cell division - paper 1

• Cell division


  1. Body cells divide to form 2 identical daughter cells by going through a series of stages-the cell cycle
• Mitosis


  • Important for growth and repair of cells (e.g. replacement of skin cells)
  • Also used for asexual reproduction
• Stage 1


  1. Cell grows bigger

  2. DNA replicates (chromosomes duplicate)

  3. Increase in number of sub-cellular structures, such as ribosomes and mitochondria
• Stage 2


  1. Complete sets of chromosomes is pulled to each end of cell

  2. Nucleus divides to form 2 nuclei
• Stage 3


  Cytoplasm and cell membrane divide to form 2 identical daughter cells
• Stem cell


  Undifferentiated cell that can develop into 1 or more specialised cells
• Types of stem cells

  • Adult stem cells
  • Embryonic stem cells
• Adult stem cells


  • Found in specific parts of the body in adults and children (e.g. bone marrow)
  • Can only differentiate to form certain types of cell (e.g. stem cells in bone marrow can only differentiate into types of blood cell)
• Advantages of adult stem cells

  • Fewer ethical issues - adults can consent to have their stem cells removed and used
• Disadvantages of adult stem cells

  • Requires a donor - possible long wait time to find someone suitable
• Embryonic stem cells


  • Found in early human embryos (often taken from spare embryos from fertility clinics)
  • Can differentiate into any type of specialised cell in the body (e.g. nerve cell, muscle cell)
• Advantages of embryonic stem cells

  • Can treat a wide range of diseases as it can form any specialised cell
• Disadvantages of embryonic stem cells

  • Ethical issues - the embryo is destroyed (potential human life)
• Plant meristem

  Meristem regions in roots/shoots of plants can differentiate into all cell types
• Advantages of plant meristems

  • rare plants can be prevented from going extinct
• Disadvantages of plant meristems

  • Genetically identical plants - whole crops can become infected with disease at once because they are genetically identical
• Stem cells can be cloned to produce large numbers of identical cells
• therapeutic cloning

  • cells from a patient’s body are used to create a cloned early embryo of themselves
  • stem cells from this embryo can be used for medical treatments
  • these stem cells have the same genes as the patient so they are less likely to be rejected when transplanted