1. Eye

Question 1

Eyelids

Function

Answer 1

Function:

• Protect the cornea from mechanical damage
• Prevent excess light from entering the eye and damaging the retina by squinting
• Helps spread tears over the cornea and conjunctiva
• Wipes dust particles off the cornea by blinking

Question 2

Eyelashes

Function

Answer 2

Function:

• Help to shield eye from dust particles

Question 3

Tear Glands

Function

Answer 3

Function:

• Secrete tears to wash away dust particles
• Keep cornea moist for atmospheric oxygen to dissolve so that oxygen can diffuse into the cornea
• Lubricate the conjunctiva, helping to reduce friction when the eyelids move

Question 4

Conjunctiva

Structure & Function

Answer 4

Structure:

• Thin, transparent membrane covering the sclera

Function:

• Secretes mucus to keep the front of the eyeball moist

Question 5

Sclera

Structure & Function

Answer 5

Structure:

• Tough, white outer covering of the eyeball
• Continuous with cornea

Function:

• Protects eyeball from mechanical damage

Question 6

Choroid

Structure & Function

Answer 6

Structure:

• Middle layer of the eyeball between the sclera and retina

Function:

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

Question 7

Retina

Structure & Function

Answer 7

Structure:

• The intermost layer of the eyeball
• Contains photoreceptors (rods and cones)

Function:

• Light-sensitive layer where images are formed

Question 8

Cornea

Structure & Function

Answer 8

Structure:

• Transparent layer in front of eye (beneath the conjunctiva)
• Continuous with sclera

Function:

• Refracts light towards lens

Question 9

Iris

Structure & Function

Answer 9

Structure:

• Consists of 2 sets of involuntary muscles, the circular muscles and radial muscles
• Surrounds the pupil
• In front of the lens

Function:

• Adjusts the amount of light entering the eye by changing the size of the pupil

Question 10

Pupil

Structure & Function

Answer 10

Structure:

• Hole in the centre of iris
• Appears black because the choroid is visible through it

Function:

• Allows light to enter the eye

Question 11

Lens

Structure & Function

Answer 11

Structure:

• Transparent, biconvex, elastic crystalline body

Function:

• Changes curvature or thickness to refract light onto the retina

Question 12

Suspensory Ligaments

Structure & Function

Answer 12

Structure:

• Connective tissue
• Attached to the edge of the lens and the ciliary body

Function:

• Transfer the effect of the ciliary muscles to the lens

Question 13

Ciliary Body

Structure & Function

Answer 13

Structure:

• Consists of ciliary muscles

Function:

• Controls the curvature or thickness of the lens

Question 14

Aqueous Humour

Structure & Function

Answer 14

Structure:

• Transparent, watery fluid
• In front of the lens

Function:

• Refracts light onto the lens
• Serves as a medium for the diffusion of oxygen and nutrients
• Keeps eyeball firm

Question 15

Vitreous Humour

Structure & Function

Answer 15

Structure:

• Transparent, jelly-like fluid

Function:

• Refracts light onto retina
• Keeps the eyeball firm

Question 16

Fovea (Yellow Spot)

Structure & Function

Answer 16

Structure:

• Greatest concentration of cones but no rods

Function:

• Part of the retina that best resolves images, where images are focused onto it
• Gives detailed colour vision in bright light

Question 17

Blind spot

Structure & Function

Answer 17

Structure:

• Found over the optic nerve
• No photoreceptors

Function:

• Area on the retina where neurones leave the eye

Question 18

Optic Nerve

Structure & Function

Answer 18

Structure:

• Composed of sensory neurones

Function:

• Trasmists nerve impulses from photoreceptors to brain

Question 19

Cones

Properties

Answer 19

• Cones enable us to see colours in bright light
• There are 3 types of cones: red, green and blue cones
• Each cone contains different pigments which absorbs light of different wavelengths
• Most concentrated at the yellow spot/fovea
• Cones do not work well in dim light

Question 20

Rods

Properties

Answer 20

• Rods are more sensitive to light than cones
• Rods enable us to see in dim light, but only in black and white
• Contain the light sensitive pigment, visual purple (rhodopsin)
• Rods lie outside the fovea in the more peripheral parts of the retina

Question 21

Rhodopsin (Visual Purple)

Properties

Answer 21

• Found in rods
• Visual purple is bleached when the eye is exposed to bright light, It takes a while for visual purple to reform when you walk from a bright place to a dimly lit room
• Requires Vitamin A for the formation of visual purple

Question 22

Accommodation

Definition

Answer 22

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

Accomodation is achieved by the following structures:

• Ciliary muscles to alter the shape of the lens
• Suspensory ligaments which transfer the effect of the ciliary muscles to the lens
• Elasticity of the lens

Question 23

Describe the changes in the eye when focusing on a near object

Process

Answer 23

1. Ciliary muscles contract, reducing the pull on the suspensory ligaments
2. Suspensory ligaments slacken
3. Lens becomes thicker and more convex
4. Focal length decreases
5. Light rays from the near object are brought to focus on the retina
6. Photoreceptors are stimulated. Nerve impulses are produced and transmitted to the brain via the optic nerve.

Question 24

Describe the changes in the eye when focusing on a distant object

Process

Answer 24

1. Ciliary muscles relax, pulling on the suspensory ligaments
2. Suspensory ligaments become taut
3. Lens becomes thinner and longer
4. Focal length increases
5. Light rays from the distant object are brought to focus on the retina
6. Photoreceptors are stimulated. Nerve impulses are produced and transmitted to the brain via the optic nerve.

Question 25

Simple reflexes in the Eye | Function + Types

Answer 25

Simple reflex actions have protective functions. 1. Pupil reflex - strong light causes pupils to become smaller to protect retina 2. Blink reflex - any object seen coming towards the eyes cause the eyelids to close 3. Tearing reflex - dust sensed by the conjunctiva causes an increase in tear flow to wash it away *These are cranial reflex actions, where the reflex centre is in the brain.*

Question 26

Describe pupil reflex in bright light | Process

Answer 26

1. Photoreceptors in the retina detect an increase in the light intensity. 2. Nerve impulses are sent along the sensory neurone in the optic nerve to the brain. 3. The brain returns nerve impulses along the motor neurone to the radial and circular muscles of the iris. 4. The radial iris muscles relax while the circular iris muscles contract. 5. The diameter of the pupil decreases, allowing less light to enter the eye.

Question 27

Describe pupil reflex in dim light | Process

Answer 27

1. Photoreceptors in the retina detect a decrease in the light intensity. 2. Nerve impulses are sent along the sensory neurone in the optic nerve to the brain. 3. The brain returns nerve impulses along the motor neurone to the radial and circular muscles of the iris. 4. The radial iris muscles contract while the circular iris muscles relax. 5. The diameter of the pupil increases, allowing more light to enter the eye.