Cell

Two types of cells are recognized in living things. Prokaryotes (literally, "before the nucleus") are cells that have no distinct nucleus. Most prokaryotic organisms are single-celled, such as bacteria and algae. Eukaryotic (literally, "true nucleus") organisms, on the other hand, have a distinct nucleus and a highly organized internal structure. Distinct organelles, the small structures that each perform a specific set of functions, are present within eukaryotes. These organelles are bound by membranes. Prokaryotes, in addition to their lack of a nucleus, also lack these membrane-bound organelles.