UPSC Prelims 2018 · GS Paper I
Question 2: Environment and Ecology
Which of the following leaf modifications occur(s) in the desert areas to inhibit water loss ?
- 1.Hard and waxy leaves
- 2.Tiny leaves
- 3.Thorns instead of leaves
Select the correct answer using the code given below :
AnswerUPSC’s answer is (d).
Desert plants cut transpiration by shrinking the leaf surface and sealing it. Leaves can be tiny, which reduces the area exposed to heat and wind; hard and waxy, with a thick cuticle that blocks evaporation; or reduced to thorns or spines, as in cacti, where the green stem then does the photosynthesis. All three are water-saving adaptations of xerophytes, so all three statements are correct.
- 1. A thick waxy cuticle cuts evaporation from the leaf.
- 2. A small leaf area reduces transpiration.
- 3. Leaves turn into spines in cacti, and the stem photosynthesises.
How you could have got this
- If you were sure statement 1 is correct, (a), (b) and (c) go: each of them leaves 1 out.
What you needed to know: A thick waxy cuticle cuts evaporation from the leaf.
Only (d) is left. You didn’t need statements 2 or 3.
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) Incomplete: leaves out hard and waxy leaves, which are also an adaptation.
- (b) Incomplete: tiny leaves are only one of the three adaptations.
- (c) Incomplete: thorns are only one of the three adaptations.
- (d) Right: waxy, tiny and thorn-like leaves all reduce water loss.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2018, General Studies Paper I, Series A. The paper on upsc.gov.in.