What adaptation allows C4 plants to minimize photorespiration?

C4 plants have a unique anatomical and physiological adaptation that significantly reduces photorespiration, which is a wasteful process that occurs when the enzyme RuBisCO reacts with oxygen instead of carbon dioxide during photosynthesis. The correct answer highlights that C4 plants have clustered mesophyll cells surrounding bundle-sheath cells.

This arrangement allows for an efficient separation of the initial carbon fixation and the Calvin cycle, which occur in different types of cells. In C4 photosynthesis, carbon dioxide is initially fixed in mesophyll cells into a four-carbon compound, which is then transported to the bundle-sheath cells. Here, the four-carbon compound is decarboxylated to release carbon dioxide in close proximity to RuBisCO. By concentrating CO2 around RuBisCO, C4 plants minimize the chances of photorespiration, as the increased concentration of carbon dioxide reduces the likelihood that RuBisCO will bind to oxygen instead.

This mechanism is particularly advantageous in hot and dry environments, where stomatal openings may be limited to conserve water, as it allows for effective photosynthesis even under conditions that typically lead to higher rates of photorespiration in C3 plants.