A level-readyAll subjects · Biology · WBI12 (Unit 2)
Stem cells and their use in medicine
Stem cells can become many types of cell. That makes them promising for treating disease, but using them raises questions society has to decide.
Key definitions
- Stem cell: an undifferentiated cell that can divide repeatedly and can differentiate into specialised cells.
- Totipotent: can give rise to every cell type, including the cells of the placenta. The zygote and the cells of the very early embryo are totipotent.
- Pluripotent: can give rise to all the cell types of the body, but not the placenta.
- Morula: a solid ball of cells formed by the first divisions of the zygote (about 16 cells).
- Blastocyst: a hollow ball of cells formed a few days after fertilisation. Its outer layer forms the placenta; its inner cell mass is made of pluripotent cells that form the embryo.
Uses in medicine
Stem cells could replace damaged or lost cells: for example bone marrow transplants for leukaemia (already used), and research into treatments for type 1 diabetes, Parkinson's disease, spinal cord injuries and damaged heart muscle. They are also used to test new drugs and to study development.
Sources include embryos (pluripotent cells from the inner cell mass), adult tissues such as bone marrow (fewer cell types), and induced pluripotent stem (iPS) cells, adult cells reprogrammed to become pluripotent.
How society decides
- Embryonic stem cells: obtaining them destroys the embryo, which some people object to on religious or moral grounds.
- Governments set laws, and regulatory bodies license and monitor research (in the UK, the Human Fertilisation and Embryology Authority).
- Scientists share findings through peer-reviewed journals and conferences, and must get informed consent from donors.
- Risks include rejection by the immune system and cells dividing uncontrollably to form tumours.
Worked example
Explain why cells from the inner cell mass are described as pluripotent and not totipotent.
- They can form any cell type of the body.
- They cannot form the placenta, which comes from the outer layer.
Answer: They can form all body tissues but not placental cells.
Check yourself
- Which cells are totipotent?
- Cells of the inner cell mass only
- Adult bone marrow cells
- The zygote and the cells of the very early embryo
- Red blood cells
Show answer
The zygote and the cells of the very early embryo. Only the earliest cells can make placenta as well as body cells.
- What can a pluripotent stem cell NOT become?
- Placental cells
- Nerve cells
- Muscle cells
- Blood cells
Show answer
Placental cells. Pluripotent cells form all body cells but not the placenta.
- What is a morula?
- A hollow sphere of cells containing an inner cell mass
- An adult stem cell
- A solid cluster of about 16 cells formed by early divisions of the zygote
- A type of gamete
Show answer
A solid cluster of about 16 cells formed by early divisions of the zygote. The morula comes before the hollow blastocyst.
- In a blastocyst, which cells are pluripotent?
- The outer layer that forms the placenta
- The inner cell mass
- The zona pellucida
- The cortical granules
Show answer
The inner cell mass. The inner cell mass forms the embryo.
- What is the main ethical objection to using embryonic stem cells?
- They cannot divide
- They are taken from adult patients
- They only form one type of cell
- The embryo is destroyed when the cells are removed
Show answer
The embryo is destroyed when the cells are removed. Some believe the embryo has a right to life.
- What are induced pluripotent stem cells?
- Cells taken from the placenta
- Adult cells reprogrammed to become pluripotent
- Bacteria that make stem cells
- Totipotent cells from a zygote
Show answer
Adult cells reprogrammed to become pluripotent. iPS cells avoid destroying embryos.
- Which is a risk of stem cell therapy?
- They cannot divide at all
- They always cure disease
- They lower blood pressure
- Transplanted cells may divide uncontrollably and form tumours
Show answer
Transplanted cells may divide uncontrollably and form tumours. Uncontrolled division could form a tumour; rejection is also a risk.
Sources
Last updated 7 November 2026. Spotted a mistake? Tell us.