CBSE Class 4 Science – 6. Teeth and Microbes (Notes)

Teeth –The hard-white organs in our mouth that we use for biting are called teeth.

Babies are born without any teeth.

 

What are the important of teeth?

They help us to bite and chew the food.

They help in speaking.

They also give shape to our face.

 

Set of teeth:

Humans and most other mammals have two sets of teeth – milk teeth and permanent teeth.

 

      

There are four different types of teeth in humans:

Incisors

Incisors are present at the front of the mouth.

These teeth are adapted for cutting food into small, chewable pieces.

Humans have 8 incisors, 4 incisors in each jaw.

Canines

Canines are situated at the ‘corners’ of the dental arches.

They are characteristically sharp and elongated.

Their primary function is to grip and tear food (tough food such as meat).

Humans have 4 canines, 2 in each jaw.

Premolars

Premolars are teeth located behind the canines.

These teeth have a flat surface, which is adapted for crushing food.

Humans have 8 premolars, 4 in each side of the jaws.

Molars

Molars are the largest of the teeth.

It has a large and flat biting surface, which is well-adapted for grinding food.

Humans have 12 molars, 6 in each jaw.

(4 of those are wisdom teeth, which is also called the third molar.)

 

Structure of teeth

 

It is a graphic image of the structure of a tooth. As seen in the above image.

The part of the tooth which is above the gum is called the crown.

The part of the tooth which is inside the gums is called the root.

Root holds the tooth firmly in place.

 

The three layers of tooth are-                                      

Enamel – The substance by which outer layer of the crown is made of is enamel.

Enamel is the hardest part in the body. It is harder than the bone.

Dentine – The beneath layer of the enamel is called dentine.

Dentine is not as hard as enamel.

Pulp – The innermost part of the tooth that contains nerves and blood vessels is called pulp.

 

Why the teeth decay?

While eating food, small pieces of food get stuck between our teeth.

If we don’t remove these small pieces of food, germs will grow on it.

Acids produced by these germs harm the enamel.

After sometimes small holes called cavities will form on the teeth.

It starts hurting when the cavity reaches the pulp.

 

We should take care our teeth by following mentioned steps:

Brush teeth twice a day. In the morning and at night before going to sleep.

We should wash our mouth with water after having every meal.

Floss your teeth daily (regularly).

 

Microbes – Tiny organisms that cannot be seen with the naked eye is called microbes.

Ex-bacteria, viruses, protozoa, fungus, algae etc.

A microbe is a very small living thing, which we can only see by microscope.

Microbes can be seen only through the microscope hence they are also called microscopic organisms.

Microbes are found everywhere, in the air, in water, in soil and even inside our body.

Some microbes are useful to us, whereas some are harmful.

They grow in the presence of food, air, moisture and warmth.

Our mouth provides a favourable condition for their growth.

 

Protozoan Diseases

1. Dengue – Fever transmitted by mosquito bite of infected Aedes mosquito.
2. Malaria – Fever transmitted by mosquito bite of infected Anopheles mosquito.
3. Chikungunya – Fever transmitted by mosquito bite of infected Yellow fever mosquito.
4. Amoebic dysentery – Stomach infection transmitted by contaminated food, drink.

 

Bacterial Diseases – Treated with Antibiotics

1. Typhoid – Fever with red spots on chest transmitted by contaminated food, drink
2. Cholera – Infection of small intestine transmitted by contaminated water.
3. Plague – Fever transmitted by fleas.
4. Tuberculosis (TV) – Growth of nodules in lungs transmitted by air.
5. Tetanus – Stiffness of jaw and other muscles; bacterial infection on wounds.

 

Viral Diseases –

1. Common cold – Running nose and fever; Spread through air.
2. Measles – Fever and red rash; spread through air
3. Swine Flu – Fever; Spread through air.
4. Polio – Affects nervous system; Spread through the faces of infected person.
5. Korona– Fever, cough, affect respiratory system, spread through droplets.

 

Fungal Diseases –

1. Ringworm – Small itchy round patches on any body part; Contact with infected person or their clothes through touch.
2. Athlete’s foot – Itchy patches between fingers; Contact with infected person or their clothes through touch.

 

Useful microbes:

Some bacteria help in producing curd from milk.

Some help in producing vitamins in our body. Some bacteria help in digestion of food.

Some fungus helps in making bread and Burn

Bacteria and fungi help in the decay of dead plants and animal waste to form manure.