Autotrophs are Manufacturers of Food
An Autotroph – “ Self-Feeding”, from the Greek autos “Self” and trope “Nourishing”, is an organism that fabricates complex organic compounds such as carbohydrates, fats, and proteins from simple substances present in its surroundings. In short, they are the producer organisms that can make their food by photosynthesis or chemosynthesis and occupy the first trophic level.
Photoautotrophs – Manufacturers of Food by Photosynthesis
Photoautotrophs are autotrophic organisms that carry out photosynthesis using energy from sunlight, carbon dioxide as terminal electron acceptor and water, converted into organic materials used in cellular functions such as biosynthesis and respiration. There are fabricators in a food chain like plants on land and algae on the water (Eukaryotes). In the case of Prokaryotes, Purple Sulphur bacteria and Cyanobacteria are photoautotrophic prokaryotes.
Chemotrophs – Manufacturers of Food by chemosynthesis
Chemotrophs are organisms that make their food by chemosynthesis. It is a process that synthesises organic compounds from carbon dioxide using chemical energy by utilising inorganic compounds like hydrogen sulphide, sulphur, ammonium and ferrous iron as reducing agents found in hostile environments like deep-sea vents, where light cannot easily penetrate.
Examples: Methanogens, Halophiles, Nitrifiers, Thermoacidophiles
Lithotrophs
Lithotrophs are consumers of rocks. They are autotrophs that use an inorganic substrate of mineral origin as reducing agents or electron donors for the biosynthesis of organic compounds. Hence they are also called Chemolithotrophs. They produce a particular toxin that dissolves the minerals present in the rocks.
Examples: Purple sulphur bacteria, Nitrifying bacteria, and Hydrogen oxidisers.
Also, check out our post about Saprophytes.