Derived from the Greek meaning a ‘true nut’, or ‘true kernel’ (with the ‘nut’ being the nucleus), it is a term used to cover all living organisms except bacteria and blue-green algae (i.e., cyanobacteria) that belong to the prokaryote grouping. The cells of eukaryotes have a clearly defined nucleus bounded by a cell membrane, within which DNA, having been derived from histones, is formed into distinct chromosomes. In addition to a well-defined nucleus, they also have a cytoskeleton, and contain mitochondria, choloroplasts (structures within the cells of plants containing the green pigment chlorophyll), and organelles, all of which are lacking in the cells of prokaryotes. For further structures in such cells, see figure below.
