Eye and ear structure and function — A/L Biology

What must I remember about Eye and ear structure and function?

• Eye tunic architecture: Outer fibrous tunic (opaque sclera and transparent cornea), middle vascular tunic (choroid, ciliary body, and pigmented iris with pupil), and inner neural tunic (retina containing photoreceptors).
• Photoreceptors: Rods (contain Rhodopsin; high sensitivity to dim light, peripheral vision, achromatic) and Cones (contain Iodopsin/Photopsins; low sensitivity, high visual acuity, daylight and color vision concentrated in the Fovea Centralis).
• Visual Accommodation: For near vision, ciliary muscles contract -> suspensory ligaments slacken -> elastic lens becomes rounder and more convex, increasing refractive power; for distant vision, ciliary muscles relax, tension on suspensory ligaments flattens lens.
• Ear structural divisions: External ear (pinna, external acoustic meatus) collects sound waves; Middle ear (tympanic membrane, auditory ossicles: malleus, incus, stapes, and Eustachian tube) amplifies and transmits sound pressure to oval window; Inner ear (cochlea and vestibular apparatus) converts mechanical waves to neural signals.
• Hearing & Equilibrium mechanisms: Sound vibrations pass into perilymph of scala vestibuli -> displace basilar membrane in cochlea -> bend stereocilia of hair cells in Organ of Corti against tectorial membrane -> generate impulses in auditory nerve; Semicircular canals detect rotational acceleration (dynamic), while utricle and saccule detect gravitational tilt and linear acceleration (static equilibrium).

Test yourself (1 minute)

1. Visual defects & corrections

   Myopia (nearsightedness, eyeball too long; corrected with concave diverging lens); Hyperopia (farsightedness, eyeball too short; corrected with convex converging lens); Presbyopia (aging lens loses elasticity).

2. Middle ear impedance matching

   The area ratio between large tympanic membrane and small oval window (~17:1), combined with ossicular lever action, magnifies sound pressure ~20-fold to move inner ear perilymph fluid.

3. Fovea centralis vs Blind spot

   Fovea centralis has only cones, zero rods, 1:1 ganglion ratio yielding maximum visual acuity; Optic disc (blind spot) lacks photoreceptors because optic nerve axons exit eye.

Practise Eye and ear structure and function questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 5

What should I study first?

What comes next?

Next in the syllabus

Where does Eye and ear structure and function fit in the syllabus?

Year 2 · Term 1