CAM stands for crassulacean metabolism, also known as CAM photosynthesis. CAM photosynthesis is a carbon fixation pathway in some plants that evolved as an adaptation to arid conditions. In these plants, the stomata stay closed to reduce the amount of water leaving the plant, then open at night to collect carbon dioxide. The CO2 is stored in malate, a four-carbon acid. The precollected CO2 concentrates around RuBisCo. The plant uses the carbon dioxide collected in the night to perform photosynthesis in the day.