The two main types of cells that make up living organisms are prokaryotic and eukaryotic cells. Prokaryotic cells are simpler, smaller, and lack a nucleus, typically represented by bacteria and archaea. In contrast, eukaryotic cells are larger, more complex, and possess membrane-bound organelles, including a nucleus where genetic material is stored. This distinction is fundamental to biology, as it shapes the functional capabilities of organisms, from unicellular life forms to highly organized multicellular organisms like plants and animals.