Prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO. They are generally smaller and multiply more rapidly than eukaryotic cells. The organisation of the prokaryotic cell is fundamentally similar even though they exhibit a wide variety of shapes and functions.

Prokaryotes have a cell wall surrounding the cell membrane except in mycoplasma. Most prokaryotic cells have a chemically complex cell envelope consisting of three layers – the outermost glycocalyx, followed by the cell wall and then the plasma membrane. A specialised differentiated form of cell membrane called mesosome is characteristic of prokaryotes, which are essentially infoldings of cell membrane.

There is no well-defined nucleus in prokaryotic cells. The genetic material is basically naked, not enveloped by a nuclear membrane. In addition to the genomic DNA (single chromosome/circular DNA), many bacteria have small circular DNA called plasmids. The plasmid DNA confers certain unique phenotypic characters like resistance to antibiotics.

Prokaryotic cells lack membrane bound organelles like the ones in eukaryotes. The only organelles found are ribosomes, which are non-membrane bound. The semi-fluid matrix filling the cell is the cytoplasm. Prokaryotes have something unique in the form of inclusions.

The four basic shapes of bacteria are bacillus (rod like), coccus (spherical), vibrio (comma shaped) and spirillum (spiral).