Why is photorespiration considered detrimental to plants?

Photorespiration is considered detrimental to plants primarily because it occurs when oxygen competes with carbon dioxide for the enzyme RuBisCO. In the process of photosynthesis, RuBisCO typically catalyzes the reaction between carbon dioxide and ribulose bisphosphate (RuBP) to produce organic molecules that the plant can use for energy. However, under certain conditions, especially when the concentration of carbon dioxide is low and the concentration of oxygen is high (often due to factors like high temperatures and light intensity), RuBisCO can instead bind to oxygen. This alternative reaction leads to the formation of a byproduct that the plant cannot efficiently use for energy, ultimately wasting energy and reducing the overall yield of photosynthesis.

This competitive inhibition reduces the availability of carbon dioxide for the Calvin cycle, thereby decreasing the efficiency of photosynthesis. As a result, the plant's ability to synthesize food is compromised, and it may lead to slower growth and reduced productivity. Therefore, the competition of oxygen with carbon dioxide for RuBisCO plays a critical role in why photorespiration is harmful to plants.