The pathway of electrons in photosynthesis is shown with red arrows in the diagram below. Each step in this pathway is a coupled oxidation-reduction reaction. Water is oxidized as a result of the light reaction of Photosystem II. From Photosystem II, electrons pass to plastoquinone (PQ) to cytochromes (Cyt) to plastocyanin (PC). Another light reaction at Photosystem I activates electrons for transfer to ferredoxin, and finally to NADP+.

The overall equation for non-cyclic electron transport

Water is oxidized to oxygen, releasing protons. The protons become part of the energy source for ATP synthesis. The electrons from water eventually reduce NADP+ to NADPH.