Q18 of 216 Page 456

How are involuntary actions and reflex actions different from each other?

OR


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


(ii) Sameer was studying in his room. Suddenly he smells something burning and sees smoke in the room. He rushes out of the room immediately. Was Sameer’s action voluntary or involuntary? Why?

Involuntary Action: These actions occur without the thinking of a person or his conscious.


The brain controls it.


Example: Churning of stomach, heartbeat.


Reflex action: Spontaneous action for any stimulus.


It is controlled by the spinal cord.


Example: knee-jerk when the hammer strikes knee.


OR


Signals in a synapse from the axonal end of one neuron to dendritic end of another neuron but not the reverse is because of the chemicals/ neurotransmitter released at the axonal end where electric signals get converted to chemical signals. These neurotransmitters from axonal end move towards dendrites of another neuron, and hence, the signal gets transmitted.


More from this chapter

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16

(i) Distinguish between ionic and covalent compounds under the following properties:

(a) The strength of forces between constituent elements


(b) The solubility of compounds in water


(c) Electrical conduction in substances


(ii) Explain how the following metals are obtained from their compounds by the reduction process:


(a) Metal M which is in the middle of the reactivity series.


(b) Metal N which is high up in the reactivity series.


Given one example of each type.


OR


(i) Distinguish between ‘roasting’ and ‘calcination’. Which of these two is used for sulphide ores and why?


(ii) Write a chemical equation to illustrate the use of aluminium for joining cracked railway lines.


(iii) Name the anode, the cathode and the electrolyte used in the electrolytic refining of impure copper.

 17

A salt X is formed, and gas is evolved when ethanoic acid reacts with sodium hydrogen carbonate.

Name the salt X and the gas evolved. Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named. Also, write chemical equation of the reaction involved.

 19

(i) What is myopia? State the two causes of myopia. With the help of labelled ray diagrams show

(a) The eye defect myopia


(b) Correction of myopia using a lens.


(ii) Why is the normal eye unable to focus on an object placed within 10 cm from the eye?

 20

Draw an appropriate schematic diagram showing common domestic circuits and discuss the importance of fuse. When is it that a burnt out fuse should be replaced by another fuse of identical rating?