A desert mammal can produce very concentrated urine because it has
Correct answer: C. a much longer loop of Henle, which builds a steeper salt gradient in the medulla
- A. a larger Bowman's capsule
- B. more glomeruli per kidney
- C. a much longer loop of Henle, which builds a steeper salt gradient in the medulla
- D. no collecting ducts
Explanation
The loop works as a countercurrent multiplier, making the medulla progressively saltier towards the tip, and the collecting duct passing through that region loses water by osmosis. A longer loop maintains a steeper gradient, so more water can be withdrawn and the urine leaves more concentrated, which is exactly the adaptation seen in the kangaroo rat. Filtration rate is unrelated to how concentrated the final urine is.
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The kidney and urinary system remove nitrogenous wastes, regulate water and ion balance, and help maintain blood pH through filtration, selective reabsorption and secretion. Questions cover nephron structure, ultrafiltration, the loop of Henle, collecting ducts, urine formation and the roles of ADH and aldosterone, while distinguishing excretion from egestion.
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