Nutrition is defined as a process by which living beings obtain food, change food into simple absorbable forms and use it to make substances needed by the body.
Only plants can make their own food. Animals eat plants or other animals. There are two main modes of nutrition:
autos: self; trophos: food
The green plants, algae and cetain bacteria manufacture their own food through photosynthesis. They are termed autotrophs and their mode of nutrition autotrophic nutrition. They are the producers of the food chain as all organisms depend for food on them.
heteros: different; trophos: food
The organisms, which depend on other organisms for their food, are called heterotrophs and their mode of nutrition is heterotrophic nutrition. Heterotrophic nutrition is of various types.
holos = whole; zoic = animal
Holozoic nutrition includes ingestion, digestion and absorption of food as in Amoeba, frogs and human beings.
Organisms that live on or inside other living organisms, and derive their food from them are called parasites and the nutrition is called parasitic nutrition. Cuscuta or Dodder plant (Amar bel) is a parasite on green plants.
When a white cottony growth develop on your wet leather shoes or belts especially when they get wet during rainy days, it is a fungus. The fungus grows and feeds on substances, which were once part of the living organisms, such as stored food, wood, leather and rotten plant products. Some common examples are mushrooms, bread mould, yeast, etc.
Organisms that derive their food from dead and decaying organisms are called saprotrophs. Saprotrophs help in cleaning the environment by decomposing the dead and decaying organic matter.