We explain what the monera kingdom is, what its characteristics are and its importance. Also, how the beings of this kingdom are classified and examples.
The monera kingdom comprises the most primitive and simplest forms of life.
What is the kingdom Monera?
The Monera kingdom is the set of microorganisms that have the most primitive and simple life forms. They are characterized by being of prokaryotic type, that is, their cells do not have a nucleus and the genetic material is located freely in the cytoplasm. For example: salmonella, serpulin and lactobacilli.
The broadest categories into which living beings are classified They are called kingdoms. Although the names and criteria have been changing since the beginning of biology, the most widely used classification today is:
There are doubts regarding the transition between the prokaryotic cellular world and that of eukaryotes, a process that was key in the development of the most complex multicellular beings. However, all theories suggest that a pair of unicellular organisms they would have developed some type of symbiosis increasingly narrower.
This way, one became part of the other’s bodyand took charge of some internal functions of the cell until giving rise to a new type of individual. All theories agree that the kingdom monera is evolutionarily prior to all the others who are known.
Nowadays the term monera (which includes archaea and bacteria) is out of usebecause although both types of organisms do not have a nucleus or organelles and are prokaryotes, archaea do have a nucleolus. Therefore, they are considered to be two different kingdoms: archaea on the one hand and bacteria on the other.
Origin of the term monera
Edóard Pierre Chatton discovered that bacteria did not have a cell nucleus.
The term “monera” comes from the Greek moneres (“simple”)and has changed in specific meaning over time:
- In 1866, Ernst Haeckel was the first to propose a classification of life based on the then young theory of evolution, highlighting three kingdoms: animal, plant and protist, bringing together in the last all the “simple” forms, among which were the moneras or moneres, the most primitive forms of life and the base of the evolutionary tree.
- In 1920, Edóard Pierre Chatton discovered that bacteria did not have a cell nucleus.This made it possible to distinguish between prokaryotic and eukaryotic life.
- In 1939, Fred Alexander Barkley used the term “monera.” to refer to the first, much more primitive ones. According to him, this kingdom was divided into archeopyta (cyanobacteria) and schizophyta (bacteria).
- Subsequently, Herbert Copeland reorganized the kingdoms of life by proposing four categories: animals, plants, protists (simple eukaryotes) and moneras (prokaryotes). To this classification Robert Whittaker added the kingdom of fungi (Fungi) and it is this version, revised in 2000, that we use today.
General characteristics of the Monera kingdom
Members of the kingdom Monera can be very diverse in their form and lifestyles. However, they have some minimal characteristics that point to their evolutionary and biological simplicity, such as:
- Size. Beings of the monera kingdom are between 3 to 5 micrometers in length. They are the smallest living beings that exist in nature.
- Unicellular organisms. The beings of the Monera kingdom are unicellular prokaryotic organisms, that is, completely autonomous cells that do not form tissues or more complex organisms.
- Without organelles. The beings of the Monera kingdom do not have a cell nucleus, mitochondria or plastids, which is why they differ from eukaryotic cells that are larger and more complex internally.
- Reproduction. The beings of the Monera kingdom always reproduce asexually, which in turn can occur by binary fission (never by mitosis) or by conjugation or limited exchange of genetic material (parasexuality). This represents an evolutionary disadvantage with respect to sexual reproduction, which allows for greater margins of genetic variety.
- circular DNA. Beings of the Monera kingdom lack a nucleus, so their DNA is dispersed in the cytoplasm and is shaped like a circle instead of a double helix.
- Locomotion. Beings of the monera kingdom usually move through flagella, although they can also be immobile.
- Nutrition. The beings of the Monera kingdom are usually heterotrophic (saprophytic, parasitic or symbiotic), but they can also be autotrophic (photosynthetic or chemosynthetic).
Classification of the Monera kingdom
Initially, this kingdom was subdivided into two categories: bacteria and archaea, each with its own subclassification. However, after the discovery of ribosomal DNA, a new prokaryotic classification could be established into four different segments:
- MendosicutesArchaea or archaebacteria. Its name means “ancient”, since at first it was assumed to be a species of protobacteria. Their classification is difficult, given that they are very small, but they have metabolic pathways and internal processes more similar to eukaryotes than to traditional prokaryotes. However, they are much more versatile in their nutrition than eukaryotes and can inhabit hostile environments.
- Mollicutes, Tenericutes or mycoplasmas. A type of mainly parasitic bacteria, which lack the cell wall of most bacteria and have a rather simplified shape and genetic code.
- Gracilicutes or gram-negative bacteria. It is a supergroup of bacteria that make up the groups Spirochaetes, Proteobacteria, Planktobacteria. They have a thin murein skin and a double plasma membrane, which is why they are not susceptible to Gram staining, acquiring a pink color instead of blue under this procedure.
- Firmicutes or gram-positive bacteria. Also called endobacteria, they have a thick cell wall and are shaped like a bacillus or coccus. In this category are gram positive bacteria, those that respond to Gram dye by acquiring a blue or violet color. They are associated with numerous fermentation processes of organic matter.
Moneras and protists
Monera and protists are different kingdoms. However, share their biological simplicity and both are, for the most part, unicellular organisms.
But a gigantic evolutionary difference separates them: the presence of a cell nucleus, that is, Protists are eukaryotes while moneras are prokaryotes..
Moneras in the three domains
At the end of the 20th century, scientist Carl Richard Woese proposed a classification of organisms not into kingdoms but into three large domains, orders or superkingdoms:
- Eukarya. It is the domain that includes all living beings whose cells have well-defined nuclei: plants, animals, fungi and protists.
- Archea. It is the domain that includes extremely simple and abundant prokaryotes on the planet, but difficult to grow in the laboratory. They are organisms accustomed to extreme habitats from which they take advantage of chemical energy, such as near volcanoes or hot springs. They are part of the “original kingdoms” along with bacteria.
- Bacterium. Initially called eubacteria, it is the domain that includes the oldest beings on the planet. It includes a wide variety of living beings that have in common the fact of not having a cell nucleus.
Habitat of the Monera kingdom
Some moneras live in perfect symbiosis in the human or animal intestine.
The monkeys They are very resistant life formswhich are found in practically all possible habitats on the planet, forming colonies of individuals that exploit the nutritional resources around them.
We can find them in the intestine of most animalsThey may be in perfect symbiosis with them or, on the contrary, parasitizing their blood and tissues in infections capable of killing them.
Also They are found in fresh and salt watersin the polar ice, on the seabed where light does not reach, and even in mineral rocks underground.
Importance of coins
The kingdom Monera was the first to exist.
Since even today we can find moneras in habitats hostile to other forms of life, it is believed that Their simplicity and primitive character allowed them to emerge in hostile conditions that existed on our planet in its early stages.
That is to say that the kingdom monera It was the first to exist. Understanding it is, therefore, understanding the very origin of life on our planet.
Examples of monera
Examples of members of the Monera kingdom are the various bacteria known to mankind, such as:
- Escherichia coli. It is a gram-negative bacillus that often parasitizes the human digestive tract.
- Clostridium tetani. It is a very common bacteria in the soil and in the digestive tract of animals, which can cause tetanus in humans, a lethal disease, when it enters the blood.
- Plantoea stewartii. It is a bacterium that affects plants, especially different types of corn, and is commonly combated in North American crops.
Virus
Viruses are a very particular case of biology, because despite being extremely simple biological forms, They are not found among the monerasand must be classified completely independently.
Strictly speaking, viruses are much more basic than bacteria, but they cannot survive without them. They depend on them (and other types of cells) to reproduce: they inject them with their parasitic genetic material and thus the bacteria are forced to synthesize the virus proteins.
From a certain point of view, It is unknown if viruses really are life formsor something entirely different.