11.8 Smell, taste and touch

many grooves on the surface How do we taste? p.107 - Tongue is the sense organ that detects flavour. many grooves on the surface - Inside the grooves there are many taste buds which are taste receptors.

Microscopic view of taste buds (x100) - Section through upper surface of tongue: groove taste bud Microscopic view of taste buds (x100) hair of sensory cell sensory cell food brain

- Flavouring chemicals in food dissolve in the saliva, Process to taste food - Flavouring chemicals in food dissolve in the saliva, => stimulates the taste buds to send messages, => messages are transmitted to the brain to give us the taste of the food. sensory cell chemicals in food

- Humans have four kinds of taste buds - Humans have four kinds of taste buds. They can detect four kinds of tastes: sweet, sour, salty and bitter. - 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 of the tongue are more sensitive in detecting a certain taste than the others: bitter sour salty sweet

Do you know ? p.107 ‘Spicy’ is not a taste. It is the sensation of pain in the tongue resulting from the destruction of taste buds by the ‘hot’ food like chilly. It is spicy!

- Nose is the sense organ that How do we smell ? p.108 - Nose is the sense organ that detects smell. - There are millions of smell receptors inside our nose. nasal cavity

brain nerve magnify nasal cavity mucus lining inside sensory cell chemicals in food

Some chemicals in the food diffuse into the air. Process to smell 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 chemicals in the food diffuse into the air.

- There are more than 10 000 different smells in the world. The human nose can detect 4000 different types of them.

Do you know ? Why do warm foods have stronger flavour than cold foods? This is because when food is heated, more chemicals in food diffuse into the air.

Why? Little Scientist Sensitivity of smell Put a cup of coffee under your nose. Breathe in 10 times slowly. Does the smell of coffee become stronger, weaker or disappear? Why?

- We can get used to a smell. After we smell something for some time, the smell receptors stop sending messages to the brain.

Do you know ? To tell the true taste of a chocolate ice-cream, which of the following sense organs should we use? eye ear tongue nose skin

Let us do to know more about ‘taste’. Experiment Centre 11.6

Does smell affect taste? Experiment Centre 11.6 p.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 and taste 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 away the unpleasant feeling.

Our tongue can only distinguish about 4 different tastes Our tongue can only distinguish about 4 different tastes.But our nose can distinguish about 4000 different chemicals. Our nose can tell us not only the sweet taste of ice-cream, but also whether it is chocolate flavour or not. Thus, when our nose is also used to sense the food, the food ‘tastes’ better.

Why do the elders like to take in food with strong flavour? Do you know ? Why do the elders like to take in food with strong flavour? 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.

Skin - 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: > 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 temperature .

- The skin contains millions of nerve endings that detect Skin as a sense organ p.112 - The skin contains millions of nerve endings that detect pain

- The skin contains millions of nerve endings that detect Skin as a sense organ p.112 - The skin contains millions of nerve endings that detect pain touch

- The skin contains millions of nerve endings that detect Skin as a sense organ p.112 - The skin contains millions of nerve endings that detect pain touch temperature

- The skin contains millions of nerve endings that detect Skin as a sense organ p.112 - The skin contains millions of nerve endings that detect pain touch temperature pressure

- Nerve endings are stimulated to produce messages. brain spinal cord messages These messages are sent to the brain to give us different sensations.

- The nerve endings are not evenly spread over our body - 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 tongue accidentally. temperature pressure pain touch

In which part of our body is the skin most sensitive to touch? Experiment Centre 11.7 p.113 1 Ask your partner to close his/her eyes. Touch his/her fingertip with either the smooth paper or the sandpaper. In which part of our body is the skin most sensitive to touch? 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 with the sandpaper. Watch out !

1 2 3 4 5 5 Put the results in the table using the following signs: 4 Repeat steps 1 to 3 on other parts of the body including back of hand, forearm, elbow and back of neck. 1 2 3 4 5 Fingertip Back of hand Forearm Back of neck Elbow Test Part of the body S = smooth paper　 = correct answer R = sandpaper = wrong answer

________________ 6 From the results of the tests, a in which part of our body is the skin most sensitive to touch? ___________________________ Fingertip. b in which part of our body is the skin least sensitive to touch? ________________ 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

Carpenters use their fingertips to feel how rough or smooth a surface is Chinese doctors use their fingertips to examine the patient’s pulse

What is your opinion? Try to do Experiment Centre 11.8 Can the skin tell us the correct temperature? You have a fever! Are you sure? I’d rather check it out with a thermometer! What is your opinion? Try to do Experiment Centre 11.8

Is our skin reliable in detecting temperature? Experiment Centre 11.8 p.115 Is our skin reliable in detecting temperature? hot water tap water iced water

a How does your right forefinger feel? _______ (Hot/Cold) 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) Hot b How does your left forefinger feel? _______ (Hot/Cold) Cold hot water tap water iced water

2 Quickly put both fingers into the beaker of tap water. a How does your right forefinger feel now? _______ (Hot/Cold) Cold b How does your left forefinger feel now? _______ (Hot/Cold) Hot iced water hot water tap water

Our skin _________ (is/is not) reliable in detecting the temperature of water. iced water tap water hot water