WELCOME TO

nbb

I

Form 2

Chapter 1 The world through

our senses

1

1.1 Sensory Organs and Their Functions

A sensory organ is an organ that enables the body to respond to stimuli.

A stimulus is a change in the surroundings that can be detected by the sensory organs.

The five sensory organs are eye, ear, nose, tongue and skin.

2

Sensory organ Sense Stimuli

Eye Sight Light

Ear Hearing Sound

Nose Smell Chemical in air

Tongue Taste Chemical in foods

Skin Touch Pressure, heat, cold, touch, pain

• The ability of the sensory organs to detect stimuli is called senses.

StimulusPathway from stimulus to response.

Receptor in sensory organ

Sensorynerves Brain

Effectors(muscle)

Motornerves

1.2 Sense of Touch

Dermis

■"i

Fatty tissue f(Sub cut a lie

ous layer)Nerve Pressure

Receptor Stimuli (sensitive to)

Cold receptors Cold substances

Heat receptors Heat

Pain receptors Pain

Pressure receptors Large pressure

Touch receptors Small pressure (touch )

1.2 Sense of Touch

• The skin is a sensory organ which responds to the sense of touch.

• There are five types of receptors in the skin.

o

• The sensitivity of the skin depends on(a) the thickness of epidermis(b) the number of receptors present

• Fingertip and neck are more sensitive .

• Elbow , knee and back side are less sensitive to touch.

Braille letters are specifically designed symbols for stimulating the fingertips, which allows blind people to read

1.3 Sense of Smell

Olfactorv nerve

Sensory cell

Nasal cavity

NostrilLubang hi dung

1.3 Sense of SmellMucus is produced to help keep the receptors moist.

When you inhale, the chemicals from the air enter the nasal cavity and dissolve in the mucus.

The smell receptors are stimulated.

The impulse of smell receptors are sent to the brain by the olfactory nerves for interpretation.

9

When we catch a cold, too much mucus is produced and this makes the receptors less sensitive.

Cold = flu (selsema) 10

1.4Sense of

Taste

Our tongues detect five flavors:sweet, salty, sour, bitter, andumami. LTinarni is describedas “savoriness,” and hasbeen known to theJapanese for centuries.Scientists have onlyrecently found areceptor for it.

TasteTastesignal

Contraryto popular

belief, yousense all tastes,

to varying degrees, onall parts of your tongue. Taste cellscan perceive more than one flavor.

1.4 Sense of Taste

-The tongue contains many taste buds. The taste buds are the taste receptors.- There are four types of taste receptors.

-These receptors are sensitive to sweet, salty, sour and bitter tastes.

How do you taste?• The taste buds are able to detect

the taste of the food when the food is dissolved in saliva.

The taste receptors will be stimulated and impulses are produced.

The impulses are sent to the brain for interpretation.

13

1.5 Sense of Hearing

Cochlea

Ear / °val canal window Eustachian tube

1.5 Sense of Hearing

The ear is a sensory organ for hearing and balancing.

The car can bedivided intothree sections:i) outer ear,ii) middle ear and• • • \ •

in) inner ear.

15

How do we hear ?1. The pinna collects sound

waves and directs them into the auditory canal and to the eardrum.

2. The eardrum begins to vibrate and the vibrations are transferred to the ossicles

i Eardrum(Tympanicmembrane]

SemicirciJtarcanals

16

3. The ossicles magnify the vibrations and pass them to the oval window.

4. The oval window transmits the vibrations to the cochlea.

5. The cochlea converts the vibrations into impulses

6. The impulses are sent by the auditory nerves to the brain for interpretation.

Semicircular carta

18

1.6 Sense of Sight

SuspensoryligamentsLens

Choroid

Cornea

Pupil

RetinaYellow spot (fovea)Optic

Aqueoushumour

Conjunctiva

Sclere

Blind spot

How do we see ?• When you look at an object, the light rays from the object enter the

eye.• The light rays are refracted by cornea, aqueous humour, lens and

vitreous humour.• An image is formed on the retina. Impulses are produced and are

sent to the brain by the optic nerves..

Aqueous

humour

Cornea

etina

*

LensIris A Image

Light ray IVitreous humour 20

1.7 Light and Sight

I Light is a form of energy and lighttravels in straight lines. This causesthe formation of eclipses.

• Light cannot travel through opaque objects. Thus, shadows are formed.

21

Light can be reflected

When light hits a surface, some of it bounces off or isreflected. Mirrors are very shiny surfaces designed to reflect nearlyall the light that hits them.

When you look in a flat mirror, you see a reflection of yourself which is the same size as you but back to front.

22

Light can be refracted• When light travels from one medium to another of

different density, its speed changes.• This causes the light ray to bend.• This is known as refraction.

23

Effect of light refraction

a) The swimming pool appears to be shallower than its actual depth.

b) A straw in a glass of water appears to be bent.

\

Vision defectsThere are three defects of vision:(a) Short-sightedness ( Rabun jauh ) j l K )

can see near objects clearly but not distant objects.

(b) Long-sightedness ( Rabun dekat ®M)can see far objects clearly but not near objects.

(c) Astigmatism (Rabun silau M'O'L)both far and near objects are blur .

25

R e t i n aA s t i gm a t i cC o r n ea

/( ii i

P L e n s /M u lt i p le f o ca l p o in t s a r e o n o r

I m ag e so nr e t in aa r eb l u rr yN o r m a lC o r n e o

Short-sightedness

Long-sightedness

Astigmatism

can see near objects clearly

can see far objects clearly

both far and near objects are blur

The images of distant objects are formed in front of the retina.

Using diverging (concave)

The images of nearby objects are formed at the back of retina.

using converging (convex) lens.

A

Caused by irregular surface of the cornea.

Using cylindrical lenses.

Light

Testing astigmatism ( text pg 23)

Normal eye Have an astigmatism

Close your right eye and hold this page about one arm’s length from your left eye.Look at the figure .

27

Optical illusion

Man Playhig Horn... Or Woman Silihouette?{hint: woman&>r$quof'5 right eye is the Mack speck bi front o/Jy>m handle)

Two Faces... Or One?

(hint: two faces sideproft&eSzhett£p;ar one facefront view)

Optical illusion

Old Woman,...Or Youttg Girt? hhi£;The old woman's nose is the young girls chin,

nkbpj(a)

Sometimes our brains do not accurately interpret what we see.

• This phenomenon is known as optical illusion.

A aab&fo,,..<2r&teac&?

iAj? iEMr.t ca Jsicfc'-.uj itj^. £?££■ rtf&Sia is joi>fcsrur

It's amazing how our brain works.This should be proof enough, we don't always see what we think we see.

3U

Text book pg 24

Blind spot

This boy is chasing a butterfly - time to end this madness.Close your left eye and look at the boy with your right eye. Then move your head closer to or further from the screen until ... the butterfly disappears !You can't see the butterfly because it's exactly in front of your blind spot, the place where the optical nerves enter the eye.

When images fall on the blind spot, they cannot be seen.

31

Stereoscopic (binocular) vision

• Stereoscopic vision is a vision involving both eyes.

• Humans and most predators have stereoscopic vision.

Advantages of stereoscopic vision

(a) Able to see objects in three dimensions.

(b) Able to estimate the distance accurately.

33

Monocular visionMonocular vision is a vision involving only one eye.

Animals of prey normally have monocular vision.

Monocular vision has a wider scope of vision.

This enables the prey to detect the presence of predators easily

34

The various devices used to overcome thelimitations of sight include

• microscope,• magnifying glass,• telescope,• binoculars,

ultrasound scanning device,X-ray and periscope.

35

1.8 Sound and HearingSound is produced when objects vibrate.

A medium is needed for the sound to travel

Hence, sound cannot travel through vacuum.

solid liquid gas

i n

fast moderate slow

_ _ f@ Experiment;Speed of sound though difference medium jQ show sound cannot travel through vacuum

I'm beautifuli'm beautiful

Sound can be reflected

• Sound can be reflected by smooth and hard surfaces and it is absorbed by soft and rough surfaces.

• Echo is the reflected sound. Echo can be used to:(a) estimate the depth of sea(b) identify a school offish(c) detect the presence of submarines

■ 3d w a r n V-irrifTilkd IlMI 3ftp

nrilcniid t - : i & L~lplicfn sihedd

Hearing defects

There are two major types of(a) The first type involves the outer and middle ear.

For example, the earwax can block sound waves and cause temporary loss of hearing.

(b) The second type involves damage to the inner ear. For example, toxins are produced as a result of diphtheria or scarlet fever. These toxins damage the cochlea and cause permanent loss of hearing.

Protect our ears

Don't do this !!

Use earplug or earmuffs

Loud music

cause hearing loss39

How to overcome hearing loss ?

Hearing aid Surgery Artificial cochlea

A small incision is matte in the tympanic membrane

Tube inserted to drain fluid

Graft tissue is taken from

temporaLis fascia

Graft patch in pLace over defect

he 40

Human hearing limit

• Our ears can only detect sound of frequencies between 20 Hz and 20000 Hz.

• Sounds with frequencies 20 000 Hz and

• above are ultrasonic sounds. These sounds can be detected by animals such as bats, cats and dolphins.

Stereophonic hearing

• Stereophonic hearing is hearing with both ears.• Stereophonic hearing helps us to determine the

direction of sound.

1.9 Stimuli and Responses in Plants

Plants respond tostimuli like light,water , touch andgravity.

Different parts of theplant respond todifferent stimuli.

43

b e # <

\ y \

• ’ ’ ’ • # L I .F ! / ■ ■ f > i ' 1 ■ * 7 1

m uj j j ?

■ l u 4P i t c h e r P l a n t s M i m o s a p u d i c a

• There are two types of responses:(a) Tropism

Tropism is the directional growth of the part of a plant in response to an external stimulus.

(b) Nastic movementsThe direction of the response is not dependent on the direction of the stimulus

A1

1 i 1H n | ' 5

(a) Phototropism : (b) Geotropism : (c) Hydrotropism : (d) Thigmotropism:Response Response Response Responseto light to gravity to water to touch

• When the part of the plant grows towards the stimulus, it is called positive tropism.

• When the part of the plant grows away from the stimulus, it is called negative tropism.

Shoot is negative geotropi

Roots are positive geotropism .

46