UPSC Prelims 2021 CSAT Paper II · Q1 of 79 Comprehension medium

Passage

Directions for the following 4 (four) items : Read the following four passages and answer the items that follow. Your answers to these items should be based on the passages only. Passage – 1 Researchers simulated street lighting on artificial grassland plots containing pea-aphids, sap-sucking insects, at night. These were exposed to two different types of light — a white light similar to newer commercial LED lights and an amber light similar to sodium street lamps. The low intensity amber light was shown to inhibit, rather than induce, flowering in a wild plant of the pea family which is a source of food for the pea-aphids in grasslands. The number of aphids was also significantly suppressed under the light treatment due to the limited amount of food available.

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

  1. (a) Low intensity light has more adverse effect on the plants as compared to high intensity light.
  2. (b) Light pollution can have a permanent adverse impact on an ecosystem. ✓ UPSC's answer
  3. (c) White light is better for the flowering of plants as compared to the light of other colours.
  4. (d) Proper intensity of light in an ecosystem is important not only for plants but for animals too.

Why the answer is (b)

• The passage describes a simulation where street lighting (light pollution) affected pea-aphids and their food source, a wild plant.

• The amber light inhibited flowering in the plant, which reduced the food supply for the aphids.

• Consequently, the number of aphids was significantly suppressed due to this limited food availability.

• This chain of events demonstrates that artificial light disrupts the relationship between plants and animals within the ecosystem.

• Therefore, the most critical inference is that light pollution can have a permanent adverse impact on an ecosystem, as it alters biological processes and population dynamics.

Why the other options are wrong

(a) Low intensity light has more adverse effect on the plants as compared to high intensity…
The passage does not compare the effects of low-intensity light against high-intensity light; it only compares white and amber lights.
(c) White light is better for the flowering of plants as compared to the light of other…
The passage states that amber light inhibited flowering, but it does not provide evidence that white light is superior for flowering compared to other colors.
(d) Proper intensity of light in an ecosystem is important not only for plants but for…
While the passage shows light affects both plants and animals, the specific inference about 'proper intensity' is not the central point; the focus is on the adverse impact of artificial light pollution on the ecosystem.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2021, held on 10 October 2021. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

Reading the answer is not the same as getting it right under a clock. Practise this question with UPSC's negative marking, and anything you miss goes into an error notebook until you get it right twice.

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