BIO 2 GO! Interactions of Organisms in an Ecosystem Energy and Biomass Pyramids

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1 BIO 2 GO! Interactions of Organisms in an Ecosystem 3525 Energy and Biomass Pyramids Interrelationships and Interdependencies among different organisms in an ecosystem are affected by factors in the environment. These relationships contribute to the stability of an ecosystem. Upon successful completion of this unit, you should be able to do the following: 1. Describe an energy pyramid. 2. Explain how an energy pyramid is useful. 3. Relate a food chain to an energy pyramid. 4. Describe a biomass pyramid. 5. Explain how a biomass pyramid is useful. 6. Use the following words in their correct context: Energy pyramid Biomass pyramid Food chain Producer Herbivore Carnivore Omnivore Decomposer

2 Pyramids of Energy and Biomass 3525 Energy Pyramid An energy pyramid is an easy way to see the amount of energy loss from one trophic level to the next. Each layer in the pyramid represents one trophic level. Producers (green plants) are always located at the bottom. Herbivores (like a cow) contain less energy and make up the second level from the bottom. Carnivores (wolves) that feed on herbivores form the next level. At the top level are carnivores that feed on other carnivores (like humans). Note that organisms on the top layers of the pyramid store less energy than those located at the base. REMEMBER THIS!!! The total amount of energy available is reduced when moving up the energy pyramid. As you know energy from the sun is used by plants in photosynthesis to make food (glucose) for all other organisms. When we and all organisms on earth eat we get energy. If we did not eat, we would not have any energy, and we would die. A car needs gas, which is its energy, in order to work. Without gas, the car would not do anything or go anywhere. Our bodies are just like that! We can show how the energy moves through an ecosystem by drawing a food chain or by an energy pyramid. Energy pyramids are cool because they show us with a picture how much energy we get by what we eat. Think about it! Some things that you eat will give you more energy than others. Have you every wondered why? Energy pyramids are related to food chains. Look at the example of a food chain: Sun---Producer---Herbivore---Carnivore---Carnivore---Decomposer The food chain tells us the order that organisms are consumed by other organisms. This is useful information if you are studying an ecosystem.

3 However, an energy pyramid provides even more information because the energy pyramid also shows how much energy is transferred to the next organism. Remember, one of the main reasons any organism eats is to gain energy. No energy, no life. An energy pyramid is a diagram that shows the trophic levels as blocks that are stacked on top of each other. The lowest trophic level (producers) is at the bottom. The width of the block shows how much energy is available at that level. Take a look! Top Carnivore Carnivore Herbivores Producers Question 1: Look at the energy pyramid above. Which trophic level contains the most available energy? Which trophic level contains the least amount of available energy? Only about 10% of the energy is passed to the next level. The rest is used or is lost as heat. That means that 90% of the energy is used by the organisms to live. REMEMBER THIS!!! Only 10% of the available energy is passed from one trophic level to the next.

4 Since most of the available energy is lost between trophic levels, organisms at the top of the pyramid have to constantly search for more food. Most humans expect to eat three times every day! Question 2: How much available energy is lost when a carnivore consumes an herbivore? Question 3: Assume that a field of green plants produced 1,000 calories of energy. A cow was allowed to eat all of the green plants in that field. How much of the 1,000 calories of energy would the cow receive? Question 4: From question #3, assume that the cow was then taken to the market and sold as beef. How much of the original 1000 calories of energy are now available to the person who purchases the beef? Biomass Pyramid The pyramid of biomass looks exactly the same as the energy pyramid. What is biomass? Biomass is the dry weight of tissue and other organic matter in an ecosystem. REMEMBER THIS!!! Biomass is the amount of organic matter that is found in an area. Biomass pyramids are often more useful than energy pyramids. Ecologists sometimes use biomass pyramids to more accurately determine the amount of energy in an ecosystem. The results though are the same as the energy pyramid. Only 10% of the biomass is available to use at the next higher trophic level.

5 True or False 3525 Energy and Biomass Pyramids SELF TEST 1. The lowest trophic level of any ecosystem is occupied by the producers. 2. The number of organisms in a trophic level is always directly proportional to the amount of energy at that level. 3. An energy pyramid shows the trophic levels as blocks stacked on one another. 4. An energy pyramid shows how much energy is transferred from one organism to the next. 5. Energy pyramids are not related to food chains at all. 6. Biomass pyramids have little use when determining how much energy is in an ecosystem. 7. Only 10% of the biomass is available to organisms at the next higher trophic level. 8. There is more energy available at the top of the energy pyramid than at the bottom. 9. An example of a carnivore is a cow. 10. Biomass is the amount of organic matter found in an area. Fill in the Blank decomposers food chain biomass trophic herbivores energy 1. The term is given to the bacteria that break down dead tissue. 2. In an ecosystem, decreases at each higher trophic level. 3. A path of energy through the trophic levels of an ecosystem is called a(n). 4. An energy pyramid shows the amount of energy contained in the bodies of organisms at each level. 5. are organisms that eat only plants. 6. is the dry weight of tissue and other organic matter in an ecosystem.

6 Matching 1. Producers 2. Consumers 3. Energy Pyramid 4. Decomposer 5. Omnivore 6. Carnivore 7. Food Chain 8. Biomass Pyramid A. Model that shows the available energy in a trophic level. B. Organisms that get their food by eating other organisms. C. Breaks down dead organisms in the environment. D. Organisms that make organic nutrients for an ecosystem using energy from the sun. E. Tells us the order that organisms are eaten by other organisms F. Eats only meat. G. Shows the amount of organisms in an ecosystem by measuring their dry weight. H. Eats both plants and meat Answer the following: 1. Examine the energy pyramid and explain why most ecosystems seldom have more than four or five trophic levels. 2. From an energy or biomass viewpoint, is it better to for humans to be vegetarians or carnivores? Explain your answer in terms of available energy and biomass.

7 3525 Energy and Biomass Pyramids Answer Sheet Top Carnivore Carnivore Herbivores Producers Question 1: Look at the energy pyramid above. Which trophic level contains the most available energy? Which trophic level contains the least amount of available energy? Question 2: How much available energy is lost when a carnivore consumes an herbivore? Question 3: Assume that a field of green plants produced 1,000 calories of energy. A cow was allowed to eat all of the green plants in that field. How much of the 1,000 calories of energy would the cow receive? Question 4: From question #3, assume that the cow was then taken to the market and sold as beef. How much of the original 1000 calories of energy are now available to the person who purchases the beef?