Topic 2c: The eye - PAPER ONE

Question 1

Cornea

Answer 1

Refracts light into the eye

Question 2

Iris

Answer 2

Controls how much light enters the pupil (made up of circular and radial muscles)

Question 3

Lens

Answer 3

Changes shape to refract light, focusing it onto the retina

Question 4

Retina

Answer 4

Light sensitive and covered in receptor cells called rods and cones that detect light

Question 5

Rods

Answer 5

More sensitive in dim light but can’t sense colour

Question 6

Cones

Answer 6

Sensitive to different colours but not good in dim light

Question 7

How is information sent from the eye to the brain?

Answer 7

• Information from light is converted into electrical impulses
• Optic nerve carries these impulses from the receptors to the brain

Question 8

What happens to the eye when looking at distant objects?

Answer 8

• Ciliary muscle relaxes, allowing suspensory ligaments to pull tight
• The lens is pulled to be less rounded so the light is refracted less

Question 9

What happens to the eye when looking at close objects?

Answer 9

• Ciliary muscle contracts which slackens the suspensory ligaments
• The lens is more rounded so the light is refracted more

Question 10

Explain why people are long-sighted and how to correct it

Answer 10

• Can’t focus on close objects because the lens can’t refract the light enough, so the image is focused behind the retina (and the image appears blurry)
• Fixed by using convex lenses

Question 11

Explain why people are short-sighted and how to correct it

Answer 11

• Can’t focus on distant objects because the lens refracts the light too much, so the image is focused in front of the retina (and the image appears blurry)
• Fixed by using concave lenses

Question 12

What happens to the eye in bright/dim light?

Answer 12

In bright light:
Circular muscles contract, radial muscles relax so the pupil constricts

In dim light:
Radial muscles contract, circular muscles relax so the pupil dilates

Question 13

What are cataracts?

Answer 13

• Cataract is a cloudy part on the lens causing people to have blurred vision and colours appear less vivid
• Caused by a build up of proteins
• Can be treated by replacing the faulty lens with an artificial one

Question 14

Why are people colourblind? - is there a cure?

Answer 14

• Most common form is red-green colour blindness, caused when red or green cones in the retina are not working properly
• No cure as cone cells can’t be replaced