With reference to the planet Earth, consider the following statements

With reference to the planet Earth, consider the following statements

Q. 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?

(a) I and II
(b) II only
(c) I and III
(d) None of the above statements is correct

20. पृथ्वी ग्रह के संदर्भ में, निम्नलिखित कथनों पर विचार कीजिए :

I. वर्षा वन, महासागरों द्वारा उत्पादित ऑक्सीजन की तुलना में अधिक ऑक्सीजन उत्पादित करते हैं।
II. समुद्री पादप-प्लवक और प्रकाश-संश्लेषी जीवाणु विश्व में ऑक्सीजन का लगभग 50% उत्पादित करते हैं।
III. वायुमंडलीय हवा में विद्यमान ऑक्सीजन की तुलना में, सुचारू रूप से ऑक्सीकृत पृष्ठ-जल में अनेक गुना अधिक ऑक्सीजन होती है।

उपर्युक्त कथनों में से कौन-सा/कौन-से सही है/है?

(a) I और II
(b) केवल II
(c) I और III
(d) उपर्युक्त कथनों में से कोई भी सही नहीं है

Answer: The correct answer is (b).

Explanation:

Statement I: Rain forests produce more oxygen than that produced by oceans.

  • Statement I is incorrect: Although rainforests (like the Amazon) are called the “lungs of the Earth,” they do not produce more oxygen than oceans.
  • In reality, oceans are the largest source of oxygen production on Earth, mainly due to the action of marine phytoplankton and photosynthetic bacteria.
  • Estimates suggest that oceans contribute about 50–80% of Earth's oxygen, which is more than terrestrial forests.
  • Statement II: Marine phytoplankton and photosynthetic bacteria produce about 50% of the world's oxygen.

Statement II is correct: Marine phytoplankton (microscopic plant-like organisms) and photosynthetic bacteria (such as cyanobacteria) in the oceans are responsible for producing roughly half of the world's oxygen through photosynthesis.

  • This is a well-established scientific fact and is accepted in standard biology and environmental science textbooks.
  • Statement III: Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air.

Statement III is incorrect: The dissolved oxygen content in surface water is actually much lower than the concentration of oxygen in atmospheric air.

  • Even well-oxygenated water contains only about 8–10 mg/L of dissolved oxygen, while air contains about 21% oxygen by volume.
  • Thus, the statement that surface water contains “several folds higher” oxygen than air is incorrect.

Source:

https://oceanservice.noaa.gov/facts/ocean-oxygen.html
https://www.usgs.gov/special-topics/water-science-school/science/dissolved-oxygen-and-water