Ingestion, Digestion, Absorption and Assimilation of Food — BIOLOGY STD 7 — Question

Teeth grow twice in human lifetime, temporary teeth and permanent teeth. The teeth which grow at the age of 6-7 months are called temporary teeth. They are 20 in number. These teeth start falling off around the age of 6-12 years and are replaced by a new set of teeth, called permanent teeth. There are total 32 teeth in the two jaws. There are four kinds of teeth in each jaw. These are incisors (8), canines (4) premolars (8) and mo 1 ar&i (12VJhere are 16 teeth in each jaw.

Incisors : These are situated at the front and are flat and straight with sharp edges, which are used for biting and cutting the food.
Canines : These are situated one on either side of the incisors in each jaw. There are two canines in*each jaw. These are sharp and pointed and are used for holding and tearing the food.
Premolars : There are 4 premolars in each jaw, situated next to the canines. Each premolar has one or two roots and two cusps. These are used for crushing and grinding the food.
Molars : These are 6 molars in each jaw. The molars have more than one root. These are used for crushing and grinding the food. The last molar of each side in each jaw is also called wisdom tooth because it appears last generally at the age of 17-20 years.
The ingested food is first broken down in mouth when we chew it with our teeth. This process is called mastication or mechanical digestion. It prepares the food for chemical digestion that is, the digestion by the action of enzymes.