Structurally, prokaryotic organisms are far simpler than eukaryotic life forms. Yet, prokaryotes are functionally or metabolically diverse with regards to the reactions they mediate or stresses they can endure. Prokaryotes do not possess membrane-bound organelles such as a nucleus, endoplasmic reticulum, mitochondria, or chloroplasts. Therefore, prokaryotes can not separate metabolically incompatible biochemical processes into discrete compartments. The inability to compartmentalize cellular processes poses a bottleneck for the biochemical and structural evolution of prokaryotes. As a result, prokaryotes have diversified with regards to biochemical abilities while remaining structurally simple.