B. A proton gradient drives the formation of ATP from ADP and inorganic phosphate via ATP synthase.
Explanation:
Light reaction of photosynthesis includes the splitting of water in the presence of sunlight and electron transfer from PSII to PSI via an electron transport system. During the transfer of electron through cytochrome of the electron transport system, the proton concentration gradient is generated across thylakoids. The proton concentration gradient is harvested to drive ADP phosphorylation by the catalytic site of ATP synthase accompanied by downhill movement protons through its proton channels.
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