Autotroph

"Producer (biology)" redirects here. For other uses, seeProducer (disambiguation).

See also:Primary production

Overview of cycle between autotrophs andheterotrophs.Photosynthesisis the main means by which plants, algae and many bacteria produce organic compounds and oxygen from carbon dioxide and water (green arrow).

Anautotrophis an organism that can convertabioticsources of energy into energy stored inorganic compounds,which can be used byother organisms.Autotrophs produce complexorganic compounds(such ascarbohydrates,fats,andproteins) using carbon from simple substances such as carbon dioxide,generallyusing energy from lightorinorganic chemical reactions.Autotrophs do not need a living source of carbon or energy and are theproducersin a food chain, such as plants on land oralgaein water. Autotrophs canreducecarbon dioxide to make organic compounds for biosynthesis and as stored chemical fuel. Most autotrophs use water as thereducing agent,but some can use other hydrogen compounds such ashydrogen sulfide.

Theprimary producerscan convert the energy in the light (phototrophandphotoautotroph) or the energy in inorganic chemical compounds (chemotrophsorchemolithotrophs) to buildorganic molecules,which is usually accumulated in the form ofbiomassand will be used as carbon and energy source by other organisms (e.g.heterotrophsandmixotrophs). The photoautotrophs are the main primary producers, converting the energy of the light into chemical energy throughphotosynthesis,ultimately building organic molecules fromcarbon dioxide,aninorganiccarbon source.Examples ofchemolithotrophsare somearchaeaandbacteria(unicellular organisms) that producebiomassfrom theoxidationof inorganic chemical compounds, these organisms are calledchemoautotrophs,and are frequently found inhydrothermal ventsin the deep ocean. Primary producers are at the lowesttrophic level,and are the reasons why Earth sustains life to this day.

Mostchemoautotrophsarelithotrophs,using inorganic electron donors such as hydrogen sulfide,hydrogen gas,elementalsulfur,ammoniumandferrous oxideas reducing agents and hydrogen sources forbiosynthesisand chemical energy release. Autotrophs use a portion of theATPproduced during photosynthesis or the oxidation of chemical compounds to reduceNADP⁺to NADPH to form organic compounds.

History

The termautotrophwas coined by the German botanistAlbert Bernhard Frankin 1892.It stems from the ancient Greek wordτροφή(trophḗ), meaning "nourishment" or "food". The first autotrophic organisms likely evolved early in the Archean but proliferated across Earth'sGreat Oxidation Eventwith an increase to the rate of oxygenicphotosynthesisbycyanobacteria.Photoautotrophs evolved fromheterotrophicbacteria by developingphotosynthesis.The earliest photosynthetic bacteria usedhydrogen sulphide.Due to the scarcity of hydrogen sulphide, some photosynthetic bacteria evolved to use water in photosynthesis, leading tocyanobacteria.

Variants

Some organisms rely onorganic compoundsas a source ofcarbon,but are able to uselightorinorganic compoundsas a source of energy. Such organisms aremixotrophs.An organism that obtains carbon from organic compounds but obtains energy from light is called aphotoheterotroph,while an organism that obtains carbon from organic compounds and energy from the oxidation of inorganic compounds is termed achemolithoheterotroph.

Evidence suggests that some fungi may alsoobtain energyfromionizing radiation:Suchradiotrophic fungiwere found growing inside a reactor of theChernobyl nuclear power plant.

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

Examples

There are many different types of autotrophs in Earth's ecosystems.Lichenslocated in tundra climates are an exceptional example of a primary producer that, by mutualistic symbiosis, combines photosynthesis byalgae(or additionally nitrogen fixation by cyanobacteria) with the protection of a decomposerfungus.Also, plant-like primary producers (trees, algae) use the sun as a form of energy and put it into the air for other organisms.There are of course H₂O primary producers, including a form of bacteria, andphytoplankton.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 also the main way that primary producers take energy and produce/release it somewhere else. Plants, coral, bacteria, and algae do this. During photosynthesis, primary producers take energy from the sun and convert it into energy, sugar, and oxygen. Primary producers also need the energy to convert this same energy elsewhere, so they get it from nutrients. One type of nutrient is nitrogen.

Ecology

Green fronds of amaidenhair 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.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 allecosystemsin 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 calledprimary production.Other organisms, calledheterotrophs,take in autotrophs asfoodto carry out functions necessary for their life. Thus, heterotrophs – allanimals,almost allfungi,as well as mostbacteriaandprotozoa– depend on autotrophs, orprimary producers,for the raw materials and fuel they need.Heterotrophsobtain energy by breaking down carbohydrates or oxidizing organic molecules (carbohydrates, fats, and proteins) obtained in food.Carnivorousorganisms rely on autotrophs indirectly, as thenutrientsobtained from their heterotrophic prey come from autotrophs they have consumed.

Most ecosystems are supported by the autotrophicprimary productionofplantsandcyanobacteriathat capturephotonsinitially released by thesun.Plants can only use a fraction (approximately 1%) of this energy forphotosynthesis.The process ofphotosynthesissplits a water molecule(H₂O), releasing oxygen (O₂) into the atmosphere, andreducingcarbon dioxide (CO₂) to release thehydrogen atomsthat fuel themetabolicprocess ofprimary production.Plants convert and store the energy of the photon into the chemical bonds ofsimple sugarsduring photosynthesis. These plant sugars arepolymerizedfor storage as long-chaincarbohydrates,including other sugars, starch, and cellulose; glucose is also used to makefatsandproteins.When autotrophs are eaten byheterotrophs,i.e., consumers such as animals, thecarbohydrates,fats,andproteinscontained in them become energy sources for theheterotrophs.Proteins can be made usingnitrates,sulfates,andphosphatesin the soil.

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.

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 that were delivered from space was either too heterogeneous to support microbial growth or too reduced to be fermented. Instead, they consider that the first cells were autotrophs.These autotrophs might have beenthermophilicandanaerobicchemolithoautotrophs that lived at deep sea alkaline hydrothermal vents. Catalytic Fe(Ni)S minerals at these environments are shown to catalyze biomolecules like RNA.This view is supported by phylogenetic evidence as the physiology and habitat of thelast universal common ancestor(LUCA) was inferred to have also been a thermophilic anaerobe with a Wood-Ljungdahl pathway, its biochemistry was replete with FeS clusters and radical reaction mechanisms, and was dependent upon Fe, H₂,and CO₂.The high concentration of K⁺present within the cytosol of most life forms suggest that early cellular life hadNa⁺/H⁺antiportersor possibly symporters.Autotrophs possibly evolved into heterotrophs when they were at low H₂partial pressures where the first form of heterotrophy were likely amino acid and clostridial type purine fermentationsand photosynthesis emerged in the presence of long-wavelength geothermal light emitted by hydrothermal vents. The first photochemically active pigments are inferred to be Zn-tetrapyrroles.

See also

• Electrolithoautotroph
• Electrotroph
• Heterotrophic nutrition
• Organotroph
• Primary nutritional groups

External links

• "Lichen Biology and the Environment".lichen.Archived fromthe originalon 21 June 2013.Retrieved11 May2014.
• "Lichens".herbarium.usu.edu.Archived fromthe originalon 1 January 2014.
• "Lichens".archive.bio.ed.ac.uk.