Life cannot exist without energy. Energy is inevitable for the day – to- day life activities. This energy is derived from food. Food is defined as a composite mixture of various substances which sustain life activities. Foodstuff is defined as anything which can be used as food. The foodstuff of animals is composed of the following six components:

Carbohydrates, Proteins, Lipids, Vitamins, Minerals and water

Role of Food

Food has four important functions in the life of animals. They are as follows:

It supplies energy which maintains the day-to-day life activities. Food is essential for the growth and repair of body and its parts. It gives temperature for the body. Certain type of food materials like vitamins regulate the activities of animals.


Carbohydrates are the cheapest sources of energy in the animal food. Carbohydrates are hydrates of carbon with an empirical formula Cn(H_2O). Hydrogen and oxygen are combined in the same ratio as in water (H_2O). Hence they were named as carbohydrates. But a number of carbohydrates, discovered later, do not have H and O in the above proportion; again some carbohydrates contain N_2 and S. Still the unsuitable name, carbohydrates, is retained. Carbohydrate is defined as an organic compound that contains carbonyl group, namely aldehyde or ketone in addition to two or more alcohol groups or that yields such compounds on hydrolysis. Eg. Glucose, Fructose, Sucrose, Lactose, Cellulose, Starch, Glycogen, etc.

Physiological Role of Carbohydrates

Carbohydrate has the following functions:

It is the main source of energy. Energy is essential for day- to-day activities. It plays main role in metabolism.


The term ‘protein’ is derived from a Greek word ‘protes’ meaning ‘prime’ or ‘first importance’. Proteins are complex organic nitrogenous compounds. They contain C, H_2,O_2,N_2 and S. Some proteins also contain P and Fe. Proteins are defined as high molecular weight polymers in which the building blocks are the aminoacids. Amino acids are the basic units of proteins. Each protein is formed of several amino acids. Eg. Albumin, Globulin, Haemoglobin, etc.

Physiological Role of proteins

In the animal world, protein has the following functions:

Most of the enzymes are protein in nature. The enzymes function as biocatalysts. The hormones secreted by endocrine glands are protein in nature. Haemoglobin transports gases. Immunoglobulin of blood plasma acts as antibodies. Proteins are essential for the growth and repair of animals. They supply energy and heat

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