Kerala SSLC Biology Chapter 2 Notes Windows of Knowledge English Medium
Sense organs are windows which lead sensations like fabulous sights, varied sounds, different smells, drooling tastes and touch into our consciousness. The sense organs help to understand the changes of our surroundings. The receptors which perform specific functions together form sense organs. This unit explains the sense organs eye, ear, nose, tongue and skin in detail.
→ About eighty percent of our sensations are provided by the eye.
→ Layers of the eye : Sclera, Choroid, Retina
→ Cornea : Slightly projected transparent anterior part of sclera.
→ Iris : Part of the choroid seen behind the cornea.
→ Pupil : The aperture seen at the centre of the iris.
→ Yellow spot: The part of the retina where plenty of photoreceptors are present.
→ Power of accommodation : The capacity’ of the eye to change the curvature of lens depending on the distance between eye and the object by adjusting the focal length.
→ Night blindness : Condition in which a person cannot see objects clearly in dim light.
→ Xerophthalmia: Due to the prolonged deficiency of Vitamin A, the conjunctiva and cornea will become dry and opaque.
→ Colour blindness : Persons with this defect cannot distinguish green and red colours.
→ Glaucoma : The condition in which the. reabsorption of aqueous humour does not occur, it causes an increase in the pressure.
→ Cataract: It is a condition in which the lens of the eyes become opaque resulting in blindness.
→ Parts of ear : External ear, middle ear, internal ear
→ Tympanum : A thin circular membrane that separates external ear from the middle ear.
→ Eustachian tube : Connects middle ear and pharynx.
→ Organ of Corti: Constituted of basilar membrane and sensory hair cells.
→ Chemoreceptors seen inside the mouth and tongue help us to detect taste.
→ Papillae : The projected structures seen on the surface of the tongue.