Mitosis and cancer — Edexcel GCSE Combined Science

Revision notes

4 short notes, in the order of the specification. Each one in short:

1. The cell cycle and mitosis

   The cell cycle is the repeating sequence in which cells grow and divide. In interphase the cell grows and copies its DNA. In mitosis the nucleus divides, in four stages: prophase, metaphase, anaphase and telophase. Finally, in cytokinesis, the cytoplasm and cell membrane divide to make two separate cells.

2. What mitosis produces

   Mitosis produces two daughter cells that are genetically identical to the parent cell and to each other. Each daughter cell is diploid, with two sets of chromosomes. Human body cells have 46 chromosomes in 23 pairs. Because the DNA is copied in interphase and shared equally in mitosis, each daughter cell also has 46 chromosomes.

3. Why mitosis is important

   Mitosis is important for growth, repair and asexual reproduction. A multicellular organism grows by making more genetically identical cells by mitosis. Damaged or worn-out cells, for example in cut skin, are replaced by mitosis. In asexual reproduction one parent produces genetically identical offspring by mitosis, with no mixing of genetic information.

4. Cancer

   Cancer is the result of changes in cells that lead to uncontrolled cell division. Normally cell division is controlled, so a tissue makes only the cells it needs. In cancer, cells keep dividing by mitosis when they should not, which can form a mass of cells called a tumour. The key idea is that the division is uncontrolled.