Primary nutritional groups
Encyclopedia
Primary nutritional groups are groups of organism
s, divided according to the sources of energy and carbon, needed for living, growth and reproduction. The sources of energy can be light and organic or inorganic compounds; the sources of carbon can be of organic or inorganic origin.
The terms aerobic respiration, anaerobic respiration
and fermentation
do not refer to primary nutritional groups, but simply reflect the different use of possible electron acceptors in particular organisms, such as O2 in aerobic respiration, or NO3-, SO42- or fumarate in anaerobic respiration, or various metabolic intermediates in fermentation. Because all ATP-generating steps in fermentation involve modifications of metabolic intermediates instead of the use of an electron transport chain
fermentation is often referred to as substrate-level phosphorylation
.
s: Light is absorbed in photo receptors
and transformed into chemical energy.
Chemotroph
s: Bond energy
is released from a chemical compound
.
The freed energy is stored as potential energy in ATP
, carbohydrate
s, lipid
s or protein
s. Eventually, the energy is used for life processes as moving, growth and reproduction.
Some bacteria can alternate phototrophy and chemotrophy, depending on availability of light.
s: Organic compounds are used as electron donor
.
Lithotroph
s: Inorganic compounds are used as electron donor.
The electron
s from reducing equivalent
s are needed by both, phototrophs and chemotrophs, to keep running reduction-oxidation reactions
that transfer energy. The electron donors are taken up from the environment.
Organotrophic organisms are often also heterotrophic, using organic compounds as sources of electrons and carbon at the same time. Similarly, lithotrophic organisms are often also autotrophic, using inorganic sources of electrons and CO2 as inorganic carbon source.
Some lithotrophic bacteria can utilize diverse sources of electrons, depending on availability of possible donors.
s: Organic compounds are metabolized
to get carbon for growth and development.
Autotroph
s: Carbon dioxide
(CO2) is used as source of carbon.
Such mixotroph
ic organisms may dominate their habitat
, due to their capability to use more resources than either photoautotrophic or organoheterotrophic organisms.
s are generally easy to categorise. All animals are heterotrophic, as are fungi. Plants are generally photoautotrophic. Some eukaryotic microorganisms, however, are not limited to just one nutritional mode. For example, some algae live photoautotrophically in the light, but shift to chemoorganotrophy in the dark. Even higher plants retained their ability to respire heterotrophically on the starch at night which had been synthesised phototrophically during the day.
Prokaryote
s show a great diversity of nutritional categories. For example, purple sulfur bacteria
and cyanobacteria are generally photoautotrophic where as purple non-sulfur bacteria are photoorganotrophic. Some bacteria are limited to only one nutritional group, whereas others are facultative
and switch from one mode to the other, depending on the nutrient sources available.
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s, divided according to the sources of energy and carbon, needed for living, growth and reproduction. The sources of energy can be light and organic or inorganic compounds; the sources of carbon can be of organic or inorganic origin.
The terms aerobic respiration, anaerobic respiration
Anaerobic respiration
Anaerobic respiration is a form of respiration using electron acceptors other than oxygen. Although oxygen is not used as the final electron acceptor, the process still uses a respiratory electron transport chain; it is respiration without oxygen...
and fermentation
Fermentation (biochemistry)
Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...
do not refer to primary nutritional groups, but simply reflect the different use of possible electron acceptors in particular organisms, such as O2 in aerobic respiration, or NO3-, SO42- or fumarate in anaerobic respiration, or various metabolic intermediates in fermentation. Because all ATP-generating steps in fermentation involve modifications of metabolic intermediates instead of the use of an electron transport chain
Electron transport chain
An electron transport chain couples electron transfer between an electron donor and an electron acceptor with the transfer of H+ ions across a membrane. The resulting electrochemical proton gradient is used to generate chemical energy in the form of adenosine triphosphate...
fermentation is often referred to as substrate-level phosphorylation
Substrate-level phosphorylation
Substrate-level phosphorylation is a type of metabolism that results in the formation and creation of adenosine triphosphate or guanosine triphosphate by the direct transfer and donation of a phosphoryl group to adenosine diphosphate or guanosine diphosphate from a phosphorylated reactive...
.
Primary sources of energy
PhototrophPhototroph
Phototrophs are the organisms that carry out photosynthesis to acquire energy. They use the energy from sunlight to convert carbon dioxide and water into organic material to be utilized in cellular functions such as biosynthesis and respiration.Most phototrophs are autotrophs, also known as...
s: Light is absorbed in photo receptors
Photosynthetic pigment
A photosynthetic pigment is a pigment that is present in chloroplasts or photosynthetic bacteria and captures the light energy necessary for photosynthesis.- Plants :...
and transformed into chemical energy.
Chemotroph
Chemotroph
Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic or inorganic . The chemotroph designation is in contrast to phototrophs, which utilize solar energy...
s: Bond energy
Bond energy
In chemistry, bond energy is the measure of bond strength in a chemical bond. It is the heat required to break one Mole of molecules into their individual atoms. For example, the carbon-hydrogen bond energy in methane E is the enthalpy change involved with breaking up one molecule of methane into...
is released from a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
.
The freed energy is stored as potential energy in ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
, carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
s, lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
s or protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s. Eventually, the energy is used for life processes as moving, growth and reproduction.
Some bacteria can alternate phototrophy and chemotrophy, depending on availability of light.
Primary sources of reducing equivalents
OrganotrophOrganotroph
An organotroph is an organism that obtains hydrogen or electrons from organic substrates . Antonym: Lithotroph- See also :* Lithotroph* Heterotroph* Primary nutritional groups...
s: Organic compounds are used as electron donor
Electron donor
An electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process....
.
Lithotroph
Lithotroph
A 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 chemolithotrophs are exclusively microbes; No known macrofauna possesses the ability to utilize inorganic...
s: Inorganic compounds are used as electron donor.
The electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s from reducing equivalent
Reducing equivalent
In biochemistry, the term reducing equivalent refers to any of a number of chemical species which transfer the equivalent of one electron in redox reactions...
s are needed by both, phototrophs and chemotrophs, to keep running reduction-oxidation reactions
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
that transfer energy. The electron donors are taken up from the environment.
Organotrophic organisms are often also heterotrophic, using organic compounds as sources of electrons and carbon at the same time. Similarly, lithotrophic organisms are often also autotrophic, using inorganic sources of electrons and CO2 as inorganic carbon source.
Some lithotrophic bacteria can utilize diverse sources of electrons, depending on availability of possible donors.
Primary sources of carbon
HeterotrophHeterotroph
A heterotroph is an organism that cannot fix carbon and uses organic carbon for growth. This contrasts with autotrophs, such as plants and algae, which can use energy from sunlight or inorganic compounds to produce organic compounds such as carbohydrates, fats, and proteins from inorganic carbon...
s: Organic compounds are metabolized
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
to get carbon for growth and development.
Autotroph
Autotroph
An autotroph, or producer, is an organism that produces complex organic compounds from simple inorganic molecules using energy from light or inorganic chemical reactions . They are the producers in a food chain, such as plants on land or algae in water...
s: Carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) is used as source of carbon.
Table
| Energy source | Reducing equivalent source | Carbon source | Name |
|---|---|---|---|
| Light Photo- |
Organic -organo- |
Organic -heterotroph |
Photoorganoheterotroph |
| Carbon dioxide -autotroph |
Photoorganoautotroph | ||
| Inorganic -litho- |
Organic -heterotroph |
Photolithoheterotroph | |
| Carbon dioxide -autotroph |
Photolithoautotroph | ||
| Chemical compounds Chemo- |
Organic -organo- |
Organic -heterotroph |
Chemoorganoheterotroph |
| Carbon dioxide -autotroph |
Chemoorganoautotroph | ||
| Inorganic -litho- |
Organic -heterotroph |
Chemolithoheterotroph | |
| Carbon dioxide -autotroph |
Chemolithoautotroph |
Mixotrophs
Some, usually unicellular, organisms can switch between different metabolic modes, for example between photoautotrophy and chemoheterotrophy.Such mixotroph
Mixotroph
A mixotroph is a microorganism that can use a mix of different sources of energy and carbon. Possible are alternations between photo- and chemotrophy, between litho- and organotrophy, between auto- and heterotrophy or a combination of it...
ic organisms may dominate their habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
, due to their capability to use more resources than either photoautotrophic or organoheterotrophic organisms.
Examples
All sorts of combinations may exist in nature. For example most cyanobacteria are photoautotrophic, since they use light as an energy source, water as electron donor, and CO2 as a carbon source. Fungi are chemoorganotrophic since they use organic carbon as both an electron donor and carbon source. EukaryoteEukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
s are generally easy to categorise. All animals are heterotrophic, as are fungi. Plants are generally photoautotrophic. Some eukaryotic microorganisms, however, are not limited to just one nutritional mode. For example, some algae live photoautotrophically in the light, but shift to chemoorganotrophy in the dark. Even higher plants retained their ability to respire heterotrophically on the starch at night which had been synthesised phototrophically during the day.
Prokaryote
Prokaryote
The prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. The organisms that have a cell nucleus are called eukaryotes. Most prokaryotes are unicellular, but a few such as myxobacteria have multicellular stages in their life cycles...
s show a great diversity of nutritional categories. For example, purple sulfur bacteria
Purple sulfur bacteria
The purple sulfur bacteria are a group of Proteobacteria capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in hot springs or stagnant water. Unlike plants, algae, and cyanobacteria, they do not use water as their...
and cyanobacteria are generally photoautotrophic where as purple non-sulfur bacteria are photoorganotrophic. Some bacteria are limited to only one nutritional group, whereas others are facultative
Facultative
Facultative means "optional" or "discretionary" , used mainly in biology in phrases such as:* Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production...
and switch from one mode to the other, depending on the nutrient sources available.
See also
- Mixotrophic
- Autotrophic
- Heterotrophic
- Organotrophic
- Lithotrophic
- PhototrophPhototrophPhototrophs are the organisms that carry out photosynthesis to acquire energy. They use the energy from sunlight to convert carbon dioxide and water into organic material to be utilized in cellular functions such as biosynthesis and respiration.Most phototrophs are autotrophs, also known as...
ic - Chemotrophic
- ChemosynthesisChemosynthesisIn biochemistry, chemosynthesis is the biological conversion of one or more carbon molecules and nutrients into organic matter using the oxidation of inorganic molecules or methane as a source of energy, rather than sunlight, as in photosynthesis...