(b) Nucleus of a cell: Nucleus is a membrane bound organelle found in eukaryotic cells. It is the master of the cell that commands all the functioning of the cell. It is generally located in the center of the cell and is spherical in shape. Nucleus contains genetic material present in coiled form called chromatin and at the time of cell division it condenses to form chromosomes which contains DNA or RNA. It is separated from the cytoplasm by nuclear membrane.