An
autotroph is an
organismIn biology, an organism is any living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole...
that produces complex
organic compoundAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
s from simple inorganic
moleculeA molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense...
s using energy from light (by
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
) or inorganic chemical reactions.
Autotrophs are the
producers400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
in a
food chainFood chains describe the eating relationships between species within an ecosystem or a particular living place. Many types of food chains or webs are applicable depending on habitat or environmental factors...
, such as
plantPlants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
s on land or
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in...
in water. Bacteria which derive energy from oxidizing inorganic compounds (such as
hydrogen sulfideHydrogen sulfide is the chemical compound with the formula H
2S. This colorless, toxic and flammable gas is partially responsible for the foul odor of rotten eggs and flatulence....
,
ammoniumThe ammonium cation is a positively charged polyatomic cation of the chemical formula NH. It has a formula weight of 18.05 and is formed by the protonation of ammonia...
and ferrous
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
) are chemoautotrophs, and include the
lithotrophA lithotroph is an organism that uses an inorganic substrate to obtain reducing equivalents for use in biosynthesis or energy conservation via aerobic or anaerobic respiration. Known lithotrophs are exclusively microbes or plants; No known macrofauna possesses the ability to utilize inorganic...
s.
Autotrophs are fundamental to the food chains of all
ecosystemsAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
in the world.
An
autotroph is an
organismIn biology, an organism is any living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole...
that produces complex
organic compoundAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
s from simple inorganic
moleculeA molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense...
s using energy from light (by
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
) or inorganic chemical reactions.
Autotrophs are the
producers400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
in a
food chainFood chains describe the eating relationships between species within an ecosystem or a particular living place. Many types of food chains or webs are applicable depending on habitat or environmental factors...
, such as
plantPlants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
s on land or
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in...
in water. Bacteria which derive energy from oxidizing inorganic compounds (such as
hydrogen sulfideHydrogen sulfide is the chemical compound with the formula H
2S. This colorless, toxic and flammable gas is partially responsible for the foul odor of rotten eggs and flatulence....
,
ammoniumThe ammonium cation is a positively charged polyatomic cation of the chemical formula NH. It has a formula weight of 18.05 and is formed by the protonation of ammonia...
and ferrous
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
) are chemoautotrophs, and include the
lithotrophA lithotroph is an organism that uses an inorganic substrate to obtain reducing equivalents for use in biosynthesis or energy conservation via aerobic or anaerobic respiration. Known lithotrophs are exclusively microbes or plants; No known macrofauna possesses the ability to utilize inorganic...
s.
Ecology
Autotrophs are fundamental to the food chains of all
ecosystemsAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
in the world. They take energy from the environment in the form of sunlight or inorganic chemicals and use it to create energy-rich molecules such as
carbohydrateCarbohydrates
[Means "hydrates of carbon"] or saccharides
[The word comes from the Greek σάκχαρον, sákcharon, meaning "sugar").] are the most abundant of the four major classes of biomolecules...
s. This mechanism is called
primary production400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
. Other organisms, called
heterotrophA Heterotroph is an organism that uses organic carbon for growth. This contrasts with autotrophs, such as plants, which are able to directly use sources of energy, such as light to produce organic substrates from inorganic carbon dioxide.- Ecology :Heterotrophs are known as consumers in food...
s, take in autotrophs as
foodFood is any substance, usually composed of carbohydrates, fats, proteins and water, that can be eaten or drunk by an animal, including humans, for nutrition or pleasure. Items considered food may be sourced from plants, animals or other categories such as fungus or fermented products like alcohol...
to carry out functions necessary for their life. Thus, heterotrophs — all
animalAnimals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously...
s, almost all fungi, as well as most bacteria and
protozoaProtozoa or Cornelius protozoans Protozoa or Cornelius protozoans Protozoa or Cornelius protozoans (from Greek πρῶτον proton "first" and ζῷα zoa "animals"; singular protozoon; (the word "protozoan" is originally an adjective, used as a noun) are microorganisms classified as unicellular eukaryotes....
— depend on autotrophs for the energy and raw materials they need. Heterotrophs obtain energy by breaking down organic molecules (carbohydrates,
fatFats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...
s, and
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s) obtained in food. Carnivorous organisms ultimately rely on autotrophs because the
nutrientA nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. Nutrients are the substances that enrich the body. They build and repair tissues, give heat and energy, and regulate body processes...
s obtained from their heterotroph prey come from autotrophs they consumed.
Variants
There are some species of organisms that require
organic compoundAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
s as a source of
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, but are able to use light or inorganic compounds as a source of energy. Such organisms are not defined as autotrophic, but rather as heterotrophic. An organism that obtains carbon from organic compounds but obtains energy from light is called a
photoheterotrophPhotoheterotrophs are heterotrophic organisms that use light for energy, but cannot use carbon dioxide as their sole carbon source. Consequently, they use organic compounds from the environment to satisfy their carbon requirements. They use compounds such as carbohydrates, fatty acids and...
, while an organism that obtains carbon from organic compounds but obtains energy from the oxidation of inorganic compounds is termed a
chemoheterotroph.
Evidence suggests that some fungi may also obtain energy from radiation. Such
radiotrophic fungiRadiotrophic fungi are a recent discovery, first seen as black molds growing inside and around the Chernobyl Nuclear Power Plant. These fungi appear to use the pigment melanin to convert gamma radiation into chemical energy for growth...
were found growing inside a reactor of the
Chernobyl nuclear power plantThe Chernobyl Nuclear Power Plant is a decommissioned nuclear power plant near the city of Prypiat, Ukraine, 18 km northwest of the city of Chernobyl, 16 km from the border of Ukraine and Belarus, and about 110 km north of Kiev. It was the site of the Chernobyl disaster in 1986, but...
.
Flowchart
- Autotroph
- Chemoautotroph
- Photoautotroph
- Heterotroph
A Heterotroph is an organism that uses organic carbon for growth. This contrasts with autotrophs, such as plants, which are able to directly use sources of energy, such as light to produce organic substrates from inorganic carbon dioxide.- Ecology :Heterotrophs are known as consumers in food...
- Chemoheterotroph
- Photoheterotroph
Photoheterotrophs are heterotrophic organisms that use light for energy, but cannot use carbon dioxide as their sole carbon source. Consequently, they use organic compounds from the environment to satisfy their carbon requirements. They use compounds such as carbohydrates, fatty acids and...
Autotrophs are the producers in an ecosystem
Footnotes
α. The word autotroph comes from the
GreekGreek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical...
autos = self and
trophe = nutrition, related to
trephein = to make solid, congeal, thicken