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Question #46274
The Question
In a terrestrial ecosystem dominated by the Detritus Food Chain (DFC), rapid decomposition of leaf litter significantly lowers the rhizosphere pH. A dominant plant species in this ecosystem exhibits the floral formula % ⚥ K(5) C1+2+(2) A(9)+1 G1. Over time, this species begins to exhibit severe chlorosis primarily in its older leaves. Which of the following is the most scientifically accurate explanation for this phenomenon?
Options
- A.
The acidic soil inhibits Rhizobium multiplication and leghemoglobin function, causing a systemic nitrogen deficiency where mobile nitrogen is translocated away from older leaves.
- B.
The low pH denatures the Mo-Fe protein (nitrogenase) located in the mesophyll chloroplasts, preventing the reduction of atmospheric nitrogen.
- C.
Humic acids from the DFC directly enter the root nodules and bind to leghemoglobin, increasing its oxygen affinity and irreversibly oxidizing nitrogenase.
- D.
The plant, belonging to Solanaceae, fails to absorb immobile elements like nitrogen in acidic soils, leading to chlorosis in senescing tissues.
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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
Fabaceae Floral Formula|Detritus Food Chain Dominance|Nitrogen Cycling
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating Morphology (Fabaceae floral formula), Ecosystems (DFC acidity), and Mineral Nutrition (N-fixation conditions and mobility).
The trap relies on students failing to connect ecological conditions (soil pH) with physiological failures (nodulation), misidentifying the location of nitrogenase (nodule vs mesophyll), or forgetting the mobility rules of nitrogen (deficiency symptoms in older vs younger leaves).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Morphology of Flowering Plants - Class 11 |
| Concept | Fabaceae Floral Formula |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |