2021 GS Paper I, all questions

UPSC Prelims 2021 · GS Paper I

Question 26: Environment and Ecology

Which one of the following is a filter feeder?

aCatfish
bOctopus
cOyster
dPelican

AnswerUPSC’s answer is (c).

Filter feeders strain tiny food particles, such as plankton, out of the water that they pump through their bodies. Oysters do this with their gills, like mussels and clams. Catfish are bottom-feeding omnivores, octopuses are active predators, and pelicans catch fish by scooping them up in their bills. Remember: oyster, clam, mussel, sponge and baleen whale are filter feeders.

Why each option is right or wrong
  • (a) Wrong: catfish are bottom-feeding omnivores, not filter feeders.
  • (b) Wrong: octopuses are active predators.
  • (c) Right: oysters filter plankton from water through their gills.
  • (d) Wrong: pelicans catch fish by scooping them up.

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 I, Series A. The paper on upsc.gov.in.