an arrow from leaves to a grasshopper shows that the grasshopper eats the leaves. Energy and nutrients are moving from the leaves to the grasshopper. Next, a frog might prey on the grasshopper, a snake may eat the frog, and then a hawk might eat the snake. The food chain would be: leaves → grasshopper → frog → snake → hawk. A food chain cannot continue to go on and on. For example the food chain could not be: leaves → caterpillar → spider → frog → lizard → fox → hawk. Food chains only have 4 or 5 total levels. Therefore, a chain has only 3 or 4 levels for energy transfer. 12
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Chapter 4. Food Webs
FIGURE 4.1 This food chain includes producers and consumers. How could you add decomposers to the food chain?
In an ocean ecosystem, one possible food chain might look like this: phytoplankton → krill → fish → shark. The producers are always at the beginning of the food chain, bringing energy into the ecosystem. Through photosynthesis, the producers create their own food in the form of glucose, but also create the food for the other organisms in the ecosystem. The herbivores come next, then the carnivores. When these consumers eat other organisms, they use the glucose in those organisms for energy. In this example, phytoplankton are eaten by krill, which are tiny, shrimp-like animals. The krill are eaten by fish, which are then eaten by sharks. Could decomposers be added to a food chain? Each organism can eat and be eaten by many different types of organisms, so simple food chains are rare in nature. There are also many different species of fish and sharks. So a food chain cannot end with a shark; it must end with a distinct species of shark. A food chain does not contain the general category of "fish," it will contain specific species of fish. In ecosystems, there are many food chains. Since feeding relationships are so complicated, we can combine food chains together to create a more accurate flow of energy within an ecosystem. A food web ( Figure 4.2) shows the feeding relationships between many organisms in an ecosystem. If you expand our original example of a food chain, you could add deer that eat clover and foxes that hunt chipmunks. A food web shows many more arrows, but still shows the flow of energy. A complete food web may show hundreds of different feeding relationships.
FIGURE 4.2 Food web in the Arctic Ocean.
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www.ck12.org Vocabulary
• carnivore: Organism that feeds on other animals. • consumer: Organism that must consume other organisms to obtain food for energy. • decomposer: Organism that obtains nutrients and energy by breaking down dead organisms and animal wastes. • food chain: Diagram that shows feeding interactions in an ecosystem through a single pathway. • food web: Diagram that shows feeding interactions between many organisms in an ecosystem through multiple intersecting pathways. • herbivore: Animal that eats producers to obtain energy. • producer: Organism that produces food for itself and other organisms. Summary
• A food chain is a diagram that shows feeding interactions in an ecosystem through a single pathway. • A food web is a diagram that shows feeding interactions between many organisms in an ecosystem through multiple intersecting pathways. Practice
Use the resource below to answer the questions that follow. • Build A Food Web at http://www.sciencesource2.ca/resources/SS_active_art/active_art/SEinteractive_gr09_c h01_pg31/index.html 1. 2. 3. 4.
What do the Loons and Arctic Tern have in common in the food web? What do the Beluga and the sea duck have in common in the food web? What species in the food web feed on zooplankton (animal plankton)? When you build your own food web what must it contain to be healthy? How many healthy food webs could you build?
Review
1. What is the difference between a food chain and a food web? 2. What is the herbivore in the following food chain: algae ->fish ->herons?
References 1. Flower image copyright Laurent Renault, 2010; caterpillar image copyright ngstyle, 2010; frog image copyright zaharch, 2010; snake image copyright ananas, 2010; tree image copyright sabri deniz kizil, 2010; composite created by CK-12 Foundation. . Used under licenses from Shutterstock.com 2. CK-12 Foundation. . CC-BY-NC-SA 3.0
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C HAPTER
Chapter 5. Energy Pyramids
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Energy Pyramids
• Define energy pyramids. • Explain the flow of energy through an ecosystem using an energy pyramid.
How much energy could be gained from the warthog? If the cheetah is successful in capturing the warthog, he would gain some energy by eating it. But would the cheetah gain as much energy as the warthog has ever consumed? No, the warthog has used up some of the energy it has consumed for its own needs. The cheetah will only gain a fraction of the energy that the warthog has consumed throughout its lifetime. Energy Pyramids
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 herbivore’s 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 5.1). 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 5.1) 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. 15
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FIGURE 5.1 As illustrated by this ecological pyramid, it takes a lot of phytoplankton to support the carnivores of the oceans.
Vocabulary
• ATP: Adenosine triphosphate; a molecule containing a large amount of energy that can be used for many metabolic processes in the cell. • autotroph: Organism that produces complex organic compounds from simple inorganic molecules using a source of energy such as sunlight. • cellular respiration: Process of breaking down glucose to obtain energy in the form of ATP. • energy: Ability to do work. • energy pyramid: Diagram showing how energy decreases from lower to higher trophic levels. • heterotroph: Organism which obtains carbon from outside sources. • producer: Organism that produces food (glucose) for itself and other organisms. • trophic level: Feeding position in a food chain.
Summary
• As energy is transferred along a food chain, energy is lost as heat. • Only about 10% of energy of one step in a food chain is stored in the next step in the food chain.
Practice
Use the resource below to answer the questions that follow. • Ecological Pyramids at http://www.youtube.com/watch?v=NJplkrliUEg (4:03)
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Chapter 5. Energy Pyramids
MEDIA Click image to the left for more content.
1. What are three types of ecological pyramids? How do their shapes compare? 2. Do you think it would be possible to construct a pyramid where the number of carnivores was more than the number of herbivores? Think carefully about the different possibilities. 3. Do you think it would be possible to construct a pyramid where the biomass of carnivores was more than the biomass of herbivores? How does this compare to a numbers pyramid. 4. What consumes energy at each trophic level? How does this contribute to energy loss between trophic levels? 5. What do you think you could learn about an ecosystem by comparing three different types of pyramids for an ecosystem? How is this information different than the information you could gain from looking at a single pyramid? Review
1. When an herbivore eats a plant, what happens to 90% of the energy obtained from that plant? 2. In a forest community, caterpillars eat leaves, and birds eat caterpillars. Draw an energy pyramid using this information.
References 1. CK-12 Foundation. . CC-BY-NC-SA 3.0
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C HAPTER
6
Symbiosis
• Compare and contrast mutualism, commensalism, and parasitism.
Do interactions between species always result in harm? A commensal shrimp on another sea organism, possibly a sea cucumber. As commensal shrimp they neither bring a benefit nor have a negative effect on their host. Symbiotic Relationships
Symbiosis is a close relationship between two species in which at least one species benefits. For the other species, the relationship may be positive, negative, or neutral. There are three basic types of symbiosis: mutualism, commensalism, and parasitism. Mutualism
Mutualism is a symbiotic relationship in which both species benefit. An example of mutualism involves goby fish and shrimp (see Figure 6.1). The nearly blind shrimp and the fish spend most of their time together. The shrimp 18
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Chapter 6. Symbiosis
maintains a burrow in the sand in which both the fish and shrimp live. When a predator comes near, the fish touches the shrimp with its tail as a warning. Then, both fish and shrimp retreat to the burrow until the predator is gone. From their relationship, the shrimp gets a warning of approaching danger. The fish gets a safe retreat and a place to lay its eggs.
FIGURE 6.1 The multicolored shrimp in the front and the green goby fish behind it have a mutualistic relationship.
Commensalism
Commensalism is a symbiotic relationship in which one species benefits while the other species is not affected. One species typically uses the other for a purpose other than food. For example, mites attach themselves to larger flying insects to get a “free ride.” Hermit crabs use the shells of dead snails for homes.
Parasitism
Parasitism is a symbiotic relationship in which one species (the parasite) benefits while the other species (the host) is harmed. Many species of animals are parasites, at least during some stage of their life. Most species are also hosts to one or more parasites. Some parasites live on the surface of their host. Others live inside their host. They may enter the host through a break in the skin or in food or water. For example, roundworms are parasites of mammals, including humans, cats, and dogs (see Figure 6.2). The worms produce huge numbers of eggs, which are passed in the host’s feces to the environment. Other individuals may be infected by swallowing the eggs in contaminated food or water. Some parasites kill their host, but most do not. It’s easy to see why. If a parasite kills its host, the parasite is also likely to die. Instead, parasites usually cause relatively minor damage to their host. Summary
• • • •
Symbiosis is a close relationship between two species in which at least one species benefits. Mutualism is a symbiotic relationship in which both species benefit. Commensalism is a symbiotic relationship in which one species benefits while the other species is not affected. Parasitism is a symbiotic relationship in which one species (the parasite) benefits while the other species (the host) is harmed. 19
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FIGURE 6.2 Canine Roundworm.
The roundworm
above, found in a puppy’s intestine, might eventually fill a dog’s intestine unless it gets medical treatment.
Practice
Use this resource to answer the questions that follow. • http://www.hippocampus.org/Biology → Non-Majors Biology → Search: Interactions Within Communities 1. 2. 3. 4.
What are the three types of symbiotic relationships? Describe the three symbiotic relationships. Describe an example of a symbiotic relationship involving humans. Describe a symbiotic relationship involving plants and bacteria.
Review
1. Define mutualism and commensalism. 2. Explain why most parasites do not kill their host. Why is it in their own best interest to keep their host alive?
References 1. Haplochromis. . CC-BY-SA 3.0 2. Joel Mills. . CC-BY-SA 2.5
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C HAPTER
Chapter 7. Processes of the Water Cycle
7
Processes of the Water Cycle
• Describe the water cycle and describe the processes that carry water between reservoirs. • Define the processes by which water changes state and explain the role each plays in the water cycle.
Where have these water molecules been? Because of the unique properties of water, water molecules can cycle through almost anywhere on Earth. The water molecule found in your glass of water today could have erupted from a volcano early in Earth’s history. In the 21
www.ck12.org intervening billions of years, the molecule probably spent time in a glacier or far below the ground. The molecule surely was high up in the atmosphere and maybe deep in the belly of a dinosaur. Where will that water molecule go next? The Water Cycle
The movement of water around Earth’s surface is the hydrological (water) cycle ( Figure 7.1). 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.
FIGURE 7.1 Because it is a cycle, the water cycle has no beginning and no end.
Solar Energy
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. Oceans
Most of Earth’s water is stored in the oceans, where it can remain for hundreds or thousands of years. Atmosphere
Water changes from a liquid to a gas by evaporation to become water vapor. The Sun’s 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 22
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Chapter 7. Processes of the Water Cycle
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. For a little fun, watch this video. This water cycle song focuses on the role of the sun in moving H2 O from one reservoir to another. The movement of all sorts of matter between reservoirs depends on Earth’s internal or external sources of energy (7c): http://www.youtube.com/watch?v=Zx_1g5pGFLI&feature=related (2:38).
MEDIA Click image to the left for more content.
This animation shows the annual cycle of monthly mean precipitation around the world: http://en.wikipedia.org/ wiki/File:MeanMonthlyP.gif . Streams and Lakes
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. Soil
A significant amount of water infiltrates into the ground. Soil moisture is an important reservoir for water ( Figure 7.2). Water trapped in soil is important for plants to grow. Groundwater
Water may seep through dirt and rock below the soil and then through pores infiltrating the ground to go into Earth’s 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. Biosphere
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 7.3), a process known as transpiration. An online guide to the hydrologic cycle from the University of Illinois is found here: http://ww2010.atmos.uiuc.edu /%28Gh%29/guides/mtr/hyd/home.rxml . How the water cycle works and how rising global temperatures will affect the water cycle, especially in California, are the topics of this Quest video. 23
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FIGURE 7.2 The moisture content of soil in the United States varies greatly.
FIGURE 7.3 Clouds form above the Amazon Rainforest even in the dry season because of moisture from plant transpiration.
Watch it at http://www.kqed.org/quest/television/tracking-raindrops/.
MEDIA Click image to the left for more content.
Human Uses
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 7.4). 24
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Chapter 7. Processes of the Water Cycle
FIGURE 7.4 Pont du Gard in France is an ancient aqueduct and bridge that was part of of a well-developed system that supplied water around the Roman empire.
Summary
• The water cycle describes all of the reservoirs of water and the processes that carry it between them. • Water changes state by evaporation, condensation, and sublimation. • Plants release water through their leaves by transpiration. Practice
Use this resource to answer the questions that follow. http://www.hippocampus.org/Earth%20Science → Environmental Science → Search: Water Cycle 1. What is condensation? 2. List the types of precipitation. 3. What is infiltration? 4. What is surface runoff? 5. Explain what happens with groundwater. 6. Explain the difference between evaporation and transpiration. Review
1. What is transpiration? 2. Describe when and how sublimation occurs. 3. What is the role of the major reservoirs in the water cycle?
References 1. Courtesy of US Geological Survey. . Public Domain 25
www.ck12.org 2. Courtesy of NASA’s Earth Observatory. . Public Domain 3. Courtesy of Jeff Schmaltz/NASA’s Earth Observatory. . Public Domain 4. Filip Fuxa. . Used under license from Shutterstock.com
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C HAPTER
Chapter 8. Photosynthesis
8
Photosynthesis
• Explain the role of the leaf in photosynthesis.
Oxygen —the oxygen that we breath —is just a waste product of what reaction? Every split second that sunlight hits that leaf, photosynthesis is initiated, bringing energy into the ecosystem. It could be said that this is one of the most important - if not the absolutely most important - biochemical reactions. And it all starts with the leaf. Factories for Photosynthesis
Photosynthesis is the process that uses energy from the sun, together with carbon dioxide and water, to make glucose and oxygen. The primary role of photosynthesis is to make the carbohydrate, suggesting that oxygen, which is released back into the atmosphere, is just a waste product. You can think of a single leaf as a photosynthesis factory. A factory has specialized machines to produce a product. It’s also connected to a transportation system that supplies it with raw materials and carries away the finished product. In all these ways, a leaf resembles a factory. The cross section of a leaf in Figure 8.1 lets you look inside a leaf “factory.” A leaf consists of several different kinds of specialized tissues that work together to make food by photosynthesis. The major tissues are mesophyll, veins, and epidermis. • Mesophyll makes up most of the leaf’s interior. This is where photosynthesis occurs. Mesophyll consists mainly of parenchymal cells with chloroplasts. • Veins are made primarily of xylem and phloem. They transport water and minerals to the cells of leaves and carry away dissolved sugar. 27
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FIGURE 8.1 There’s more to a leaf than meets the eye. Can you identify the functions of each of the labeled structures in the diagram?
• The epidermis of the leaf consists of a single layer of tightly-packed dermal cells. They secrete waxy cuticle to prevent evaporation of water from the leaf. The epidermis has tiny pores called stomata (singular, stoma) that control transpiration and gas exchange with the air. For photosynthesis, stomata must control the transpiration of water vapor and the exchange of carbon dioxide and oxygen. Stomata are flanked by guard cells that swell or shrink by taking in or losing water through osmosis. When they do, they open or close the stomata (see Figure 8.2).
Summary
• Specialized cells and tissues in leaves work together to perform photosynthesis. Practice
Use this resource to answer the questions that follow. • http://www.hippocampus.org/Biology → Non-Majors Biology → Search: Photosynthetic Structures 1. 2. 3. 4. 5. 28
Describe the role of the leaf in photosynthesis. Why do leaves have veins? What is the purpose of stomata? Why is the size and shape of the leaf important? What is the main role of the chloroplast?
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Chapter 8. Photosynthesis
FIGURE 8.2 For photosynthesis, stomata must control the transpiration of water vapor and the exchange of carbon dioxide and oxygen. Stomata are flanked by guard cells that swell or shrink by taking in or losing water through osmosis.
When they do, they
open or close the stomata.
Review
1. Explain how a leaf is like a factory. 2. Explain the role of stomata during photosynthesis.
References 1. H McKenna, modified by CK-12 Foundation. . CC-BY-SA-2.5 2. CK-12 Foundation. . CC-BY-NC-SA 3.0
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C HAPTER
9
Carbon Cycle
• Give an overview of the carbon cycle.
How could releasing this much pollution into the atmosphere not be a poor idea? Burning of fossil fuels, such as oil, releases carbon into the atmosphere. This carbon must be cycled - removed from the atmosphere - back into living organisms, or it stays in the atmosphere. Increased carbon in the atmosphere contributes to the greenhouse effect on Earth. The Carbon Cycle
Flowing water can slowly dissolve carbon in sedimentary rock. Most of this carbon ends up in the ocean. The deep ocean can store carbon for thousands of years or more. Sedimentary rock and the ocean are major reservoirs of stored carbon. Carbon is also stored for varying lengths of time in the atmosphere, in living organisms, and as fossil fuel deposits. These are all parts of the carbon cycle, which is shown in Figure 9.1. The carbon cycle is discussed in the following video: http://www.youtube.com/watch?v=0Vwa6qtEih8 (1:56). Carbon in the Atmosphere
Though carbon can be found in ocean water, rocks and sediment and other parts of the biosphere, the atmosphere may be the most recognizable reservoir of carbon. Carbon occurs in various forms in different parts of the carbon cycle. Some of the different forms in which carbon appears are described in Table 9.1.
TABLE 9.1: Form of Carbon Carbon Dioxide Carbonic Acid 30
Chemical Formula CO2 H2 CO3
State Gas Liquid
Main Reservoir Atmosphere Ocean
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Chapter 9. Carbon Cycle
TABLE 9.1: (continued) Form of Carbon Bicarbonate Ion Organic Compounds
Other Carbon Compounds
Chemical Formula HCO3 − Examples: C6 H12 O6 (Glucose), CH4 (Methane) Examples: CaCO3 (Calcium Carbonate), CaMg(CO3 )2 (Calcium Magnesium Carbonate)
State Liquid(dissolved ion) Solid Gas
Main Reservoir Ocean Biosphere Organic Sediments (Fossil Fuels)
Solid Solid
Sedimentary Rock, Shells, Sedimentary Rock
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FIGURE 9.1 The Carbon Cycle. Carbon moves from one reservoir to another in the carbon cycle. What role do organisms play in this cycle?
KEY: C = Carbon, O = Oxygen, H = Hydrogen Carbon in Carbon Dioxide
Carbon cycles quickly between organisms and the atmosphere. In the atmosphere, carbon exists primarily as carbon dioxide (CO2 ). Carbon dioxide cycles through the atmosphere by several different processes, including those listed below. • • • • • • • • •
Living organisms release carbon dioxide as a byproduct of cellular respiration. Photosynthesis removes carbon dioxide from the atmosphere and uses it to make organic compounds. Carbon dioxide is given off when dead organisms and other organic materials decompose. Burning organic material, such as fossil fuels, releases carbon dioxide. Carbon cycles far more slowly through geological processes such as sedimentation. Carbon may be stored in sedimentary rock for millions of years. When volcanoes erupt, they give off carbon dioxide that is stored in the mantle. Carbon dioxide is released when limestone is heated during the production of cement. Ocean water releases dissolved carbon dioxide into the atmosphere when water temperature rises. Carbon dioxide is also removed when ocean water cools and dissolves more carbon dioxide from the air.
Because of human activities, there is more carbon dioxide in the atmosphere today than in the past hundreds of thousands of years. Burning fossil fuels and producing concrete has released great quantities of carbon dioxide into the atmosphere. Cutting forests and clearing land has also increased carbon dioxide into the atmosphere because these activities reduce the number of autotrophic organisms that use up carbon dioxide in photosynthesis. In addition, clearing often involves burning, which releases carbon dioxide that was previously stored in autotrophs. Summary
• Carbon must be recycled through living organisms or it stays in the atmosphere. • Carbon cycles quickly between organisms and the atmosphere. • Due to human activities, there is more carbon dioxide in the atmosphere today than in the past hundreds of thousands of years. 32
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Chapter 9. Carbon Cycle
Practice I
Use these resources to answer the questions that follow. • http://www.hippocampus.org/Earth Science → Environmental Science → Search: Carbon Cycle 1. Describe the role of each of the following in the carbon cycle: a. b. c. d. e. f. g. h.
photosynthesis respiration diffusion decomposition combustion sedimentation volcanism weathering
• http://www.hippocampus.org/Biology → Biology for AP* → Search: The Carbon Cycle 1. 2. 3. 4. 5. 6. 7.
What is the role of carbon in organic compounds? How is carbon used in primary producers? How is CO2 returned to the atmosphere by living organisms? How much CO2 is removed from the atmosphere by plants? What are fossil fuels? How are they formed? What is CaCO3 ? What is its role in the carbon cycle? Why is the amount of atmospheric CO2 lowest during the Northern Hemisphere summer?
Practice II
• Label the Diagram of Carbon Cycle at http://www.neok12.com/diagram/Carbon-Cycle-01.htm . Review
1. What is the role of the carbon cycle. 2. Why is cycling carbon important? 3. Describe a major method that carbon is cycled.
References 1. CK-12 Foundation. . CC-BY-NC-SA 3.0
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C HAPTER
10
Nitrogen Cycle in Ecosystems
• Describe nitrogen’s roles as a nutrient. • Define nitrogen fixation and explain how it occurs.
Lentils, anyone? Why are legumes important to biological cycles? Nitrogen gas, as found in the atmosphere, is not useful to organisms. Legumes have bacteria in their root nodules that fix nitrogen. Putting legumes into a crop rotation reduces fertilizer costs and makes the soil and the crops healthier. Nitrogen as a Nutrient
Nitrogen (N2 ) is vital for life on Earth as an essential component of organic materials, such as amino acids, chlorophyll, and nucleic acids such as DNA and RNA. ( Figure 10.1). Chlorophyll molecules, essential for photosynthesis, contain nitrogen. Nitrogen Fixing
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 10.2). 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 34
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Chapter 10. Nitrogen Cycle in Ecosystems
FIGURE 10.1 (a) Nucleic acids contain nitrogen (b) Chlorophyll molecules contain nitrogen
FIGURE 10.2 The nitrogen cycle.
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www.ck12.org 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.
Up the Food Chain
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. This very thorough video on the nitrogen cycle with an aquatic perspective was created by high school students: http ://www.youtube.com/watch?v=pdY4I-EaqJA&feature=related (5:08).
MEDIA Click image to the left for more content.
Summary
• Nitrogen is an essential component of many organic molecules. • Nitrogen is fixed when it is changed into a form that organisms can use. • Bacteria and some fungi fix organic nitrogen into ammonia and nitrifying bacteria oxidize it to nitrates.
Practice
Use this resource to answer the questions that follow. http://www.youtube.com/watch?v=ZCogeBk92NA
MEDIA Click image to the left for more content.
1. What percentage of the air is nitrogen? 2. How is nitrogen removed from the air? 3. What contributes nitrogen to the soil? 4. What happens to soil nitrates? 5. How is nitrogen released from the soil? 36
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Chapter 10. Nitrogen Cycle in Ecosystems
Review
1. Describe how nitrogen is fixed. 2. Why are legumes important as nitrogen fixers? 3. How is nitrogen fixed in an aquatic environment?
References 1. (a) Madeleine Price Ball; (b) Slashme. . (a) CC-BY-SA 2.5; (b) Public Domain 2. CK-12 Foundation. . CC-BY-NC-SA 3.0
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C HAPTER
11
Nitrogen Cycle in Ecosystems
• Describe nitrogen’s roles as a nutrient. • Define nitrogen fixation, and explain how it occurs.
Why are these fish dead? In a dead zone, there is so little oxygen that fish can’t live. What causes the oxygen to disappear? Indirectly, it’s nitrogen. The Nitrogen Cycle
Living things need nitrogen. Nitrogen is a key element in proteins. Like carbon, nitrogen cycles through ecosystems. The nitrogen cycle is pictured below ( Figure 11.1). Fixing Nitrogen
Air is about 78 percent nitrogen. Decomposers release nitrogen into the air from dead organisms and their wastes. However, producers such as plants can’t 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. It’s called “fixing” nitrogen. Human Actions and the Nitrogen Cycle
Nitrogen is one of the most important nutrients needed by plants. That’s 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? 38
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Chapter 11. Nitrogen Cycle in Ecosystems
FIGURE 11.1 The nitrogen cycle includes air, soil, and living things.
Rain dissolves fertilizer in the soil. Runoff carries it away. The fertilizer ends up in bodies of water, from ponds to oceans. Nitrogen is a fertilizer in the water. Since there is a lot of nitrogen, it causes algae to grow out of control. Pictured below is a pond covered with algae ( Figure 11.2). 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 ( Figure 11.2). The U.S. states outlined on the map have rivers that drain into the Gulf of Mexico. The rivers drain vast agricultural lands. The water carries fertilizer from these areas into the Gulf. This very thorough video on the nitrogen cycle with an aquatic perspective was created by high school students: http ://www.youtube.com/watch?v=pdY4I-EaqJA (5:08).
MEDIA Click image to the left for more content.
Vocabulary
• dead zone: Zone in an ocean or lake where organisms cannot live because there is little or no oxygen. • nitrogen cycle: Movement of nitrogen through the atmosphere, soil, and biosphere. 39
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FIGURE 11.2 The pond on the left is covered with algae because there is too much nitrogen in the water. The red-shaded area in the map on the right is a dead zone in the Gulf of Mexico. It’s called the hypoxic (“low oxygen”) zone in the figure.
Summary
• Nitrogen is an essential part of many molecules needed by living organisms. • Nitrogen is fixed when it is changed into a form that organisms can use. • Dead zones come about when excess nitrogen in the water causes algae to grow out of control. Decomposers use oxygen to decompose the algae when they die. The lack of oxygen makes it impossible for other organisms to live in that zone. Practice
Use the resource below to answer the questions that follow. • The Nitrogen Cycle at http://www.youtube.com/watch?v=ZCogeBk92NA (1:12)
MEDIA Click image to the left for more content.
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Chapter 11. Nitrogen Cycle in Ecosystems
What percentage of the air is nitrogen? How is nitrogen removed from the air? What contributes nitrogen to the soil? What happens to soil nitrates? How is nitrogen released from the soil?
Review
1. Describe how nitrogen is fixed. 2. How do dead zones come about? 3. Why does the Gulf of Mexico contain such a large dead zone?
References 1. Reindeer: Image copyright Andrea Kaulitzki, 2010; modified by CK-12 Foundation. . Used under license from Shutterstock.com 2. Pond: Image copyright Ratikova, 2010; Map: Courtesy of US Government. . Pond: Used under license from Shutterstock.com; Map: Public Domain
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C HAPTER
12
Tropisms
• Define tropism and explain examples of tropisms.
Why are these plants turning sideways? Plants respond to their environment in how they grow. In this picture, the light source is probably off to the right side. As a result, the plants grow in this direction to get more light. Tropisms
Plants may not be able to move, but they are able to change how they grow in response to their environment. Growth toward or away from a stimulus is known as a tropism ( Table 12.1). Auxins, a class of plant hormones, allow plants to curve in specific directions as they grow. The auxin moves to one side of the stem, where it starts a chain of events that cause rapid cell growth on just that one side of the stem. With one side of the stem growing faster than the other, the plant begins to bend.
TABLE 12.1: Tropisms Type of Tropism Phototropism Gravitropism Thigmotropism
Stimulus light gravity touch
Phototropism
You might have noticed that plants bend toward the light. This is an example of a tropism where light is the stimulus, known as phototropism ( Figure 12.1). To obtain more light for photosynthesis, leaves and stems grow toward the light. On the other hand, roots grow away from light. This is beneficial for the roots, because they need to obtain water and nutrients from deep within the ground. 42
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Chapter 12. Tropisms
FIGURE 12.1 These seedlings bending toward the sun are displaying phototropism.
Gravitropism
So, how do the roots of seeds underground know to grow downward? How do the roots deep in the soil know which way is up? Gravitropism is a growth toward or away from the pull of gravity ( Figure 12.2). Shoots, the new growth of a plant, also show a gravitropism, but in the opposite direction. If you place a plant on its side, the stem and new leaves will curve upward.
FIGURE 12.2 These shoots are exhibiting gravitropism: they are growing against the pull of gravity.
Thigmotropism
Plants also have a touch response called thigmotropism. If you have ever seen a morning glory or the tendrils of a pea plant twist around a pole, then you know that plants must be able to sense the pole. Thigmotropism works much like the other tropisms. The plant grows straight until it comes in contact with the pole. Then, the side of the stem that is in contact with the pole grows slower than the opposite side of the stem. This causes the stem to bend around the pole. 43
www.ck12.org Vocabulary
• • • • •
gravitropism: Growth in response to gravity. phototropism: Growth in response to light. shoot: New growth of a plant. thigmotropism: Growth in response to touch. tropism: Growth toward or away from a stimulus.
Summary
• Tropisms are growth toward or away from a stimulus. • Types of tropisms include gravitropism (gravity), phototropism (light), and thigmotropism (touch). Practice
Use the resource below to answer the questions that follow. • Phototropism and Auxin at http://www.youtube.com/watch?v=4-2DZo2ppAY (2:13)
MEDIA Click image to the left for more content.
1. Explain how scientists determined that the signal for phototropism was occurring in the growing tip of a plant? 2. Explain how scientists determined the signal for phototropism migrated up and down a plant shoot but did not move across the plant shoot? 3. How did an agar block help scientists determine that some substance moving through the plant was responsible for the phototropic response? Review
1. If you tip a plant on its side, what will happen? Why? 2. The tendril of a bean meets a metal pole. What will happen to the tendril? Why?
References 1. Russell Neches (Flickr: r_neches). . CC-BY 2.0 2. Image copyright Marie C. Fields, 2012. . Used under license from Shutterstock.com
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