Very simple living cell or organism that contains genetic material (RNA, DNA or analogue) that is not separate from the rest of the cell. The term is also used for non-Terragen organisms of a similar level of complexity. Their cell structure is relatively simple and lacks a nucleus and any but the simplest organelles. Terragen examples include bacteria, archaea, and cyanobacteria. Organisms comparable to Old Earth prokaryotes are widely distributed through the universe, and are far better able to survive extreme conditions than eukaryote-grade life. However, it is very rare (but not unknown) for prokaryote cells to develop into higher life-forms.