<P> The thylakoids are the site of the light - dependent reactions of photosynthesis . These include light - driven water oxidation and oxygen evolution, the pumping of protons across the thylakoid membranes coupled with the electron transport chain of the photosystems and cytochrome complex, and ATP synthesis by the ATP synthase utilizing the generated proton gradient . </P> <P> The first step in photosynthesis is the light - driven reduction (splitting) of water to provide the electrons for the photosynthetic electron transport chains as well as protons for the establishment of a proton gradient . The water - splitting reaction occurs on the lumenal side of the thylakoid membrane and is driven by the light energy captured by the photosystems . It is interesting to note that this oxidation of water conveniently produces the waste product O that is vital for cellular respiration . The molecular oxygen formed by the reaction is released into the atmosphere . </P> <P> Two different variations of electron transport are used during photosynthesis: </P> <Ul> <Li> Noncyclic electron transport or Non-cyclic photophosphorylation produces NADPH + H and ATP . </Li> <Li> Cyclic electron transport or Cyclic photophosphorylation produces only ATP . </Li> </Ul>

The three molecular complexes contained in the thylakoid membrane are