UPSC Prelims 2013 · GS Paper I
Question 33: Science and Technology
Consider the following organisms :
- 1.Agaricus
- 2.Nostoc
- 3.Spirogyra
Which of the above is/are used as biofertilizer/biofertilizers?
AnswerUPSC’s answer is (b).
Nostoc is a nitrogen-fixing cyanobacterium used as a biofertiliser, especially in paddy fields, along with Anabaena and Azolla. Agaricus is a mushroom, an edible fungus grown as food, not as a fertiliser. Spirogyra is a filamentous green alga of ponds and does not fix nitrogen. Only Nostoc qualifies.
- 1. Agaricus is an edible mushroom.
- 2. Nostoc is a nitrogen-fixing cyanobacterium used in rice fields.
- 3. Spirogyra is a green alga that does not fix nitrogen.
How you could have got this
- If you were sure statement 1 is not correct, (a) goes: it includes 1.
What you needed to know: Agaricus is an edible mushroom.
- Then, if you were sure statement 3 is not correct, (c) and (d) go: each of them includes 3.
What you needed to know: Spirogyra is a green alga that does not fix nitrogen.
Only (b) is left. You didn’t need statement 2.
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. Agaricus is a mushroom, not a biofertiliser.
- (b) Correct. Nostoc fixes atmospheric nitrogen.
- (c) Wrong. Spirogyra is not a biofertiliser.
- (d) Wrong. Spirogyra is not a biofertiliser and Nostoc is left out.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper I, Series A. The paper on upsc.gov.in.