Biology Notes

Edusmart Study Centre

Biology Notes

Class 10

1. How are our eyes protected? • Eyes are situated in the eye-socket of the skull • Eyelids with eyelash protect from dust and other particles • Tears keep eyes wet , washes away the dust particles and prevent infection • The conjunctiva covers the front portion of the eye except cornea 2. Which are the 3 layers of human eye? • Sclera –The outermost, strong layer, that gives shape. Its transparent anterior portion is the cornea. • Choroid - Middle layer of blood capillaries, which supply nutrients and oxygen. Its anterior dark screen with pupil is the iris. A convex lens is placed behind the iris. • Retina- The innermost layer on which, the image forms. The optic nerve starts from the retina. 3. The fluids filled in the chambers of eye ? • Aqueous humour – A watery fluid seen in the aqueous chamber [between cornea and lens] oozes from the blood. This fluid supplies nutrients and oxygen to cornea and lens. • Vitreous humour - A jelly like fluid filled with in the vitreous chamber [between lens and retina], helps to maintain the shape of eyeball. 4. Differentiate between blind spot and yellow spot. Blind spot is a part of retina from where the optic nerve begins. No photoreceptors at this spot, hence no vision. Yellow spot is the point of highest vision in the retina, where more cone cells seen. Images form in and around the yellow spot. 5. How can our lens adjust its focal length according to the distance from objects? [ How is power of accommodation possible?] When we look at a distant object, the ciliary muscles are in a relaxed position so as to keep the ligaments tight. Therefore the curvature of lens decreases to fix the image on retina. When we look at a near object, the ciliary muscles contract to loosen the ligaments. When ligaments relax, the curvature of lens increases naturally ,to focus the image on retina. 6. Differentiate Rod cells and Cone cells. ROD CELLS CONE CELLS • Receptor region is rod shaped Receptor region is cone shaped • Contain the pigment rhodopsin Contain the pigment photopsin • Stimulated by dim light Stimulated by intense light • Help vision in dim light Help for coloured vision Rod cells and Cone cells are modified nerve cells. Under dim light, rhodopsin dissociates to form retinal and opsin to produce impulses from rod cells. Under intense light, photopsin dissociates to form retinal and opsin to produce impulses fromcone cells.

7. Experience of vision Light rays from the object cornea Aqueous humour (pupil) lens vitreous humour image on retina stimulation in the photo receptors dissociation of rhodopsin/photopsin impulses optic nerve coordination of images by cerebrum[binocular vision] perfect vision

8. Different kinds of nerves ? • Sensory nerves [ carries impulses from sense organs to the brain and spinal cord] • Motor nerves [ carries impulses from brain and spinal cord to different organs] • Mixed nerves [nerves composed of both sensory and motor fibres]

9. The protective covering of nerve fibres (axons) ? Mention its function. Myelin sheath. To provide nutrients, function as an insulator and protects the nerve fibre, increases the speed of impulse transmission and gives white appearance ('white matter').

10. What is impulse? How are they form in nerve receptors ? Impulses are electro-chemical messages flowing through nerves. An impulse is created by the variation in the electrical equilibrium existing on either side of the plasma membrane of the receptor cells, due to certain stimulus.

11. Draw the flow chart for transmission of impulse Impulse due to stimulus dendrites dendrons cyton axon axonites synaptic knob secretion of neurotransmitter to the synaptic cleft adjacent dendrites