AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Water contains very little dissolved oxygen (about 1%) compared to air (21%). So, to obtain the required amount of oxygen, aquatic fish must breathe water much more rapidly and pass larger volumes over their gills. Terrestrial mammals breathe air, which is far richer in oxygen, so fewer breaths are needed.
The key point examiners expect is the low oxygen content of water vs. air. Fish compensate by increasing breathing rate to extract enough oxygen through gills. Note: the source passages do not directly state this, but it is standard NCERT Class 10 Biology knowledge from Chapter 5 (Life Processes, Respiration section). If your exam provides a specific passage on this, quote from it; otherwise, use this core reasoning. Keep the answer focused on the cause-effect link: low O₂ in water → faster breathing rate.