Nucleus (The Hereditary Organelle):

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A dense, generally round (spherical) but sometimes cylindrical nucleus is present at the centre of a cell. It stains deeply, is mostly spherical, WBC has lobed nuclei. The nucleus contains; nuclear membrane, nucleoplasm or nuclear sap, chromatin material and nucleolus.

Image showing the nucleus.

Image Showing the Nucleus.

Image showing the nucleus.

Functions: Nucleus controls all the cellular activities of the cell. All cytoplasmic activities occur by instructions from the nucleus. Nucleus contains chromosomes which are responsible for reproduction as well as transmission of genetic information from one generation to the next. The nucleus controls cell metabolism and other activities of the cell, hence, it is also called Master or Director of the cell.

Nuclear membrane:

A double-layered membrane that encloses the nucleus has pores called nuclear pores that allow exchange of materials between nucleus and cytoplasm. Membrane is made up of lipids and proteins (like plasma membrane) and has ribosomes attached on the outer membrane which make the outer membrane rough. The pores allow the transport of large molecules in and out of nucleus, and the membranes keep the hereditary material in contact with the rest of the cell.

Function: Encloses the contents of the nucleus.


It is a jelly-like substance present within the nucleus; the chromatin material and nucleolus are suspended in it. It is transparent, semi-fluid and contains a large number of enzymes which are required for the synthesis and functioning of DNA, RNA, etc.

Function: Chromatin material and nucleolus are suspended in it.

Chromatin material:

It is in the form of network of thread like structures called chromosomes. Chromosomes are visible during cell division only when they condense and appear as rod-like structures. Chromosomes are mainly made up of DNA (deoxyribonucleic acid) and contain genes. They are the hereditary material of the cell. On staining the chromosomes, two regions can be identified in the chromatin material; Heterochromatin has less DNA and genetically less active than euchromatin which has more DNA and genetically more active

Function: Chromatin material contains hereditary information in the form of chromosome. Hence it is responsible for the transmission of genetic information.


It is more or less a dense spherical or oval structure present within the nucleus. Most prominent in a non-living cell and contains DNA, RNA and proteins. Store house for RNA and proteins; it disappears during cell division and reappears in daughter cells.

Function: Nucleolus is a site within the nucleus where ribosomes are formed.