Class 7 Science

Nutrition: Digestion in Human

The digestive system of humans is well developed. It consists of the gut or alimentary canal, along with many associated digestive glands. The alimentary canal is divided into mouth, oesophagus, stomach, small intestine, large intestine and rectum.

Mouth

The food is ingested through mouth. The mouth contains tongue, teeth and salivary glands. Teeth break the food into smaller particles. This process is called mastication. The chewed food is mixed with saliva. Saliva is a watery fluid secreted by the salivary glands. Saliva contains a type of enzyme called the salivary amylase, which converts starch into sugar.

Teeth

Our teeth cut, tear and grind the food before we swallow it. There are four types of teeth in our mouth.

  1. Incisors: These are flat and chisel-shaped teeth. They lie in the front of the mouth. There are eight incisor teeth: four in the upper jaw and four in the lower jaw. The incisor teeth are well adapted for cutting and biting of food items.
  2. Canines: These are round shaped, sharp and pointed teeth. Canines are well adapted to hold and tear the food. There are four canine teeth found in human.
  3. Premolars: There are two premolars on each side of each jaw. Premolars help in crushing and grinding the food. There are 8 premolar teeth in an adult human.
  4. Molars: There are two molars on both sides in both the jaws. They have almost a flat surface with small projections. These teeth are meant for fine grinding of food.

There are 12 molar teeth including the wisdom teeth in an adult human. The 4 molar teeth are also called wisdom teeth. Wisdom teeth usually grow between the ages of 18 to 21.

The tooth is covered with a white substance called enamel. It is the hardest substance in the human body.

Milk teeth and Permanent teeth

Humans get two sets of teeth in their lifetime. The first set comes out when we are babies. They are called milk teeth. Milk teeth last until we are about 8 years old. Milk teeth are replaced by the second set of teeth which are called permanent teeth.

An adult human has 32 teeth in all: 16 in each jaw.

Review Questions

Question 1: How many types of teeth are found in human beings?

Answer: There are four types of teeth in human beings. These are called incisors, canines, premolars and molars.

Question 2: How many incisors are found in an adult human?

Answer: There are 8 incisors, 4 in lower and 4 in upper jaw, found in an adult human.

Question 3: What is the function of incisors?

Answer: Incisors are used to cut and bite the food.

Question 4: How many canines are found in an adult human?

Answer: There are four canine found in an adult human.

Questions 5: What is the function of Canines?

Answer: Canines are the type of teeth, which help to hold and tear the food.

Question 6: How many premolars are found in an adult human?

Answer: There are 8 premolars found in an adult human.

Question 7: What is the function of premolars?

Answer: Premolars help in crushing and grinding the food.

Question 8: How many molars are found in an adult human?

Answer: There are 12 molars are found in an adult human.

Question 9: What is wisdom tooth?

Answer: Wisdom teeth are molar teeth that grow usually between the ages of 18 to 21 in an human. These are the last teeth to grow in human beings.

Question 10: How many teeth does a human adult have?

Answer: A human adult has 32 teeth in all: 16 teeth in each jaw.

Question 11: What do you understand by milk and permanent teeth?

Answer: Human has two sets of teeth. These are called milk teeth and permanent teeth. Milk teeth start growing at the baby stage and are replaced gradually by permanent teeth from the age of 8 year.

Question 12: What is Enamel?

Answer: The white substance that covers our teeth is called enamel. It is the hardest substance in the human body.