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Question #46810
The Question
A researcher alters the soil pH of a leguminous crop, severely inhibiting the nitrogenase enzyme complex of its root nodule symbionts. Over time, the plant exhibits a marked decrease in the translocation of photosynthates from leaves to roots. Which of the following best explains the molecular basis of this transport failure?
Options
- A.
Nitrogen deficiency reduces the synthesis of H+-ATPase pumps in companion cells, diminishing the proton gradient required for active sucrose-H+ symport.
- B.
The lack of fixed nitrogen causes the root nodules to cease ATP production, directly starving the phloem sieve tubes of the energy required for mass flow.
- C.
Reduced nitrogen availability inhibits the conversion of glucose to sucrose in the mesophyll, preventing the passive diffusion of sugars into the phloem.
- D.
The symbiotic interference triggers a stress response that closes plasmodesmata, shifting the plant entirely to apoplastic phloem loading.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Companion Cell-Sieve Tube Symport|Decomposition Rate Modifiers|Ecotone and Edge Effect
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating 'Mineral Nutrition' with 'Transport in Plants'.
Students often memorize that phloem loading is active but fail to recognize that the transport machinery (H+-ATPase pumps) are proteins dependent on the plant's nitrogen status.
The trap (Option B) exploits the misconception that roots provide the energy for downward mass flow, whereas mass flow is a passive physical process driven by active loading at the source.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Anatomy of Flowering Plants - Class 11 |
| Concept | Companion Cell-Sieve Tube Symport |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |