Nervous system

Fast control requires signals to travel rapidly between a stimulus, the central nervous system, and an effector. The nervous system performs this function through electrical impulses carried by neurons, allowing quick responses such as withdrawing a hand. Thus option B is correct. The digestive, respiratory, and excretory systems perform important physiological functions, but they are not the main system for rapid coordination of responses.

Plants lack the nervous system and specialised neurons found in animals, but they still coordinate growth and responses. They do this through chemical messengers called plant hormones or phytohormones, including auxin, gibberellin, cytokinin, ethylene, and abscisic acid. Neurons, bones, and blood cells are animal structures, not the plant mechanism. Thus, option A is correct.

The nervous system is the main rapid control and coordination system in humans. Receptors detect changes, sensory neurons carry impulses to the central nervous system, and motor neurons transmit commands to muscles or glands. The digestive, excretory, and respiratory systems perform important life processes, but they are not the primary system for rapid coordination. Therefore, option A is correct.

The spinal cord is usually the main integration centre for a reflex action because it provides a short pathway that produces a rapid protective response. Sensory information enters the spinal cord, is processed through an interneuron, and a motor impulse travels to the effector. Therefore option B is correct. The brain can receive information and may later interpret it, but the heart, liver and lung are not the usual control centres of a reflex arc.

The central nervous system, or CNS, consists of the brain and spinal cord. It receives and processes information, coordinates responses and communicates with the rest of the body through peripheral nerves. Therefore option A is correct. The peripheral nervous system includes nerves outside the brain and spinal cord, while the endocrine and digestive systems use hormones or digestive organs and are not formed by these two structures.

Quick responses require signals to travel rapidly from a receptor to an effector. Nervous control uses electrical impulses along neurons and chemical transmission at synapses, so it acts much faster than endocrine control. Therefore option A is correct. Hormones travel through the blood and usually act more slowly, while digestion and respiration are physiological processes, not independent control systems for every rapid response.

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 governing concept is stimulus detection by specialised sensory receptors. A thorn prick directly stimulates receptors in the skin, including receptors associated with touch and pain. These receptors generate nerve impulses that travel through sensory nerves toward the central nervous system. Therefore option A is correct. Bright light activates photoreceptors in the eye, sweet taste activates taste receptors in the tongue, and a bell activates auditory receptors in the ear.

The governing concept is the organisation of the nervous system. The central nervous system consists of the brain and spinal cord, while the peripheral nervous system includes nerves outside them. These nerves connect the central system with sensory receptors, muscles, glands, and other body parts, carrying signals in both directions. Therefore option A is correct. Hormone production, blood filtration, and digestion are functions of other organs or systems.

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.