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Macrofauna and lithotrophs can form symbiotic relationships, in which case the lithotrophs are called "prokaryotic symbionts". An example of this is chemolithotrophic bacteria in giant tube worms or plastids , which are organelles within plant cells that may have evolved from photolithotrophic cyanobacteria-like organisms.
Organotrophs use organic compounds as electron/hydrogen donors. Lithotrophs use inorganic compounds as electron/hydrogen donors.. The electrons or hydrogen atoms from reducing equivalents (electron donors) are needed by both phototrophs and chemotrophs in reduction-oxidation reactions that transfer energy in the anabolic processes of ATP synthesis (in heterotrophs) or biosynthesis (in autotrophs).
Heterotrophs occupy the second and third tropic levels of the food chain while autotrophs occupy the first trophic level. [7] Heterotrophs may be subdivided according to their energy source. If the heterotroph uses chemical energy, it is a chemoheterotroph (e.g., humans and mushrooms).
A lithoautotroph is an organism that derives energy from reactions of reduced compounds of mineral (inorganic) origin. [1] Two types of lithoautotrophs are distinguished by their energy source; photolithoautotrophs derive their energy from light, while chemolithoautotrophs (chemolithotrophs or chemoautotrophs) derive their energy from chemical reactions. [1]
Phototrophs can be either autotrophs or heterotrophs. If their electron and hydrogen donors are inorganic compounds (e.g., Na 2 S 2 O 3, as in some purple sulfur bacteria, or H 2 S, as in some green sulfur bacteria) they can be also called lithotrophs, and so, some photoautotrophs are also
Thus, heterotrophs – all animals, almost all fungi, as well as most bacteria and protozoa – depend on autotrophs, or primary producers, for the raw materials and fuel they need. Heterotrophs obtain energy by breaking down carbohydrates or oxidizing organic molecules (carbohydrates, fats, and proteins) obtained in food.
Chemoheterotrophs (or chemotrophic heterotrophs) are unable to fix carbon to form their own organic compounds. Chemoheterotrophs can be chemolithoheterotrophs , utilizing inorganic electron sources such as sulfur, or, much more commonly, chemoorganoheterotrophs , utilizing organic electron sources such as carbohydrates , lipids , and proteins .
An organotroph is an organism that obtains hydrogen or electrons from organic substrates. This term is used in microbiology to classify and describe organisms based on how they obtain electrons for their respiration processes.