Question

Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain.

Answer 1

Breathing rates differ because air and water provide oxygen differently. Air contains about 21% O₂ and allows rapid diffusion, so terrestrial animals with lungs achieve high gas-exchange rates with intermittent ventilation. Water holds far less dissolved O₂ and has much slower diffusion; therefore, aquatic animals rely on large surface-area gills, continuous unidirectional flow and countercurrent exchange to extract sufficient oxygen. Water’s higher density and viscosity make ventilation more energetically costly, so many aquatic species have lower metabolic or adjusted ventilation frequencies. Thus differences in oxygen availability, diffusion and medium mechanics explain contrasting breathing rates