To connect structure with function, name the part and then say what it does for the organ. In the eye: the cornea and lens focus light, the iris controls how much enters, and the retina detects it.
This lesson belongs to coordination and responses. The eye is a good example because it is a receptor organ that feeds into the nervous pathway in tracing a reflex.
What does each part of the eye do?
| Part | Function |
|---|---|
| Cornea | Refracts (bends) light as it enters the eye |
| Iris | Controls the size of the pupil, so it controls how much light enters |
| Pupil | The opening where light enters |
| Lens | Changes shape to focus light onto the retina |
| Retina | Contains light receptor cells that detect light |
| Optic nerve | Carries impulses from the retina to the brain |
Always pair each part with a verb: bends, controls, focuses, detects, carries.
Worked example
Explain what happens to the eye when a person walks from a dim room into bright sunlight. Include the parts involved.
Step 1, stimulus: bright light is detected by receptors in the retina.
Step 2, pathway: impulses travel along the optic nerve and through the nervous system as in a reflex.
Step 3, effector: muscles in the iris contract, making the pupil smaller.
Step 4, result: less light enters the eye. This protects the retina from damage and helps the image remain clear.
Step 5, focus: the cornea and lens still bend and focus the light that enters onto the retina.
Model answer: in bright light the iris muscles make the pupil smaller, so less light reaches the retina, which protects it.
The mistake to watch for
A frequent mix-up is to say that the lens detects light or that the retina focuses it.
Mistaken answer: “The retina focuses the light and the lens detects it.”
The parts and jobs are swapped.
The correction is a memory line in the direction light travels: cornea and lens bend and focus, iris controls the amount, retina detects, optic nerve carries. When you write an answer, follow the path of the light from front to back.
Check yourself
1. Which part contains the light receptor cells?
Show answer
The retina.
2. Name the structure that carries impulses from the eye to the brain.
Show answer
The optic nerve.
3. In dim light, what would you expect the iris to do to the pupil, and why?
Show answer
The pupil gets larger, so more light enters the eye and more can reach the retina, which makes it easier to see.
Where this leads next
Put all five lessons together in the coordination and responses practice set.
If matching parts to functions is the step that costs you marks, a teacher in online one-to-one Biology tuition can build it with you using your own diagrams.