Q. With reference to the planet Earth, consider the following statements:
- Rain forests produce more oxygen than that produced by oceans.
- Marine phytoplankton and photosynthetic bacteria produce about 50% of the world’s oxygen.
- 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) None of the above statements is correct
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Answer & Explanation:
✅Correct Answer: (b) II only
Explanation:
Statement I – Incorrect
Tropical rainforests are often called the “lungs of the Earth,” but they do not produce more oxygen than oceans. While rainforests do generate large amounts of oxygen through photosynthesis, they also consume nearly the same amount through respiration and decay. In contrast, oceans collectively produce more oxygen, mainly due to microscopic organisms.
Statement II – Correct
Marine phytoplankton, algae, and photosynthetic bacteria (such as Prochlorococcus) are responsible for around 50% of global oxygen production.
- Prochlorococcus alone contributes nearly 20% of the oxygen in Earth’s atmosphere.
Thus, oceans play a dominant role in maintaining atmospheric oxygen levels.
Statement III – Incorrect
Even in well-oxygenated surface waters, the dissolved oxygen content is about 8 mg per litre, whereas atmospheric air contains roughly 210 mg of oxygen per litre. Hence, air contains far more oxygen than water, not the other way around. Therefore, Statement III is incorrect.
Why Other Options Are Incorrect
- Option (a) is incorrect because Statement I is wrong.
- Option (c) is incorrect because Statement III is wrong.
- Option (d) is incorrect because Statement II is correct.