Monera

Figure 1. Five kingdoms.

In some systems of biological classification, Monera is a kingdom that comprises most living things with a prokaryotic cell organization. For this reason, the kingdom also has been called Prokaryotae.

Kingdom Monera historically included the bacteria, blue-green algae (cyanobacteria or blue-green bacteria), and the archaebacteria (Towle 1989). At times, four phyla of Kingdom Monera were recognized: Archaebacteria, Schizopyta (bacteria), Cyanophyta (the phytosynthetic cyanobacteria), and Prochlorophyta (symbiotic photosynthetic bacteria). However, the unique nature of the archaebacteria has led to classifications where they are not included with Monera.

In the five kingdom system of biological classification, the other kingdoms are Protista, Fungi, Plantae, and Animalia. In the six kingdom system, the archaebacteria are separated into their own kingdom, Archaebacteria or Archaea.

Although the kingdom level traditionally was the highest level, in recent years a higher classification level has been promoted called a "domain" or "superkingdom." It includes three major groups: the Archaea, Bacteria, and Eukaryota. Some place Monera as a kindgom under the domain Bacteria; however, in originator Carl Woese's popular three-domain system, Monera no longer exists, as life is divided into multiple main divisions incorporated within the three domains Bacteria, Archaea, and Eukarya.

Monera in biological classification

For two centuries, from the mid-18th century until the mid-20th century, organisms were generally considered to belong to one of two kingdoms, Plantae (plants, including bacteria) or Animalia (animals, including protozoa). This system was proposed by Carolus Linnaeus in the mid-18th century. However, this classification had obvious difficulties, including the problem of placing fungi, protists, and prokaryotes. There are single-celled organisms that fall between the two categories, such as Euglena, that can photosynthesize food from sunlight and yet feed by consuming organic matter.

In 1866, Ernst Haeckel proposed a three kingdom system that added Protista as a new kingdom that contained most microscopic organisms (Haeckel 1866). One of his eight major divisions of Protista was called Moneres. Haeckel's Moneres subcategory included known bacterial groups such as Vibrio. Haeckel's Protista kingdom also included eukaryotic organisms now classified as Protist. Later, Haeckel proposed a fourth kingdom, which he called Monera. It was later decided that Monera proved to be too diverse to be seriously considered one single kingdom.

In 1969, Robert Whittaker published a proposed five kingdom system (Figure 1) for classification of living organisms (Whittaker 1969). Whittaker's system placed most single celled organisms into either the Monera (prokaryotes— bacteria and blue-green algae) or the Protista (eukaryotes). The other three kingdoms in his system were the eukaryotic Fungi, Animals, and Plants. This system was widely used for three decades, and remains popular today.

Subsequently, a higher level classification was recognized called the "Domain." One of the reasons such a classification has been developed is because research has revealed the unique nature of anaerobic bacteria (called Archaeobacteria, or simply Archaea). These "living fossils" are genetically and metabolically very different from oxygen-breathing organisms. Various numbers of kingdoms are recognized under the domain category, including doing away entirely with the kingdom level.

Figure 2. A phylogenetic tree of living things, based on rRNA sequence data, showing the separation of bacteria, archaea, and eukaryotes.

The three-domain system was introduced by Carl Woese in 1990. Based on molecular phylogeny studies, Woese proposed that the prokaryotes (monerans) be divided into two separate groups: Bacteria and Archaea.

This gave three groupings: Archaea, Bacteria, and Eukaryota. In his 1990 proposed phylogeny (Woese 1990), these three kingdoms are all rooted in a universal common ancestor and this is the most widely accepted categorical phylogeny accepted today (see diagram to the right). However, the most modern interpretation for these three kingdoms is the "Universal and Eukaryote Phylogenetic Tree" based on 16s rDNA as presented on the Tree of Life website (Sogin 2006).

Woese's three-domain system, based upon genetic relationships rather than obvious morphological similarities, divided life into 23 main divisions, all incorporated within the three domains of Bacteria, Archaea, and Eucarya. In this scheme, Kingdom Monera no longer exists.

In some classifications, however, authorities keep the kingdom system as the higher-level classification, and thus Monera, but recognize a sixth kingdom, the Archaebacteria.

Coexisting with these schemes is one dividing living organisms into the two main divisions of prokaryote (cells that lack a nucleus: bacteria, etc.) and eukaryote (cells that have a nucleus and membrane-bound organelles: animals, plants, fungi, and protists).

Thus, today there are several competing top classifications of life, some of which omit Monera:

• The three-domain system of Carl Woese, with top-level groupings of Archaea, Eubacteria, and Eukaryota domains;
• The two-empire system, with top-level groupings of Prokaryota (or Monera) and Eukaryota empires.
• The five-kingdom system with top-level groupings of Monera, Protista, Fungi, Plantae, and Animalia.
• The six-kingdom system with top-level groupings of Archaebacteria, Monera, Protista, Fungi, Plantae, and Animalia.

Overall, the majority of biologists accept the domain system, but a large minority uses the five-kingdom method. A small minority of scientists adds Archaea or Archaebacteria as a sixth kingdom but do not accept the domain method.

Linnaeus 1735 2 kingdoms	Haeckel 1866 3 kingdoms	Chatton 1937 2 empires	Copeland 1956 4 kingdoms	Whittaker 1969 5 kingdoms	Woese et al. 1977 6 kingdoms	Woese et al. 1990 3 domains
(not treated)	Protista	Prokaryota	Monera	Monera	Eubacteria	Bacteria
					Archaebacteria	Archaea
		Eukaryota	Protista	Protista	Protista	Eukarya
Vegetabilia	Plantae			Fungi	Fungi
			Plantae	Plantae	Plantae
Animalia	Animalia		Animalia	Animalia	Animalia

References

ISBN links support NWE through referral fees

. . , .

See also

• Bacterial cell structure
• Kingdom (biology)

Monera also called Prokayotae it is the kingdom of prokaryotic organisms that are unicellular that is a single-celled: consisting of a single cell & lack a true cell nucleus.

External links

• Bacterial evolution by Carl Woese (1987). Woese reviewed the historical steps leading to the use of the term "Monera" and its later abandonment (full text online). Entrez PubMed 2439888

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

• Monera  ^history

The history of this article since it was imported to New World Encyclopedia:

• History of "Monera"

Note: Some restrictions may apply to use of individual images which are separately licensed.