ANSWERS OF ASSIGNMENT-3

HUMAN EYE

CLASS-VIII

A1. Cornea

A2. Retina

A3. i) Myopia   ii) Hypermetropia

A4. Myopia

A5. In a bright light, the iris contracts the pupil of an eye to allow less light to enter the eye. When we enter the dim-lit room, iris takes some time to expand the pupil of an eye to allow more light to enter the eye so that image of the object forms on retina.

A6. Two eyes are better than one eye because the field of view with two eyes is more than with one eye.

A7. Myopia. This defect can be corrected by using a concave lens.

A8. Iris controls the amount of light entering the eye by controlling the size of the pupil and is also responsible for the colour of the eye.

A9. a) Ciliary muscle

       b) Optic nerve

A10. Persistence of vision

A11. It remains unchanged because the image distance in the eye is fixed as it is the distance between the eye lens and the retina.

A12. Convex lens

A13. A hypermetropic eye can have normal far point. If he uses spectacles of converging lens, he will have more converging power than needed and the distant object may get focused in front of the retina. As a result, the distant objects will appear blurred.

A14. Chickens have very few rod cells and therefore cannot differentiate in dim light.

A15. a) Cornea

 b) After eye tissue is recovered, the technician carefully places it in a special container, where it is submerged in a chemical preservation solution to keep it healthy during transport, storage and laboratory evaluation. If stored properly and refrigerated, corneas can be preserved for as long as 14 days after their recovery, though most are usually used much quicker.

 c) Death due to unknown causes. People who die due to infections such as rabies, syphilis, infectious hepatitis and AIDS, cannot donate.