The sequence of the one-way gaseous exchange mechanism in a fish is?

  • A mouth --> operculum -> gills
  • B mouth -> gills > operculum
  • C operculum > gills -> mouth
  • D gills -> operculum --> mouth
jamb 2021biology

The correct answer is B. mouth -> gills > operculum

Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. In some fish, capillary blood flows in the opposite direction to the water, causing counter-current exchange. The gills push the oxygen-poor water out through openings in the sides(opercula) of the pharynx.

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