PROKARYOTE

Prokaryotes (pronounced /proʊˈkæri.oʊts/ or /proʊˈkæriəts/) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. The organisms that have a cell nucleus are called eukaryotes. Most prokaryotes are unicellular, but a few such as myxobacteria have multicellular stages in their life cycles.  The word prokaryote comes from the Greek πρό- (pro-) "before" + καρυόν (karyon) "nut or kernel". Prokaryotes do not have a nucleus, mitochondria, or any other membrane-bound organelles. In other words, neither their DNA nor any of their other sites of metabolic activity are collected together in a discrete membrane-enclosed area. Instead, everything is openly accessible within the cell, some of which is free-floating.

Prokaryotes belong to two taxonomic domains: the bacteria and the archaea. Archaea were recognized as a domain of life in 1990. These organisms were originally thought to live only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats.