Control and Coordination

Nerve messages are electrical or electrochemical signals conducted rapidly along specific neurons and pathways, producing relatively immediate responses. Hormones are chemical messengers released by endocrine glands and transported through the bloodstream to target cells; their effects are usually slower and may last longer. Therefore option A correctly compares both systems. B reverses their usual timing, while C and D are biologically false.

Adrenaline is released during fear, stress, or danger and prepares the body for a rapid emergency response. It increases heart rate, breathing efficiency, blood flow to muscles, and the availability of glucose for immediate energy. This coordinated fight-or-flight response explains why option A is correct. Adrenaline is not a plant-only substance, does not induce sleep, and does not cause phototropism, so B, C, and D are incorrect.

Fear activates the body’s emergency response. Adrenaline helps the liver convert stored glycogen into glucose and release more glucose into the blood, supplying quick energy to muscles and other organs. Hence option B is correct. Insulin generally promotes glucose uptake and storage, estrogen mainly regulates reproductive functions, and cytokinin is a plant hormone involved in cell division, so none of those fits the situation.

The coiling of a tendril is a directional growth response called thigmotropism. When one side of the tendril touches a support, auxin-related growth effects produce unequal elongation on the two sides. The untreated or less-contacted side grows relatively faster, bending the tendril around the support. Therefore A is correct; the other options describe no valid mechanism for plant tendril coiling.

The governing idea is tropic movement: plant parts show directional growth in response to external stimuli. A root growing toward water demonstrates positive hydrotropism, while a stem growing toward light demonstrates positive phototropism. These observations support option A, showing that different organs can respond directionally to different stimuli. B denies plant coordination, and C and D contradict the examples given.

Hormonal regulation commonly produces gradual effects that develop over a long period and may influence many body systems. During adolescence, hormones cause progressive changes such as growth, maturation of reproductive organs, and development of secondary sexual characteristics over months or years. Thus option A best illustrates a long-lasting hormonal effect. The other choices are rapid protective reflexes or responses, mainly associated with nervous 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 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.

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.

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.

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 the organization of the nervous system. Neurons join to form connected pathways, and an impulse travels from a receptor through sensory neurons and processing centres to a particular motor neuron and effector. This wiring directs the message to the required body part. Hormones do not block nerves, blood does not create impulses, and muscles do not receive light; therefore option A is correct.

The governing concept is tropic movement, which is a directional growth response to an external stimulus. A root growing away from light shows negative phototropism. Because it grows in the direction of gravitational pull, it shows positive geotropism, also called positive gravitropism. Chemotropism and thigmotropism involve chemicals and touch respectively, so they do not describe both observations; option A is correct.

The governing concept is the distinction between growth-dependent and growth-independent plant movements. A stem bends toward light through unequal growth, so it is a growth movement. A Mimosa leaf folds rapidly because of changes in cell turgor at the pulvinus, not because of new growth, so it is non-growth-based. The pair in option A therefore correctly represents both types.

The governing concept is coordination in living organisms. Animals use the nervous system for rapid responses and hormones for slower, longer-lasting regulation. Plants have no brain or nervous system; they coordinate activities mainly through chemical messengers such as plant hormones and through growth responses. Therefore option A correctly compares both groups. The other choices assign structures that do not perform control in the stated organisms.

A synapse is the small junction or gap through which one neuron communicates with the next neuron. Usually, the first neuron releases neurotransmitters, which cross this gap and trigger a signal in the next neuron. If a medicine blocks these chemical messages, transmission becomes weak or stops. Therefore, option A is correct; the other options describe biologically unrelated or impossible effects.

Adrenaline, also called epinephrine, is released by the adrenal glands during sudden fear, danger, or intense stress. It prepares the body for a rapid emergency response by increasing heart rate, breathing rate, and blood supply to skeletal muscles. Therefore, suddenly seeing danger is the best answer. Peaceful sleep, calm study, and ordinary digestion do not normally cause this strong fight-or-flight response.

A stimulus is a detectable change in the surroundings or inside an organism that can initiate a response. A response is the resulting action or change. In phototropism, light provides the directional stimulus, and the plant stem bends toward the light as its growth response. Therefore, option A correctly identifies both parts; the other pairings confuse organs, substances, and actions.

A receptor is a specialised cell or sensory structure that detects a particular stimulus and converts it into a nerve signal. The retina contains photoreceptors, namely rods and cones, that respond to light entering the eye. Hence, “retina and light” is the correct match. The tongue mainly detects taste, the ear detects sound, and the nose detects chemical odours, so the other pairings are mismatched.

Control and coordination allow different organs and systems to receive information, respond appropriately, and work together in a properly timed manner. The nervous system provides rapid control, while hormones provide chemical regulation that may be slower and longer lasting. This integration maintains effective body functions. Therefore, option A is correct; the other choices are narrow, unrelated, or incomplete descriptions.

The governing concept is synaptic transmission. Neurons at a synapse are separated by a microscopic gap, so the electrical impulse cannot simply pass through continuous cytoplasm. When the impulse reaches the axon terminal, it triggers release of neurotransmitter chemicals; these diffuse across the synaptic cleft and stimulate the next neuron. Thus option A gives the necessary reason. The other choices assign impossible functions to the axon, dendrite or spinal cord.