Milk Teeth : The first set of teeth grows during infancy and they fall off at the age between six to eight years. These are termed milk teeth.

Permanent Teeth : The second set that replaces milk teeth are called the permanent teeth.

• The permanent teeth may last throughout life or fall off during old age.

Types of teeth : 

(i) Molar : Molars are used for chewing and grinding. 

(ii) Premolar : Premolars are used for chewing and grinding. 

(iii) Canine : Canines are used for piercing and tearing. 

(iv) Incisor : Incisors are used for bitting and cutting. 

Ingestion : The process of taking food into the body is called ingestion.

Test for starch in food : We take two test tube named A and B. Take one teaspoonful of boiled rice in test tube A. In test tube B keep one teaspoonful of boiled rice after chewing. Add 3–4 mL of water in both the test tubes. Now pour 2–3 drops of iodine solution in each test tube and we observe that test tube turns it colour into blue of blackinsh. It show that the presence of starch in food. 

• The saliva breaks down the starch into sugars.

Tooth decay : When we do not clean our teeth and mouth after eating,
many harmful bacteria also begin to live and grow in it. These bacteria break down the sugars present from the leftover food and release
acids. The acids gradually damage the teeth. This is called tooth decay.

Stomach : The stomach is a thick-walled bag. Its shape is like a flattened J and it is the widest part of the alimentary canal. It is a gland which secretes digestive juice. 

Functions of Stomach : 

(i) It receives food from the food pipe at one end and opens into the small intestine at the other.

(ii) The inner lining of the stomach secretes mucous, hydrochloric acid and digestive juices.

(iii) It also provides acidic medium to the food. 

Mucous : Mucous is a watery substance secreted by inner lining of stomach. 

Role of mucous in Stomach: The mucous protects the inner lining of the stomach. 

Role of acids in Stomach : 

(i) The acid kills many bacteria that enter along with the food. 

(ii) It provides acidic medium in stomach. 

(iii) The digestive juices rich in acids which break down the proteins into simpler substances.

The small intestine : 
The small intestine is highly coiled and is about 7.5 metres long. It receives secretions from the liver and the pancreas. Besides, its wall also secretes juices.

Functions of small Intestine : 

(i) It absorbs nutrients like fat, protiens, carbohydrates and some minerals. 

(ii) Its wall also secretes juices.

Liver : The liver is a reddish brown gland situated in the upper part of the abdomen on the right side. It is the largest gland in the body.

Bile Juice : Bile jiuce is a secretion of liver that is stored in sac called the gall bladder. 

Functions of Bile : The bile plays an important role in the digestion of fats. 

Pancreas : The pancreas is a large cream coloured gland located just below the stomach. 

Functions of Pancreas : 

(i) The pancreatic juice acts on carbohydrates and proteins and changes them into simpler forms.

Absorption : Digested food is obsorbed by the wall of the intestine and passes into the blood vessels. This process is called absorption. 

Villi : The inner walls of the small intestine have thousands of finger-like outgrowths. These are called villi.

Functions of Villi : 

(i) The villi increases the surface area for absorption of the digested food.

(ii) Each villus has a network of thin and small blood vessels close to
its surface.

(iii) The surface of the villi also absorbs the digested food materials.

Assimilation : The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by the body. This is
called assimilation.

Realising of Energy from Disgested food: In the cells, glucose breaks down with the help of oxygen into carbon dioxide and water, and energy is released. 

Large intestine : The large intestine is wider and shorter than small intestine. It is about 1.5 metre in length. It starts from the end of small intestine. 

Functions of Large Intestine: 

(i) It absorbs water and some salts from the undigested food material.

Egestion : The faecal matter is removed through the anus from time-to-time. This is called egestion.

Grass Eating Animals: cows, buffaloes, Goats, Sheep and dears etc. 

Rumen : Grass eating animals like cows, buffaloes and goats quickly
swallow the grass and store it in a separate part of the stomach called
rumen. 

Cud : In the rumen the food gets partially digested and is called cud.

Rumination : After swallowing the food it inters into rumen and later the cud returns to the mouth in small lumps and the animal chews it. This process is called rumination