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Their metabolism is far more varied than that of eukaryotes, leading to many highly distinct types. For example, prokaryotes may obtain energy by chemosynthesis. [34] Prokaryotes live nearly everywhere on Earth, including in environments as cold as soils in Antarctica, [35] or as hot as undersea hydrothermal vents and land-based hot springs. [33]
Eukaryotes may be either unicellular or multicellular. In comparison, prokaryotes are typically unicellular. Unicellular eukaryotes are sometimes called protists. Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion (fertilization).
Eukaryotic cells contain membrane bound organelles. Some examples include mitochondria, a nucleus, or the Golgi apparatus. Prokaryotic cells probably transitioned into eukaryotic cells between 2.0 and 1.4 billion years ago. [31] This was an important step in evolution. In contrast to prokaryotes, eukaryotes reproduce by using mitosis and meiosis.
Archaea (/ ɑːr ˈ k iː ə / ⓘ ar-KEE-ə) is a domain of organisms.Traditionally, Archaea only included its prokaryotic members, but this since has been found to be paraphyletic, as eukaryotes are now known to have evolved from archaea.
It consists of all bacteria, which are prokaryotes (lacking nucleus), thus, Domain Bacteria is made up solely of prokaryotic organisms. [62] [63] Some examples are: Cyanobacteria – photosynthesising bacteria related to the plastids of eukaryotes. [64] Spirochaetota – Gram-negative bacteria involved in human diseases like syphilis and lyme ...
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.
Prokaryotes are not as structurally complex as eukaryotes, and were once thought to have little internal organization, and lack cellular compartments and internal membranes; but slowly, details are emerging about prokaryotic internal structures that overturn these assumptions. [2]
Although it was generally accepted that one could distinguish prokaryotes from eukaryotes on the basis of the presence of a nucleus, mitosis versus binary fission as a way of reproducing, size, and other traits, the monophyly of the kingdom Monera (or for that matter, whether classification should be according to phylogeny) was controversial ...