UPPSC 2025 Prelims GS Paper-I · Question 66 of 150

Correct — B, Both 1 and 2. Statement 1 is true: dolphins and whales are cetaceans — aquatic mammals, not fish — and they breathe atmospheric air using lungs. Over evolutionary time their nostrils migrated from the tip of the snout to the top of the head, forming the blowhole, so the animal can exhale and inhale by breaking the surface with only the crown of its head. A muscular flap seals the blowhole while the animal is submerged. Statement 2 is also true: the earthworm has no lungs, no gills and no tracheae. It respires cutaneously — oxygen dissolves in the film of moisture on its body surface and diffuses through the thin, permeable skin into a dense network of capillaries lying just beneath, where the respiratory pigment carried in the blood transports it onward. That is precisely why an earthworm must keep its skin moist, and why it comes to the surface when the soil is waterlogged. Both statements stand, so the key marks (b).

• (a)Only 2 — It accepts the earthworm but rejects the blowhole. That usually comes from treating whales and dolphins as fish. They are mammals — warm-blooded, giving birth to live young and suckling them — and they never developed gills; they must surface to breathe through the blowhole, which is why a drowning cetacean is a real danger.
• (c)Neither 1 nor 2 — Both statements are in fact correct, so rejecting both is doubly wrong. The blowhole is the standard textbook example of a nostril relocated for surface breathing, and cutaneous respiration in the earthworm is the standard example of gas exchange without any specialised respiratory organ.
• (d)Only 1 — It accepts the blowhole but denies that earthworms breathe through the skin. The earthworm has no specialised respiratory organ at all — no lungs, gills or tracheal tubes — so the moist body wall is its only gas-exchange surface. This is the option chosen by candidates who assume every animal must possess a dedicated breathing organ.

Animals exchange gases in ways that follow their body plan, not simply their habitat. Very small or thin-bodied animals such as the earthworm rely on plain diffusion across the moist general body surface (cutaneous respiration). Insects run air directly to the tissues through a branching tracheal system opening at spiracles. Fish and most aquatic larvae use gills. Terrestrial vertebrates — and air-breathing aquatic mammals like whales and dolphins — use lungs. Cetaceans are the clearest proof that ancestry beats habitat: they returned to the sea but kept mammalian lungs, and simply moved the nostril to the top of the head.

The paper pairs a 'looks like a fish but isn't' item with a 'no visible breathing organ' item. Each statement on its own is easy; the difficulty is manufactured by the four-way code, because a candidate who is confident about one statement and hesitant about the other is pushed towards 'Only 1' or 'Only 2'. Two anchors settle it: cetacean = mammal = lungs + blowhole, and earthworm = moist permeable skin = cutaneous respiration. Neither claim has an exception worth worrying about at prelims level, so the answer is 'both'.

• Whales and dolphins are cetaceans — mammals that breathe air with lungs; the blowhole is the nostril, shifted to the top of the head so the animal can breathe while barely surfacing
• Toothed whales (dolphins, porpoises, sperm whale) have a single blowhole; baleen whales (blue whale, humpback) have a paired, twin blowhole
• A muscular flap keeps the blowhole shut underwater, so water does not enter the airway; the visible 'spout' is warm exhaled air condensing, not a jet of seawater
• The earthworm has no lungs, gills or tracheae — oxygen diffuses through its moist, permeable skin into capillaries just below the surface, which is why the skin must stay moist and why earthworms emerge when soil is waterlogged
• Contrasting patterns worth memorising: insects respire through a tracheal system opening at spiracles, fish use gills, and frogs use lungs plus moist skin

• Classing whales and dolphins as fish and therefore assuming gills — they are mammals with lungs
• Assuming an animal with no visible respiratory organ, such as the earthworm, must breathe through some hidden lung
• Confusing breathing (the exchange of gases with the environment) with cellular respiration (the release of energy from glucose inside the cell)

UPPSC puts the organ itself in the question — 'X breathes through …' or a two-statement code like this one. UPSC prefers the mechanism and the odd-one-out: 'How do most insects respire?', the site of gaseous exchange, or which animals belong to a given functional group.

• practice — not a real PYQ

  Which one of the following animals respires through its moist skin?

  • (a)Cockroach
  • (b)Earthworm
  • (c)Rohu fish
  • (d)Sparrow

  Answer(b) Earthworm — the cockroach uses a tracheal system, the rohu uses gills and the sparrow uses lungs.

• practice — not a real PYQ

  The blowhole of a whale is a modification of which of the following structures?

  • (a)Gill slit
  • (b)Nostril
  • (c)Mouth
  • (d)External ear opening

  Answer(b) Nostril — in cetaceans the nostrils migrated to the top of the head, so the animal can breathe by exposing only the crown while swimming.