A single eukaryotic organism can have trillions of cells, although yeast are unicellular; bacterial cells, on the other hand, have only one cell. Whereas eukaryotic cells include a variety of membrane-bound organelles, such as the nucleus, mitochondria (in animals), chloroplasts (plants' answer to mitochondria), Golgi bodies, the endoplasmic reticulum and lysosomes, bacterial cells have no organelles.
