UPSC Prelims 2021 · GS Paper I
Question 20: Environment and Ecology
In the nature, which of the following is/are most likely to be found surviving on a surface without soil?
- 1.Fern
- 2.Lichen
- 3.Moss
- 4.Mushroom
Select the correct answer using the code given below.
AnswerUPSC’s answer is (c).
Lichens and mosses can survive on bare surfaces such as rock, tree bark and walls without soil. Lichens are a fungus-alga partnership that gets nutrients from air, dust and rain, and mosses absorb water and nutrients directly through their leaves and have only simple rhizoids. Ferns need soil or humus and moisture for their roots. Mushrooms need decaying organic matter or soil to feed on. Remember: lichen and moss are pioneer colonisers of bare rock.
- 1. Ferns depend on soil or humus and moisture.
- 2. Lichens grow on bare rock and bark, absorbing nutrients from air and rain.
- 3. Mosses can grow on rock and walls, taking water and nutrients through their surface.
- 4. Mushrooms need decaying organic matter or soil as their food source.
How you could have got this
- If you were sure statement 1 is not correct, (a) and (d) go: each of them includes 1.
What you needed to know: Ferns depend on soil or humus and moisture.
- Then, if you were sure statement 3 is correct, (b) goes: it leaves 3 out.
What you needed to know: Mosses can grow on rock and walls, taking water and nutrients through their surface.
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: ferns and mushrooms need soil or organic matter.
- (b) Wrong: lichen survives, but moss does too.
- (c) Right: lichen and moss can live on bare surfaces.
- (d) Wrong: ferns and mushrooms need soil or organic matter.
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.