Class 7 Science Nutrition in Animals
All organisms, including humans, require food for growth, to repair damaged part of their bodies and for obtaining energy to carry out life processes. The process of taking food by an animal and its utilisation in the body is called animal nutrition. Nutrition in animals takes place in five steps: Ingestion, Digestion, Absorption, Assimilation
1. Ingestion: The process of taking food into the body is called ingestion. When we put food into our mouth with hands, we are ingesting the food. However, different animals ingest food in different ways and have special organs
for this purpose.
2. Digestion: The food of most animals consists of complex, insoluble substances which cannot be absorbed by the animal’s body in this form. The process in which the food containing large, insoluble substances is broken down
into small, soluble substances (which can be absorbed by our body) is called digestion.
3. Absorption: The process in which the simple soluble digested food substances are absorbed into the body fluids is called absorption.
4. Assimilation: The process by which the absorbed food is taken in by the body cells and used for energy, growth and repair, is called assimilation.
5. Egestion: A part of the food which we eat remains undigested and unabsorbed which cannot be used by the body. The process by which the undigested food is removed out from the body is called egestion.
Human Digestive System
The human digestive system consists of the alimentary canal and its associated glands. The human digestive system consists of buccal cavity (mouth), oesophagus (food pipe), stomach, small intestine, large intestine, rectum
and anus. There are also some glands which are associated with the human digestive system like the salivary gland, liver and pancreas. Salivary glands are located in our mouth. The liver is a reddish-brown gland situated in the upper
part of the abdomen on the right side. The liver is the largest gland in the body. The pancreas is a large, cream coloured gland located just below the stomach. The ducts of the various glands open into the alimentary canal and pour the secretions of their digestive juices into the alimentary canal. A long tube running from the mouth to the anus of a human being in which digestion and absorption of food take place is called the alimentary canal. The alimentary canal is also known as gut or digestive tract. In humans, it is 8 to 9 metres long. The alimentary canal
is a continuous canal which has many parts such as mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus. A wave-like movement caused by the alternate contraction and relaxation of the muscles of
the alimentary canal is called peristalsis which pushes the food forward in the alimentary canal. We will now describe how food gets digested when it passes through the various parts of the alimentary canal.