A centrally important discussion in biology deals with the differences between eukaryotic and prokaryotic cells. The structure of eukaryotic and prokaryotic cells differ in a number of fundamental ways beyond simply the presence of a nucleus or other membrane bound compartments. When I was in school I learned that prokaryotic cells were thought to have no cytoskeleton. However, recent research has shown that some prokaryotic cells do possess a cytoskeleton, so you can scratch that one off your list.