AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Aquatic organisms like fish use oxygen dissolved in water for breathing. The amount of dissolved oxygen in water is much less compared to the oxygen present in air. Therefore, aquatic organisms have to breathe much faster to absorb sufficient oxygen to meet their body's requirements.
Source: Life Processes, Chapter 5
The examiner expects two clear points: (1) aquatic organisms use dissolved oxygen from water, and (2) dissolved oxygen in water is far less than in air — so faster breathing compensates for the low oxygen availability. Both points are needed for full 2 marks. Avoid writing about terrestrial breathing mechanisms; just contrast oxygen availability in water vs. air.