The eye detects light and controls its entry
| English | Français |
|---|---|
| retina/ˈretɪnə/ | rétine |
| optic nerve/ˈɒptɪk nɜːv/ | nerf optique |
| iris/ˈaɪrɪs/ | iris |
What would explain this observation?
- In dim light the eye can admit more light by changing its pupil size. The pupil is an opening, not the structure that detects the image.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- The · Le retina 视网膜 contains receptors sensitive to light intensity and colour. The optic nerve 视神经 carries information from the eye towards the brain. The sclera is a tough outer layer; the transparent cornea admits and refracts light. The iris 虹膜 controls the diameter of the pupil. The lens refracts light to focus an image on the retina.
- retina: The light-sensitive layer containing receptors; iris: The structure controlling pupil diameter; optic nerve: A nerve carrying information from the eye towards the brain.
Which structure contains receptors sensitive to light and colour?
In dim light the iris allows a larger pupil, admitting more light; in bright light it reduces the opening. This is different from accommodation, which changes lens shape for focusing. Ciliary muscles and suspensory ligaments control lens shape. Correct diagram labels must distinguish a boundary, an opening, a transparent structure and a nerve.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- In dim light the iris allows a larger pupil, admitting more light; in bright light it reduces the opening. This is different from accommodation, which changes lens shape for focusing. Ciliary muscles and suspensory ligaments control lens shape. Correct diagram labels must distinguish a boundary, an opening, a transparent structure and a nerve.
- Use a teacher-provided eye cross-section and safe ordinary-light observations or photographs. Locate each structure and write its function. Do not shine intense lights or lasers into an eye, touch eye structures or apply medicines. Compare pupil-size diagrams at the same scale rather than mistaking an enlarged image for an actual physiological change.
Which two habits make the investigation or model in this case more defensible?
Use a teacher-provided eye cross-section and safe ordinary-light observations or photographs. Locate each structure and write its function. Do not shine intense lights or lasers into an eye, touch eye structures or apply medicines. Compare pupil-size diagrams at the same scale rather than mistaking an enlarged image for an actual physiological change.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a supplied circular-pupil model changes diameter from 2 mm to 4 mm. Radius doubles, so opening area increases by a factor of 2² = 4. This geometrical model concerns the opening; it does not imply that a person perceives exactly four times the brightness or that the retina has enlarged.
A circular-pupil model doubles radius. Calculate its area ratio final/initial. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A circular-pupil model doubles radius. Calculate its area ratio final/initial.
The result is 4 . Known: a supplied circular-pupil model changes diameter from 2 mm to 4 mm. Radius doubles, so opening area increases by a factor of 2² = 4. This geometrical model concerns the opening; it does not imply that a person perceives exactly four times the brightness or that the retina has enlarged.
Check the conclusion and its limits
- The iris controls pupil size; the pupil does not itself contract as a muscle. The optic nerve carries information and does not refract light. Bright/dim adaptation and near/far focusing require different explanations. All eye objectives in this acquired AQA section are both-tier Biology content.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
The pupil is the muscle that contracts to focus on a near object. This claim is false: The iris controls pupil size; the pupil does not itself contract as a muscle. The optic nerve carries information and does not refract light. Bright/dim adaptation and near/far focusing require different explanations. All eye objectives in this acquired AQA section are both-tier Biology content.
The eye detects light and controls its entry: In dim light the iris allows a larger pupil, admitting more light; in bright light it reduces the opening. This is different from accommodation, which changes lens shape for focusing. Ciliary muscles and suspensory ligaments control lens shape. Correct diagram labels must distinguish a boundary, an opening, a transparent structure and a nerve.
The pupil is the muscle that contracts to focus on a near object.
The iris controls pupil size; the pupil does not itself contract as a muscle. The optic nerve carries information and does not refract light. Bright/dim adaptation and near/far focusing require different explanations. All eye objectives in this acquired AQA section are both-tier Biology content.
The light-sensitive layer containing receptors: write the technical term.
retina means The light-sensitive layer containing receptors.