The main difference between autotrophic organisms and heterotrophic organisms is that the former produce their own food, while the latter rely on other organisms for food. Autotrophs create nutritional organic substances from simple inorganic sources like carbon dioxide. Heterotrophs cannot produce organic compounds from inorganic substances.
Autotrophs are also called “primary producers” or “self feeders.” They produce energy through photosynthesis and chemosynthesis. Photoautotrophs use sunlight or chemical energy to transform water and carbon dioxide into glucose (i.e. sugar) that provides them energy and makes cellulose for cell walls. Examples of photoautotrophs are plants, algae, phytoplankton and a small number of bacteria.
Chemoautotrophs utilize energy from chemical reactions, typically between hydrogen sulfide and oxygen, to produce food. Their main source of carbon is carbon dioxide. Examples of chemoautotrophs are bacteria in hot water springs, hydrothermal vents in sea floor and those inside active volcanoes.
Heterotrophs depend on the organic matter produced by other organisms. Photoheterotrophs use sunlight for energy but cannot utilize carbon dioxide as a source of carbon. They obtain carbon from fatty acids, alcohol and carbohydrates. Examples of photoheterotrophs are heliobacteria, green non-sulfur bacteria and purple non-sulfur bacteria.
Chemoheterotrophs acquire energy by consuming living or dead organisms. Animals, bacteria, fungi and nearly all pathogens belong to this category.