Autotroph

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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). Auto-and heterotrophs.png
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 produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide, [1] generally using energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis). [2] They convert an abiotic source of energy (e.g. light) into energy stored in organic compounds, which can be used by other organisms (e.g. heterotrophs). 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 (in contrast to heterotrophs as consumers of autotrophs or other heterotrophs). 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.

Contents

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] [ non-primary source needed ] 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. [7] 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. [8]

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. [9]

Flowchart to determine if a species is autotroph, heterotroph, or a subtype AutoHeteroTrophs flowchart.png
Flowchart to determine if a species is autotroph, heterotroph, or a subtype

Examples

There are many different types of primary producers out in the Earth's ecosystem at different states. Fungi and other organisms that gain their biomass from oxidizing organic materials are called decomposers and are not primary producers. However, 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. Also, plant-like primary producers (trees, algae) use the sun as a form of energy and put it into the air for other organisms. [3] There are of course H2O primary producers, including a form of bacteria, and phytoplankton. 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 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. [4] [3]

Ecology

Green fronds of a maidenhair fern, a photoautotroph Colpfl27a.jpg
Green fronds of a maidenhair fern, 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. [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. [10] 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 photon into the chemical bonds of simple sugars during photosynthesis. These plant sugars are polymerized for storage as long-chain carbohydrates, including other sugars, 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. [11] Proteins can be made using nitrates, sulfates, and phosphates in the soil. [12] [13]

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. [14]

Origin of autotrophs

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. [15] These autotrophs might have been thermophilic and anaerobic chemolithoautotrophs that lived at deep sea alkaline hydrothermal vents. Catalytic Fe(Ni)S minerals at these environments are shown to catalyze biomolecules like RNA. [16] This view is supported by phylogenetic evidence as the physiology and habitat of the last 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. [15] [17] The high concentration of K+ present within the cytosol of most life forms suggest 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] and 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. [20]

See also

Related Research Articles

<span class="mw-page-title-main">Nutrition</span> Provision to cells and organisms to support life

Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient nutrients causes malnutrition. Nutritional science is the study of nutrition, though it typically emphasizes human nutrition.

<span class="mw-page-title-main">Photosynthesis</span> Biological process to convert light into chemical energy

Photosynthesis is a biological process used by many cellular organisms to convert light energy into chemical energy, which is stored in organic compounds that can later be metabolized through cellular respiration to fuel the organism's activities. The term usually refers to oxygenic photosynthesis, where oxygen is produced as a byproduct and some of the chemical energy produced is stored in carbohydrate molecules such as sugars, starch, glycogen and cellulose, which are synthesized from endergonic reaction of carbon dioxide with water. Most plants, algae and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the biological energy necessary for complex life on Earth.

Primary nutritional groups are groups of organisms, divided in relation to the nutrition mode according to the sources of energy and carbon, needed for living, growth and reproduction. The sources of energy can be light or chemical compounds; the sources of carbon can be of organic or inorganic origin.

<span class="mw-page-title-main">Heterotroph</span> Organism that ingests organic carbon for nutrition

A heterotroph is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but not producers. Living organisms that are heterotrophic include all animals and fungi, some bacteria and protists, 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. The term is now used in many fields, such as ecology in describing the food chain.

<span class="mw-page-title-main">Primary production</span> Synthesis of organic compounds from carbon dioxide by biological organisms

In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are known as primary producers or autotrophs, and form the base of the food chain. In terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae predominate in this role. Ecologists distinguish primary production as either net or gross, the former accounting for losses to processes such as cellular respiration, the latter not.

<span class="mw-page-title-main">Chemosynthesis</span> Biological process building organic matter using inorganic compounds as the energy source

In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules and nutrients into organic matter using the oxidation of inorganic compounds or ferrous ions as a source of energy, rather than sunlight, as in photosynthesis. Chemoautotrophs, organisms that obtain carbon from carbon dioxide through chemosynthesis, are phylogenetically diverse. Groups that include conspicuous or biogeochemically important taxa include the sulfur-oxidizing Gammaproteobacteria, the Campylobacterota, the Aquificota, the methanogenic archaea, and the neutrophilic iron-oxidizing bacteria.

<span class="mw-page-title-main">Biological carbon fixation</span> Series of interconnected biochemical reactions

Biological carbon fixation or сarbon assimilation is the process by which inorganic carbon is converted to organic compounds by living organisms. The compounds are then used to store energy and as structure for other biomolecules. Carbon is primarily fixed through photosynthesis, but some organisms use a process called chemosynthesis in the absence of sunlight.

<span class="mw-page-title-main">Phototroph</span> Organism using energy from light in metabolic processes

Phototrophs are organisms that carry out photon capture to produce complex organic compounds and acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a common misconception that phototrophs are obligatorily photosynthetic. Many, but not all, phototrophs often photosynthesize: they anabolically convert carbon dioxide into organic material to be utilized structurally, functionally, or as a source for later catabolic processes. All phototrophs either use electron transport chains or direct proton pumping to establish an electrochemical gradient which is utilized by ATP synthase, to provide the molecular energy currency for the cell. Phototrophs can be either autotrophs or heterotrophs. If their electron and hydrogen donors are inorganic compounds they can be also called lithotrophs, and so, some photoautotrophs are also called photolithoautotrophs. Examples of phototroph organisms are Rhodobacter capsulatus, Chromatium, and Chlorobium.

A chemotroph is an organism that obtains energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs). The chemotroph designation is in contrast to phototrophs, which use photons. Chemotrophs can be either autotrophic or heterotrophic. Chemotrophs can be found in areas where electron donors are present in high concentration, for instance around hydrothermal vents.

Lithotrophs are a diverse group of organisms using an inorganic substrate to obtain reducing equivalents for use in biosynthesis or energy conservation via aerobic or anaerobic respiration. While lithotrophs in the broader sense include photolithotrophs like plants, chemolithotrophs are exclusively microorganisms; no known macrofauna possesses the ability to use inorganic compounds as electron sources. 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. Chemolithotrophs belong to the domains Bacteria and Archaea. The term "lithotroph" was created from the Greek terms 'lithos' (rock) and 'troph' (consumer), meaning "eaters of rock". Many but not all lithoautotrophs are extremophiles.

Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.

Heterotrophic nutrition is a mode of nutrition in which organisms depend upon other organisms for food to survive. They can't make their own food like Green plants. Heterotrophic organisms have to take in all the organic substances they need to survive.

A consumer in a food chain is a living creature that eats organisms from a different population. A consumer is a heterotroph and a producer is an autotroph. Like sea angels, they take in organic moles by consuming other organisms, so they are commonly called consumers. Heterotrophs can be classified by what they usually eat as herbivores, carnivores, omnivores, or decomposers. On the other hand, autotrophs are organisms that use energy directly from the sun or from chemical bonds. Autotrophs are vital to all ecosystems because all organisms need organic molecules, and only autotrophs can produce them from inorganic compounds. Autotrophs are classified as either photoautotrophs or chemoautotrophs.

In ecology, the term productivity refers to the rate of generation of biomass in an ecosystem, usually expressed in units of mass per volume per unit of time, such as grams per square metre per day. The unit of mass can relate to dry matter or to the mass of generated carbon. The productivity of autotrophs, such as plants, is called primary productivity, while the productivity of heterotrophs, such as animals, is called secondary productivity.

A food chain is a linear network of links in a food web starting from producer organisms and ending at an apex predator species, detritivores, or decomposer species. A food chain also shows how organisms are related to each other by the food they eat. Each level of a food chain represents a different trophic level. A food chain differs from a food web because the complex network of different animals' feeding relations are aggregated and the chain only follows a direct, linear pathway of one animal at a time. Natural interconnections between food chains make it a food web.

This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions from sub-disciplines and related fields, see Glossary of cell biology, Glossary of genetics, Glossary of evolutionary biology, Glossary of ecology, Glossary of environmental science and Glossary of scientific naming, or any of the organism-specific glossaries in Category:Glossaries of biology.

The evolution of photosynthesis refers to the origin and subsequent evolution of photosynthesis, the process by which light energy is used to assemble sugars from carbon dioxide and a hydrogen and electron source such as water. The process of photosynthesis was discovered by Jan Ingenhousz, a Dutch-born British physician and scientist, first publishing about it in 1779.

<span class="mw-page-title-main">Carbon source (biology)</span> Source of carbon in a biological context

A carbon source is a carbon-containing molecule that is used by an organism to synthesise biomass. Such sources may be organic or inorganic. Heterotrophs must use organic molecules as a source of both carbon and energy. In contrast, autotrophs may use inorganic materials as a source for both, such as inorganic chemical energy (chemolithotrophs) or light (photoautotrophs). The carbon cycle, which begins with an inorganic carbon source and progresses through the biological carbon fixation process, includes the biological use of carbon as one of its components.[1]

<span class="mw-page-title-main">Marine primary production</span> Marine synthesis of organic compounds

Marine primary production is the chemical synthesis in the ocean of organic compounds from atmospheric or dissolved carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are called primary producers or autotrophs.

<span class="mw-page-title-main">Photoautotrophism</span> Organisms that use light and inorganic carbon to produce organic materials

Photoautotrophs are organisms that use light energy and inorganic carbon to produce organic materials. Eukaryotic photoautotrophs absorb energy through the chlorophyll molecules in their chloroplasts while prokaryotic photoautotrophs use chlorophylls and bacteriochlorophylls present in free-floating thylakoids in their cytoplasm. All known photoautotrophs perform photosynthesis. Examples include plants, algae, and cyanobacteria.

References

  1. ↑ Morris, J. et al. (2019). "Biology: How Life Works", 3rd edition, W. H. Freeman. ISBN   978-1319017637
  2. ↑ Chang, Kenneth (12 September 2016). "Visions of Life on Mars in Earth's Depths". The New York Times . Retrieved 12 September 2016.
  3. 1 2 3 4 5 6 7 "What Are Primary Producers?". Sciencing. Retrieved 8 February 2018.
  4. 1 2 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.
  5. ↑ Mauseth, James D. (2008). Botany: An Introduction to Plant Biology (4 ed.). Jones & Bartlett Publishers. p.  252. ISBN   978-0-7637-5345-0.
  6. ↑ Frank, Albert Bernard (1892–93). Lehrbuch der Botanik (in German). Leipzig: W. Engelmann.
  7. ↑ 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. doi:10.1016/j.cub.2023.09.040. ISSN   0960-9822.
  8. ↑ Townsend, Rich (13 October 2019). "The Evolution of Autotrophs". University of Wisconsin-Madison Department of Astronomy. Retrieved 3 May 2019.
  9. ↑ Melville, Kate (23 May 2007). "Chernobyl fungus feeds on radiation". Archived from the original on 4 February 2009. Retrieved 18 February 2009.
  10. ↑ 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)
  11. ↑ Beckett, Brian S. (1981). Illustrated Human and Social Biology. Oxford University Press. p. 38. ISBN   978-0-19-914065-7.
  12. ↑ 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)
  13. ↑ Smith, Gilbert M. (2007). A Textbook of General Botany. Read Books. p. 148. ISBN   978-1-4067-7315-6.
  14. ↑ 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.
  15. 1 2 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.
  16. ↑ Martin, William; Russell, Michael J (29 October 2007). "On the origin of biochemistry at an alkaline hydrothermal vent". Philosophical Transactions of the Royal Society B: Biological Sciences. 362 (1486): 1887–1926. doi:10.1098/rstb.2006.1881. ISSN   0962-8436. PMC   2442388 . PMID   17255002.
  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.
  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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