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 photo-synthetic 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?
Explanation:
Statement I: This statement is incorrect. The oceans, primarily through the photosynthesis of marine phytoplankton, produce the majority of the Earth's oxygen, estimated to be between 50% and 80%. While rainforests are important, their net contribution to atmospheric oxygen is less than that of the oceans, partly due to high respiration rates within the ecosystem. Statement II: This statement is correct. Marine phytoplankton and photosynthetic bacteria are the primary producers of oxygen on Earth, contributing a significant portion (often cited as 50% or more) of the oxygen in our atmosphere. Statement III: This statement is incorrect. The solubility of oxygen in water is relatively low. Atmospheric air contains approximately 21% oxygen. Even fully saturated (well-oxygenated) surface water at typical temperatures contains dissolved oxygen concentrations that are significantly *lower* than the concentration of oxygen in atmospheric air, not 'several folds higher.' For example, at 20°C, saturated freshwater contains about 9 mg/L of dissolved oxygen, which is a tiny fraction of the oxygen concentration in air. Explanation: Only Statement II is correct.