cell division - the cell cycle

• Humans begin life as 1 cell but end up with 50 billion cells!
• Cell division


  New cells are produced by old cells dividing
• Reasons for new cells to be produced

  • Growth and repair of body cells
  • Production of specialised sex cells
• Mitosis


  One type of cell division required for growth and repair
• Meiosis


  Another type of cell division required for production of specialised sex cells
• Humans have 46 chromosomes or 23 pairs (23 chromosomes from the mother and 23 chromosomes from the father)
• Diploid number


  When there are two copies of each chromosome
• The Cell Cycle


  1. Interphase - growth phase, DNA replication, organelle copying

  2. Mitosis - nucleus divides to produce two genetically identical nuclei

  3. Cytokinesis - cytoplasm divides to produce two new cells