AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
A terrestrial organism breathes air directly, which contains about 21% oxygen. Since oxygen is freely and abundantly available in the atmosphere, it can be taken in easily.
An aquatic organism, however, must use the oxygen dissolved in water, which is present in much smaller amounts. This makes obtaining sufficient oxygen harder and more energy-consuming for aquatic organisms.
Source: Life Processes, Chapter 5, Section 5.1
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The examiner expects two clear points: (1) oxygen is more abundant/easily available in air than dissolved in water, and (2) this gives the terrestrial organism an advantage in meeting its oxygen needs for respiration. Avoid over-explaining; two focused comparative sentences are enough for 2 marks.