“Lichen” for a plant species sensitive to air pollution, used as an indicator species is. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. A sound explanation connects the stated pattern to a causal pathway and distinguishes it from alternatives that describe different levels of organization or different ecological processes. The remaining alternatives—“Cactus”, “Bamboo”, “Parthenium”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Ecological interpretation requires separating the immediate process from its broader consequence. A mechanism operating through physiology or behavior can scale up to alter survival, reproduction, abundance, distribution, and community structure. Linking the wording to measurable consequences for fitness, abundance, or flux gives the conclusion its scientific meaning and prevents a purely mnemonic interpretation. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.
Ref:
NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation
