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Monera Kingdom: what it is, characteristics, classification and examples

The term monera or mónera was introduced by Haeckel in 1986 as a phylum within the Protista kingdom. Later, in 1969, Robert H. Whittaker proposed the classification of life forms in 5 kingdoms of nature: Animalia, Plantae, Protista, Fungi and Monera. This classification has been accepted as accurate until recently, considering the Monera kingdom as one that encompasses microscopic unicellular organisms without a defined nucleus, also known as prokaryotes, differentiating between archaebacteria and eubacteria. However, with the development of new identification techniques and the work of Woese in the 1980s, it was observed that the so-called archaebacteria presented important structural and molecular differences with bacteria and, therefore, had to be considered independently with respect to these, under a new perspective of domains: Archaea and Bacteria.

If you want to know more about the Monera kingdom: what it is, characteristics, classification and examples , keep reading this AgroCorrn article, in which we will explain the peculiarities of this kingdom.

What is the Monera kingdom and its importance

In nature there are 5 kingdoms: the Animalia kingdom , the Plantae kingdom , the Fungi kingdom , the Monera kingdom and the Protista kingdom . The Monera kingdom (from the word “moneres” = “simple”) or monera kingdom is made up of prokaryotic organisms , that is, unicellular beings lacking a defined nucleus and with sizes between 3 and 5 μm, within which are the bacteria The Monera kingdom is made up of the oldest, most widespread and numerous organisms on Earth, present in all types of ecosystems, both aquatic and terrestrial. They are organisms whose form of nutrition can be autotrophic or heterotrophic (parasitic or saprophytic). In these other posts we talk in detail about autotrophic organisms: what they are, characteristics and examples and heterotrophic organisms: what they are, characteristics and examples .

In addition, these beings can be found in isolation or forming colonies, as a consequence of cell division without subsequent separation of the descendant cells.

Characteristics of the Monera kingdom

In addition to those already mentioned, some of the main characteristics of the Monera kingdom are:

  • They can have different shapes (cocci, bacilli, vibrios, spirilli) and some can even change shape during their development (pleomorphic), depending on the medium they occupy, the substrate …
  • As they are single-celled organisms with modest energy needs, they make use almost entirely of the glycolysis process, by which they oxidize glucose molecules from proteins, carbohydrates and fats to obtain energy. Some bacteria obtain their carbon from inorganic carbon sources, but pathogenic ones are heterotrophic and obtain their nutrients, including nitrogen, from both organic and inorganic sources.
  • They lack organelles such as mitochondria, lysosomes, plasmids, Golgi apparatus, endoplasmic reticulum, or centrosome.
  • They reproduce asexually by binary fission or excision.
  • They are decomposers and mineralizers in the environment they inhabit. In this other AgroCorrn article we explain what decomposing living things are .

Monera Kingdom: structure of the components

In addition to the previous characteristics, it should be noted that the components of the Monera kingdom are made up of a series of typical structures that are exposed below.

  • Bacterial capsule: some bacteria have a bacterial capsule, which is a structure with a protective function. It is found outside the bacterial wall, is composed of polysaccharides and amino acids, and serves to adhere to surfaces and to resist phagocytosis by macrophages or other types of microorganisms. It is usually present in parasitic forms, such as Mycobacterium tuberculosis or Diplococcus pneumoniae.
  • Bacterial wall: although it is not present in all prokaryotic cells, it is a structure of great importance, as it provides shape to the cell and keeps the structure intact and stable, protecting it from situations of osmotic stress. It is composed of polysaccharides, proteins, lipids and glutamic and diaminopimelic acids. The cell wall is also important in the context of pathogenicity because it protects the bacteria from enzymes that can degrade it and also because it has antigenic determinants (especially in Gram negative bacteria, they are responsible for toxicity in some diseases such as salmonella).
  • Plasma membrane: it is found inside the boundary delineated by the cell wall. It is thin, elastic, acts as a mechanical limit, has selective permeability, serves to transport nutrients and waste, and to detect signals from the environment. As these organisms lack internal organelles, the plasma membrane is where metabolic processes such as respiration and photosynthesis are located.
  • Cytoplasm: fluid or semi-fluid aqueous medium consisting of vitamins, salts, enzymes, carbohydrates, soluble proteins, lipids and nucleic acids. The cytoplasm is granular in consistency due to the presence of a high number of ribosomes.
  • Periplasmic space: it is a region in the cell wall of Gram negative bacteria, located between the outer membrane and the cytoplasmic, of great importance. It is composed of a periplasmic fluid that presents hydrolytic enzymes and binding proteins for the uptake and processing of nutrients.
  • Absence of nucleus: nucleic acid (DNA, double helix and circular) is in an area called nucleoid that is more electrodense than the rest but lacks a membrane around it.
  • Bacterial endospore: typical structure of bacteria that forms inside and serves to resist adverse conditions.
  • Pili and fimbriae: some bacteria have fimbriae or different types of hair, which are important for adhesion to surfaces.
  • Flagella: prokaryotic cells that move do so through structures called flagella, different from those that a eukaryotic cell may present.
  • Ribosomes: the ribosomes of bacteria, which have a protein synthesis function, are different from those of eukaryotic cells in the sedimentation coefficient, since prokaryotes have a coefficient of 70, as do those of mitochondria and chloroplasts (the which supports the theory of the bacterial origin of these organelles).
  • Inclusion bodies: they are a kind of organelles that can serve for magnetic orientation, to store carbon, nitrogen or phosphorous reserves and for buoyancy (such as gas vacuoles, which allow them to rise or fall in an aqueous environment) .

Classification of the Monera kingdom

As mentioned at the beginning of this article, formerly, within the Monera kingdom, two types of organisms were differentiated: eubacteria and archaebacteria. However, it was later concluded that the latter had an evolutionary history totally independent of bacteria and came to be considered as two separate groups: archaea and bacteria. Thus, this is the classification of the Monera kingdom :

Archeas (ancient “archaebacteria”)

They are the oldest prokaryotes existing on Earth and are characterized by inhabiting environments with extreme conditions (for example, hot springs and saline areas), because they have a cell wall with a characteristic structure that allows them to survive such conditions. They share characteristics both with bacteria (such as, for example, their prokaryotic cell structure, their types of metabolism, such as nitrogen fixation or denitrification, etc.) and with eukaryotic cells (for example, they have autotrophic nutrition, they lack peptidoglycans in cell wall and possess RNA polymerases with multiple polypeptides, among other things). They present nucleotide sequences in their unique t-RNA and r-RNA.

Bacteria (former “eubacteria”)

The name of eubacteria means “true bacteria”, and they have the typical characteristics mentioned above, such as having rigid cell walls composed of peptidoglycans, locomotion with the help of flagella, presence of pili on the cell surface that help in sexual reproduction and also pathogens to attach to a host they are going to invade, and so on.


Known as blue-green algae because they were considered as such for a long time, they are the only prokaryotic organisms capable of oxygenic photosynthetic processes. They are the largest prokaryotic organisms, being able to reach dimensions of up to 60 micrometers. Some, in addition, are capable of fixing nitrogen and have developed specialized cells called heterocysts to be able to combine this process (which cannot take place in the presence of oxygen) with that of oxygenic photosynthesis. As prokaryotic organisms, the presence of gas vacuoles stands out in some types, which favors their buoyancy. The characteristic color of some of these organisms is given by the combination of phycobilin and chlorophyll a, but other species can be green, brown, yellow, black or red due to other pigments such as carotenoids and phycoerythrin. Although most cannot exist in the absence of light, certain species can if there is a sufficient supply of glucose to serve as a source of carbon and energy.

Examples of the Monera kingdom

To finish, these are some examples within the monera kingdom :

  • Archaea: Haloquadratum walsby, halophilic archaea , Ignicoccus hospitalis , which establishes symbiotic relationships or Pyrolobus fumarii , which can live in conditions of extreme temperatures.
  • Bacteria: Escherichia coli, present in the intestinal flora of humans and aids in the digestion of food; Clostridium botulinum , responsible for the production of botulinum toxin, which can cause botulism.
  • Blue-green algae (cyanobacteria): Anabaena azollae maintains a symbiotic relationship with the Azolla genus of aquatic ferns , Nostoc sphaericum.

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