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Question #47649
The Question
During intense symbiotic nitrogen fixation in legume root nodules, the host plant cells deliver abundant sucrose to fuel the process. However, under conditions of extreme nitrogenase activity, the host cell's TCA cycle may stall, leading to localized metabolic starvation despite the high sugar supply. Which of the following best explains the primary biochemical reason for this phenomenon?
Options
- A.
The bacteroids competitively inhibit the host's mitochondrial electron transport chain to maintain the anaerobic environment required by nitrogenase.
- B.
Continuous withdrawal of α-ketoglutarate for ammonia assimilation depletes the host's amphibolic pool faster than anaplerotic reactions can replenish it.
- C.
The massive requirement of 16 ATP per N2 fixed completely depletes the host's cytosolic ATP, preventing the initial priming steps of glycolysis.
- D.
Accumulation of unassimilated ammonia in the host cytosol directly denatures the enzymes of the Krebs cycle, specifically succinate dehydrogenase.
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
Alpha_Ketoglutarate|Nitrogenase|Symbiotic_Nitrogen_Fixation
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often view the TCA cycle purely as a catabolic, energy-yielding pathway and forget its NCERT-highlighted 'amphibolic' nature.
The trap relies on students memorizing the '16 ATP' cost of nitrogen fixation (Option C) and assuming energy depletion causes the stall, missing the critical structural carbon drain (α-ketoglutarate) required to detoxify and assimilate the newly fixed ammonia.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Respiration in Plants - Class 11 |
| Concept | Amphibolic Pathway |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |