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A prokaryote (/ p r oʊ ˈ k ær i oʊ t,-ə t /; less commonly spelled procaryote) [1] is a single-celled organism whose cell lacks a nucleus and other membrane-bound organelles. [2] The word prokaryote comes from the Ancient Greek πρό (pró), meaning 'before', and κάρυον (káruon), meaning 'nut' or 'kernel'. [3]
A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea
Monera (/məˈnɪərə/) (Greek: μονήρης (monḗrēs), "single", "solitary") is historically a biological kingdom that is made up of prokaryotes. As such, it is composed of single-celled organisms that lack a nucleus. The taxon Monera was first proposed as a phylum by Ernst Haeckel in 1866.
Prokaryote – A group of organisms whose cells lack a membrane-bound cell nucleus, or any other membrane-bound organelles, including bacteria. Bacterial cells – A prokaryotic cell belonging to the mostly unicellular Domain Bacteria. Archea cell – A cell belonging to the prokaryotic and single-celled microorganisms in Domain Archea.
Eukaryotes are organisms whose cells have a nucleus enclosed within membranes, whereas prokaryotes are the organisms that do not have a nucleus enclosed within a membrane. [ 1 ] [ 2 ] [ 3 ] The three-domain system of classifying life adds another division: the prokaryotes are divided into two domains of life, the microscopic bacteria and the ...
[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.
Most have a single plasma membrane and cell wall, and lack a periplasmic space; the exception to this general rule is Ignicoccus, which possess a particularly large periplasm that contains membrane-bound vesicles and is enclosed by an outer membrane.
The archaea (Greek for ancient [79]) constitute a domain and kingdom of single-celled microorganisms. These microbes are prokaryotes, meaning they have no cell nucleus or any other membrane-bound organelles in their cells. Archaea were initially classified as bacteria, but this classification is outdated. [80]