UPSC Prelims 2012 · CSAT
Question 7: Reading Comprehension
How do pesticides act as agents for the selection of resistant individuals in any pest population ?
- 1.It is possible that in a pest population the individuals will behave differently due to their genetic makeup.
- 2.Pests do possess the ability to detoxify the pesticides.
- 3.Evolution of pesticide resistance is equally distributed in pest population.
Which of the statements given above is/are correct ?
AnswerUPSC’s answer is (b).
Selection needs variation. Pests in a population differ genetically, and some carry traits such as the ability to detoxify the chemical, for example with enzymes that break it down. The pesticide kills the susceptible individuals and spares these, so resistant ones breed and their share rises. Statement 3 is the opposite of how it works: resistance starts in a minority and is unevenly spread, not equally distributed. The passage does not itself discuss resistance, so this rests on basic biology.
- 1. Genetic differences mean some pests survive a dose that kills others, giving selection something to act on.
- 2. Detoxification is a standard mechanism of resistance; individuals that can break down the chemical survive.
- 3. Resistance begins in a few individuals and becomes common only after repeated selection, so it is not equally distributed.
How you could have got this
- If you were sure statement 2 is correct, (a) and (c) go: each of them leaves 2 out.
What you needed to know: Detoxification is a standard mechanism of resistance; individuals that can break down the chemical survive.
- Then, if you were sure statement 3 is not correct, (d) goes: it includes 3.
What you needed to know: Resistance begins in a few individuals and becomes common only after repeated selection, so it is not equally distributed.
Only (b) is left. You didn’t need statement 1.
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. Statement 2 is also true, so 1 alone is incomplete.
- (b) Right. Genetic variation (1) and the ability to detoxify (2) explain the selection; statement 3 is false.
- (c) Wrong. Statement 3 is false because resistance is unevenly spread.
- (d) Wrong. It wrongly includes statement 3.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2012, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.