A single cell can, in principle, become an entire organism. Cloning and stem-cell research sit at the boundary between biology and ethics, and GCSE examiners test both. This guide covers the science behind somatic cell nuclear transfer and the difference between embryonic and adult stem cells, then addresses the debates you are expected to evaluate.
What is a stem cell and why does it matter?
A stem cell is an undifferentiated cell — one that has not yet taken on a specialised function. It has two defining properties:
- Self-renewal — it can divide repeatedly to produce more stem cells.
- Differentiation — under the right conditions it can develop into a specialised cell type (muscle, nerve, blood, etc.).
These two properties make stem cells the body's repair and growth system. During early embryonic development, virtually every cell is a stem cell; as development proceeds, cells receive chemical signals that switch genes on or off and cause them to specialise — a process called differentiation.
Once a cell has differentiated, it typically loses the ability to become other cell types. This is why a liver cell cannot become a nerve cell. Stem cells retain that potential.
What is the difference between embryonic and adult stem cells?
| Property | Embryonic stem cells | Adult stem cells |
|---|---|---|
| Source | Inner cell mass of a blastocyst (early embryo, day 5–7) | Specific tissues in the body (e.g. bone marrow, skin, gut lining) |
| Potency | Pluripotent — can become almost any cell type in the body | Multipotent — can become only a limited range of related cell types |
| Availability | Obtained by destroying an embryo | Can be harvested without destroying tissue (e.g. bone marrow aspiration) |
| Risk of rejection | High — genetically different from the patient | Lower — can be harvested from the patient themselves |
| Ethical controversy | High — destruction of a human embryo | Lower |
Pluripotent means "able to form many types" — embryonic stem cells can form any cell type except the placenta (that would require totipotent cells, which are the very first two or four cells of an embryo). Multipotent means limited to a family of related cell types: haematopoietic stem cells in bone marrow can become any blood cell, but cannot become a nerve cell.
What is cloning and how does it work?
Cloning produces a genetic copy of an organism (or a cell). In biology, two types are relevant at GCSE:
Reproductive cloning produces a new organism genetically identical to an existing one. The method used is somatic cell nuclear transfer (SCNT):
- Take a body cell (somatic cell) from the organism to be cloned — this contains a full, diploid nucleus with a complete set of DNA.
- Take an egg cell (oocyte) from a donor and remove its nucleus (enucleation), leaving an empty cytoplasm.
- Insert the somatic nucleus into the enucleated egg.
- Apply an electric shock or chemical signal to stimulate the egg to divide.
- The embryo that develops is a genetic copy of the organism that donated the somatic cell.
- Implant the embryo into a surrogate mother, who carries it to term.
The first mammal cloned this way was Dolly the sheep, produced in 1996 at the Roslin Institute in Edinburgh. Dolly was cloned from a mammary gland cell of a six-year-old Finn Dorset sheep. The experiment proved that the nucleus of a specialised adult cell still contains all the genetic information needed to direct the development of a complete organism.
Therapeutic cloning uses the same SCNT technique but the embryo is not implanted into a uterus. Instead, stem cells are harvested from the blastocyst at around day five. Because the somatic cell came from the patient, these stem cells are genetically matched to that patient — the immune system is far less likely to reject tissues grown from them.
What are the uses of stem cells?
Stem cells are already used in medicine and have significant potential for future treatments:
Current uses:
- Bone marrow transplants — the most established stem cell therapy. Haematopoietic stem cells from a donor's bone marrow replace a leukaemia patient's destroyed blood cell-producing tissue. This has been used since the 1960s.
- Skin grafts — stem cells from a patient's own skin are grown in the laboratory to produce sheets of skin for grafting onto burn wounds.
Potential future uses:
- Growing replacement pancreatic beta cells for Type 1 diabetes patients
- Replacing dopamine-producing neurons lost in Parkinson's disease
- Repairing spinal cord injuries
- Growing replacement heart muscle after a heart attack
The key advantage of therapeutically cloned stem cells over adult stem cells is that they are pluripotent — they can form a wider range of tissues — and are genetically matched to the patient, reducing rejection.
What ethical arguments surround embryonic stem cell research?
GCSE examiners frequently award marks for presenting balanced arguments — listing one side only will not score full marks on a 4- or 6-mark question.
Arguments in favour:
- The embryos used (typically spare IVF embryos) would otherwise be destroyed.
- The potential to cure currently untreatable diseases justifies the research.
- An early-stage blastocyst has no nervous system and cannot feel pain.
- Scientific progress requires the freedom to investigate new areas.
Arguments against:
- Human life begins at fertilisation; destroying an embryo destroys a human life.
- Many religious traditions hold that embryos deserve full moral protection.
- Adult stem cells and induced pluripotent stem cells (iPSCs) may achieve the same results without destroying embryos.
- Therapeutic cloning could lead incrementally towards reproductive cloning of humans.
Induced pluripotent stem cells (iPSCs) — adult cells reprogrammed back to a stem-cell-like state — represent a more recent development mentioned in some specifications. They avoid the embryo controversy but currently have higher cancer risk and are less predictably pluripotent.
How do you structure a GCSE ethics answer on stem cells?
For a typical 4-mark "evaluate" question:
- Give one or two scientific points in favour with a brief explanation.
- Give one or two scientific/ethical points against with a brief explanation.
- Offer a conclusion that weighs the evidence (you may sit on the fence, but be explicit about why).
Examiners reward specific points (e.g. "embryos used in research are spare IVF embryos that would otherwise be discarded") over vague ones (e.g. "some people think it is wrong"). Use subject vocabulary: pluripotent, differentiate, SCNT, blastocyst, rejection.
What is natural cloning and how does it relate to this topic?
Plants clone naturally via runners (strawberries), bulbs (daffodils), and cuttings. Identical twins are natural human clones — one fertilised egg splits into two genetically identical embryos. Neither raises ethical concerns, which illustrates that the controversy is specifically about deliberate reproductive cloning of humans, not genetic identity itself.
Frequently asked questions
Why was Dolly the sheep significant?
Before Dolly, scientists believed that once a cell had differentiated into a specialised type — such as a mammary gland cell — the genes needed for other functions were permanently switched off and could not be reactivated. Dolly proved this wrong. A differentiated nucleus, when placed in an enucleated egg, could be reprogrammed by the cytoplasm to support the development of an entire new organism. This was a fundamental discovery about the flexibility of DNA expression.
What is the difference between therapeutic and reproductive cloning?
Both begin with somatic cell nuclear transfer (SCNT) to produce an embryo genetically matched to a donor. The difference is what happens next. In therapeutic cloning, the embryo is grown to the blastocyst stage (about five days) and stem cells are harvested to grow replacement tissues — the embryo is never implanted. In reproductive cloning, the embryo is implanted into a surrogate mother and allowed to develop into a new living organism. Human reproductive cloning is currently illegal in the UK.
Could cloned stem cells be rejected by the patient?
Stem cells produced by therapeutic cloning are genetically identical to the patient's own cells and so should not be rejected by the immune system. This is a major advantage over embryonic stem cells from unrelated donors. However, mitochondria in the egg cell come from the egg donor, and there is some small risk that mitochondrial proteins could trigger a mild immune response.
Are there alternatives to embryonic stem cells?
Yes. Adult stem cells can be harvested from bone marrow, fat tissue, or blood without destroying an embryo, but they are multipotent rather than pluripotent. Induced pluripotent stem cells (iPSCs), developed by Shinya Yamanaka in 2006 (Nobel Prize 2012), are adult cells reprogrammed to behave like embryonic stem cells by introducing specific transcription factor genes. iPSCs avoid the embryo controversy, but researchers are still working to ensure they are safe enough for routine clinical use.
Professor Darwin at aitutors.me can walk you through the ethics question formats, quiz you on the vocabulary, and help you practise balanced evaluation answers before your GCSE biology paper.