Nutrition in Animals Class 7 Science

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In the Large Intestine

The food that remains undigested and unabsorbed passes from the small intestine to the large intestine, which is wider and shorter than the small intestine. It is about 1.5 metres in length. The large intestine absorbs most of the
water from the undigested food material. Due to the removal of water, the undigested food becomes semi-solid. Then the undigested food (or waste material) is stored in a part called rectum of the large intestine. This undigested
food (semi-solid food) is passed out from the body through the anus in the form of faeces. This is called egestion.


The teeth are present in the mouth which helps in biting and chewing different types of food While eating, the teeth cut and grind food substances to break it down into simpler and smaller particles. The teeth are coated with
enamel which is the hardest substance in the body. Beneath this is the dentine, which is softer than enamel. Teeth are of four types – incisors, canines, premolars and molars.
(i) Incisors (cutting teeth): These are four flat and blade-like teeth present in the front part of each jaw. These teeth are used to bite and cut the food into small pieces.
(ii) Canine (tearing teeth): These are present on the either side of the incisors. They are two in number in each jaw. These are sharp and pointed and help in tearing the food.

(iii) Premolars (grinding teeth): There are two premolars next to each canine (four in number in each jaw). These are broad and flat teeth. They grind food and break it into small pieces.

(iv) Molars (grinding teeth): The remaining teeth in the jaw are three molars on either side of premolars (six in number in each jaw). These teeth are also flat and broad. They are larger than premolars. These teeth are also used to crush and grind food.



Milk teeth and Permanent teeth

Humans have milk teeth during childhood. Milk teeth begin to appear when the child is just a few months old. There are 20 milk teeth, 10 in each jaw – 4 incisors, 2 canines and 4 molars. The milk teeth loosen and begin to fall off
between the age of 6 and 8 years. When milk teeth fall off in a child, another set of teeth grow in their place. The second set of teeth is called permanent teeth. The permanent teeth grow in place of milk teeth. The permanent set
of teeth remains till the old age.

Tooth Decay and Toothache

When we eat food, small bits of it get stuck between our teeth. Sometimes, these bits of food stay between our teeth if we do not brush your teeth carefully. The bacteria present in our mouth react with the leftover food and form
acids. These acids affect the tooth enamel, which starts decaying. This is called tooth decay.

Tooth decay causes the following :
1. Holes or cavities in the teeth;
2. Foul smell
3. Loosening of teeth;
4. Toothache;
5. Stomach disorders.
Tooth decay can be avoided by the following ways.
(a) We should avoid eating too many sweets, ice creams, and chocolates.
(b) We must brush our teeth at least twice a day in the morning and at night, before going to bed.
(c) We must floss our teeth every day. A dental floss is a special strong thread that is moved back and forth through the spaces between our teeth to remove the food stuck between our teeth, that cannot be removed by brushing.

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NCERT Solutions and Additional Questions-answers

Chapter 2: Nutrition in animals (NCERT Solutions and Additional Questions)