An autotroph 's an organism that produces complex organic compounds from simple inorganic molecules using energy from light (by photosynthesis) or inorganic chemical reactions. Autotrophs are the producers in a food chain, such as plants on land or algae in water. Bacteria which derive energy from oxidizing inorganic compounds (such as hydrogen sulfide, ammonium and ferrous iron) are chemoautotrophs, and include the lithotrophs. Autotrophs are fundamental to the food chains of all ecosystems.… (More on Autotroph)