Q19 of 216 Page 473

i. List the parts of the human eye that control the amount of light entering into it. Explain how they perform this function.

ii. Write the function of retina in human eye.


iii. Do you know that the corneal-impairment can be cured by replacing the defective cornea with the cornea of the donated eye? How and why should we organise groups to motivate the community members to donate their eyes after death?

i) The parts of the human eye controlling the amount of light entering it are:


Iris and Pupil.


Iris is the part of the eye surrounding the pupil. It adjusts the size of the pupil based on the intensity of light received by the eye. (contracts the eye if light received is large, dilates the pupil if light received by the eye is less.


Pupil is the opening in the iris through which light passes before reaching the lens and getting focussed at the retina. Hence the pupil allows light to enter the eyes.


ii) Retina is a thin and delicate tissue lining the inner eye. It varies in thickness from 0.1mm to 0.5 mm (thickest near the optic disk). The sensory photoreceptor cells i.e. rods and cones are present here. These generate excitatory responses to light and sends electrical signals to the brain due to which visual information is processed. The retina thus also acts as a screen on which image is formed.


iii) Yes, the corneal-impairment can be cured by replacing the defective cornea with the cornea of the donated eye.


We can encourage eye donation because of a number of reasons and the following initiatives can be taken:


a) Various campaigns can be conducted to support the cause.


b) Millions of people are suffering from corneal blindness hence donating an eye can be helpful for them who can see with those eyes donated since eyes are functional even after death of a person so people can be encouraged to donate their eyes after death.


More from this chapter

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17

Elements forming ionic compounds attain noble gas configuration by either gaining or losing electrons from their outermost shells. Give reason to explain why carbon cannot attain noble gas configuration in this manner to form its compounds. Name the type of bonds formed in ionic compounds and in the compounds formed by carbon. Also give reason why carbon compounds are generally poor conductors of electricity.

OR


i. State the meaning of functional group in a carbon compound. Write the functional group present in (a) ethanol and (b) ethanoic acid and also draw their structures.


ii. Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an additional reaction to occur write the chemical equation giving the name of the reactant and the product of such a reaction.

 18

i. Name the part of brain which controls

A. voluntary action,


B. involuntary action.


ii. What is the significance of the peripheral nervous system? Name the components of this nervous system and distinguish between the origin of the two.


iii. A. Identify the glands that secrete


• Insulin


• Thyroxin


B. Explain with an example how the timing and amount of hormone secreted are regulated in human body.

 20

i. Define electromagnetic induction.

ii. Two coils P and S are wound over the same iron core. Coil P is connected to battery and key and the coil S is connected to galvanometer. Draw a suitable diagram of this arrangement and write your observations when:


A. Current in the coil P is started by closing the key.


B. Current continues to flow in coil P.


C. Current in coil P is stopped by removing the key.


Explain the reason for such observations.


OR


Briefly explain an activity to plot the magnetic field lines around a bar magnet. Sketch the field pattern for the same specifying field directions.


A region A has magnetic field lines relatively closer than another region B. Which region has stronger magnetic field. Give reason to support your answer.

 21

i. What is ‘Chipko Movement’? Why should we conserve forests?

ii. Suggest any four changes that you would like to be incorporated in the life-style of students of your age to move towards a sustainable use of available resources.


iii. An environmentalist on visit to your school suggested the use of three R’s to save the environment. Explain what he meant by three R’s and how you would follow his advice at home.