Free Human Digestive System MCQs with Answers

• A. protein
• B. starch
• C. fat
• D. cellulose

Explanation: Salivary amylase hydrolyses starch to the disaccharide maltose, so carbohydrate digestion is the only kind that starts in the mouth.

• A. digests proteins directly into amino acids
• B. emulsifies the fat in the food
• C. kills most swallowed bacteria and gives pepsin the acid pH it needs
• D. neutralises the acid arriving from the mouth

Explanation: The acid brings the stomach contents to about pH 2, which is the optimum for pepsin and also converts inactive pepsinogen into pepsin…

• A. an active enzyme would digest the protein of the cells that make it
• B. pepsinogen is easier to store in the blood
• C. pepsin cannot be transported across a membrane
• D. pepsinogen digests fat before it is converted

Explanation: Pepsin is a protease, and the cells that secrete it are themselves made of protein, so it is released as an inactive precursor and…

• A. contains the enzyme lipase
• B. converts fatty acids into glycerol
• C. makes the duodenum acidic
• D. emulsifies fat into tiny droplets, greatly increasing the surface area for lipase

Explanation: Bile salts are detergents that break large fat globules into a suspension of tiny droplets, and since lipase can only act at the surface…

• A. gall bladder
• B. pancreas
• C. gastric glands
• D. salivary glands

Explanation: Pancreatic juice contains lipase along with amylase and trypsinogen, and it enters the duodenum through the pancreatic duct, which is also…

• A. enterokinase secreted by the wall of the duodenum
• B. hydrochloric acid from the stomach
• C. bile salts from the gall bladder
• D. salivary amylase

Explanation: Enterokinase, an enzyme of the intestinal lining, removes a short peptide from trypsinogen and unmasks its active site, after which…

• A. stomach
• B. large intestine
• C. small intestine
• D. oesophagus

Explanation: The small intestine is long, folded and covered in villi and microvilli, so its absorptive surface is measured in hundreds of square…

• A. A dense network of blood capillaries
• B. A single layer of epithelial cells covering it
• C. Microvilli on the free surface of its cells
• D. A thick covering of muscle around each villus

Explanation: A villus is adapted by being thin walled, richly supplied with blood and lymph and covered in microvilli, all of which shorten the…

• A. the digestion of protein
• B. the absorption of water and mineral salts
• C. the secretion of bile
• D. the absorption of amino acids

Explanation: Undigested material entering the colon is very fluid, and the reabsorption of water and salts turns it into semi solid faeces, which is…

• A. a wave of contraction of circular muscle behind the food that pushes it along the gut
• B. the churning of food by the teeth
• C. the return of food from the stomach to the mouth
• D. the absorption of nutrients into the blood

Explanation: Circular muscle contracts behind the bolus and longitudinal muscle contracts in front of it, so a wave of narrowing travels along the tube…

• A. cardiac sphincter
• B. anal sphincter
• C. pyloric sphincter
• D. ileocaecal sphincter

Explanation: The pyloric sphincter opens periodically to release small squirts of chyme into the duodenum, so that the acid can be neutralised and the…

• A. Conversion of excess glucose into glycogen
• B. Deamination of surplus amino acids and formation of urea
• C. Production of bile
• D. Secretion of insulin into the blood

Explanation: Insulin is secreted by the beta cells of the islets of Langerhans in the pancreas, not by the liver, though the liver is the main organ…

• A. breaking large fat globules into many small droplets
• B. hydrolysing fat into fatty acids and glycerol
• C. converting fat into glycogen
• D. dissolving fat completely in water

Explanation: Emulsification is a physical change only: the chemical nature of the fat is unaltered and only the size of the droplets changes, which is…

• A. stops the stomach from emptying
• B. stimulates the gastric glands to secrete more gastric juice
• C. is secreted by the pancreas
• D. digests protein in the stomach

Explanation: Gastrin is released into the blood by cells in the stomach lining when food arrives and returns to the same organ to increase the output…

• A. only by simple diffusion, so absorption stops when concentrations are equal
• B. by osmosis through the capillary wall
• C. by active transport, so it can be taken up even against a concentration gradient
• D. through the lacteals along with fats

Explanation: Absorption must continue until almost all the glucose is recovered, and that means moving it out of the gut even when the concentration…

• A. an excess of bile in the stomach
• B. a shortage of hydrochloric acid
• C. eating too much fibre
• D. infection with the bacterium Helicobacter pylori

Explanation: Helicobacter pylori survives the acid by living under the mucus layer, and the inflammation it causes lets acid and pepsin damage the wall…

• A. molars
• B. incisors
• C. canines
• D. wisdom teeth only

Explanation: Molars and premolars have broad ridged surfaces that crush food between them and greatly increase the area available to the digestive…

• A. supplies energy slowly over several hours
• B. adds bulk that stimulates peristalsis and prevents constipation
• C. is absorbed by the villi as cellulose
• D. provides the essential amino acids

Explanation: Humans have no cellulase, so fibre passes through unchanged, but its bulk holds water and stretches the gut wall, which keeps peristalsis…

• A. ingestion
• B. egestion
• C. assimilation
• D. absorption

Explanation: Assimilation is the last stage of nutrition, in which the absorbed molecules are actually built into cell components or oxidised for…

• A. deficient in vitamin C
• B. deficient in iodine
• C. excessive in fat
• D. sufficient in energy but severely deficient in protein

Explanation: Where the diet is mostly starch, energy intake may be adequate but protein is not, so plasma protein falls, fluid is not drawn back into…