Previous Year 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 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
Detailed Solution
Statement I is incorrect: Microscopic photosynthetic organisms in the oceans—principally phytoplankton, algae and cyanobacteria—produce approximately half of Earth’s oxygen. Therefore, it is incorrect to say that rainforests produce more oxygen than the oceans.
Rainforests produce substantial oxygen through photosynthesis, but much of it is consumed again through plant respiration, microbial decomposition of organic matter and other biological processes.
Statement II is correct: Marine phytoplankton and photosynthetic bacteria are major oceanic primary producers. According to NOAA, at least approximately half of Earth’s oxygen production comes from the ocean, with most of it being produced by photosynthetic plankton.
Statement III is incorrect: Well-oxygenated surface water contains dissolved oxygen, but its concentration is far lower than the oxygen present in atmospheric air. The atmosphere contains approximately 21% oxygen by volume, whereas water can dissolve only a limited quantity of oxygen. The solubility of oxygen in water also decreases as temperature increases.