What key characteristic distinguishes eukaryotic cells from prokaryotic cells?

The distinguishing characteristic that sets eukaryotic cells apart from prokaryotic cells is the presence of a nucleus. In eukaryotic cells, the nucleus serves as a membrane-bound organelle that houses the cell's genetic material (DNA) in a well-defined structure. This organization allows for more complex regulation of gene expression and is fundamental to the more advanced processes seen in multicellular organisms.

In contrast, prokaryotic cells do not have a nucleus; instead, their genetic material is located in a region called the nucleoid, which is not enclosed by a membrane. This key difference enables eukaryotic cells to carry out more sophisticated cellular functions and is associated with the development of multicellularity and greater cellular complexity.

While other components mentioned, such as mitochondria or ribosomes, are present in eukaryotic cells, they do not uniquely distinguish them from prokaryotic cells since some prokaryotes also contain ribosomes (albeit in a different structure) and lack mitochondria. The presence of a cell membrane is common to both eukaryotic and prokaryotic cells and is therefore not a distinguishing feature.