Cells in which the genetic material is not packaged within a nucleus. This differs from eukaryotic cells in which DNA is contained in the nucleus. Prokaryotic cells are generally much smaller than eukaryotic cells and have much less genetic material.

The prokaryotes consist of two groups the Eubacteria (true bacteria) and Archaebacteria (ancient bacteria); the genetic differances between the Eubacteria and Archaebacteria are as great as that between the prokaryotes and the eukaryotes.