[Campbell Biology P.1039] The text describes the loop of Henle as a 'countercurrent multiplie... | Practice Question

The text describes the loop of Henle as a 'countercurrent multiplier system.' How does this system fundamentally differ from the countercurrent heat exchanger in endotherms or gas exchange in fish gills, as mentioned in the passage?

  • A: The loop of Henle system primarily relies on maintaining a heat gradient, while others rely on solute gradients.
  • B: Unlike the other examples, the loop of Henle system requires active transport and energy expenditure to create its concentration gradient.
  • C: The loop of Henle system involves only passive diffusion, whereas the others involve active processes.
  • D: The other systems reduce loss or maximize gain, while the loop of Henle system only functions to increase solute concentration.

Explanation

The text explicitly states: 'In contrast, the countercurrent system of the loop of Henle involves active transport and thus an expenditure of energy. The active transport of NaCl from the filtrate in the upper part of the ascending limb of the loop maintains a high salt concentration in the interior of the kidney, enabling the kidney to form concentrated urine. Such countercurrent systems, which expend energy to create concentration gradients, are called countercurrent multiplier systems.' This clearly distinguishes it from other countercurrent systems mentioned heat exchangers, gas exchange in gills which primarily involve passive movement along gradients.