What do prokaryotes lack that distinguishes them from eukaryotes?

Prokaryotes are characterized by the absence of a nucleus, which is a fundamental distinction between them and eukaryotes. In prokaryotic cells, the genetic material is typically organized in a single circular chromosome located in a region called the nucleoid, rather than being enclosed within a membrane-bound nucleus. This structural difference is significant as it reflects the simpler organization of prokaryotic cells compared to the more complex organization of eukaryotic cells, which have multiple linear chromosomes housed within a defined nucleus.

The other components mentioned, such as mitochondria and chloroplasts, are organelles typically found in eukaryotic cells and not in prokaryotes, but they are not the defining feature that distinguishes prokaryotes from eukaryotes. Additionally, ribosomes, which are essential for protein synthesis, are present in both prokaryotic and eukaryotic cells, so they do not serve as a distinguishing factor. Thus, the lack of a nucleus is the key trait that sets prokaryotes apart from eukaryotes.