UPSC Prelims 2008 · General Studies
Question 20: Environment and Ecology
Consider the following:
- 1.Rice fields
- 2.Coal mining
- 3.Domestic animals
- 4.Wetlands
Which of the above are sources of methane, a major greenhouse gas?
AnswerThe answer is (d).
All four are sources of methane. Rice fields release it because flooded soils have little oxygen and bacteria there produce methane. Coal mining frees methane trapped in coal seams. Domestic animals such as cattle and buffaloes emit it during digestion (enteric fermentation). Wetlands are the largest natural source, as plant matter decays in waterlogged conditions. Methane traps far more heat per molecule than carbon dioxide.
- 1. Flooded rice paddies emit methane from bacterial decay.
- 2. Coal seams hold methane that escapes during mining.
- 3. Cattle and buffaloes emit methane while digesting fodder.
- 4. Waterlogged wetlands produce methane as plant matter decays.
How you could have got this
- If you were sure statement 2 is correct, (a) goes: it leaves 2 out.
What you needed to know: Coal seams hold methane that escapes during mining.
- Then, if you were sure statement 4 is correct, (b) and (c) go: each of them leaves 4 out.
What you needed to know: Waterlogged wetlands produce methane as plant matter decays.
Only (d) is left. You didn’t need statements 1 or 3.
This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Leaves out coal mining and domestic animals, which also emit methane.
- (b) Leaves out rice fields and wetlands, both important sources.
- (c) Leaves out wetlands, a major natural source.
- (d) All four are methane sources.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2008, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.