This topic accounts for approximately 18% of your exam marks.
stable
Very High
Stable18%
Cell structure and organelle function appear on nearly every paper; one of the highest-frequency topics.
What a stem cell is
A stem cell is an undifferentiated that can divide by mitosis to produce more stem cells, and that can also differentiate into specialised cells
Two key abilities make stem cells special:
Self-renewal: they can keep dividing indefinitely to produce more stem cells
Differentiation: when given the right chemical signals, they can develop into specialised cell types
Two types: embryonic and adult
Embryonic stem cells
Adult stem cells
Source
Very early embryos (a few days old)
Certain tissues in the adult body (bone marrow, gut lining, skin)
What they can become
Any cell type in the body. They are pluripotent
A limited range of cell types, usually closely related to the tissue they came from. Bone marrow stem cells, for example, can only become blood cells
Availability
Limited (need an embryo)
More accessible (can be taken from a living donor or the patient themselves)
Uses of stem cells in medicine
Stem cells offer the possibility of replacing damaged cells in diseases where the body's own cells have stopped working properly. This is called therapy. Real and proposed applications include:
Bone marrow transplants for treating leukaemia (a cancer of the blood). Healthy bone marrow stem cells from a donor are transplanted into the patient and produce new, healthy blood cells.
Using stem cells to grow new skin for severe burns victims
Treating Parkinson's disease by replacing damaged nerve cells in the brain
Repairing spinal cord injuries by growing new nerve tissue
Replacing damaged retinal cells in some forms of blindness
Growing new heart muscle after a heart attack
Advantages of stem cell therapy
Can treat conditions that have no other cure (paralysis, certain blindness, some cancers)
Can replace cells exactly, restoring full function instead of just managing symptoms
If the patient's own stem cells are used, there is no risk of rejection because the new cells carry the same antigens as the patient
Disadvantages and risks
Ethical concerns about embryonic stem cells, since their use involves destroying a human embryo
Risk of rejection if donor stem cells are used. The recipient is put on immunosuppressant drugs that stop their immune system from attacking the transplanted cells, but this leaves them more open to infections
Risk of cancer: stem cells divide rapidly, and if they continue to divide uncontrollably after transplantation they can form a tumour
Risk of viral infection carried over from the donor cells
The technology is still expensive and experimental for most conditions
Ethical issues
Major: many people view the destruction of an embryo as the destruction of a potential human life