Eukaryota
All cellular life is divided into three domains: Eukaryota, Eubacteria, and Archaea.
The Eukaryota, of which we and all other multicellular animals are members, are distinguished from the other two domains by several characteristics. The DNA molecule is contained within the nucleus, and is organized in chromosomes and wound around proteins called histones. The eukaryote cell possesses a cytoskeleton, made of actin filaments and microtubules, which is used in movement, fagocytosis, and in maintaining the shape of the cell. Eukaryotes contain organelles, the best known of which are the mitochondria and chloroplasts (although some lineages have lost their mitochondria). According to the endosymbiotic theory, these two organelles were once free-living bacteria that got incorporated in the eukaryote cell.
Eukaryota contains both unicellular and multicellular organisms, and encompass the groups Protista, Fungi, Plantae, and Animalia.
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