Although only 2 nm wide, the total length of DNA in the 46 chromosomes of an adult human cell is about 1.8 metres.

This has to be packed into a nucleus which is only 6 μm in diameter. This is the equivalent of trying to get an 18 km length of string into a ball which is only 6 cm in diameter! In order to prevent the DNA getting tangled up into knots, a precise scaffolding made of protein molecules is used. The DNA is wound around the outside of these protein molecules. The combination of DNA and proteins is called chromatin.

What is the name of this protein to coil the DNA?

The cell cycle is the regular sequence of events that takes place between one cell division and the next. It has three phases, namely _________ , ___________ and _________.

Which statement is correct about kinetochores?

What are the names of the structures appear blue and pink in the diagram?

Which of the followings are biological significance of mitosis?

1. Growth

2. Immune response

3. Asexual reproduction

4. Replacement of cells and repair of tissues

Growth of a multicellular organism is a result of parent cells dividing to produce genetically identical daughter cells.

What does 'genetically identical' mean?

The diagram shows three cells (labelled A, B and C) from a root tip which have been stained to show chromosomes. Which option gives the correct order of mitotic cell cycle?

Each chromosome consists of two identical chromatids. Each chromatid contains a single DNA molecule, formed when DNA replicates during ___________ .

Cancers are thought to start when changes occur in the genes that control cell division. The particular term for the changed gene that causes cancer is an oncogene. A change in any gene is called a _________ .