Class of organisms, composed of one or more cells containing a membrane-enclosed nucleus and organelles, that constitutes one of the three distinct evolutionary lineages of modern-day organisms; also called eukarya. Includes all organisms except viruses and prokaryotes.
One of the three domains of life. They contain a nucleus and can be microorganisms, like yeast and protozoa, or multicellular organisms like plants and animals. Also called Eukarya.
Organisms making up one of the three branches on the phylogenetic tree of life. Their characteristic feature is that their cells have a defined nucleus containing most of the organism's DNA. See Archaea and Bacteria.