C4 and Cam Photosynthesis

Part A

      C4 and CAM photosynthesis are considered advantageous to plants that exhibit them because of the special “add-on” features they display. C4 photosynthesis reduces photorespiration and water loss. The reduction of photorespiration is due to the fact that carbon dioxide is moved to a specialized cell known as a bundle sheath cell which surrounds the leaf veins and they themselves are surrounded by mesophyll cells. (Photosynthesizing cells) Bundle sheath cells rarely ever come in contact with an intercellular space thus minimal oxygen reaches them. This lack of oxygen allows rubisco to fix with carbon dioxide without having to compete with oxygen. Therefore, little photorespiration takes place and photosynthesis is more efficient.
      The higher rates of photosynthesis in C4 plants allow them to reduce the amount of time their stomata are open which reduces water loss. (Stomata open to allow carbon dioxide to enter) This advantage allows C4 plants to live in dry, arid climates such as deserts. Examples of C4 plants include sugarcane and crab grass.

      CAM plants follow a similar pathway to C4 plants with some minor differences. Instead of OOA (oxaloacetate) being converted into malate, it is converted into malic acid. The malic acid is then transported to the vacuole of a cell instead of bundle sheath cells like in a C4 plant. The main advantage of CAM plants is that their stomata are open at night which greatly reduces water loss. During this time, the malic acid is transported out of the vacuole and converted back to OOA, releasing carbon dioxide. The carbon dioxide is fixed with rubisco and photosynthesis can proceed during the day.

Part B

Three major differences between C3 photosynthesis and C4 and CAM photosynthesis are the fixing enzymes they use, their production rates, and their ability to adjust to arid climates. C3 photosynthesis uses the fixing enzyme rubisco to fix carbon dioxide into PGA. However, both C4 and CAM...