UPPSC 2025 Prelims GS Paper-I · Question 21 of 150

Correct — D, Only 1. Statement 1 is the settled ecological fact: earthworms swallow soil along with dead leaves and other organic litter, grind it in the gizzard and void it as casts, converting large pieces of organic matter into rich humus and so improving soil fertility — their casts carry roughly 40 per cent more humus than the top nine inches of the soil they live in. Their burrowing also loosens, aerates and drains the soil, which is why Indian farmers call them the farmer's friend and why Charles Darwin devoted his last book (1881) to them, writing that 'it may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures'. Statement 2 fails on the number. An earthworm does not have a single heart, but neither does it have two pairs: in the standard description of earthworm anatomy a pair of muscular aortic arches rings the coelom in each of segments seven to eleven and acts as hearts, pumping blood into the ventral vessel — five pairs, not two. Since only statement 1 stands, the answer is Only 1.

• (a)Only 2 — This is the exact inversion of the truth. It rejects the one statement that is beyond dispute — the earthworm's role in building soil fertility — and keeps the one that is wrong on its number.
• (b)Both 1 and 2 — Tempting, because statement 1 is obviously true and statement 2 sounds like a textbook detail. But the anatomical claim is wrong: the aortic arches that serve as the earthworm's hearts are described as a pair in each of segments seven to eleven, i.e. five pairs, not two.
• (c)Neither 1 nor 2 — Chosen by candidates who spot that statement 2 is wrong and then over-correct. Statement 1 is correct — improving soil structure and fertility is precisely what earthworms are famous for.

Earthworms are terrestrial annelids: segmented, burrowing invertebrates that feed on dead and decaying organic matter, which makes them detritivores rather than decomposers in the microbial sense — they fragment litter and pass it through the gut, and microbes finish the mineralisation. They have a closed circulatory system, in which blood stays inside vessels: a dorsal and a ventral longitudinal vessel are linked by muscular aortic arches that contract like hearts. Ecologically they are classic 'ecosystem engineers' — their burrows aerate and drain the soil and their casts return nutrients to it.

Only one half of this question is doing any work. Statement 1 is a claim every syllabus repeats, so the examiner is really asking whether you will accept a precise-sounding number attached to a familiar animal. The safe habit with such items is to ask whether you have ever actually met that number in a textbook. 'Two pairs of hearts' is not the figure any standard description gives; it is the sort of half-remembered fragment that feels authoritative because it is specific. Note also that the exact number of arches quoted varies with the species being dissected, so what you should carry away is the principle — several pairs of aortic arches, not one heart and not two pairs.

• Earthworms convert large pieces of organic matter into rich humus, improving soil fertility; their casts contain about 40 per cent more humus than the top nine inches of the soil in which the worm lives
• Standard descriptions give several pairs of aortic arches acting as hearts, and the count differs by species and textbook: four pairs in Pheretima posthuma, the earthworm Indian courses dissect (lateral hearts in segments 7 and 9, latero-oesophageal in 12 and 13), five pairs in the Lumbricus account (segments 7 to 11). No standard description gives two — which is all the question needed
• The earthworm has a closed circulatory system: blood is confined to vessels, with dorsal and ventral longitudinal vessels linked by the aortic arches
• Darwin's last book (1881) was on earthworms and vegetable mould: 'It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures'
• Earthworms are detritivores — UPSC 2021 asked exactly this, grouping them with millipedes and woodlice and excluding jellyfish and seahorses

• Accepting a precise-sounding anatomical number because the other statement in the pair is obviously true
• Over-correcting to 'Neither 1 nor 2' once you have caught the false statement
• Treating 'earthworm' as one species — the number of aortic arches quoted depends on the species being described, so memorise the principle rather than a bare figure

UPPSC bolts a precise anatomical number onto a familiar organism and asks you to reject the number; UPSC prefers the ecological angle — where the earthworm sits in a food chain, or how vermicompost works.

• practice — not a real PYQ

  In an ecosystem, the earthworm is best classified as a

  • (a)producer
  • (b)detritivore
  • (c)primary carnivore
  • (d)chemoautotroph

  Answer(b) detritivore — it fragments dead organic matter, which microbial decomposers then mineralise.

• practice — not a real PYQ

  Which one of the following statements about the earthworm's circulatory system is correct?

  • (a)It is open, the blood bathing the body cavity directly
  • (b)It is closed, with blood confined to vessels and muscular aortic arches acting as hearts
  • (c)It is absent; gases diffuse directly through the skin only
  • (d)It is closed in the juvenile and open in the adult

  Answer(b) It is closed, with blood confined to vessels and muscular aortic arches acting as hearts — the arches are described as a pair in each of segments seven to eleven.