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The transfer of Energy in the Food Chain
When herbivores eat green plants they are taking energy into their bodies. We can represent the amount of energy taken in by a herbivore as an energy circle.
The herbivore will use this energy for movement and other body activities, such as reproduction and movement. Some parts of the plant which was eaten cannot be digested by the herbivore; the energy in these parts of the plant passes out of the herbivore's body as waste. Some of the energy, however, is used for growth and remains as organic matter in the herbivore's body. It is this energy which can be eaten by the secondary consumer.
As you can see from the diagram, only about 10% of the energy which the plant used for growth is taken into the body of the carnivore. The second consumer uses some of this energy for its own body activities and some of the energy will be wasted. Therefore, the amount of energy available for the tertiary consumer is only 1% of the energy which the primary consumer gained from the plant.
As the energy is passed along the food chain much of it is either used or lost. Therefore there is a limit to the number of organisms in a food chain. The top carnivore is usually the third or fourth consumer.