18. CAM Plant

This is picture of pineapples. A pineapple represents a CAM plant. A CAM plant is one that utilizes the crassulacean acid metabolism (CAM) as an adaptation to hot and dry climates. The crassulacean acid metabolism begins with the stomata (pores on the leaves that allow the transferring of gases) opening at cool and humid hours (at night), thus permitting the uptake of carbon dioxide. The carbon dioxide then reacts with phosphoenolpyruvate carboxylase (an enzyme that catalyzes the addition of bicarbonate (HCO₃⁻) to phosphoenolpyruvate (PEP)) to form oxaloacetic acid. This acid reacts with dehydrogenase (an enzyme that oxidizes a substrate) and forms malic acid, which is stored in the vacuoles at night. Over night the pH of the vacuoles and cytoplasm significantly decreases, causing the enzymes to stop functioning. When daylight comes, the stomata closes and the malic acid breaks down and forms carbon dioxide (as well as other products) which will be used to react with the enzyme RuBisCo and enter the Calvin Cycle. This form of photosynthesis preserves water via closed stomata and evapotranspiration. Other examples of CAM plants, exists in arid climates such as orchids and cacti.