2 Teeth and Digestion

13

Teeth and Digestion2

Curious Curie

Now when my teeth are falling, should I avoid brushing my teeth?

Then, Sachin’s father gave him an assignment to �nd out answers to the following questions :1. What would happen if all our teeth were of one kind? Had that been suitable for our

eating habits?2. Is the set of teeth di�erent in people with non-vegetarian diet from people with

vegetarian diet?Help Sachin in �nding the answers.

You will learn about

• Sets of teeth

• Kinds of teeth

• Parts of a tooth

• Care of teeth

• Digestion of food

• Microbes

While brushing, Sachin and his father discussed about the importance of teeth. Sachin’s father told him that teeth help in biting and chewing of food. The food is cut and chewed into smaller pieces. This helps in proper digestion of food. Teeth also make the speech clear. Healthy teeth make our smile more beautiful. Teeth are important part of our body and we must take proper care of them by brushing teeth twice a day.

14

CHAPTER 2: TEETH AND DIGESTION

Sets of teethWe have two sets of teeth in our life time. These are :

Milk teeth : They are the �rst set of teeth. They are 20 in number, 10 each in upper and lower jaw.

Permanent teeth : They are the second set of teeth that replace the milk teeth. They are 32 in number, 16 are in the upper jaw and 16 in the lower jaw.

Sets of teeth in our life

(Fig. 2.01) Milk teeth

Incisors

Canine

Molars

Upper jaw

The new born has no teeth.

First tooth appears at the age of 6 months.

All 20 milk teeth grow by the age of 2 to 3 years.

Milk teeth begin to fall at 6 years and are replaced by a permanent set of teeth.

Set of 28 permanent teeth grows in between 6 to 12 years of age.

4 wisdom teeth appear between the age of 12 to 21 years. They are the third molars.

An adult has 16 teeth in each jaw.

At old age, permanent teeth fall out.

(Fig. 2.02) Permanent teeth

Premolars

Molars

Incisors

Canine

Upper jaw

15


Kinds of teethThere are four kinds of permanent teeth : incisors, canines, premolars and molars.Incisors or cutting teeth, are the four front, �at-shaped teeth in each jaw. They help to bite the food.

Canines or tearing teeth, are sharp, pointed teeth. They are two in each jaw, one on either side of the incisors. They help to tear the food.

Premolars or cracking teeth, are four broad teeth in each jaw, two on either side of canines. They help to crush the food.

Molars or grinding teeth, are broader than premolars. They are six in each jaw, three on either side of premolars. They help to grind the food.

The number and kinds of teeth in a permanent set of teeth are as following :

Incisors Canines Premolars Molars

Upper jaw 4 2 4 6

Lower jaw 4 2 4 6

Total 8 4 8 12

Parts of a toothA tooth has distinct three parts. The top part is called the crown. Below it, are the neck and the root. When you look at your teeth in the mirror, only the crown is visible. The neck and root are embedded in the gums.

(Fig. 2.03) Kinds of teeth

The wisdom teeth are four rearmost molars on each side of our upper and lower jaw. The wisdom tooth got its name because it appears much later than other teeth, at an age when people are presumably wiser than a child. However the third molar, the wisdom tooth, is not indicative of wisdom of a person.

Wisdom tree

Teacher’s Note :- Take some clay and build the shape of each tooth, like make �at-shaped incisor, sharp-pointed canine, broad premolar and molar. With the help of your clay models, teach the role of each tooth.

16


The parts of a tooth are :

1. Enamel : The white cover of a tooth is called enamel. It is the hardest part in our body. It protects the tooth from wear and tear.

2. Dentine : It lies below the enamel. It is hard but softer than the enamel. It forms the bulk of a tooth.

3. Pulp : It lies inside the dentine. It is soft and has nerves and blood vessels in it. Blood vessels bring nutrients to the tooth.

4. Root : It is �xed inside the gum. It helps the tooth to stay in its proper place.

Care of teethWe must take care of our teeth, as we do not get another set if we lose the permanent set of teeth. When we eat, small pieces of food can get stuck in spaces between the teeth. If these food particles are not removed, they will cause the growth of microbes.

Plaque is a layer on the teeth formed by microbes, mostly bacteria. Bacteria feed on the sugar present in the food and produce acid. The acid corrodes the enamel, then it corrodes the dentine. Such bacterial action makes a hole in the tooth known as cavity. When the bacteria reach the nerves, present in the pulp, they cause pain.

(Fig. 2.05) Cavity formation in a tooth

(Fig. 2.04) Structure of a tooth

Root

Neck

CrownEnamelDentine

Pulp

Tooth decay not only causes cavity but also toothache, bad breath and bleeding gums. It can also cause indigestion.

17


1. Brush your teeth twice in a day. In the morning, on waking up and at night, before sleeping.

2. Brush your teeth up-down, back-forth and behind the teeth, gently with a soft brush.

3. Rinse your mouth well after every meal.4. Avoid eating chocolates, sticky candies and sweets.5. Keep salads and lemon in your regular diet. They

supply you with vitamins and minerals to keep the teeth healthy. Drink plenty of milk. It gives you calcium which is good for teeth.

6. Use a dental �oss to clean food particles stuck in spaces between the teeth.

7. Visit your dentist for regular check up once in every six months.

Up and Down

Back and Forth

Behind the Teeth

(Fig. 2.06) Correct way of brushing teeth

Dental floss

In praise ..

Dr. Pierre Fauchard (1678-1761) is called the father of modern dentistry. He was one of the �rst to identify that the cause of dental caries was sugar and not a worm, as it was thought at that time.

We can keep our teeth and gums healthy by practising the following:

Quick CheckTick (ü) the correct answer : 1. _______ are called tearing teeth.

(a) Incisors (b) Canines (c) Premolars (d) Molars 2. _______ is the hardest substance in our body.

(a) Enamel (b) Dentine (c) Pulp (d) Gum 3. _______ is a layer on the teeth formed by microbes.

(a) Crown (b) Cavity (c) Plaque (d) Enamel

18


In the previous chapter, we learnt that we need food for energy, but how is food used by our body? The food we eat is a complex substance. It has to be broken down and changed into simpler form, so that it is easily absorbed in our body.The process of changing complex form of food into simpler form is called digestion. Digested food is carried by the blood to all the parts of the body. The food is then converted into energy.

The process of digestion : Digestive system is an organ system formed of a set of organs that work together in the process of digestion.

Digestion of food

(Fig. 2.07) Digestive system

Mouth

Food Pipe

Salivary glands

LiverStomach

Small Intestine

Large Intestine

Gall bladder

Pancreas

Rectum

1. Mouth : Digestion starts in the mouth. Teeth chew food and break it into smaller pieces. There are three pairs of salivary glands in our mouth. They release a digestive juice, called saliva. The saliva mixes well with the food while chewing. It makes the food soft to swallow. Saliva changes complex carbohydrates into simple sugars. A lump of soft, semi-digested food swallowed is called bolus.

2. Food pipe : After mouth, comes the food pipe through which the bolus passes into the stomach.

3. Stomach : The stomach is a hollow, muscular bag. The food is churned and mixed with the digestive juices. The digestive juices break down the protein into simpler forms. The food remains in stomach for up to four hours. From the stomach, the food is pushed into a long, coiled tube called the small intestine.

4. Small intestine : It is the longest part of the digestive system. Intestinal juices mix with the food and break it down further. Here, juices come from the intestinal wall, liver, pancreas and gall bladder. These juices complete the digestion of the food that makes it ready to be absorbed. Intestinal wall has hair-like outgrowths which are richly supplied with blood vessels. Most nutrients are absorbed into the blood along with water. The blood carries the absorbed nutrients to various parts of the body.

19


MicrobesMicrobes are tiny organisms that cannot be seen with naked eyes, hence they are also called microorganisms. Many microbes are microscopic, which means they can only be seen under a microscope. Unlike humans, the body of some microbes comprises of a single cell. They are, therefore, called single-celled microorganisms. The conditions which favour growth of microbes are warmth, moisture, food and air, because of which they can grow everywhere. They can grow in places like our mouth, air, soil, water, inside or outside our body. Some microbes are useful to us while others are harmful. Harmful microbes are called germs.

5. Large intestine : The undigested food pass into a wider tube called the large intestine. The remaining water is absorbed through the walls of the large intestine into the blood vessels.

6. Rectum : The undigested semi-solid waste accumulates inside the rectum. Then it passes out through the anus as excreta.

Bacteria ProtozoaViruses(Fig. 2.08) Types of microbes

Fungi

Kinds of microbes

Microbes are of four kinds : bacteria, viruses, protozoa and fungi.• Bacteria : Bacteria are single-celled microorganisms. They are mainly of three shapes :

rod, spiral or round. Some of them cause diseases like food poisoning, acne, typhoid, tuberculosis, pneumonia, etc.

• Viruses : Viruses are extremely small microorganisms. They are seen only under powerful microscopes. They cause diseases like measles, mumps, dengue, chicken pox, common cold, �u, etc.

• Protozoa : Protozoans are single-celled microorganisms. They are bigger than bacteria and live in wet places. Some of them live in plant and animal bodies. They cause diseases, like dysentry, malaria, sleeping sickness, etc.

• Fungi : Fungi are organisms which grow on dead and decaying matter. Some fungi are useful, like the yeast makes the bread soft. Some fungi cause diseases, such as ringworm, athelete’s foot, etc.

20


Useful microbes• Some bacteria change milk into curd.• Some microbes decay dead bodies of plants and animals.• Some bacteria reside in our intestine and help us by producing vitamin K in our

body.• Some bacteria help in the digestion of roughage in animals, like cow and sheep.• Yeast is used to make bread and cake.• Some fungi produce antibiotics which are used as medicines.

Watch Word

sMilk teeth – First set of teeth that grows in children

Permanent teeth – Second set of teeth that replaces the milk teeth

Incisors – Teeth that help to cut and bite the food

Canines – Teeth that help to tear the food

Premolars – Teeth that help to crush the food

Molars – Teeth that help to grind the food

Digestion – The process of breaking down of food into simpler form

Digestive system – An organ system formed of a set of organs that digest the food

Microbes – Very small organisms that cannot be seen with naked eyes

Let Us Recall

y Humans have two sets of teeth: milk teeth and permanent teeth.

y Teeth are of four kinds : incisors, canines, premolars and molars.

y A tooth has three parts : crown, neck and root.

y A tooth is made up of : enamel, dentine and pulp.

y We must take care of our teeth. We must brush our teeth twice in a day.

21


Practice Test - 1

A. Tick (ü) the correct answer :

1. Digestion begins in ___________.(a) stomach (b) mouth (c) food pipe (d) small intestine

2. The number of permanent teeth is __________ .(a) 38 (b) 32 (c) 20 (d) 36

3. The four front chisel-like teeth in each jaw are ___________ .(a) canines (b) molars (c) premolars (d) incisors

4. The hardest part of the body is ____________ .(a) enamel (b) dentine (c) bone (d) gum

5. Pneumonia is a disease caused by ____________ .(a) virus (b) bacteria (c) protozoa (d) fungi

6. When you bite an apple, the impression on the fruit is most likely of __________.(a) wisdom teeth (b) canines (c) incisors (d) molars

Test Match

y The process of changing complex form of food into simpler form is called digestion.

y Digestive system comprises mouth, food pipe, stomach, small intestine, large intestine, rectum and anus.

y Apart from these organs, liver, gall bladder and pancreas are involved in the digestion.

y Microbes are tiny living organisms. They are of four kinds : bacteria, virus, protozoa and fungi.

22


B. Match the following :

1. Food pipe Water is absorbed in it

2. Small intestine Semi-solid waste is thrown out through it

3. Stomach Food passes through it into stomach

4. Large intestine Hollow, muscular bag

5. Mouth Longest part of the digestive system

6. Anus Three pairs of salivary glands are present

C. Circle the odd one out :

1. Incisor, Canine, Molar, Floss

2. Enamel, Dentine, Pulp, Plaque

3. Typhoid, Tuberculosis, Pneumonia, Sleeping sickness

4. Liver, Pancreas, Rectum, Gall bladder

D. State True or False (T/F) :

1. Saliva changes complex carbohydrates into simple sugars.

2. In the milk teeth set, there is more teeth in the lower jaw.

3. Dentine is the hardest part of the tooth.

4. Most microbes are too small to be seen with naked eyes.

Practice Test - 2

A. Tick (ü) the correct answer :

1. Digestive juices in small intestine come from intestinal wall and __________.

(a) liver (b) pancreas (c) gall bladder (d) all of these

2. The number of teeth an adult has in each jaw is __________ .

(a) 22 (b) 16 (c) 32 (d) 14

23


3. Out of 32 teeth, the number of molars is ___________ .

(a) 16 (b) 12 (c) 10 (d) 8

4. The microbes that have three main shapes, rod, spiral and round, are ___________ .

(a) bacteria (b) viruses (c) protozoa (d) fungi

B. Very Short Answer Type Questions

1. Name the outer most layer of a tooth.

2. What is digestion?

3. Name the nutrients that keep our teeth and gums healthy.

4. Which of the microbes produces antibiotics?

C. Short Answer Type Questions

1. Name the organs which pour their digestive juices in small intestine.

2. Name the kinds of teeth we have and give their numbers in each set of teeth.

3. Name two bacterial and two viral diseases.

4. De�ne microbes. Write four conditions which favour their growth.

D. Long Answer Type Questions

1. How do cavities form?

2. What are the roles of di�erent kinds of teeth?

3. How should we take care of our teeth?

4. Draw a labelled diagram of a tooth.

5. How is food digested and absorbed in the small intestine?

HOTS Questions

1. After reading this lesson, Sonu has reduced eating chocolates. Can you explain why?

2. Why plain bread, rice or chapati tastes a little sweet when it is chewed properly?

HOTS Questions

24


Value Based QuestionYou have noticed that at night, after dinner, your mother gets so tired that she often skips brushing her teeth. How can you help your mother with her work to ensure she does not skip brushing?

Indoor Activity

A lesson from a dentistA class can be arranged with a dentist. The doctor will discuss with the help of charts and models about the structure of a tooth. The doctor will explain how does a cavity form and how it can be prevented. Learners will write a report about the discussion and highlight the new values they have learnt.

Outdoor Activity

During the rainy season, go to the shaded part of the school garden along with your teacher. Observe the mushrooms without touching them. Make notes and draw a diagram in your science notebook.

Note : Some mushrooms are poisonous.

Documents

2 Teeth and Digestion