Stem Cells

• Embryonic stem cells

  • Fertilised egg undergoes mitosis and forms a ball of cells called an embryo
  • They continue to undergo mitosis to form specialised cells (e.g. nerve cells, muscle cells) - differentiation
  • Over time, the cells form the adult organism
  • Cells in the early embryo have not differentiated - can differentiate into any type of body cell
• Stem cell


  An undifferentiated cell which can produce more cells of the same type and can differentiate to form other types of cells.
• Adult stem cells

  • Stem cells in bone marrow differentiate to form cells found in our blood (RBC, WBC, platelets)
  • Cannot differentiate into any type of cell
• Bone marrow transplants

  • Leukaemia - a cancer of the bone marrow
  • Treated by destroying patient's existing bone marrow using radiation
  • Patient then receives a transplant of bone marrow from a donor
  • Stem cells in the bone marrow can now divide and form new bone marrow - can also differentiate and form blood cells
  • Problems - donor has to be compatible with patient, viruses can be passed from donor to patient
• Therapeutic cloning

  • An embryo is produced with same genes as the patient
  • Stem cells can be transplanted into patient without being rejected
  • Once inside, stem cells can differentiate to replace cells that have stopped working correctly
  • Could be useful for diabetes or paralysis
  • There are ethical or religious objections
• Plant stem cells

  • Roots and buds contain meristem tissue that can differentiate into any type of plant tissue - at any point in the plant's life
  • Used to clone a rare plant to stop it going extinct or produce cloned crop plants for farmers