Control and Coordination

The governing concept is the source and function of endocrine hormones. Insulin is produced by the beta cells of the islets of Langerhans in the pancreas and helps regulate blood glucose. Therefore, option A is correct. The thyroid secretes thyroxine, the pituitary releases several controlling hormones, and the adrenal gland secretes hormones such as adrenaline; these are different from insulin.

The governing concept is the emergency or fight-or-flight response. In sudden danger, adrenaline released by the adrenal glands increases heart rate, breathing readiness, and the supply of glucose and blood to active muscles. Thus, option A is correct. Insulin regulates blood glucose, thyroxine mainly influences metabolism, and auxin is a plant hormone, so they do not provide the characteristic rapid emergency response in humans.

The governing concept is the relationship between an endocrine gland and its hormone. Adrenaline is secreted by the adrenal glands, which are located above the kidneys and help coordinate the body’s rapid response to stress or danger. Therefore, option A is correct. The pancreas produces insulin, the thyroid produces thyroxine, and the ovaries produce reproductive hormones, so these alternatives are not the source of adrenaline.

The governing concept is the mineral requirement for thyroid-hormone synthesis. Iodine is incorporated into thyroxine, which is produced by the thyroid gland and helps regulate metabolism. Therefore, option A is correct. If dietary iodine is insufficient, thyroxine production may be disturbed and the thyroid can enlarge, producing goitre. Iron, calcium, and sodium are important nutrients or ions but are not the specific element asked for.

The governing concept is the source of thyroxine in the endocrine system. Thyroxine is produced and secreted by the thyroid gland in the neck, and it helps regulate the body’s metabolic activities, growth, and development. Hence option A is correct. The pituitary controls several other glands, the pancreas secretes insulin, and the testes produce male reproductive hormones; none of these is the main source of thyroxine.

The governing concept is the link between iodine nutrition and thyroid function. Iodine is required to synthesise thyroxine; when iodine intake is too low, the thyroid may be unable to make enough hormone and can enlarge, causing goitre. Therefore, option A is correct. Diabetes is mainly associated with problems involving insulin, scurvy with vitamin C deficiency, and rickets with vitamin D or mineral deficiency.

The governing concept is endocrine control of growth. Growth hormone, also called somatotropin, is released by the pituitary gland and supports the growth of bones and other body tissues, especially during childhood and adolescence. Therefore option A is correct. Insulin regulates blood glucose, adrenaline prepares the body for emergencies, and auxin is a plant hormone, so these distractors do not control overall human body growth.

The governing concept is the function of endocrine glands. Growth hormone is produced and secreted by the anterior part of the pituitary gland, which influences several other endocrine glands and is therefore often called the master gland. Hence option A is correct. The thyroid mainly secretes thyroxine, the adrenal glands secrete hormones such as adrenaline, and the pancreas secretes insulin and glucagon.

The governing concept is hormonal regulation of puberty. During adolescence, the testes produce increasing amounts of testosterone. This hormone contributes to secondary sexual characteristics in boys, including a deeper voice, facial and body hair, increased muscle development, and maturation of the reproductive system. Thus option A is correct. Estrogen is principally associated with female reproductive development, while insulin and thyroxine have different metabolic roles.

The governing concept is endocrine control of puberty. Estrogen is mainly secreted by the ovaries and helps produce female secondary sexual characteristics during adolescence, such as breast development and changes in body shape. Therefore option A is correct. Testosterone is more strongly associated with male secondary sexual characteristics, adrenaline supports emergency responses, and auxin regulates growth responses in plants rather than humans.

The governing concept is receptor-specific action. Hormones are transported through the bloodstream and may reach many tissues, but they produce a response only where cells contain the matching receptor. The hormone binds to that receptor and initiates a specific cellular change, so option A is correct. Hormones do not destroy all cells, are not restricted to bones, and generally do enter and circulate in the blood; therefore options B, C, and D are incorrect.

The governing concept is the comparison between nervous and hormonal coordination. Nervous control sends electrical impulses along neurons and uses rapid neurotransmitter action at synapses, so it usually produces a response much faster than endocrine control. Hormones must be released into the blood, transported, and detected by target cells. Hence option A is correct. Hormonal responses are often slower but may last longer; the words “always equal” make option C incorrect.

The governing concept is the characteristic time course of endocrine coordination. Hormones are released by endocrine glands into the bloodstream, travel to target cells, and alter cellular activity through specific receptors. This transport and action usually make the response slower to begin than a nerve impulse, while the effect can persist after the initial stimulus. Therefore option A is correct; the other choices incorrectly describe hormonal action as momentary, instantly ending, or ineffective.

The governing concept is sensory coordination by the ear. The outer and middle ear transmit sound vibrations, and the inner ear contains the cochlea for hearing. It also contains the semicircular canals and vestibular apparatus, which detect head movement and help maintain balance. Thus option A is correct. Taste and smell are mainly detected by receptors in the tongue and nasal cavity, while blood sugar is monitored by physiological systems rather than the ear.

The governing concept is reception of chemical stimuli. Taste receptors are sensory cells located mainly in taste buds on the tongue. Dissolved food chemicals stimulate these receptors, which generate nerve signals that travel to the brain for identification of taste. Therefore option A is correct. The eye contains photoreceptors for light, the lungs contain receptors related to breathing, and bones do not serve as the main location of taste receptors.

The governing concept is the role of skin sensory receptors in detecting environmental stimuli. Different receptors in the skin respond to contact or touch, temperature changes, pressure, and sometimes pain. Their signals travel through sensory neurons to the central nervous system, where the information is interpreted. Hence option A is correct. Light is detected mainly by the retina, sound by the inner ear, and taste by receptors in taste buds.

The governing concept is protection of delicate organs by the skeletal system. The brain is soft and highly sensitive, so it is enclosed in the hard skull, which forms the cranium and absorbs or deflects many external impacts. Therefore, option A is correct. Ribs protect the heart and lungs, the backbone encloses the spinal cord, and the jaw supports the mouth rather than the brain.

The relevant concept is skeletal protection of the nervous system. The spinal cord is a delicate bundle of nerve tissue carrying messages between the brain and the body. It runs through the vertebral canal formed by the vertebrae of the backbone, so option A is correct. The skull encloses the brain, ribs protect chest organs, and the shoulder bone does not surround the cord.

The nervous system provides rapid control and communication in the body. Neurons receive information and transmit electrical impulses along nerve fibres; chemical signals then pass across synapses. This allows quick responses such as withdrawing a hand from a hot object. Therefore option A, the nervous system, is correct. The digestive and respiratory systems perform processing and gas exchange, while the skeletal system mainly provides support and protection, so none of those is the primary rapid messaging system.

The basic structural and functional unit of the nervous system is called a neuron. It is a specialised cell that receives, processes and transmits nerve impulses through its dendrites, cell body and axon. Therefore, option A is correct. A blood cell transports substances, a muscle cell produces contraction, and a skin cell forms protective covering; none of these is the specific name for a nerve cell.