stem cells

• Stem cell


  An undifferentiated cell which can give rise to more cells of the same type and can differentiate into other types of cells
• Fertilization


  1. Sperm cell joins with ovum

  2. Fertilized ovum undergoes mitosis

  3. Forms a ball of cells called an embryo

  4. Cells continue to undergo mitosis and begin to form specialized cells

  5. Process of differentiation
• Embryonic stem cells


  • Cells in early stage embryo that have not differentiated and are capable of differentiating into any type of body cell
• Adult stem cells


  • Stem cells found in adult organisms that cannot differentiate into any other type of cell, e.g. bone marrow stem cells
• Bone marrow transplant


  1. Patient's existing bone marrow is destroyed

  2. Patient receives transplant of bone marrow from donor

  3. Stem cells in bone marrow divide and form new bone marrow and blood cells
• Problems with bone marrow transplants

  • Donors must be compatible with patient
  • Risk of viruses being passed from donor to patient
• Therapeutic cloning


  1. Embryo is produced with same genes as patient

  2. Stem cells from embryo can be transplanted into patient without being rejected

  3. Stem cells can then differentiate to replace cells that have stopped working correctly
• Therapeutic cloning could be useful for a range of medical conditions such as diabetes or paralysis
• Some people have ethical or religious objections to therapeutic cloning procedure
• Plant stem cells


  • Found in meristem tissue at root tips and buds
  • Can differentiate into any type of plant tissue at any point in plant's life
• Using plant stem cells

  1. Clone rare plants to stop them going extinct

  2. Produce cloned crop plants that are resistant to diseases