UPSC Previous Year Question | Prelims GS | 2025

With reference to the planet Earth, consider the following statements: I. Rain forests produce more oxygen than that produced by oceans. II. Marine phytoplankton and photosynthetic bacteria produce about 50% of world's oxygen. III. Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air. Which of the statements given above is/are correct?

  1. I and II
  2. II only
  3. I and III
  4. None of the above statements is correct

Answer

Correct Answer

II only

Explanation

Oceans, through marine phytoplankton and photosynthetic bacteria, actually produce more oxygen than rain forests overall (roughly half of the world's oxygen), making Statement I incorrect but Statement II correct. Well-oxygenated surface water does not contain several times higher oxygen concentration than atmospheric air (dissolved oxygen in water is actually much lower by volume than in air), making Statement III incorrect.

Topics: environment, oceanography, oxygen production