autotroph

{{Cleanup|date=June 2024|reason=Needs revisions for better readability and clarity.}}

File:Auto-and heterotrophs.pngs. 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,Morris, J. et al. (2019). "Biology: How Life Works", 3rd edition, W. H. Freeman. {{ISBN|978-1319017637}} generally using energy from light or inorganic chemical reactions.{{cite news |last= Chang |first= Kenneth |title= Visions of Life on Mars in Earth's Depths |url= https://www.nytimes.com/2016/09/13/science/south-african-mine-life-on-mars.html |date= 12 September 2016 |work= The New York Times |access-date= 12 September 2016 |archive-date= 12 September 2016 |archive-url= https://web.archive.org/web/20160912225220/http://www.nytimes.com/2016/09/13/science/south-african-mine-life-on-mars.html |url-status= live }} 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.{{Cite web|url=https://sciencing.com/primary-producers-8138961.html|title=What Are Primary Producers?|website=Sciencing|language=en|access-date=2018-02-08|archive-date=14 October 2019|archive-url=https://web.archive.org/web/20191014195302/https://sciencing.com/primary-producers-8138961.html|url-status=live}} 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.{{cite journal|last1=Post|first1=David M|year=2002|title=Using Stable Isotopes to Estimate Trophic Position: Models, Methods, and Assumptions|journal=Ecology|volume=83|issue=3|pages=703–718|doi=10.1890/0012-9658(2002)083[0703:USITET]2.0.CO;2}}

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.{{Cite journal |last=Bruslind |first=Linda |date=2019-08-01 |title=Chemolithotrophy & Nitrogen Metabolism |url=https://open.oregonstate.education/generalmicrobiology/chapter/chemolithotrophy-nitrogen-metabolism/ |journal=General Microbiology |language=en}} 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. Chemolithoautotrophs are microorganisms that synthesize energy through the oxidation of inorganic compounds.{{Cite web |date=2017-05-09 |title=5.10A: The Energetics of Chemolithotrophy |url=https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Boundless)/05:_Microbial_Metabolism/5.10:_Chemolithotrophy/5.10A:_The_Energetics_of_Chemolithotrophy |access-date= |website=Biology LibreTexts |language=en}} They can sustain themselves entirely on atmospheric CO₂ and inorganic chemicals without the need for light or organic compounds. They enzymatically catalyze redox reactions using mineral substrates to generate ATP energy.{{Cite web |date=2018-02-06 |title=14: Chemolithotrophy & Nitrogen Metabolism |url=https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Bruslind)/14:_Chemolithotrophy_and_Nitrogen_Metabolism |access-date= |website=Biology LibreTexts |language=en}} These substrates primarily include hydrogen, iron, nitrogen, and sulfur. Its ecological niche is often specialized to extreme environments, including deep marine hydrothermal vents, stratified sediment, and acidic hot springs.{{Cite journal |last1=Deng |first1=Wenchao |last2=Zhao |first2=Zihao |last3=Li |first3=Yufang |last4=Cao |first4=Rongguang |last5=Chen |first5=Mingming |last6=Tang |first6=Kai |last7=Wang |first7=Deli |last8=Fan |first8=Wei |last9=Hu |first9=Anyi |last10=Chen |first10=Guangcheng |last11=Chen |first11=Chen-Tung Arthur |last12=Zhang |first12=Yao |date=2023-12-05 |title=Strategies of chemolithoautotrophs adapting to high temperature and extremely acidic conditions in a shallow hydrothermal ecosystem |journal=Microbiome |volume=11 |issue=1 |pages=270 |doi=10.1186/s40168-023-01712-w |doi-access=free |issn=2049-2618 |pmc=10696704 |pmid=38049915}} Their metabolic processes play a key role in supporting microbial food webs as primary producers, and biogeochemical fluxes.

History

The term autotroph was coined by the German botanist Albert Bernhard Frank in 1892.{{Cite book|title=Lehrbuch der Botanik|url=https://www.biodiversitylibrary.org/bibliography/29599#/summary|last=Frank|first=Albert Bernard|year=1892–93|publisher=W. Engelmann|location=Leipzig|language=de|access-date=14 January 2018|archive-date=7 March 2023|archive-url=https://web.archive.org/web/20230307124024/https://www.biodiversitylibrary.org/bibliography/29599#/summary|url-status=live}}{{cite web |url=https://www.scienceabc.com/nature/what-are-autotrophs.html |title=What Are Autotrophs? |date=11 March 2019 }} It stems from the ancient Greek word {{wikt-lang|grc|τροφή}} ({{Transliteration|grc|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.{{Cite journal |last1=Crockford |first1=Peter W. |last2=Bar On |first2=Yinon M. |last3=Ward |first3=Luce M. |last4=Milo |first4=Ron |last5=Halevy |first5=Itay |date=November 2023 |title=The geologic history of primary productivity |url=https://doi.org/10.1016/j.cub.2023.09.040 |journal=Current Biology |volume=33 |issue=21 |pages=4741–4750.e5 |doi=10.1016/j.cub.2023.09.040 |pmid=37827153 |bibcode=2023CBio...33E4741C |s2cid=263839383 |issn=0960-9822 |access-date=5 December 2023 |archive-date=15 March 2024 |archive-url=https://web.archive.org/web/20240315091640/https://www.cell.com/current-biology/abstract/S0960-9822(23)01286-1?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982223012861%3Fshowall%3Dtrue |url-status=live |doi-access=free }} 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.{{Cite web|url=http://www.astro.wisc.edu/~townsend/static.php?ref=diploma-4#toc-The_Evolution_of_Autotrophs|title=The Evolution of Autotrophs|last=Townsend|first=Rich|date=13 October 2019|website=University of Wisconsin-Madison Department of Astronomy|access-date=3 May 2019|archive-date=8 July 2022|archive-url=https://web.archive.org/web/20220708065825/http://www.astro.wisc.edu/~townsend/static.php?ref=diploma-4#toc-The_Evolution_of_Autotrophs|url-status=live}}

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.{{cite web |url=http://www.scienceagogo.com/news/20070422222547data_trunc_sys.shtml |title=Chernobyl fungus feeds on radiation |last=Melville |first=Kate |date=23 May 2007 |access-date=18 February 2009 |archive-url=https://web.archive.org/web/20090204184150/http://scienceagogo.com/news/20070422222547data_trunc_sys.shtml |archive-date=4 February 2009 |url-status=live}}

File:AutoHeteroTrophs flowchart.png

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.

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

Image:Colpfl27a.jpg, a photoautotroph]]

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

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.{{cite book |title=Energy, Economic Growth, and the Environment |last=Schurr |first=Sam H. |date=19 January 2011 |isbn=9781617260209 |location=New York |oclc=868970980}} 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.{{cite book |last=Beckett |first=Brian S. |title=Illustrated Human and Social Biology |year=1981 |publisher=Oxford University Press |page=38 |url=https://books.google.com/books?id=-mYIPXC0gEgC&pg=PA38 |isbn=978-0-19-914065-7 |access-date=16 August 2020 |archive-date=15 March 2024 |archive-url=https://web.archive.org/web/20240315091624/https://books.google.com/books?id=-mYIPXC0gEgC&pg=PA38#v=onepage&q&f=false |url-status=live }} Proteins can be made using nitrates, sulfates, and phosphates in the soil.{{Cite book|last=Odum, Eugene P. (Eugene Pleasants), 1913-2002.|title=Fundamentals of ecology|date=2005|publisher=Thomson Brooks/Cole|others=Barrett, Gary W.|isbn=0-534-42066-4|edition=5th|location=Belmont, CA|pages=598|oclc=56476957}}{{cite book |last=Smith |first=Gilbert M. |title=A Textbook of General Botany |year=2007 |publisher=Read Books |page=148 |url=https://books.google.com/books?id=jmQUgBUaB_wC&pg=PA148 |isbn=978-1-4067-7315-6 |access-date=16 August 2020 |archive-date=15 March 2024 |archive-url=https://web.archive.org/web/20240315091638/https://books.google.com/books?id=jmQUgBUaB_wC&pg=PA148 |url-status=live }}

=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.{{cite book |doi=10.1016/B978-012088449-0.50004-2 |chapter=Primary Production in Tropical Streams and Rivers |title=Tropical Stream Ecology |pages=23–42 |year=2008 |last1=Davies |first1=Peter M. |last2=Bunn |first2=Stuart E. |last3=Hamilton |first3=Stephen K. |isbn=9780120884490 }}

Origin of autotrophs

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.{{Cite journal |last1=Weiss |first1=Madeline C. |last2=Preiner |first2=Martina |last3=Xavier |first3=Joana C. |last4=Zimorski |first4=Verena |last5=Martin |first5=William F. |date=2018-08-16 |title=The last universal common ancestor between ancient Earth chemistry and the onset of genetics |journal=PLOS Genetics |volume=14 |issue=8 |pages=e1007518 |doi=10.1371/journal.pgen.1007518 |issn=1553-7390 |pmc=6095482 |pmid=30114187 |doi-access=free }} These autotrophs might have been thermophilic and anaerobic chemolithoautotrophs that lived at deep sea alkaline hydrothermal vents. This view is supported by phylogenetic evidence{{dash}}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.{{Cite journal |last=Stetter |first=Karl O |date=2006-10-29 |title=Hyperthermophiles in the history of life |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=361 |issue=1474 |pages=1837–1843 |doi=10.1098/rstb.2006.1907 |issn=0962-8436 |pmc=1664684 |pmid=17008222}} 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.{{Cite journal |last1=Sousa |first1=Filipa L. |last2=Thiergart |first2=Thorsten |last3=Landan |first3=Giddy |last4=Nelson-Sathi |first4=Shijulal |last5=Pereira |first5=Inês A. C. |last6=Allen |first6=John F. |last7=Lane |first7=Nick |last8=Martin |first8=William F. |date=2013-07-19 |title=Early bioenergetic evolution |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |language=en |volume=368 |issue=1622 |pages=20130088 |doi=10.1098/rstb.2013.0088 |issn=0962-8436 |pmc=3685469 |pmid=23754820}} 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.{{Cite journal |last1=Schönheit |first1=Peter |last2=Buckel |first2=Wolfgang |last3=Martin |first3=William F. |date=2016-01-01 |title=On the Origin of Heterotrophy |url=https://www.researchgate.net/publication/284132666 |journal=Trends in Microbiology |language=en |volume=24 |issue=1 |pages=12–25 |doi=10.1016/j.tim.2015.10.003 |pmid=26578093 |issn=0966-842X |access-date=4 December 2022 |archive-date=15 March 2024 |archive-url=https://web.archive.org/web/20240315091633/https://www.researchgate.net/publication/284132666_On_the_Origin_of_Heterotrophy |url-status=live }} 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.{{Cite journal |last1=Martin |first1=William F |last2=Bryant |first2=Donald A |last3=Beatty |first3=J Thomas |date=2017-11-21 |title=A physiological perspective on the origin and evolution of photosynthesis |journal=FEMS Microbiology Reviews |volume=42 |issue=2 |pages=205–231 |doi=10.1093/femsre/fux056 |issn=0168-6445 |pmc=5972617 |pmid=29177446}}

References

External links

{{cite web|title=Lichen Biology and the Environment|url=http://www.lichen.com/biology.html|website=www.lichen.com|access-date=2014-05-11|archive-url=https://archive.today/20130621092559/http://www.lichen.com/biology.html|archive-date=2013-06-21|url-status=dead}}
{{cite web|title=Lichens|url=http://herbarium.usu.edu/fungi/funfacts/lichens.htm|website=herbarium.usu.edu|url-status=dead|archive-url=https://web.archive.org/web/20140101004257/http://herbarium.usu.edu/fungi/funfacts/lichens.htm|archive-date=2014-01-01}}
{{cite web|title=Lichens|url=http://archive.bio.ed.ac.uk/jdeacon/microbes/lichen.htm|website=archive.bio.ed.ac.uk}}

Category:Trophic ecology

Category:Microbial growth and nutrition

Category:Biology terminology

Category:Plant nutrition