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Article: Digestion
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- Biology
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CopyrightCOPYRIGHT 2002 The Gale Group Inc. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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Digestion
Digestion breaks down foods into nutrient molecules that are small enough to be absorbed into an animal's circulatory system. Following digestion, nutrients
are delivered to cells, where energy is extracted from their chemical bonds. Digestion often begins with a mechanical tearing apart of food into smaller pieces, which are then chemically dismantled in a stepwise fashion.
Because digestive chemicals are harsh, food processing in an animal's body takes place in compartments. Some single-celled organisms, such as protista, sequester food particles in food vacuoles, where
enzymes
break them down. Simple multicellular organisms, such as hydra and flatworms, have ...