Lesson overview
The eye: How does your eye cope with bright light and near objects?
Follow the light from a book through a large model eye and name each part it passes, then turn up a desk lamp, read the pupil’s diameter on a millimetre scale and graph how it changes. For the Supplement, focus the model on a near book and a far tree, and look at the rods and cones of the retina as the light fades.
Suggested sequence
- Lesson 1 · Your eye and its parts. Sense organs and their receptors, the structures of the eye, and what each part does to the light. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · The pupil reflex. The pupil narrows in bright light and widens in dim light; (Supplement) the circular and radial muscles of the iris. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · Focusing and the retina. Supplement: accommodation for near and far objects, rods and cones, and the fovea. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 10 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 10 questions, 15 min, lesson closed.
Learning goals
Part 1: Your eye and its parts
- Describe sense organs as groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals (14.2.1)
- Identify in diagrams and images the structures of the eye: cornea, iris, pupil, lens, retina, optic nerve and blind spot (14.2.2)
- Describe the function of each part of the eye: the cornea refracts light; the iris controls how much light enters the pupil; the lens focuses light on to the retina; the retina contains light receptors, some sensitive to light of different colours; the optic nerve carries impulses to the brain (14.2.3)
Part 2: The pupil reflex
- Explain the pupil reflex in terms of changes in light intensity and pupil diameter: brighter light gives a narrower pupil, less light enters and the retina is protected; dim light gives a wider pupil, more light enters; read a pupil diameter from a scale and describe a trend from a table (14.2.4, practical skills)
- Supplement: explain the pupil reflex in terms of the antagonistic action of circular and radial muscles in the iris (S14.2.5)
Part 3: Focusing and the retina
- Supplement: explain accommodation to view near and distant objects in terms of the contraction and relaxation of the ciliary muscles, tension in the suspensory ligaments, shape of the lens and refraction of light (S14.2.6)
- Supplement: describe the distribution of rods and cones in the retina of a human (S14.2.7)
- Supplement: outline the function of rods and cones: greater sensitivity of rods for night vision; three different kinds of cones, absorbing light of different colours, for colour vision (S14.2.8)
- Supplement: identify in diagrams and images the position of the fovea and state its function (S14.2.9)
Misconceptions to listen for
- “The nose responds to air.” — The nose responds to chemicals carried in the air, which is how you smell things.
- “Each stimulus goes with only one sense organ.” — Two organs respond to chemicals: the tongue to chemicals in food and drink, the nose to chemicals in the air.
- “A single receptor cell that responds to one kind of stimulus.” — A sense organ holds many receptor cells, grouped together. The retina of one eye has millions.
- “A group of receptor cells that respond to every kind of stimulus.” — Each sense organ responds to one kind of stimulus: the ear's receptors respond to sound but not to light.
- “A group of nerve cells that carry the impulses to the brain.” — That describes a nerve. A sense organ is made of receptor cells, which detect a stimulus and start the impulses.
- “The pupil.” — The pupil is a hole, so it looks black in everyone's eye. The coloured ring around it is the iris.
- “The cornea.” — The cornea is a clear window, so you see the colour behind it, not a colour of its own.
- “The lens.” — The lens is clear and lies behind the pupil, so its colour does not show from the front.
- “The optic nerve carries light to the brain.” — No light reaches the brain. The optic nerve carries impulses, started by the receptors in the retina.
- “The cornea focuses light on to the retina.” — Focusing on to the retina is the lens's job. The cornea refracts the light first, as it enters.
Scope
Sense organs and the eye (14.2.1–14.2.9): sense organs as groups of receptor cells responding to light, sound, touch, temperature and chemicals; the cornea, iris, pupil, lens, retina, optic nerve and blind spot and the function of each; the pupil reflex; and, for the Supplement, the antagonistic circular and radial muscles of the iris, accommodation for near and distant objects, the distribution and function of rods and cones, and the fovea. The ear, the tongue and the nose are only named with their stimulus; eye defects and glasses, the other layers of the eye by name, and how the brain makes sense of an image are not covered. Lenses and rays are in Physics 3.2, nerves and reflexes in the module before this one, and adrenaline in the module on hormones.