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Key concept
Stem cells are unspecialised cells that can divide by mitosis and differentiate into specialised cell types. They are found in embryos and in some adult tissues like bone marrow.
Stem cells connect the cells topic to real-world medicine and ethical debates. For the Supplement tier, you need to understand what stem cells are, where they are found, how they can be used in medicine, and the ethical arguments for and against their use.
What Are Stem Cells?
A stem cell is an undifferentiated cell capable of:
Self-renewal: dividing by mitosis to produce more stem cells.
Differentiation: developing into specialised cells with specific structures and functions.
Differentiation is the process by which a cell becomes specialised for a particular function. During differentiation, specific genes are switched on and others are switched off, leading to the development of particular structures (e.g. Haemoglobin production in red blood cells).
Types of Stem Cells
Embryonic stem cells: found in early embryos (blastocysts). They are pluripotent: they can differentiate into almost any cell type in the body.
Adult stem cells: found in specific tissues such as bone marrow and skin. They are multipotent: they can only differentiate into a limited range of cell types (e.g. Bone marrow stem cells can become different blood cell types).
Plants retain stem cells in meristems (root tips and shoot tips) throughout their lives. This is why plants can continue growing and regenerating throughout their lifespan, unlike most animals.
Medical Uses and Ethical Issues
Medical uses of stem cells:
Treating leukaemia and other blood disorders using bone marrow transplants.
Potential to grow replacement tissues for damaged organs (e.g. Nerve cells for spinal cord injuries, insulin-producing cells for type 1 diabetes).
Testing new drugs on stem-cell-derived tissues instead of animals.
Arguments for stem cell research:
Could cure currently incurable diseases and reduce suffering.
Adult stem cell research uses the patient's own cells, avoiding ethical concerns.
Arguments against embryonic stem cell research:
Embryos are destroyed in the process: some consider this taking a human life.
Risk of stem cells forming tumours if differentiation is not controlled.
Alternative sources (adult stem cells, induced pluripotent stem cells) may reduce the need for embryonic sources.
Try a focused question (3 marks)
Explain why embryonic stem cells are more useful than adult stem cells for medical research. (3 marks)
Show the answer and marking guidance
Embryonic stem cells are pluripotent: they can differentiate into almost any cell type.
Adult stem cells are multipotent: they can only differentiate into a limited range of cell types.
This means embryonic stem cells have a wider range of potential medical applications / can be used to treat more conditions.
Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.
Common mix-ups to avoid
Check these points against your own answer before moving on.
Saying stem cells can become "any cell": embryonic stem cells are pluripotent (almost any), not totipotent (absolutely any).