Eukaryotes are organisms whose bodies have cells that contain a nucleus and organelles and that are enclosed by plasma membranes. This group, or domain, called eukaryota, contains four subgroups, or kingdoms: animals, plants, fungi, and protists. Protists include protozoa, slime molds and some algae.
The other two domains of life, bacteria and archaea, have prokaryotic cells, which are simpler than eukaryote cells, including lacking organelles except for ribosomes, which produce proteins. It is now thought that eukaryotes evolved from prokaryotes roughly two billion years ago.