Here's why:

* Prokaryotes are a domain of life that includes bacteria and archaea. They are simple, single-celled organisms that lack a nucleus and other membrane-bound organelles.

* Eukaryotes, on the other hand, are organisms whose cells have a nucleus and other membrane-bound organelles. This includes plants, animals, fungi, and protists.

So, the key difference between prokaryotes and eukaryotes is the presence or absence of a nucleus.