Q70.In deserts, Kangaroos can survive without drinking water because of the following reasons
A. Dependence on protein rich diet
B. Greater ADH level in the blood
C. Absence of sweat glands
D. Dependence on metabolic water
Choose the correct answer from the options given below :
(1) A Only
(2) C and D Only
(3) A, B, C and D
(4) A, B and D Only
The correct answer is option (4): A, B and D Only.
Kangaroo Desert Water Survival
Desert kangaroos (often referring to kangaroo rats, adapted marsupials like bettongs, or red kangaroos) survive without drinking water through multiple physiological adaptations. They rely on metabolic water (D) from oxidizing seeds/fats (0.5g water per gram seeds), produce highly concentrated urine via long kidney loops, and minimize loss through nocturnal behavior and burrowing.
Detailed Reasons
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A. Protein-rich diet: Proteins yield metabolic water during deamination (urea formation), though they require more water for excretion than fats/carbs; desert-adapted diets emphasize seeds over pure protein.
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B. Greater ADH level: Antidiuretic hormone (vasopressin) concentrates urine 5x more than humans, triggered by blood osmolality—key for zero free water intake.
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C. Absence of sweat glands: True for kangaroo rats (no sweating, unlike true kangaroos which pant); evaporative cooling via nasal countercurrent exchange instead.
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D. Metabolic water: Primary source—cellular respiration (C6H12O6 + 6O2 → 6CO2 + 6H2O) provides all hydration needs.
Option Analysis
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Option (1) A Only: Too narrow; ignores ADH and metabolic water.
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Option (2) C and D Only: Misses ADH (B) and protein contribution (A); sweating absence alone insufficient.
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Option (3) A, B, C and D: Includes C, but kangaroo rats don’t sweat (use dry feces/nasal cooling); true kangaroos have minimal glands but pant.
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Option (4) A, B and D Only: Correct combo—metabolic water + ADH + protein metabolism sustain hydration without drinking.
Introduction: How Kangaroos Can Survive Without Drinking Water
NEET ecology tests desert adaptations like “Kangaroos can survive without drinking water” via protein diet, ADH, and metabolic water. Master why option (4) A, B, D fits kangaroo rats/red kangaroos, enabling zero external water intake in arid zones. This guide details mechanisms and exam strategy.
Key Adaptations Explained
Kangaroo rats (Dipodomys) and desert kangaroos thrive via:
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Metabolic water (D): Fat oxidation yields 1.07g H2O/g; seeds provide bulk.
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High ADH (B): Kidneys form hypertonic urine (9000 mOsm/L vs. human 1200).
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Protein diet (A): Urea from proteins contributes water, excreted as uric acid minimally.
Nocturnal foraging + burrows cut respiratory loss 50%.
Why Not Sweat Glands (C)?
Kangaroo rats lack them entirely (nasal cooling); larger macropods pant minimally. C distracts but doesn’t apply universally—making (4) precise.
NEET Answer: Option (4) A, B, D Confirmed
Combines diet, hormones, metabolism. Trap: Confusing rats (no sweat) with true kangaroos (some glands).
