CBSE Class 7 Science Notes Chapter 2 Nutrition in Animals
All animals require food for obtaining energy, growth, repair of damaged parts and functioning of the body. The process of taking food by an animal and its utilisation in the body is called animal nutrition.

Plants can prepare their own food by the process of photosynthesis but animals get their food from plants, either directly by eating plants or indirectly by eating other animals that eat plants. Some animals eat both plants and other animals.

The components of food such as carbohydrates are complex substances which cannot be utilised by the body. So, they are broken down into simpler substances. The process of breakdown of complex components of food into simpler substances is called digestion. There are two methods of digesting food, i.e. physical method (including chewing and grinding of food in mouth) and chemical method (addition of digestive juices to the food by the body itself).

Different Ways of Taking Food
Different types of animals show different modes of nutrition. Some animals filter tiny food particles and feed upon them, while some swollen the animals they prey upon. The mode of nutrition in different animals depends upon the special structure or organ for taking food inside the body.

Starfish
It is a marine animal which is covered by hard shells of calcium carbonate. It has a unique mode of nutrition. It opens the shell of its prey and pops out its stomach through its mouth surrounding the soft body of its prey. The starfish after capturing its prey brings bach its stomach inside its own body. This food is then digested slowly by starfish.

Digestion in Humans
The food components pass through a continuous canal and get digested in each compartment. This is called an alimentary canal, it is ‘the tract or canal running from mouth to anus of human being where digestion and absorption of food take place.’
The alimentary canal can be divided into various compartments:

The buccal cavity

Food pipe or oesophagus

Stomach

Small intestine

Large intestine ending in the rectum

The anus

The main digestive glands which secrete digestive juices are

salivary gland

liver

pancreas

Various processes involved in utilisation of food in humans are

The process of taking food into the body is called ingestion.

The process by which the food containing large insoluble substances is broken down into small water-soluble substances is called digestion. There are two methods of digesting food, i.e. physical method (including chewing and grinding of food in mouth) and chemical method (addition of digestive juices to the food by the body itself).

The process by which the digested food passes through the intestinal wall into the bloodstream is called absorption.

The process by which the absorbed food is taken in body cells and used for energy, growth and repair is called assimilation.

The process by which the undigested food is removed from the body is called egestion.

Carbohydrates, fats and proteins are large insoluble substances which cannot pass through the walls of our intestine and get absorbed in that form. Therefore, these substances are broken down into small water-soluble substances. This is done by the process of digestion.

The carbohydrates get broken down into simple sugar called glucose, while fats in fatty acid and glycerol and proteins get broken down into amino acids during digestion. These simpler compounds are easily absorbed by the walls of small intestine into the blood.