Super Kingdom prokaryota and Eukaryota
All cellular organisms so far studied fall naturally into one of two major groups, the prokaryota and eukaryota
The prokaryotes appeared about 3500 million years ago and comprise a variety of organisms collectively known as bacteria. All the cells of prokaryotes (pro=before+karyon=nucleus)lake true nuclie. In other words their genetic material (DNA) is not enclosed by nuclear membranes, and lies free in cytoplasm.
Eukaryotes includes protoctista, fungi, green plants and animals. They appeared first in the late pre-Cambrain period, About 2000 million years ago and probably evolved from prokaryots. The cells of eukaryots (Eu=true) are much more complex and are characterizad by true nucleus i.e.,genetic material is enclosed by nuclear envelope to form a definite, easily recognizable structure.