Control and Coordination

Insulin is a hormone released by the pancreas that helps body cells take up glucose and thereby keeps blood glucose within a suitable range. If insulin production is insufficient, glucose remains in the bloodstream and the blood sugar level may rise. Persistent elevation is associated with diabetes. The other options describe unrelated effects involving balance, vision, or plant growth, so option A is correct.

Fear activates the body’s emergency or fight-or-flight response. The adrenal glands release adrenaline, which increases heart rate and breathing rate, directs more blood towards active muscles, and helps make energy available quickly. Insulin mainly regulates blood glucose, estrogen is a reproductive hormone, and auxin controls plant growth. Therefore adrenaline is the only option that explains the rapid heartbeat during fear.

The medulla is a part of the hindbrain that regulates several involuntary activities needed for survival. Breathing continues automatically even when we are not consciously thinking about it, so its control is associated with the medulla. Drawing uses conscious forebrain activity, taste detection involves sensory pathways, and bending of a stem is a plant growth response, not a nervous-system action. Therefore, option A is correct.

The forebrain is responsible for higher mental functions such as thinking, reasoning, memory, interpretation of sensations, and conscious decision-making. Solving a difficult question requires understanding, recalling information, and applying logic, so it depends strongly on the forebrain. Quickly withdrawing from heat is a spinal reflex, heartbeat is involuntary, and downward root growth is geotropism. Thus, option A is correct.

A tropic movement is a directional growth response to a specific external stimulus. In this case, water or moisture is the stimulus, and the root grows toward it. Directional growth toward water is called positive hydrotropism. Phototropism is a response to light, chemotropism to chemicals, and thigmotropism to touch or contact. Therefore, the correct response is hydrotropism, option A.

Cytokinins are plant hormones that promote cell division and support the formation of new tissues. Consequently, they are associated with actively growing regions, including young tissues and developing fruits, where cells are dividing rapidly. They are not restricted to dry leaves or dead woody parts, and regions with no growth would not require high cytokinin activity. Therefore, option A correctly identifies the relevant plant parts.

Gibberellin is a plant growth hormone that promotes stem elongation and can contribute to an increase in overall plant height. It also has roles in seed germination and other growth processes, but stem elongation is the key effect tested here. Blood-sugar control, fear-related heartbeat, and pupil-size regulation are animal physiological functions involving hormones or the nervous system, not gibberellin. Hence, option A is correct.

The governing concept is the distinction between voluntary and involuntary actions. A voluntary action is performed consciously according to a person’s choice, so writing is voluntary. Heartbeat is controlled automatically by the autonomic nervous system and continues without conscious instruction, so it is involuntary. Therefore, option A gives the correct order. Option B reverses the two actions, while options C and D do not provide a correct voluntary–involuntary pair.

The governing concept is physical protection of the central nervous system. The skull forms a hard bony covering, while cerebrospinal fluid surrounds the brain and spinal cord within their protective membranes. This fluid cushions the nervous tissue, helps absorb shocks, and provides a stable surrounding medium. Therefore option A is correct. Bile aids fat digestion, saliva begins digestion, and blood sugar is a nutrient level rather than a protective fluid.

The governing concept is the pupillary light reflex, an involuntary protective response. In bright light, circular muscles of the iris contract and the pupil becomes smaller, limiting the amount of light entering the eye and protecting the retina from excessive stimulation. The pupil does not make food, amplify sound, or regulate blood sugar, 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 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.

The central nervous system needs strong skeletal protection. The brain is enclosed within the skull, while the spinal cord passes through and is protected by the vertebral column, or backbone. Thus option A correctly pairs each nervous-system organ with its protective structure. Ribs mainly protect organs in the chest, and the thigh bone, skin, pancreas, thyroid, and ovary do not form the protective coverings of the brain and spinal cord.

The governing concept is stimulus-response coordination. A stimulus is a detectable change, either outside the organism, such as light or heat, or inside it, such as a change in water level. A response is the action or adjustment produced after detection, such as bending or withdrawing a hand. Hence option A is correct; the other options confuse stimuli with hormones or body parts and make false absolute claims.

Receptor specificity means that a particular receptor is adapted to detect a particular type of stimulus, such as light, sound, heat, or chemicals. Detection is the first step in coordination; the nervous system or another control system can produce an appropriate response only after the correct stimulus has been identified. Option A expresses this sequence. Options B, C, and D incorrectly describe receptor function or location.

A tropic movement is a directional growth response to a specific external stimulus. Light produces phototropism, gravity produces geotropism or gravitropism, and water produces hydrotropism. Chemotropism, however, is a response to chemical substances, not to sound. Therefore option D is the incorrect match. The other three pairs correctly connect each stimulus with its corresponding tropism.

Plants do not possess an animal-like nervous system, brain, or spinal cord, so their coordination is generally slower and depends on chemical signals and changes in growth. Nevertheless, plants respond to light, gravity, water, touch, and other stimuli through hormones and specialised growth movements. Option A correctly states both the limitation and the compensating feature. Options B, C, and D contradict basic plant physiology.

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.

The governing concept is the division of roles in coordination. A receptor detects a change such as heat, pressure, or light and converts it into a signal. An effector then carries out the response; muscles contract and glands secrete substances. Hence option A is correct. Option B reverses the definitions, while options C and D assign unrelated functions to both structures.

The governing concept is control and coordination as a life function. Organisms detect internal or external stimuli, process information, and coordinate the activities of different organs so that a suitable response occurs at the right time. Hence option A is the broadest and correct explanation. The other choices describe neither coordination nor the diversity of organisms: they restrict it to colouring food, making bones, or plants alone.

The governing concept is sensory receptors and stimulus detection. Receptors in the eye respond to light, those in the ear detect sound, receptors in the nose detect smell-related chemicals, and taste receptors on the tongue respond to dissolved substances. Therefore, option A correctly matches the organs and stimuli. The other options describe unrelated functions or incorrectly place these receptors only in plant roots.