With reference to the planet Earth, consider the following statements:

1. Rain forests produce more oxygen than that produced by oceans.
2. Marine phytoplankton and photosynthetic bacteria produce about 50% of world’s oxygen.
3. 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

Explanation

Statement I is incorrect

• The amount of oxygen produced in the Ocean is much greater (50-70%) than the oxygen produced by rainforests on land (estimated at 30%).

Statement II is correct

• Approximately half of all the oxygen on Earth comes from phytoplankton in the ocean. Larger kelp and seaweed are also producers of oxygen in the ocean. This brings the total ocean oxygen production up to 50-80%. The smallest photosynthetic organism, Prochlorococcus, produces 20% of the world’s oxygen all alone.

Statement III is incorrect

• This is scientifically inaccurate. Even well-oxygenated water holds far less oxygen than air. Dissolved oxygen in water is typically 8–14 mg/L, whereas atmospheric air contains ~210,000 mg/L of oxygen (21% of 1,000,000 mg/L).

Answer: (b) II only; Difficulty Level: Medium