Eukaryotic cells are characterized by their membrane-bound organelles, including a defined nucleus containing their genetic material. In contrast, prokaryotic cells lack these structures, with their DNA typically found in a nucleoid region. Eukaryotes are generally larger and more complex and include organisms such as plants, animals, and fungi. Prokaryotes, which include bacteria and archaea, are simpler and smaller. The differences in cellular organization play a crucial role in the complexity and functionality of organisms in each group.