The eye (biology only) — AQA GCSE Biology
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The eye (biology only) explained
The eye has structures whose shapes and positions suit their functions.
Read the full explanation
The cornea refracts light into the eye, the iris controls pupil diameter, and the lens fine-tunes focus onto the retina, where receptors detect light. Accommodation is the lens changing shape to focus near or distant objects. To focus a near object, the ciliary muscle contracts, suspensory ligaments slacken, and the lens becomes thicker and more curved. To focus a distant object, the ciliary muscle relaxes, ligaments tighten, and the lens becomes thinner and flatter. Adaptation to dim light occurs in the iris: the radial muscles contract and circular muscles relax, widening the pupil so more light enters the retina.
Your focus
- Relate eye structures such as cornea, iris, lens and retina to their functions.
- Describe how the eye accommodates to focus on near and distant objects.
- Explain how the iris adapts the pupil in dim light.
The eye (biology only) exam tips
Marking Points
- The cornea refracts light and the lens fine-tunes focus onto the retina.
- Accommodation is the lens changing shape to focus on near or distant objects.
- For a near object, ciliary muscle contracts, suspensory ligaments slacken, and the lens becomes thicker and more curved.
- For a distant object, ciliary muscle relaxes, suspensory ligaments tighten, and the lens becomes thinner and flatter.
- In dim light, radial muscles in the iris contract and circular muscles relax, widening the pupil.
- In bright light, circular muscles contract and radial muscles relax, narrowing the pupil to protect the retina.
Examiner Tips
- 💡Use the sequence ciliary muscle, suspensory ligaments, lens shape when explaining accommodation.
- 💡State the direction of change clearly: near objects need a thicker lens, distant objects need a thinner lens.
- 💡For adaptation to dim light, name both muscle groups and their actions in the iris.
Common Mistakes
- Saying the lens becomes thicker for distant objects; correction: the lens becomes thinner and flatter for distant objects and thicker and more curved for near objects.
- Confusing the roles of ciliary muscle and suspensory ligaments; correction: ciliary muscle contraction slackens the ligaments, allowing the lens to become thicker.
- Thinking the pupil widens because the lens changes; correction: pupil diameter is controlled by the iris muscles, not the lens.