If we do not clean our teeth and mouth after eating, many harmful bacteria start to live in it. These bacteria breakdown the sugars present from the leftover food and release acids. The acids gradually damage the teeth. This is called tooth decay. It causes tooth loss in many cases.

(i) The problem is of tooth decay which causes toothache.
(ii) One should clean the teeth with a toothbrush twice a day. Chocolates should be avoided.
(iii) She is aware and concerned about the problems arising in the teeth especially of younger children.

(i) No, the step taken by Rajesh was not right.
(ii) It can lead to addiction and can affect the health adversely.
(iii) We should not be influenced from others of taking any food supplements that might harm our health.

The food enters into the buccal cavity through mouth. It is chewed by the teeth and mixed with saliva. Saliva contains an enzyme called ptyalin (salivary amylase) which converts complex carbohydrates like starch into sugar. That is why the bread taste becomes sweet after chewing. This type of digestion is called salivary digestion.

The various components of food are as following:
(i) Carbohydrates
(ii) Fats
(iii) Proteins
(iv) Vitamins
(v)Minerals
(vi) Water and Roughage

Carbohydrates are complex substances. These complex substances cannot be utilised as such as we eat. They are broken down into simpler substances like glucose. This process is called digestion of carbohydrates.

There are four kinds of teeth in human beings situated in each jaw:
(i) Incisor: They are two in number and help to cut and bite food.
(ii) Canine: They are four in number and help in piercing and tearing of food.
(iii) Premolar: They are four in number and help in chewing and grinding the food. 
(iv) Molar: They are six in number and also help in chewing and grinding the food like premolar teeth.

The animals which have a separate part of stomach (rumen) are called ruminants. In this part the food is partially digested and is called cud. But later the cud returns to mouth in small lumps and the animal chews it. This process is called rumination or chewing cud. These animals are called ruminants.

The inner lining of stomach secretes the following
component:
(i) Mucous: It protects the lining of stomach. 
(ii) Hydrochloric acid: It kills the germs and makes the food acidic. 
(iii) Digestive juices: They help to break the proteins into simple substances.

The various components of food are as following:
(i) Carbohydrates
(ii) Fats
(iii) Proteins
(iv) Vitamins
(v)Minerals
(vi) Water and Roughage

If we do not clean our teeth and mouth after eating, many harmful bacteria start to live in it. These bacteria breakdown the sugars present from the leftover food and release acids. The acids gradually damage the teeth. This is called tooth decay. It causes tooth loss in many cases.

(i) It helps in talking.
(ii) It helps to mix saliva with the food.
(iii)It also helps in swallowing food.

The inner lining of stomach secretes the following component:
(i) Mucous: It protects the lining of stomach. 
(ii) Hydrochloric acid: It kills the germs and makes the food acidic. 
(iii) Digestive juices: They help to break the proteins into simple substances.

(i) It helps in talking.
(ii) It helps to mix saliva with the food.
(iii)It also helps in swallowing food.

Sometimes when we eat hurriedly, talks or laughs while eating, the flap-like valve (called epiglottis) which closes the passage of windpipe remains open. Therefore, the food may enter into the windpipe. Coughing helps to clear the passage and returns the food particle back to the foodpipe.

The difference between milk teeth and permanent teeth are

After surgical removal of gall bladder, A' would face problems in digestion of fat and fatty substances when consumed in bulk. This is because the bile juice stored in the gall bladder helps in digestion of fats.

The various components of food and their simpler forms are

Parts of digestive canal that are involved in following processes are
(a) small intestine
(b) buccal cavity
(c) stomach
(d) small intestine
(e) large intestine

Glucose is a simple sugar or carbohydrate which is broken down in the presence of oxygen into CO₂ and H₂O and releases instant energy. Glucose is easily absorbed by the blood, hence provides instant energy to the body.

Cellulose is the carbohydrate that can be digested by ruminants but not by humans because ruminants have a large sac-like structure called rumen which is located between the small intestine and large intestine. Certain bacteria are present in rumen which helps in digesting cellulose.

Bile juice is produced by the liver and stored in gall bladder. It helps in digestion of fats present in food.

Villi are the finger-like projections in the inner walls of the small intestine.
Function Villi increases the surface area for absorption of digested food.