Control and Coordination

A neuron has a directional structure for transmitting information. Dendrites are the branched extensions that receive signals from receptors or from the axon endings of neighbouring neurons and carry them toward the cell body. Hence option A, dendrite, is correct. The axon generally carries impulses away from the cell body, a nerve ending passes the signal onward, and a muscle is a separate type of tissue.

The axon is the usually long projection of a neuron that conducts nerve impulses away from the cell body toward another neuron, a muscle or a gland. Thus option B is correct. Dendrites normally receive incoming signals and conduct them toward the cell body. The nucleus controls cell activities, while the cell membrane encloses the cell and regulates exchange; neither is the specialised conducting projection asked about here.

The small specialised junction or gap between two communicating neurons is called a synapse. When an impulse reaches the end of one neuron, chemicals called neurotransmitters are released and cross the synaptic gap to influence the next neuron. Therefore, option B is correct. A gland secretes substances, a bone provides support, and a blood vessel transports blood; none of these describes the connection between neurons.

The forebrain is the major region associated with higher mental functions such as thinking, learning, reasoning, memory and conscious interpretation of sensory information. In particular, the cerebrum forms its large and important part. Thus option A is correct. The midbrain participates in certain visual and auditory responses, the hindbrain helps regulate balance and involuntary activities, and the spinal cord conducts impulses and mediates many reflexes.

The cerebellum helps maintain posture, balance and coordination of voluntary movements. It receives information about body position and adjusts the activity of muscles so that walking, standing and other movements remain smooth and controlled. Therefore option B is correct. The cerebrum supports conscious thought and voluntary decisions, the medulla controls several involuntary functions, and the spinal cord conducts impulses and participates in reflex actions.

The governing concept is nervous coordination of involuntary activities. The medulla, a part of the hindbrain, helps regulate vital automatic functions such as breathing, heartbeat, and blood pressure. Therefore, option A is correct. An axon and a dendrite are parts of a neuron that transmit signals, while the thyroid is an endocrine gland and does not directly control these rapid involuntary actions.

A voluntary action is performed consciously and can be started, stopped, or modified according to a person’s will. Walking normally involves conscious control of skeletal muscles, so option A is the correct example. Heartbeat and digestion continue automatically, and pupil contraction is a protective involuntary response to light. These distractors are controlled without deliberate choice.

The governing concept is the distinction between conscious and automatic actions. An involuntary action occurs without deliberate control, and the heartbeat continues rhythmically even when we are asleep or not thinking about it. Hence, option C is correct. Writing, running, and jumping generally require conscious decisions and coordinated movement of skeletal muscles, so they are voluntary actions.

Sensory receptors are specialised structures that detect particular stimuli. The retina is the light-sensitive layer at the back of the eye; its photoreceptors respond to light and begin the process of vision. Therefore, option A is correct. The eardrum detects vibrations related to sound, taste receptors are located in the tongue, and skin receptors detect touch, pressure, temperature, or pain.

The governing concept is reception of environmental stimuli by sense organs. Skin contains receptors that detect touch and may also detect pressure, temperature, and pain; therefore, option A is correct. Light receptors are associated with the retina, taste receptors are concentrated in taste buds of the tongue, and sound detection involves structures of the ear. Thus the alternatives belong to different sensory systems.

Hormones are chemical messengers produced by endocrine glands and released into the blood. They travel to particular target organs or tissues and regulate processes such as growth, metabolism, reproduction, and stress responses, often more slowly than nerve impulses. Therefore, option A is correct. They are not energy sources, digestive juices, or waste products, although they influence many body functions.

Thyroxine is a hormone produced by the thyroid gland, and iodine is an essential raw material for its synthesis. This hormone helps regulate metabolism, growth, and development, so option A is correct. The pancreas produces hormones such as insulin, while the testes and ovaries produce reproductive hormones. Those glands do not make thyroxine, making them unsuitable alternatives.

Iodine is needed by the thyroid gland to synthesise thyroxine. When iodine intake is insufficient, thyroxine production may fall and the thyroid can enlarge in an effort to capture more iodine; this swelling is called goitre. Therefore, option A is correct. Diabetes is associated with impaired insulin regulation, night blindness commonly with vitamin A deficiency, and asthma with airway inflammation.

Blood glucose is regulated mainly through hormones produced by the pancreas. Insulin lowers blood glucose by helping body cells take up glucose and by promoting its storage as glycogen, so option A is correct. Adrenaline generally raises glucose during stress, while thyroxine regulates metabolism and growth hormone supports growth; neither is the primary hormone tested here for blood-sugar control.

The governing concept is endocrine control of blood glucose. Insulin is a hormone produced by the beta cells of the islets of Langerhans in the pancreas. After a rise in blood glucose, insulin helps body cells take up glucose and promotes its storage, thereby lowering blood sugar. Therefore, option A is correct. The thyroid produces thyroxine, the pituitary releases several regulatory hormones, and the adrenal gland secretes hormones such as adrenaline.

The governing concept is the emergency or fight-or-flight response. During fear or danger, the adrenal glands release adrenaline into the blood. It increases heart rate and breathing rate, directs more blood toward skeletal muscles, and makes stored energy rapidly available. Thus option A is correct. Insulin mainly regulates blood glucose, thyroxine influences metabolism and development, and estrogen is chiefly involved in female reproductive development and functions.

The governing concept is hormone secretion by endocrine glands. Adrenaline is produced mainly by the adrenal medulla, the inner region of the adrenal glands situated above the kidneys. It is released during stress, fear, or danger and prepares the body for rapid action. Therefore, option A is correct. The pancreas secretes insulin, the thyroid secretes thyroxine, and the salivary glands release saliva rather than adrenaline.

The governing concept is coordination through endocrine glands. Growth hormone is secreted by the anterior lobe of the pituitary gland. It stimulates the growth of bones and body tissues and supports protein synthesis, particularly during the growing years. Hence option A is correct. The pancreas produces insulin, the adrenal gland produces adrenaline and other hormones, while the thyroid produces thyroxine, which regulates metabolism and contributes to normal development.

The governing concept is tropic movement, in which a plant grows directionally in response to an external stimulus. When the stimulus is light and growth occurs toward it, the response is called positive phototropism. For example, a young shoot bends toward a light source as auxin distribution promotes greater growth on the shaded side. Therefore, option A is correct; geotropism responds to gravity, hydrotropism to water, and chemotropism to chemicals.

The governing concept is geotropism, also called gravitropism. Roots usually grow downward, in the direction of the gravitational pull, so they show positive geotropism or positive gravitropism. This direction helps roots anchor the plant and reach soil resources. Therefore, option B is correct. Growth against gravity is negative geotropism and is more typical of shoots; roots generally do not grow toward light or upward.