We eat various types of food which has to pass through the same digestive tract. It also has to be converted to substances small enough to be utilised by our body. This needs various processess that can be studied as follows.

Passage of food through alimentary canal or gut

Food is cut and crushed by our teeth in the mouth and mixed with saliva to make it wet and slippery lump called bolus (This process is called as mastication).

This bolus is suitable to pass through oesophagus. Saliva is secreted by three pairs of salivary glands. First pair is located at the side of the jaw called as submandibular, second pair is located below the tongue called as sublingual

and Food in the form of a soft slimy substance where some proteins and carbohydrates have already been broken down is called chyme. Now the food material passes from the stomach to the small intestine.

Here the ring like muscles called pyloric sphincters relax to open the passage into the small intestine.

The sphincters are responsible for regulating the opening of the passage such that only small quantities of the food material may be passed into the small intestine at a time.

third pair is located at the side of the ear called parotid glands. Saliva mainly contains an enzyme amylase (ptyalin) which helps in the breakdown of complex carbohydrates to simple ones. This process of breaking down of complex substances into simple substance with the help of enzymes and obsorbed into the body is called digestion. The tongue helps in mixing the food and pushing it into the next part. The lower jaw also helps in the whole process.

We can find out the effect of salivary amylase on carbohydrates to observe what might be happening in our mouth. p To know the chemical nature of the saliva perform the activity- 7 of co-ordination in life process of this text book.

The soft food mixed with saliva passes through oesophagus or food pipe by wave like movements called peristaltic movement to the stomach.

At the stomach, food gets churned with gastric juice and HCl. Now the food is in semisolid condition. The digestion of food goes on as most proteins are broken down into smaller molecules with the help of enzyme pepsin acting on them.