B5 The Eye

Question 1

The tissues in the eye are all adapted for their functions.

Names the parts of the eye 8

Answer 1

Cornea
Iris
Pupil
Lens
Retina
Ciliary muscles
Suspensory ligaments
Optic nerve

Question 2

See p83 for diagram of the eye

Answer 2

.

Question 3

What and where is the cornea found?

Answer 3

The cornea is the transparent outer layer found at the front of the eye.

Question 4

What does the cornea do?

Answer 4

It refracts (bends) light into the eye.

Question 5

What does the iris do?

Answer 5

The iris contains muscles that allow it to control the diameter of the pupil and therefore how much light enters the eye.

Question 6

What is the pupil?

Answer 6

The hole in the middle of the eye. It allows light to enter the eye and is controlled by the muscles in the iris.

Question 7

What does the lens do?

Answer 7

Refracts light, focusing it onto the retina.

Question 8

What does the retina contain?

Answer 8

Receptor cells sensitive to light.

Question 9

What is the shape of the lens controlled by?

Answer 9

Ciliary muscles and suspensory ligaments.

Question 10

What does the optic nerve do?

Answer 10

It carries impulses from the receptors on the retina to the brain.

Question 11

Why does the iris reflex adjust for bright light?

Answer 11

To stop very bright light damaging the retina.

Question 12

How does the iris reflex work in bright light?

Answer 12

When light receptors in the eye detect very bright light, a reflex is triggered that makes the pupil smaller.

The circular muscles in the iris contract and the radial muscles relax.

This reduces the amount of light that can enter the eye.

Question 13

How does the iris reflex work in dim light?

Answer 13

The radial muscles contract and the circular muscles relax, which makes the pupil wider.

Allowing more light to enter the eye.

Question 14

How can you investigate these reflex actions?

Answer 14

By dimming the lights and timing how long it takes for you pupils (or a friends) to widen.

When you turn up the lights, you can see the pupils return to normal as the circular muscles in the iris contract.

Question 15

See diagram on p83 for how iris reflex works.

Answer 15

.

Question 16

What is accommodation?

Answer 16

The eye focusing light on the retina by changing the shape of the lens.

Question 17

How does the eye look at near objects?

Answer 17

The ciliary muscles contract, which slackens the suspensory ligaments.

The lens becomes fat (more curved).

This increases the amount by which it refracts light.

Question 18

How does the eye look at distant objects?

Answer 18

The ciliary muscles relax, which allows the suspensory ligaments to pull tight.

This makes the lens go thin (less curved).

So it refracts light by a smaller amount.

Question 19

See p 83 for how focusing reflex works.

Answer 19

.

Question 20

What makes a person short or long sighted?

Answer 20

If the lens cannot refract the light by the right amount (so that it converges on the retina) the person will be short or long sighted.

Question 21

Explain how the eye focuses on an object that’s close to it. (4 marks)

Answer 21

The Ciliary muscles contract (1 mark), which slackens the suspensory ligaments (1 mark). The lens becomes fat/more curved (1 mark). This increases the amount by which it refracts light, so the image is focused on the retina (1 mark)