Which phase of photosynthesis uses light to produce ATP and NADPH?

• A. Light dependent reactions
• B. Calvin cycle
• C. Photosystem I
• D. Stroma

Answer: (A)

Light energy drives the production of ATP and NADPH in the light-dependent reactions, which occur in the thylakoid membranes. In these reactions, water is split by photosystem II, releasing oxygen and electrons. The electrons move through an electron transport chain, creating a proton gradient that powers ATP synthase to make ATP. The electrons are then transferred to photosystem I and finally to NADP+, forming NADPH via ferredoxin-NADP+ reductase. These two energy carriers—ATP and NADPH—are generated here to fuel the next stage, the Calvin cycle, in the stroma, which uses them to fix carbon. The other options refer to components or locations rather than the phase that directly uses light to produce ATP and NADPH.