All Free Biology MCQs with Answers

131. A reflex action such as withdrawing the hand from a hot object is fast because

• A. the impulses travel through the cerebrum first
• B. only one neurone is involved in the whole pathway
• C. hormones carry the message directly to the muscle
• D. the response is organised in the spinal cord without waiting for the brain

Explanation: The reflex arc is completed at spinal level, so the muscle contracts before the impulses climbing to the brain arrive and the pain is consciously felt, which is what makes the response protective. The brain is informed afterwards and can modify or suppress some reflexes, but it is not needed for the action itself. At least three neurones are involved, and hormones are far too slow for this.

132. In the spinal cord, unlike the cerebrum, the grey matter

• A. lies on the inside and the white matter surrounds it
• B. lies on the outside and the white matter is central
• C. is entirely absent
• D. contains only myelinated fibres

Explanation: The butterfly shaped core of grey matter contains the cell bodies and synapses, while the outer white matter is made of myelinated axons running up and down the cord, and myelin is what makes that region look white. In the brain the arrangement is inverted, with the grey cortex outside. Recognising the pattern is how a spinal cord section is identified under the microscope.

133. The part of the brain concerned with intelligence, memory and voluntary action is the

• A. cerebellum
• B. cerebrum
• C. medulla oblongata
• D. hypothalamus

Explanation: The cerebrum is the largest part of the human brain, and its folded cortex carries the sensory, motor and association areas responsible for thought, language, memory and conscious decision. Its folding increases the surface area enormously within the fixed volume of the skull. The cerebellum and medulla handle coordination and vital automatic functions and have nothing to do with conscious thought.

134. Damage to the cerebellum would most likely result in

• A. loss of memory
• B. failure of breathing
• C. loss of balance and jerky, poorly coordinated movement
• D. inability to see

Explanation: The cerebellum receives information from the muscles, joints and balance organs of the ear and smooths the commands sent by the cerebrum, so injury to it leaves movement clumsy and unsteady even though strength is normal. Alcohol depresses the cerebellum, which is why an intoxicated person staggers. Breathing is controlled by the medulla and vision is processed in the occipital lobe of the cerebrum.

135. Heart rate, breathing rate and the diameter of blood vessels are controlled by the

• A. cerebrum
• B. cerebellum
• C. corpus callosum
• D. medulla oblongata

Explanation: The medulla lies at the top of the spinal cord and contains the cardiac, respiratory and vasomotor centres, all of which work without conscious control, so an injury there is very quickly fatal. Because these centres monitor carbon dioxide and blood pressure and correct them, the medulla is a key homeostatic organ. The corpus callosum is only the bundle of fibres joining the two cerebral hemispheres.

136. The part of the brain that regulates body temperature, thirst and hunger, and controls the pituitary gland is the

• A. hypothalamus
• B. cerebellum
• C. medulla oblongata
• D. occipital lobe

Explanation: The hypothalamus is the meeting point of the nervous and endocrine systems: it monitors the temperature and water potential of the blood, generates thirst and hunger, and releases factors that control the anterior pituitary while making the hormones the posterior pituitary stores. Its small size is out of all proportion to its importance in homeostasis. The occipital lobe deals with vision alone.

137. Insulin lowers the concentration of glucose in the blood by

• A. converting glycogen in the liver into glucose
• B. increasing the uptake of glucose by cells and its storage as glycogen in the liver and muscle
• C. increasing the excretion of glucose in the urine
• D. stopping the digestion of carbohydrate in the gut

Explanation: Insulin from the beta cells of the islets of Langerhans makes cell membranes more permeable to glucose and stimulates the enzymes that build glycogen, so glucose leaves the blood. Glucagon from the alpha cells does the opposite, breaking glycogen down when blood glucose falls, and the two hormones form a negative feedback pair. Glucose in the urine is a symptom of untreated diabetes, not the way the hormone works.

138. A person whose diet lacks iodine may develop a goitre because

• A. iodine is needed to make insulin
• B. iodine destroys the thyroid gland directly
• C. the thyroid cannot make enough thyroxine and enlarges under continued stimulation by the pituitary
• D. excess iodine accumulates in the neck

Explanation: Thyroxine contains iodine, so a shortage means output falls, and the low blood level removes the negative feedback on the pituitary, which keeps releasing thyroid stimulating hormone until the gland swells visibly. This is why iodised salt is used to prevent goitre in areas where the soil is deficient. Insulin is made in the pancreas and contains no iodine at all.

139. Which of the following is NOT an effect of adrenaline?

• A. Increased heart rate
• B. Conversion of glycogen to glucose in the liver
• C. Dilation of the bronchioles
• D. Increased peristalsis and secretion in the gut

Explanation: Adrenaline prepares the body for fight or flight, so it diverts blood and resources to the heart, muscles and lungs and slows digestion rather than speeding it up. Raising heart rate, releasing glucose for respiration and widening the airways all fit that pattern, which is the quickest way to answer this kind of question. It is secreted by the adrenal medulla and acts within seconds.

140. Salivary amylase begins the digestion of

• 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. It works best near neutral pH and is destroyed once the food reaches the acid of the stomach, which is why chewing time matters. Humans secrete no cellulase at all, so cellulose passes through as roughage.