The primary distinction between prokaryotic and eukaryotic cells is the presence of a nucleus and membrane-bound organelles. Prokaryotic cells, which include bacteria, lack a true nucleus; their genetic material is free-floating within the cell. Eukaryotic cells, which comprise animals, plants, fungi, and protists, have a defined nucleus that houses their DNA, as well as various organelles that perform specialized functions. This distinction is fundamental in biology, influencing cell complexity, organization, and functionality across different forms of life.