Where is NADPH formed in the light-dependent reactions?

• A. In the lumen of the thylakoids.
• B. In the cytosol.
• C. In the stroma after transfer via ferredoxin-NADP+ reductase.
• D. In the mitochondria.

Answer: (C)

NADPH is formed on the stromal side of the thylakoid membrane, after electrons have been transferred to ferredoxin and then to ferredoxin-NADP+ reductase. This enzyme uses NADP+ in the stroma to accept those electrons and produces NADPH there. The lumen is where protons are pumped to generate the proton gradient for ATP synthase, so it’s not the site of NADPH production. NADPH (and ATP) are then used in the stroma for the Calvin cycle.