Edexcel iGCSE Biology-3.41-3.42 The Human Eye: Structure and Function- Study Notes- New Syllabus
Edexcel iGCSE Biology-3.41-3.42 The Human Eye: Structure and Function- Study Notes- New syllabus
Edexcel iGCSE Biology-3.41-3.42 The Human Eye: Structure and Function- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.
Key Concepts:
3.41 describe the structure and function of the eye as a receptor
3.42 understand the function of the eye in focusing on near and distant objects, and in responding to changes in light intensity
Structure and Function of the Eye
🌱 Introduction
The eye is a sense organ that detects light and allows vision.
It contains specialized cells called photoreceptors that convert light into electrical impulses for the nervous system.
🧩 Key Structures of the Eye
- Cornea: Transparent outer layer at the front of the eye; refracts light into the eye.
- Sclera: White, tough outer layer; provides protection and support.
- Iris: Coloured part of the eye; contains muscles that control the pupil size → regulates light entering the eye.
- Pupil: Opening in the centre of the iris; adjusts diameter depending on light intensity.
- Lens: Transparent, flexible structure behind the pupil; focuses light onto the retina by changing shape (accommodation).
- Ciliary Muscles: Muscles attached to the lens; change lens shape to focus on near or distant objects.
- Retina: Inner layer at the back of the eye; contains photoreceptor cells:
– Rods → detect light intensity (black & white).
– Cones → detect colour (red, green, blue).
Converts light into electrical impulses. - Optic Nerve: Carries electrical impulses from retina to brain.
- Vitreous Humour: Jelly-like substance inside the eye; helps maintain shape of the eyeball.
🔹 Function of the Eye as a Receptor
- Detects light intensity and colour.
- Adjusts pupil size to prevent damage from bright light.
- Focuses light on retina → forms clear images.
- Converts light into nerve impulses → sent via optic nerve to brain.
📊 Summary Table
| Structure | Function |
|---|---|
| Cornea | Refracts light into the eye |
| Sclera | Protection & support |
| Iris | Controls pupil size |
| Pupil | Lets light in |
| Lens | Focuses light on retina |
| Ciliary Muscles | Change lens shape for focusing |
| Retina (rods & cones) | Converts light into electrical impulses |
| Optic Nerve | Sends impulses to brain |
| Vitreous Humour | Maintains eyeball shape |
📌 Quick Recap
Eye = receptor for light.
Detects intensity, colour, and images.
Electrical impulses sent via optic nerve → brain interprets them.
Iris + pupil + lens help control light entry and focus.
Function of the Eye: Focusing and Light Regulation
🌱 Introduction
The eye adjusts to focus on objects at different distances and adapts to changes in light intensity.
Two key functions:
– Accommodation → focusing on near and distant objects.
– Light intensity adjustment → regulating how much light enters the eye.
🔍 1. Focusing on Near and Distant Objects (Accommodation)
- Lens changes shape with the help of ciliary muscles:
- Distant objects: ciliary muscles relax → lens becomes thin & less curved → light focused on retina.
- Near objects: ciliary muscles contract → lens becomes thicker & more curved → light focused on retina.
- Purpose → ensures a clear image forms on the retina.
💡 2. Responding to Changes in Light Intensity
- Pupil adjusts size to control light entering the eye (controlled by iris muscles):
- Bright light: circular iris muscles contract → pupil becomes smaller → prevents retinal damage.
- Dim light: radial iris muscles contract → pupil enlarges → more light enters → improves vision.
📊 Summary Table
| Function | Mechanism | Effect |
|---|---|---|
| Focusing on near objects | Ciliary muscles contract → lens thickens | Clear image of near objects |
| Focusing on distant objects | Ciliary muscles relax → lens thins | Clear image of distant objects |
| Bright light adaptation | Circular iris muscles contract → pupil constricts | Protects retina from damage |
| Dim light adaptation | Radial iris muscles contract → pupil dilates | More light enters → improves vision |
📌 Quick Recap
Accommodation → lens changes shape for near/distant vision.
Light regulation → iris adjusts pupil size for protection and optimal vision.
Both functions ensure clear and safe vision under different conditions.