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Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. [1] This takes place through a pilus. [2] [full citation needed] It is a parasexual mode of reproduction in bacteria. Escherichia coli conjugating using F-pili. These long and robust ...
Combined with the five-kingdom model, this created a six-kingdom model, where the kingdom Monera is replaced by the kingdoms Bacteria and Archaea. [16] This six-kingdom model is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus. [ 13 ]
Ciliate conjugation is a sexual phenomenon that results in genetic recombination and nuclear reorganization within the cell. [24] [22] During conjugation, two ciliates of a compatible mating type form a bridge between their cytoplasms. The micronuclei undergo meiosis, the macronuclei disappear, and haploid micronuclei are exchanged over the bridge.
The five-kingdom model remained the accepted classification until the development of molecular phylogenetics in the late 20th century, when it became apparent that protists are a paraphyletic group from which animals, fungi and plants evolved, and the three-domain system (Bacteria, Archaea, Eukarya) became prevalent. [200]
According to Hogg, this new classification scheme prevented "the unnecessary trouble of contending about their supposed natures, and of uselessly trying to distinguish the Protozoa from the Protophyta". In 1866, Ernst Haeckel (1834–1919) proposed the name "Protista" for the primigenial kingdom and included bacteria in this third kingdom of life.
For the Prokaryotes (Bacteria and Archaea) the rank kingdom has not been used till 2024 [115] (although some authors referred to phyla as kingdoms [73]). The category of kingdom was included into the Bacteriological Code in November 2023, [ 116 ] the first four proposals ( Bacillati , Fusobacteriati , Pseudomonadati , Thermotogati ) were ...
A variety of multi-kingdom systems were proposed, and the Kingdoms Protista and Protoctista became established in biology texts and curricula. [ 22 ] [ 23 ] [ 24 ] By 1954, Protozoa were classified as "unicellular animals", as distinct from the "Protophyta", single-celled photosynthetic algae, which were considered primitive plants. [ 25 ]
The three-domain system adds a level of classification (the domains) "above" the kingdoms present in the previously used five- or six-kingdom systems.This classification system recognizes the fundamental divide between the two prokaryotic groups, insofar as Archaea appear to be more closely related to eukaryotes than they are to other prokaryotes – bacteria-like organisms with no cell nucleus.