How do C4 plants avoid photorespiration?

C4 plants have evolved a specialized mechanism to minimize photorespiration, which is a process that can decrease the efficiency of photosynthesis under certain conditions. By performing photosynthesis in different cells, C4 plants effectively separate the initial carbon fixation from the Calvin cycle in two distinct types of cells: mesophyll cells and bundle sheath cells.

In C4 photosynthesis, carbon dioxide is initially captured in the mesophyll cells and converted into a four-carbon compound, which is then transported to the bundle sheath cells. In these cells, the four-carbon compound releases carbon dioxide for use in the Calvin cycle, which is more efficient under conditions of high oxygen levels and low carbon dioxide availability. This compartmentalization helps C4 plants maintain a higher concentration of carbon dioxide in the bundle sheath cells, significantly reducing the likelihood of oxygen fixation and thus minimizing photorespiration.

This adaptation allows C4 plants to thrive in hot and dry environments, where photorespiration would otherwise be a significant drawback for traditional C3 plants.