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Question #47647
The Question
The TCA cycle functions as an amphibolic pathway where intermediates like α-ketoglutarate and oxaloacetate are continuously withdrawn for the synthesis of amino acids. This continuous withdrawal requires the replenishment of carbon skeletons to prevent a metabolic bottleneck. If a plant is grown in soil with highly deficient phosphorus, it eventually suffers from systemic senescence. Which of the following best explains the primary physiological reason for this metabolic collapse?
Options
- A.
Phosphorus is an immobile element within the plant, causing immediate necrosis of young apical meristems due to the inability to synthesize nucleic acids.
- B.
Reduced photophosphorylation limits ATP and NADPH, halting carbon fixation; thus, the continuous withdrawal of TCA intermediates drains the carbon pool without replenishment.
- C.
The withdrawal of α-ketoglutarate for reductive amination directly consumes ATP; without phosphorus, toxic ammonia accumulates and denatures TCA enzymes.
- D.
Phosphorus deficiency prevents the transamination of oxaloacetate into pyruvic acid, trapping carbon skeletons in the mitochondria and halting the amphibolic pathway.
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
Pyruvate|Oxaloacetate|Nutrient_Immobility
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students must integrate three distinct NCERT chapters: Mineral Nutrition (Mobility of P), Photosynthesis (ATP/NADPH requirement for carbon fixation), and Respiration (Amphibolic nature of the TCA cycle).
The primary trap is Option A, which plays on the 'Not/Except' location trap by confusing the immobility of Phosphorus in the soil with its high mobility within the plant tissue.
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 |