Autotrophs and Heterotrophs
An autotroph is an organism that can use external energy source and simple INorganic molecules to make complex organic molecules. The source of carbon is carbon dioxide. Autotrphs that use light energy e.g. plants, protoctist and photosynthetic prokaryotes, are called photoautotrophs. Some use chemical energy these are chemoautotrophs inluding nitrifying bacteria which obtain energy by oxidising ammonia to nitrite or nitrite to nitrate.
A heterotroph is an organism that needs to take in complex organic molecules (carbs, proteins lipids) to act as a source of energy and usable carbon compounds.