Products of cyclic vs noncyclic photophosphorylation Which one of the following is produced by both cyclic and noncyclic photophosphorylation during the light reactions of photosynthesis?

Introduction / Context:
Photosynthetic organisms can route electrons either cyclically around photosystem I or noncyclically from water through photosystems II and I to NADP+. The outputs of these routes differ, and distinguishing them is a common exam theme in plant physiology and bioenergetics.

Given Data / Assumptions:

• Cyclic photophosphorylation uses PSI and cytochrome b6f but does not split water.
• Noncyclic photophosphorylation uses PSII and PSI, splits water, releases O2, and reduces NADP+ to NADPH.
• Both routes generate a proton motive force used by chloroplast ATP synthase.

Concept / Approach:

Cyclic flow returns electrons to PSI and only drives ATP formation. Noncyclic flow yields ATP, NADPH, and O2. Therefore, the only product common to both is ATP, which balances stromal energy demands when extra ATP is required for the Calvin cycle relative to NADPH supply.

Step-by-Step Solution:

Verification / Alternative check:

Measurements of lumen acidification and ATP synthesis persist during PSI-only illumination, confirming ATP production without O2 or NADPH in cyclic mode.

Why Other Options Are Wrong:

NADPH and O2 require noncyclic flow. Carbohydrate is produced in the Calvin cycle, not directly by the light reactions. NADH is a respiratory, not photosynthetic, reductant in chloroplasts.

Common Pitfalls:

Equating any light reaction with oxygen evolution; only PSII activity produces O2 from water splitting.

Final Answer:

ATP