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 14 of 15

1. Q261 CBSE 2019
   What ​is a ​nerve impulse ​? State the direction followed by ​a nerve impulse while travelling in the body ​of an ​organism.
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   A nerve impulse is the electrical message carried along a nerve fibre, travelling from dendrite to cell body to axon to nerve ending.

   Nerve impulse: The information (message) carried along a nerve fibre in the form of an electrical signal (electrical impulse) is called a nerve impulse. Direction: The impulse is picked up at the tips of the dendrites of a neuron. It travels from the dendrite to the cell body, and then along the axon to its end (the nerve ending). There it releases chemicals that cross the synapse and start a similar impulse in the dendrite of the next neuron: dendrite $\to$ cell body $\to$ axon $\to$ nerve ending $\to$ synapse $\to$ dendrite of the next neuron. In the body, impulses thus travel from the receptors along sensory nerves to the brain or spinal cord, and from there along motor nerves to the muscles or glands.

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2. Q262 CBSE 2019
   How ​is ​the ​movement of leaves of the sensitive plants ​different from the movement of a ​shoot towards ​light ?
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   Leaves fold quickly on touch, whatever its direction, without growth; the shoot bends slowly towards light by growth.

   The movement of the leaves of the sensitive plant (touch-me-not) differs from the movement of a shoot towards light as follows. 1. Direction of the stimulus: the leaves fold up in response to touch, and the movement does not depend on the direction of the touch; the shoot moves in the direction of the stimulus, towards the light (phototropism). 2. Growth: the folding of the leaves is not a growth movement, since the cells change shape by losing water; the bending of the shoot is a growth movement, since auxin makes the shaded side of the shoot grow faster. 3. Speed: the leaves fold within seconds and open again later; the shoot bends slowly, over hours or days, and the bend is permanent.

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3. Q263 CBSE 2019
   List ​in tabular form two differences ​between reflex ​action and ​walking.
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   A reflex action is involuntary and controlled by the spinal cord; walking is voluntary and controlled by the brain.

   (i) Nature: A reflex action is an involuntary action - it happens automatically, without our will; walking is a voluntary action - we do it by our will. (ii) Control: A reflex action is controlled by the spinal cord; walking is controlled by the brain (started by the cerebrum, with posture and balance maintained by the cerebellum).

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4. Q264 CBSE 2019
   (a) Name the part ​of human ​brain ​which controls ​

   1. (i)voluntary actions, and
   2. (ii)​involuntary actions. (b) Write the function of peripheral nervous ​system. Name the components of this ​system stating their origin.
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   The fore-brain controls voluntary and the hind-brain (medulla) involuntary actions; the PNS links the CNS with the body through cranial and spinal nerves.

   (a) (i) Voluntary actions are controlled by the fore-brain, mainly the cerebrum. (ii) Involuntary actions are controlled by the hind-brain, mainly the medulla (medulla oblongata); the mid-brain also controls some involuntary actions. (b) The peripheral nervous system facilitates communication between the central nervous system (the brain and the spinal cord) and the other parts of the body: it carries messages from the receptors to the brain and spinal cord, and instructions from them to the muscles and glands. Its components are the cranial nerves, which arise from the brain, and the spinal nerves, which arise from the spinal cord.

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5. Q265 CBSE 2019
   Nervous and hormonal ​systems ​together ​perform the function ​of control and coordination ​in human ​beings. ​Justify this statement with the help of an example.
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   The hypothalamus links the two systems: nerve signals make it release a hormone that works through the pituitary and thyroid to regulate metabolism.

   The two systems are linked through the hypothalamus, a part of the brain: it receives nerve signals and, in response, releases hormones, so a message started by the nervous system is carried on by the hormonal system. Example: The hypothalamus releases a hormone that stimulates the pituitary gland; the pituitary secretes thyroid-stimulating hormone, which makes the thyroid gland secrete thyroxine; thyroxine regulates carbohydrate, protein and fat metabolism in the body. When the thyroxine level falls (as when the diet lacks iodine), this chain is switched on more strongly. The nervous system starts the response and the hormonal system completes it.

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6. Q266 CBSE 2019
   “Nervous and hormonal ​systems together ​perform the function ​of ​control and coordination ​in ​human ​beings.” Justify the statement.
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   Nerves give fast, direct control and hormones slower, widespread control; the two are linked, so together they control and coordinate the body.

   The nervous system gives direct and very quick control: a network of neurons carries electrical impulses to and from the brain and spinal cord, so that particular muscles and glands respond at once. The hormonal (endocrine) system gives indirect, slower but longer-lasting control: glands release hormones into the blood, which reach all organs and make them speed up or slow down according to the situation, as in growth and metabolism. The two systems are linked and complement each other: the brain, through the hypothalamus, controls the pituitary gland, and in an emergency nerve signals make the adrenal glands release adrenaline, which prepares the whole body to respond. Hence the nervous and hormonal systems together perform control and coordination.

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7. Q267 CBSE 2019
   Draw a ​diagram of neuron and name ​and ​label the part

   1. (a)​where ​information is acquired,
   2. (b)through which information travels ​as an electric ​impulse, and
   3. (c)where the electric impulse must be converted ​into a chemical signal for onward transmission.
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   Dendrite acquires information, the axon carries it as an electric impulse, and the nerve ending converts it into a chemical signal at the synapse.

   Diagram: a neuron with branched dendrites, a cell body containing the nucleus, a long axon and branched nerve endings; the impulse runs from the dendrites to the nerve endings (see the labelled figure). (a) Dendrite (the dendritic tip): information is acquired here. (b) Axon: the information travels along it as an electric impulse. (c) Nerve ending (axon terminal) at the synapse: here the electric impulse sets off the release of chemicals that carry the signal across the synapse to the next neuron.

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8. Q268 CBSE 2019
   State the function of each ​of ​the ​following ​plant hormones ​:

   1. (a)Gibberellins
   2. (b)Auxins
   3. (c)Abscisic ​acid
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   Gibberellins make the stem elongate, auxins make cells grow longer and bend the shoot towards light, and abscisic acid inhibits growth and causes wilting.

   (a) Gibberellins: help in the growth of the stem by making it elongate (they also break the dormancy of seeds). (b) Auxins: are made at the shoot tip and help cells to grow longer; by diffusing to the shady side of a shoot they make it bend towards light. (c) Abscisic acid: inhibits growth; its effects include wilting of leaves (it also closes stomata and keeps seeds and buds dormant).

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9. Q269 CBSE 2019
   Trace the ​sequence ​of ​events which ​occur when ​a bright light ​is focused on your ​eyes.
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   Retinal receptors detect the light, a sensory neuron carries the impulse to the brain, and a motor neuron makes the pupil contract.

   Bright light is detected by the receptor cells of the retina $\to$ the impulse travels along the sensory neuron $\to$ to the brain, which processes it $\to$ a command travels along the motor neuron $\to$ to the eye muscles (the muscles of the iris) $\to$ the pupil contracts (becomes smaller) and the eyelids may blink or close, so less light enters the eye.

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10. Q270 CBSE 2019
    What is feedback ​mechanism of ​hormonic regulation. Take the example ​of insulin ​to ​explain this ​phenomenon.
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    In feedback regulation, the level of the controlled substance decides hormone release; rising blood sugar raises insulin secretion and falling blood sugar reduces it.

    Feedback mechanism: the timing and amount of a hormone released are regulated by the level of the substance that the hormone controls. A change in that level is detected by the gland, which then increases or decreases its secretion so that the level returns to normal. Example of insulin: when the sugar level in the blood rises (for example after a meal), the cells of the pancreas detect it and secrete more insulin, which lowers the blood sugar. As the blood sugar level falls, insulin secretion is reduced. In this way the blood sugar level itself keeps the secretion of insulin, and hence its own level, under control.

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11. Q271 CBSE 2019
    What are plant hormones ? ​Name the plant hormones ​responsible for ​the following :

    1. (i)​Growth of stem
    2. (ii)Promotion of ​cell ​division
    3. (iii)Inhibition ​of growth
    4. (iv)Elongation of cells
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    Gibberellins promote stem growth, cytokinins cell division, abscisic acid inhibits growth and auxins elongate cells.

    Plant hormones (phytohormones) are chemical substances that help to coordinate growth, development and responses to the environment in plants. (i) Growth of stem: gibberellins (auxins also help). (ii) Promotion of cell division: cytokinins. (iii) Inhibition of growth: abscisic acid (ABA). (iv) Elongation of cells: auxins (gibberellins also help).

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12. Q272 CBSE 2019
    List in ​tabular ​form ​three distinguishing features ​between ​cerebrum and ​cerebellum.
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    The cerebrum (fore-brain) is the thinking part that starts voluntary actions; the cerebellum (hind-brain) keeps posture and balance and makes actions precise.

    (i) Part of the brain: The cerebrum is the main part of the fore-brain (the largest part of the brain), while the cerebellum is a part of the hind-brain. (ii) Main function: The cerebrum is the main thinking part of the brain, the seat of intelligence, memory and reasoning, while the cerebellum maintains the posture and balance (equilibrium) of the body. (iii) Voluntary actions: The cerebrum initiates voluntary actions, while the cerebellum makes them precise, as in walking in a straight line, riding a bicycle or picking up a pencil. $$\begin{array}{lll}\text{Feature}& \text{Cerebrum}& \text{Cerebellum}\\ \text{Part of the brain}& \text{main part of the fore-brain}& \text{part of the hind-brain}\\ \text{Main function}& \text{thinking: intelligence, memory, reasoning}& \text{maintains posture and balance}\\ \text{Voluntary actions}& \text{initiates them}& \text{makes them precise (walking, cycling)}\end{array}$$

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13. Q273 CBSE 2019
    1. (a)Plants do not ​have any nervous ​system but ​yet, if we touch a sensitive plant, some ​observable changes take place in its leaves. Explain how could this plant ​respond to the external stimuli ​and how it is communicated.
    2. (b)Name the hormone that needs to be administered to (i) increase ​the height ​of a dwarf plant. (ii) cause rapid cell division in fruits and seeds.
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    The touch signal passes cell to cell and cells at the leaflet base lose water and shrink; the hormones are gibberellin and cytokinin.

    (a) When the sensitive plant (touch-me-not) is touched, its leaflets fold up and the leaf droops. The cells at the point of touch detect the stimulus and pass the information on from cell to cell by electrical-chemical means, since plants have no nerves or other specialised tissue for conducting information. The cells at the base of the leaflets and of the leaf then change shape by changing the amount of water in them: they lose water and shrink, so the leaves fold. This movement is brought about by swelling and shrinking of cells, not by growth. (b)(i) Gibberellin (auxin also earns credit). (b)(ii) Cytokinin.

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14. Q274 CBSE 2019
    Why does the ​flow of signals in a synapse ​from axonal end ​of ​one neuron ​to ​dendritic ​end of another neuron take place but not ​in the reverse direction ? Explain.
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    Only the axonal end releases chemicals and only the next neuron's dendritic end has receptors for them, so the signal cannot flow in reverse.

    In a neuron the electrical impulse travels from the dendrite to the cell body and then along the axon to its end, the nerve ending. At the end of the axon the impulse sets off the release of some chemicals. These chemicals cross the gap, the synapse, and start a similar electrical impulse in the dendrite of the next neuron. The chemicals are released only at the axonal end, and only the dendritic end of the next neuron has receptors that respond to them; a dendrite releases no such chemicals. So a signal can cross the synapse only from the axon of one neuron to the dendrite of the next, never in the reverse direction: the flow is unidirectional.

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15. Q275 CBSE 2019
    1. (a)Why is ​the ​use ​of iodised salt advisable ​? Name the disease caused due to deficiency of iodine in our diet and state its one ​symptom.
    2. (b)How ​do nerve impulses travel in the ​body ​? Explain.
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    Iodised salt supplies iodine for thyroxin, preventing goitre (swollen neck); a nerve impulse travels dendrite, cell body, axon, then chemically across the synapse.

    (a) Iodine is necessary for the thyroid gland to make the hormone thyroxin, which regulates carbohydrate, protein and fat metabolism in the body for balanced growth. Iodised salt supplies this iodine through the diet, so its use is advisable. Disease: goitre. Symptom: a swollen neck (enlarged thyroid gland). (b) Information received at the tip of a dendrite of a nerve cell sets off a chemical reaction that creates an electrical impulse. The impulse travels from the dendrite to the cell body, and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the gap (synapse) between the two neurons and start a similar electrical impulse in a dendrite of the next neuron. In this way the impulse travels from neuron to neuron, and finally to muscle cells or glands. Path: dendrite → cell body → axon → nerve ending → chemicals across the synapse → dendrite of the next neuron.

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16. Q276 CBSE 2019
    What ​is ​hydrotropism ​? Design an ​experiment ​to demonstrate this ​phenomenon.
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    Hydrotropism is growth in response to water; roots that grow out of a perforated dish bend back up towards its moist base.

    Hydrotropism: the directional growth movement of a part of a plant in response to water. Roots grow towards water (positive hydrotropism). Experiment: (i) Soak a few seeds (such as gram or pea) in water overnight. (ii) Place a layer of moist cotton in a petri dish that has small holes (perforations) in its base. (iii) Put the soaked seeds on the moist cotton and place the dish on the mouth of an empty, dry beaker. Keep the cotton moist and leave the set-up for a few days. (iv) Observation: the roots of the germinating seeds first grow downwards and pass out through the holes into the dry air of the beaker. (v) After some time the roots bend and grow back upwards, towards the moist base of the petri dish. Conclusion: the roots grow towards the moisture, even against the pull of gravity; this demonstrates hydrotropism. (Any other relevant experiment earns credit, for example seedlings grown in dry soil in a trough with a porous pot of water buried on one side: after a few days their roots are found bent towards the pot.)

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17. Q277 CBSE 2018
    1. (a)Name ​one gustatory receptor and one ​olfactory ​receptor present in human beings.
    2. (b)​Write a and b in the given flow chart of neuron ​through which information travels as an electrical impulse.

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    Taste buds are gustatory receptors, the nose lining holds olfactory receptors; a is the cell body and b the axon.

    (a) Gustatory receptor (detects taste): the taste buds on the tongue. Olfactory receptor (detects smell): the olfactory receptors in the lining of the nose. (b) a: cell body (cyton); b: axon. Dendrite → cell body → axon → end point of neuron (nerve endings)

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18. Q278 CBSE 2018
    Different ​parts of brain are associated with specific functions. Name ​the part of human brain ​which perform the ​following functions :

    1. (a)Sensation of ​feeling full
    2. (b)Vomiting
    3. (c)Picking up ​a pencil
    4. (d)Riding a ​bicycle
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    The hypothalamus gives the feeling of fullness, the medulla controls vomiting, and the cerebellum controls picking up a pencil and riding a bicycle.

    (a) Sensation of feeling full: the hypothalamus, in the fore-brain (the centre associated with hunger). (b) Vomiting: the medulla (medulla oblongata), in the hind-brain. (c) Picking up a pencil: the cerebellum, in the hind-brain (precision of voluntary actions). (d) Riding a bicycle: the cerebellum, in the hind-brain (precision of voluntary actions, posture and balance).

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19. Q279 CBSE 2018
    Name the hormones ​secreted ​by ​the following ​endocrine glands and specify ​one function ​of ​each :

    1. (a)Thyroid
    2. (b)​Pituitary
    3. (c)Pancreas
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    Thyroid secretes thyroxin, pituitary secretes growth hormone, and pancreas secretes insulin, which regulates blood sugar level.

    (a) Thyroid: thyroxin (thyroxine). Function: it regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. (b) Pituitary: growth hormone. Function: it regulates the growth and development of the body. (c) Pancreas: insulin. Function: it regulates the blood sugar level, lowering it when it rises. (The pancreas also secretes glucagon, which raises the blood sugar level; either hormone with its function is correct.)

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20. Q280 CBSE 2018
    What ​is geotropism ​? Draw ​a ​labelled diagram of a potted ​plant ​showing positive geotropism ​and negative ​geotropism.
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    Geotropism is growth of a plant part in response to gravity: roots show positive geotropism and the shoot shows negative geotropism.

    Geotropism is the directional growth movement of a part of a plant in response to gravity (the pull of the earth). Growth towards gravity is positive geotropism and growth away from it is negative geotropism. Diagram: a potted plant (see the figure) in which the roots grow downwards into the soil, towards gravity, labelled positive geotropism, and the shoot grows upwards, away from gravity, labelled negative geotropism; the pot, the soil and the direction of gravity are also marked.

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