Prokaryotes lack a true nucleus and other membrane-bound organelles. This is what distinguishes them from eukaryotes.

Here's a breakdown:

* Nucleus: Prokaryotes have a single, circular chromosome located in a region called the nucleoid, but it's not enclosed within a membrane like the nucleus of eukaryotic cells.

* Organelles: Prokaryotes lack the complex internal membrane systems and organelles found in eukaryotic cells, such as mitochondria, Golgi apparatus, endoplasmic reticulum, etc.

Therefore, prokaryotes are simpler in structure than eukaryotes.