Carl Woese of the University of Illinois divides life into 23 major divisions, which are grouped into three domains: Bacteria, Archaea, and Eukaria; Bacteria (several thousand species) differ from Archaea (175 species) (microscopic species, however, constitute more than 80% of the planet’s biomass) in the composition of their fats and the presence/absence of peptidoglycan; Eukaria are the nucleated cells that constitute complex organisms (millions of species).
