Stem Cells (WJEC GCSE Biology: Combined Science)

• The term stem cell can be defined as follows:

An undifferentiated cell that has the ability to divide an unlimited number of times

• Stem cells can give rise to different cell types through the process of differentiation
  • These different cell types are known as specialised cells; these cells are adapted to carry out specific functions
  • Specialised cells allow the bodies of multicellular organisms to function

Types of stem cell

• The cells in mature tissues generally lose the ability to divide and differentiate, but some groups of stem cells remain:
  • In plants stem cells are found in the tips of growing roots and shoots
    • The tissue in these regions is known as meristem tissue
  • In animals, there are two broad categories of stem cells
    • Embryonic stem cells are found in early embryos; they have the potential to differentiate into any cell type
    • Adult stem cells are only found in certain locations, e.g. bone marrow, and can only differentiate into a few different cell types
      • They are predominantly used to replace old cells and repair damaged tissue

Animal stem cell types table

Stem cell type	Source	Potential of cell	Can give rise to cell types
Embryonic stem cells	The inside layer of an embryo	Retains ability to differentiate	All the different types of specialised cells found in the body
Adult stem cells	Bone marrow	Limited ability to differentiate	Cells of the blood, e.g. red blood cells, white blood cells
	Skin	Limited ability to differentiate	Cells found in the different layers of the skin
	Other organs, e.g. liver and brain	Limited ability to differentiate	Cells found in these organs
	Umbilical cord blood	Limited ability to differentiate	Cells of the blood, muscle and nerve tissue

Stem cells in medicine

• Stem cell technology has the potential to allow the repair of damaged organs in medical treatments
  • New tissue could be grown from stem cells to replace damaged tissues, e.g. in conditions such as:
    • Type 1 diabetes: insulin-producing pancreatic cells could be produced to replace damaged cells in the pancreas
    • Paralysis: healthy nerve cells could be used to repair damaged tissue in the nervous system
• Adult stem cells can be cultured in the lab and encouraged to differentiate into some types of specialised cells
  • This type of treatment has already been used to replace faulty blood cells in sickle cell disease
• Scientists are interested in extracting stem cells from embryos
  • These embryonic stem cells can then be encouraged to differentiate into most types of specialised cell
  • Such stem cell treatments could provide a wide variety of medical treatments
  • Some people have ethical concerns around the use of embryonic stem cells in medicine
• Scientists hope to be able to use treatments involving tissue grown from a patient's own stem cells; this would avoid problems such as:
  • The need for tissue typing
  • A shortage of organ donors
  • Transplant rejection

Evaluating the use of stem cells in medicine

• There are many benefits and risks associated with the use of stem cells in medicine, as well as considerable ethical and social concerns

Evaluating stem cells in medicine table

Benefits of using stem cells	Concerns around stem cell treatments	Social issues	Ethical issues
Potential to treat a wide - variety of diseases Organs developed from a patient's own stem cells reduces the risk of organ rejection and the need to wait for an organ donor Adult stem cells are already used successfully in a variety of treatments	Stem cells cultured in the lab could become infected with a virus which could be transmitted to the patient There is a risk of cultured stem cells accumulating mutations and developing into cancer cells Low numbers of stem cell donors and difficulty in locating a good match between donors and patients	Stem cells can be collected before birth (from amniotic fluid) or after birth (umbilical cord blood) and stored by a clinic but this can be expensive and so isn't an option for everyone A lack of peer-reviewed clinical evidence of the success of stem cell treatment means that there is a level of distrust There is a lack of education available to explain what stem cells can and cannot be used for	Stem cells may be sourced from unused embryos produced in IVF treatment - is it right to use them? Who gives permission? Is it right to create embryos through therapeutic cloning and then destroy them? Who owns them? Should an embryo be treated as a person with human rights or as a commodity?