Nucleus - Nucleus is the control unit of the cell. It controls the cellular activities of the cell.

Structure - It is spherical in shape. It is composed of the following structures:

Nuclear membrane: It is a double membrane separating the contents of the nucleus from the cytoplasm. The narrow space between the two membranes is called the perinuclear space. Nuclear membrane has tiny holes called nuclear pores. These holes allow specific substances to be transferred into a cell and out from it.

Nucleoplasm/Nuclear matrix: It is a homogenous granular fluid present inside the nucleus. It contains the nucleolus and chromatin. Nucleolus is a spherical structure that is not bound by any membrane. It is rich in protein and RNA molecules and is the site for the formation of ribosomes. Chromatin is an entangled mass of thread-like structures. It contains DNA and some basic proteins called histones.