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.