Here's why:

* Eukaryotic cells are complex cells that have a membrane-bound nucleus containing their genetic material (DNA). This nucleus is responsible for controlling cellular activities and ensuring proper inheritance of genetic information.

* Prokaryotic cells, on the other hand, lack a true nucleus. Their DNA is located in a region called the nucleoid, which is not enclosed by a membrane.

Therefore, organisms like animals, plants, fungi, and protists (all eukaryotes) utilize a nucleus, while bacteria and archaea (prokaryotes) do not.