Major reactions of photosynthesis

The light reaction The energy of light is used to energize electrons in the reaction center chlorophyll molecules of a photosystem. The electrons are then passed on to an electron transport chain. The missing electrons in the reaction center are replenished when 2H₂O is split to O₂, 4H⁺ and 4e⁻. The electron moves through the electron transport chain until it energizes the cytochrome b/f complex to pump protons into the thylakoid lumen and is then passed to photosystem I (PS-I) where it is re-energized and passed to NADP reductase, generating NADPH. PS-I can also function alone to transport H⁺. Adenosine triphosphate (ATP) is generated by H⁺ passing through the enzyme ATP synthase located in the thylakoid membrane. The two products of the light reactions are therefore NADPH and ATP.