UPSC Prelims 2022— Question 43

This question belongs to Environment & Ecology and tests Wetland Filtration. The concept has to be interpreted through ecological processes, environmental governance or species-level facts. UPSC often combines one familiar ecological statement with a subtly overbroad or geographically incorrect statement. Option D is the keyed answer because Aquatic plants absorb heavy metals and excess nutrients. is the combination or identification that satisfies the conditions in the question. A useful way to solve the question is to separate the individual propositions from the answer-code combinations. A statement can look broadly reasonable while still being incorrect because it uses an absolute term, assigns a function to the wrong institution, confuses two related concepts, or places a feature in the wrong region or period. The keyed response should therefore be treated as the outcome of checking each proposition rather than as a memory-only exercise. Option A: The water cycle in wetlands involves surface runoff, subsoil percolation and evaporation. — this is not the correct choice. It fails the question's test because it does not represent the required combination, institution, location, mechanism or historical association. The distractor is plausible only if a related concept is confused with the one actually asked. Option B: Algae form the nutrient base upon which fish, crustaceans, molluscs, birds, reptiles and mammals thrive. — this is not the correct choice. It fails the question's test because it does not represent the required combination, institution, location, mechanism or historical association. The distractor is plausible only if a related concept is confused with the one actually asked. Option C: Wetlands play a vital role in maintaining sedimentation balance and soil stabilization. — this is not the correct choice. It fails the question's test because it does not represent the required combination, institution, location, mechanism or historical association. The distractor is plausible only if a related concept is confused with the one actually asked. Option D: Aquatic plants absorb heavy metals and excess nutrients. — this is the correct choice under the final key. It matches the relevant Wetland Filtration principle and satisfies the question's wording. The exam-oriented takeaway is to identify the governing fact first and only then map it to the answer code. This reduces errors caused by choosing an option because one individual statement appears familiar. For database use, the classification and explanation should be read together: the subject gives the broad domain, the topic identifies the recurring UPSC theme, and the subtopic records the precise knowledge point tested. This also makes the question useful for later topic-wise search and revision.