Concept:Gills are the specialised respiratory organs that allow fish to extract oxygen from water.
Explanation:Fish need oxygen to live, and they breathe oxygen dissolved in water.
Water enters the fish through its mouth and passes over the gill filaments.
Gill filaments are thin, thread-like tissues with many blood vessels.
Oxygen (
O2) from water diffuses into the fish’s blood, and carbon dioxide (
CO2) diffuses out.
The buccal cavity only helps pump water towards the gills; it does not perform gas exchange.
The swim bladder helps the fish control buoyancy, not breathing.
Lungs are not used by fish for breathing in water.
Thus, gills are the correct structures for breathing in water.
Answer:B. gills