[5 Mark Question Answer]

Question 15 Marks

With the help of suitable example, describe reflex action.

Answer

Reflex actions are automatic responses to stimuli. These actions are not under the control of the animal. They are of definite and mechanical type. Peripheral nervous system and spinal cord both control certain action and the brain is not in action.
Some examples of reflex actions are :
$1.$ Pupil becomes narrow when strong light falls on it.
$2.$ The aroma of the food makes the mouth watering.
$3.$ The hand is withdrawn as we touch the hot plate.
$4.$ Flow of bile from the gall bladder into the duodenum.
$5.$ A loud thud may lead to opening of the mouth.
In a reflex action brain is not involved, removing the hand on touching a hot plate is a reflex action. The impulse of heat goes from the hand to the spinal cord and the order is sent back to the muscles of the hand to remove the hand from the hot plate.

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Question 25 Marks

With the help of a suitable diagram describe the structures of a neuron.

Answer

Nervous system consists of special cells called nerve cells or neurons. It has a main cell body called cyton. It gives out many processes called dendrites. From it a very long process is given out. It is called axon or nerve fibre.

The cell body has a nucleus. The dendrites get the message from the organs and send this message to the axon through the cell body. Then the axon sends the message to muscles to contrast or to the gland for secretion.
The neurons make contact with one another through their processes. The axon at its end branches and meets the dendrites of another neuron. The meeting point is called synapse. The message is passed on from one axon to the dendrites of another neuron. How the message goes ? It is like this :
Organ $\rightarrow$ Message goes to dnedrites $\rightarrow$ Cell body $\rightarrow$ Axon $\rightarrow$ Muscles or glands

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BIOLOGY [5 Mark Question Answer]

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