GCSE Biology (AQA)

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Adaptation to Dim Light

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Homeostasis and Response The Human Nervous System

Adaptation to Dim Light

2:06 The Eye
Spec 4.5.2.3
Previous Eye Structure Next Accommodation
  • The iris contains muscles that control the size of the pupil.
  • The pupil is a black hole that allows light into the eyeball.
  • Pupil size changes through muscle contraction and relaxation.
  • The size of the pupil determines the amount of light let in.
  • Large pupils let in more light, but too much light can damage the retina.
  • The retina contains light receptors and is located at the back of the eye.
  • Pupil size adjusts to different light levels: smaller in bright light and larger in low light.
  • The adjustment of pupil size is a reflex and cannot be controlled voluntarily.
  • The iris reflex can be tested by covering one eye, which causes both pupils to dilate in response to perceived darkness.
  • This reflex test can help identify issues with the nervous system.
  • Medical professionals use light exposure to test pupil response during examinations.

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