Autotrophic Nutrition
         When organisms make their food from simple inorganic substances like H2O and CO2, than it is called Autotrophic Nutrition. Such organisms are called Autotrophs.
         All Green plants are Autotrophs or Producers because they make their own food by the process of photosynthesis.
(i)     Photoautotrophs : Those which utilize sunlight for preparing their food. e.g. plants, algae, purple red and green bacteria.  
(ii)     Chemoautotrophs : Those which utilize chemical energy for preparing their food. e.g. Nitrifying bacteria, iron bacteria, sulphur bacteria, methane bacteria.