2021 CSAT, all questions

UPSC Prelims 2021 · CSAT

Question 1: Reading Comprehension

Passage – 1 · as printed by UPSC
Passage beginning “Researchers simulated street lighting on artificial…”

Which one of the following statements best reflects the most critical inference that can be made from the passage given above ?

aLow intensity light has more adverse effect on the plants as compared to high intensity light.
bLight pollution can have a permanent adverse impact on an ecosystem.
cWhite light is better for the flowering of plants as compared to the light of other colours.
dProper intensity of light in an ecosystem is important not only for plants but for animals too.

AnswerUPSC’s answer is (b).

The passage describes a chain of effects: amber night lighting, like street lamps, suppressed flowering in a wild pea-family plant, that plant feeds the aphids, and aphid numbers fell as a result. So artificial light at night disturbed a plant and then the insect that depends on it, which is damage at the level of the ecosystem. That is the widest inference the passage supports. Remember for critical-inference questions: pick the option that generalises the passage's own cause-and-effect chain, and reject options that bring in comparisons the passage never tested.

Why each option is right or wrong
  • (a) Only low-intensity amber light was tested; nothing compares it with high intensity, so no claim about which is worse follows.
  • (b) Right: night lighting cut a food plant's flowering and then the aphids' numbers, showing light pollution can damage an ecosystem.
  • (c) The passage reports no benefit of white light for flowering; it describes only amber light inhibiting flowering.
  • (d) Animals were affected only indirectly through lost food, and intensity was never varied, so a general point about proper intensity is unsupported.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2021, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.