UPSC Prelims 2021 GS Paper I · Q26 of 98 Environment & Ecology easy

Which one of the following is a filter feeder?

  1. (a) Catfish
  2. (b) Octopus
  3. (c) Oyster ✓ UPSC's answer
  4. (d) Pelican

Why the answer is (c)

• Filter feeders strain suspended food particles from water. Oysters draw water over their gills and trap plankton and organic matter — option (c).

• Catfish (a) are bottom-feeding predators/scavengers; octopuses (b) actively hunt crabs and molluscs; pelicans (d) scoop fish with their pouch — none filter water.

• Because they filter up to 50 gallons a day, oysters improve water quality, which is why oyster reefs are valued in coastal restoration.

• Hence option (c).

Why the other options are wrong

(a) Catfish
Catfish are bottom feeders, not filter feeders.
(b) Octopus
Octopuses are active predators.
(d) Pelican
Pelicans scoop fish; they do not filter water.

Asked in the GS Paper I 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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