Nervous system

The governing concept is the difference between neural and hormonal coordination. A nerve impulse travels rapidly along a specific neuron and reaches a particular target through connected nerve pathways. Hormones are chemical messengers released into the bloodstream, so their transport and action generally take longer and may be more widespread. Hence option A correctly explains the usual speed advantage; the other statements are false or irrelevant.

The governing concept is involuntary control by the hindbrain. The medulla oblongata contains centres that regulate vital automatic activities such as breathing, heartbeat and blood-vessel actions. These processes continue without conscious decision and are essential for survival, which explains the term life-supporting functions. Memory, taste perception and formation of a hand bone are not the principal roles of the medulla.

A receptor is a specialised cell or organ that detects a stimulus such as heat, light, pressure, or a chemical change. The information is transmitted through a control pathway to an effector, such as a muscle or gland, which carries out the response. Therefore option A correctly states their relationship. The other choices assign unrelated functions and do not describe a receptor-effector pathway.

The governing concept is division of function among brain regions. The cerebellum coordinates signals from muscles, joints, and the inner ear so that posture, balance, and precise voluntary movements remain controlled while cycling. Hence option B is correct. The cerebrum supports thinking and conscious decisions, the medulla regulates important involuntary actions, and the spinal cord mainly conducts impulses and participates in reflex pathways rather than being the chief balance centre.

The governing concept is the contrast between rapid nervous control and slower, longer-lasting hormonal control. A thorn prick requires an immediate, localized response, and a nerve impulse can quickly activate the muscles that withdraw the foot. Therefore option A is correct. Growth, blood-glucose regulation, and adolescent changes develop or adjust over longer periods and are mainly associated with endocrine hormones rather than an instant nerve response.

Nervous control uses electrical impulses along neurons and chemical transmission at synapses, so its response is generally rapid and localised. Hormonal control uses endocrine glands that release hormones into the blood; these reach target tissues more slowly, and their effects often last longer. Thus option A gives the correct broad comparison. The words “always” in option B make it false, and C and D incorrectly restrict both systems.

The cerebellum is a major part of the hindbrain that coordinates voluntary muscular activity, posture, and balance. Damage can therefore cause unsteady movement, difficulty walking, and poor coordination, making body balance the best answer. Blood sugar is mainly regulated hormonally by the pancreas, thyroxine is produced by the thyroid gland, and smell begins with receptors in the nose and is processed through olfactory pathways.

The spinal cord is a major component of the central nervous system. It carries sensory information from the body to the brain and motor instructions from the brain to different body parts, and it also coordinates many reflexes. Because damage could interrupt these vital pathways, the vertebral column provides strong physical protection. Thus, option A is correct.

The governing concept is directional transmission in a neuron. Dendrites generally receive a stimulus, the cell body processes it, and the axon carries the nerve impulse towards its axon terminal. This fixed direction prevents confused or backward signalling and ensures that the appropriate next neuron, muscle or gland receives the message in sequence. Therefore option A is correct; the other options describe digestion, blood-glucose regulation or plant growth, none of which explains neuronal coordination.

The governing concept is coordination through two complementary communication systems. Nervous control uses electrical impulses along specific neurons, so it is rapid, precise and usually short-lived. Hormones are released by endocrine glands and carried in the blood, so their action may reach several target organs and last longer. Together they coordinate immediate reactions as well as sustained processes. Hence option A is correct; the remaining options contradict the functions and distribution of both systems.

Seeing appetising food provides a visual stimulus. Receptors in the eye send nerve impulses to the brain, where the information is processed. The brain then sends signals that stimulate the salivary glands to secrete saliva, preparing the mouth for digestion. This pathway shows coordination among a sense organ, the nervous system, and an effector gland; the other options are incorrect.

A response pathway includes a receptor, coordinating centre, nerve pathway, and effector. A muscle is an effector because it carries out the response by contracting after receiving a suitable nerve signal. If the signal arrives but contraction does not occur, the final action cannot be completed. Therefore the effector is essential; a receptor only detects the stimulus and a synapse only transfers signals.

A receptor detects a stimulus, but it does not decide what the body should do. The brain or spinal cord acts as the control centre: it receives and interprets the nerve message, selects an appropriate response, and sends instructions through motor neurons to an effector such as a muscle or gland. Therefore, option A is correct. The other options describe functions unrelated to nervous coordination.

The governing concept is synaptic transmission. When an electrical impulse reaches the end of one neuron, chemicals called neurotransmitters cross the synaptic gap and stimulate the next neuron. If a drug blocks their release or action, the signal cannot pass normally, so the response may be delayed, weakened, or stopped. Therefore option A is correct. Options B, C, and D do not describe the specific effect of blocking a synapse.

In a reflex pathway, a receptor detects the stimulus, a control centre processes the impulse, and an effector produces the response. Skin contains receptors that detect heat or touch; the spinal cord coordinates the rapid reflex; and a muscle contracts to move the hand. Therefore option A gives the correct order. The other combinations confuse receptors, effectors, glands, hormones, or plant structures and do not form a valid reflex pathway.

The nervous system coordinates responses through a sequence: receptors first detect a stimulus, sensory neurons carry information to the central nervous system, and motor pathways activate an effector. The effector then produces the response. Thus option A gives the correct order. The remaining choices list functions of plants, kidneys, bones, or imaginary processes rather than the three main nervous-system roles.

Bright light acts as a stimulus detected by the eye. Circular muscles in the iris contract automatically, reducing the pupil’s diameter and limiting the amount of light entering the eye. Because this adjustment occurs without conscious choice and is coordinated through the nervous system, option A is correct. It is not voluntary hormonal control, plant hydrotropism, or insulin production in muscle.

The governing concept is nervous coordination of posture, movement, and balance. The cerebellum receives information about body position and helps coordinate the timing and strength of skeletal-muscle contractions. Damage can therefore produce unsteady walking and poor balance. Option A correctly states this relationship. The other choices wrongly assign the cerebellum roles in blood sugar production, thyroxine secretion, or transport of water in plants.

The governing concept is sensory transduction in vision. Light entering the eye is focused on the retina, where photoreceptors such as rods and cones absorb light and initiate electrical nerve signals. These signals are carried through retinal neurons and the optic nerve to the brain for interpretation. If photoreceptors fail, the first conversion step is disrupted, so later visual processing cannot receive accurate information. Thus option A is correct; the other choices concern unrelated body functions.

The cerebrum is the major part involved in conscious activities such as thinking, learning, memory, interpretation of sensations, and voluntary actions. The cerebellum does not perform these higher mental tasks; it coordinates muscular activity and helps maintain posture and balance. Therefore option A correctly separates their roles. Insulin and auxin are hormones, while digestion and plant roots are unrelated to these brain regions.

The governing concept is that the cerebellum coordinates muscular activity, posture, precision and body balance. Walking on a rope requires continuous adjustment of many muscles so that the body does not fall, making option A the clearest example. Lowering blood sugar is mainly associated with insulin, root growth towards water is hydrotropism, and thyroxine formation is an endocrine function of the thyroid gland.

The central nervous system, consisting mainly of the brain and spinal cord, receives, processes, and coordinates information. The peripheral nervous system consists of nerves outside the brain and spinal cord; these nerves carry sensory messages toward the central system and motor commands away from it to muscles or glands. Therefore, option A correctly states the two-way functional relationship. The other options wrongly assign digestion, hormone production, plant functions, or blood filtration to these systems.