Digestion

Article By:

Devillez, Edward J. Department of Zoology, Miami University, Oxford, Ohio.

Last reviewed:August 2019

DOI:https://doi.org/10.1036/1097-8542.194500

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• Digestion (invertebrate), published June 2014:Download PDF Get Adobe Acrobat Reader

The process by which the complex organic molecules in foods are broken down into simpler units that can be utilized by cells for energy or incorporated into living cells. Digestion converts food to an absorbable form by breaking it down to simpler chemical compounds. Frequently, there is an essential mechanical pretreatment of the food to be digested, either before or after the food is taken into the body. Mechanical treatment is especially needed in herbivorous animals that depend on the utilization of cellulose and other plant materials, or where the prey has a hard exoskeleton. Many animals have devices for crushing, grinding, or mixing. Overall, the final processes of digestion are always chemical. Reactions in chemical digestion commonly involve hydrolysis, which accelerates the addition of water to the food molecules and results in their cleavage to simpler units (Fig. 1). The water brings about the decomposition, and the hydrolytic digestive enzymes accelerate the process. See also: Cellulose; Digestive system; Enzyme; Food; Hydrolysis

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