biological kingdoms



We explain what the biological kingdoms are and the history of these sets of species. In addition, the characteristics of each one.

The most accepted Realms system was proposed by Thomas Cavalier-Smith in 2015.

What are the biological kingdoms?

In the biology, and especially the taxonomy, Kingdom is called each of the large groups in which the species of known living beings are classified, according to their evolutionary kinship, that is, to their place of origin in the long history of the life. It is the second level of classification of the living beings, below the domains and above the phyla (or phylum).

Throughout the history of the science, the human being He has made efforts to understand the dynamics of origin and change inherent in life, and for this he has developed these classification systems, which in turn have varied greatly over time.

As scientists understand more and more in detail the characteristics of living things, new possibilities for classification appear and old assumptions are considered obsolete. For that reason there are various systems of classification in biological kingdoms, not always coincident with each other.

The most recent and most accepted system is the one proposed by the Anglo-Canadian Thomas Cavalier-Smith in 2015, although there is still debate about it in the community specialized scientist.

History of the biological kingdoms

Carlos Linnaeus proposed a classification of two kingdoms: Vegetabilia and Animalia.

The first systems for classifying life date back to ancient times, when ancient philosophers proposed approaches to life by distinguishing between its basic observable properties. Thus, we have:

  • Two kingdom system. Attributed to the Greek philosopher Aristotle (IV BC), it divided living beings into two large categories, based on what the theorist called "vegetative soul" and "sensitive soul." In the first case, it translated into the ability to grow, nourish and reproduce, while in the second this also included desire, movement and the perception. This system was inherited a long time later by the famous Swedish scientist and naturalist Carlos Linnaeus, who proposed in 1735 a classification system of two kingdoms proper: Vegetabilia Y Animalia.
  • Three kingdom system. A third kingdom would emerge for the first time in 1858, when the English biologist Richard Owen realized the difficulty of classifying certain microorganisms based on the two kingdoms of Linnaeus, and proposed a third: Protozoa, composed of microscopic beings formed by cells nucleated. This new kingdom was renamed Proctista in 1860 by the also English John Hogg, although in his considerations he also proposed the existence of a "mineral kingdom", which was later discarded by Ernst Haeckel, father of protistology, who in 1865 baptized the third kingdom as Protista and included in it all forms of microscopic life with animal, vegetable and mixed characters, but distinguishing for the first time between single-celled organisms Y multicellular.
  • Four kingdoms system. As microbiology progressed, the three-kingdom system required rethinking, as the distinction between prokaryotic organisms (without cell nucleus) and eukaryotes (with cell nuclei) became more evident and important. And to distinguish between nucleated and non-nucleated microorganisms, Herbert Copeland in 1938 proposed a system of four kingdoms: Animalia, Plantae, Protoctist and a new group for bacteria enucleated: Monera.
  • Five kingdoms system. The fifth kingdom arose in 1959 when Robert Whittaker found that the fungi were a totally different group from the plant, and in 1969 he proposed a system of five kingdoms that included the Fungi (mushrooms), and kept all four of Copeland. This was one of the most popular systems in history.
  • Six kingdoms system. The advancement of techniques for studying and exploring the DNA Y RNA In the second half of the 20th century it revolutionized many of the assumptions of biology, allowing Carl Woese and G. Fox to reinvent the system and propose six different kingdoms: Bacterium, Archaea, Protista, Plantae, Animalia Y Fungi. These six kingdoms are divided, in turn, into two domains: Prokaryota (Bacteria and Archea) Y Eukaryota (the rest). In many places this is the accepted system.
  • Seven kingdoms system. The work of the Canadian Cavalier-Smith and later developers, he proposed the creation of the kingdom Chromista to distinguish diatoms, oomycetes and similar algae, and recovering the name Protozoa for the rest of the eukaryotic microorganisms. Thus, the seven kingdoms would be the two of prokaryotes: Archaea Y Bacterium, and five from eukaryotes: Protozoa, Chromista, Plantae, Fungi, Animals.

Kingdom bacterium

Bacteria lead photosynthetic, saprophytic, and even parasitic existence.

One of the two kingdoms of prokaryotic organisms, that is, without a cell nucleus and with much simpler and smaller cellular structures, it encompasses the most abundant and diverse unicellular microscopic beings on the planet, which lead a photosynthetic, saprophytic and even parasitic existence, in practically all the habitats of the world. They have a peptidoglycan wall that allows them to be classified into two types: Gram negative (they present double wall) or Gram positive (they present single wall).

Kingdom archaea

This is the other type of known prokaryotes, lacking peptidoglycan cell walls, non-pathogenic and present in very extreme habitats, since their nutrition is based on chemosynthesis, that is, the use of chemical reactions specific in environments anaerobic (in the absence of oxygen). The existence of archaea or archaebacteria was known since the 18th century, but their difference from bacteria was not understood until the 20th century.

Kingdom protozoa

Protists possess heterotrophic nutrition, either saprophytic or predatory.

This kingdom is considered the basal group of the eukaryotes, that is, the first to emerge, from which the others would later have come off. It is a paraphyletic group, that is, it includes the first common ancestor but not all of their descendants.

Here we can find, then, eukaryotic unicellular microorganisms, usually flagellated, without a cell wall and that do not form tissues, dedicated to a heterotrophic nutrition, either saprophytic or of predation from other microorganisms, such as bacteria and other protists.

Kingdom chromist

It is a eukaryotic kingdom of organisms without too many common characteristics, but which can be summarized in various types of algae, which were traditionally classified within the plant or fungal kingdom, given that they may or may not present chlorophyll or additional pigments. Many chromists, in fact, can lead a parasitic life. This group includes unicellular and multicellular algae, oomycetes and apicomplexes.

Kingdom plant

The organisms of the kingdom plantae are characterized by their still life.

A group of photosynthetic multicellular eukaryotes, that is, that carry out the synthesis of sunlight, absorbing CO2 atmospheric and releasing oxygen in return. This group is indispensable for the support of life as we know it, especially terrestrial plants. They are characterized by cells with a cellulose wall, by their immobile life and by their reproduction sexual or asexual depending on the species and the conditions given.

Kingdom fungi

Fungi reproduce by spores, both sexually and asexually.

The mushroom kingdom, that is, of aerobic and heterotrophic multicellular eukaryotic organisms, incapable of synthesizing their nutrients and therefore dedicated to a saprophytic or parasitic existence: either they act as decomposers of the organic material, or they infect the bodies of other living organisms. They have a cell wall like plants, but made of chitin instead of cellulose, and they reproduce by means of spores, both sexually and asexually.

Kingdom animalia

The animalia kingdom can be divided into two groups: vertebrates and invertebrates.

The last kingdom is that of animals, that is, that of eukaryotic multicellular organisms endowed with their own mobility and a heterotrophic metabolism, supported by the breathing: the consumption of oxygen and organic matter from other living beings, for their oxidation and obtaining chemical energy and CO2 expulsion. Animals are an enormously diverse kingdom, spread across aquatic habitats, terrestrial and even of air, which can be divided into two groups: vertebrates and invertebrates, depending on whether or not they have a backbone and endoskeleton.

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