All Free Biology MCQs with Answers

151. Which of the following is NOT a function of the liver?

• 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 that insulin acts on. The liver does regulate blood glucose by storing and releasing glycogen, deaminate amino acids the body cannot store, make bile, detoxify drugs and store iron and several vitamins. Confusing the organ that makes a hormone with the organ that responds to it is the trap here.

152. Emulsification of fat means

• 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 why bile needs no enzyme to do it. Hydrolysis into fatty acids and glycerol is the chemical step, and it is carried out afterwards by lipase acting on the enlarged surface. Fat never truly dissolves in water, since it is non polar.

153. The hormone gastrin

• 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 of acid and pepsinogen, an example of hormonal rather than nervous control of digestion. Secretin and cholecystokinin work later, from the duodenum, to call for pancreatic juice and bile. A hormone is a chemical messenger, so gastrin does no digesting itself.

154. Glucose is absorbed from the small intestine into the blood

• 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 there has fallen below that in the blood, which requires energy from ATP. This is why the epithelial cells of the villi are rich in mitochondria. Osmosis applies to water alone, and the lacteals absorb the products of fat digestion rather than sugars.

155. Most peptic ulcers are now known to be associated with

• 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 beneath, so most ulcers are cured with antibiotics together with an acid reducing drug. Stress and spicy food may aggravate the symptoms but are no longer regarded as the cause. Ulcers form where acid is present, so a shortage of acid cannot explain them.

156. The teeth adapted for grinding and crushing food are the

• 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 enzymes. Incisors are chisel shaped for cutting and canines are pointed for tearing, matching the mixed diet of an omnivore. Wisdom teeth are simply the third molars and are only a part of the grinding set, not a separate type.

157. Dietary fibre, or roughage, is important even though it is not digested because it

• 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 regular and shortens the time waste stays in the colon. Diets low in fibre are linked with constipation, piles and cancer of the colon. Because it is not broken down, fibre supplies no energy and no amino acids.

158. The use of absorbed food materials by the body cells for growth and repair is called

• 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 energy. Absorption is the earlier step of moving them from the gut into the blood, which is the usual confusion. Egestion is the removal of undigested material as faeces and is not excretion, since that waste never entered the body's cells.

159. Kwashiorkor in young children is caused by a diet that is

• 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 the capillaries and the child develops the characteristic swollen abdomen along with poor growth and a fatty liver. Marasmus, by contrast, is a shortage of both energy and protein and produces severe wasting. Vitamin C deficiency causes scurvy and iodine deficiency causes goitre.

160. The forelimb of a whale, a bat and a human have the same arrangement of bones but perform different functions. Such organs are described as

• A. analogous
• B. homologous
• C. vestigial
• D. acquired

Explanation: Homologous organs share a common structural plan and a common embryonic origin because they were inherited from a shared ancestor, and their different uses are the result of divergent evolution. Analogous organs are the opposite case: same job, different structure and origin. Vestigial organs are reduced remnants that have lost their original function altogether.