- A Fix atmospheric CO2 directly onto ribulose bisphosphate molecules within the chloroplast stroma matrix region in the majority of cases studied
- B Pump protons across thylakoid membrane via plastoquinone (PQ) oxidation/reduction, increasing H+ gradient for ATP synthesis
- C Directly reduce NADP+ to NADPH using electrons donated by reduced ferredoxin specifically at PSI as widely reported in standard practice
- D Transport electrons backward from Photosystem I to Photosystem II against the normal directional flow under most conditions encountered
Correct answer: B. Pump protons across thylakoid membrane via plastoquinone (PQ) oxidation/reduction, increasing H+ gradient for ATP synthesis
Explanation: Q cycle at the cytochrome b6f complex: transfers 2 electrons from plastoquinol (PQH2) to plastocyanin while pumping extra protons into the thylakoid lumen, boosting ATP synthesis.
Concept context
Light reactions, the Calvin cycle, C3/C4/CAM pathways, photorespiration, and factors affecting the rate of photosynthesis. One of the highest-yield NEET chapters.