15: Detecting the Environment - Problems

Question 1

The photomicrograph below shows a parts of the longitudinal section of the wall of the human eyeball. Layer P is sensitive to light and layer Q contains many capillaries.
Identify cell X and support your answer with one observable feature from the photomicrograph. (2)

Answer 1

Cone cell,
because cell X is in cone shape.

Question 2

The photomicrograph below shows a parts of the longitudinal section of the wall of the human eyeball. Layer P is sensitive to light and layer Q contains many capillaries.
Name layer Q and state two functions of it. (3)

Answer 2

Choroid
It contains a black pigment that absorbs light. This reduces reflection of light within the eye and thus helps form a sharp image on the retina.
It is rich in capillaries which supply nutrients and oxygen to the retina and sclera and remove wastes from them.

Question 3

The photomicrograph below shows a parts of the longitudinal section of the wall of the human eyeball. Layer P is sensitive to light and layer Q contains many capillaries.
Explain why detachment of layer P from Q may result in vision loss. (2)

Answer 3

If layer P (retina) is detached from layer Q (choroid), some photoreceptors in the retina cannot obtain enough oxygen and nutrients from the capillaries in layer Q.
The photoreceptors die and can no longer generate nerve impulses when light falls on them. This results in vision loss.

Question 4

The diagram below shows a section of the human eye.
Describe how the size of part Y changed when a person walks out from a dark room into bright light, and explain the importance of the change. (3)

Answer 4

When a person walks out from a dark room into bright light, the circular muscles of the iris contract and the radial muscles relax.
As a result, part Y (pupil) constricts.
This prevents the photoreceptors in the retina from being damaged by bright light.

Question 5

Patients of presbyopia cannot focus clearly on near objects. Suggest why ageing of structure X may be a cause of presbyopia. (3)

Answer 5

Aged/weakened structure X (ciliary muscle) is not able to generate enough force for contraction when focusing on near objects.
The tension in the suspensory ligament remains at a point which is higher than the required tension.
Therefore, the lens cannot become thick enough to focus light rays from a near object onto the retina.

Question 6

A boy was waiting for a bus at a bus stop. He saw a bus coming. The photographs below how what he saw when the bus was 15m away from the bus stop and at the bus stop.
Describe and explain the changes which occurred in the boy’s eyes when the bus approaches the bus stop. (3)

Answer 6

When the bus was approaching the bus stop, the degree of contraction of the ciliary muscles in the boy’s eyes increased.
The tension in the suspensory ligaments decreases and the suspensory ligaments become more and more slackened.
The lens becomes thicker and thicker in attempt to focus more and more light rays from the approaching bus onto the retina.