At the most fundamental level, a big gap exists between forms of life whose cells have nuclei (eukaryotes, such as plants, animals, and fungi) and those that don’t (prokaryotes such as bacteria and blue-green algae) (b).
b. “The prokaryotes came first; eukaryotes (all plants, animals, fungi and protists) evolved from them, and to this day biologists hotly debate how this transition took place, with about 20 different theories on the go.... [What was thought to be an intermediate between prokaryotes and eukaryotes] is no longer tenable.” Katrin Henze and William Martin, “Essence of Mitochondria,” Nature, Vol. 426, 13 November 2003, p. 127.
