Your eyes are incredible organs that are designed to capture light and allow you to see.

The pupil looks black but it’s actually a small,

round opening.

The white part of your eye is a tough, outer covering

called the sclera.

The round coloured part of your eye is called the iris.

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1

If the light around you is very bright, your pupils get smaller to protect your eyes from too much light entering them.

How Does Light Affect Pupil Size?

If there is not enough light, your pupils dilate, or get bigger, to let in as much light as possible.

A pupil that has got smaller A dilated, or enlarged, pupil

Tiny muscles in your irises make your pupils get bigger or smaller.

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2

Try this investigation to discover how your pupils change size in different lights.

Remember! Never directly

shine a light into your eyes – you could damage

them!

Equipment: • A mirror • A timer

Method: 1. Look in a mirror at your eyes and observe the size of your pupils. Record your

observations. What do you think will happen if the amount of light in the room changes? Write down your predictions.

Predictions:I predict that when the lights are on my pupils

I predict that when the room is dim/dark my pupils

I predict that when the lights come back on, my pupils

2. Close the curtains or blinds in the room. Lower or turn off the lights so the room is dim.

3. After 30 seconds in your dim room, turn the lights back on. Observe your pupils in the mirror again. Have they changed? Did they change as the lights came back on? Note down or draw your observations.

4. Repeat this process of darkening the room and turning the lights back on, observing and recording how your pupils respond.

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Results:

Conclusion

My results show that

Did your predictions match the results?

Do you have any further questions about how your pupils work? How could you investigate this?

3

How light/dark the room is Observation of your pupils

Lights on

Lights back on after 30 seconds in a dark/dim room

Lights on (repeated)

Lights back on after 30 seconds in a dark/dim room (repeated)