Prokaryotes are one of the most prodigious and one of the simplest forms of life on the planet. They are principally characterised by a complete absence of large membrane bound organelles that are present in eukaryotes. Prokaryotes are also smaller (0.5 -5 micrometers long) compared to eukaryotes, which can be up to 40 micrometers long. Prokaryotes do not have a nucleus and their DNA floats freely in the cytoplasm as many plasmids.

Prokaryotes can have a great many features that a basic eukaryote generally does not have. Some secrete about themselves a slime capsule (principally for protection). Some can manipulate their plasma membrane to create proto-organelles for photosynthesis, or nitrogen fixation. Some grow villi, others, flagellum.

Prokaryotes are bacteria, or archaea, they do not exist as defacto multicellular organisms but often form colonies.