- Books Name
- Science Made Easy Science Book
- Science Made Easy
- CBSE Class 9
• It is called the brain of the cell as it controls all the activities of cell.
→ Composition of Nucleus
• The nucleus has a double layered covering called nuclear membrane.
• The nuclear membrane has pores which allow the transfer of material from inside the nucleus to
• The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell
is about to divide.
→ Functions of chromosomes
• Chromosomes contain information for inheritance of features from parents to next generation in
the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and
• DNA molecules contain the information necessary for constructing and organising cells.
• Functional segments of DNA are called genes.
• In non-dividing cell, this DNA is present as part of chromatin material.
• Chromatin material is visible as entangled mass of thread like structures. Whenever the cell is
about to divide, the chromatin material gets organised into chromosomes and perform cell division
→ Functions of Nucleus
• The nucleus plays a central role in cellular reproduction. It is the process by which a single cell
divides and forms two new cells.
• It also plays a crucial part, along with the environment, in determining the way the cell will develop
and what form it will exhibit at maturity, by directing the chemical activities of the cell.
• In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the
absence of a nuclear membrane.
• Such an undefined nuclear region containing only nucleic acids is called a nucleoid.