Furthermore, C 4 metabolism is continuous as long as there is light available, while CAM occurs only at night. C 4 plants capture the CO 2 in one type of cell tissue (mesophyll) and then transfer it to another type of tissue (bundle sheath cells) so that carbon fixation may occur via the Calvin-Benson cycle. In some ways, CAM resembles C4 photosynthesis, except that CAM plants contain no bundle sheath cells. By thus reducing evapotranspiration rates during gas exchange, CAM allows plants to grow in environments that would otherwise be far too dry for plant growth or, at best, subject them to severe drought stress. In the daytime, the malic acid is removed from the vacuoles and cleaved to produce CO 2 so that it can be utilized by the enzyme RuBisCO in the Calvin-Benson cycle in the chloroplast stroma. Malate is easily broken down into pyruvate and CO 2, after which pyruvate is phosphorylated to regenerate phosphoenolpyruvate (PEP). CAM plants store these four-carbon intermediates and other simple organic compounds in their vacuoles. This is begun when the three-carbon compound phosphoenolpyruvate is carboxylated into oxaloacetate which is then reduced to form malate. Their stomata then open during the cooler and more humid nighttime hours, allowing uptake of carbon dioxide for use in carbon fixation. Some xerophytes perform photosynthesis using Crassulacean acid metabolism (or CAM).ĬAM plants close their stomata during the day in order to conserve water by preventing evapotranspiration. Some shed their leaves during the dry season others, such as cacti, orchids, and bromeliads store water in vacuoles. Some have small, thick leaves with a low surface-area-to-volume ratio. Plants adapted to thrive in dry climates are called xerophytes. Essential Laboratory Skills Guide Synopsis
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