Which organisms are characterized by cells that contain nuclei?

Eukaryotes are distinguished by the presence of a nucleus within their cells. This nucleus serves as a membrane-bound compartment that houses the cell's genetic material, specifically DNA. Organisms classified as eukaryotes include a diverse range of life forms such as animals, plants, fungi, and protists. The complexity of eukaryotic cells allows for the development of specialized structures and functions, contributing to the overall complexity of the organisms themselves.

In contrast, prokaryotes, which comprise bacteria and archaea, do not have a nucleus. Their genetic material is typically located in a region called the nucleoid, which is not membrane-bound. The absence of a nucleus is a fundamental characteristic that separates prokaryotes from eukaryotes.

Monera, an outdated classification, refers to a group that includes prokaryotic organisms, especially bacteria. Viruses, while they contain genetic material, are not considered living organisms and do not possess cellular structures, including nuclei.