2011 GS Paper I, all questions

UPSC Prelims 2011 · GS Paper I

Question 21: Environment and Ecology

Human activities in the recent past have caused the increased concentration of carbon dioxide in the atmosphere, but a lot of it does not remain in the lower atmosphere because of

  1. 1.its escape into the outer stratosphere.
  2. 2.the photosynthesis by phytoplankton in the oceans.
  3. 3.the trapping of air in the polar ice caps.

Which of the statements given above is/are correct ?

a1 and 2
b2 only
c2 and 3
d3 only

AnswerThe answer is (b).

The oceans absorb a large share of the carbon dioxide humans release. Phytoplankton take it up in photosynthesis, and when they die some of the carbon sinks to the deep sea; carbon dioxide also dissolves directly in sea water, and land plants absorb it too. It does not escape into the outer stratosphere, because it is well mixed in the lower atmosphere and held by gravity. Trapping in polar ice is minor. So only statement 2 is correct.

  • 1. Carbon dioxide stays in the lower atmosphere; it does not escape upward.
  • 2. Phytoplankton photosynthesis takes up large amounts of carbon dioxide.
  • 3. Air trapped in polar ice is a negligible sink.

How you could have got this

  1. If you were sure statement 1 is not correct, (a) goes: it includes 1.

    What you needed to know: Carbon dioxide stays in the lower atmosphere; it does not escape upward.

  2. Then, if you were sure statement 3 is not correct, (c) and (d) go: each of them includes 3.

    What you needed to know: Air trapped in polar ice is a negligible sink.

Only (b) is left. You didn’t need statement 2.

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) Statement 1 is false: the gas does not escape to the outer stratosphere.
  • (b) Right: photosynthesis by phytoplankton removes carbon dioxide.
  • (c) Ice caps trap only a trace; this is not a main sink.
  • (d) Ice trapping is minor, and it excludes the true statement 2.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2011, General Studies Paper I, Series A. The paper on upsc.gov.in.