Prokaryotes and eukaryotes Three letters that divide the living world into two universes. Prokaryotes are single-celled living organisms that do not have a formalized cell nucleus and cell organelles. This type of organism includes bacteria and archaea. Eukaryotes - the cells of these organisms have formalized, envelope-limited nuclei. More importantly, these nuclei contain DNA. Plants, fungi, animals, and of course humans are all eukaryotes.