CDS (II) 2022 General Knowledge · Question 71 of 120

Correct — B, Small intestine. NCERT puts it without qualification: 'From the stomach, the food now enters the small intestine. This is the longest part of the alimentary canal which is fitted into a compact space because of extensive coiling.' Standard anatomy gives it about six and a half metres in a cadaver and roughly three to five metres in a living adult, where muscle tone keeps it contracted, against about one and a half metres of large intestine. Its three parts are the duodenum at 20 to 25 centimetres, the jejunum at about two and a half metres and the ileum at about three metres. The length is not accidental — the small intestine is where digestion is completed and where almost all absorption happens, so it needs surface area, which it gets from length, from internal folds and from the finger-like villi that line it.

• (a)Stomach — The stomach is a wide muscular bag, not a long tube — roughly 25 centimetres from the cardiac to the pyloric end when empty. Its job is storage and the churning of food with acid and pepsin, which needs volume rather than length.
• (c)Large intestine — The large intestine is wider than the small intestine but far shorter, about one and a half metres. It is named for its diameter, not its length, which is exactly the confusion this option is designed to exploit.
• (d)Rectum — The rectum is the terminal segment, about 12 to 15 centimetres long, and is part of the large intestine. It holds faecal matter before defecation and does no digestion at all.

The alimentary canal runs from mouth to anus through the oesophagus, stomach, small intestine and large intestine. The small intestine is where the pancreatic enzymes and bile arrive, where carbohydrate, protein and fat digestion is finished, and where the products cross into the blood. Its inner lining carries villi, and each villus carries microvilli, so the absorptive surface is many times what the bare tube would offer.

The trap is entirely in the names. 'Large' and 'small' describe the width of the two intestines, not their length, so a candidate reading quickly can convince themselves that the large intestine must be the longer one. NCERT also adds a comparative point worth carrying, since it converts the fact into understanding: the length of the small intestine differs among animals according to diet, being longer in herbivores, whose cellulose takes time to break down, and shorter in carnivores such as tigers, whose meat is easier to digest. Note the paper's own phrasing — 'can be of maximum length' is an unusual way to ask which part is longest, but the intent is not in doubt.

• The small intestine is the longest part of the human alimentary canal.
• It is about six and a half metres in a cadaver and roughly three to five metres in a living adult; the large intestine is about one and a half metres.
• Its three parts are the duodenum, about 20 to 25 centimetres, the jejunum, about two and a half metres, and the ileum, about three metres.
• The large intestine is named for its greater diameter, not for its length.
• The lining of the small intestine carries villi, which multiply the surface available for absorption.
• Herbivores have a relatively longer small intestine than carnivores, because cellulose takes longer to digest.

• Reading 'large' as longer; the adjectives describe diameter.
• Treating the rectum as a separate organ rather than as the terminal part of the large intestine.
• Quoting a single fixed length for the small intestine; cadaver and living measurements differ considerably because of muscle tone.

As a which-part-is-longest item, as a match-the-part-to-its-function item, or as a villi and absorption item.

• practice — not a real PYQ

  The finger-like projections that line the inner surface of the small intestine and increase the area for absorption are called

  • (a)Sphincters
  • (b)Villi
  • (c)Alveoli
  • (d)Nephrons

  Answer(b) Villi — each villus is richly supplied with blood vessels that carry absorbed food away.

• practice — not a real PYQ

  Herbivores generally have a longer small intestine than carnivores because

  • (a)they eat more frequently
  • (b)cellulose in plant food takes longer to digest
  • (c)they have smaller stomachs
  • (d)they absorb water through the intestine

  Answer(b) cellulose in plant food takes longer to digest — meat is easier to break down, so carnivores manage with a shorter one.