Photorespiration is a biochemical process in C3 plants in which some O2 does bind to RuBisCO as it has both a carboxylase and the oxygenase activity. It results in the formation of one molecule of phosphoglycerate and phosphoglycolate instead of being converted to 2 molecules of PGA and hence CO2 fixation is decreased. In this pathway of photorespiration, there is neither synthesis of sugars, nor ATP. Instead, it results in the utilisation of ATP with the release of CO2. In C4 plants, photorespiration does not occur. This is because they have a mechanism to increase the intracellular concentration of CO2 at the enzyme site so that RuBisCO functions as a carboxylase minimising the oxygenase activity.