Given below are two statements: Statement I: Possibility of oxygen depletion…
2023
Given below are two statements:
Statement I: Possibility of oxygen depletion is high in running and turbulent water bodies.
Statement II: Oxygen is added to water by photosynthesis of green plants, algae and cyanobacteria.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer: D. Statement I is incorrect but Statement II is correct — ConceptDissolved oxygen in surface water is controlled by oxygen inputs and oxygen-consuming processes. The main inputs are atmospheric reaeration and…
- A.
Both Statement I and Statement II are correct
- B.
Both Statement I and Statement II are incorrect
- C.
Statement I is correct but Statement II is incorrect
- D.
Statement I is incorrect but Statement II is correct
Show answer & explanation
Correct answer: D
Concept
Dissolved oxygen in surface water is controlled by oxygen inputs and oxygen-consuming processes. The main inputs are atmospheric reaeration and oxygenic photosynthesis; respiration and decomposition are important sinks.
Turbulent flow generally strengthens air–water mixing and gas exchange. In daylight, green plants, algae and cyanobacteria release oxygen during photosynthesis.
Application
Statement I links running, turbulent water with a high possibility of oxygen depletion. Turbulence instead promotes reaeration, so the stated general relationship is reversed.
Statement II identifies oxygenic photosynthesis as a source of oxygen in water. Green plants, algae and cyanobacteria release oxygen during this light-driven process.
Contrast
“Both Statement I and Statement II are correct” retains the reversed relationship in Statement I.
“Both Statement I and Statement II are incorrect” overlooks oxygen production by photosynthetic organisms.
“Statement I is correct but Statement II is incorrect” reverses the roles of both turbulence and photosynthesis.
Cross-check
The same oxygen budget gives the check: turbulent reaeration adds oxygen from the atmosphere, and photosynthesis adds biologically produced oxygen; depletion is associated with oxygen demand, not turbulence by itself.
Result
Statement I is incorrect, whereas Statement II is correct.