w1z4rd
Valued Senior Member
Correct, it is a collection of cells that have adapted to live together, much like aphids and ants. In fact, our cell nucleus was originally a bacterium.
At the risk of looking like im nit picking, I believe it was that Mitochondrion that evolved from bacterium as explain here:
http://en.wikipedia.org/wiki/Endosymbiotic_theory
However if you can offer me more information on the cell nucleus I would be happy to read more about it.