What key feature distinguishes prokaryotic cells from eukaryotic cells?

The distinguishing feature that sets prokaryotic cells apart from eukaryotic cells is that prokaryotic cells lack membrane-bound organelles. In prokaryotes, which include bacteria and archaea, cellular processes occur in the cytoplasm or at the cell membrane, rather than being compartmentalized within organelles like the nucleus, mitochondria, or endoplasmic reticulum found in eukaryotic cells. This lack of compartmentalization is a fundamental characteristic of prokaryotes, contributing to their simpler structure and organization compared to eukaryotic cells.

In contrast, other features mentioned in the choices highlight misconceptions. Prokaryotic cells do not have a nucleus; they contain their genetic material in a nucleoid region. Additionally, they do not have complex, membrane-bound organelles, which are typical features of eukaryotic cells. Furthermore, while there are variations in size, prokaryotic cells are generally smaller than eukaryotic cells, which contradicts the idea that they are larger. Therefore, the correct understanding focuses on the absence of membrane-bound organelles in prokaryotes.