The nucleus is a region of a eukaryotic cell that contains chromosomes and controls the structure and function of the cell. The simplest organisms, the bacteria, do not have a nucleus and are termed prokaryotes. All the organisms with a clearly defined nucleus in their cells are termed eukaryotes.
The nucleus appears as a rather large spherical, ovoid or sometimes elongated structure in the cell. It is generally central located, although in plant cells with one large vacuole it may be more to the side. The nucleus is colourless, translucent and more dense than the cytoplasm. It is formed by the following components:
An Electron Microscope image of the nucleus