Mitosis (Edexcel IGCSE Biology (Modular): Unit 2): Revision Note

Mitosis

• Mitosis is defined as nuclear division giving rise to genetically identical cells

• Mitosis is used for:

  • growth

  • repair of damaged tissues

  • replacement of cells

  • asexual reproduction 

• Most body cells have two copies of each chromosome

• We describe these cells as diploid

• When cells divide their chromosomes double beforehand (also known as duplication)

• This ensures that when the cell splits in two, each new cell still has two copies of each chromosome (is still diploid)

The process of mitosis

• Just before mitosis, each chromosome in the nucleus copies itself exactly (forms X-shaped chromosomes)

• Chromosomes then line up along the centre of the cell where cell fibres pull them apart

• The cell divides into two; each new cell has a copy of each of the chromosomes

The process of cell division by mitosis

Importance of Mitosis

• All cells in the body (excluding gametes) are produced by mitosis of the zygote

• Mitosis occurs during:

  • Growth: mitosis produces new cells

  • Repair: to replace damaged or dead cells

  • Asexual reproduction: mitosis produces offspring that are genetically identical to the parent

• Mitosis is important for replacing cells e.g, skin cells, and red blood cells, and for allowing growth (production of new cells e.g. when a zygote divides to form an embryo)