All Free Biology MCQs with Answers

561. The ring of muscle at the junction of the oesophagus and the stomach is called the

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

Explanation: The cardiac sphincter opens to admit food and closes to stop acid reflux into the oesophagus. The pyloric sphincter guards the stomach's exit, and mixing these two up is a classic error.

562. The enzyme present in human saliva is

• A. amylase
• B. pepsin
• C. trypsin
• D. lipase

Explanation: Salivary amylase starts splitting starch into maltose right in the mouth, which is why bread tastes sweet if chewed long enough. Pepsin and trypsin digest protein further down the tract.

563. The organ that mixes food with saliva, tastes it and rolls it into a bolus for swallowing is the

• A. hard palate
• B. tongue
• C. pharynx
• D. epiglottis

Explanation: The tongue's muscles manipulate food during chewing and push the bolus backwards to trigger swallowing, while its taste buds sample it. The epiglottis only guards the airway during the swallow itself.

564. The hardest substance in the human body is

• A. dentine
• B. bone
• C. enamel
• D. cement

Explanation: Enamel caps the crown of the tooth with a layer of mineral crystals harder even than bone, enabling it to withstand years of grinding. Once lost it cannot regenerate, which is why decay is permanent.

565. The enzyme of the gastric juice that digests protein is

• A. amylase
• B. lipase
• C. maltase
• D. pepsin

Explanation: Pepsin breaks proteins into peptides in the strongly acidic stomach, working best near pH 2. Amylase and maltase handle carbohydrates and cannot function at such acidity.

566. The pancreas is called a mixed gland because it

• A. is attached to both the liver and the stomach
• B. has both exocrine and endocrine functions
• C. stores bile between meals
• D. secretes hormones only

Explanation: Its ducts deliver digestive enzymes into the duodenum, an exocrine role, while its islets of Langerhans release insulin and glucagon into the blood, an endocrine role. Both jobs in one organ earn it the name mixed.

567. Bile produced by the liver is stored and concentrated in the

• A. gall bladder
• B. spleen
• C. kidney
• D. appendix

Explanation: The gall bladder holds bile between meals and squeezes it into the duodenum when fat arrives. The liver makes bile continuously, so confusing maker with storehouse is the trap here.

568. Bile differs from the other digestive juices in that it

• A. contains a strong acid
• B. contains pepsin
• C. digests starch
• D. contains no digestive enzyme

Explanation: Bile helps fat digestion purely physically, by emulsifying large drops into tiny ones that lipase can attack. Every other major juice contributes an enzyme, making bile the odd one out.

569. The final products of protein digestion are

• A. fatty acids and glycerol
• B. glucose
• C. amino acids
• D. maltose

Explanation: Proteases and peptidases cut polypeptides down to single amino acids, which are absorbed and rebuilt into the body's own proteins. Fatty acids come from fats and glucose from carbohydrates.

570. Complete digestion of fats yields

• A. glucose and water
• B. fatty acids and glycerol
• C. starch
• D. amino acids

Explanation: Lipase splits the three ester bonds of a triglyceride, releasing glycerol and three fatty acids. These are absorbed into the lacteals rather than the blood capillaries.