UPSC Prelims 2014 · GS Paper I
Question 19: Environment and Ecology
Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth?
- 1.Volcanic action
- 2.Respiration
- 3.Photosynthesis
- 4.Decay of organic matter
Select the correct answer using the code given below.
AnswerUPSC’s answer is (c).
Carbon dioxide is added to the atmosphere by volcanic eruptions, by respiration of plants and animals, and by the decay of organic matter, where decomposers release the carbon back as carbon dioxide. Photosynthesis does the opposite: green plants take carbon dioxide out of the air and fix it into sugars. So statements 1, 2 and 4 add carbon dioxide, and statement 3 removes it.
- 1. Volcanic action releases carbon dioxide into the atmosphere.
- 2. Respiration releases carbon dioxide.
- 3. Photosynthesis takes carbon dioxide out of the air.
- 4. Decomposition releases carbon dioxide.
How you could have got this
- If you were sure statement 1 is correct, (b) goes: it leaves 1 out.
What you needed to know: Volcanic action releases carbon dioxide into the atmosphere.
- Then, if you were sure statement 3 is not correct, (a) and (d) go: each of them includes 3.
What you needed to know: Photosynthesis takes carbon dioxide out of the air.
Only (c) is left. You didn’t need statements 2 or 4.
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) Wrong. Photosynthesis removes carbon dioxide, and this omits respiration and decay.
- (b) Wrong. Volcanic action and decay also add carbon dioxide.
- (c) Right. Volcanoes, respiration and decay add carbon dioxide.
- (d) Wrong. Photosynthesis removes carbon dioxide.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2014, General Studies Paper I, Series A. The paper on upsc.gov.in.