Where the ATP and NADPH actually come from
Linear electron flow starts at photosystem II, not I — the numbering records the order of discovery, not the order of events, and that alone costs marks every year. The oxygen-evolving complex strips electrons from water, releasing O2 as a by-product, and those electrons travel through plastoquinone, the cytochrome b6f complex, plastocyanin and then photosystem I before ferredoxin and FNR hand them to NADP+ to make NADPH. The useful work happens at cytochrome b6f, which pumps protons into the thylakoid lumen. That gradient — lumen pH can fall to about 5 against a stromal pH near 8 — is what drives ATP synthase. Light does not make ATP directly; it makes a proton gradient, and the gradient makes ATP.