How does the nucleus differ in prokaryotic cells and eukaryotic cells?
The most important difference is that in prokaryotes the nucleus is naked ie not bound by a nuclear membrane whereas in eukaryotes the nucleus is bound by a double layered nuclear membrane.
There is no nucleus in prokaryotic cells. The term prokary- is from the Greek pro - meaning before, and karyon - meaning kernel or nut, which refers to the nucleus (http://www.etymonline.com/). This refers to the fact that the earliest cells were prokaryotic, existing before eukaryotic cells. The genetic material in a prokaryotic cell is not enclosed by a membrane and consists of a circular molecule of DNA.
Eukaryotic cells have a membrane-enclosed nucleus which contains the genetic material. The term eukary- is from the Greek eu - meaning well or good, and karyon - meaning kernel or nut (http://www.etymonline.com/. This refers to the fact that eukaryotic cells have a well-defined nucleus.