Q.100 In vertebrates, the variations in the structure and function of nephrons are directly linked to the
osmoregulatory requirements of the organisms depending on the habitats they live in. From the
options given below, identify the correct combination that truly represents the adaptation seen in
desert mammals:
i. Long loops of Henle
ii. Short loop of Henle
iii. Hyperosmotic urine
iv. Large volume of urine
v. Removal of nitrogen as uric acid
(A) Options i and iii (B) Options ii and iii (C) Options i and iv (D) Options i and v
Desert mammals adapt with long loops of Henle to produce hyperosmotic urine, minimizing water loss in arid habitats.
The correct answer is (A): Options i and iii.
Nephron Adaptations Explained
Desert mammals (kangaroo rats, gerbils) face extreme water scarcity, requiring urine concentration >5,000 mOsm/L (vs. human ~1,200 mOsm/L). Long loops of Henle create/countercurrent multiplier establishes medullary hypertonicity (NaCl/urea gradient). Vasa recta countercurrent exchange preserves gradient. Collecting ducts (aquaporin-2 upregulated by vasopressin) reabsorb water passively, yielding hyperosmotic urine.
Option Breakdown
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i. Long loops of Henle: Correct—extends countercurrent system, multiplies NaCl gradient ~1,200→5,000 mOsm/L from cortex to papilla tip.
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ii. Short loop of Henle: Wrong—aquatic/freshwater vertebrates; minimal gradient, dilute urine.
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iii. Hyperosmotic urine: Correct—urine > blood osmolality (300 mOsm/L); conserves water maximally.
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iv. Large volume of urine: Wrong—amphibians/aquatics; desert mammals produce minimal volume (~0.1-0.5 ml/100g/day).
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v. Removal of nitrogen as uric acid: Wrong—birds/reptiles (insoluble, water-saving); mammals use urea (soluble).
Answer choices: (A) i+iii ✓ | (B) ii+iii ✗ | (C) i+iv ✗ | (D) i+v ✗
Introduction to Desert Mammals Nephron Adaptations
Desert mammals nephron adaptations feature long loops of Henle generating hyperosmotic urine—essential GATE Life Sciences physiology. Kangaroo rats concentrate urine 5x human maximum via countercurrent multiplier, tolerating 0.2 ml water/100g/day intake.
Countercurrent Mechanism
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Long Henle: Descending limb (permeable) equilibrates; thick ascending actively pumps NaCl out.
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Medullary gradient: 300→5,000 mOsm/L; urea recycling amplifies.
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Result: Collecting duct extracts ~90% water → hyperosmotic urine.
Adaptation Matching
| Feature | Desert Mammals | Other Habitats |
|---|---|---|
| Loop length | Long (i ✓) | Short (freshwater) |
| Urine type | Hyperosmotic (iii ✓) | Hypoosmotic (marine) |
| Urine volume | Minimal | Large (iv ✗) |
| Nitrogen waste | Urea | Uric acid (birds,v ✗) |
GATE Strategy
Desert mammals nephron adaptations = long Henle + concentrated urine = (A). Contrast: freshwater fish (short loops, dilute urine); birds (uric acid, loop-less). PYQ pattern: habitat → nephron structure. Master vasa recta recycling.
