stem cells

• Stem cells are undifferentiated cells in an organism that produce many more cells of the same type and specialised cells by differentiation
• Stem cells in animals:

  
  

  A zygote is a single cell formed when an egg and sperm join together this divides into form a ball of cells called an embryo the embryo contains embryonic stem cells which differentiate to form many different specialised cell types.

  
  

  Adult animals retain some stem cells the bone marrow also contains adult stem cells these form many cell types including blood cells
• Stem cells in plants are found in meristems, which are found in the tips of shoots and roots it differentiates throughout the life of the plant

  • in roots to form root hair cells
  • in shoots to form mesophyll cells
• Stem cells may be able to help treat conditions such as diabetes and paralysis . Injected stem cells may be able to replace damaged or missing cells in the pancreas or nervous system .
• Advantages of embryonic stem cells

  • easy to extract from embryo
  • produce any type of cell
• Disadvantage of embryonic stem cells

  • embryo destroyed when cells removed - some people think embryos have a right to life
• Advantage of all stem cells:

  • replace faulty cell with a healthy cell so person is well again
• Risk of all stem cells:

  • stem cells may not stop dividing and so may cause cancer
  • risk of viral infections
• Advantage of adult stem cells:

  • no embryo destroyed so not a ethical issue
  • if taken from the person to be treated will not cause rejection by the body
• Disadvantage of adult stem cells:

  • produces less variety of cells