<P> In oxidative phosphorylation, electrons are transferred from a low - energy electron donor (e.g., NADH) to an acceptor (e.g., O) through an electron transport chain . In photophosphorylation, the energy of sunlight is used to create a high - energy electron donor and an electron acceptor . Electrons are then transferred from the donor to the acceptor through another electron transport chain . </P> <P> Photosynthetic electron transport chains have many similarities to the oxidative chains discussed above . They use mobile, lipid - soluble carriers (quinones) and mobile, water - soluble carriers (cytochromes, etc .). They also contain a proton pump . It is remarkable that the proton pump in all photosynthetic chains resembles mitochondrial Complex III . </P> <P> Photosynthetic electron transport chains are discussed in greater detail in the articles Photophosphorylation, Photosynthesis, Photosynthetic reaction center and Light - dependent reaction . </P> <P> Electron transport chains are redox reactions that transfer electrons from an electron donor to an electron acceptor . The transfer of electrons is coupled to the translocation of protons across a membrane, producing a proton gradient . The proton gradient is used to produce useful work . About 30 work units are produced per electron transport . </P>

Where is oxygen used in the electron transport chain