A food chain does not consist of a set amount of organic matter and energy being passed along like a baton from one organism to another. In reality, the baton gets smaller and smaller with each transfer. When an herbivore eats a plant, it does not get all the energy the plant received from the sun. This decrease is because the herbivore may not eat all parts of the plant, and it may not be able to digest what it does eat. These undigested plant parts are excreted as waste. The same holds true for other organisms along the food chain (i.e., when one organism eats a second, the consumer does not receive all the energy obtained by and contained within the second organism).
Another reason energy obtained by one organism isn’t passed on in the food chain is because it is no longer available (Second Law of Thermodynamics). Some energy has already been used by the first organism. A plant uses some of the energy it receives to grow and function. A herbivore uses its energy to grow, but also to look for food and run away from predators. A predator uses large amounts of energy to chase after its food in addition to its regular life processes (e.g., breathing, digesting food, moving). The energy these organisms use eventually leaves their bodies in the form of heat.
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The amount of energy that is transferred from one organism to the next varies in different food chains. Generally, about ten percent of the energy from one level of a food chain makes it to the next. |
