What are stem cells, how are they used in medicine, and what is cloning?
The nature of stem cells and the differences between embryonic and adult stem cells, cell differentiation and potency, the medical uses of stem cells, the principles of reproductive and therapeutic cloning, and the associated ethical issues.
A CCEA Life and Health Sciences answer on stem cells and cloning: the nature of embryonic and adult stem cells, differentiation and potency, the medical uses of stem cells, reproductive and therapeutic cloning, and the ethical issues.
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What this dot point is asking
CCEA wants you to explain what stem cells are, distinguish embryonic from adult stem cells, explain differentiation and potency, describe the medical uses of stem cells, explain the principles of reproductive and therapeutic cloning, and discuss the ethical issues. It applies the genetics of the unit to regenerative medicine and cloning, areas of major scientific and public interest.
Stem cells, differentiation and potency
Stem cells differ in their potency, the range of cell types they can form. Embryonic stem cells, from a very early embryo, are pluripotent: they can develop into almost any type of cell in the body. Adult (tissue) stem cells, found in tissues such as bone marrow, skin and the gut, are multipotent: they can form only a limited range of cell types related to their tissue (for example bone marrow stem cells form the different blood cells). Differentiation works because all body cells contain the same genes, but a specialised cell only expresses the genes it needs, which is why a muscle cell and a nerve cell look and behave so differently despite sharing the same DNA.
Medical uses of stem cells
The promise of stem cells is regenerative medicine: repairing or replacing tissues the body cannot regenerate well on its own. Embryonic stem cells are the most versatile because they are pluripotent, but adult stem cells avoid the ethical problem of using embryos and carry a lower risk of rejection if taken from the patient. Research also uses induced pluripotent stem cells, made by reprogramming adult cells, which may combine versatility with fewer ethical concerns.
Cloning and ethical issues
Cloning produces genetically identical cells or organisms. In reproductive cloning, the aim is to make a new individual genetically identical to an existing one: the nucleus of a body cell is placed into an egg cell whose own nucleus has been removed, and the resulting embryo is implanted to develop (as in Dolly the sheep). In therapeutic cloning, the aim is not a new individual but to produce embryonic stem cells genetically matched to a patient, so tissues or cells can be grown for treatment without rejection; the early embryo is used as a source of stem cells. These technologies raise significant ethical issues: using embryonic stem cells or therapeutic cloning destroys an early embryo, which some regard as a potential human life; there are concerns about the moral status of the embryo, about consent, and about the potential misuse of reproductive cloning. A good answer recognises both the medical benefits and these concerns, and notes that the area is tightly regulated.
Examples in context
Example 1. Bone marrow transplants for leukaemia. A patient with leukaemia can be treated with a bone marrow transplant, where donated adult stem cells re-establish healthy blood-cell production. This is the most established clinical use of stem cells and shows the value of multipotent adult stem cells in treating disease.
Example 2. Therapeutic cloning to avoid rejection. In therapeutic cloning, stem cells genetically matched to a patient could grow replacement tissue (for example insulin-producing cells for diabetes) that the patient's immune system would not reject. This illustrates the medical aim of cloning and why it is distinguished sharply from reproductive cloning in the ethical debate.
Try this
Q1. State two features that define a stem cell. [2 marks]
- Cue. It is unspecialised, can self-renew (divide repeatedly), and can differentiate into specialised cells.
Q2. State the difference in potency between embryonic and adult stem cells. [2 marks]
- Cue. Embryonic stem cells are pluripotent (almost any cell type); adult stem cells are multipotent (a limited range).
Q3. State the aim of therapeutic cloning. [1 mark]
- Cue. To produce embryonic stem cells matched to a patient for treatment, not to create a new individual.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA A2 56 marksExplain what stem cells are, describe the difference between embryonic and adult stem cells, and explain why stem cells are useful in medicine.Show worked answer →
The answer needs the definition, the embryonic versus adult comparison, and the medical value.
What stem cells are: stem cells are unspecialised cells that can divide repeatedly (self-renew) and can differentiate into specialised cell types.
Embryonic versus adult: embryonic stem cells come from an early embryo and are pluripotent, meaning they can develop into almost any type of cell in the body. Adult (tissue) stem cells are found in tissues such as bone marrow and are multipotent, meaning they can develop into only a limited range of cell types related to their tissue. Embryonic stem cells are therefore more versatile, but their use raises ethical concerns because an embryo is destroyed.
Medical value: because stem cells can differentiate, they could be used to replace cells damaged by disease or injury, for example to treat leukaemia (bone marrow stem cells), to repair tissues, or potentially to treat conditions such as Parkinson's disease, diabetes and spinal injury.
Markers reward unspecialised cells that self-renew and differentiate, the pluripotent (embryonic) versus multipotent (adult) distinction, and at least one clear medical use.
CCEA A2 55 marksDistinguish between reproductive cloning and therapeutic cloning, and give one ethical issue associated with the use of embryonic stem cells.Show worked answer →
Define both kinds of cloning, then give an ethical issue.
Reproductive cloning: the aim is to produce a new individual that is genetically identical to an existing organism. The nucleus from a body cell of the organism is placed into an egg cell whose nucleus has been removed, and the embryo that develops is implanted to grow into a new individual (as with Dolly the sheep).
Therapeutic cloning: the aim is not to produce a new individual but to produce embryonic stem cells that are genetically identical to a patient, so they can be used to grow tissues or cells for treatment without rejection. The early embryo is used as a source of stem cells rather than being implanted.
Ethical issue (any one): the use of embryonic stem cells (or therapeutic cloning) destroys an early embryo, which some people consider to be a potential human life; other concerns include the status of the embryo, consent, and the risk of cloning being misused.
Markers reward reproductive cloning producing a genetically identical individual, therapeutic cloning producing stem cells for treatment (not a new individual), and one valid ethical issue.
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Sources & how we know this
- CCEA GCE Life and Health Sciences specification — CCEA (2016)