Ch 15 Detecting the environment

Question 1

Process of seeing

Answer 1

1. Light rays from an object enter the eye. They are refracted and focused onto the retina by the cornea, lens, aqueous humour and vitreous humour.
2. A real and inverted image is formed on the retina
3. The photoreceptors on the retina are stimulated by the light. They generate nerve impulses. The nerve impulses travel along the optic nerve to the visual centre in the cerebrum of the brain
4. The visual centre interprets the nerve impulses as an upright image of the object

Question 2

Distribution of photoreceptors on retina

Answer 2

Yellow spot: concentrated with cone cells, no rod cells
Blind spot: no rod cells and cone cells

Question 3

Seeing in bright light

Answer 3

1. Circular muscles contract.
2. Radial muscles relax.
3. The pupil constricts.
4. Less light is allowed to enter the eye.

• prevents the photoreceptors in the retina from being damaged by bright light

Question 4

Seeing in dim light

Answer 4

1. Radial muscles contract
2. Circular muscles relax
3. The pupil dilates
4. More light is allowed to enter the eye

• allows the photoreceptors to be stimulated to generate nerve impulses so that a clear image can be seen

Question 5

Focusing on near objects

Answer 5

1. Ciliary muscles contract
2. The tension in the suspensory ligaments is reduced. The suspensory ligaments become slackened
3. The lens becomes thicker (more convex) due to its elasticity. The thicker lens refracts light more so that the light rays from the near object are focused onto the retina

Question 6

Focusing on distant objects

Answer 6

1. Ciliary muscles relax
2. The tension in the suspensory ligaments is increased. The suspensory ligaments become tightened
3. The lens is pulled and becomes thinner (less convex). The thinner lens refracts light less so that light rays from the distant object are focused onto the retina

Question 7

Interpreting a graph of changes in curvature of the lens over a period of time

Answer 7

1. The lens remains thick. The person is looking at a stationary near object
2. The lens becomes less convex. The object is moving away from the person
3. The lens becomes more convex. The object is moving towards the person.
4. The lens remains thin. The person is looking at a stationary distant object.

Question 8

Process of hearing

Answer 8

1. Sound waves collected by the pinna are directed to the eardrum
2. Sound waves cause the eardrum to vibrate
3. The ear bones amplify and transmit the vibrations to the oval window
4. The oval window vibrates, causing the perilymph in the cochlea to vibrate
5. Vibrations in the perilymph are transmitted to the endolymph of the cochlea
6. The sensory hair cells in the central canal of the cochlea are stimulated. They generate nerve impulses. The nerve impulses travel along the auditory nerve to the auditory centre in the cerebrum of the brain to produce the sensation of hearing
7. Vibrations in the perilymph are transmitted to the round window. The round window releases the fluid pressure of perilymph into the air in the middle ear.

Question 9

Studies on phototropism

Answer 9

Mica plate: stops lateral transport of auxins
Agar block: allows auxins to diffuse into the agar block

Question 10

Using coleoptiles to study phototropism

Answer 10

1. Response to light is easy to observe
2. Grow rapidly
3. Small and easy to handle, easy to be grown in large numbers

Question 11

Phototropism - Light from all directions

Answer 11

1. Auxins are produced at the shoot tip and root tip
2. When light comes from all directions, the auxins in the region of elongation of the shoot and that of the root are distributed evenly
3. The shoot grows straight upwards while the root grows straight downwards

Question 12

Phototropism -Unilateral light

Answer 12

1. Auxins are produced at the shoot tip and root tip
2. Under unilateral light, auxins move from the illuminated side to the shaded side of the shoot and that of the root
3. In the shoot, the high auxin concentration on the shaded side promotes cell elongation there. The shoot bends towards the light.
   In the root, the high auxin concentration on the shaded side inhibits growth there. The root bends away from the light.

Question 13

Why a coloured object is perceived as being more colourful in bright light than dim light?

Answer 13

• Rod cells cannot distinguish colours
• Cone cells are responsible for colour vision
• Cone cells are only stimulated in bright light
• Larger number of cone cells are stimulated in bright light than dim light