[Campbell Biology P.1027] Sockeye salmon are euryhaline osmoregulators that migrate between f... | Practice Question

Sockeye salmon are euryhaline osmoregulators that migrate between freshwater rivers and the ocean. When a sockeye salmon moves from a freshwater river to the ocean, what osmotic challenge does it primarily face, and what is its typical osmoregulatory response as described by the text for a hyperosmotic environment?

  • A: It faces a hypoosmotic environment and would actively absorb water.
  • B: It faces a hyperosmotic environment and would actively discharge excess water.
  • C: It faces a hyperosmotic environment and would actively take in water to offset osmotic loss while actively excreting salts.
  • D: It faces a hypoosmotic environment and would actively take in water to offset osmotic loss.

Explanation

The ocean environment is hyperosmotic compared to the salmon's internal osmolarity human blood is 300 mOsm/L, seawater is 1000 mOsm/L, indicating marine fish are typically hypoosmotic to seawater . The text states that in a hyperosmotic environment, an osmoregulator 'must instead take in water to offset osmotic loss'. This strategy also typically involves actively excreting excess salts gained from drinking seawater.