Describe how the mammalian eye is structurally adapted to its function.

K.C.S.E Biology Q & A - MODEL 2017PP2QN08

Describe how the mammalian eye is structurally adapted to its function.

answers

• Has the eyelid; which protects the cornea from mechanical/physical/chemical damage;
•  Eye lid; protects the eye from bright light by reflex action;
•  Sclera/Sclerotic layer;  which contains (inelastic) collagen fibres which protects/maintains shape of the eyeball;
•  Cornea; transparent to allow light pass through/has convex shape to refract light towards the retina;
•  Conjunctiva (thin) epithelium for protection of cornea/has goblet cells for secretion of mucus for lubrication/ transparent to allow light pass through;
•  Choroid/choroid layer;  rich in blood vessels/highly vascularized, supplying the retina with nutrients/oxygen/remove metabolic wastes/covered with (black) pigment cells to prevent reflection of light within the eye;
•  Ciliary muscles; have (contractile) muscles that contract/relax to alter the shape of the lens during accommodation;
•  Lens; transparent to allow light pass through/elastic to allow adjustment of the shape of lens/ biconvex to refract light/focus light onto retina;
•  Iris; — has radial and circular muscles to alter diameter/size of the pupil, hence controlling the amount of light entering the eye/contain pigments that absorb light and stop it getting through to the retina;
•  Vitreous homour; — clear/transparent to allow light pass through/is a fluid that refracts light rays onto the retinal maintain shape of the eye balls supports the eye;
•  Retina; contains cones, rods/photoreceptors to perceive light;
•  Optic nerve;- has sensory neurons/nerve cells that transmit impulses to the brain;
•  Fovea (centralis); — (most sensitive part of retina) contains numerous/high concentration of cones for visual acuity/accurate vision;
•  Pupil ; a hole/an aperture/opening in the iris, lets in light;
•  Suspensory ligaments;-are fibrous/inelastic fibres that hold lens in position;
•  Aqueous humour  is clear/transparent to allow light to pass through/is a fluid/liquid (exerting hydrostatic pressure) to maintain the shape of the eyeball/refract light rays onto the lens/cornea/contain glucose for nourishment;
•  Blind spot  a point where the optic nerve leaves the eye to the brain/passage of blood vessels since has no photoreceptors;