External Structure

Question 1

Iris

Answer 1

Circular muscles and radial muscles in the iris control the size of the pupil.

Contains pigment which gives the eye its colour.

Question 2

Pupil

Answer 2

A hole in the centre of the iris which allows light to enter the eye.

Question 3

Sclera

Answer 3

Tough white outer covering of the eyeball which protects the eyeball from

mechanical damage.

Question 4

Conjuctiva

Answer 4

Thin transparent membrane covering the sclera. It secrets mucus, lubricating the front of the eyeball.

Question 5

Cornea

Answer 5

Transparent refractive layer covering the iris and pupil.

Question 6

Tear gland

Answer 6

Secretes tears – wash away dust particles, lubricate the conjunctiva (reduce
friction when eyelids move), keep cornea moist for atmospheric oxygen to
dissolve

Question 7

Eyelid

Answer 7

Protects cornea from mechanical damage.

Squinting is the partial closure of eyelids (prevents excess light from entering
the eye, prevents damage of light-sensitive tissue, retina).
Blinking spreads tears over the cornea and conjunctiva, wiping dust particles off the cornea

Question 8

Eyelashes

Answer 8

Shield the eye from dust particles.