Autotroph

"Producer (biology)" redirects here. For other uses, see Producer (disambiguation).
See also: Primary production
Overview of cycle between autotrophs and heterotrophs. Photosynthesis is the main means by which plants, algae and many bacteria produce organic compounds and oxygen from carbon dioxide and water (green arrow).

An autotroph is an organism that can convert abiotic sources of energy into energy stored in organic compounds, which can be used by other organisms. Autotrophs produce complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,[1] generally using energy from light or inorganic chemical reactions.[2] Autotrophs do not need a living source of carbon or energy and are the producers in a food chain, such as plants on land or algae in water. Autotrophs can reduce carbon dioxide to make organic compounds for biosynthesis and as stored chemical fuel. Most autotrophs use water as the reducing agent, but some can use other hydrogen compounds such as hydrogen sulfide.

The primary producers can convert the energy in the light (phototroph and photoautotroph) or the energy in inorganic chemical compounds (chemotrophs or chemolithotrophs) to build organic molecules, which is usually accumulated in the form of biomass and will be used as carbon and energy source by other organisms (e.g. heterotrophs and mixotrophs). The photoautotrophs are the main primary producers, converting the energy of the light into chemical energy through photosynthesis, ultimately building organic molecules from carbon dioxide, an inorganic carbon source.[3] Examples of chemolithotrophs are some archaea and bacteria (unicellular organisms) that produce biomass from the oxidation of inorganic chemical compounds, these organisms are called chemoautotrophs, and are frequently found in hydrothermal vents in the deep ocean. Primary producers are at the lowest trophic level, and are the reasons why Earth sustains life to this day.[4]

Most chemoautotrophs are lithotrophs, using inorganic electron donors such as hydrogen sulfide, hydrogen gas, elemental sulfur, ammonium and ferrous oxide as reducing agents and hydrogen sources for biosynthesis and chemical energy release. Autotrophs use a portion of the ATP produced during photosynthesis or the oxidation of chemical compounds to reduce NADP+ to NADPH to form organic compounds.[5]

History

The term autotroph was coined by the German botanist Albert Bernhard Frank in 1892.[6][7] It stems from the ancient Greek word τροφή (trophḗ), meaning "nourishment" or "food". The first autotrophic organisms likely evolved early in the Archean but proliferated across Earth's Great Oxidation Event with an increase to the rate of oxygenic photosynthesis by cyanobacteria.[8] Photoautotrophs evolved from heterotrophic bacteria by developing photosynthesis. The earliest photosynthetic bacteria used hydrogen sulphide. Due to the scarcity of hydrogen sulphide, some photosynthetic bacteria evolved to use water in photosynthesis, leading to cyanobacteria.[9]


Variants

Some organisms rely on organic compounds as a source of carbon, but are able to use light or inorganic compounds as a source of energy. Such organisms are mixotrophs. An organism that obtains carbon from organic compounds but obtains energy from light is called a photoheterotroph, while an organism that obtains carbon from organic compounds and energy from the oxidation of inorganic compounds is termed a chemolithoheterotroph.

Evidence suggests that some fungi may also obtain energy from ionizing radiation: Such radiotrophic fungi were found growing inside a reactor of the Chernobyl nuclear power plant.[10]

Flowchart to determine if a species is autotroph, heterotroph, or a subtype

Examples

There are many different types of autotrophs in Earth's ecosystems. Lichens located in tundra climates are an exceptional example of a primary producer that, by mutualistic symbiosis, combines photosynthesis by algae (or additionally nitrogen fixation by cyanobacteria) with the protection of a decomposer fungus. As there are many examples of primary producers, two dominant types are coral and one of the many types of brown algae, kelp.[3]

Photosynthesis

Gross primary production occurs by photosynthesis. This is the main way that primary producers get energy and make it available to other forms of life. Plants, many corals (by means of intracellular algae), some bacteria (cyanobacteria), and algae do this. During photosynthesis, primary producers receive energy from the sun and use it to produce sugar and oxygen.

Ecology

Green fronds of a maidenhair fern, a photoautotroph
See also: Primary production

Without primary producers, organisms that are capable of producing energy on their own, the biological systems of Earth would be unable to sustain themselves.[3] Plants, along with other primary producers, produce the energy that other living beings consume, and the oxygen that they breathe.[3] It is thought that the first organisms on Earth were primary producers located on the ocean floor.[3]

Autotrophs are fundamental to the food chains of all ecosystems in the world. They take energy from the environment in the form of sunlight or inorganic chemicals and use it to create fuel molecules such as carbohydrates. This mechanism is called primary production. Other organisms, called heterotrophs, take in autotrophs as food to carry out functions necessary for their life. 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. Carnivorous organisms rely on autotrophs indirectly, as the nutrients obtained from their heterotrophic prey come from autotrophs they have consumed.

Most ecosystems are supported by the autotrophic primary production of plants and cyanobacteria that capture photons initially released by the sun. Plants can only use a fraction (approximately 1%) of this energy for photosynthesis.[11] The process of photosynthesis splits a water molecule (H2O), releasing oxygen (O2) into the atmosphere, and reducing carbon dioxide (CO2) to release the hydrogen atoms that fuel the metabolic process of primary production. Plants convert and store the energy of the photons into the chemical bonds of simple sugars during photosynthesis. These plant sugars are polymerized for storage as long-chain carbohydrates, such as starch and cellulose; glucose is also used to make fats and proteins. When autotrophs are eaten by heterotrophs, i.e., consumers such as animals, the carbohydrates, fats, and proteins contained in them become energy sources for the heterotrophs.[12] Proteins can be made using nitrates, sulfates, and phosphates in the soil.[13][14]

Primary production in tropical streams and rivers

Aquatic algae are a significant contributor to food webs in tropical rivers and streams. This is displayed by net primary production, a fundamental ecological process that reflects the amount of carbon that is synthesized within an ecosystem. This carbon ultimately becomes available to consumers. Net primary production displays that the rates of in-stream primary production in tropical regions are at least an order of magnitude greater than in similar temperate systems.[15]

Origin of autotrophs

Main article: Abiogenesis § Deep sea hydrothermal vents

Researchers believe that the first cellular lifeforms were not heterotrophs as they would rely upon autotrophs since organic substrates delivered from space were either too heterogeneous to support microbial growth or too reduced to be fermented. Instead, they consider that the first cells were autotrophs.[16] These autotrophs might have been thermophilic and anaerobic chemolithoautotrophs that lived at deep sea alkaline hydrothermal vents. This view is supported by phylogenetic evidence – the physiology and habitat of the last universal common ancestor (LUCA) is inferred to have also been a thermophilic anaerobe with a Wood-Ljungdahl pathway, its biochemistry was replete with FeS clusters and radical reaction mechanisms. It was dependent upon Fe, H2, and CO2.[16][17] The high concentration of K+ present within the cytosol of most life forms suggests that early cellular life had Na+/H+ antiporters or possibly symporters.[18] Autotrophs possibly evolved into heterotrophs when they were at low H2 partial pressures where the first form of heterotrophy were likely amino acid and clostridial type purine fermentations.[19] It has been suggested that photosynthesis emerged in the presence of faint near infrared light emitted by hydrothermal vents. The first photochemically active pigments are then thought to be Zn-tetrapyrroles.[20]

See also

References

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  2. ^ Chang, Kenneth (12 September 2016). "Visions of Life on Mars in Earth's Depths". The New York Times. Archived from the original on 12 September 2016. Retrieved 12 September 2016.
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  4. ^ Post, David M (2002). "Using Stable Isotopes to Estimate Trophic Position: Models, Methods, and Assumptions". Ecology. 83 (3): 703–718. doi:10.1890/0012-9658(2002)083[0703:USITET]2.0.CO;2.
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  7. ^ "What Are Autotrophs?". 11 March 2019.
  8. ^ Crockford, Peter W.; Bar On, Yinon M.; Ward, Luce M.; Milo, Ron; Halevy, Itay (November 2023). "The geologic history of primary productivity". Current Biology. 33 (21): 4741–4750.e5. Bibcode:2023CBio...33E4741C. doi:10.1016/j.cub.2023.09.040. ISSN 0960-9822. PMID 37827153. S2CID 263839383. Archived from the original on 15 March 2024. Retrieved 5 December 2023.
  9. ^ Townsend, Rich (13 October 2019). "The Evolution of Autotrophs". University of Wisconsin-Madison Department of Astronomy. Archived from the original on 8 July 2022. Retrieved 3 May 2019.
  10. ^ Melville, Kate (23 May 2007). "Chernobyl fungus feeds on radiation". Archived from the original on 4 February 2009. Retrieved 18 February 2009.
  11. ^ Schurr, Sam H. (19 January 2011). Energy, Economic Growth, and the Environment. New York. ISBN 9781617260209. OCLC 868970980.{{cite book}}: CS1 maint: location missing publisher (link)
  12. ^ Beckett, Brian S. (1981). Illustrated Human and Social Biology. Oxford University Press. p. 38. ISBN 978-0-19-914065-7. Archived from the original on 15 March 2024. Retrieved 16 August 2020.
  13. ^ Odum, Eugene P. (Eugene Pleasants), 1913-2002. (2005). Fundamentals of ecology. Barrett, Gary W. (5th ed.). Belmont, CA: Thomson Brooks/Cole. p. 598. ISBN 0-534-42066-4. OCLC 56476957.{{cite book}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
  14. ^ Smith, Gilbert M. (2007). A Textbook of General Botany. Read Books. p. 148. ISBN 978-1-4067-7315-6. Archived from the original on 15 March 2024. Retrieved 16 August 2020.
  15. ^ Davies, Peter M.; Bunn, Stuart E.; Hamilton, Stephen K. (2008). "Primary Production in Tropical Streams and Rivers". Tropical Stream Ecology. pp. 23–42. doi:10.1016/B978-012088449-0.50004-2. ISBN 9780120884490.
  16. ^ a b Weiss, Madeline C.; Preiner, Martina; Xavier, Joana C.; Zimorski, Verena; Martin, William F. (16 August 2018). "The last universal common ancestor between ancient Earth chemistry and the onset of genetics". PLOS Genetics. 14 (8): e1007518. doi:10.1371/journal.pgen.1007518. ISSN 1553-7390. PMC 6095482. PMID 30114187.
  17. ^ Stetter, Karl O (29 October 2006). "Hyperthermophiles in the history of life". Philosophical Transactions of the Royal Society B: Biological Sciences. 361 (1474): 1837–1843. doi:10.1098/rstb.2006.1907. ISSN 0962-8436. PMC 1664684. PMID 17008222.
  18. ^ Sousa, Filipa L.; Thiergart, Thorsten; Landan, Giddy; Nelson-Sathi, Shijulal; Pereira, Inês A. C.; Allen, John F.; Lane, Nick; Martin, William F. (19 July 2013). "Early bioenergetic evolution". Philosophical Transactions of the Royal Society B: Biological Sciences. 368 (1622): 20130088. doi:10.1098/rstb.2013.0088. ISSN 0962-8436. PMC 3685469. PMID 23754820.
  19. ^ Schönheit, Peter; Buckel, Wolfgang; Martin, William F. (1 January 2016). "On the Origin of Heterotrophy". Trends in Microbiology. 24 (1): 12–25. doi:10.1016/j.tim.2015.10.003. ISSN 0966-842X. PMID 26578093. Archived from the original on 15 March 2024. Retrieved 4 December 2022.
  20. ^ Martin, William F; Bryant, Donald A; Beatty, J Thomas (21 November 2017). "A physiological perspective on the origin and evolution of photosynthesis". FEMS Microbiology Reviews. 42 (2): 205–231. doi:10.1093/femsre/fux056. ISSN 0168-6445. PMC 5972617. PMID 29177446.


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