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    Class 10 Class 12

    Control and Coordination
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    Draw the structure of a neuron and explain its function.
    Diagram of a neuron to show its structure:
    Diagram of a neuron to show its structure:Fig. Structure of a neuronF
    Fig. Structure of a neuron

    Function: Dendrites of a neuron collect information from the receptors and pass it to the cell body in the form of electrical impulse. From the cell body impulse passes along the axon to its end. At end of the axon, the electrical impulse sets off the release of certain chemicals (chemical neurotransmitters). These cemicals cross the gap (synapse) between the endings of the axon and dendrites of the next neuron and start a similar electric impulse in the dendrites. Thus information received travels along the neurons of a nerve to the effector muscles or gland. On reaching to the desired muscle or gland, axon endings from Neuromuscular junction (synapse between axon endings and muscle cells) through which information delivered from neuron to muscles or glands.
    Diagram of a neuron to show its structure:Fig. Structure of a neuronF
    Fig. Neuromuscular junction
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    Which of the following is a plant hormone?
    • Insulin
    • Thyroxin
    • Oestrogen
    • Cytokinin

    D.

    Cytokinin
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    What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
    Movement in sensitive plant: The movement in sensitive plant leaves takes place in response to touch (shock) stimulus. When terminal pinnule is touched, the stimulus is conducted to its base and the pinnules droop down. This happen in change in osmotic pressure (decrease) causing shrinkage. When the stimulus time is over, osmotic pressure increases and the cells swell, the pennules become normal. This is an example of growth independent movement.
    Movement in sensitive plant: The movement in sensitive plant leaves t

    Fig. The sensitive plant

    Thus, movement happens at a point different from the point of touch (stimulus). So, the information that a touch has occurred communicated through electrical-chemical means from cell to cell, but not through specialised tissues. Plant cells change in shape by changing amount of water in them, resulting in swelling or shrinking, during movement.

    Movement in our legs: Our legs are provided with nerves which have connection with muscles. To lift the leg, the brain passes information to nerves.

    The information travels as an electrical impulse. On reaching leg muscles impulse is converted into a chemical signal and the muscles contract to lift the leg. Movement of legs takes place due to muscle contraction and relaxation which is under the control of our nervous system.

    When nerve impulse reaches the muscle cells move by changing their shape. Special proteins cause both change in shape and their arrangement in the cell in response to nervous electrical impulses.
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    The gap between two neurons is called a 

    • dendrite

    • synapse

    • axon

    • impulse

    B.

    synapse

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    • Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

    Nervous system

    Hormonal system

    1.

    The nervous system controls the various functions by the units called neurons.

    1.

    Hormones are chemical messangers secreted by endocrine (ductless) glands.

    2.

    Neurons form two types of nerves (a) sensory nerves which receive the information to convey to brain or spinal cord.

    2.

    Hormones are directly poured into blood. Later on they diffuse to body cells, and also cell to cell.
     

    (b) Motor nerves which carry the response message to muscles or glands.

    		  

    They are synthesised at a places away from where they act and simple diffuse to the area of action.

    3.

    Nervous system has a network of nerves spread through out the body.

    3.

    Hormonal system does not has such a network.

    4.

    (a)    Dendrites of a neuron acquire information.

    4.

    Cells have special molecules on their surface to recognise information carried by hormones to act up accordingly.
     

    (b)    Information travels as an electric impulse through cell body and axon.

    		  

    Hormones are not conducted through electrical impulses.
     

    (c) The impulse is converted into a chemical signals for onward transmission.

    		    

    5.

    Nervous system does not use feedback mechanism in generating electrical impulse or producing neurochemical transmitter (especially at synapsis).

    5.

    The timing and amount of hormone released are regulated by feedback mechanisms.

    6.

    In nervous system, electrical impulses are generated for quick transmission of information. But there are limitation— (i) impulses will reach only those cells that connect by nervous tissue.

    6.

    Hormones are chemical messenger that diffuse to a cells of the body. The body cells, using special molecules on their surfaces, recognise information and even transmit it. Hormones are synthesised at places away from where they act.
     

    (ii) Once an electrical impulse is generated in a cell and transmitted, the cell takes some time to generate another impulse. That is cells cannot continuously create and transmit electrical impulses.

    		  

    Hormones can reach all cells of the body (through blood in animals), regardless of nervous connections and it can be done steadily and persistently.
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