[5 Mark Question Answer]

Question 15 Marks

Enumerate the common defects of vision, their causes and the possible methods of correcting them.

Answer

Defect of vision	Cause	Corrective measure
Myopia	Lengthening of eye ball from front to back or the lens is too curved.	Using suitable concave lens
Hyperopia	Shortening of eye ball from front to back or the lens is too flat.	Using suitable convex lens
Astigmatism	Uneven curvature of the cornea	Using suitable cylindrical lenses
Presbyopia	Loss of flexibility of lens	Using suitable convex lens
Cataract	Lens turning opaque	Surgery or use of convex lens or implantation of plastic lens.
Colour blindness	Genetic defect	No control measure
Squint	Formation of cross-eye	Surgery and suitable exercise

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Question 25 Marks

Describe the mechanism of focusing the image of a distant object in your eye when you raise your head after reading a book.

Answer

While reading a book, the lens is more convex or rounded due to contraction of ciliary muscles because the book is usually read from a short distance. When we raise our head and look at a distant object, the ciliary muscles relax to build the tension on the suspensory ligament so that they can stretch the lens. This change in the curvature of the lens makes us focus on distant object.

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Biology [5 Mark Question Answer]

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