Control and Coordination

The governing concept is division of labour among brain regions. The cerebellum coordinates voluntary muscular movements, posture, and balance, so its disturbance can cause staggering while walking. Normal thinking and memory make major forebrain involvement less likely in this case. The thyroid and pancreas are endocrine organs and do not primarily coordinate immediate balance and locomotion. Hence option A is the best answer.

The medulla contains centres that help regulate vital involuntary activities, including breathing and heartbeat. These functions continue without conscious control and are essential for maintaining life. Therefore damage or disturbance to the medulla can seriously disrupt both and may be life-threatening, making option B correct. Drawing is a higher cerebral function, while the plant responses in options C and D are controlled by plant growth mechanisms, not the medulla.

Bright light is the stimulus, and light-sensitive receptors in the eye detect its increased intensity. Nervous signals then reach the muscles of the iris, which contract to make the pupil smaller and limit the amount of light entering the eye. This is a coordinated, largely involuntary response, so option A is correct. The other choices confuse reflex coordination with conscious will, hormone action, or blood-glucose regulation.

Nervous control is rapid and specific because electrical impulses travel along particular neurons and nerve pathways to connected target regions. This pathway-based arrangement limits direct reach to tissues connected with nerves. Hormones, in contrast, are released into the bloodstream and may reach target organs far from the secreting gland, although only cells with suitable receptors respond. Thus option A correctly identifies the limitation; the other statements reverse or exaggerate the properties of the two systems.

Seeing danger begins with the sense organs and nervous system, which rapidly analyse the stimulus and prepare an immediate response. The nervous system also stimulates the adrenal glands, causing adrenaline release. Adrenaline then supports the longer-lasting emergency response by increasing heart rate, breathing, and blood supply to muscles. Therefore option A shows both rapid nervous control and chemical hormonal control together. The other events do not involve this coordinated body response.

Adrenaline is an emergency hormone that prepares the body for rapid action. Its effects include increasing heart rate and breathing rate. Faster circulation delivers more blood and glucose to active muscles, while faster breathing improves oxygen intake; these support increased aerobic respiration and ATP production. Thus option A gives the relevant change. The other choices are unrelated to the emergency response and cannot explain increased energy supply to muscles.

Blood glucose is regulated partly by insulin, a hormone produced by the beta cells of the pancreatic islets. Insulin promotes uptake and storage of glucose, so inadequate insulin can leave too much glucose in the blood. Therefore the pancreas is the gland most directly related to the stated condition, making option B correct. The thyroid, adrenal, and pituitary glands produce important hormones, but none is the primary source of insulin.

The thyroid gland needs iodine to synthesise thyroxine. When iodine intake is insufficient, thyroxine production may fall, and reduced thyroid hormone feedback can stimulate the gland to work harder. This increased stimulation may enlarge the thyroid, producing a swelling called goitre. Thus option A correctly connects iodine deficiency, reduced thyroxine formation, and thyroid enlargement. The remaining choices incorrectly mix insulin, adrenaline, auxin, roots, and blood-glucose regulation.

Growth hormone, secreted by the pituitary gland, supports the growth of bones and other body tissues during childhood. If its secretion is too low during this period, normal linear growth may be reduced, leading to unusually short stature or dwarfism. Therefore option A is the likely consequence. Reflex speed is not directly determined by growth hormone, insulin is not made in the retina, and a root cannot transform into an ovule; those options are biologically unrelated.

The governing concept is negative feedback, a self-regulating mechanism of the endocrine system. When the blood concentration of a hormone becomes sufficiently high, it sends an inhibitory signal to the relevant gland or control centre, reducing further secretion and helping maintain internal balance. Thus option A is correct. A reflex arc is a rapid nervous pathway, whereas hydrotropism and chemotropism are directional growth responses in plants.

Hormones are carried widely by the blood, but a response occurs only where cells possess the appropriate receptors. These receptors have a specific chemical shape and can recognize a particular hormone, so the organ becomes its target organ. Therefore option A is correct. Blood does reach many organs, hormones do not normally turn into bone, and the brain does not block all hormonal action.

Plant organs can respond to more than one environmental stimulus. Growth towards water is called hydrotropism, while growth away from light is negative phototropism. These responses may occur together because the root is integrating directional information from water and light rather than responding to only one stimulus. Therefore option A is correct; the other choices incorrectly apply animal nervous functions or restrict the root to sound alone.

The governing concept is chemotropism, a directional growth response to a chemical stimulus. The ovule and surrounding tissues release chemical substances that guide the pollen tube toward the female reproductive structure. Phototropism, in contrast, is growth in response to light. Thus option A is correct. A spinal cord, adrenaline and blood sugar are animal regulatory concepts and do not explain pollen-tube guidance in a flower.

The governing concept is thigmotropism, a growth response to touch. When one side of a tendril contacts a support, growth is not equal on its two sides. Cells on the side away from contact generally elongate more, producing curvature that wraps the tendril around the support. Therefore option A is correct. The other choices wrongly attribute the movement to a heart, an animal hormone or a spinal cord.

Mimosa leaf folding is a rapid, non-growth movement caused mainly by changes in water content and turgor pressure in specialized cells. Tendril coiling is a slower growth movement in which touch produces unequal elongation on opposite sides. Thus option A correctly distinguishes the mechanisms. Neither response requires a brain, blood, insulin or a spinal cord because these are not plant nervous-control structures.

Phototropism is a growth movement because unequal cell elongation causes a plant part to bend toward or away from light, and the change is associated with lasting growth. Mimosa folding is a rapid non-growth movement caused by reversible water and turgor changes in cells. Therefore option A is correct. Both phenomena occur in plants, and neither is controlled only through blood.

Cytokinin is a plant hormone whose principal school-level function is to promote cell division, especially in regions where new cells are actively being formed. Increased cell production supports growth and development in meristems and other growing tissues. Therefore option A is correct. Blood-sugar control, heartbeat regulation and reflex arcs belong to animal physiology and are not functions of cytokinin in plants.

The governing concept is coordination in plants. Plants lack a brain, spinal cord, and animal-like nervous system, so they coordinate many responses through chemical messengers such as plant hormones. These chemicals alter cell division, elongation, growth direction, and sometimes movements. Hence option A is correct; the remaining options incorrectly apply animal nervous-system structures to plants.

The governing concept is tropism, in which plant organs show directional growth in response to stimuli. Shoots commonly show positive phototropism by growing toward light, while roots commonly show positive geotropism by growing in the direction of gravity. Thus option A correctly combines the two responses. The other choices use absolute or impossible claims and incorrectly mention a spinal cord.

The governing concept is the stimulus-response pathway. A stimulus is a detectable change, such as pain caused when a thorn pricks the skin. The nervous system processes the signal and activates muscles, producing withdrawal of the foot as the response. Therefore option A is correct. Option B reverses the sequence, while the other choices confuse organs or hormones with stimulus and response roles.