Evolution of photosynthesis in an environment with much more than it otherwise would be, it performs more efficiently. A second mechanism, CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. The most important benefit of CAM to the plant is the ability to leave most leaf stomata closed during the day. This reduces water loss due to evapotranspiration. The stomata open at night to collect , which is stored as the four-carbon acid malate, and then used during photosynthesis during the day. The pre-collected is concentrated around the enzyme RuBisCO, increasing photosynthetic efficiency. More
Photosynthesis allowing carbon fixation to 3-phosphoglycerate by RuBisCO. Sixteen thousand species of plants use CAM. Cyanobacteria possess carboxysomes, which increase the concentration of around RuBisCO to increase the rate of photosynthesis. An enzyme, carbonic anhydrase, located within the carboxysome releases CO from the dissolved hydrocarbonate ions (HCO). Before the CO diffuses out it is quickly sponged up by RuBisCO, which is concentrated within the carboxysomes. HCO ions are made from CO outside the cell by another carbonic anhydrase and are actively pumped into the cell by a membrane protein. They cannot cross the membrane as they are charged, and within the