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


  • Found in adult organisms, cannot differentiate into any other type of cell (e.g. bone marrow stem cells form blood cells)
• Bone marrow transplant


  1. Patient's existing bone marrow destroyed

  2. Patient receives transplant of donor bone marrow

  3. Stem cells divide and form new bone marrow

  4. Stem cells differentiate and form blood cells
• Problems with bone marrow transplants

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


  1. Embryo produced with same genes as patient

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

  3. Stem cells can differentiate to replace malfunctioning cells
• Therapeutic cloning could be useful for medical conditions like diabetes or paralysis
• Some people have ethical or religious objections to therapeutic cloning
• 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
• Uses of plant stem cells

  • Clone rare plants to prevent extinction
  • Produce cloned crop plants resistant to diseases