Energy Flow Through The Food Chain: The 10 Percent Rule of Energy Flow
Food chains show how energy moves through an ecosystem, the combined physical and biological elements in an environment. In a food chain, producers, organisms that make their own food, provide food for animals called first-level consumers. These animals are then eaten by second-level consumers, which may be consumed by third-level consumers. Scientists estimate that only 10 percent of the producers' energy is passed to the first-level consumer. This activity will help put that amount into perspective.
10 ml graduated cylinder; Cup filled with 100 ml of water; Medicine dropper; Three small paper cups
- Label cup 1 ''first-level consumer," cup 2 ''second-level consumer," and cup 3 ''third-level consumer." The large cup filled with 100 ml of water represents the producer. For this activity we will assume that the producer possesses 100 units of energy.
- A first-level consumer eats the producer and absorbs only 10 percent of its energy. Use the graduated cylinder to pour 10ml of the producer's water into cup 1.
- The second-level consumer eats the first-level consumer and gets only 10 percent of its energy. Use the graduated cylinder to pour 1 ml of water from cup 1 into cup 2.
- The third-level consumer eats the second-level consumer and gets only 10 percent of its energy. Use the medicine dropper to transfer 0.1 ml of water from cup 2 into cup 3.
- If the food chain had continued to the next level, what percentage of energy would the fourth-level consumer have received from the third-level consumer? How much water would you have transferred into the fourth-level consumer's cup?
- Judging from this activity, why do you think most food chains never go higher than second- or third-level consumers?
- The fourth-level consumer would have received 10 percent of the energy from the third-level consumer. You would have put 0.01 ml of water into the fourth-level consumer's cup.
- There is not enough energy available to continue the food chain after the second-level or third-level consumers.
Do some research and draw a pyramid of energy showing the following organisms in the correct order: caterpillar, grass, snake, lizard, and hawk. Label the percentage of energy each organism gets through the food chain.
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