What structural feature distinguishes eukaryotic cells from prokaryotic cells?

The presence of a nucleus is the key structural feature that distinguishes eukaryotic cells from prokaryotic cells. In eukaryotic cells, the nucleus is a membrane-bound organelle that houses and protects the cell's genetic material, allowing for more complex regulation of gene expression and cellular processes. This compartmentalization of the genetic material is a defining characteristic of eukaryotes, facilitating processes like transcription and translation to occur in distinct cellular areas.

In contrast, prokaryotic cells do not have a nucleus; their genetic material is located in a region called the nucleoid, which is not enclosed by a membrane. This fundamental difference in cellular organization is one of the primary distinctions between these two major classes of life forms.

While other options, like a complex cytoskeleton or ribosomes, may also differ between eukaryotes and prokaryotes, they do not serve as the definitive feature that clearly separates the two cell types. The cell membrane, present in both, serves similar functions across cell types and is not a distinguishing feature. Therefore, the presence of a nucleus is the most significant characteristic that sets eukaryotic cells apart.