15: Detecting the Environment

Question 1

What is the definition of irritability?

Answer 1

Irritability is the ability of detecting stimuli and giving appropriate responses.

Question 2

State the type of receptor and the stimulus detected in the eye.

Answer 2

Photoreceptors which detect light.

Question 3

State the type of receptor and the stimulus detected in the ear.

Answer 3

Mechanoreceptors which detect sound.

Question 4

State the type of receptor and the stimulus detected in the nose.

Answer 4

Chemoreceptors which detect chemicals in the air.

Question 5

State the type of receptor and the stimulus detected in the tongue.

Answer 5

Chemoreceptors which detect chemicals in food.

Question 6

State the types of receptors and the stimuli detected in the skin.

Answer 6

Thermoreceptors which detect temperature, and mechanoreceptors which detect pressure.

Question 7

State the function of the eyebrow.

Answer 7

It prevents sweat from running into the eye.

Question 8

State the function of the eyelash.

Answer 8

It traps dust and prevents it from entering the eye.

Question 9

State the functions of the eyelid.

Answer 9

It can be closed to protect the eye from dirt and strong light.
It also spreads tears over the eye surface when we blink.

Question 10

State the functions of the tear gland.

Answer 10

It produces tears which contain sodium, chloride and lysozyme that can kill bacteria. Tears also keep the eye moist and clean.

Question 11

State the function of the tear duct.

Answer 11

It drains tears into the nasal cavity.

Question 12

State the structure in which the eyeball is located in the skull.

Answer 12

The orbit

Question 13

How many pairs of eye muscles are attached on the eyeball to the skull?

Answer 13

3

Question 14

State the functions of the conjunctiva.

Answer 14

It covers part of the front surface of the eyeball and the inner surface of eyelids, but not the cornea. It helps keep the front part of the eye moist and lubricated.

Question 15

State the properties and functions of the sclera.

Answer 15

It is the outermost layer of the eyeball, which is a tough white coat.
It protects the inner structures and maintains the shape of the eyeball.
It also provides a surface for the attachment of eye muscles.

Question 16

State the properties and functions of the cornea.

Answer 16

It is a transparent layer of tissue at the front part of the eye. It allows light to enter the eye.
Its curved surface helps refract and focus light onto the retina.
It has no capillaries and it obtains nutrients and oxygen from the aqueous humour.

Question 17

State the properties and functions of the choroid.

Answer 17

It is the middle layer of the eyeball. It contains a black pigment which absorbs light, which reduces reflection of light within the eye and helps form a sharp image.
It is rich in capillaries which supply nutrients and oxygen to the retina and sclera and remove wastes from them.

Question 18

State the properties and functions of the iris.

Answer 18

It is continuous with the choroid.
It is made up of muscles, it controls the size of pupil so as to regulate the amount of light entering the eye.
It contains a pigment which determines its colour.

Question 19

State the properties and functions of the pupil.

Answer 19

It is the opening at the centre of the iris. It allows light to enter the eye.
Its size is controlled by the iris.

Question 20

State the properties and functions of the retina.

Answer 20

It is the innermost layer of the eyeball.
It contains many photoreceptors / light-sensitive cells, including rod cells and cone cells, and nerve fibres.

Question 21

State the properties and functions of the optic nerve.

Answer 21

It is grouped from the nerve fibres in the retina.
It transmits nerve impulses generated from the photoreceptors in the retina to the sensory area of the cerebrum of the brain.

Question 22

State the properties of the yellow spot.

Answer 22

It is the central region of the retina.
It has a high density of cone cells but it has no rod cells.

Question 23

State the properties of the blind spot.

Answer 23

It is the region of the retina where the optic nerve leaves the eyeball.
It has no rod cells or cone cells.

Question 24

Use three words to describe the appearance of the lens.

Answer 24

Transparent, elastic, biconvex

Question 25

State the properties and functions of the lens.

Answer 25

It is transparent, elastic, and biconvex in shape. It **refracts and focuses light** onto the retina. Its thickness can be adjusted by the ciliary body so that light from objects at different distances is focused onto the retina. It is made up of living cells which have **no nuclei**. It has **no capillaries** and it obtains nutrients and oxygen from the aqueous humour.

Question 26

State the properties and functions of the suspensory ligament and ciliary body.

Answer 26

The lens is held in position by **suspensory ligaments** which are connected to the **ciliary body**. The ciliary body consists of a ring of muscles called **ciliary muscles**. It controls the tension of the suspensory ligaments, thereby changing the thickness of the lens.

Question 27

State the properties and functions of the aqueous humour.

Answer 27

It fills the anterior chamber between the cornea and the lens. It is a watery fluid produced by **the ciliary body**. It supplies nutrients and oxygen to the **cornea and lens** by diffusion from the capillaries in the choroid. It helps to maintain the shape pf the eyeball and refract light onto the retina.

Question 28

State the properties and functions of the vitreous humour.

Answer 28

It fills the posterior chamber between the retina and the lens. It is a jelly-like fluid and it helps to maintain the shape pf the eyeball and refract light onto the retina.