What do prokaryotic cells lack that is found in eukaryotic cells?

Prokaryotic cells are characterized by the absence of a membrane-bound nucleus, which is a defining feature of eukaryotic cells. In prokaryotes, the genetic material is not enclosed within a nucleus but is instead found in a region called the nucleoid. This fundamental difference is one of the main distinctions between prokaryotic and eukaryotic organisms.

While eukaryotic cells contain a well-defined nucleus where the cell's genetic information is stored and organized, prokaryotic cells rely on a more simplistic structure without compartmentalization of genetic material. Consequently, this lack of a nucleus is critical in understanding the differences in cellular organization, complexity, and functioning between these two types of organisms.

The other options—DNA, cell membrane, and ribosomes—are present in both prokaryotic and eukaryotic cells, as they are essential components for all living cells to function properly.