What is the role of ferredoxin in photosynthesis?

• A. It transfers electrons from PSI to ferredoxin-NADP+ reductase, producing NADPH.
• B. It captures light energy to generate ATP.
• C. It transports CO2 into the stroma.
• D. It accepts electrons from PSII to reduce plastoquinone.

Answer: (A)

Ferredoxin’s job is to carry electrons from photosystem I to the enzyme that makes NADPH. After PSI is excited by light, it passes electrons to ferredoxin, a small iron-sulfur protein in the stroma. Ferredoxin then donates those electrons to ferredoxin-NADP+ reductase, which uses them to convert NADP+ into NADPH. This NADPH provides the reducing power for the Calvin cycle to fix CO2 into sugars. This step is separate from ATP production, which comes from the proton gradient driving ATP synthase. Ferredoxin is not involved in CO2 transport or in transferring electrons from PSII to plastoquinone.