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Coordination in animals

Accommodation
Activity 2.7:
Task 2.13
Investigating the control of the intensity Search from the library and internet
of light entering the eye sources for animations about eye
FOR ONLINE READING ONLY
Materials accommodation and pupil reflex. Watch
Source of light and a mirror the videos and with the aid of relevant
diagrams write short notes about your
Procedure observation.
1. Work in pairs. Examine the pupil of
your partner’s eye in dim light. This is the ability of the eye to adjust the

2. Shine the light in the eye and note structure of the lens in order to focus the
the effect. image on the retina. Accomodation involves

3. Look at your right eye in a mirror. two processes namely; reflex adjustment
Cover your left eye by hand for one of the size of the pupil and refraction of
minute remove the hand and observe light rays. When the eye focuses on a
in a mirror. nearby object, the divergent light rays

Questions are refracted by cornea, ciliary muscles
contract while suspensory ligaments relax,
1. Explain the changes in pupil size in the lens becomes more convex (fatter) and
each case. light rays is focused on retina as shown in

2. What does step 3 tell you about the Figure 2.21(a). When the eye focuses on
mechanism controlling pupil size in distant objects, parallel rays are refracted
both eyes? by the cornea, ciliary muscles relax while

Precaution: The activity should suspensory ligaments contract, lens become
be done in moderate light to avoid less convex (thinner) and light rays are
negative side effects of light. focused on the retina as shown in Figure
2.21(b).

Diverging rays from
nearby object Loose ligament

Nearby object
Image

Thick eye lens

Ciliary muscle contract
(a)

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BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 50 KAMISHNA 23/10/2025 11:52:38

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