In fact, they do not have any membrane bound organelle whatsoever. However, eukaryotes do have a nucleus, and they do contain membrane bound organelles, such as the mitochondria or the endoplasmic reticulum. Now, prokaryotes are mostly unicellular, but some multicellular prokaryotes do in fact exist, while eukaryotes come in both types, we have unicellular and multicellular eukaryotes, as we'll see in a future lecture. Now, all prokaryotes have cell walls, but not all eukaryotes have cell walls. For example, plants do have cell walls, but we humans do not have any cell walls. Animals do not have cell walls around our cell.