autotroph

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      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, generally using energy from light or inorganic chemical reactions. 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. 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.
      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.


      History


      The term autotroph was coined by the German botanist Albert Bernhard Frank in 1892. 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. 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.


      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.


      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



      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. 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. Proteins can be made using nitrates, sulfates, and phosphates in 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



      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. 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. 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. 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. 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.


      See also


      Electrolithoautotroph
      Electrotroph
      Heterotrophic nutrition
      Organotroph
      Primary nutritional groups


      References




      External links


      "Lichen Biology and the Environment". www.lichen.com. Archived from the original on 21 June 2013. Retrieved 11 May 2014.
      "Lichens". herbarium.usu.edu. Archived from the original on 1 January 2014.
      "Lichens". archive.bio.ed.ac.uk.

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    Autotroph - Definition, Types and Examples - Biology Dictionary

    Oct 28, 2018 · Autotrophs are organisms that can produce their own food, using materials from inorganic sources. The word “autotroph” comes from the root words “auto” for “self” and “troph” for “food.” An autotroph is an organism that feeds itself, without the assistance of …

    Autotroph - Wikipedia

    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.

    Autotroph | Photosynthesis, Carbon Cycle, Energy | Britannica

    Autotroph, in ecology, an organism that serves as a primary producer in a food chain. Autotrophs obtain energy and nutrients by harnessing sunlight through photosynthesis (photoautotrophs) or, more rarely, obtain chemical energy through oxidation (chemoautotrophs) to make organic substances from.

    What Is an Autotroph? Definition and Examples - ThoughtCo

    Feb 28, 2020 · An autotroph is an organism that can produce its own food using inorganic substances. In contrast, heterotrophs are organisms that cannot produce their own nutrients and require consumption of other organisms to live.

    Meaning, Types, and Autotrophs vs Heterotrophs - GeeksforGeeks

    May 17, 2024 · An autotroph is an organism that uses energy from light or inorganic chemical reactions to produce complex organic compounds from simple substances like carbon dioxide. What is the Difference Between Autotrophs and Heterotrophs Examples?

    Autotroph - Education | National Geographic Society

    Nov 18, 2024 · An autotroph is an organism that can produce its own food using light, water, carbon dioxide, or other chemicals. Because autotrophs produce their own food, they are sometimes called producers.

    Autotroph - Definition and Examples - Biology Online Dictionary

    Jun 24, 2022 · In biology and ecology, an autotroph is an organism capable of making nutritive organic molecules from inorganic materials. It could be through photosynthesis (involving light energy) or chemosynthesis (involving chemical energy).

    Autotrophs (Primary Producer) – Definition, Types, Examples

    Feb 17, 2023 · Autotrophs are organisms that can make their own food using inorganic materials. They either use water, carbon dioxide, and energy from sunlight or use a variety of chemicals to prepare food. Since autotrophs produce their own food, they are also called primary producers. Examples of Autotrophs.

    Autotroph vs Heterotroph - Difference and Comparison | Diffen

    Autotrophs are organisms that can produce their own food from the substances available in their surroundings using light (photosynthesis) or chemical energy (chemosynthesis). Heterotrophs cannot synthesize their own food and rely on other organisms — …

    Autotroph: Definition, Classification, And Examples - Science ABC

    Jun 2, 2024 · Autotrophs are organisms that use inorganic chemicals to produce their own food. The term “autotroph” was first coined by a botanist, Albert Bernhard Frank, in 1892. The term “autotroph” is a combination of two Greek words: “auto” …