Science notes, unit 3

Humans

Textbook Science Year 3 (DLP), pages 29–58

What this chapter covers

You can name the three types of teeth and say what each one does (3.1.1)
You can name the parts of a tooth (3.1.2)
You can compare milk teeth and permanent teeth (3.1.3)
You can explain how to take care of your teeth (3.1.4)
You can name the seven classes of food and give examples (3.2.1)
You can say why each class of food is important (3.2.2)
You can plan a balanced meal using the Malaysian Food Pyramid (3.2.3)
You can explain what happens when we do not eat a balanced diet (3.2.4)
You can explain what digestion means (3.3.1)
You can put the parts of the food flow in order, from mouth to anus (3.3.2)
You can say what happens to digested food and undigested food (3.3.3)
You can name actions that disturb digestion and their effects (3.3.4)

Kina pops a grape into her mouth. Where does the grape go? How does it change? In this unit you will learn about your teeth, the food you eat, and how your body digests food.

A grape being crushed by teeth, then squeezed in a narrow tube — The grape is chewed into small pieces, then it goes down a narrow tube. (Textbook p. 29)

3.1Our teeth

Three types of teeth

We have three types of teeth. Each type has a different job.

Type of tooth	Where it is	Its job (function)
Incisors	At the front	To cut food
Canines	Beside the incisors, pointed	To tear food
Molars	At the back, wide and flat	To grind food

An open mouth showing canines, molars and incisors with their functions — Incisors cut, canines tear, molars grind. (Textbook p. 30)

Try it at the school canteen

Bite a piece of roti canai with your front teeth. Your incisors cut it.
Pull a piece of chicken off the bone. Your canines tear it.
Chew a mouthful of rice. Your molars grind it until it is soft.

Sing this! "Our incisors to chop and cut, our canines to tear apart, our molars to grind the food." Sing it to the tune of Papaku Pulang!

Inside a tooth

If we cut a tooth in half, we can see its parts. This cut is called a cross section.

Cross section of a tooth labelled enamel, dentine, gum, nerves and blood vessels — Cross section of a tooth. (Textbook p. 32)

Part	What it is
Enamel	The hard, white outside layer. It protects the tooth.
Dentine	The layer under the enamel.
Gum	The pink part that holds the tooth in place.
Nerves	They let you feel hot, cold and pain.
Blood vessels	Tiny tubes that carry blood to the tooth.

Did you know? Enamel is the hardest thing in your whole body. It is even harder than bone!

Milk teeth and permanent teeth

Humans have two sets of teeth. The first set is the milk teeth. When a milk tooth falls out, a permanent tooth grows in its place. "Permanent" means it stays for life.

A small mouth with milk teeth and a bigger mouth with permanent teeth — Left: milk teeth set. Right: permanent teeth set. (Textbook p. 35)

	Milk teeth	Permanent teeth
Number of teeth	20 (8 incisors, 4 canines, 8 molars)	32 (8 incisors, 4 canines, 20 molars)
Enamel and dentine	Thin	Thick
Size and strength	Smaller, not strong	Bigger, stronger
Life span	Short (not permanent)	Long (permanent)
When they grow	Start at 6 months old, complete at 3 years old	Start at 6 years old, complete at 21 years old

Same: both sets have the same three types of teeth: incisors, canines and molars.

Both sets have 8 incisors and 4 canines. Only the number of molars is different (8 and 20). That is why permanent teeth have 12 more teeth.

Taking care of our teeth

After we eat, bits of food get stuck between our teeth. If we do not remove them, germs grow there. Germs are tiny living things that can make us sick. They make our teeth decay (rot and get holes).

Brush
Brush every surface with toothpaste, at least twice a day.

Floss
Move dental floss back and forth between your teeth.

See a dentist
Go for a check-up once every six months.

Rinse your mouth with water after eating.
Eat less sweet food, like ice cream, cakes and sweet drinks.

Teeth with black decay — Teeth that are not cleaned can decay. (Textbook p. 38)

Dentists can help when teeth have problems. Some dental treatments are:

Fillings, braces, dentures and root canal treatment — **Fillings** fill holes. **Braces** straighten teeth. **Dentures** are false teeth. **Root canal treatment** cleans inside a tooth. (Textbook p. 38)

Teeth pictures: Science Year 3 (DLP) textbook, pp. 29–38.

Adam is 7 years old. His front tooth fell out. Is it a milk tooth or a permanent tooth? What will happen next?

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It is a milk tooth. A permanent tooth will grow in its place.

3.2Food and a balanced diet

Seven classes of food

Food can be put into seven groups. Each group is called a class of food.

Class of food	Examples	Why we need it
Carbohydrate	Rice, bread, noodles, potatoes	Gives us energy
Protein	Fish, chicken, meat, eggs, milk, prawns	For growth
Fats	Cooking oil, butter, cheese	Warms the body
Vitamins	Fruits and vegetables, like papaya and tomatoes	Keeps us healthy
Minerals	Anchovies (ikan bilis), salt, milk	Keeps us healthy
Fibre	Vegetables like cabbage and kangkung, fruits	Prevents constipation
Water	Plain water, juice	Controls body temperature

Constipation means it is hard to pass out faeces (poo).

Rani's porridge

Rani is sick in hospital. Aishah brings her rice porridge with prawns, chicken, anchovies, vegetables, water and a little oil. The porridge has many classes of food, so it helps Rani grow strong and get well again.

A balanced diet

A balanced diet is a meal that has all the classes of food in the right amounts.

We can plan a balanced meal with the Malaysian Food Pyramid. The bottom is the biggest level, so we eat the most of it. The top is the smallest level, so we eat the least.

The Malaysian Food Pyramid with four levels — The Malaysian Food Pyramid. (Textbook p. 44, source: Ministry of Health Malaysia)

Level	How much	Food
Level 4 (top)	Eat less	Fat, oil, salt and sugar
Level 3	Eat in moderation (not too much)	Fish, chicken, meat, beans, milk
Level 2	Eat plenty	Fruits and vegetables
Level 1 (bottom)	Eat adequately (enough)	Rice, noodles, bread, cereal, potatoes

A plate with rice, fried fish, tempeh, green vegetables and watermelon — Rice, fish, tempeh, vegetables and watermelon: a balanced meal. (Textbook p. 45)

Did you know? A plate of nasi lemak with rice, egg, ikan bilis, peanuts, cucumber and sambal has food from every level of the pyramid!

When we do not eat a balanced diet

Eating too much of one kind of food, or not enough of another, can make us unwell.

Habits and effects: fried food and getting fat, sweets and tooth decay, no vegetables and constipation — Habits and their effects. (Textbook p. 47)

Habit	Effect
Eating too much fried and oily food	Getting too fat (obesity)
Eating too many sweet foods	Tooth decay
Not eating vegetables	Constipation

Food pictures: Science Year 3 (DLP) textbook, pp. 40–47.

Name the class of food in each: (a) papaya (b) ikan bilis (c) bread.

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(a) Vitamins (b) Minerals (also protein) (c) Carbohydrate

3.3Digestion

Digestion is breaking down food into smaller pieces so that the body can absorb (take in) its nutrients. Nutrients are the good things in food that our body needs.

In the mouth

Digestion starts in the mouth. Our teeth break food into small pieces. Our tongue and saliva (spit) make the food soft. Then it is easy to swallow.

Did you know? Your mouth makes about one litre of saliva every day. That is about two small bottles of water!

The flow of food

Food travels through five parts of the body, in this order:

Flow chart: mouth, oesophagus, stomach, intestine, anus — The flow of food during digestion.

A boy showing the mouth, oesophagus, stomach, intestine and anus — The parts of the food flow in our body. (Textbook p. 50)

Part	What happens
1. Mouth	Teeth chew. Tongue and saliva make the food soft.
2. Oesophagus	A narrow tube. It takes food from the mouth to the stomach.
3. Stomach	Food is broken into even smaller pieces.
4. Intestine	Nutrients are absorbed into the body.
5. Anus	Food the body does not need leaves as faeces (stool).

The grape in the oesophagus, stomach and intestine — The grape's journey: oesophagus, stomach and intestine. (Textbook p. 52)

Undigested food becomes faeces at the anus — Undigested food becomes faeces and leaves through the anus. (Textbook p. 53)

The oesophagus is the food tube. It is not the tube for air. Say it like this: "ee-SOF-a-gus".

Actions that disturb digestion

Eating while running causes vomiting; eating too fast causes coughing; talking while eating causes choking — Actions and their effects. (Textbook p. 54)

Action	Effect
Eating while running or jumping	Vomiting, stomach ache
Eating too fast	Coughing, choking
Talking or laughing while eating	Choking
Eating late at night	Stomach ache

Sit down, chew slowly and finish your food before you talk or play.

Digestion pictures: Science Year 3 (DLP) textbook, pp. 29, 50, 52–54.

Put these in order: stomach, mouth, anus, oesophagus, intestine.

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Mouth, oesophagus, stomach, intestine, anus.

Summary

Remember	Key fact
Types of teeth	Incisors cut, canines tear, molars grind
Parts of a tooth	Enamel, dentine, gum, nerves, blood vessels
Milk teeth / permanent teeth	20 teeth, short life / 32 teeth, long life
Dental care	Rinse, brush twice a day, floss, see the dentist every six months
7 classes of food	Carbohydrate, protein, fats, vitamins, minerals, fibre, water
Balanced diet	All classes of food in the right amounts (Malaysian Food Pyramid)
Digestion	Breaking food into small pieces so nutrients can be absorbed
Flow of food	Mouth, oesophagus, stomach, intestine, anus
Disturbs digestion	Eating while running, talking or laughing; eating too fast or late at night