BPSC 70th CCE Prelims General Studies · Question 116 of 143

Correct — D, Small intestine. NCERT's Class 10 chapter on Life Processes puts it in one sentence: 'The small intestine is the site of the complete digestion of carbohydrates, proteins and fats. It receives the secretions of the liver and pancreas for this purpose.' More precisely, bile made in the liver is concentrated and stored in the gall bladder and delivered through the common bile duct into the duodenum, the first and shortest part of the small intestine, where the pancreatic duct opens alongside it. Bile does two distinct jobs there, and both explain why the duodenum and not any other part of the gut is the delivery point. First, it neutralises: NCERT notes that 'the food coming from the stomach is acidic and has to be made alkaline for the pancreatic enzymes to act. Bile juice from the liver accomplishes this in addition to acting on fats.' Pancreatic enzymes such as trypsin and lipase work in an alkaline medium, so the acid chyme leaving the stomach must be neutralised the moment it arrives, not later. Second, it emulsifies: 'Fats are present in the intestine in the form of large globules which makes it difficult for enzymes to act on them. Bile salts break them down into smaller globules increasing the efficiency of enzyme action' — NCERT's own comparison is with the action of soap on dirt. Note also what bile is not: it contains no digestive enzyme. It is a secretion of bile salts, bile pigments, cholesterol and water that prepares fat for lipase rather than digesting it. Since the whole point of the delivery is to condition food for enzymes that act in the small intestine, any part of the canal upstream or downstream of that would be useless — and the three wrong options are precisely one upstream, one upstream, and one downstream.

• (a)Oesophagus — The food pipe, and no more than that. NCERT describes it simply as the passage by which food is taken from the mouth to the stomach, moved along by the peristaltic contractions that occur all along the gut. No gland empties into it and no digestion of consequence happens there, so bile arriving in the oesophagus would meet food that has not yet been acidified, let alone reduced to chyme.
• (b)Stomach — The most tempting wrong answer, because the stomach is where fatty food feels heaviest and where a lot of digestion is happening. But its secretions come from the gastric glands in its own wall — hydrochloric acid, the protein-digesting enzyme pepsin, and protective mucus — and its medium is deliberately acidic, which is the opposite of what bile is delivered to create. Bile entering the stomach would work against pepsin, not with it.
• (c)Large intestine — Downstream of the point that matters. By the time material reaches the large intestine, digestion and absorption in the small intestine are already over; NCERT's account of the large intestine is that its walls absorb more water from the unabsorbed food, after which the residue is removed via the anus. Delivering a digestive aid there would be too late to act on anything.

The alimentary canal is one continuous tube — mouth, oesophagus, stomach, small intestine, large intestine, anus — and the digestive glands are separate organs that empty their secretions into it at fixed points. That distinction is what most questions on this topic test. The salivary glands empty into the mouth and supply ptyalin, which begins starch digestion. The gastric glands lie in the stomach wall itself and supply hydrochloric acid, pepsin and mucus, working in an acid medium. The liver and the pancreas are outside the canal and both deliver into the duodenum: the liver's bile, stored in the gall bladder, neutralises the acid and emulsifies fat, while pancreatic juice supplies trypsin for protein and lipase for emulsified fat. The intestinal glands in the wall of the small intestine then complete the job, converting proteins to amino acids, complex carbohydrates to glucose, and fats to fatty acids and glycerol. Absorption follows in the same organ, across the finger-like villi that multiply the surface area and pass the products into a rich network of blood vessels. Only water absorption and the formation of residue are left for the large intestine.

The reasoning route here does not need the name of a duct. Ask instead what bile is for, and then ask where that purpose could possibly be served. Bile makes an acid mixture alkaline and breaks fat globules into smaller ones so that enzymes can reach them — so it must be delivered wherever those enzymes are about to act. Fat-digesting enzymes act in the small intestine, and nowhere else in the canal, so bile has to arrive there. That single chain of reasoning eliminates all three wrong options at once: the oesophagus carries food that has not yet been acidified, the stomach must stay acidic for pepsin to work, and the large intestine handles material from which the digestible fraction has already been removed. A second and even faster filter uses order alone. Sequence the four options along the canal — oesophagus, stomach, small intestine, large intestine — and ask which one lies between the acid stage and the absorption stage. There is exactly one such position, and that is where a neutralising secretion has to enter. Building the habit of laying options out in physiological order is worth more on this topic than memorising duct names, because BPSC's biology questions in this range are almost always about which structure does which job.

• NCERT, Life Processes: 'The small intestine is the site of the complete digestion of carbohydrates, proteins and fats. It receives the secretions of the liver and pancreas for this purpose'
• Bile is made in the liver, stored and concentrated in the gall bladder, and released through the common bile duct into the duodenum, the first part of the small intestine
• Bile has no digestive enzyme of its own; it neutralises the acid chyme so pancreatic enzymes can act, and its bile salts emulsify fat — NCERT compares this to the action of soap on dirt
• The stomach's own secretions come from gastric glands in its wall: hydrochloric acid, the protein-digesting enzyme pepsin, and mucus that protects the lining from the acid
• The pancreas delivers into the same region: trypsin for proteins and lipase for emulsified fats, both requiring an alkaline medium
• The small intestine's inner lining carries villi, finger-like projections richly supplied with blood vessels, which increase the surface area for absorption; the large intestine absorbs mainly water

• Believing bile digests fat; it emulsifies fat, and the digestion is done by pancreatic lipase
• Assuming an organ that feels involved in fat digestion, such as the stomach, must receive bile — the stomach's medium is deliberately acidic
• Confusing the alimentary canal with the digestive glands; the liver and pancreas lie outside the canal and only deliver into it

BPSC's biology block asks single-structure, single-function questions of exactly this shape — which part receives, which gland secretes, which tissue transports — and the wrong options are always other real parts of the same system doing real but different jobs. UPSC asked this material mainly in its older papers and as matching sets, pairing enzymes with the substrates they act on or classifying a substance as vitamin, enzyme, hormone or protein, so the same facts have to be held as a table rather than as a single sentence.

• practice — not a real PYQ

  Bile secreted by the liver is stored in which organ ?

  • (a)Pancreas
  • (b)Gall bladder
  • (c)Spleen
  • (d)Duodenum

  Answer(b) Gall bladder — it stores and concentrates bile between meals and releases it through the common bile duct into the duodenum.

• practice — not a real PYQ

  Which of the following is secreted by the gastric glands of the stomach ?

  • (a)Trypsin
  • (b)Bile salts
  • (c)Pepsin
  • (d)Ptyalin

  Answer(c) Pepsin — with hydrochloric acid and mucus; trypsin comes from the pancreas, bile salts from the liver and ptyalin from the salivary glands.