eye

Question 1

cornea, conjunctiva, eyelid, pupil

Answer 1

-dome shape transparent layer that is able to refract light rays into eyes
-mucus membrane covering sclera that secretes mucus to keep the front of eye moist
-protects the cornea from excessive damage, closing eye to stop light, blinking to spread tears so dust can be removed
-hole in the centre of the iris that allows light to enter eye

Question 2

sclera, lens, ciliary body, suspensory ligament, choroid

Answer 2

-tough white outer layer covering of eyeball that continuous to cornea
-transparent circular biconvex structure that changes shape and thickness to refract light onto retina
-contains ciliary muscles that control thickness and curvature of lens
-attaches the edge of lens to ciliary body
-black pigmented middle layer that prevents the internal reflection of light, contains blood vessels that bring oxygen and nutrients to eyeball and remove metabolic waste

Question 3

vitreous chamber, aqueous chamber, blind spot, optic nerve, fovea, retina

Answer 3

-space behind lens filled with vitreous humour, transparent jelly like substance that keeps the eyeball firm and refracts light onto retina
-space between cornea and lens, contains aqueous humour, transparent water like fluid that keeps the front of the eye firm and refracts light into pupil
-region where optic nerve leaves the eye, no rods and cones, not sensitive to light
-nerve that transmit nerve impulses to brain upon stimulation of photoreceptors
-small yellow depression where images are focused that contains cones but no rods, allows person to see in detail in bright light
-contains photoreceptors consisting of cones and rods

Question 4

how does the iris control the amount of light entering our eyes

Answer 4

-in bright light, circular muscles contract while radial muscles relax, constricting pupil, less light enters eyes

Question 5

describe pupil reflex

Answer 5

-stimulus, change in light intensity
-receptors within the retina causes nerve impulses to be transmitted via sensory neurone in the optic nerve to brain, to motor neurone, effector in iris

Question 6

focusing on distant object

Answer 6

-ciliary muscles relax, pulling on the suspensory ligaments which become taut pulling on the edge of the lens
-lens becomes thinner and less biconvex, increasing focal length
-light rays are focused on the retina, stimulating photoreceptors
-nerve impulses transmitted to the brain which is interpreted by the brain that allows the person to see the object

Question 7

describe rods and cones

Answer 7

-rods are more sensitive to light than cones
-enable us to see in dim light, only in black and white
-contains visual purple that gets bleached when exposed to bright light, prevents impulses sent to brain, cannot be seen in bright light time taken for it to reform in order to see in the dark, thats why we leave and bright room and enter dimly lit room cannot see anything for some time, vitamin a defiencty suffer from night blindness