What distinguishes C4 plants from C3 plants in terms of photosynthesis?

C4 plants are distinguished from C3 plants by their unique process of photosynthesis, which involves a spatial separation of carbon fixation and the Calvin cycle. In C4 plants, carbon dioxide is initially fixed into a four-carbon compound in the mesophyll cells, a process that occurs before entering the Calvin cycle in the bundle-sheath cells. This adaptation allows C4 plants to thrive in conditions of high temperature and light intensity, where C3 plants are less efficient due to photorespiration, which can occur when stomata open to allow CO2 in but also facilitates water loss and leads to a decrease in photosynthetic efficiency.

By separating the initial carbon fixation from the Calvin cycle, C4 plants can effectively concentrate CO2 in their bundle-sheath cells, which reduces the chance of oxygen interfering with the process and enhances the overall efficiency of photosynthesis. This adaptation not only assists in maximizing carbon fixation but also helps in managing water loss, as C4 plants can keep their stomata closed longer in hot conditions while still maintaining efficient photosynthesis.