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Question #45441
The Question
A desert mammal in deep aestivation experiences profound metabolic suppression, including the downregulation of the Renin-Angiotensin-Aldosterone System (RAAS). If unexpectedly aroused by an unseasonal temperature spike, the animal is highly vulnerable to rapid dehydration. Which of the following physiological states best explains this immediate vulnerability?
Options
- A.
Reduced Na+/K+ ATPase activity in the thick ascending limb has dissipated the medullary interstitial osmotic gradient, rendering ADH ineffective at concentrating urine.
- B.
Suppressed aldosterone levels cause the descending limb of Henle's loop to actively secrete Na+, reversing the counter-current multiplier.
- C.
The sudden arousal induces a compensatory surge in Atrial Natriuretic Factor (ANF), which directly blocks obligatory water reabsorption in the Proximal Convoluted Tubule (PCT).
- D.
Downregulation of RAAS leads to the permanent degradation of Aquaporin-2 channels in the collecting duct, preventing facultative water reabsorption.
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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
Diapause|Osmotic_Gradient|Descending_Loop_of_Henle
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often mistakenly believe that the presence of ADH and Aquaporin-2 channels alone is sufficient to concentrate urine.
This question tests the deeper NCERT concept that facultative water reabsorption in the collecting duct is entirely dependent on the medullary interstitial osmotic gradient, which is actively maintained by the Loop of Henle.
By introducing 'metabolic suppression', it forces the student to connect ATP depletion with the failure of the active transport in the ascending limb.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Chemical Coordination and Integration - Class 11 |
| Concept | RAAS Mechanism |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |