Autotrophs are of two types

$(i)$ Chemoautotrophs The organisms performing chemosynthesis are called chemoautotrophs. They were anaerobic. Chemoautotrophs has the ability to synthesis organic molecules from inorganic raw materials. Such mode of nutrition is present even now in some bacteria, $e \cdot g$., sulphur bacteria, iron bacteria, nitrifying bacteria

$(ii)$ Photoautotrophs The photosynthesis organisms, the photoautotrophs, contains the pigment chlorophyll, which is formed by the combination of simple chemicals. They prepared organic food by using solar energy captured with the help of chlorophyll. They lacks the biochemical pathways to produce oxygen. They are still anaerobic and utilize hydrogen from the sources other than water