What does the acronym CAM stand for in photosynthesis?

CAM stands for Crassulacean Acid Metabolism in photosynthesis. It is a carbon-fixation strategy that helps plants conserve water by separating carbon dioxide uptake and the Calvin cycle between night and day.

CAM plants generally open their stomata at night, when cooler temperatures reduce evaporative water loss. They fix incoming carbon dioxide into four-carbon organic acids, especially malic acid, and store those acids in vacuoles. During the day, the stomata close; the stored acids release carbon dioxide inside the leaf, allowing the Calvin cycle to continue while limiting gas exchange and dehydration.

The name refers to the family Crassulaceae, which includes jade plants and Sedum, where the pattern was studied—not to a compound called “crassulacean acid.” Early observations of daily acidity changes in succulent leaves date to the nineteenth century, while the term is associated with work by Ranson and Thomas around 1940. Cacti, pineapple, agave, and some orchids use CAM. CAM is often confused with C₄ photosynthesis: both concentrate carbon dioxide around Rubisco, but CAM separates the steps mainly in time, whereas C₄ plants separate them mainly by cell type.