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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.
Kingdom monera. They belong to the prokaryote characteristics of kingdom monere. they are unicellular organism. they show different mode of nutrition such as autotrophic, heterotrophic,parasitic; they lack mitochondria; they have few organelles which are not membrane bounds; flagellum serves as the locomotory organ; reproduction is both sexual ...
Both eukaryotes and prokaryotes contain ribosomes which produce proteins as specified by the cell's DNA. Prokaryote ribosomes are smaller than those in eukaryote cytoplasm, but similar to those inside mitochondria and chloroplasts , one of several lines of evidence that those organelles derive from bacteria incorporated by symbiogenesis .
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 ]
[3] [4] In the three-domain model, the first two are prokaryotes, single-celled microorganisms without a membrane-bound nucleus. All organisms that have a cell nucleus and other membrane-bound organelles are included in Eukarya and called eukaryotes. Non-cellular life, most notably the viruses, is not included in this system.
The development of microscopy revealed important distinctions between those organisms whose cells do not have a distinct nucleus (prokaryotes) and organisms whose cells do have a distinct nucleus . In 1937 Édouard Chatton introduced the terms "prokaryote" and "eukaryote" to differentiate these organisms. [9]
Eukaryotes have a nucleus in their cells, and include: Protists – many unicellular eukaryotes including malarial parasites, amoeba, and diatoms. [69] Kingdom Fungi – eukaryotes such as mushroom, yeast, and mould; all fungi. Kingdom Plantae – all plants. Kingdom Animalia – all animals.
Originally, Linnaeus established three kingdoms in his scheme, namely for Plants, Animals and an additional group for minerals, which has long since been abandoned. Since then, various life forms have been moved into three new kingdoms: Monera, for prokaryotes (i.e., bacteria); Protista, for protozoans and most algae; and Fungi.