Fig. 1 Light reactions of photosynthesis and photophosphorylation associated with thylakoid membranes inside chloroplasts leading to production of NADPH and ATP used in CO₂ assimilation. Photons are absorbed by chlorophyll antennae in both photosystem II (PSII) and photosystem I (PSI). Water is oxidized by PSII, yielding O₂ and protons in the lumen. Coordinated activity of PSII and the cytochrome (cyt) b₆f complex pumps protons from stroma to lumen. This involves cycling of plastoquinone between oxidized (Q) and reduced (QH₂) states. As drawn, a "Q-cycle" is associated with cyt b₆f. Electrons are transferred from cyt b₆f to PSI via plastocyanin (PC). In noncyclic electron transport, e^- are then transferred from PSI via ferredoxin (Fd) to FNR (ferredoxin-NADP reductase), which leads to reduction of NADP. The dashed line (– – –) indicates cyclic transport in which e^- flow from PSI back to the cyt complex via Fd. Protons move from lumen to stroma through CF_o-CF₁ ATP synthase, which catalyzes ADP phosphorylation (about 3 protons/ATP)

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