There are two main categories of cells:
* Eukaryotic cells: These cells have a true nucleus, which contains their genetic material (DNA) enclosed within a membrane. Most organisms you can see with the naked eye, like plants, animals, fungi, and protists, are made up of eukaryotic cells.
* Prokaryotic cells: These cells lack a true nucleus. Their DNA is located in a region called the nucleoid, but it's not enclosed within a membrane. Bacteria and archaea are examples of organisms made up of prokaryotic cells.
So, while eukaryotic cells always have a nucleus, prokaryotic cells do not.
