Any plant that produces, as the first step in photosynthesis, *oxaloacetic acid , which contains four carbon atoms (see Hatch-Slack pathway). Over 100 species of C4 plants have been identified, most of which are tropical. Examples include maize, sugar cane, sorghum, Bermuda grass, and many desert plants. C4 plants require 30 molecules of ATP and 24 molecules of water to synthesize a molecule of glucose (*C3 plants need only 18 molecules of ATP and 12 molecules of water). However C4 plants produce more glucose for a given leaf area than C3 plants and consequently grow more quickly. They can also continue to photosynthesize at high light intensities and low carbon dioxide concentrations (see compensation point) and, most significantly, do not exhibit *photorespiration. Compare crassulacean acid metabolism. See also Kranz structure.
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