2.11 The eye

Question 1

cornea

Answer 1

a curved transparent disc at the front of the eye
does most of the focusing, refracting

Question 2

pupil

Answer 2

a circular opening whose size is controlled by the iris

Question 3

iris

Answer 3

a ring of muscles with a hole in the middle
the iris controls how much light enters the eye

Question 4

lens

Answer 4

This is soft, flexible and transparent
Its shape can be changes to fine tune the focusing of light onto the retina

Question 5

ciliary muscles

Answer 5

a ring of muscle at the edge of the eye which circles the lens
when it contracts the lens gets fatter
when it relaxes the lens gets thinner

Question 6

suspensory ligament

Answer 6

strong fibres which attach the lens to the ciliary muscle

Question 7

retina

Answer 7

contains light sensitive cells called rods and cones

Question 8

optic nerve

Answer 8

consists of many neurones which carry impulses from the retina to the brain

Question 9

fovea

Answer 9

the region of the retina with the greatest number of cones

Question 10

conjunctiva

Answer 10

a mucous membrane that covers the eye to prevent infection

Question 11

What happens to the iris in dim light?

Answer 11

radial muscles contract
circular muscles relax
iris narrower
pupil dilates

Question 12

What happens to the iris in bright light?

Answer 12

radial muscles relax
circular muscles contract
iris wider
pupil constricts

Question 13

What is light intensity detected by?

Answer 13

retina

Question 14

What are the effectors in the iris reflex?

Answer 14

muscles in the iris
circular muscles
radial muscles

Question 15

What is the name of the changes in the eye that take place to allow us to see objects at different distances?

Answer 15

accommodation

Question 16

What happens when focusing on a far away object?

Answer 16

Light rays entering eye are almost parallel when they reach the cornea so the lens
does not need to refract them much to focus light onto the retina

Relaxing ciliary muscles
suspensory ligaments are pulled tight
Lens is pulled thin and has a less convex shape
Therefore there is less refraction of light.

Question 17

What happens when focusing on a object close up?

Answer 17

Light rays entering eye are spreading out (diverging) so the lens needs to refract the
light to ensure it focusses onto the retina

Contracting the ciliary muscles
suspensory ligaments slacken
Lens is not stretched out so becomes thicker with more is more convex shape, short and fat
Therefore there is more refraction of light