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?

Correct Answer:

(b) II only

Explanation of the Correct Answer:

• Statement II: Marine phytoplankton and photosynthetic bacteria produce about 50% of the world's oxygen
  • Correct. Scientific studies (National Aeronautics and Space Administration (NASA), NOAA, and peer-reviewed journals) confirm that marine phytoplankton, cyanobacteria, and algae are responsible for producing approximately 50–70% of Earth's oxygen supply through photosynthesis.
  • Despite being microscopic, they occupy vast areas of ocean surface and contribute significantly to global oxygen production.

Why Other Options Are Incorrect:

• Statement I: Rain forests produce more oxygen than that produced by oceans
  • Incorrect. Though rainforests like the Amazon are highly productive and contribute around 20% of global oxygen, oceans surpass them in total oxygen generation due to the sheer biomass and surface area of marine phytoplankton.
• Statement III: Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air
  • Incorrect. The oxygen concentration in atmospheric air (~21%) is far greater than the dissolved oxygen in water, even in well-oxygenated surface water (~8–10 mg/L or ~0.001%).
  • Water holds much less oxygen compared to air because of its physical properties. Therefore, this statement is scientifically false.
• Thus:
  • (a) I and II – Incorrect (I is wrong)
  • (c) I and III – Incorrect (Both are wrong)
  • (d) None of the above – Incorrect (II is correct)

Relevant Supplementary Information

Table: Evaluation of Statements

Related Concepts:

• Phytoplankton: Microscopic marine organisms that perform photosynthesis and are primary oxygen producers in aquatic ecosystems.
• Photosynthetic bacteria: Such as cyanobacteria, which were among Earth’s earliest oxygen producers.
• Dissolved oxygen in water: Typically 5–14 mg/L depending on temperature, salinity, and pressure.
• Atmospheric oxygen: ~21% by volume, far more than what water can hold.

Current Relevance:

• The role of oceans in climate regulation and oxygen balance is increasingly recognized in international climate frameworks.
• Ocean health threats (e.g., warming, acidification, pollution) may impact phytoplankton populations and thus influence oxygen production.
• Misconceptions about rainforests being the sole “lungs of the Earth” often obscure the significant role of marine ecosystems.

Table: Concepts Related to Global Oxygen Production and Dissolved Oxygen