Flexi Says: In photorespiration molecular oxygen, O2, competes with CO2 for the active site of ribulose bisphosphate carboxylase, leading to an oxidation and loss of the ribulose bisphosphate acceptor. It reduces the efficiency of photosynthesis as carbon is oxidized, which is the reverse of photosynthesis (the reduction of carbon to carbohydrate) and it is now necessary to resynthesize the ribulose bisphosphate and to start reduction process again. This is highly wasteful of the energy that has been collected from the light, and causes the rubisco to operate at perhaps a quarter of its maximal rate.
