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SolveItNCERT · CBSE · NEET

NCERT Exemplar · Class 10 Science Control and Coordination

53 questions · 53 still being checked

Long Answer Questions 45–53 (part 5 of 5)

  1. Exercise 45

    Draw the structure of a neuron and explain its function.

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    NCERT’s answer
    Hints— Cell body Dendrite Axon
    A neuron has branched dendrites that pick up a stimulus, a cell body (cyton) with the nucleus, and a long axon carrying the impulse onward. \[\text{stimulus} \to \text{dendrite} \to \text{cell body} \to \text{axon} \to \text{axon terminal (synapse)} \] At the axon terminal the impulse triggers release of a chemical (neurotransmitter) into the synaptic gap, passing the signal to the next neuron or to a muscle/gland. Answer: A neuron receives a stimulus through its dendrites, conducts it as an electrical impulse via the cell body and axon, and releases a neurotransmitter at the synapse to relay the signal onward.

  2. Exercise 46

    What are the major parts of the brain? Mention the functions of different parts.

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    Hints— Fore brain Mid brain Hind brain Give its functions
    The brain has three regions.
    Forebrain: cerebrum — thinking, voluntary action, sensory-motor association, memory; hypothalamus — hunger, thirst, body temperature.
    Midbrain: reflex movements of the eyes and head in response to visual and auditory stimuli.
    Hindbrain: cerebellum — posture, balance, precision of voluntary acts; pons — relays impulses between cerebrum and cerebellum; medulla — involuntary actions such as blood pressure, salivation, vomiting.
    Answer: Forebrain — thought and voluntary control; midbrain — eye and head reflexes; hindbrain — balance and involuntary actions.

  3. Exercise 47

    What constitutes the central and peripheral nervous systems? How are the components of central nervous system protected?

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    NCERT’s answer
    Hints— Brain and spinal cord Brain box and vertebral column.
    CNS = brain + spinal cord, the control and processing centre. PNS = nerves linking CNS to the body: $\displaystyle 12$ pairs of cranial nerves (from the brain) and $\displaystyle 31$ pairs of spinal nerves (from the spinal cord). Protection: the skull encases the brain and the vertebral column encases the spinal cord; both also sit inside cerebrospinal fluid within three membranous meninges, cushioning them from jolts. Answer: CNS (brain + spinal cord) and PNS ($\displaystyle 12$ cranial + $\displaystyle 31$ spinal nerve pairs) make up the nervous system; the CNS is shielded by bone (skull, vertebrae) and by CSF-filled meninges.

  4. Exercise 48

    Mention one function for each of these hormones :
    (a)
    Thyroxin
    (b)
    Insulin
    (c)
    Adrenaline
    (d)
    Growth hormone
    (e)
    Testosterone.

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    NCERT’s answer
    (a)
    Thyroxin regulates carbohydrate, fat and protein metabolisms
    (b)
    Insulin — regulates blood sugar
    (c)
    Adrenaline — increases heart rate and supply of blood to various organs
    (d)
    Growth hormone — regulates growth and development
    (e)
    Testosterone — controls the changes of body features associated with puberty in male
    (a) Thyroxin — regulates carbohydrate, fat and protein metabolism, setting the body's basal metabolic rate. (b) Insulin — lowers blood glucose by promoting its uptake and storage as glycogen. (c) Adrenaline — prepares the body for an emergency: raises heart rate and breathing rate, redirects blood to skeletal muscles. (d) Growth hormone — promotes growth of bones and muscles, overall body growth. (e) Testosterone — brings about male secondary sexual characteristics at puberty.

  5. Exercise 49

    Name various plant hormones. Also give their physiological effects on plant growth and development.

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    Hints— Auxin Gibberellin Cytokinin Abscisic acid
    Auxin — synthesised at the shoot tip; promotes cell elongation, causing the shoot to bend towards light (phototropism). Gibberellin — promotes stem elongation. Cytokinin — promotes cell division, concentrated in growing regions such as fruits and seeds. Abscisic acid — inhibits growth; causes wilting of leaves and stomatal closure in response to stress (the ‘stress hormone’). Answer: Auxin, gibberellin and cytokinin promote growth; abscisic acid inhibits it.

  6. Exercise 50

    What are reflex actions? Give two examples. Explain a reflex arc.

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    NCERT’s answer
    Hints— Definition Nerve impulses
    A reflex action is a sudden, involuntary response of a muscle or gland to a stimulus, controlled by the spinal cord without conscious involvement of the brain. Examples: withdrawing the hand from a hot object; the knee-jerk on tapping below the kneecap.Pathway: \[\text{Stimulus} \to \text{Receptor} \to \text{Sensory neuron} \to \text{Relay neuron (spinal cord)} \to \text{Motor neuron} \to \text{Effector} \to \text{Response} \]The receptor senses the stimulus; the sensory neuron carries the impulse to the spinal cord, where the relay neuron passes it straight to a motor neuron -- bypassing the brain -- so the effector responds before the sensation is consciously felt.Answer: A reflex arc runs receptor → sensory neuron → spinal cord (relay neuron) → motor neuron → effector, giving an involuntary, rapid response.

  7. Exercise 51

    "Nervous and hormonal systems together perform the function of control and coordination in human beings." Justify the statement.

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    NCERT’s answer
    Hints— Nerve impulses Dendritic end and axonal end Role of hormones Roles of blood, muscles and glands.
    Neurons carry electrical impulses -- signalling is almost instant but brief, driving fast actions like movement and reflexes.\[\text{Stimulus} \xrightarrow{\text{nerve impulse (ms)}} \text{immediate, brief response} \]Hormones travel in blood -- slower to arrive, but the effect is sustained and reaches every cell, regulating growth, metabolism and reproduction.\[\text{Stimulus} \xrightarrow{\text{hormone (blood)}} \text{delayed, sustained response} \]The hypothalamus links them: nervous tissue that itself secretes hormones controlling the pituitary. In danger, nerves give an instant reflex while adrenaline sustains raised heart rate and blood pressure -- the two systems complement, not duplicate, each other.Answer: Nervous control is fast and brief (electrical); hormonal control is slower but sustained (chemical); together, linked at the hypothalamus, they give both rapid and long-term coordination.

  8. Exercise 52

    How does chemical coordination take place in animals?

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    NCERT’s answer
    Different endocrine glands secrete different hormones. These hormones are released into blood which carry them to specific tissues or organs called target tissues or target organs. In the target tissues, hormone triggers a particular biochemical or physiological activity.
    Endocrine glands are ductless: they release hormones straight into the blood.\[\text{Stimulus} \to \text{Endocrine gland} \to \text{Hormone (into blood)} \to \text{Target organ (matching receptor)} \to \text{Response} \]The hormone circulates to every cell but acts only where a matching receptor is present, e.g. insulin from the pancreas lowers blood glucose by acting on liver and muscle cells.\[\text{Blood glucose} \uparrow \Rightarrow \text{Pancreas} \to \text{Insulin} \Rightarrow \text{Blood glucose} \downarrow \]Once the level falls, the stimulus for secretion is removed -- a feedback loop that keeps the amount of hormone matched to need.Answer: Endocrine glands secrete hormones into the blood on a stimulus; the hormones circulate to all cells but act only on target cells with matching receptors, producing the response; secretion is regulated by feedback (e.g. insulin and blood glucose).

  9. Exercise 53

    Why is the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron but not the reverse?

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    NCERT’s answer
    When an electrical signal reaches the axonal end of a neuron, it releases a chemical substance. This chemical diffuses towards the dendrite end of next neuron where it generates an electrical impulse or signal. Hence, the electrical signal is converted into a chemical signal at the axonal end. Since these chemicals are absent at the dendrite end of the neuron the electrical signal, cannot be converted into chemical signal.
    A synapse is one-way because the neurotransmitter is stored only in vesicles at the axon terminal, and its receptors sit only on the dendrite/cell body of the next neuron.\[\text{Impulse (axon terminal)} \to \mathrm{Ca^{2+}} \text{ influx} \to \text{vesicle fusion} \to \text{neurotransmitter released into cleft} \to \text{receptor binding (dendrite)} \to \text{new impulse} \]The axon terminal has no receptors to receive a chemical signal, and the dendrite has no vesicles to release one, so the electrical-to-chemical-to-electrical conversion can run only from axon to dendrite, never in reverse.Answer: Because the transmitter is released only from vesicles in the axon terminal and is detected only by receptors on the receiving dendrite, signal flow at a synapse is fixed from axon to dendrite.