Control and Coordination

The governing concept is tropic movement, in which a plant part grows directionally in response to an external stimulus. Growth towards water is hydrotropism, while a growth response related to light is phototropism; roots commonly show negative phototropism by growing away from light. Therefore option A identifies the relevant stimulus-based growth responses. Thigmotropism and chemotropism are caused by touch and chemicals, so option B does not match the stated stimuli.

A growth-based plant movement results from unequal or directional growth and is generally irreversible. The stem bending towards light is phototropism, root growth towards water is hydrotropism, and pollen-tube growth towards the ovule is chemotropism. All three are plant tropisms, so option A is correct. Mimosa folding is a rapid nastic movement rather than growth; the other options describe animal or physiological processes.

Non-growth-based plant movements are usually rapid and reversible because they result from changes in the water content and turgor pressure of cells, not from the production of new cells. In Mimosa, a stimulus causes water to move out of particular motor cells, making the leaf fold. Thus option A is correct. Options B and C describe growth, while option D is chemotropism, a directional growth response.

Adrenaline is a hormone released during danger, fear, or intense stress. It prepares the body for rapid action by increasing cardiac output and commonly increasing the rate and depth of breathing, so more oxygen and nutrients can reach active muscles. Hence option A is correct. Root gravitropism is a plant response, insulin is produced by pancreatic beta cells rather than the retina, and a Mimosa leaf cannot become a seed.

The nervous and endocrine systems coordinate body functions in complementary ways. The nervous system transmits rapid electrical signals for immediate, targeted responses, such as withdrawing from danger. Endocrine glands release hormones into the blood; these act more slowly but may influence several organs and last longer. Thus option A correctly describes their combined importance. The remaining choices assign unrelated or impossible functions to both systems.

Plants lack an animal-like brain and nervous system, but they are not passive. They detect environmental stimuli and coordinate responses through chemical signals, changes in growth, and rapid changes in cell water content. Phototropism, hydrotropism, gravitropism, thigmotropism, and chemotropism illustrate this ability. Therefore option A is correct; the other options deny plant sensitivity or incorrectly impose animal structures and blood-based control on plants.

The central idea of Control and Coordination is that organisms detect internal or external stimuli and organise suitable responses. Animals mainly use receptors, the nervous system, and hormones, whereas plants rely largely on chemical messengers and changes in growth or cell turgor. Thus option A includes the major mechanisms and applies to living organisms broadly. The other choices restrict coordination to nutrition, bones, or only one group of organisms, so they are incorrect.

Neurons have functional polarity. Dendrites generally receive stimuli or signals, the cell body integrates them, and the axon carries the resulting nerve impulse away towards another neuron or an effector. This organised direction prevents random transmission and helps a response reach the correct destination. Therefore A is correct. The other choices describe unrelated processes and do not explain the role of dendrites and axons in signalling.

Touching a hot object activates pain receptors in the skin. The sensory impulse reaches the spinal cord, which quickly sends a motor command to withdraw the hand; this is a reflex action that reduces injury. At the same time, the impulse also travels to the brain, where pain is consciously perceived, often slightly later. Therefore A is correct, while B, C and D contradict the reflex pathway.

Tropisms are directional growth responses to external stimuli. Phototropism is a response to light, thigmotropism to touch, and chemotropism to chemicals. When a root bends or grows toward a source of water, the defining stimulus is moisture or water, so the response is hydrotropism. Gravity may also influence roots through geotropism, but the situation specifically highlights growth toward water. Hence B is correct.

Nervous coordination uses electrical impulses and synaptic signals, so it can act very quickly and precisely on particular effectors. Endocrine coordination releases hormones into the blood; these may act more slowly, reach target tissues, and produce effects that last longer. Working together allows the body to respond rapidly while also maintaining longer-term regulation such as growth, metabolism and reproduction. Therefore A is correct; B, C and D are false.

The governing concept is hormonal coordination during the emergency or “fight-or-flight” response. When fear occurs, adrenaline increases heart activity and redirects more blood toward skeletal muscles. This supplies additional oxygen and glucose for rapid contraction and action. Therefore option A is correct. The other options describe photosynthesis, an impossible blood-sugar effect, or vision, none of which explains adrenaline’s muscular response.

The governing concept is thyroid hormone production and feedback regulation. Iodine is a necessary raw material for making thyroxine in the thyroid gland. When iodine is deficient, thyroxine production falls; the body may stimulate the thyroid more strongly, causing enlargement of the gland, known as goitre. Therefore option A is correct. The other choices incorrectly connect iodine with insulin transport, reflex arcs, or neuron structure.

The governing concept is control of involuntary, vital activities by the brainstem. The medulla helps regulate breathing, heartbeat, and other automatic functions that must continue without conscious effort. Serious damage can therefore threaten life, unlike many ordinary muscle injuries that mainly impair local movement. Option A is correct. The other options incorrectly attribute skin-colour production, plant-hormone production, or only taste detection to the medulla.

The governing concept is phototropism, in which unequal auxin distribution causes unequal cell elongation on the two sides of a stem. The side with greater elongation becomes longer and the stem bends toward the side with less growth. If auxin remains equally distributed, elongation on both sides is nearly equal, so the growth difference and resulting bending decrease. Therefore option A is correct; the other options describe biologically impossible changes unrelated to auxin-controlled growth.

The governing concept is thigmotropism, a directional growth response to touch. When a tendril contacts a support, growth on its two sides becomes unequal. The side away from the support generally elongates more, while the contacted side grows less, causing the tendril to curve and coil around the support. Thus option A correctly explains the evidence. A spinal cord, blood pumping, and thyroxine production are animal functions and cannot account for this plant movement.

The governing concept is classification of receptors according to the kind of stimulus they detect. Olfactory receptors in the nose respond to chemicals present in air, while taste receptors in the tongue respond to dissolved chemicals in food and saliva. Because both systems detect chemical stimuli rather than light, pressure, or gravity, they are called chemoreceptors. Therefore option A is correct; the remaining choices describe unrelated or impossible functions.

The governing concept is coordination of balance by the vestibular apparatus of the inner ear. The semicircular canals and related structures detect head movement and changes in body orientation, then send signals to the brain. The brain combines these signals with information from the eyes and muscles to maintain posture and equilibrium. If inner-ear signals are faulty, balance can be disturbed despite normal vision. Therefore option A is correct; the other options are unrelated endocrine or plant functions.

The governing concept is nervous coordination followed by glandular response. Seeing attractive food provides a visual stimulus detected by the eyes. Nerve impulses travel to the brain, where the information is processed; the brain then activates autonomic pathways to the salivary glands, causing secretion of saliva. Thus option A correctly identifies coordination among a sense organ, the brain, and an effector gland. The other options combine unrelated plant and animal structures or invent nonexistent connections.

The governing concept is the receptor–coordinator–effector pathway. A receptor detects the stimulus, the nervous system processes the information and transmits a command, and the effector produces the final response. If the muscle receives the signal but cannot contract, detection and transmission may have occurred, while the response-producing effector link has failed. Therefore option A is correct. The other options refer to earlier stages or to hormonal secretion, which is not required for every muscle response.

The governing concept is coordinated directional growth, or tropic response. Roots commonly show positive hydrotropism and grow towards water, while stems commonly show positive phototropism and grow towards light. These opposite responses in different organs demonstrate that plant parts detect and respond to different environmental stimuli according to their functions and needs. Therefore option A is correct. Options B, C, and D wrongly deny coordination or reverse the usual tropic responses.

The governing concept is hormonal coordination during the emergency or stress response. Anticipation of a race can produce excitement or stress, causing the adrenal glands to release adrenaline. This hormone increases heart rate and helps direct the body toward rapid muscular activity. Phototropism concerns plant growth, insulin regulates blood glucose rather than taste, and roots do not grow through spinal control. Thus, option A is correct.

The governing concept is endocrine regulation of metabolism. Thyroxine, secreted by the thyroid gland, helps regulate the rate at which cells use nutrients and release energy. If its level is deficient, metabolic activity and several normal body functions may become slower or disturbed, subject to the cause and severity of deficiency. A synapse, retina, and tendril have different roles, so they do not explain this effect. Option A is correct.

The governing concept is the stimulus-response pathway. A receptor detects the stimulus, the control centre receives and interprets the information, and the effector carries out the instructed action. These parts form a linked chain, so failure of any one part can interrupt or distort the response even if the other parts work normally. The other options wrongly deny the role of one component. Therefore, option A is correct.

The governing concept is the difference between plant and animal coordination. Plants lack a nervous system and usually respond through chemical messengers, changes in cell growth, and movements such as tropisms; these responses are often relatively slow. Animals possess nervous tissue that can transmit rapid electrical signals, although they also use hormones. Plants do not have a human-like brain, and they are not always faster. Hence, option A is correct.