Here's why:
* Eukaryotic cells are defined by the presence of a nucleus. This is a membrane-bound organelle that contains the cell's genetic material (DNA) in the form of chromosomes.
* Prokaryotic cells, on the other hand, lack a nucleus. Their DNA is located in a region called the nucleoid, which is not enclosed by a membrane.
While other structures like ribosomes, mitochondria, and the cell membrane are found in most eukaryotic cells, they are not universally present in *all* eukaryotic cells.
