12.4.1 Relate the Structures of Human Auditory (Ear) and Visual (Eye) Receptors with Their Functions
Eye:
- Cornea: Refracts light.
- Lens: Focuses light onto retina.
- Retina: Contains photoreceptors (rods for low light, cones for color).
- Optic Nerve: Transmits visual signals to brain.
- Function: Converts light into electrical signals for vision.
Ear:
- Pinna: Collects sound waves.
- Eardrum: Vibrates with sound.
- Ossicles: Amplify vibrations to cochlea.
- Cochlea: Contains hair cells that convert vibrations into electrical signals.
- Auditory Nerve: Transmits signals to brain.
- Function: Converts sound vibrations into electrical signals for hearing.
12.4.2 Differentiate Between Pupil Reflex in Dim and Bright Light
Dim Light:
Pupil dilates (enlarges) due to relaxation of iris circular muscles and contraction of radial muscles. Allows more light to enter the retina for better vision.
Bright Light:
Pupil constricts (narrows) due to contraction of iris circular muscles and relaxation of radial muscles. Reduces light entry to protect retina from damage.
12.4.3 Relate Image Formation in the Human Eye with Ibn-al-Haitham’s Dark Chamber
Human Eye:
Light enters through cornea, is focused by the lens, and forms an inverted image on the retina. Similar to a camera, the eye adjusts focus via lens shape changes (accommodation).
Ibn-al-Haitham’s Dark Chamber (Camera Obscura):
Light passes through a small hole into a dark chamber, forming an inverted image on the opposite wall. Ibn-al-Haitham used this to study optics, demonstrating how light projects images, analogous to the eye’s mechanism.
12.4.4 Differentiate Between Defects of Eye (Short and Long Sightedness)
| Feature | Short Sightedness (Myopia) | Long Sightedness (Hyperopia) |
| Definition | Difficulty seeing distant objects. | Difficulty seeing near objects. |
| Cause | Eyeball too long or cornea/lens too curved; image forms in front of retina. | Eyeball too short or cornea/lens too flat; image forms behind retina. |
| Symptoms | Blurry distant vision (e.g., reading road signs). | Blurry near vision (e.g., reading a book). |
| Correction | Concave (diverging) lens. | Convex (converging) lens. |
12.4.5 Illustrate How Short and Long Sightedness Can Be Treated Using Ray Diagrams
Short Sightedness (Myopia):
- Problem: Light rays focus in front of the retina.
- Correction: Concave lens diverges light rays before they enter the eye, allowing focus on the retina.
- Ray Diagram:
Object → Light rays converge → Concave lens diverges rays → Focus on retina
Long Sightedness (Hyperopia):
- Problem: Light rays focus behind the retina.
- Correction: Convex lens converges light rays to focus on the retina.
- Ray Diagram:
Object → Light rays diverge → Convex lens converges rays → Focus on retina
12.4.6 Relate the Role of Vitamin A with Vision and Effects of Its Deficiency
Role of Vitamin A:
- Essential for producing rhodopsin, a pigment in rod cells of the retina that detects low light.
- Supports maintenance of corneal and conjunctival tissues.
Effects of Deficiency:
- Night blindness (impaired vision in dim light due to reduced rhodopsin).
- Dry eyes (xerophthalmia), leading to corneal damage.
- Severe cases may cause blindness.