We explain what a domain is and its relationships with the biological kingdoms. Also, some of its main features.
What is a domain?
In biology, Domain, sometimes also called empire or superkingdom, is understood as the broadest taxonomic category in which known living beings are classified. That is, it is the broadest category into which the different kingdoms of life, according to the most recent and widely accepted classification models in the community specialized scientist.
The current system in the matter is the one proposed by the American microbiologist Carl Richard Woese in 1990, and is known as the three-domain system, since it organizes the different kingdoms of life (which are generally animalia, plant, fungi, protist, bacteria and archaea) into three large groups or domains, based on their fundamental cellular characteristics: bacteria domain, archaea domain and eukarya domain.
The first two domains, bacteria and archaea, cover the world of prokaryotic organisms, that is, those that lack cell nucleus and they are much simpler and smaller than those belonging to the remaining domain, the eukaryotes. The latter have cells larger, more complex and endowed with a cell nucleus where its DNA, and therefore can be single-celled organisms or multicellular.
Thus, all known life fits into one of these domains, perhaps with the exception of the virus, whose parasitic and acellular existence remains so mysterious that it is not yet possible to determine whether they are really living beings.
Dominion and kingdom
Domains are the broadest category of the life, in which the different known kingdoms are organized. These, for their part, are the immediately lower categories (although in some systems super-kingdoms are also understood as an intermediate category between domain and kingdom, or even as an alternative: two super-kingdoms, eukaryota and prokaryota, instead of three domains), among which living beings are distributed based on their evolutionary, metabolic, cellular and behavioral similarities.
There are various systems classification of life that propose 3, 4, 5, 6 and up to 7 different kingdoms. The most common includes the following:
- Bacteria kingdom. Where are the prokaryotic organisms simplest and most primitive of all, the most prevalent on the planet, dedicated to all kinds of nutritional functions: photosynthesis, chemosynthesis, parasitism, predation, etc.
- Archaea kingdom. Initially considered part of the bacterial kingdom (and called archaebacteria) it was later verified that they have substantial evolutionary differences that allow them to be a kingdom (and a domain) apart from the bacteria, with those who share their prokaryotic existence, but with different behaviors (habitats extremes, chemisynthetic nutrition) and cellular characteristics that resemble eukaryotes.
- Proctist kingdom. Also called protista and formerly moneras, is the kingdom where all eukaryotic unicellular organisms are contemplated, a sort of step between prokaryotic life and multicellular kingdoms. Here come the protozoa, unicellular algae and other eukaryotic microorganisms of various eating habits.
- Kingdom plantae. The plant kingdom, that is, that of plants, those immobile multicellular eukaryotic organisms that feed on photosynthesis: the biochemical composition of sugars from Water, the carbon dioxide and the sunlight, thanks to a specialized pigment they have, called chlorophyll. Its cells house it in their plastids, and they also have a rigid cellulose cell wall.
- Fungi kingdom. The kingdom of fungi, intermediate between plant and animal, since they are not autotrophs like plants, but still immobile. They feed on the decomposition of organic material, either in a saprophytic or parasitic way, and they reproduce by means of spores. Their eukaryotic cells have a cell wall, but made of chitin.
- Animalia Kingdom. The animal kingdom, with its enormous variety of genera and species from multicellular organisms, heterotrophs, eukaryotes, endowed with mobility, sexual reproduction and a metabolism based on the breathing, that is, of the oxidation of glucose obtained from organic matter consumed from other living beings. Their cells lack a cell wall.
Bacteria domain
The bacterial domain coincides with the kingdom of the same name, within which are exclusively prokaryotic organisms, with a simple and primitive cellular structure, which are considered the most abundant forms of life on the planet, and surely the first to emerge in the evolutionary broth. of the early Earth.
They can be obtained in practically all habitats, even within (in symbiotic or parasitic relationship) of some multicellular organisms, and dedicated to various types of metabolic activity: photosynthesis, such as cyanobacteria (blue-green algae), decomposition of matter organic, etc.
Archaea domain
Along with the bacterium domain, the archaea domain covers the entire prokaryotic world. It also coincides with the kingdom of the same name, in which archaebacteria or archaea are included, prokaryotic organisms that exhibit certain similarities with eukaryotic life, despite existing in very specific and generally hostile habitats (leading an extremophilic life) such as waters. subterranean boiling plants, although they have also been found among microorganisms that make up the marine plankton.
Eukarya domain
The eukarya or eukaryotic domain is the broadest of the three, in the sense that it includes a diverse set of kingdoms: animals, plants, fungi and all protists, that is, all forms of eukaryotic life, possessing cells with specific cell nuclei (where DNA is housed) and other complex cellular organelles.
The evolutionary step from prokaryotes to eukaryotes is still difficult to understand, but it is also key in the formation of organisms more complex, such as multicellular cells, in which cells sacrifice their independence to form a more complex and interconnected organized whole. The creatures in this domain are called eukaryotes.