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Question #46300
The Question
A researcher applies a targeted chemical to a young dicotyledonous stem that permanently inactivates the intrafascicular cambium immediately after primary growth. As the plant continues its apical growth, the newly formed distal tissues exhibit severe energy depletion and a failure to synthesize structural lipids and proteins. Which of the following best explains the primary physiological bottleneck causing this distal starvation?
Options
- A.
The fixed diameter of the primary phloem restricts the mass flow of photoassimilates, limiting the substrate flux required to drive the amphibolic respiratory pathways in distal sinks.
- B.
The transition to 'closed' vascular bundles directly inhibits the mitochondrial enzymes, preventing the withdrawal of acetyl CoA and α-ketoglutarate.
- C.
The absence of secondary xylem prevents the upward translocation of respiratory intermediates like oxaloacetic acid from the root system to the shoot apex.
- D.
The lack of secondary growth restricts oxygen diffusion to the distal tissues, forcing a shift from an amphibolic TCA cycle to strictly catabolic anaerobic fermentation.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Amphibolic Pathway|Vascular Bundle|Xylem/Phloem Transport
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Bridging Plant Anatomy (vascular capacity via secondary growth) with Plant Physiology (amphibolic nature of respiration).
Students often fail to realize that the 'open' nature of dicot vascular bundles is a prerequisite for scaling up the mass flow of assimilates needed to sustain the high metabolic flux of amphibolic pathways in growing distal sinks.
The trap in Option C tests the misconception that respiratory intermediates themselves are translocated long-distance, rather than their precursor (sucrose).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Anatomy of Flowering Plants - Class 11 |
| Concept | Vascular Bundle Openness |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |