SB2h

Question 1

What are all the parts of the eye and what are their functions? (8)

Answer 1

1. Cornea: clear, colourless covering - focuses light, for protection
2. Pupil: dark part of the eye - hole in iris to allow light to enter
3. Iris: coloured part of the eye - muscles in the iris can dilate or constrict the pupil, changing its size to allow more or less light
4. Lens: for focusing close or far
5. Ciliary muscles: alter shape of lens
6. Optic nerve: contains bundles of neurones
7. Retina: layers of rods and cones (receptor cells)
8. Blood vessels: bring blood to eye

Check Biology book page 44.

Question 2

What do the rods and cones in the retina do?

Answer 2

Rods: Receptor cells that detect difference in light intensity, not colour.

Cones: Receptor cells that are sensitive to the colour of light. There are cones used for detecting red, blue and green colours.

Question 3

How does information from cones reach the brain?

Answer 3

Cones generate impulses in sensory neurones which lead into the brain through the optic nerve. The information from all the cones is processed into full colour vision at the back of the cerebral hemispheres.

Question 4

Why is our colour vision poor in dim light?

Answer 4

Rods are more sensitive than cones and work well in very dim light, while cones only work in bright light.

Question 5

What is short-sightedness and how can we correct it?

Answer 5

Short-sightedness is when distant objects appear blurred. This is either because the eyeball is too long or the cornea is too curved and bends the rays more than it should, so the image is focused in front of the retina.

Short-sightedness can be corrected by a diverging (concave) lens to spread out rays before reaching the eye.

Check Biology book page 45.

Question 6

What is long-sightedness and how can we correct it?

Answer 6

Long-sightedness is when close objects appear blurred. This is either because the eyeball is too short or the cornea is not curved enough and does not bend the rays enough, so the image is focused behind the retina.

Long-sightedness can be corrected by a converging (convex) lens to bend rays before reaching the eye.

Check Biology book page 45.

Question 7

What is a cataract?

Answer 7

Protein build-up inside the lens which makes it cloudy.

Question 8

How can we fix a lens with a cataract?

Answer 8

Full vision can be restored by replacing the clouded lens with a plastic one.

Question 9

How do people become colour-blind? Is there a cure?

Answer 9

They have some cones that do not work properly. Colour-blindness cannot be corrected.