Here's why:

* Prokaryotes are single-celled organisms that lack a nucleus and other membrane-bound organelles. Their DNA is located in a region called the nucleoid, but it's not enclosed within a membrane.

* Eukaryotes, on the other hand, have a nucleus that contains their DNA, as well as other membrane-bound organelles.

Bacteria are the prime example of prokaryotes. While archaea are also prokaryotes, bacteria are the most commonly known and studied group.