During the Z-scheme of photosynthesis, a proton gradient across the thylakoid membrane is created primarily by the movement of protons into the thylakoid lumen, not into the stroma. Key contributors include: oxidation of water by Photosystem II, which releases protons into the lumen; electron transport through carriers, which pumps protons into the lumen; and reduction of NADP , which consumes electrons and contributes indirectly to proton movement. In contrast,protons released into the stroma during water splitting do not help in building the proton gradient across the thylakoid membrane, so this process does not contribute to the proton motive force used for ATP synthesis.