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Viridiplantae species all have cells with cellulose in their cell walls, and primary chloroplasts derived from endosymbiosis with cyanobacteria that contain chlorophylls a and b and lack phycobilins. Corroborating this, a basal phagotroph Archaeplastida group has been found in the Rhodelphydia. [16]
Archaea and bacteria have generally similar cell structure, but cell composition and organization set the archaea apart. Like bacteria, archaea lack interior membranes and organelles. [68] Like bacteria, the cell membranes of archaea are usually bounded by a cell wall and they swim using one or more flagella. [119]
Some of these groups (Oomycete and Myxogastria) have been transferred out of the Kingdom Fungi, in part because of fundamental biochemical differences in the composition of the cell wall. Most true fungi have a cell wall consisting largely of chitin and other polysaccharides. [28] True fungi do not have cellulose in their cell walls. [16]
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 ]
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.
Even though bacteria are prokaryotic cells like Archaea, their cell membranes are instead made of phospholipid bilayers, with none of the ether linkages that Archaea have. Internally, bacteria have different RNA structures in their ribosomes, hence they are grouped into a different category. In the two- and three-domain systems, this puts them ...
Eugene Koonin and others, noting that the archaea share many features with eukaryotes, argue that rudimentary eukaryotic traits such as membrane-lined compartments were acquired before endosymbiosis added mitochondria to the early eukaryotic cell, while the cell wall was lost. In the same way, mitochondrial acquisition must not be regarded as ...
In 2009, Cavalier-Smith gave his reason for making a new kingdom, saying: [7] I established Chromista as a kingdom distinct from Plantae and Protozoa because of the evidence that chromist chloroplasts were acquired secondarily by enslavement of a red alga, itself a member of kingdom Plantae, and their unique membrane topology. [7]