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Question #46266
The Question
A botanist observes a mutant C3 plant where the NPP/GPP (Net Primary Productivity to Gross Primary Productivity) ratio has shifted from 0.5 to 0.2 due to a massive increase in cellular respiration. Simultaneously, the chloroplasts exhibit an unusually high rate of chemiosmotic ATP synthesis exclusively via cyclic photophosphorylation. Despite the abundant stromal ATP, the development of fruit biomass (sink) is severely restricted. Which of the following is the most accurate physiological explanation for this observation?
Options
- A.
The high stromal ATP downregulates the genetic expression of sink-strength determinants in the fruit, preventing active phloem unloading.
- B.
The restricted fruit biomass is a direct consequence of the lowered NPP/GPP ratio, as respiratory losses deplete the photoassimilates available for translocation, irrespective of chloroplast ATP generation.
- C.
Cyclic photophosphorylation lacks PSII activity, causing a deficit in O2 evolution that directly inhibits the Calvin cycle and reduces GPP.
- D.
The excess ATP from cyclic photophosphorylation forces the Calvin cycle to fix more CO2, but the lack of NADPH prevents the reduction of 3-PGA, leading to a toxic buildup that destroys the fruit sink.
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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
Fruit Structure DNA|Productivity Ratios|Chemiosmotic ATP Synthesis Logic
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often confuse the bioenergetic flux of a single organelle (ATP production in chloroplasts) with the whole-plant net carbon allocation (NPP).
The trap relies on the misconception that high ATP automatically translates to high biomass, ignoring the ecological equation NPP = GPP - R and the absolute requirement of NADPH for carbon fixation.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Morphology of Flowering Plants - Class 11 |
| Concept | Fruit Structure DNA |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |