Chapter 6 · Control and Coordination

NCERT Class 10 Science Chapter 6 Exercises

All 12 questions of NCERT Class 10 Science Chapter 6 Exercises (Control and Coordination), in the book's order, each with its answer and a step-by-step solution.

1. Q1
   Which ​of the ​following ​is ​a ​plant hormone?

   1. (a)Insulin
   2. (b)Thyroxin
   3. (c)Oestrogen
   4. (d)Cytokinin.
   Show answer

   (d) Cytokinin.

   Step-by-step solution →
2. Q2
   The ​gap ​between two ​neurons ​is ​called ​a

   1. (a)dendrite.
   2. (b)synapse.
   3. (c)axon.
   4. (d)impulse.
   Show answer

   (b) synapse.

   Step-by-step solution →
3. Q3
   The brain is responsible for

   1. (a)thinking.
   2. (b)regulating the heart beat.
   3. (c)balancing the body.
   4. (d)all of the above.
   Show answer

   (d) all of the above.

   Step-by-step solution →
4. Q4
   What is the function ​of receptors ​in our body? ​Think of situations ​where ​receptors do not ​work properly. ​What problems are likely to ​arise?
   Show answer

   Receptors detect changes and turn them into impulses; if they fail, the stimulus goes undetected and no response follows.

   Receptors are the specialised tips of some nerve cells, located in our sense organs, whose function is to detect a particular kind of change in the surroundings and convert it into an electrical impulse in a sensory neuron. They are the input end of the nervous system: the impulse they generate travels to the brain or the spinal cord, which decides on the response and sends it out along a motor neuron to a muscle or a gland. Each type answers one kind of stimulus — gustatory receptors detect taste and olfactory receptors smell, while receptors in the eye detect light, those in the inner ear sound and balance, and those in the skin heat, touch and pain. If receptors do not work properly, the stimulus is never detected at all, so no impulse is generated and no response follows, even though the nerves, the brain and the muscles are healthy. Damaged olfactory receptors leave a person unable to smell a gas leak, smoke or spoilt food; damaged gustatory receptors make food tasteless, take away the appetite and hide the bitterness that warns of a harmful substance; damage to the receptors of the eye or the inner ear causes loss of sight, or of hearing and of balance; and damage to the heat, touch and pain receptors of the skin is the most dangerous, because a burn or a cut is not felt, the protective reflex is never triggered, and the injury goes unnoticed and may become infected.

   Step-by-step solution →
5. Q5
   Draw the structure ​of ​a ​neuron ​and ​explain its function.
   Show answer

   A neuron receives information at the dendrites, conducts it as an electrical impulse along the axon and hands it on chemically at the terminals.

   A neuron has three regions, and they are drawn in the order the impulse travels through them. (i) The dendrites are the branched fibres at one end; information from the environment is acquired at their specialised tips, where a chemical reaction creates an electrical impulse. (ii) The cell body, which contains the nucleus and the cytoplasm, receives that impulse next and keeps the cell alive. (iii) The axon is the single long fibre that carries the impulse away from the cell body to its far end; where it is covered by a myelin sheath, that insulating layer stops the impulse leaking away and lets it travel faster. The axon ends in branched axon terminals, and there the electrical impulse sets off the release of chemicals. These chemicals cross the synapse — the gap — and start a similar electrical impulse in a dendrite of the next neuron, or deliver the message to a muscle cell or a gland. The function of the neuron is therefore to receive information at one end, conduct it as an electrical impulse in one direction only, and hand it on chemically at the other; a network of such cells is what carries information from one part of the body to another.

   Step-by-step solution →
6. Q6
   How ​does phototropism ​occur ​in ​plants?
   Show answer

   Light makes auxin move to the shaded side of the shoot; those cells grow longer, so the shoot bends towards the light.

   Phototropism is the directional growth movement a plant makes in response to light: a shoot grows towards it and a root away from it. It is brought about by a hormone, not by any muscle. Auxin is synthesised at the tip of the shoot and helps the cells to grow longer. When light falls on one side of the plant, the auxin at the tip diffuses towards the shady side, so its concentration becomes higher on the side away from the light. That higher concentration stimulates the cells on the shaded side to grow longer than the cells on the lit side. One side of the shoot is now longer than the other while its thickness is unchanged, so the shoot curves, and since the longer shaded side forms the outside of the curve, the tip turns towards the light. Because the bend is produced by growth, it is slow and permanent: turning the plant round does not straighten the old bend, and only the newly grown part answers the new direction of the light.

   Step-by-step solution →
7. Q7
   Which signals ​will get ​disrupted ​in case ​of ​a spinal cord injury?
   Show answer

   Sensory signals going up to the brain, motor signals coming down from it, and reflexes relayed through the injured part of the cord.

   The signals disrupted are those that had to travel between the body and the brain through the injured part of the cord, together with the reflexes relayed there. (i) Sensory signals coming up from the parts of the body below the injury no longer reach the brain, so touch, pain and temperature are not felt in those parts. (ii) Motor instructions going down from the brain no longer reach the muscles below the injury, so voluntary movement of those parts is lost — this is what paralysis means. (iii) Reflex arcs whose relay lies at or below the level of the injury are disrupted, so those reflex actions are no longer carried out. (iv) The involuntary control that the cord exercises over organs below the injury, such as the bladder and the bowel, is disturbed as well. Signals that do not pass through the injured stretch are unaffected: thinking, sight, hearing, smell and speech continue as before, and so do the involuntary actions run directly by the medulla, such as the heart beat and breathing, provided the injury lies below the brain stem. Nothing in the receptors, the neurons or the muscles is itself damaged; what has been lost is the route between them.

   Step-by-step solution →
8. Q8
   How ​does ​chemical coordination occur ​in ​plants?
   Show answer

   Plants coordinate chemically, through hormones that diffuse from where they are made: auxin, gibberellins and cytokinins promote growth, abscisic acid inhibits it.

   Plants have neither a nervous system nor muscles, so all of their control and coordination is chemical. When a stimulus is received the information is passed from cell to cell by electrical-chemical means, but there is no specialised tissue in a plant for conducting it. The coordination itself is carried out by plant hormones, which are synthesised at places away from where they act and simply diffuse to the area of action; this makes their action slow, but steady, persistent, and able to reach cells that no nerve could. Auxin, made at the shoot tip, helps the cells to grow longer, and its uneven distribution is what makes a shoot bend towards light. Gibberellins, like auxins, help in the growth of the stem. Cytokinins promote cell division and are present in greater concentration in regions of rapid cell division, such as in fruits and seeds. These three promote growth; a plant also needs a signal to stop, and abscisic acid is a hormone that inhibits growth, its effects including the wilting of leaves. Because all of these act by changing growth, the plant's responses appear as directional growth movements, or tropic movements — phototropism towards light, geotropism in response to gravity, hydrotropism towards water and chemotropism towards a chemical, as when a pollen tube grows towards an ovule.

   Step-by-step solution →
9. Q9
   What ​is ​the need for ​a system of ​control and coordination in ​an organism?
   Show answer

   Control and coordination detect changes, make organs act together, protect the body in time and keep internal conditions steady.

   A multicellular organism is built of many specialised tissues, each doing a different job, and it can behave as one living thing only if their activities are matched to one another. A system of control and coordination is needed for four reasons. (i) To detect changes in the surroundings and answer them appropriately: each kind of change calls for a different response, and the response has to be selected and its amount decided, not merely produced. (ii) To make several organs act together: seeing a danger is useless unless the legs move, and the working muscles then need the heart to beat faster and the breathing to quicken at the same moment — when adrenaline is secreted the heart rate rises, the blood is diverted from the digestive system and the skin to the skeletal muscles, and the breathing rate increases, all together. (iii) To protect the body fast enough: touching a flame has to be answered before the skin is burnt, so the connection is made in the spinal cord as a reflex rather than being thought about. (iv) To keep the internal conditions of the body steady and its growth in order: thyroxin regulates carbohydrate, protein and fat metabolism, growth hormone regulates growth and development, and insulin regulates the level of sugar in the blood, with the timing and amount of each hormone controlled by feedback mechanisms. Without such a system the organs would work at cross purposes, the body could not respond usefully or in time to its environment, and its internal conditions would drift outside the narrow range in which its cells can survive.

   Step-by-step solution →
10. Q10
    How ​are ​involuntary ​actions ​and reflex actions ​different from ​each ​other?
    Show answer

    A reflex is a sudden, spinal-cord response to a stimulus; an involuntary action is a continuous activity controlled by the medulla.

    Both are alike in one respect — neither is under our thinking control — so the differences lie elsewhere. (1) Control centre: a reflex action is decided in the **spinal cord**, where the reflex arc is formed, the information reaching the brain only afterwards; an involuntary action is controlled by the **medulla** in the hind-brain. (2) Trigger: a reflex action is a sudden response to a stimulus, usually one that could harm the body; an involuntary action needs no stimulus at all and continues whether anything happens or not. (3) Speed and duration: a reflex is extremely fast and over in a moment, and its speed is the whole reason for routing it through the cord, since the thinking of the brain would be too slow; an involuntary action is continuous and is regulated in rate rather than triggered. (4) Muscles used: a reflex usually moves the skeletal muscles, which we can also move at will at other times; involuntary actions work the smooth muscle of the internal organs and the cardiac muscle of the heart, which can never be moved at will. (5) Examples: reflex actions include pulling the hand back from a hot object, the narrowing of the pupil in bright light, blinking and sneezing; involuntary actions include the beating of the heart, breathing, the movement of food through the alimentary canal, blood pressure, salivation and vomiting.

    Step-by-step solution →
11. Q11
    Compare ​and ​contrast nervous ​and hormonal mechanisms for control and coordination in ​animals.
    Show answer

    Both coordinate organs; the nervous system is fast, electrical and short-lived along fixed paths, the hormonal one slow, chemical, lasting and carried by blood.

    **Similarities**. Both are systems of control and coordination: each carries information from one part of the body to another so that different organs act together, each is set going by a change the body has detected, each produces a response in a target tissue, both are coordinated by the brain, and both do harm when the message is too strong or too weak. Chemicals are used by both — the nervous system at every synapse and the hormonal system throughout. **Differences**. (1) Nature of the message: nervous coordination travels as an electrical impulse within each neuron and becomes chemical only while crossing a synapse; hormonal coordination is chemical from beginning to end. (2) Route and target: a nerve impulse follows a fixed chain of neurons and can reach only cells connected by nervous tissue, ending at one particular muscle or gland; a hormone is poured into the blood, which carries it to every part of the body, and only the cells able to detect it — the target organ — respond. (3) Speed: the nervous message arrives in a fraction of a second, the hormonal one after seconds, minutes or hours, because it has to be carried round by the blood. (4) Duration: a nervous response is brief and stops with the impulse, and the cell must reset before it can send another, so impulses cannot be created continually; a hormonal response is long-lasting and can be kept up steadily and persistently. (5) Regulation: a nerve impulse begins and ends with its stimulus, while the timing and amount of a hormone are controlled by feedback — a rise in blood sugar makes the pancreas secrete more insulin, and the secretion falls again as the level drops. (6) Examples: withdrawing the hand from a flame, blinking and all voluntary movement are nervous; growth (growth hormone), metabolism (thyroxin), blood sugar (insulin), the changes of puberty (testosterone and oestrogen) and the body's preparation for danger (adrenaline) are hormonal.

    Step-by-step solution →
12. Q12
    What is the ​difference between ​the ​manner ​in which movement ​takes place ​in a sensitive plant and ​the movement in ​our legs?
    Show answer

    The sensitive plant folds its leaflets as cells lose water, without muscle cells; legs move when muscle cells shorten on a nerve impulse.

    Both movements are independent of growth, but the mechanisms have nothing else in common. (1) The signal: in the sensitive plant the point touched is not the point that moves, so information is passed from cell to cell by electrical-chemical means, and there is no specialised tissue anywhere in the plant for conducting it; in our body the instruction travels as an electrical impulse along nerve cells, from the brain through the spinal cord and out along a motor neuron to the muscle. (2) The cells that move: a plant has no muscle cells at all, while our legs are moved by muscle cells. (3) The change of shape: plant cells change shape by changing the amount of water in them — water moves out of the cells at the base of the leaflets, they lose their turgidity and shrink, and the leaflet folds and droops, opening again later when the water returns; a muscle cell has special proteins that change their shape and arrangement in response to a nervous electrical impulse, giving the cell a shorter form, and the shortening pulls on the bone and moves the leg. (4) Control and direction: the plant's folding is automatic, is over in seconds and is not directional with respect to the stimulus — the leaflets fold the same way whichever side is touched; our leg movement is voluntary, decided in the fore-brain, and we choose its direction, its extent and whether to make it at all.

    Step-by-step solution →