UPSC Prelims 2021 · GS Paper I
Question 27: Environment and Ecology
In case of which one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrient to enter the cycle?
AnswerUPSC’s answer is (c).
In the phosphorus cycle, rock is the main reservoir. Weathering and erosion release phosphate into soil and water, where plants take it up. Unlike carbon, nitrogen and sulphur, phosphorus has no significant gaseous phase in the atmosphere. Carbon and nitrogen cycle mainly through the air, and sulphur also has atmospheric and volcanic pathways. Remember: phosphorus is a sedimentary cycle, with rocks as its source.
Why each option is right or wrong
- (a) Wrong: the carbon cycle draws mainly on the atmosphere and oceans.
- (b) Wrong: the nitrogen cycle draws on atmospheric nitrogen fixed by microbes.
- (c) Right: rock weathering is the main release of phosphorus into the cycle.
- (d) Wrong: sulphur also has important atmospheric and volcanic sources.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2021, General Studies Paper I, Series A. The paper on upsc.gov.in.