by Q. With reference to the planet Earth, consider the following statements:
UPSC Civil Services Examination (Prelims) 2025 – General Studies Paper I
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?
(a) I and II
(b) II only
(c) I and III
(d) I, II and III
Answer: (b) II only
- Statement I is incorrect: While rainforests are called the “lungs of the Earth”, oceans (via phytoplankton and cyanobacteria) produce 50–80% of global oxygen.
- Statement II is correct: Marine plankton and cyanobacteria are responsible for about 50% of Earth’s oxygen through photosynthesis.
Statement III is incorrect: Surface water has lower oxygen concentration than air — oxygen is more soluble in air than in water, hence the statement is false.
Answer: (c) II and III only
