" action, and there are also structures so distinct from the rest of the cell ‘jelly’, like cells within cells, that the best explanation of their presence is that that is indeed what they are. These semi-autonomous ‘cells within the cell’ are called organelles. As we saw in Chapter Four, Lynn Margulis has explained how the ancestors of the organelles used to be separate, bacteria "

― John Gribbin , In the Beginning: The Birth of the Living Universe (Fundamental Questions Book 1)