Control and Coordination

Tendrils show thigmotropism, a directional response to touch. Contact with a support changes growth patterns on the two sides of the tendril; the side away from the contact may elongate more, producing unequal growth and coiling around the support. The response is therefore a physical growth change, not a conscious sensation. Tendrils have no brain, and blood or hearing is irrelevant, so option A is correct.

Receptors are specialised structures that detect particular stimuli. Receptors in the nose respond to molecules present in air and produce the sensation of smell, while taste receptors in the tongue respond to dissolved chemicals in food. Since their stimulus is chemical rather than light, sound, or gravity, they are called chemical receptors. Thus option A is correct.

The vestibular parts of the inner ear detect head movement and help the brain judge body position and balance. Their information is compared with signals from the eyes and muscles. If the inner-ear signals become abnormal or inconsistent, the brain may interpret the body as moving when it is not, producing dizziness or loss of balance. The remaining options are biologically unrelated.

The shoot commonly shows positive phototropism by growing towards light, which improves light capture for photosynthesis. The root commonly shows positive gravitropism by growing downward, helping it anchor the plant and absorb water and minerals. These opposite directional responses demonstrate coordination in plants and show that different organs respond to different stimuli according to their functions. Hence A is correct.

Before a race, excitement and anticipation activate the sympathetic stress response. The adrenal glands release adrenaline, which increases heart rate and breathing and directs more blood toward skeletal muscles. These changes prepare the body for rapid action. Insulin regulates blood glucose, while auxin and cytokinin are plant hormones, so they do not explain the runner’s immediate heartbeat increase. Therefore B is correct.

Thyroxine is a hormone secreted by the thyroid gland. It helps regulate the body’s metabolic rate and supports normal growth and development. If its level is too low, cellular energy use and several body processes may slow or become abnormal; prolonged deficiency can also affect development. A photoreceptor, synapse, and tendril are structures, not the function of thyroxine. Hence A is correct.

Plants do not possess a nervous system with a brain, spinal cord, and specialised nerves. Their coordination commonly depends on chemical messengers such as plant hormones, which alter growth or other physiological activities and may act relatively slowly. Animals use electrical impulses in neurons, often producing rapid responses, with hormones also supporting longer-term control. Thus option A gives the valid comparison.

Running demands immediate energy and oxygen from skeletal muscles. The sympathetic response and adrenaline increase heart activity and redirect a greater share of blood toward working muscles, while digestive activity is temporarily reduced. This prepares the body for rapid action, often called the fight-or-flight response. Therefore option A is correct; sleep, hydrotropism, and thyroid enlargement do not explain this blood-flow redistribution.

The cerebrum is the major region associated with conscious thought, memory, learning, reasoning, and voluntary actions. The cerebellum does not perform these higher mental functions; it fine-tunes muscular activity and helps maintain posture, balance, and coordinated movement. Thus option A correctly distinguishes their roles. The other options incorrectly describe brain regions as glands, digestive organs, or plant hormones.

The governing concept is stimulus response in plants. Plants lack a brain and an animal-like nervous system, but their cells detect environmental changes and coordinate responses through chemical signals and growth movements. Shoots may bend towards light, roots respond to gravity and water, and tendrils react to touch. Thus option A is correct; B, C, and D wrongly assign animal features to plants.

The governing concept is hormonal balance and regulation of growth. Growth hormone from the pituitary supports the normal growth of bones and other tissues, but its effect depends on an appropriate amount and developmental stage. Too little may cause inadequate growth, whereas too much can cause abnormal excessive growth. Hence option A is correct. Options B and C are biologically false, while D contradicts the hormone’s known role.

The governing concept is the difference between rapid neural control and slower hormonal control. Endocrine glands release hormones into the blood, so their effects usually begin more slowly than a reflex. However, hormones can reach target organs and regulate growth, metabolism, development, and other sustained changes over longer periods. Therefore option A is correct. B reverses the comparison, while C and D contradict how endocrine signals work.

The governing concept is the coordinated stimulus-response pathway. A receptor detects a change, a control centre interprets the information, and an effector produces the response. If any link fails—such as detection, transmission, interpretation, or movement—the final response may be delayed, incorrect, or absent, disturbing body functions. Thus A is correct. B, C, and D make sweeping statements that conflict with normal physiology.

The governing concept is control and coordination as a common life function. Organisms detect internal or external stimuli, process information, and produce suitable responses. Animals use nervous signals for rapid actions and hormones for slower, lasting regulation, while plants coordinate through chemical signals and growth movements. Therefore option A gives the complete conclusion. B denies an obvious life process, C wrongly gives plants nerves, and D confuses two different signalling systems.

A synapse is the junction or narrow gap between two neurons. When an impulse reaches the end of one neuron, chemical messenger molecules help carry the signal across this gap to the next neuron. If their amount becomes very low, the next neuron may receive insufficient stimulation, so message transmission becomes weak or may fail. Option A follows this mechanism; the other choices describe impossible or unrelated changes.

In the usual flow through a neuron, dendrites receive information from a receptor or another neuron. The signal is integrated in the cell body and then travels along the axon to its terminal, where it can influence the next cell across a synapse. Therefore option A correctly describes the direction. Axons do not release messages into blood, nuclei do not send hormones into the spinal cord, and synapses do not always reverse signals.

Chemical messengers released at a synapse stimulate receptors on the next neuron. Normally, removal or breakdown of the messenger helps terminate the signal and prevents continuous stimulation. If a drug blocks its breakdown, the messenger can remain active for longer, so excitation in the next neuron may be prolonged. Option A is correct. The other options describe effects that do not follow synaptic physiology and confuse neural, sensory or endocrine functions.

Feeling touch indicates that the skin receptor and sensory pathway can detect the stimulus and carry information toward the central nervous system. Lifting the hand, however, requires a motor command to travel from the nervous system through a motor nerve to the muscles, which act as effectors. Difficulty in movement therefore points to the motor nerve or effector, making option B correct. The sensory and skin receptor choices would better explain loss of sensation, not weakness of movement.

Blood glucose normally rises after a meal, but insulin released by pancreatic beta cells helps body cells take up and use glucose, bringing the level back toward normal. If glucose remains high for a prolonged period, the body may be producing too little insulin or the cells may not respond effectively to it. Therefore option A is the most suitable conclusion. Auxin and the spinal cord do not regulate blood glucose in this manner.

Negative feedback maintains a physiological variable near its normal level by reducing the original corrective response once the imbalance is corrected. Insulin lowers elevated blood glucose by promoting glucose uptake and storage. When blood sugar returns to the normal range, the stimulus for increased insulin release becomes smaller, so insulin secretion should decrease rather than continue rising. Thus option A is correct; the remaining choices contradict feedback regulation or confuse different organs and hormones.