NEED FOR FOOD
Everything needs energy to do some job e.g. to operate machines, electricity, steam, fuels like coal, petrol, wood etc are burned to get energy. Similarly, living organisms require energy to carry out their diverse activities of life. They maintain the complex structure of cells, excrete waste material, and reproduce for continuation of their race. They grow in size during their life span as they are small when born and are large when adult. A considerable amount of energy is required to carry out the functions of life. The organisms, therefore, need to have some source of energy in order to maintain their life. Organisms get their energy from food. The type of food depends upon the kind of organism using the food. Some organisms use inorganic compounds to get their energy requirements. Some organisms use vegetables (plants) while some others require flesh (animals) as their food.
The organisms burn up their food (metabolize) to get a special form of energy called ATP (Adenosine triphosphate) which is used by them to carry out their functions of life.
NUTRITION OF FOOD AND THEIR IMPROTANCE
The food of organisms and the organic compounds, building their bodies are almost same. Their bodies are composed of carbohydrates, proteins and fats etc. These substances are used by organisms as their food. They get energy from these substances. They use the components of food in growth and repairing of damaged tissues. Thus substances acquired by organisms to obtain energy are called nutrients and the process by which they are obtained is called nutrition.
The food of all organisms which depends upon already prepared food has been found to consist of six basic components. These are as follows:
3. Fats, Oils