2021 CSAT — Q1
Passage
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?
Thinking pathway
Locate. This asks for the best-supported inference — the conclusion the passage forces, not merely one that’s plausible; do not pick the option that sounds biggest — find the line the inference must rest on, then match. The passage’s chain is one treatment → two effects: amber light “inhibit[s]… flowering” of the pea plant, AND “the number of aphids was also significantly suppressed… due to the limited amount of food available.” Plant hit, then animal hit.
Test (find-the-line-then-match). The forced inference is the one the two-part chain entails: the light regime is important for both the plant and the animal that feeds on it. (d) says exactly that — intensity matters “not only for plants but for animals too.” That is the passage’s own structure restated, nothing added.
Eliminate by anatomy. (a) is a comparison the passage doesn’t make — the passage tests one amber low-intensity light and never compares it against high-intensity light for adversity, so “more adverse than high intensity” is a comparison the text never makes. (c) is a claim the passage never makes — white LED light is named as the other treatment, never shown “better for flowering”; it is the option that rewards skim-recall of the word “white.” (b) over-states the case — “permanent adverse impact on an ecosystem” inflates a single short study’s finding into irreversible system-wide damage the text does not claim. Key: (d).
Evidence in the text
“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… The number of aphids was also significantly suppressed under the light treatment due to the limited amount of food available.” — the passage records a SINGLE light treatment that disrupts BOTH the plant (flowering inhibited) AND the animals (aphid numbers fall): light intensity matters for plants and animals alike → (d). (a) compares low-vs-high adversity the passage never ranks; (c) endorses white light the passage never tests as “better”; (b) over-reads a one-study finding into “permanent” ecosystem damage.
Worked rationale
The experiment exposes a grassland system to amber street-lamp-type light. Two things follow in the text: the pea plant’s flowering is inhibited, and the pea-aphids that feed on it are suppressed because their food is reduced. So one light variable cascades through both a plant and an animal.
- (d) captures that cascade: proper light intensity matters for plants and for animals. Correct.
- (a) invents a low-vs-high-intensity adversity comparison the passage never runs.
- (c) claims white light is “better” for flowering — the passage shows amber inhibits, but never ranks white as superior for flowering.
- (b) leaps to “permanent” ecosystem-level harm from one study.
Answer: (d).
Why the other options miss
- A a comparison the passage doesn’t make: the passage studies one amber low-intensity treatment and never compares its adversity to high-intensity light; the comparison is imported, not read.
- B too strong for what the passage says: “permanent adverse impact on an ecosystem” hardens a single experiment’s flowering/aphid result into irreversible, system-wide damage the text does not assert. The trap is that it sounds like the grand “critical inference.”
- C a claim the passage never makes: “white light is better for flowering” rides the recalled word “white,” but the passage only shows amber inhibits flowering; it never establishes white as superior.
Specialist insight
“Most critical inference” baits you toward the most sweeping-sounding option — here (b)‘s “permanent… ecosystem.” Resist it. The critical inference is the one the lines force, and the passage’s load-bearing structure is the two-step cascade (plant flowering down → aphid food down → aphids down). The only option that names both ends of that cascade is (d). When a “biggest claim” option adds a word the passage never earns — “permanent,” “more adverse than,” “better than” — it is bait, not the inference.
The grand-sounding "permanent ecosystem impact" (b) overshoots one study; the forced inference is the plant-and-animal cascade the text actually traces, so (d).