An autotroph or primary producer is an organism that produces complex
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s (such as
carbohydrate
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...
s,
fats, and
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s) using
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
from simple substances such as
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
,
[Morris, J. et al. (2019). "Biology: How Life Works", 3rd edition, W. H. Freeman. ] generally using energy from light (
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
) or inorganic chemical reactions (
chemosynthesis).
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
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...
s on land or
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
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
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ).
Examples of substances that are commonly reducing agents include the Earth met ...
, but some can use other hydrogen compounds such as
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
.
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
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...
, which is usually accumulated in the form of
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...
and will be used as carbon and energy source by other organisms (e.g.
heterotrophs and
mixotrophs A mixotroph is an organism that can use a mix of different sources of energy and carbon, instead of having a single trophic mode on the continuum from complete autotrophy at one end to heterotrophy at the other. It is estimated that mixotrophs co ...
). The photoautotrophs are the main primary producers, converting the energy of the light into chemical energy through
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
, ultimately building organic molecules from
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
, an
inorganic carbon source.
Examples of
chemolithotrophs are some
archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...
and
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
(unicellular organisms) that produce
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...
from the
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
of inorganic chemical compounds, these organisms are called
chemoautotrophs, and are frequently found in
hydrothermal vent
A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspo ...
s in the deep ocean. Primary producers are at the lowest
trophic level
The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it ...
, 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
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
,
ammonium
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaterna ...
and
ferrous oxide as reducing agents and hydrogen sources for
biosynthesis
Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecul ...
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 (), meaning "nourishment" or "food". The first autotrophic organism developed about 2 billion years ago. Photoautotrophs evolved from
heterotroph
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 ...
ic bacteria by developing
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
. The earliest photosynthetic bacteria used
hydrogen sulphide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
. Due to the scarcity of hydrogen sulphide, some photosynthetic bacteria evolved to use water in photosynthesis, leading to
cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
.
Variants
Some organisms rely on
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s as a source of
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
, but are able to use
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...
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
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
: Such
radiotrophic fungi were found growing inside a reactor of the
Chernobyl nuclear power plant.
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,
lichen
A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.[algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...]
(or additionally nitrogen fixation by cyanobacteria) with the protection of a decomposer
fungus
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
. 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 H
2O primary producers, including a form of bacteria, and
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
...
. 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
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
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s 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
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 ...
. Other organisms, called
heterotroph
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 ...
s, take in autotrophs as
food
Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is in ...
to carry out functions necessary for their life. Thus, heterotrophs – all
animal
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...
s, almost all
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
, as well as most
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
and
protozoa
Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
– 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
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...
organisms rely on autotrophs indirectly, as the
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excre ...
s obtained from their heterotrophic prey come from autotrophs they have consumed.
Most ecosystems are supported by the autotrophic
primary production
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 ...
of
plants and
cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
that capture
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alwa ...
s initially released by the
sun. Plants can only use a fraction (approximately 1%) of this energy for
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
. The process of
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
splits a water molecule (H
2O), releasing oxygen (O
2) into the atmosphere, and
reducing carbon dioxide (CO
2) to release the
hydrogen atoms that fuel the
metabolic
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
process of
primary production
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 ...
. 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
carbohydrate
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...
s, including other sugars, starch, and cellulose; glucose is also used to make
fats and
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s. When autotrophs are eaten by
heterotroph
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 ...
s, i.e., consumers such as animals, the
carbohydrate
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...
s,
fats, and
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s contained in them become energy sources for the
heterotrophs.
Proteins can be made using
nitrate
Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
s,
sulfates, and
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
s 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 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 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. 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, H
2, and CO
2.
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.
Autotrophs possibly evolved into heterotrophs when they were at low H
2 partial pressures and photosynthesis emerged in the presence of long-wavelength geothermal light at hydrothermal vents.
See also
*
Electrolithoautotroph
*
Electrotroph
*
Heterotrophic nutrition
*
Organotroph
*
Primary nutritional groups
References
External links
*
*
*
{{Modelling ecosystems
Trophic ecology
Microbial growth and nutrition
Biology terminology
Plant nutrition