Sensory Organs

Question 1

What is a sensory organ?

Answer 1

An organ used to detect stimuli in the surroundings

Question 2

Name the sensory organs

Answer 2

1. Eyes
2. Ears
3. Nose
4. Skin
5. Tongue

Question 3

Name the parts of the eye (i)

Answer 3

Choroid- Black layer that prevents reflection of light and supplies oxygen & nutrients to the eye

Retina- Layer containing photoreceptors (detects light & produce nerve impulses)

Yellow spot- Part of retina most sensitive to light

Optic nerves: Nerve fibres carrying nerve impulses from the retina to the brain to be interpreted

Blind spot: Part of retina (not sensitive to light) as there are no photoreceptors and exit point for optic nerve fibres

Question 4

Name the parts of the eye (ii)

Answer 4

Vitreous humour: Transparent jelly-like substance (maintains shape of eyeball) and (focuses light to the retina)

Conjunctiva: Transparent membrane & protects front part of sclera

Aqueous humour: Transparent fluid (maintain the shape of eyeball) & (focuses light into the eye)

Pupil: Opening in the centre of iris (controls the quantity of light entering the eye)

Iris: Coloured part of eye (controls size of pupil)

Question 5

Name the parts of the eye (iii)

Answer 5

Cornea: Transparent layer (refracts and focuses light onto retina)

Suspensory ligaments: Strong fibres (hold position of eye lens)

Cilliary muscle: Change thickness of eye lense through contractions and relaxations

Eye lense: Transparent and elastic convex lense (focuses light onto retina)

Sclera: Strong layer maintaining and protects shape of eye

Question 6

Photoreceptors: Rod cells & Cone cells

Answer 6

Rod cells: Sensitive to light intesities
Example: faint light

Cone cells: Sensitive to colours of light. There are three types of cells
Example: red light, green light, blue light

Question 7

Parts of ear (i)

Answer 7

Earlobe: Collects and directs sound waves

Ear canal: Directs sound waves to eardrums

Eardrum: Vibrates according frequency of sound waves & transfer vibrations to ossicles

Question 8

Parts of ear (ii)

Answer 8

Ossicles (three small bones)- Amplify sound vibrations & transfer to oval window

Oval window- Collects & transfer sound vibrations to cochlea

Eustachian tube: Balance air pressure on eardrum

Question 9

Parts of ear (iii)

Answer 9

Cochlea (fluid)- Converts sound vibration into nerve impulses

Semicircular canals (fluid)- Detects position of head & balance body

Auditory nerve: Send nerve impulses to brain to be interpreted

Question 10

Parts of nose (smell)

Answer 10

Smell (definition)- Chemical substances in the air

Sensory cells:
● 10 million cells located at roof of nasal cavity
● Tiny and covered in mucus
● Chemical substance dissolve into mucus and stimulate producing nerve impulse
● Nerve impulses sent to brain to determine the smell

Question 11

Structure of tongue

Answer 11

● Tiny papillae covered by taste buds containing 10-50 taste receptors
● Taste receptors detects sweet, salty, sour, bitter and umami

● Chemical substances in food dissolve in saliva & diffuse into taste buds –> stimulate taste receptors producing nerve impulses
● Nerve impulses are sent to brain to interpret the tastes

Front part- Sweet
Front arc part- Salty
Right & left parts- Sour
Back part- Bitter
Middle part- Umami

Question 12

Parts of skin

Answer 12

● Made up of thin outer layer (epidermis) & inner layer (dermis)
● Nerve impulse is produced through stimulation of receptor in skin –> brain to interpret

○ Cold receptor: Detects cold stimuli
○ Pain receptor: Detects pain stimuli
○ Heat receptor: Detects heat stimuli
○ Touch receptor: Detects touch stimuli
○ Pressure receptor: Detects pressure exerted

Question 13

Sensitivity of skin towards stimuli

Answer 13

Factors:
● Number of receptors
● Thickness of epidermis

Example: tip of finger is most sensitive as there are large number of receptors & thin epidermis

Question 14

Short-sightedness (explanation)

Answer 14

Condition
○ Able to see near objects
○ Cannot focus on distant object

Causes:
□ Eye lens is too thick
□ Eyeball is too long

▪︎Light from distant objects is focused in front of retina

Method of correction
> Concave lense

Question 15

Long-sightedness (Explanation)

Answer 15

Condition
○ Able to see distant objects clearly
○ Cannot focus on near objects

Causes
□ Eye lens too thin
□ Eyeball too short

▪︎ Light from near objects is focused behind the retina

Method of correction
> Convex lens

Question 16

Astigmatism (explanation)

Answer 16

Condition
○ Prevents light from focusing properly on retina
○ Vision become blurred (any distance)

Causes
▪︎ Irregular curvature of cornea or lens

Method of correction
> Cylindrical lens

Question 17

Limitations of Hearing

Answer 17

◇ Human can detect sound between 20 Hz to 20 000 Hz
◇ Children has a more elastic eardrums than older people

Causes of hearing defects
; Bacterial infection
; Injury
; Aging process
; Exposure to loud noises