Living things are categorized into kingdoms, including the now-defunct Moneran realm for creatures without cores. Monerans lack nuclei and organelles, reproduce through binary fission, and are divided into bacteria and cyanobacteria. Monera was later separated from Protista, and in 1991, archaea and bacteria replaced Monera.
Scientists often categorize both living and nonliving things to better understand the world and its inhabitants. Living organisms can be grouped into kingdoms. Though no longer in use, the Moneran realm has long been used as a classification for creatures that lack cores. Single-celled organisms in this kingdom were known as monerans or prokaryotes.
The practice of grouping living organisms in biology is called taxonomy. In the 19th and most of the 20th century, scientists distinguished biological organisms as plants, animals, or microscopic single-celled organisms that fell somewhere in between. A scientist named Ernst Haeckel dubbed the latter group Protista and included Monera as one of eight divisions in this grouping.
Monetaries were differentiated from their counterparts by some significant differences. In most cells, a nucleus is the central life force. It guides the cell in the breakdown, growth and reproduction of food. Moneri carry out these processes without the aid of a nucleus or other complex structures known as organelles. Rather, they are based on molecules found within the cell.
These cells can survive on their own, although they can be found in groups. The process of reproduction in monrans is also different, as they do not undergo cellular mitosis like most other cells. Rather, they multiply via binary fission or a simple cleavage of the cell.
Two further divisions distinguish monrans from each other: bacteria and cyanobacteria. Bacteria are found almost everywhere in the world and survive by adhering to surfaces with a sticky cell wall and thereby gaining food and moisture. These creatures are also very hardy, as they can survive temperatures and conditions nearly uninhabitable for other living organisms. For example, they can breathe without the use of oxygen. Cyanobacteria, on the other hand, are more like plants as they undergo photosynthesis and provide an important food source in the world’s oceans.
By the mid-20th century, scientists had separated Moneran as an entirely separate entity from Protista. In this new system, any single-celled organism lacking a nucleus was considered a Moneran, while any similar organism with complex closed-nucleus structures – or organelles – retained the name Protista. Animalae, Plantae, and Fungi completed this five-kingdom system of classification.
In 1991, a new taxonomy system gained general recognition among the scientific community. Under this new system, the kingdom Monera was discarded in favor of two distinct groupings: archaea and bacteria. While most scientists accepted this new system, a few resisters kept the old system.
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