Photorespiration is a process that occurs during photosynthesis in some plants (C3 plants). During the process, the enzyme RuBisCO oxygenates RuBP wasting energy produced during the process of photosynthesis. Normally, RuBusCO adds carbon dioxide to RuBP and performs a key reaction in the Calvin–Benson cycle. However, due to the high concentration of oxygen and low concentration of carbon dioxide, RuBisCO adds oxygen to RuBP. As a result, RuBisCO performs oxygenation instead of carboxylation under the conditions of low carbon dioxide reducing the efficiency of photosynthesis. As a result, photorespiration is observed in C3 plants at low CO2 concentrations.