Metabolism
noun: all the chemical processes by which cells produce the energy and substances necessary for life. Food is separated (dissociated) into the parts it is made up of to produce heat and energy, to repair tissues, and to help growth to happen.
noun: the organic processes in a cell or organism that are necessary for life
noun: the marked and rapid transformation of a larva into an adult that occurs in some animals

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Metabolism ("change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are:

(1) the conversion of the energy in food to energy available to run cellular processes;
(2) the conversion of food to building blocks for proteins, lipids, nucleic acids, and some carbohydrates;
(3) and the elimination of metabolic wastes. [Metabolism]