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Question
Explain the terms ‘adaptation’ and ‘accommodation’ with reference to the eye.
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Solution
Adaptation is the ability to adjust vision in bright and dark areas. When we enter a dark room from bright light, the rhodopsin pigment broken down in bright light is regenerated. It dilates the pupil and allows more light to enter the eyes. This is called dark adaptation. On the other hand, if we enter bright area from a dark room, the rhodopsin pigment is bleached. This constricts the pupil and reduces the light entering the eyes. This is called 'light adaptation'
Accommodation is the process of focusing the eye at different distances. This is mainly brought about by a change in the curvature of the lens. When the ciliary muscles contract, the lens becomes thicker and we are able to focus a nearby object. On the other hand when the ciliary muscles relax, the lens remains stretched i.e. the normal condition and we are able to focus on distant object.
RELATED QUESTIONS
Millions of people in the developing countries of the world are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organised a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission, how would you contribute in this noble cause?
(i) State the objective of organising such campaigns.
(ii) List two arguments which you would give to motivate the people to donate their eyes after death.
(iii) List two values which are developed in the persons who actively participate and contribute in such programmes.
Name one defect of vision (or eye) which cannot be corrected by any type of spectacle lenses.
Name the body part with which the terms myopia and hypermetropia are connected.
What is the far point of a person suffering from myopia (or short-sightedness)?
The defect of vision which cannot be corrected by using spectacles is:
(a) myopia
(b) presbyopia
(c) cataract
(d) hypermetropia
The diagram alongside represents a section of a mammalian eye.
(i) Label the parts 1 to 5 of the diagram.
(ii) State the function of the parts labelled 4 and 5.
(iii) With the help of a diagram show the short sightedness.
Give Reason:
Why do we see clearly in the central region of the retina?
Given below is a diagram showing a defect of vision. Name the defect of vision and draw an accurately labelled diagram to correct this defect.
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power:
Observe the following diagram and answer questions following it:
- Identify the defect of vision shown.
- List its two causes.
- Name the type of lens used for the correction of this defect.
