B9.2 : Eyes

Question 1

Parts of the eye

Answer 1

1. Cornea
2. Fovea
3. lens
4. Iris
5. Retina
6. Optic nerve

Question 2

Cornea

Answer 2

The transparent frontal part of the eye that refracts light.

Question 3

Fovea

Answer 3

A small pit in the retina that provides the clearest vision of all.

Question 4

Lens

Answer 4

Focuses light onto the retina.

Question 5

Iris

Answer 5

Controls pupil diameter and, therefore, the quantity of light reaching the retina.

Question 6

Retina

Answer 6

Full of receptor cells, which are sensitive to both the brightness (light intensity) and the colour of light.

Question 7

Optic Nerve

Answer 7

1. Transmits visual information (as electrical impulses) from the retina to the brain.
2. At the point where the optic nerve and retina meet, there is a ‘blind spot’ where no light can be detected.

Question 8

Accommodation

Answer 8

Accommodation is the process of changing lens shape in order to focus on an object as its distance from the eye changes.

Question 9

Adapting to dim light

Answer 9

1. In dim light, the iris increases the pupil size (dilation) to allow as much light as possible to reach the retina.
2. Example of reflex arc
3. The iris controls how our eyes adapt to different light levels by controlling the size of the pupil

Question 10

Adapting to bright light

Answer 10

1. In bright light, the iris decreases the pupil size (contraction) to reduce the amount of light that reaches the retina.
2. Example of reflex arc
3. The iris controls how our eyes adapt to different light levels by controlling the size of the pupil

Question 11

Controlling pupil size in light

Answer 11

1. Control of pupil size is achieved by circular and radial muscles in the iris working antagonistically (opposite to one another):
2. Circular muscles contract to make the iris larger (smaller pupil).
3. Radial muscles contract to make the iris smaller (larger pupil).

Question 12

Receptor cells in the retina

Answer 12

1. Rod cells

2. Cone cells

Question 13

Rod cells

Answer 13

1. type of receptor cells in the retina
2. Detect visual information without colour.
3. Essential in low light conditions (night vision).
4. Not present in fovea.
5. High density across all of retina.

Question 14

cone cells

Answer 14

1. type of receptor cells in the retina
2. Detect colour.
3. Three different types for detecting wavelengths of light in greens, reds and blues.
4. Present in low density across all of the retina.
5. Densely packed in the fovea.

Question 15

Focusing on a close object

Answer 15

1. ciliary muscle contract
2. suspensory ligaments loosen
3. lenses thicken and rounden, causing a significant refraction of light rays

Question 16

Focusing on a distant object

Answer 16

1. relaxation of ciliary muscle
2. suspensory ligaments tighten
3. lenses become flatter and thinner resulting in only minor refraction (bending) of light rays