crassulacean acid metabolism (CAM) Photosynthesis by the C4 pathway in which carbon dioxide is taken up during the night, when the plant's stomata are open, and fixed into malic acid. During the day, when the stomata are closed, carbon dioxide is released from malic acid for use in the Calvin cycle. This is important for plants that live in arid conditions as it enables them to keep their stomata closed during the day to reduce water loss from evaporation. Crassulacean acid metabolism is common in succulent plants of desert regions, including cacti and spurges, and in certain ferns. It is so named because it was originally studied in plants belonging to the family Crassulaceae, which includes stonecrops and houseleeks.

crassulacean acid metabolism (CAM) A method of carbon dioxide fixation that conserves water in members of the Crassulaceae and certain other succulent, drought-resisting plants. At night, when the external temperature is low enough for stomata to be open, carbon dioxide enters them and is incorporated into organic acids. In the day, when the stomata remain closed so as to conserve water, these acids are decarboxylated and the carbon dioxide is used for photosynthesis in the Calvin cycle.

crassulacean acid metabolism (CAM) A method of carbon dioxide fixation that conserves water in certain succulent, drought-resisting plants. At night, when the external temperature is low enough for stomata to be open, carbon dioxide enters them and is incorporated into organic acids. In the day, when the stomata remain closed so as to conserve water, these acids are decarboxylated and the carbon dioxide is used for photosynthesis in the Calvin cycle.