Living Things Need Energy

Transcription

1 2 Living Things Need Energy Key Concept Energy and matter flow between organisms and their environment. What You Will Learn Producers, consumers, and decomposers have specific functions in an ecosystem. Energy flows from one organism to another in food chains. Many food chains make up a food web. The availability of living and nonliving resources affects all organisms. Why It Matters Studying how organisms interact will help you understand how organisms obtain and use energy. Vocabulary herbivore food chain carnivore food web omnivore energy pyramid Graphic Organizer In your Science Journal, make a Pyramid Chart that shows the energy relationship between the sun and the organisms in Figure 1. Could you survive on only water and vitamins? Eating food satisfies your hunger because it provides two things you cannot live without energy and nutrients. All organisms need energy and matter, or nutrients, to survive. For example, black-tailed prairie dogs, which live in the grasslands of North America, eat grass and seeds to get the energy they need. Like all organisms, prairie dogs require energy to carry out all life processes. The Energy Connection Organisms in every community can be divided into three groups based how they function in that community. These groups are producers, consumers, and decomposers. These groups also explain how organisms get the energy and nutrients they need. Examine Figure 1 to see how energy and nutrients flow through an ecosystem. Producers Organisms that change the energy in sunlight into chemical energy or food are called producers. Producers do this through the process of photosynthesis. Most producers are green plants, but algae and some bacteria are also producers. Grasses are the main producers in a prairie ecosystem. Examples of producers in other ecosystems include cordgrass and algae in a salt marsh and trees in a forest. Why is sunlight important to producers? 6.5.a Energy Sunlight is the source of energy for almost all living things. Producer Plants use solar energy to make food. Figure 1 Most living things get their energy either from the sun or from eating other organisms. Primary Consumer The black-tailed prairie dog (herbivore) eats leaves and grass in the grasslands of western North America. Secondary Consumer All of the prairie dogs in a colony watch for enemies, such as coyotes (carnivore), hawks, and badgers. Occasionally, a prairie dog is killed and eaten by a coyote. 554

2 Consumers Not all organisms can make their own food like producers can. Some organisms must eat other organisms to obtain energy and nutrients. These organisms are called consumers. There are several kinds of consumers. A consumer that eats only plants is called an herbivore, such as a grasshopper or a bison. A consumer that eats other animals is called a carnivore, such as a badger or an owl. Consumers that eat both plants and animals are called omnivores. The grasshopper mouse is an omnivore that eats insects and grass seeds. Scavengers are also omnivores. The turkey vulture is a scavenger in the prairie. A vulture will eat what is left after a coyote has killed and eaten part of an animal. Scavengers also eat animals and plants that have died from natural causes. herbivore (HUHR buh VAWR) an organism that eats only plants carnivore (KAHR nuh VAWR) an organism that eats animals omnivore (AHM ni VAWR) an organism that eats both plants and animals food chain (FOOD CHAYN) the pathway of energy transfer through various stages as a result of the feeding patterns of a series of organisms Decomposers Organisms that get energy and nutrients by breaking down dead organisms are called decomposers. Bacteria, shown in Figure 2, and fungi are decomposers. Decomposers produce simple materials, such as water and carbon dioxide, that can be used by other organisms. Decomposers are nature s recyclers. Food Chains Figure 1 shows a food chain. A food chain is a diagram that shows how energy and nutrients are transferred from one organism to another. Producers, such as plants, form the base of the food chain. Herbivores, such as prairie dogs, are also called primary consumers because they are the first consumers in the food chain. Organisms, such as coyotes, that eat primary consumers are called secondary consumers. Organisms that eat secondary consumers are called tertiary consumers (TUHR shee ER ee kuhn SOOM uhrz). A turkey vulture is a tertiary consumer because it is the third consumer in the food chain shown in Figure 1. But few organisms eat just one kind of food. Thus, simple food chains are rare. Tertiary Consumer Aturkey vulture (scavenger) may eat a dead coyote. A scavenger can pick bones completely clean. Figure 2 All materials from dead organisms are broken down by bacteria and fungi that live in the soil. 6.5.a Students know energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis and then from organism to organism through food webs. 6.5.b Students know matter is transferred over time from one organism to others in the food web and between organisms and the physical environment. 6.5.c Students know populations of organisms can be categorized by the functions they serve in an ecosystem. 6.5.e Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition. Section 2 Living Things Need Energy 555

3 food web (FOOD WEB) a diagram that shows the feeding relationships between organisms in an ecosystem Food Webs The energy and nutrient connections in nature are more accurately shown by a food web than by a food chain. A food web is a diagram that shows the feeding relationships between organisms in an ecosystem. Figure 3 shows a simple food web. A food web is made up of many food chains. Notice that an arrow goes from the prairie dog to the coyote and shows that the prairie dog is eaten by the coyote. The prairie dog is also eaten by the mountain lion. Energy moves from one organism to the next in one direction in a food web. Each organism uses energy for its life processes. During these processes, some energy is lost to the environment as heat. Any energy not immediately used by an organism is stored in its cells. Only the energy stored in an organism s cells can be used by the next consumer. Using the food web below, identify a secondary consumer. Explain your choice. 6.5.b, 6.5.c Figure 3 The arrows show how energy moves when one organism eats another. Most consumers eat a variety of foods and can be eaten by a variety of other consumers. 556 Chapter 16 Interactions of Living Things

4 Decreasing number of organisms Decreasing amount of energy Energy Pyramids Only a small part of the energy an organism obtains is transferred to the next consumer in a food chain. Thus, many more organisms have to be at the base of a food chain than at the top of a food chain. For example, in a prairie community, there must be more grass than prairie dogs and more prairie dogs than coyotes. The amount of energy at each level of a food chain can be seen in an energy pyramid. An energy pyramid is a diagram that shows an ecosystem s loss of energy. Only about 10% of the energy in each level of the energy pyramid is transferred to the next level of the pyramid. An example of an energy pyramid is shown in Figure 4. You can see that the energy pyramid has a large base and a small top. Less energy is available at higher levels of the pyramid because most of the energy has already been used at the lower levels. Figure 4 The pyramid represents energy. As you can see, more energy is available at the base of the pyramid than at the pyramid s top. energy pyramid (EN uhr jee PIR uh mid) a triangular diagram that shows an ecosystem s loss of energy, which results as energy passes through the ecosystem s food chain energy pyramid? Why are only a few animals at the top of an 6.5.b Section 2 Living Things Need Energy 557

5 Figure 5 As the wilderness was settled, the gray wolf population in the United States declined. Wolves and the Energy Pyramid Even a single species can be very important to the flow of energy in an environment. Gray wolves, shown in Figure 5, are consumers that control the popu lations of many other animals. Gray wolves may eat anything from a lizard to an elk. Because gray wolves are predators that are not usually preyed upon, wolves belong at the top of the energy pyramid. Once common throughout much of the United States, gray wolves were almost wiped out as the wilderness was settled. Without wolves, some species, such as elk, were no longer controlled, and their populations began to grow. The overpopulation of elk in some areas led to overgrazing. The overgrazing left too little grass to support the elk and other herbivore populations that depended on the grass for food. Without enough food, these herbivore populations began to decline. The decline in herbivore populations was quickly followed by declines in other predator populations because there were not enough prey. Soon, almost all of the species in the area were affected by the loss of the gray wolves. Why did the decline of the wolf population affect the populations of other organisms in the community? 6.5.e Quick Lab How Are the Organisms in a Food Chain Connected? Try this activity to see how changes in parts of a food chain can affect the whole food chain. Try It! 1. On a desk, place 15 green beads to represent grass, 9 brown beads to represent elk, and 4 yellow beads to represent wolves. 2. Roll the numbered cube. The number rolled represents how many elk the wolves have eaten. Remove this number of elk from the desk. Because some elk were removed, more grass can grow. Multiply the number of elk that were removed by two. This number represents how many beads of grass can be added to the desk. 3. Roll the numbered cube. The number rolled represents how much grass the elk have eaten. Multiply this number by two. This number represents how many beads of grass should be removed from the desk. The number of wolves remains the same. 4. Roll the numbered cube. This number represents how much the grass has grown. Add this number of beads of grass to the desk. Think About It! 5. What do you think will happen to the elk and wolf populations after step 4? 6. What would happen to the balance in the ecosystem if all of the elk were eaten by the wolves? 6.5.b 6.5.e 15 min 558 Chapter 16 Interactions of Living Things

6 Balance in Ecosystems Gray wolves were brought back to Yellowstone National Park in The reintroduced wolves soon began to breed. As they become reestablished in the park, wolves kill the old, injured, and diseased elk. This process is reducing the number of elk. The smaller elk population is letting more plants grow. So, the numbers of herbivores, such as snowshoe hares, and the carnivores that eat the hares, such as foxes, are increasing. All organisms in a food web are important for the health and balance of other organisms in the food web. However, the reintroduction of wolves is also a source of controversy. Ranchers that live near the park are worried about their livestock because wolves will eat cows and sheep if given the chance. Energy Pyramids In your Science Journal, draw an energy pyramid for a river ecosystem that has four levels algae, insect larvae, bluegill fish, and bass. The algae get 10,000 units of energy from sunlight. If each level uses 90% of the energy it receives from the previous level, how many units of energy do the bass receive? Review 6.5.a, 6.5.b, 6.5.c, 6.5.e Summary Producers that use photosynthesis transfer the energy in sunlight into chemical energy. Consumers eat producers and other organisms to obtain energy and nutrients. Decomposers break down all of the materials in dead organisms to obtain energy and nutrients. Food chains represent how energy and nutrients are transferred from one organism to another. Energy pyramids show how energy is lost at each level of the food chain. All organisms have important roles in a food web. 1 Use herbivores, carnivores, and omnivores in separate sentences. 2 Describing Describe how energy enters a food web through plants. 3 Demonstrating Draw a food chain. Identify the producer, primary consumer, secondary consumer, and tertiary consumer. 4 Justifying Explain the importance of decomposers. 5 Describing Explain how producers, consumers, and decomposers are linked in a food chain. 6 Identifying Relationships Explain how food chains and food webs are related. 7 Making Inferences Why is it more common to find short food chains than to find long food chains? INTERPRETING GRAPHICS Use the following graph to answer the next three questions. 8 Identifying Relationships What is the relationship between the size of the predator population and the size of the prey population? 9 Predicting Consequences What would happen to the prey population if the predator population was removed from this graph? 0 Analyzing Data Describe what is happening at A and at B. Internet Resources For a variety of links related to this chapter, go to Topic: Food Chains and Food Webs SciLinks code: HY