The big idea: Adult stem cells live in special places called niches; the niche keeps them as stem cells or tells them to divide and differentiate.
The points to remember
- A stem cell niche is the place in a tissue where stem cells live, with the supporting cells around them.
- Signals from the niche can maintain the stem cells: keep them unspecialized, dividing slowly.
- Or the niche can promote proliferation (more divisions) and differentiation, when new cells are needed.
- Bone marrow: stem cells that make red blood cells, white blood cells and platelets.
- Hair follicles: stem cells in the bulge make new hair cells, and skin cells after a wound.
- Adult stem cells are multipotent: they repair and maintain their own tissue.
Remember it as: The niche is home: it keeps stem cells waiting, then sends them to work.
Real example: a bone marrow transplant: In a bone marrow transplant for leukaemia, stem cells from a donor are put into the patient's blood. They settle in niches in the patient's bone marrow and go on making every kind of blood cell.
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How it is asked: Expect a short Paper 2 Discuss or Outline on where adult stem cells are and what they do, or a Paper 1A item asking for a stem cell's type and its location.
IB-style questionDiscuss[3 marks]
Discuss the location and function of stem cells in adult humans.
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See the answer broken into clear points, with guidance on how each point earns marks.