Heterotroph
[3][4] Living organisms that are heterotrophic include all animals and fungi, some bacteria and protists,[5] and many parasitic plants.
The term heterotroph arose in microbiology in 1946 as part of a classification of microorganisms based on their type of nutrition.
Detritivores are heterotrophs which obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces).
[8] Saprotrophs (also called lysotrophs) are chemoheterotrophs that use extracellular digestion in processing decayed organic matter.
The process is most often facilitated through the active transport of such materials through endocytosis within the internal mycelium and its constituent hyphae.
Organotrophs exploit reduced carbon compounds as electron sources, like carbohydrates, fats, and proteins from plants and animals.
[22] While these authors agreed on the gasses present and the progression of events to a point, Oparin championed a progressive complexity of organic matter prior to the formation of cells, while Haldane had more considerations about the concept of genes as units of heredity and the possibility of light playing a role in chemical synthesis (autotrophy).
[23] Evidence grew to support this theory in 1953, when Stanley Miller conducted an experiment in which he added gasses that were thought to be present on early Earth – water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2) – to a flask and stimulated them with electricity that resembled lightning present on early Earth.
[25] On early Earth, oceans and shallow waters were rich with organic molecules that could have been used by primitive heterotrophs.
[26][27] Following the evolution of autotrophs, heterotrophs were able to utilize them as a food source instead of relying on the limited nutrients found in their environment.
[28] Today, many heterotrophs and autotrophs also utilize mutualistic relationships that provide needed resources to both organisms.
[30] However this hypothesis is controversial as CO2 was the main carbon source at the early Earth, suggesting that early cellular life were autotrophs that relied upon inorganic substrates as an energy source and lived at alkaline hydrothermal vents or acidic geothermal ponds.
[31] Simple biomolecules transported from space was considered to have been either too reduced to have been fermented or too heterogeneous to support microbial growth.
Heterotrophic microbes' respiration and fermentation account for a large portion of the release of CO2 into the atmosphere, making it available for autotrophs as a source of nutrient and plants as a cellulose synthesis substrate.
[41][40] Respiration in heterotrophs is often accompanied by mineralization, the process of converting organic compounds to inorganic forms.
