Are eyes enough to enjoy this natural splendour ...? Didn't you notice the picture drawn by Raju and its caption? What is your opinion about the caption? You too might have got the opportunity to enjoy such scenes from nature. What have your blissful experiences in such situations been? — — — — —
Colourful scenes The chirping of birds The gentle pat of the breeze The intoxicating fragrance of flowers The honey-sweetness of mango
Though these are different experiences, can't they be felt at the same time? Can’t we hear, touch, smell and taste while seeing? Have you ever thought how this happens? You know that we get information about the changes in the environment through the sense organs. What are the sense organs we have? What is the function of each? Prepare a note on it. .....................................................................
Let us examine the parts of the eye. Make a list of those you know. — — —
Don't you want to know how these parts are arranged in the eye? Collect the eye of an animal from the butcher shop. Identify its morphological characteristics by observing and feeling it. Prepare a note based on the indicators. ..................................................................... Indicators — — —
Eyes enable us to see things. How are they protected? List the various means for the protection of eyes. — — — —
Colour Shape Firmness
Position of the eyes – sockets in the skull Tears
Lysozyme, the enzyme present in tears destroys germs that enter the eyes to a certain extent.
With the help of your teacher take a cross section of the eye that has been collected by you. Making use of the features you observed and the following description write a note on the structure of the eye. Fill up the blanks in Figure 1.1.
Eye – The Window opening to Nature
The eye ball has three layers. The outermost layer is the sclera. It imparts firmness to the eye ball. The transparent front portion of the sclera is the cornea. The anterior part of the eye except the cornea is protected by a membrane called conjunctiva. The middle layer, choroid contains many blood capillaries. The tissues in the eye receive oxygen and nutrients from the blood that flows through these capillaries. In the anterior part of the choroid behind the cornea there is a circular dark screen named iris. Pupil is the aperture at the centre of the iris. The pupil contracts when the intensity of light increases and dilates when it decreases. In this way it regulates the amount of light entering the eye. This is facilitated by the muscles in the iris. The convex lens is placed behind the pupil. It is connected to the ciliary muscles by ligaments.
Retina is the innermost layer of the eye where the image is formed. Cells that are stimulated by light are seen here. The part of the retina with greatest vision is called the yellow spot and that with no vision is called the blind spot. The optic nerve carrying impulses to the brain starts from the blind spot. Inside the eye there are two chambers. The chamber between the lens and the cornea is called aqueous chamber. It is filled with a watery fluid, called aqueous humour. This fluid supplies nutrients and oxygen to the cells of the cornea and the lens. The aqueous humour formed from the blood is reabsorbed into the blood itself. The large chamber seen between the lens and the retina is the vitreous chamber. It is filled with the jelly like vitreous humour which helps to maintain the shape of the eyeball.
ciliary muscles iris
vitreous chamber yellow spot
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Fig 1.1 Structure of the eye
Couldn't you identify the parts you had seen in the cross section of the eye in the figure? Now illustrate each part of the eye, their peculiarities and functions in an interrelated manner in your Science diary. A model is given below.
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