Stem Cells
This lesson covers stem cells — what they are, where they are found, how they can be used, and the ethical issues surrounding their use. This is essential content for Edexcel GCSE Biology (1BI0) Topic 2: Cells and Control. Stem cell biology is a rapidly developing field with enormous potential for treating diseases.
What Are Stem Cells?
A stem cell is an unspecialised cell that can:
- Divide by mitosis to produce more stem cells (self-renewal).
- Differentiate into specialised cell types.
This combination of properties makes stem cells uniquely valuable. Most body cells are already specialised and cannot change into different types, but stem cells retain this ability.
Types of Stem Cell
There are several types of stem cell, each with different properties:
Embryonic Stem Cells
- Found in early-stage embryos (blastocysts, about 5 days after fertilisation).
- They are pluripotent — they can differentiate into almost any cell type in the body.
- This makes them extremely useful for medical research and potential treatments.
- Embryonic stem cells are obtained from unused embryos from IVF treatment (with consent).
Adult Stem Cells
- Found in certain tissues in the adult body, particularly bone marrow and blood.
- They are multipotent — they can differentiate into a limited range of cell types.
- For example, bone marrow stem cells can produce different types of blood cell (red blood cells, white blood cells, platelets) but cannot produce nerve cells or muscle cells.
- Adult stem cells are harder to extract and grow in the laboratory than embryonic stem cells.
Meristem Cells in Plants
- Found in the meristems (growing tips of roots and shoots) of plants.
- Can differentiate into any type of plant cell throughout the life of the plant.
- Plants retain meristem cells for their entire lives, which is why plants can continue growing indefinitely.
- Meristem cells can be used to produce clones of plants quickly and cheaply (e.g., for agriculture or conservation).
| Type | Location | Potency | Key Feature |
|---|
| Embryonic stem cells | Early embryos (blastocysts) | Pluripotent (almost any cell type) | Most versatile; from IVF embryos |
| Adult stem cells | Bone marrow, blood, other tissues | Multipotent (limited cell types) | Fewer ethical concerns; limited range |
| Meristem cells | Root and shoot tips of plants | Can form any plant cell type | Plants can grow throughout their lives |
Exam Tip: Make sure you know the difference between pluripotent (can become almost any cell type — embryonic stem cells) and multipotent (can become a limited range of cell types — adult stem cells). This distinction is commonly tested.
Uses of Stem Cells in Medicine
Stem cells have enormous potential in medicine:
Current Uses
-
Treating leukaemia (blood cancer):
- A bone marrow transplant replaces the patient's damaged bone marrow with healthy bone marrow from a donor.
- The donor bone marrow contains adult stem cells that can produce healthy blood cells.
- This is a well-established treatment that has saved many lives.
-
Treating other blood disorders:
- Sickle cell disease and some immune deficiency conditions can be treated with bone marrow transplants.
Potential Future Uses
- Treating paralysis — stem cells could potentially be used to grow new nerve cells to repair spinal cord injuries.
- Treating type 1 diabetes — stem cells could be used to grow new insulin-producing beta cells in the pancreas.
- Treating heart disease — stem cells could replace damaged heart muscle cells after a heart attack.
- Growing replacement organs — in the future, it may be possible to grow whole organs from stem cells for transplant, eliminating the problem of donor shortages.
Exam Tip: When discussing potential uses of stem cells, use cautious language: "could potentially", "may in the future", "research is ongoing". These are potential treatments, not established cures.
Ethical Issues
The use of stem cells raises significant ethical concerns:
Arguments For Stem Cell Research
- Embryonic stem cells have the potential to treat or cure currently incurable diseases (e.g., Alzheimer's, Parkinson's, paralysis).
- The embryos used are from surplus IVF embryos that would otherwise be destroyed — using them for research gives them a purpose.
- Adult stem cells can be used without destroying embryos, reducing ethical concerns.
- Stem cell research could save or improve millions of lives.
Arguments Against Stem Cell Research
- Obtaining embryonic stem cells involves destroying a human embryo, which some people believe is morally wrong because they consider an embryo to be a human life from conception.
- Some religions teach that life begins at conception, making embryo destruction equivalent to taking a human life.
- There is a risk of tumour formation — transplanted stem cells could divide uncontrollably and form cancers.
- There is a risk of rejection — the patient's immune system may attack the transplanted cells unless immunosuppressive drugs are used.
- Some people worry about a "slippery slope" — that embryo research could lead to other ethically questionable practices.
| Argument | For | Against |
|---|
| Medical benefit | Could cure incurable diseases | Alternatives should be explored first |
| Embryo status | Surplus IVF embryos would be destroyed anyway | An embryo is a potential human life |
| Risk | Potential to save millions of lives | Risk of tumour formation and rejection |
| Religious view | Reducing suffering is a moral good | Many religions oppose embryo destruction |
Therapeutic Cloning vs Reproductive Cloning
It is important to distinguish between two types of cloning:
Therapeutic Cloning
- The goal is to produce embryonic stem cells that are genetically identical to the patient.
- An embryo is created using the patient's own DNA (by transferring the nucleus of a body cell into an empty egg cell).
- The embryo is grown to the blastocyst stage, and stem cells are extracted.
- Because the stem cells have the same DNA as the patient, they are less likely to be rejected by the immune system.
- The embryo is not implanted into a uterus — it is not intended to develop into a baby.
Reproductive Cloning
- The goal is to produce a genetically identical copy of an organism (a clone).
- The same nuclear transfer technique is used, but the embryo is implanted into a surrogate mother's uterus to develop into a full organism.
- Example: Dolly the sheep (1996) was the first mammal cloned from an adult cell.
- Reproductive cloning of humans is illegal in the UK and many other countries.
| Feature | Therapeutic Cloning | Reproductive Cloning |
|---|
| Purpose | To produce stem cells for treatment | To produce a genetically identical organism |
| Embryo fate | Destroyed at blastocyst stage | Implanted and developed to full organism |
| Legal status (UK) | Permitted under strict regulation | Illegal for humans |
| Ethical concerns | Embryo destruction | Creating "copies" of people; animal welfare |