Eye

Question 1

Describe sclera

Answer 1

Tough, white outer covering of eyeball
Protects eyeball from mechanical damage

Question 2

Describe choroid

Answer 2

Contains black pigments to prevent internal reflection of light
Contains blood vessels that bring oxygen and nutrients to eyeball and remove metabolic waste products

Question 3

Describe cornea

Answer 3

Transparent layer in front of eye, continuous with sclera

Question 4

Describe iris

Answer 4

Consists of two sets of involuntary muscles, the circular muscles and radial muscles. Surrounds pupil and is in front of lens

Question 5

Describe pupil

Answer 5

Hole in the centre of iris, appears black because choroid is visible through it
Allows light to enter the eye

Question 6

Describe lens

Answer 6

Transparent, biconvex, elastic crystalline body
Changes curvature or thickness to refract light onto the retina

Question 7

Describe suspensory ligament

Answer 7

Connective tissue
Attach to edge of lens to ciliary body
Transfer effect of ciliary muscle to the lens

Question 8

Describe ciliary body

Answer 8

Consists of ciliary muscles
Control curvature or thickness of lens

Question 9

Describe aqueous humour

Answer 9

Transparent, watery fluid
Refracts light onto lens and keeps eyeball firm
Serves as a medium for the diffusion of oxygen and nutrients

Question 10

Describe vitreous humour

Answer 10

Transparent jelly-like fluid
Refract light onto retina and keeps eyeball firm

Question 11

Describe fovea

Answer 11

Greatest concentration of cones but no rods.
Part of retina that best resolves images where images are focused onto it
Gives detailed colour version in bright light

Question 12

Describe blind spot

Answer 12

Found over the optic nerve as it has no photoreceptors.
An area on retina where neurones leave the eye

Question 13

Describe optic nerve

Answer 13

Composed of sensory neurones
Transmits nerve impulses from photoreceptors to brain

Question 14

Describe how cones work

Answer 14

They enable us to see colours in bright light
Each cone contains different pigments which absorbs light of different wavelengths
Most concentrated at fovea
Cones do not work well in dim light

Question 15

Describe how rods work

Answer 15

Rods are more sensitive to light
Enable us to see in dim light but only in black or white
Contain light sensitive pigment, visual purple(rhodopsin)
Lies out side of the fovea in the more peripheral parts of retina

Question 16

Why does the pupil seem red upon walking out of a dark room into a brightly lit room

Answer 16

Visual purple is bleached when the eye is exposed to bright light. It takes a while for visual purple to reform when walking back into the dimly lit room.

Question 17

Why does a vitamin A deficient diet lead to inability to see in dimly lit areas

Answer 17

Vitamin A is required for formation of visual purple, the light sensitive pigment of our eyes

Question 18

Define accomodation

Answer 18

The adjustment of lens to change curvature or thickness so that clear images at different distances are formed on the retina

Question 19

How does the eye focus on near objects

Answer 19

Ciliary muscles contract, reducing pul on suspensory ligaments. Suspensory ligaments slacken so lens become thicker and more convex, decreasing its focal length. Light rays from near object are brought to focus on retina and photoreceptors are stimulated. Nerve impulses are produced and transmitted to brain via optic nerve

Question 20

How does the eye focus on distant objects

Answer 20

Ciliary muscles relax, pulling on suspensory ligaments. Suspensory ligament becomes taut and lens become thinner and longer, increasing its focal length. Light rays from distant object are brought to focus on retina. Photoreceptors are stimulated and nerve impulses are produced and transmitted to brain via optic nerve.

Question 21

How does pupil change in size in bright light

Answer 21

Photoreceptors in retina detect increase in light intensity. Nerve impulses are sent along sensory neurone in optic nerve to brain. Brain returns impulses along motor neurone to circular and radial muscles of iris. Circular iris muscles contrat while radial iris muscles relax. Diameter of pupil decreases, allowing less light to enter

Question 22

How does pupil change size in dim light

Answer 22

Photoreceptors in retina detect decrease in light intensity. nerve impulses are sent along sensory neurone in optic nerve to brain. Brain returns impulses along motor neurone to radial and circular muscles of the iris. Radial iris muscles contract while circular iris muscles relax. Diameter of pupil increases, allowing more light to enter