11.811.8

Smell, taste Smell, taste

and touchand touch

How do we taste?How do we taste? p.107p.107

- Tongue is the sense organ that detects flavour.

many grooves

on the surfacemany grooves

on the surface

- Inside the grooves there are many taste buds which are taste receptors.

- Section through upper surface of tongue:

tastetastebudbudtastetastebudbud

groovgrooveegroovgroovee

Microscopic view oftaste buds (x100)

brainfood

sensory cellhair of sensory cell

Process to Process to taste foodtaste foodProcess to Process to taste foodtaste food

- Flavouring chemicals in food dissolve in the saliva,=> => stimulates the taste buds to send messagesmessages,,

=> => messages are transmitted to the brain to give us the taste of the food.

chemicalsin food

sensory cell

- Humans have four kinds of taste buds. They can detect four kinds of tastes: sweetsweet, soursour, salty salty and bitterbitter.

- Each kind of taste buds is not evenly distributed on the tongue. Thus, certain parts of the tongue are more sensitive to a particular taste than the others.

- Different areas Different areas of the tongue are more sensitive in detecting a certain taste than the others:

sweesweettsweesweett

bittebitterrbittebitterrsousou

rrsousourr

saltsaltyysaltsaltyy

p.107p.107

‘Spicy’ is not a taste. It is the sensation of pain in the tongue resulting fromthe destruction of taste buds by the

‘hot’ food like chilly.

It is It is spicy!spicy!

How do we smell ?How do we smell ? p.108p.108

- Nose is the sense organ that detects smellsmell.- There are millions of smell receptors inside our nose.

nasal nasal cavitycavitynasal nasal cavitycavity

magnify

chemicalschemicalsin foodin food

nasal nasal cavitcavit

yy

nasal nasal cavitcavit

yy

nervenervenervenerve

braibrainn

braibrainn

sensory sensory cellcell

sensory sensory cellcell

mucus liningmucus lininginside

Process to Process to smell foodsmell foodProcess to Process to smell foodsmell food

- When we breathe, some chemicals enter our nose

=> => chemicals dissolve in the mucus,=>=> stimulate the smell receptors to produce messages,

=> => These messages are sent to the brain to give us the odour of the food.

Some Some chemicals chemicals in in thethe foodfood diffuse diffuse

into the airinto the air..

Some Some chemicals chemicals in in thethe foodfood diffuse diffuse

into the airinto the air..

- There are more than 10 000 different smells in the world.

The human nose can detect 4000 different types of them.

Why do warm foods have stronger flavour than cold foods?

This is because when food is heated, more chemicals chemicals in food diffuse into the air.

SensitivitySensitivity of smell of smellSensitivitySensitivity of smell of smell

Put a cup of coffee under your nose. Breathe in 10 times slowly.

Does the smellof coffee become stronger, weaker weaker or disappear?

WhyWhy?WhyWhy?

Little ScientistLittle Scientist

After we smell something for some time, the smell receptorssmell receptors stop sending messages to the brain.

- We can get used to a smell.

To tell the true taste of a chocolate ice-cream, which of the following

sense organs should we use?

eyeeye

earear

tonguetongue

nosenose

skinskin

Let us do

to know more about ‘taste’.

Experiment Centre 11.6Experiment Centre 11.6

Experiment Centre 11.6Experiment Centre 11.6 p.109p.109

Does smell affect taste?

1 Work in pairs and blindfold your partner.

2 Give your partner a piece of plain potato chip to eat. Ask him/her the taste of the potato chip.

3 Hold a piece of strongly flavoured potato in front of your partner’s nose.

4 Give him/her another piece of plain potato chip to eat. Ask him/her about the taste of the potato chip.

How does the plain potato chip taste now?

Does it taste the same as before?

- We use both smell smell and tastetaste to detect the flavour of food.

Holding your nose can help take away unpleasant taste of food.

Some medicine is unpleasant to take.You can hold your nose while taking the medicine. This helps take awaythe unpleasant feeling.

Our tongue can only distinguish about 4 different tastes.But our nosecan distinguish about 4000 different chemicals.

Thus, when our nose is also used to sense the food, the food ‘tastes’ better.

Our nose can tell us not only the sweet taste of ice-cream, but also whether it is chocolate flavour chocolate flavour or not.

Why do the elders like to take in food with strong flavour?

It’s too salty!It’s too salty!

This is because the senses of smell and taste of the elders are weaker.

Food with strong flavour tastes good to the elders.

Touch is one of our five senses.

Blind people depend on touch to sense the environment.

Besides, we also depend on touch in daily life.

- The skin is the largest sense organ of human body. It is a protective covering of our body.

- Besides functioning as a sense organ, the skin also has the following functions:

SkinSkinSkinSkin

>> as a barrier to prevent dust and bacteria from getting into the body.

>> as a barrier to prevent the loss of body fluids (e.g. water) and body body temperature temperature .

- The skin contains millions of nerve endings that detect

Skin as a sense organSkin as a sense organ p.112p.112

painpain

p.112p.112

touchtouch

- The skin contains millions of nerve endings that detect

painpain

Skin as a sense organSkin as a sense organ

p.112p.112Skin as a sense organSkin as a sense organ

touchtouch

- The skin contains millions of nerve endings that detect

painpain

temperaturetemperature

temperaturetemperature

p.112p.112Skin as a sense organSkin as a sense organ

touchtouch

- The skin contains millions of nerve endings that detect

painpain

pressurepressure

- Nerve endings are stimulated to produce messages.

spinspinal al

cordcord

spinspinal al

cordcord messagmessagesesmessagmessageses

brainbrainbrainbrain

These messages are sent to the brain to give us different sensations.

temperatutemperaturere

temperatutemperaturere

pressurpressuree

pressurpressuree

painpainpainpain

touctouchh

touctouchh

- The nerve endings are not evenly spread over our body. Some parts have more and some fewer.

- The parts of our body where the skin has a large number of nerve endings are highly sensitive.e.g. Our tongue is highly sensitive. It really hurts when you bite your your tongue tongue accidentally.

Experiment Centre 11.7Experiment Centre 11.7 p.113p.113

In which part of our body is the skinmost sensitive to touch?

1 Ask your partner to close his/her eyes. Touch his/her fingertip with either the smooth paper or the sandpaper.2 Ask your partner to tell you which kind of paper is touching him/her.3 Do this five times on fingertip, using the smooth paper and the sandpaper randomly.

Do not rub the skin Do not rub the skin with the sandpaperwith the sandpaper..

Watch out !Watch out !

4 Repeat steps 1 to 3 on other parts of the body including back of hand, forearm, elbow and back of neck.

5 Put the results in the table using the following signs:

S = smooth paper　 = correct answerR = sandpaper = wrong answer

12345

FingertipFingertipBack of Back of

handhand ForearmForearmBack of Back of

neckneckElbowElbowTestTest

Part of the body

6 From the results of the tests,

a in which part of our body is the skin

most sensitive to touch?

___________________________

b in which part of our body is the skin

least sensitive to touch?

________________

Fingertip.

Back of neck.

- Our fingertips are highly sensitive to touch.

- Blind people, carpenters and Chinese doctors make good use of this feature in their daily life.

Blind people use their fingertips to ‘read’ braille

p.114p.114

Carpenters use their fingertips to feel how rough or smooth a surface is

Chinese doctors use their fingertips to examine the patient’s pulse

Are you sure??I’d rather check

it out with a thermometer!

You have a fever!

Can Can the skin the skin tell ustell us the correct the correct temperaturetemperature??Can Can the skin the skin tell ustell us the correct the correct temperaturetemperature??

What is your opinion? What is your opinion? Try to do Experiment Centre 11.8Try to do Experiment Centre 11.8

What is your opinion? What is your opinion? Try to do Experiment Centre 11.8Try to do Experiment Centre 11.8

Experiment Centre 11.8Experiment Centre 11.8 p.115p.115

Is our skin reliable in detecting temperature?

hotwater

tapwater

icedwater

1 Put your right forefinger in hot water and your left forefinger in iced water as shown for 30 seconds.

a How does your right forefinger feel?

_______ (Hot/Cold)

b How does your left forefinger feel?

_______ (Hot/Cold)

Hot

Cold

hotwater

tapwater

icedwater

2 Quickly put both fingers into the beaker of tap water.

a How does your right forefinger feel now?

_______ (Hot/Cold)

b How does your left forefinger feel now?

_______ (Hot/Cold)Hot

Cold

hotwater

tapwater

icedwater

Our skin _________ (is/is not) reliable i

n detecting the temperature of water.

hotwater

tapwater

icedwater

is not