Control and Coordination

Control and coordination means detecting internal or external changes, processing information, and organising the activities of different organs so that the body produces a suitable response. The nervous system and endocrine system help achieve this integration. Therefore option A is correct. Converting food into energy is a metabolic process, flower formation is only one plant process, and blood colour is unrelated to the definition.

A neuron carries an electrical impulse along its membrane, but two successive neurons are separated by a tiny gap called the synapse. When the impulse reaches the axon ending, neurotransmitter chemicals are released into this gap. They cross the synapse and stimulate the next neuron. Bones, blood, and food do not transmit the specific signal between neurons, so option A is correct.

The usual direction of impulse flow within a neuron is from the receiving dendrites to the cell body and then along the axon to the axon terminal. Dendrites collect signals from receptors or neighbouring neurons, while the axon carries the processed impulse away from the cell body. Therefore option A gives the correct sequence. The other choices reverse or mix the normal structural pathway.

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.

The thyroid gland produces thyroxine, a hormone involved in regulating metabolism, growth, and development. Iodine is an essential raw material for synthesising thyroxine. When dietary iodine is inadequate, thyroxine production can fall and the thyroid may enlarge in an attempt to compensate, causing goitre. Insulin and adrenaline are made by different endocrine glands, while dendrites are neuron structures.

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.

Plants lack a brain, nerves, and muscles like animals, but they can still coordinate responses. Chemical messengers such as plant hormones move between cells and influence growth. A difference in growth on opposite sides can bend a shoot, while some responses involve changes in cell water content. Therefore, chemical substances and directed growth explain plant responses; the animal structures in options B, C, and D do not perform this role in plants.

Growth movements result from permanent changes in cell size or number and generally occur slowly. Mimosa leaves fold within a short time after touch because water moves out of or between specialized motor cells, changing their turgor pressure. This is a rapid nastic response rather than growth. No new cells, stem elongation, or seed formation is required, so option A is correct.

Phototropism is the directional growth of a plant part in response to light. When light comes from one side, auxin becomes concentrated more on the shaded side of a young stem. In shoots, this promotes greater cell elongation there than on the illuminated side. The unequal growth produces curvature, causing the stem to bend toward light. Hence, 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.

The pollen tube must grow directionally through the style toward the ovule. Chemicals released by tissues around the ovule act as guidance signals and attract the growing pollen tube. Directional growth toward a chemical stimulus is called positive chemotropism. Sound and light do not guide this process, and the movement is not explained by an external electric force. Thus, option A is the correct answer.

Plant hormones may promote growth or inhibit it according to the hormone and condition. Abscisic acid, or ABA, generally suppresses growth, promotes dormancy, and helps plants respond to stress such as drought by reducing water loss through stomatal closure. Therefore, it is called a growth-inhibiting hormone. Stem elongation and increased cell division are associated with other hormones, while blood sugar is an animal-regulation concept. Option A is correct.

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 hormone specificity and receptor binding. Hormones are transported by blood to many parts of the body, but only cells with the appropriate receptors can recognise and respond to a particular hormone. These cells and organs are called target tissues or target organs. Therefore option A is correct. Blood does not flow only to selected organs, and the other statements do not explain receptor-based specificity or hormone action.

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.