Nutrition is defined as a process of intake of nutrients (like carbohydrates, fats, proteins, minerals, vitamins and water) by an organism as well as the utilisation of these nutrients by the organism. Nutrition is necessary for an organism as it provides energy to them from the food they eat. (b) There are mainly two modes of nutrition: (i) Autotrophic – Autotrophic nutrition is that mode of nutrition in which an organism makes its own food from the simple inorganic materials like carbon dioxide and water present in the surroundings (with the help of sunlight energy). Example: Green plants obtain food by autotrophic nutrition. (ii) Heterotrophic – Heterotrophic nutrition is that mode of nutrition in which an organism cannot make its own food from simple inorganic materials like carbon dioxide and water, and depends on other organisms for its food. Example: All animals obtain food by heterotrophic nutrition.