Biology Homeostasis PMDC Conceptual Practice
PMDC Verified Question 19 of 99
In marine teleost fishes, excess divalent inorganic ions such as \(\text{Mg}^{2+}\) and \(\text{SO}_4^{2-}\) ingested with seawater are excreted primarily by the:
A
Gills
B
Operculum
C
Kidneys
D
Skin
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Kidneys
Concept: Osmoregulation in marine bony fishes.

Solution: While monovalent ions (\(\text{Na}^+\), \(\text{Cl}^-\)) are actively pumped out across the gills, excess divalent ions (like \(\text{Mg}^{2+}\) and \(\text{Ca}^{2+}\)) are secreted into the urine by the kidneys.

Why other options are incorrect:
  • Option A: Gills primarily eliminate monovalent ions (\(\text{Na}^+\), \(\text{Cl}^-\)) and nitrogenous waste (ammonia).

  • Option B & Option D: The operculum is a bony flap covering the gills; skin in bony fishes is largely impermeable to ions.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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