Their structures have to do more things (in an apartment the living room is also the dining room), This analogy applies to cells because simpler prokaryotic cells, which have less structures. It also applies to more complex eukaryotic cells that have more structures, where each structure only does a singular task. (In a mansion each room, only serves one purpose.) I believe it means that even though the homes/cells may appear different, they all include the same basic essentials.
