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Question #47621
The Question
In a comparative ecological study in a hot, arid environment, a C4 plant initially exhibits superior biomass production over a C3 plant due to its Kranz anatomy and lack of photorespiration. However, when the soil nitrogen reservoir becomes severely depleted, the C4 plant loses its competitive advantage. Based on the stoichiometric resource allocation of photosynthesis, which of the following best explains this shift?
Options
- A.
The metabolic and nitrogen overhead required to synthesize the dual-enzyme system (PEPcase and Rubisco) and maintain Kranz anatomy becomes unsustainable under severe nitrogen scarcity.
- B.
Nitrogen deficiency degrades the thick, impervious walls of the bundle sheath cells, allowing oxygen entry and triggering severe photorespiration.
- C.
The lack of nitrogen prevents the regeneration of Phosphoenolpyruvate (PEP) in mesophyll cells, forcing the C4 plant to switch entirely to the C3 pathway.
- D.
Nitrogen scarcity specifically inhibits cyclic photophosphorylation in the agranal bundle sheath chloroplasts, halting the ATP supply for the Calvin cycle.
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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
Rubisco|PEP_Carboxylase|Nitrogen_Use_Efficiency
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that 'C4 plants are always superior in hot climates' and generally have high nitrogen-use efficiency.
However, this question tests the advanced application of stoichiometric constraints: the synthesis of the complex dual-pathway machinery (PEPcase + shuttle enzymes + Kranz structure) has a baseline nitrogen/energetic overhead.
When nitrogen is severely limiting, this overhead becomes a liability.
The distractors utilize NCERT facts (impervious bundle sheath walls, agranal chloroplasts) but apply them incorrectly to the stress condition.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | Kranz Anatomy Adaptations |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |