Bacteria cells are called prokaryotes, which means they lack a true nucleus. This is a defining characteristic of bacteria and other single-celled organisms like archaea.

Here's why:

* Prokaryotic means "before the nucleus." These cells do not have a membrane-bound nucleus to house their genetic material (DNA). Instead, their DNA is located in a region called the nucleoid, which is not enclosed by a membrane.

* Eukaryotic cells, like those found in plants, animals, fungi, and protists, do have a true nucleus.

So, while "lacking a nucleus" is a characteristic of bacteria cells, the more precise term to describe them is prokaryotic.