Class 10 Science · Chapter 6

Control and Coordination

286 Class 10 Science questions on Control and Coordination from the NCERT textbook, NCERT Exemplar and CBSE board papers 2018–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 8 of 15

1. Q141 CBSE 2025
   Name the ​parts of ​hind-brain of the human ​brain. Which part ​of the hind-brain controls involuntary actions such as ​blood pressure and salivation ​?
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   The hind-brain has the cerebellum, pons and medulla; the medulla controls involuntary actions such as blood pressure and salivation.

   The hind-brain consists of the cerebellum, the pons and the medulla (medulla oblongata). The medulla controls involuntary actions such as blood pressure, salivation and vomiting.

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2. Q142 CBSE 2025
   Study the given ​diagram ​and write the type of ​movement exhibited ​by ​:

   1. (a)Root, and
   2. (b)Shoot, mentioning the stimulus in each ​case.

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   The root shows positive geotropism and the shoot negative geotropism; the stimulus in both is gravity.

   (a) Root: positive geotropism; it grows downwards, towards the pull of gravity. Stimulus: gravity. (b) Shoot: negative geotropism; it grows upwards, away from the pull of gravity. Stimulus: gravity.

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3. Q143 CBSE 2025
   A person ​is making a ​list to ​purchase few things from a ​nearby market. Explain how ​the fore-brain plays an important role in ​performing this activity.
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   The fore-brain takes in the information, thinks and decides using memory, and its motor areas direct the hand muscles that write the list.

   The fore-brain is the main thinking part of the brain. While the list is being made, its sensory areas receive impulses from the eyes (for example, on seeing which items at home are finished); its association areas interpret this information by putting it together with information already stored in the brain, the memory of what is needed and what the market sells, and a decision is made about what to buy. The decision is then passed to the motor areas of the fore-brain, which control the voluntary muscles of the hand that write the list. Thinking, memory and the voluntary action of writing are all directed by the fore-brain.

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4. Q144 CBSE 2025
   Where ​are ​auxins ​synthesised ? How ​are they ​related to phototropism ?
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   Auxins are synthesised at the shoot tip; they collect on the shaded side, making it grow longer, so the shoot bends towards light.

   Auxins are synthesised at the **tip** (the apical region) of a shoot, and they then move down to the region just behind the tip where the cells are elongating. Their relation to phototropism is this: when light falls on a shoot from one side, auxin moves away from the illuminated side and collects on the shaded side. Auxin makes cells grow longer, so the cells on the shaded side elongate more than those on the lit side; that side of the shoot becomes longer and the shoot therefore bends **towards** the light. That directional growth in response to light is phototropism.

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5. Q145 CBSE 2025
   There is a hormone which regulates carbohydrates, proteins and fat metabolism ​in the human body. ​Name the hormone and the gland which ​secretes it. State ​the importance ​of iodised ​salt ​in ​our diet.
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   Thyroxine is secreted by the thyroid gland, which needs iodine from iodised salt to make it; lack of iodine causes goitre.

   The hormone is **thyroxine**, and it is secreted by the **thyroid gland**, which lies in the neck. Iodised salt matters because the thyroid gland needs iodine in order to make thyroxine, and the body cannot make iodine for itself — it has to come from the diet. A trace of iodine added to table salt supplies it, so that enough thyroxine is made and the metabolism of carbohydrates, proteins and fats stays properly regulated. If the diet is short of iodine the gland cannot make enough thyroxine and the person may develop goitre, in which the thyroid enlarges and the neck swells.

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6. Q146 CBSE 2025
   Explain ​how ​tendrils ​help ​a pea plant ​climb up other ​plants or fences.
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   The part of a tendril touching a support grows more slowly, so the tendril coils round it and anchors the weak stem.

   Tendrils are thin thread-like growths of the stem that are sensitive to touch. When a tendril meets a support, the part of the tendril in contact with the object grows more slowly than the part away from it. This unequal growth makes the tendril bend towards the support, circle around it and cling to it. The coils anchor the weak stem, so the pea plant is held up and can climb another plant or a fence.

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7. Q147 CBSE 2025
   List ​two major limitations ​of ​the use of ​electrical impulses as ​a means of communication ​between the cells in most ​multicellular ​animals.
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   Impulses reach only cells joined by nervous tissue, and a cell needs time to reset before it can send another impulse.

   (i) Electrical impulses reach only those cells that are connected by nervous tissue, and not each and every cell of the animal body. (ii) After a cell has generated and transmitted an impulse it needs time to reset its mechanisms before it can send another, so cells cannot continually create and transmit electrical impulses. These limitations are why most multicellular animals also use chemical communication.

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8. Q148 CBSE 2025
   Plants have neither ​a ​nervous ​system nor muscles, even then they respond to stimuli. For example, the leaves of ​chhui-mui ​(touch-me-not) plant when ​touched begin to ​fold up and droop.

   1. (a)How is the information communicated in “touch-me-not” plants ?
   2. (b)What enables the plant cells to bring out ​the observable response ?
   3. (c)Differentiate the movement mentioned above from the movement of tendrils in a pea plant.
   Show answer

   The signal passes cell to cell and leaflet-base cells lose water and shrink; this nastic movement is independent of growth, unlike tendril movement.

   (a) Plants have no nervous system, so the information that a leaf has been touched is passed on from cell to cell as an electrical–chemical signal (an electrical impulse together with chemical signals) which travels from the point of touch to the base of the leaflets. (b) Plant cells change shape by changing the amount of water in them. Cells at the base of the leaflets pump ions out; water follows and leaves those cells, so they lose water, shrink and lose their turgidity while the cells on the other side swell. This change in cell shape folds the leaflets and makes the leaf droop — no muscle cells are involved. (c) The touch-me-not movement is a nastic movement: it is independent of growth, is caused by a reversible change in the water content of cells, is very fast and reversible, and its direction is not decided by the direction of the stimulus. The movement of a pea tendril is a tropic (thigmotropic) movement: it is a growth movement caused by cells on the side away from the support growing longer than those touching it, is slow, is permanent, and is directional — the tendril grows towards and coils around the support.

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9. Q149 CBSE 2025
   1. (a)Define ​hormone.
   2. (b)​“Hormones should ​be secreted ​in precise ​quantities. ​We have a feedback mechanism through which this is done.” With the help of an ​example justify the statement.
   Show answer

   A hormone is a chemical messenger from a ductless gland; feedback keeps its quantity precise, as falling blood glucose reduces insulin secretion.

   (a) A hormone is a chemical messenger secreted in very small amounts by an endocrine (ductless) gland, released directly into the blood and carried to specific target organs, where it controls and coordinates growth, development and metabolism. (b) The amount matters because both excess and deficiency are harmful, so secretion is regulated by feedback. Example: after a meal the blood glucose level rises; the cells of the pancreas detect this and secrete more insulin; insulin makes the cells take up glucose and the liver store it as glycogen, so the glucose level falls; as it falls, insulin secretion is reduced. The level being controlled thus decides how much hormone is released, which is why hormones are secreted in precise quantities.

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10. Q150 CBSE 2025
    1. (a)​What ​is meant by ​reflex arc ? ​Where are ​they formed in the ​human body ?
    2. (b)Why have reflex arcs ​evolved in animals ​?
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    A reflex arc in the spinal cord is the pathway of a reflex action; it evolved because the brain's thinking is not fast enough.

    (a) A reflex arc is the pathway of a reflex action: the connection between the nerves that detect a stimulus and the nerves that make a muscle act, so that a sudden stimulus gets a quick, automatic response (receptor $\to$ sensory neuron $\to$ relay neuron $\to$ motor neuron $\to$ effector). In the human body reflex arcs are formed in the spinal cord. (b) The thinking process of the brain is not fast enough for a quick response, for example to danger. Many animals have little or none of the complex network of neurons needed for thinking, so reflex arcs are likely to have evolved as efficient ways of responding quickly without true thought processes; even in animals with complex brains they remain more efficient for quick responses.

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11. Q151 CBSE 2025
    Name ​the parts ​‘X’ and ‘Y’ ​of human ​brain in the given diagram and ​give one function of each.

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    X is the medulla, controlling involuntary actions; Y is the cerebellum, giving posture, balance and precision to voluntary actions.

    ‘X’ is the medulla (medulla oblongata) of the hind-brain. Function: it controls involuntary actions such as blood pressure, salivation and vomiting. ‘Y’ is the cerebellum of the hind-brain. Function: it is responsible for the precision of voluntary actions and for maintaining the posture and balance of the body.

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12. Q152 CBSE 2025
    What is a synapse ​? How is an ​electrical ​impulse ​created in a nerve cell and what is the ​role of ​synapse in this ​context ​?
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    A synapse is the gap between a nerve ending and the next neuron's dendrite; it passes the message on chemically, in one direction.

    A synapse is the very small gap or junction between the nerve ending, or axon terminal, of one neuron and the dendrite of the next neuron. An impulse is created when information is acquired at the tip of a dendrite; this sets off a chemical reaction there which creates an electrical impulse, and the impulse then travels from the dendrite to the cell body and along the axon to its end. At the nerve ending the electrical impulse causes the release of chemicals; these cross the synapse and set off a similar electrical impulse in the dendrite of the next neuron. The synapse thus passes the message on by turning it from electrical to chemical and back, and since only the nerve ending releases the chemical, it makes the transmission one-way.

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13. Q153 CBSE 2025
    Name the source of secretion ​and ​one ​function each ​of the ​following animal hormones :

    1. (i)Thyroxin
    2. (ii)Insulin
    3. (iii)Growth ​hormone
    Show answer

    Thyroxin comes from the thyroid and regulates metabolism, insulin from the pancreas lowers blood sugar, and growth hormone from the pituitary controls growth.

    (i) Thyroxin: secreted by the thyroid gland; it regulates carbohydrate, protein and fat metabolism in the body, and iodine is essential for the gland to make it. (ii) Insulin: secreted by the pancreas; it lowers and regulates the blood sugar level, and too little of it causes diabetes. (iii) Growth hormone: secreted by the pituitary gland; it controls the growth and development of the body, its bones and muscles, and too little of it in childhood causes dwarfism.

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14. Q154 CBSE 2025
    1. (a)List two constituents ​of Central Nervous System (CNS). How are these components protected ?
    2. (b)Write ​two ​limitations of ​the use ​of electrical impulses.
    Show answer

    The CNS (brain, spinal cord) is protected by bone, meninges and fluid; electrical impulses reach only nerve-connected cells and need reset time.

    (a) The two constituents of the central nervous system are the **brain** and the **spinal cord**. Both are very delicate and both are protected in the same three ways: the brain is enclosed in a bony box, the cranium (skull), and the spinal cord runs inside the vertebral column (backbone); inside the bone each is wrapped in three membranes called the meninges; and between the membranes there is cerebrospinal fluid, which cushions them and acts as a shock absorber. (b) Two limitations of the use of electrical impulses are: (1) an electrical impulse travels only along nerve fibres, so it can reach only those cells that are connected by nervous tissue and not each and every cell of the body; and (2) after a cell has generated and transmitted an impulse, it needs time to reset its ion distribution before it can generate and transmit a new one, so impulses cannot be created and sent continuously. These are the reasons animals also use chemical communication through hormones.

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15. Q155 CBSE 2025
    State two limitations ​of electrical impulses in multicellular organisms. Why ​is chemical ​communication better than ​electrical impulses ​as a means ​of communication between cells in multicellular organisms?
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    Impulses reach only nerve-connected cells and need reset time; chemical signals reach every cell via the blood and can be sustained.

    Two limitations of electrical impulses: (i) They reach only those cells of the body that are connected by nervous tissue, and not each and every cell of the organism. (ii) Once a cell has generated and transmitted an impulse it must take time to reset its mechanisms before it can send another, so impulses cannot be created and transmitted continuously. Chemical communication is better because a chemical compound released by one cell diffuses out and is carried by the blood to all parts of the body, so it can reach every cell and not just the cells with a nerve supply; and the cell making it can go on making it, so the signal is steady and long lasting instead of being limited by a reset time. Chemical communication is slower than an electrical impulse, but it is far more widespread and can be sustained.

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16. Q156 CBSE 2025
    What ​are ​plant hormones ? ​Where are ​they ​synthesised ​? What happens when a growing plant detects light ?
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    Plant hormones are chemical compounds made in the plant that coordinate its growth; auxin made at the shoot tip bends the shoot towards light.

    Plant hormones, or phytohormones, are chemical compounds made by the plant itself which help to control and coordinate its growth, development and response to the environment; auxin, gibberellin, cytokinin and abscisic acid are examples. They are synthesised at places away from where they act, for example auxin at the tip of the shoot and cytokinins in regions of rapid cell division such as fruits and seeds, and they simply diffuse to the area of action. When a growing plant detects light falling on one side, the auxin made at the shoot tip diffuses towards the shaded side; auxin makes those cells grow longer, so the shaded side grows more than the lit side and the shoot bends towards the light. This directional growth response is called phototropism.

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17. Q157 CBSE 2025
    A ​hormone ​‘X’ is secreted in blood ​when a person is under scary situation.

    1. (a)Identify the hormone ‘X’ and the ​gland that secretes it.
    2. (b)Explain its ​role ​in dealing with scary or ​emergency situations.
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    X is adrenaline from the adrenal glands; it speeds the heart and breathing and diverts blood to the skeletal muscles.

    (a) The hormone X is adrenaline. It is secreted by the adrenal glands, which lie one on top of each kidney. (b) Adrenaline is secreted directly into the blood and carried to different parts of the body, where it acts on its target organs. The heart beats faster, supplying more oxygen to the muscles. The muscles around the small arteries of the digestive system and the skin contract, reducing the blood supply there and diverting blood to the skeletal muscles. The breathing rate increases because of contractions of the diaphragm and the rib muscles. Together these responses prepare the body to deal with the emergency — to fight or to run away.

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18. Q158 CBSE 2025
    (a) Name ​the glands that secrete :

    1. (i)Adrenaline
    2. (ii)Thyroxin (b) ​Explain with ​example how the ​timing and ​amount of ​hormone released ​are ​regulated in the human body.
    Show answer

    Adrenaline is secreted by the adrenal glands and thyroxin by the thyroid; feedback regulates hormone release, as blood sugar level controls insulin secretion.

    (a) (i) Adrenaline is secreted by the adrenal glands, which lie on top of the kidneys. (ii) Thyroxin is secreted by the thyroid gland, in the neck. (b) The timing and amount of hormone released are regulated by a feedback mechanism: the level of the substance the hormone controls is detected, and the release of the hormone is increased or reduced to match. For example, when the sugar level in the blood rises, it is detected by the cells of the pancreas, which respond by producing more insulin; insulin lowers the blood sugar level, and as the level falls, insulin secretion is reduced. The blood sugar level itself thus decides when insulin is released and how much.

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19. Q159 CBSE 2025
    (a) Analyse ​the given situations and interpret the possible reason for each :

    1. (i)Iodine deficiency in diet ​increases the possibility of a disease of swollen ​neck in a ​person.
    2. (ii)Some people in population ​may have very short heights (dwarfs).
    3. (iii)Thick facial hairs develop in boys at the age of 10-12 ​years. (b) Explain two reasons which necessitate the need of chemical communication ​in multicellular organisms.
    Show answer

    Iodine deficiency causes goitre, too little growth hormone causes dwarfism, testosterone brings facial hair; hormones reach every cell and give a steady signal.

    (a) (i) Iodine is needed by the thyroid gland to make the hormone thyroxine. When iodine is missing from the diet the gland cannot make thyroxine, so it enlarges in trying to do so, and the enlarged thyroid shows as a swelling of the neck. The disease is goitre. (ii) Such people secreted too little **growth hormone** from the pituitary gland during childhood, so the growth of the body and of the bones was stunted and the person remained a dwarf. (iii) At about $10$-$12$ years the testes begin to secrete the male sex hormone **testosterone**, which brings about the male secondary sexual characters; thick facial hair is one of them. It is a normal change of puberty. (b) 1. An electrical impulse travels only along nerve fibres, so it reaches only the cells that nervous tissue connects to; a hormone released into the blood is carried to **every** cell of the body. 2. A nerve cell must reset itself before it can send another impulse, so nervous signalling cannot be kept up continuously; a hormone gives a slow, steady and long-lasting signal, which is what processes like growth and puberty need.

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20. Q160 CBSE 2025
    1. (a)Differentiate between ​voluntary and involuntary action.
    2. (b)Define ​reflex action. With the help ​of a flow diagram, show the correct sequence of ​path ​of Nerve ​impulse from ​place of ​its origin.
    Show answer

    Voluntary actions are controlled by the cerebrum, involuntary ones by the mid-brain and medulla; a reflex action is processed by the spinal cord.

    (a) Voluntary action: it is performed knowingly, by the person's own will, and can be started or stopped at will; it is initiated and controlled by the **cerebrum** of the fore-brain; the person is aware of it. Examples: writing, walking, speaking. Involuntary action: it takes place without any conscious will and cannot be started or stopped at will; it is controlled by the **mid-brain** and the **medulla** of the hind-brain; the person is usually unaware of it. Examples: beating of the heart, breathing, peristalsis, salivation. (b) Reflex action is a sudden, rapid and automatic response of the body to a stimulus, in which the message is processed by the spinal cord and the response is made without waiting for the brain to think, for example pulling the hand away on touching a hot object. Flow diagram (path of the nerve impulse): Stimulus $\to$ Receptor (in the skin) $\to$ Sensory neuron $\to$ Spinal cord (relay neuron) $\to$ Motor neuron $\to$ Effector (muscle) $\to$ Response.

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