Digestive System

70. Carbohydrate digestion begins in the mouth. Where is it completed?

[RRB Group D (18 Aug 2026, Shift 3)]

• (a) Oesophagus
• (b) Small intestine
• (c) Stomach
• (d) Large intestine

Answer: (b) Small intestine

Explanation: Salivary amylase begins hydrolysing starch in the mouth. Pancreatic amylase continues carbohydrate digestion in the small intestine, and intestinal brush-border enzymes convert disaccharides into absorbable monosaccharides. Therefore, the small intestine is where this digestion is completed.

69. If peristalsis in the oesophagus is impaired, what is likely to happen after swallowing?

[RRB Group D (18 Aug 2026, Shift 1)]

• (a) Starch will break down faster
• (b) Digestion will accelerate
• (c) Saliva will increase
• (d) Food will not reach the stomach efficiently

Answer: (d) Food will not reach the stomach efficiently

Explanation: The oesophagus propels a swallowed bolus by coordinated waves of muscular contraction and relaxation. These waves are called peristalsis. Interfering with this mechanism disrupts passage to the stomach, even though chewing and swallowing have already occurred.

68. What is the chief digestive function of saliva in the mouth?

[RRB Group D (14 Aug 2026, Shift 2)]

• (a) Absorbing nutrients
• (b) Carrying food directly to the stomach
• (c) Breaking down starch into simpler sugars
• (d) Destroying every bacterium

Answer: (c) Breaking down starch into simpler sugars

Explanation: Saliva contains salivary amylase, or ptyalin, which starts converting starch into maltose and shorter carbohydrates. Saliva also moistens and lubricates food, helping form a bolus. Most nutrient absorption, however, occurs later in the small intestine.

67. Why does the mouth water on seeing or thinking about appetising food?

[RRB Group D (13 Aug 2026, Shift 1)]

• (a) Stomach acid immediately increases
• (b) Salivary glands secrete saliva
• (c) Taste buds move rapidly
• (d) Intestinal enzymes are released into the mouth

Answer: (b) Salivary glands secrete saliva

Explanation: Sight, smell, and anticipation of food can trigger reflex signals from the nervous system to salivary glands. The released saliva moistens the oral cavity and prepares food for chewing, swallowing, and the initial enzymatic digestion of starch.

66. Which acid is normally produced in the stomach, and what is its approximate pH?

[RRB Group D (13 Aug 2026, Shift 1)]

• (a) Acetic acid; 6.0–7.0
• (b) Hydrochloric acid; 1.5–3.5
• (c) Lactic acid; 3.5–4.5
• (d) Citric acid; 6.5–7.0

Answer: (b) Hydrochloric acid; 1.5–3.5

Explanation: Gastric parietal cells secrete hydrochloric acid. The strongly acidic gastric environment activates pepsinogen, supports pepsin activity, and restricts many ingested microbes. The pH is variable, especially around meals, but gastric juice is characteristically highly acidic.

65. What allows the long human small intestine to occupy relatively little abdominal space?

[RRB Group D (13 Aug 2026, Shift 1)]

• (a) A rigid inner lining
• (b) Very thick walls
• (c) An unusually large diameter
• (d) Extensive coiling

Answer: (d) Extensive coiling

Explanation: The small intestine is several metres long but is packed into the abdomen in numerous coils. Its internal folds, villi, and microvilli greatly enlarge the absorptive surface. The coiling permits substantial intestinal length within a limited cavity.

64. Which structures crush food into smaller pieces during eating?

[RRB Group D (11 Aug 2026, Shift 3)]

• (a) Tongue
• (b) Stomach
• (c) Teeth
• (d) Salivary glands

Answer: (c) Teeth

Explanation: Teeth carry out mastication, the mechanical breakdown of food. Incisors cut, canines tear, and premolars and molars crush and grind. This increases food surface area for digestive enzymes, while the tongue and saliva help turn fragments into a swallowable bolus.

63. Why must the stomach maintain a suitable pH for digestive enzymes?

[RRB Group D (04 Aug 2026, Shift 2)]

• (a) To eliminate all gastric acid
• (b) To maintain the shape and activity of enzymes such as pepsin
• (c) To absorb more water
• (d) To stop every harmful bacterium

Answer: (b) To maintain the shape and activity of enzymes such as pepsin

Explanation: The shape of an enzyme and the charges at its active site depend on pH. Pepsin acts efficiently in strongly acidic gastric contents. Excessive deviation from its optimum reduces catalytic activity by changing the molecular interactions required for protein breakdown.

62. Which enzyme from the gastric glands participates in protein digestion?

[RRB Group D (04 Aug 2026, Shift 2)]

• (a) Maltase
• (b) Lipase
• (c) Amylase
• (d) Pepsin

Answer: (d) Pepsin

Explanation: Chief cells release pepsinogen, an inactive precursor that becomes pepsin in the acidic stomach. Pepsin begins breaking dietary proteins into smaller peptides. Pancreatic proteases and intestinal peptidases later continue the process toward absorbable amino acids.

61. Most absorption of digested nutrients in humans occurs in which organ?

[DSSSB MTS (01 May 2026, Shift 2)]

• (a) Small intestine
• (b) Stomach
• (c) Oesophagus
• (d) Large intestine

Answer: (a) Small intestine

Explanation: The small intestine has a large absorptive surface formed by folds, villi, and microvilli. Its epithelium transfers monosaccharides and amino acids mainly into blood, while most absorbed lipids enter lymphatic lacteals. The colon mainly reclaims water and salts.

60. In which carbohydrate form is energy chiefly stored in human liver and muscles?

[RRB NTPC Graduate CBT-I (25 Mar 2026, Shift 2)]

• (a) Glycogen
• (b) Sucrose
• (c) Cellulose
• (d) Starch

Answer: (a) Glycogen

Explanation: Glycogen is a highly branched glucose polymer synthesised and stored in liver and skeletal muscles. Liver glycogen helps regulate blood glucose between meals, whereas muscle glycogen supplies fuel for local muscular activity. Humans do not store energy as plant starch.

59. The optimal pH values for pepsin and trypsin are closest to which pair?

[UPSC NDA-II (2025)]

• (a) 2.0 and 7.9, respectively
• (b) 4.5 and 3.5, respectively
• (c) 9.5 and 4.5, respectively
• (d) 7.0 and 8.0, respectively

Answer: (a) 2.0 and 7.9, respectively

Explanation: Pepsin acts in the acidic stomach and has its optimum near pH 2. Trypsin is a pancreatic enzyme working in the relatively alkaline small intestine, near pH 8. Their contrasting requirements reflect different digestive environments.

58. Which of these is the largest gland of the human body?

[MAHA TET Paper-II, Mathematics and Science (23 Nov 2025)]

• (a) Pancreas
• (b) Liver
• (c) Adipose tissue
• (d) Adrenal gland

Answer: (b) Liver

Explanation: The liver is the largest gland and a major digestive accessory organ. It produces bile, processes absorbed nutrients, and stores glycogen. The pancreas is a mixed gland but is much smaller; adipose tissue is not the largest digestive gland.

57. What can happen to carbohydrates consumed in excess of energy needs?

[RRB NTPC Undergraduate CBT-I (19 Aug 2025, Shift 2)]

• (a) They must become proteins
• (b) They are stored as amino acids
• (c) They can be converted into fat and stored
• (d) They are all excreted immediately

Answer: (c) They can be converted into fat and stored

Explanation: Excess glucose can first replenish glycogen stores. When energy intake continues to exceed requirements, carbohydrate carbon may be converted into fatty acids through lipogenesis and stored as triglycerides. Thus, it need not be eliminated immediately in urine.

56. Which is the longest segment of the alimentary canal?

[SSC CGL Tier-I (23 Sep 2024, Shift 3)]

• (a) Stomach
• (b) Large intestine
• (c) Oesophagus
• (d) Small intestine

Answer: (d) Small intestine

Explanation: The small intestine is longer than the stomach, large intestine, and oesophagus. Its duodenum, jejunum, and ileum support extensive enzymatic digestion and nutrient absorption. Its many coils allow several metres of intestine to fit inside the abdominal cavity.

55. Which glands assist food digestion inside the stomach?

[SSC Selection Post, Higher Secondary (21 Jun 2024, Shift 2)]

• (a) Gastric glands
• (b) Pituitary gland
• (c) Thyroid gland
• (d) Pineal gland

Answer: (a) Gastric glands

Explanation: Gastric glands embedded in the stomach mucosa release hydrochloric acid, pepsinogen, and protective mucus through specialised cell types. Their secretions contribute to protein digestion and defend the gastric wall. The other glands listed primarily have endocrine functions.

54. Which pancreatic serine protease is a globular protein found in vertebrate digestion?

[SSC CHSL Tier-I (08 Jul 2024, Shift 3)]

• (a) Trypsin
• (b) Amylase
• (c) Lipase
• (d) Pepsin

Answer: (a) Trypsin

Explanation: Trypsin is released from the pancreas as trypsinogen and activated within the small intestine. As a serine protease, it breaks peptide bonds in dietary proteins. Amylase acts on starch, lipase on lipids, and pepsin functions mainly in the stomach.

53. Which enzyme is essential for the chemical digestion of fats?

[SSC JE Civil (06 Jun 2024, Shift 3)]

• (a) Lipase
• (b) Zymase
• (c) Trypsin
• (d) Invertase

Answer: (a) Lipase

Explanation: Lipase hydrolyses triglycerides into absorbable lipid products, chiefly fatty acids and monoglycerides. Pancreatic lipase is especially important in the small intestine, where bile salts have already dispersed fat droplets to increase the area available for enzyme action.

52. What is the pancreatic contribution to human digestion?

[UPSC NDA-I (2024)]

• (a) Secretion of surfactants alone
• (b) Storage and regulated release of bile
• (c) Secretion of lipase, amylase, and proteases
• (d) Production of gastric hydrochloric acid

Answer: (c) Secretion of lipase, amylase, and proteases

Explanation: The exocrine pancreas sends digestive enzymes through ducts into the duodenum. Amylase acts on carbohydrates, lipase on fats, and proteases such as trypsin on proteins. Bile is made by the liver and stored in the gallbladder.

51. What does lipase do during the process of digestion?

[SSC CGL Tier-I (20 Jul 2023, Shift 1)]

• (a) Breaks down roughage
• (b) Breaks down emulsified fats
• (c) Produces intestinal secretions
• (d) Digests proteins

Answer: (b) Breaks down emulsified fats

Explanation: Lipase is a fat-digesting enzyme. Bile salts first disperse large fat masses into small droplets, and pancreatic lipase then hydrolyses triglyceride molecules. This permits intestinal absorption of lipid digestion products and fat-soluble substances.

50. Which digestive secretion helps make acidic food from the stomach alkaline?

[SSC CGL Tier-I (17 Jul 2023, Shift 4)]

• (a) Pepsin
• (b) Gastric juice
• (c) Hydrochloric acid
• (d) Bile juice

Answer: (d) Bile juice

Explanation: Bile entering the duodenum helps create conditions appropriate for intestinal digestion, and pancreatic bicarbonate provides substantial neutralisation of acid. Bile salts additionally emulsify fats. Gastric hydrochloric acid instead creates the acidic conditions needed by stomach pepsin.

49. Which statement about the liver is NOT correct?

[SSC CGL Tier-I (21 Jul 2023, Shift 3)]

• (a) It lies predominantly in the upper left abdomen
• (b) It secretes bile stored in the gallbladder
• (c) It is the largest gland
• (d) It is reddish-brown

Answer: (a) It lies predominantly in the upper left abdomen

Explanation: The liver is located mainly in the right upper abdomen beneath the diaphragm, not predominantly on the left. It produces bile for delivery to the small intestine, while the gallbladder stores and concentrates bile between meals.

48. Consider: A. Saliva contains maltase that splits maltose. B. Saliva contains amylase that acts on starch. Which is correct?

[SSC CHSL (2022) Tier-II (26 Jun 2023, Shift 1)]

• (a) Neither statement
• (b) Only A
• (c) Both A and B
• (d) Only B

Answer: (d) Only B

Explanation: Salivary amylase initiates starch digestion in the oral cavity. Maltase, which splits maltose into glucose, acts principally at the small-intestinal brush border rather than being a typical salivary digestive enzyme. Accordingly, statement B alone is correct.

47. The liver secretes which substance that is subsequently stored in the gallbladder?

[SSC MTS (2022) (13 Jun 2023, Shift 3)]

• (a) Mucus
• (b) Bile juice
• (c) Hydrochloric acid
• (d) Oestrogen

Answer: (b) Bile juice

Explanation: Hepatocytes produce bile, which passes through bile ducts and can be stored in the gallbladder. On entering the duodenum, bile salts help disperse fats into smaller droplets. Hydrochloric acid instead comes from gastric parietal cells.

46. Triglycerides are broken down to which products during digestion?

[WBCS Mains, Science (2023)]

• (a) Fatty acids only
• (b) Amino acids
• (c) Glycerol only
• (d) Fatty acids and glycerol

Answer: (d) Fatty acids and glycerol

Explanation: Lipases hydrolyse ester bonds in triglycerides. Dietary fat digestion usually first produces free fatty acids and monoglycerides, which can be further split into glycerol and fatty acids. These products can be absorbed after incorporation into mixed micelles.

45. Which of these are NOT among the five basic taste qualities: sweet, bitter, salty, spicy, umami, sour, pungent?

[69th BPSC Preliminary Examination (2023)]

• (a) Bitter, umami, pungent
• (b) Sweet, salty, spicy
• (c) Spicy and pungent
• (d) Salty and sour

Answer: (c) Spicy and pungent

Explanation: The commonly recognised basic tastes are sweet, sour, salty, bitter, and umami. Spiciness and pungency largely involve chemesthetic activation of sensory nerve endings rather than taste receptors. They can accompany taste but are not separate basic taste qualities.

44. Which enzyme in pancreatic juice breaks down fats?

[SSC CGL Tier-I (08 Dec 2022, Shift 4)]

• (a) Protease
• (b) Pepsin
• (c) Lipase
• (d) Amylase

Answer: (c) Lipase

Explanation: Pancreatic lipase is released into the duodenum, where it hydrolyses dietary triglycerides after fat emulsification. Proteases act on proteins, whereas amylase breaks down starch. Pepsin is the protein-digesting enzyme primarily associated with the acidic stomach.

43. How does hydrochloric acid facilitate the action of pepsin?

[SSC CGL Tier-I (02 Dec 2022, Shift 2)]

• (a) It creates an acidic medium
• (b) It destroys pepsin
• (c) It creates an alkaline medium
• (d) It creates a basic medium

Answer: (a) It creates an acidic medium

Explanation: Gastric hydrochloric acid provides the low pH suitable for pepsin and also helps activate pepsinogen. Pepsin hydrolyses proteins into shorter polypeptides. An alkaline environment would reduce the activity of this gastric protease rather than improve it.

42. Which statement about the sequence of digestion is false?

[RRB Group D (11 Oct 2022, Shift 2)]

• (a) Assimilation occurs before ingestion but after absorption
• (b) Absorption and assimilation precede egestion
• (c) Digestion follows ingestion and precedes egestion
• (d) Absorption follows digestion and precedes assimilation

Answer: (a) Assimilation occurs before ingestion but after absorption

Explanation: The usual broad sequence is ingestion, digestion, absorption, assimilation, and egestion. Assimilation is the utilisation of absorbed nutrients by cells, so it cannot precede ingestion. Absorption and assimilation occur after food has entered and been processed.

41. Which secretion helps change the acidic intestinal food mass toward an alkaline state?

[RRB Group D (29 Sep 2022, Shift 2)]

• (a) Intestinal juice
• (b) Bile juice
• (c) Pancreatic juice
• (d) Gastric juice

Answer: (b) Bile juice

Explanation: The official keyed answer is bile juice. It contributes to conditions suitable for intestinal digestion, although bicarbonate-rich pancreatic juice is also a major neutraliser of acidic chyme. The change of pH permits pancreatic enzymes to operate efficiently.

40. Villi are present in which part of the body?

[RRB Group D (28 Sep 2022, Shift 3)]

• (a) Eye
• (b) Kidney
• (c) Liver
• (d) Small intestine

Answer: (d) Small intestine

Explanation: Villi are minute finger-like outgrowths of the intestinal mucosa. They greatly expand surface area and contain blood capillaries and lymphatic lacteals, permitting efficient uptake of digested nutrients. They are characteristic of the small intestine rather than the listed organs.

39. Where are carbohydrates, proteins, and fats completely digested?

[RRB Group D (17 Sep 2022, Shift 3)]

• (a) Stomach
• (b) Small intestine
• (c) Rectum
• (d) Large intestine

Answer: (b) Small intestine

Explanation: The small intestine receives bile and pancreatic secretions and produces brush-border digestive enzymes. Together these processes complete breakdown of the major dietary macromolecules. The stomach begins substantial protein digestion, while the large intestine primarily absorbs water and salts.

38. Salivary amylase helps in the digestion of which substance?

[RRB Group D (15 Sep 2022, Shift 3)]

• (a) Lipids
• (b) Proteins
• (c) Starch
• (d) Cellulose

Answer: (c) Starch

Explanation: Ptyalin, the amylase in saliva, attacks starch molecules and yields smaller carbohydrates, including maltose and dextrins. Its action begins in the mouth but diminishes when gastric acidity inactivates the enzyme. Human saliva does not contain cellulase.

37. What are the small finger-like intestinal projections that increase absorption called?

[RRB Group D (13 Sep 2022, Shift 2)]

• (a) Sphincters
• (b) Glands
• (c) Cilia
• (d) Villi

Answer: (d) Villi

Explanation: Intestinal villi project from the inner lining of the small intestine. Their thin epithelium and rich vascular and lymphatic supply support nutrient absorption. Together with microvilli they enlarge the area across which digested molecules enter the body.

36. What is the effect of bile salts during digestion?

[RRB Group D (13 Sep 2022, Shift 2)]

• (a) They divide large fat globules into small droplets
• (b) They activate enzymes that digest proteins
• (c) They themselves contain digestive lipase
• (d) They directly hydrolyse fats into fatty acids

Answer: (a) They divide large fat globules into small droplets

Explanation: Bile salts emulsify large fat globules without chemically hydrolysing triglycerides. Dividing fat into smaller droplets exposes a greater surface area to pancreatic lipase. This cooperation makes fat digestion and subsequent absorption substantially more efficient.

35. Which is NOT a function of bile juice?

[RRB Group D (09 Sep 2022, Shift 2)]

• (a) Supporting pancreatic enzyme efficiency
• (b) Dividing large fat globules
• (c) Providing conditions suitable for pancreatic enzymes
• (d) Providing a protein-digesting enzyme

Answer: (d) Providing a protein-digesting enzyme

Explanation: Bile contains bile salts and other components but no protein-digesting enzyme. Its key digestive function is emulsification of dietary lipids, along with supporting intestinal conditions. Pancreatic proteases, not bile, perform the hydrolysis of food proteins.

34. Which terminal part of the alimentary canal expels solid waste?

[RRB Group D (06 Sep 2022, Shift 2)]

• (a) Large intestine
• (b) Small intestine
• (c) Appendix
• (d) Anus

Answer: (d) Anus

Explanation: The anus is the terminal opening through which faeces are expelled during defecation. The colon absorbs water and forms faeces, whereas the rectum temporarily stores them. Anal sphincter muscles help regulate their eventual passage outside the body.

33. Which villus features aid nutrient absorption:
(i) thin walls,
(ii) large area,
(iii) food-passing pores,
(iv) rich blood capillaries?

[RRB Group D (26 Aug 2022, Shift 3)]

• (a) Only (i) and (iii)
• (b) (i), (ii) and (iv)
• (c) Only (i)
• (d) Only (ii) and (iii)

Answer: (b) (i), (ii) and (iv)

Explanation: Villi have a thin epithelial covering, a greatly increased surface area, and extensive capillaries that take up water-soluble nutrients. Their lacteals absorb most dietary lipid products. Large pores allowing whole food particles through are not a normal absorptive feature.

32. Which carbohydrate cannot be digested by human digestive enzymes?

[WBCS Mains 2021, Paper-IV (exam held May 2022)]

• (a) Starch
• (b) Cellulose
• (c) Glycogen
• (d) Glucose

Answer: (b) Cellulose

Explanation: Humans lack cellulase, the enzyme required to split the beta-1,4 bonds of cellulose. Cellulose therefore functions mainly as dietary fibre, although intestinal microbes may ferment some of it. Starch and glycogen can be hydrolysed by amylases and other enzymes.

31. Which enzyme pair does not work well in an acidic environment?

[UPSC CDS-I, General Knowledge (10 Apr 2022)]

• (a) Trypsin and pepsin
• (b) Chymotrypsin and pepsin
• (c) Trypsin and amylase
• (d) Pepsin and amylase

Answer: (c) Trypsin and amylase

Explanation: Trypsin prefers alkaline intestinal conditions, and pancreatic or salivary amylase acts best near neutral pH. Pepsin is adapted to the strongly acidic stomach. Thus, trypsin and amylase are the pair least suited to highly acidic conditions.

30. Fat digestion in the human intestine involves which pair?

[UPSC NDA-II (2022)]

• (a) Trypsin alone
• (b) Bile and lipase
• (c) Bile and amylase
• (d) Bile and pepsin

Answer: (b) Bile and lipase

Explanation: Bile salts emulsify fats into small droplets. Pancreatic lipase then catalyses the breakdown of triglycerides into smaller lipid products for absorption. Trypsin and pepsin digest proteins, while amylase targets carbohydrate starch rather than dietary fats.

29. Which organ produces bile juice?

[RRB NTPC CBT-I (21 Mar 2021, Shift 2)]

• (a) Liver
• (b) Heart
• (c) Brain
• (d) Kidney

Answer: (a) Liver

Explanation: Bile is synthesised continuously by liver cells and carried through bile ducts. The gallbladder stores and concentrates it until release into the duodenum. Bile salts assist lipid emulsification, but the liver does not produce bile-digesting enzymes.

28. Which statement about the stomach is NOT correct?

[RRB NTPC CBT-I (06 Apr 2021, Shift 1)]

• (a) Mucus protects its lining
• (b) Gastric glands release acid, pepsin and mucus
• (c) It receives the liver and pancreas secretions for digestion
• (d) HCl provides a medium for pepsin

Answer: (c) It receives the liver and pancreas secretions for digestion

Explanation: The stomach secretes gastric juice, containing acid, mucus, and pepsin-related secretions. Bile and pancreatic juice enter the duodenum of the small intestine, not the stomach. The stomach chiefly starts protein digestion and mechanically mixes food.

27. Which digestive organ has a shape resembling the letter J?

[RRB NTPC CBT-I (13 Mar 2021, Shift 2)]

• (a) Liver
• (b) Mouth
• (c) Stomach
• (d) Intestine

Answer: (c) Stomach

Explanation: The stomach is a muscular, roughly J-shaped sac connected to the oesophagus and duodenum. It stores, churns, and mixes food with gastric secretions. Its acidic juice promotes the first major stage of protein digestion.

26. In which organ is hydrochloric acid secreted?

[MPPSC State Service Preliminary Examination (2021)]

• (a) Intestine
• (b) Liver
• (c) Stomach
• (d) Pancreas

Answer: (c) Stomach

Explanation: Hydrochloric acid originates from parietal cells of the stomach lining. It produces the low pH that activates pepsinogen and favours pepsin action. Bile from the liver and alkaline pancreatic secretions have different roles after food enters the duodenum.

25. In which organ does the digestion of proteins chiefly begin?

[UPPSC PCS Preliminary Examination (2020)]

• (a) Liver
• (b) Mouth
• (c) Small intestine
• (d) Stomach

Answer: (d) Stomach

Explanation: Pepsin begins major chemical digestion of proteins in the strongly acidic stomach. The enzyme is formed by activation of pepsinogen. Pancreatic trypsin and other proteases later continue protein breakdown in the small intestine, where absorption becomes possible.

24. Which organ is an important source of the digestive enzyme lipase?

[66th BPSC Preliminary Re-examination (2020)]

• (a) Kidney
• (b) Pancreas
• (c) Liver
• (d) Heart

Answer: (b) Pancreas

Explanation: The exocrine pancreas releases pancreatic lipase into the duodenum. This enzyme hydrolyses dietary triglycerides after bile salts emulsify fats. The liver produces bile, not pancreatic lipase. Smaller contributions to fat digestion also occur elsewhere in the digestive tract.

23. Digestion of which food component starts in the human buccal cavity?

[MPPSC State Service Preliminary Examination (2019)]

• (a) Protein
• (b) Fat
• (c) Carbohydrate
• (d) None of these

Answer: (c) Carbohydrate

Explanation: Salivary amylase in the mouth initiates breakdown of starch, which is a carbohydrate. Chewing assists by increasing contact with saliva. Substantial protein digestion begins in the stomach, and most fat digestion takes place in the small intestine.

22. Which calcium compound makes up most of tooth enamel?

[UPSC NDA-I (2019)]

• (a) Calcium carbonate
• (b) Calcium sulphate
• (c) Calcium hydroxide
• (d) Calcium phosphate

Answer: (d) Calcium phosphate

Explanation: Tooth enamel is rich in hydroxyapatite, a crystalline calcium phosphate mineral. Its dense mineral structure makes enamel the hardest tissue in the human body. Enamel protects the crowns of teeth as they cut, crush, and grind food.

21. What chiefly neutralises acidic chyme entering the duodenum?

[UPSC NDA-II (2018)]

• (a) Pancreatic juice
• (b) Duodenal secretion
• (c) Large intestine secretion
• (d) Bile juice

Answer: (a) Pancreatic juice

Explanation: The pancreas releases bicarbonate-rich fluid into the duodenum, neutralising hydrochloric acid carried from the stomach. The resulting higher pH supports pancreatic enzymes. Bile also contributes to the intestinal environment, but bicarbonate is the major chemical neutraliser.

20. Damage to stomach cells that secrete acid would most strongly impair digestion of which food constituent?

[UPSC NDA-I (2018)]

• (a) Proteins
• (b) Lipids
• (c) Carbohydrates
• (d) Proteins and carbohydrates equally

Answer: (a) Proteins

Explanation: Without sufficient gastric hydrochloric acid, pepsinogen is activated poorly and pepsin works less efficiently. Since pepsin initiates digestion of proteins in the stomach, the greatest direct effect concerns proteins. Most carbohydrate and fat digestion occurs elsewhere.

19. Which animal has the comparatively shortest small intestine?

[RPSC Assistant Engineer, General Knowledge and Science (2018)]

• (a) Tiger
• (b) Cow
• (c) Elephant
• (d) Horse

Answer: (a) Tiger

Explanation: A tiger is a carnivore with a relatively short intestinal tract suited to an animal-based diet. Herbivores such as cows, elephants, and horses generally require longer digestive passages and microbial processing to extract nutrients from plant matter.

18. Gallstones most directly interfere with digestion of which nutrient?

[UPPSC PCS Preliminary Examination (2017)]

• (a) Fats
• (b) Proteins
• (c) Carbohydrates
• (d) Nucleic acids

Answer: (a) Fats

Explanation: Gallstones can obstruct bile flow into the duodenum. Reduced bile delivery impairs fat emulsification and the formation of micelles, making fat digestion and absorption less effective. This may also affect uptake of fat-soluble vitamins A, D, E, and K.

17. Assertion: Humans cannot digest cellulose.
Reason: Humans have starch-digesting diastase.

Which assessment is correct?

[UPPSC PCS Preliminary Examination (2017)]

• (a) Both true; reason explains assertion
• (b) Both true; reason does not explain assertion
• (c) Assertion true; reason false
• (d) Assertion false; reason true

Answer: (b) Both true; reason does not explain assertion

Explanation: Humans lack cellulase, so they cannot enzymatically hydrolyse cellulose. They do possess starch-digesting amylase, historically also called diastase in general contexts. Both claims are true, but the presence of starch-digesting enzymes does not explain cellulose indigestibility.

16. Antacids used for excess stomach acidity are usually what type of substance?

[CGPSC Preliminary, General Studies (2016)]

• (a) Bases
• (b) Acids
• (c) Neutral salts only
• (d) Oxidising agents

Answer: (a) Bases

Explanation: Common antacids contain weakly basic substances such as magnesium hydroxide or calcium carbonate. These react with excess gastric hydrochloric acid, reducing acidity and easing symptoms. Their neutralising action differs from the normal digestive action of stomach acid on proteins.

15. Which of these are involved in digestion of lipids: 1. bile acids, 2. lipase, 3. pepsin?

[UPPSC PCS Mains (2016)]

• (a) Only 1
• (b) Only 1 and 3
• (c) Only 1 and 2
• (d) All three

Answer: (c) Only 1 and 2

Explanation: Bile acids help emulsify dietary fats and form micelles. Lipase provides the enzyme-driven hydrolysis of triglycerides. Pepsin acts on protein rather than fat, so the relevant components are bile acids and lipase alone.

14. Match

List I (A. Proteins, B. Carbohydrates, C. Nucleic acids, D. Lipids)

with List II (1. Nitrogenous bases and pentose sugars, 2. Fatty acids and glycerol, 3. Monosaccharides, 4. Amino acids).

Choose the correct code.

[UPSC NDA-I (2016)]

• (a) A-2, B-3, C-1, D-4
• (b) A-2, B-1, C-3, D-4
• (c) A-4, B-1, C-3, D-2
• (d) A-4, B-3, C-1, D-2

Answer: (d) A-4, B-3, C-1, D-2

Explanation: Protein digestion yields amino acids; carbohydrates yield simple sugars; nucleic acid digestion yields bases, sugars, and phosphate-containing products; lipids yield fatty acids and monoglycerides or glycerol. Different enzyme groups act on each macromolecule in the alimentary canal.

13. In what form is energy stored in the liver and muscles?

[56th–59th BPSC Preliminary Examination (2015)]

• (a) Generic carbohydrate
• (b) Fat alone
• (c) Protein
• (d) Glycogen

Answer: (d) Glycogen

Explanation: Glycogen is the major readily mobilised glucose reserve in liver and skeletal muscle. The liver can release glucose into circulation as needed, whereas muscle chiefly consumes its glycogen locally during activity. Both tissues therefore store glucose as a branched polysaccharide.

12. Which is NOT a function of the liver?

[UPSC NDA-II (2014)]

• (a) Converting glucose into glycogen
• (b) Producing urea
• (c) Removing aged red blood cells
• (d) Absorbing digested food and water from undigested material

Answer: (d) Absorbing digested food and water from undigested material

Explanation: The liver stores glycogen, synthesises urea, and participates in clearance of old red blood cells via resident macrophages. Most nutrient absorption occurs in the small intestine, while the large intestine reclaims water, so these are not liver functions.

11. Where is digestion of carbohydrates, proteins, and fats completed?

[UPSC NDA-I (2013)]

• (a) Stomach
• (b) Liver
• (c) Small intestine
• (d) Large intestine

Answer: (c) Small intestine

Explanation: The small intestine receives pancreatic enzymes and bile, and its lining supplies additional enzymes. Together they complete the main digestive reactions for carbohydrates, proteins, and fats. Nutrients are then absorbed across the intestinal mucosa into blood or lymph.

10. Which constituent of food is digested with the help of saliva?

[Jharkhand PCS Preliminary Examination (2013)]

• (a) Protein
• (b) Starch
• (c) Cellulose fibre
• (d) None of these

Answer: (b) Starch

Explanation: Ptyalin, the salivary form of amylase, hydrolyses starch into smaller carbohydrates. Saliva also lubricates food to enable swallowing. Humans do not possess a salivary cellulase; proteins are chiefly attacked by pepsin and pancreatic proteases.

9. Saliva helps digest which nutrient?

[Rajasthan RAS/RTS Preliminary Examination (2012)]

• (a) Starch
• (b) Proteins
• (c) Fibres
• (d) Fats

Answer: (a) Starch

Explanation: Salivary amylase initiates digestion of starch in the mouth. Its action begins while food is being chewed and mixed with saliva. This early reaction contributes to carbohydrate digestion, which is finished by pancreatic and intestinal enzymes.

8. Which listed enzyme helps in the digestion of protein?

[UPPSC PCS Preliminary Examination (2010)]

• (a) Urease
• (b) Sulfatase
• (c) Trypsin
• (d) Amylase

Answer: (c) Trypsin

Explanation: Trypsin is a pancreatic protease that hydrolyses peptide bonds in the small intestine. It is secreted as inactive trypsinogen and activated after reaching the duodenum. Urease acts on urea, while amylase digests starch rather than proteins.

7. Which is the second-largest gland and provides an alkaline, enzyme-rich digestive secretion?

[UPPSC Special Mains (2008)]

• (a) Liver
• (b) Spleen
• (c) Pancreas
• (d) Salivary glands

Answer: (c) Pancreas

Explanation: The pancreas is an accessory digestive gland situated behind the stomach. Its exocrine secretions contain bicarbonate and enzymes that digest proteins, carbohydrates, and fats. The liver is larger, but its bile does not itself contain those digestive hydrolases.

6. Which item is NOT a digestive enzyme in humans?

[UPSC Civil Services Preliminary Examination (2007)]

• (a) Trypsin
• (b) Gastrin
• (c) Ptyalin
• (d) Pepsin

Answer: (b) Gastrin

Explanation: Gastrin is a hormone involved in regulating gastric acid secretion, not an enzyme. Trypsin and pepsin hydrolyse proteins, while ptyalin is salivary amylase that digests starch. Confusing digestive hormones with enzymes is a common examination trap.

5. Which descending length order of small-intestinal regions is correct?

[UPSC Civil Services Preliminary Examination (2007)]

• (a) Jejunum–duodenum–ileum
• (b) Ileum–duodenum–jejunum
• (c) Jejunum–ileum–duodenum
• (d) Ileum–jejunum–duodenum

Answer: (d) Ileum–jejunum–duodenum

Explanation: The ileum is typically the longest segment of the small intestine, followed by the jejunum, with the duodenum shortest. The duodenum is the initial receiving portion for pancreatic secretions and bile; the longer distal segments are important for absorption.

4. Assertion: All food proteins are digested only in the small intestine. Reason: Pancreatic proteases enter the small intestine.

[UPSC Civil Services Preliminary Examination (2005)]

• (a) Both are true and reason explains assertion
• (b) Both are true but reason does not explain assertion
• (c) Assertion true but reason false
• (d) Assertion false but reason true

Answer: (d) Assertion false but reason true

Explanation: Protein digestion starts in the stomach when pepsin acts in acidic gastric juice. Pancreatic proteases do enter the small intestine and continue digestion. Thus the reason is correct, but the assertion wrongly excludes gastric protein digestion.

3. Where is much of the glycogen formed from excess glucose stored?

[UPPSC PCS Mains (2004)]

• (a) Stomach
• (b) Liver
• (c) Pancreatic juice
• (d) Bile

Answer: (b) Liver

Explanation: After a meal, some absorbed glucose is converted into glycogen through glycogenesis, especially in the liver and skeletal muscles. Liver glycogen acts as a buffer for blood glucose. Neither bile nor pancreatic juice functions as a glycogen-storage site.

2. Consider:
(1) Duodenal acid stimulates secretin release.
(2) Fatty acids in the small intestine stimulate enterogastrone.

Which are correct?

[UPSC Civil Services Preliminary Examination (2003)]

• (a) Only 1
• (b) Only 2
• (c) Both 1 and 2
• (d) Neither 1 nor 2

Answer: (c) Both 1 and 2

Explanation: Acid entering the duodenum stimulates secretin release, which promotes bicarbonate secretion. Fatty nutrients in the intestine also stimulate inhibitory hormonal signals traditionally called enterogastrones, slowing gastric activity. Both mechanisms help coordinate stomach emptying with intestinal digestion.

1. Enzymes are basically composed of which type of substance?

[Uttarakhand PCS Preliminary Examination (2002)]

• (a) Fats
• (b) Sugars
• (c) Proteins
• (d) Vitamins

Answer: (c) Proteins

Explanation: Most enzymes, including digestive amylase, pepsin, and trypsin, are proteins acting as biological catalysts. Their specific three-dimensional structures permit reactions to proceed rapidly. A few naturally occurring catalytic RNA molecules exist, but typical human digestive enzymes are proteins.

Question attribution follows identified previous-year paper records, including papers held in a different year from their recruitment-cycle title. Minor wording changes were made for readability. No practice-only questions are included. For a formally authenticated question bank, each item should additionally be checked against its official examination PDF.