Nucleus is a large, centrally located spherical component of cell. It is enclosed by two nuclear membranes, collectively called nuclear envelope that are connected to the endoplasmic reticulum. Nuclear envelope contains many nuclear pores and encloses the nucleoplasm (liquid ground substance). Nuclear pores help in the transfer of materials between the nucleoplasm and the cytoplasm. Nucleolus (one or more in number) and chromatin material are embedded in the nucleoplasm. Nucleolus is rich in proteins and RNA molecules and acts as the site for ribosome formation; hence, it is referred to as ribosome factory.

The chromatin material is a thin thread-like inter-coiled mass of chromosomes and contains DNA and proteins. It is formed by repeated units of nucleosomes. It is condensed into two or more thick ribbon-like chromosomes during cell division.

Functions of nucleus:

(i) It controls all the metabolic activities of the cell.

(ii) It regulates the cell cycle.

(iii) It is responsible for the transfer of heredity traits from parent to offspring.