All Free Biology MCQs with Answers

541. Which of the following acts as an inhibitory neurotransmitter in the brain?

• A. Acetylcholine
• B. Noradrenaline
• C. Dopamine
• D. GABA

Explanation: GABA, gamma aminobutyric acid, hyperpolarises the postsynaptic membrane and calms neural activity, and many sedatives enhance its action. Acetylcholine and noradrenaline are generally excitatory at the synapses where they are best known.

542. A dog that has learned to salivate at the sound of a bell whenever food is presented shows a

• A. conditioned reflex
• B. unconditioned reflex
• C. voluntary action
• D. hormonal response

Explanation: Pavlov paired the neutral bell with food until the bell alone triggered salivation, building a reflex through experience in the cerebral cortex. Salivating to food itself is inborn and unconditioned, which is the contrast the experiment relies on.

543. Blinking of the eyes when dust touches the cornea is an example of a

• A. spinal reflex
• B. cranial reflex
• C. conditioned reflex
• D. hormonal reflex

Explanation: The reflex arc passes through the brain stem rather than the spinal cord, so it is classed as a cranial reflex. Spinal reflexes, such as knee jerk, are integrated in the spinal cord itself.

544. In a reflex arc, the motor neuron ends by stimulating an

• A. interneuron
• B. sensory receptor
• C. effector such as a muscle or gland
• D. association area

Explanation: The effector, a muscle or gland, carries out the response, completing the receptor to effector pathway. Receptors start the arc and interneurons link the two, so only the effector belongs at the motor end.

545. In a spinal reflex arc, the cell bodies of the interneurons that link sensory and motor neurons lie in the

• A. dorsal root ganglion
• B. white matter of the spinal cord
• C. cerebral cortex
• D. grey matter of the spinal cord

Explanation: Interneurons sit in the grey matter of the cord, where they synapse with the incoming sensory fibre and the outgoing motor neuron. The dorsal root ganglion holds only the cell bodies of sensory neurons, a frequent mix up.

546. The sudden constriction of the pupil when bright light falls on the eye is an example of

• A. a reflex action
• B. a conditioned response
• C. a voluntary movement
• D. a hormonal effect

Explanation: The pupil reflex is automatic, rapid and involuntary, integrated in the brain stem, meeting every criterion of a reflex. It happens even in sleep, which shows that no conscious control or learning is involved.

547. The part of the brain that acts as a relay bridge between regions and helps regulate the rhythm of breathing is the

• A. cerebellum
• B. pons
• C. thalamus
• D. hypothalamus

Explanation: The pons, whose name means bridge, connects the cerebrum and cerebellum with the medulla and contains centres that smooth the breathing rhythm. The thalamus relays sensory impulses, a different kind of bridging role.

548. The centres for visual and auditory reflexes, such as turning the head towards a sudden sound, are located in the

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

Explanation: The midbrain receives input from the eyes and ears and coordinates these quick orienting reflexes. Conscious seeing and hearing happen higher up in the cerebrum, while the medulla governs heart rate and breathing.

549. Reasoning, judgement, planning and personality are associated mainly with the

• A. occipital lobe
• B. temporal lobe
• C. parietal lobe
• D. frontal lobe

Explanation: The frontal lobes, especially the prefrontal cortex, handle higher mental functions, and damage there famously alters personality. The occipital lobe processes vision and the temporal lobe hearing and memory, so function maps onto lobe.

550. The three membranes that cover and protect the brain and spinal cord are collectively called the

• A. meninges
• B. ventricles
• C. choroid plexuses
• D. myelin layers

Explanation: The dura, arachnoid and pia mater cushion the CNS and enclose the cerebrospinal fluid, and their infection causes meningitis. Ventricles are the fluid filled cavities inside the brain, not its coverings.