Photophosphorylation

Photophosphorylation is the name given specifically to ATP synthesis that is driven by electrons set in motion by light, distinguishing it from the two other ways cells make ATP: oxidative phosphorylation, which happens during respiration, and substrate-level phosphorylation, in which ATP is generated directly from the breakdown of a metabolic substrate. Because the addition of phosphate to ADP in this case is powered specifically by a light-energised electron moving through the thylakoid membrane's carrier chain, the process is named photophosphorylation, and it takes place through two distinct routes: cyclic electron transport (section 13.11.1), involving PS I alone, and non-cyclic electron transport (section 13.11.2), involving PS I and PS II working together. The two routes differ in nearly every respect - which photosystem(s) are involved, whether water is split, and crucially, whether NADPH+H+ is pr …