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Food is the basic need of all living organisms for their existence. Early man started hunting animals and used fruits and roots of plants to meet his food requirements. Food is required to perform several functions. It is required for growth, development and body repair. It also protects the body from diseases. Food supplies proteins, carbohydrates, fats, vitamins, minerals and water to our body.
It is the combination of various organic and substances which is capable of providing
Sources of Food:Plants provide us foods like cereals, pulses, oil seeds, fruits and vegetables, on this basis plants are classified as follows :
Depending upon the mode of obtaining food, organisms are divided into two broad categories, autotrophs and heterotrophs.
Autotrophs are those organisms which make their own food with the help of solar energy from inorganic raw materials like CO2 and water. All green plants are autotrophs.
Heterotrophs are those organisms that cannot manufacture their own organic food but obtain the same from outside sources. All animals, human beings and non-green plants are heterotrophs. Heterotrophs obtain their food from biomass of either autotrophs or other heterotrophs which are ultimately dependent upon autotrophs.NCERT solutions for class 9 Science prepared by pw will help you to solve your NCERT text book exercise.