One of the two major groups of organisms on Earth, including all animals, plants, protozoa and fungi. Characterised by the possession of a cell nucleus, and other membrane-bouded cell organelles (analogue of 'organ' within the cell) such as mitochondria. Contrast with prokaryotes. The prokaryote/eukaryote distinction is much more fundamental than the animal/plant distinction (not to mention the relatively negligible human/'animal' distinction!).