All Free Biology MCQs with Answers

551. A drunk person walks unsteadily and cannot coordinate movements because alcohol mainly affects the

• A. medulla oblongata
• B. cerebellum
• C. hypothalamus
• D. pituitary gland

Explanation: The cerebellum fine tunes posture, balance and the timing of voluntary movement, so its depression by alcohol produces staggering and clumsiness. The medulla keeps the heart and lungs running, which is why severe poisoning, not drunkenness, threatens life.

552. Hormones are best described as

• A. enzymes that speed up metabolism
• B. waste products of the endocrine glands
• C. chemical messengers carried in the blood to target organs
• D. electrical signals sent along nerves

Explanation: Endocrine glands secrete hormones directly into the blood, which delivers them everywhere, but only cells with the right receptors respond. This slow, widespread chemical signalling complements the fast, wired signalling of the nervous system.

553. The pituitary gland is called the master gland because it

• A. is the largest endocrine gland
• B. sits outside the brain
• C. secretes digestive enzymes
• D. controls the secretion of several other endocrine glands

Explanation: Pituitary hormones such as TSH and ACTH direct the thyroid and adrenal cortex, and its link with the hypothalamus places it at the top of many control chains. Size is irrelevant; control is what earns the title.

554. Excess secretion of growth hormone during childhood results in

• A. gigantism
• B. dwarfism
• C. cretinism
• D. diabetes

Explanation: Before the bones stop growing, too much growth hormone drives the long bones to extraordinary length, producing gigantism. Deficiency instead causes dwarfism, and after the growth plates close, excess hormone thickens bones in acromegaly rather than lengthening them.

555. Thyroxine, the hormone of the thyroid gland, primarily controls the

• A. concentration of glucose in the blood
• B. rate of metabolism and heat production of the body
• C. amount of calcium in the bones
• D. volume of urine produced

Explanation: Thyroxine sets the basal metabolic rate of nearly every cell, which is why an overactive thyroid causes weight loss and heat intolerance. Blood glucose is governed by insulin and glucagon, and urine volume by ADH.

556. Adrenaline released from the adrenal medulla prepares the body for

• A. sleep and digestion
• B. long term growth
• C. emergency action, the fight or flight response
• D. the production of eggs

Explanation: Adrenaline raises heart rate, blood glucose and blood flow to muscles while slowing digestion, equipping the body for sudden exertion. Rest and digest is the job of the parasympathetic system, the functional opposite.

557. The hormone that raises the glucose concentration of the blood is

• A. insulin
• B. ADH
• C. thyroxine
• D. glucagon

Explanation: Glucagon from the alpha cells of the pancreas converts glycogen back to glucose in the liver, lifting blood sugar between meals. Insulin does the opposite, and the insulin glucagon pair together keeps glucose within narrow limits.

558. The correct sequence of the parts of the alimentary canal is

• A. mouth, pharynx, oesophagus, stomach, small intestine, large intestine
• B. mouth, oesophagus, pharynx, stomach, small intestine, large intestine
• C. mouth, stomach, pharynx, oesophagus, large intestine, small intestine
• D. mouth, pharynx, stomach, oesophagus, small intestine, large intestine

Explanation: Food passes through the pharynx before the oesophagus and the oesophagus before the stomach, and the small intestine always precedes the large one. Any sequence that swaps these pairs is wrong by definition.

559. The three regions of the small intestine, in order, are the

• A. jejunum, duodenum, ileum
• B. duodenum, jejunum, ileum
• C. ileum, jejunum, duodenum
• D. caecum, colon, rectum

Explanation: The duodenum receives bile and pancreatic juice, the jejunum continues digestion, and the ileum completes absorption before the large intestine. The caecum, colon and rectum belong to the large intestine instead.

560. The muscular tube that carries the bolus from the pharynx to the stomach is the

• A. trachea
• B. larynx
• C. oesophagus
• D. small intestine

Explanation: The oesophagus moves the bolus by waves of peristalsis in a matter of seconds. The trachea carries air, a fact the swallowing mechanism protects by closing it off.