Which of the following conditions favors cyclic photophosphorylation over non-cyclic photophosphorylation in plant chloroplasts?
Answer and explanation
Correct answer: A. Illumination with light of wavelength beyond 680 nm and low stromal NADP+ availability
- Step 1: Cyclic photophosphorylation involves only Photosystem I and operates primarily in stroma lamellae membranes.
- Step 2: Stroma lamellae lack Photosystem II and NADP+ reductase enzyme.
- Step 3: When illuminated with far-red light (wavelength > 680 nm) or when the stroma is depleted of (high NADPH/NADP+ ratio), electrons from P700 flow back via ferredoxin to cytochrome and plastocyanin, generating ATP without or .
Answer
Illumination with light of wavelength beyond 680 nm and low stromal NADP+ availability
Why not the others: 'High carbon dioxide availability and intense blue-green light' drives active non-cyclic electron flow and Calvin cycle turnover; 'Absence of Photosystem I...' is incorrect because cyclic photophosphorylation strictly requires Photosystem I; 'High oxygen concentration and presence of active NADP+ reductase' promotes linear electron flow towards NADP+ reduction.
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