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Question #46236
The Question
A leguminous plant with reticulate venation is grown in nitrogen-deficient soil. A mutation in its root hair cells prevents the curling response to Rhizobium Nod factors. Over time, the mass flow of phloem sap from the leaves to the roots severely declines. Based on the Munch hypothesis and mineral nutrition principles, which of the following best explains this systemic failure?
Options
- A.
Reduced synthesis of photosynthetic enzymes and carrier proteins impairs active sucrose loading into the dense veinlet network, failing to generate the high turgor pressure required at the source.
- B.
The absence of nitrogen fixation prevents the synthesis of ureides and amides, which are required to maintain the high osmotic pressure of the phloem sap during downward translocation.
- C.
Nitrogen starvation induces the degradation of the reticulate vascular cambium, physically disrupting the continuity of the sieve tube elements between the source and the sink.
- D.
The lack of nitrogen directly inhibits the active transport of water from the adjacent xylem vessels into the phloem sieve tubes, halting bulk flow.
Check Your Answer
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
Companion_Cell-Sieve_Tube_Symport|Symbiotic_Nitrogen_Fixation|Parallel_Venation
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating the anatomical site of loading (reticulate veinlets) with the biochemical requirement for active transport (nitrogen-dependent carrier proteins) and the physical driver of mass flow (turgor pressure).
The primary trap is Option B, which exploits a common misconception regarding the transport pathway of fixed nitrogen, testing the student's precise recall that nodule-derived nitrogenous compounds travel via the xylem, not the phloem.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Morphology of Flowering Plants - Class 11 |
| Concept | Leaf Venation Patterns |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |