Mitosis (Edexcel GCSE Combined Science): Revision Note

Mitosis

• Mitosis is a nuclear division that gives rise to two genetically identical diploid daughter cells

  • In a human, this diploid number is 23 pairs of chromosomes

• All body cells (and not gametes) are produced by mitosis of the zygote

• Mitosis is required for:

  • Growth: mitosis produces new cells

  • Repair: to replace damaged or dead cells

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

The Cell Cycle

• There are 3 parts of the cell cycle

  • Interphase - Just before mitosis, the DNA in the nucleus copies itself exactly (forms x-shaped chromosomes)

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

  • Cytokinesis - The cell cytoplasm and membrane divides to produce two daughter cells; each new cell has a copy of each of the chromosomes

The three stages of the cell cycle

The Stages of Mitosis

• The process of mitosis is itself made up of a series of stages that begin after interphase has occurred. These stages occur in the following order:

  • Prophase - DNA condenses, chromosomes become visible and the nuclear membrane breaks down

  • Metaphase - Chromosomes line up on the equator of the cell (the metaphase plate)

  • Anaphase - Spindle fibres (also known as cell fibres) split the chromosomes down the centre and pull one chromatid to either side of the cell

  • Telophase - New membranes form around the chromosomes at either end of the cell

The stages of mitosis