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📌 The Question:
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 the 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) None of the above statements is correct

✅ Correct Answer: (b)

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🔍 Classroom Explanation:

Statement I — Incorrect

• Tropical rainforests are vital carbon sinks, but they do not produce more oxygen than oceans.
• Oceans dominate global oxygen production due to vast photosynthetic activity by microscopic organisms.

Statement II — Correct

• Marine phytoplankton and photosynthetic bacteria contribute about 50% (or more) of the oxygen in Earth’s atmosphere.
• A key contributor is Prochlorococcus, the smallest known photosynthetic organism, which alone produces up to 20% of global oxygen.

Statement III — Incorrect

• Although surface waters are the most oxygen-rich within oceans, they contain far less oxygen than atmospheric air.
• Approximate comparison:
  • Air: ~210 mg O₂ per litre
  • Well-oxygenated seawater: ~8 mg O₂ per litre

Hence, only Statement II is correct.

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🧠 Curiosity Raiser:
How can organisms invisible to the naked eye keep the entire planet breathable?

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📚 Enrich Notes (Prelims Edge):

• Oceans = primary oxygen factory of Earth
• Rainforests = carbon sinks, not net oxygen suppliers
• Oxygen Minimum Zone (OMZ): critical concept in marine ecology
• Prochlorococcus is a favorite UPSC fact nugget

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🕊️ IAS Monk Whisper:
“The smallest lives sustain the largest systems.”