Pupil Reflex

These year we are officially sitting for the IGCSE Biology and so we have to keep learning more and more about the subject.

Continuing with Coordination from Chapter 13 of the Coursebook, we analyzed in depth the eye organ as a receptor organ. In today’s class we learned how the Pupil Reflex works. In order to do that, we used the flash of our cellphones to focus CAREFULLY on a companions eye and we wrote down our observations.

-With bright light, the pupil constricted while the size of the iris stayed the same.

-With no/dim light, the pupil dilated while the iris was not affected.

Search for a video in which the pupil reflex is explained.

Complete the following diagram:

Bright/dim light

Circular & Radial muscles of the iris


What is the effect?

In the case that the eye is exposed to bright light the circular muscles contract while the radial muscles relax. This way the pupil constricts so little light gets into the retina, and the cones there are not damaged.

In the case the the eye is exposed to dim light, the radial muscles are the ones that contract while the circular muscles relax. This way the pupil dilates/widens allowing as much light as possible into the retina, where rods can detect it.

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