Stem cells

• Humans start when a sperm cell joins with an ovum (egg cell). This is called fertilisation. The fertilised ovum now undergoes mitosis and forms a ball of cells called an embryo. Like this...

  
• Over time, these cells continue to undergo mitosis. They also change and begin to form specialised cells such a nerve cells and muscle cells. When specialised, this is called differentiation. Like this...

  
• Cells in the early embryo have not differentiated. Any cell is capable of differentiating into any type of body cell. Like this...

  
• A stem cell is an undifferentiated cell which can give rise to more cells of the same type and can differentiate to form other types of cells.
• The stem cells in bone marrow differentiate to form cells found in our blood. Like this...

  
• Bone marrow transplants:

  Leukaemia is a cancer of the bone marrow. To treat this, first the patient's existing bone marrow is destroyed using radiation. The patient then receives a transplant of bone marrow from a donor. The stem cells in the bone marrow now divide and form new bone marrow. They also differentiate and form blood cells.
• Problems with a bone marrow transplant:

  The donor has to be compatible with the patient. Otherwise the white blood cells produced by the donated bone marrow could attack the patient's body. Also there is a risk that viruses can be passed from the donor to the patient.
• Plant stem cells:

  Roots and buds contain meristem tissue. These stem cells can differentiate into any type of plant tissue, at any point in the life of the plant. We could use meristem tissue, to clone a rare plant to stop it from going extinct or we could cloned crop plants for farmers.
• In animals, there are two broad categories of stem cells.

  • Embryonic stem cells are found in early embryos - they have the potential to turn into any kind of cell type.
  • This is how an early embryo can develop into a complex multicellular organism .
  • Adult stem cells are only found in certain places (like bone marrow) and can only differentiate into a few different cell types.
  • They are predominantly used to maintain and repair damaged cells such in the blood or skin.
• Animal Stem Cells Table:

  
• Stem cells in medicine:

  • Stem cells could be used to cure many diseases in the future, such as diabetes and paralysis.
  • Scientists and doctors could use stem cell technology to repair damaged organs by growing new tissue from stem cells produced by embryos created using genetic information from the patient.
• Evaluating Stem Cells in Medicine Table:

  
• Stem cells in therapeutic cloning:

  • In therapeutic cloning, an embryo is produced with the same genes as the patient.
  • A 5-day old embryo is the best source of embryonic stem cells.
  • Stem cells from embryos created in this way are not rejected by the patient’s body.
  • So they may be used for medical treatment without the patient having to take drugs to suppress their immune system (which reduce the body’s ability to fight infection).
• The process of therapeutic cloning (part 1):

  
• The process of therapeutic cloning (part 2):