The term autotroph has been derived from two Greek wards-auto means self and troph means nutrition. In this mode of nutrition, the organisms prepare their own food from simple raw materials like water, carbon dioxide and mineral salts in the presence of sunlight.
The 5 essential steps in Holistic Nutrition are 1. Ingestion 2. Digestion 3. Absorption 4. Assimilation 5. Egestion. In the first step process food is taken inside by the organisms. Excepting a few (spiders, mosquitoes, flies which suck in liquid food), all animals consume solid food. Different organs are involved in different animals for this purpose.
All animals and non-green plants cannot make their own food. They depend on green plants directly or indirectly for their food supply. All animals and non-green plants are called heterotrophs and their mode of nutrition is called heterotrophic nutrition.
Green plants can directly use sunlight to form food from simple inorganic substances. They manufacture food from carbon dioxide and water in the presence of chlorophyll and sunlight.