Mammalian Sense Organs (Cambridge O Level Biology)

The eye is a sense organ that responds to light.

Fig. 1 is a diagram of a section through the human eye.

Fig. 1

Table 1 describes some of the functions of the parts of the eye.

Complete the table by:

• Naming the parts of the eye
• Using the letters on Fig. 1 to identify the parts of the eye.

Table 1

A pair of muscles in the eye work in opposition to each other to adjust the amount of light entering the pupil.

State the term that describes the action of a pair of muscles working in opposition to each other.

[1]

A different pair of muscles in the eye work in opposition to each other to view objects at different distances from the eye.

State the name of the process that allows the eye to view objects at different distances. 

A person visits an eye doctor to have an eye test. On the wall of the doctor’s room is a diagram of an eye.

[1]

As part of the eye test, the doctor shines a bright light into the eye and takes a picture. 

The picture shows layer Y and the choroid layer behind it.

[4]

When the bright light is shone into the eye there is a pupil reflex which causes the pupil to become smaller.

Explain how named parts of the eye and of the nervous system are involved in this pupil reflex.

Fig. 1 shows the path of light entering the front part of the eye of a person with normal vision, whilst looking at a close object.

Fig. 1

As people get older (typically 40+), their lenses lose flexibility and can't spring back into a round shape when looking at close objects.

Explain what effect a less flexible lens would have on the path of light. 

Explain the changes that occur in the normal human eye to focus on near and distant objects.

Fig. 2 shows the light path into the eye of a person with normal vision and into that of a person with long-sightedness. 

Sufferers of long-sightedness are not able to see nearby objects clearly e.g. when reading, although this can be corrected using glasses.

Fig. 2

Use the diagrams in Fig. 2 to explain why people with long-sightedness cannot see nearby objects clearly. 

As people age, their vision tends to deteriorate.

The majority of adults choose to wear glasses to correct their vision as shown in Fig. 3.

Fig. 3

The data in Fig. 3 was gathered from a survey of 4500 people.

Calculate the difference between the number of people needing no vision correction and the people who chose to use contact lenses.