Prokaryotic Cells The characteristics of prokaryotic cells apply to the bacteria and cyanobacteria (formerly known as blue-green algae), as well as to the rickettsiae, chlamydiae, and mycoplasmas. Size and shape. Prokaryotes are probably the smallest living organisms, ranging in size from 0.15 μm (mycoplasmas) to 0.25 μm (chlamydiae) to 0.45 μm (rickettsiae) to about 2.0 μm (many of the bacteria). Certain prokaryotes, such as bacteria, occur in spherical forms called cocci (singular, coccus ) or in rodlike forms called bacilli (singular, bacillus ). Some bacteria have a comma shape ( vibrio ), or a flexible, wavy shape ( spirochete ), or a corkscrew shape ( spirillum ). Some prokaryotes have a variety of shapes and sizes and are said to be pleomorphic. Rickettsiae and mycoplasmas are examples of pleomorphic microorganisms. When certain prokaryotes divide, they cling to each other in a distinct arrangement. A
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