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Question #47597
The Question
During severe desiccation stress, a plant closes its stomata and its chloroplasts shift predominantly to cyclic photophosphorylation occurring in the stroma lamellae. Which of the following best describes the physiological necessity and the resulting metabolic trade-off of this shift?
Options
- A.
It bypasses Photosystem II to conserve water from photolysis, resulting in an increased ATP/NADPH ratio that accelerates the reduction phase of the Calvin cycle.
- B.
The absence of NADP reductase activity prevents photo-oxidative damage when assimilation is stalled, but creates a bottleneck in carbon fixation due to a lack of reducing power.
- C.
It maintains continuous electron flow to generate metabolic water via the cytochrome b6f complex, ensuring cellular hydration at the expense of ATP production.
- D.
The shift activates the oxygen-evolving complex in the stroma lamellae to provide electrons directly to Photosystem I, prioritizing survival over growth.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
Cyclic Photophosphorylation Pathways|Metabolic Water Formation
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Connecting the anatomical limitation of stroma lamellae (lack of PS II and NADP reductase) with the ecological trigger (water stress/closed stomata) and the biochemical consequence (high ATP, zero NADPH, stalled Calvin cycle).
Students often fail to link the depletion of the terminal electron acceptor () to the protective role of cyclic electron flow.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | Cyclic Photophosphorylation Pathways |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |