Nucleus

The nucleus is the largest organelle in a cell. The nucleus directs all activity in the cell. It also controls the growth and reproduction of the cell. The nucleus could be compared to a manager of a company, they both control activity in there facility. The nucleus is surrounded by a nuclear membrane that protects it from other parts of the cell. It also contains a nucleolus, which is a secondary organelle.
It also contains the blueprints of the cell in the chromatin inside the nucleus. The chromatin is like long strands in the nucleus that carry DNA and proteins.