The first stage of photosynthesis happens in the thylakoid membrane where photosystems exist. It requires light without it, the reaction chain cannot start. Light is absorbed by the photosystem II to do photolysis which breaks down water to release protons, electrons and oxygen. The electrons then get excited by the light energy and go into electron transport chains, producing ATP. They repeat the excitation process as they arrive at photosystem I. They then meet up with the protons at the NADP reductase to reduce NADP, which then goes on into the next stage of photosynthesis (Calvin cycle). Protons go through ATP synthase in the electron transport chains to produce ATP at various places on the thylakoid membrane.

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