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 ______ of 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? (UPSC Prelims 2025)
Answer:
None of the above statements is correct
Notes: The correct answer is
[D] None of the above statements is correct. This question addresses common misconceptions regarding the Earth’s oxygen cycle and the solubility of gases in water.
- Statement 1 (Incorrect): While rainforests like the Amazon are often called the "lungs of the planet," they actually consume almost as much oxygen as they produce through the respiration of the plants themselves and the decomposition of organic matter. In contrast, the oceans are the primary net producers of the world's oxygen.
- Statement 2 (Incorrect): The statement is incomplete in the prompt, but scientifically, marine phytoplankton and photosynthetic bacteria (like Prochlorococcus) are responsible for producing roughly 50% to 80% of the Earth's oxygen. Even at the lower end of this estimate, they surpass the oxygen production of all tropical rainforests combined.
- Statement 3 (Incorrect): This statement contradicts the physical laws of gas solubility. Atmospheric air contains approximately 21% oxygen (about 210,000 parts per million). In contrast, well-oxygenated surface water typically contains only about 7 to 10 parts per million (ppm) of dissolved oxygen. Therefore, the concentration of oxygen in the air is thousands of times higher than in even the most well-oxygenated water.
Key Scientific Context:- Net Production: Most of the oxygen produced by land plants is used up by the soil and the plants themselves. The vast majority of the oxygen we breathe actually comes from oceanic plankton drifting in the upper layers of the sea.
- Solubility: Oxygen is not very soluble in water. Its concentration in water is influenced by temperature and salinity; colder, fresher water can hold more dissolved oxygen than warmer, saltier water.