We—you and me—inhabit a second branch, or domain, called eukaryotes. The word eukaryote is a technicality: it refers to the idea that our cells, and the cells of animals, fungi, and plants, contain a special structure called a nucleus (karyon, or “kernel,” in Greek). This nucleus, as we will soon learn, is a storage site for chromosomes. Bacteria lack nuclei and are called prokaryotes—that is, “before nuclei.”
