8.2.3The Control of Gene Expression (A Level only)
The Use of Stem Cells — AQA A Level Biology 7402 Revision Notes & Topical Questions
5 min read 9 parts Lesson 8 of 34 1 quiz
Lesson summary
8.2.3 The Use of Stem Cells — AQA A Level Biology 7402 notes: Describe and evaluate the use of stem cells in treating human disorders, including ethical issues.Stem cells are obtained from:Embryonic stem cells - taken from the inner cell mass of a blastocyst (a few-day-old embryo…
- Adult (somatic) stem cells
- Umbilical cord blood
- Induced pluripotent stem cells (iPS cells)
- repair or replace damaged tissues
- Bone marrow transplants
- Replacement of damaged cells
Section 1 of 9Sources of stem cells
Stem cells are obtained from:
1Embryonic stem cells
Embryonic stem cells taken from the inner cell mass of a blastocyst (a few-day-old embryo), often an embryo left over from in vitro fertilisation. They are pluripotent and divide indefinitely in culture.
2Adult (somatic) stem cells
Adult (somatic) stem cells found in tissues such as bone marrow, skin and the gut lining. They are multipotent or unipotent and are limited in the number of divisions.
3Umbilical cord blood
Umbilical cord blood contains multipotent haematopoietic stem cells, collected at birth with no harm to the baby.
4Induced pluripotent stem cells (iPS cells)
Induced pluripotent stem cells (iPS cells) body cells reprogrammed by introducing genes for transcription factors that return them to a pluripotent state.
Section 2 of 9Medical uses
Stem cells can be directed to differentiate by using suitable growth factors in culture and then used to repair or replace damaged tissues:
1Bone marrow transplants
Bone marrow transplants using haematopoietic stem cells to treat leukaemia and other blood disorders; this is established treatment. The patient's own diseased marrow is destroyed by chemotherapy or radiation, and new stem cells repopulate the marrow.
2Replacement of damaged cells
Replacement of damaged cells in diseases such as type 1 diabetes (insulin-producing beta cells), Parkinson's disease (dopamine neurones), spinal cord injury, macular degeneration (retinal cells) and heart disease (cardiac muscle).
3Treating burns
Treating burns by growing skin from stem cells.
4Research and drug testing
Research and drug testing growing human tissue to test new drugs or to study how diseases develop, reducing the need for animal testing.
iPS cells made from a patient's own cells would be genetically identical to the patient, so would not be rejected by the immune system and would require no immunosuppressive drugs.
Section 3 of 9Advantages and limitations
| Source | Advantages | Disadvantages |
|---|---|---|
| Embryonic | Pluripotent, can form any body tissue; grow rapidly | Embryo is destroyed; risk of rejection; may form tumours; ethical objections |
| Adult | No embryo is destroyed; patient's own cells so no rejection | Limited potency; difficult to obtain and grow |
| Cord blood | Painless to collect; ethical | Limited quantity; mostly blood cells |
| iPS | No embryo; patient-matched; pluripotent | Risk of tumours from the reprogramming genes; expensive; technique still developing |
Section 4 of 9Ethical and social issues
The main objection to using embryonic stem cells is that an embryo is a potential human life, and destroying it is considered by some to be wrong.
Ethical and social issues
Others argue that the embryos used are surplus embryos from fertility treatment that would otherwise be discarded, that the embryo at the blastocyst stage has no nervous system or ability to feel, and that the potential to cure serious disease outweighs these concerns.
There are also concerns about informed consent of donors, the commercialisation of body tissues, equity of access to expensive treatments, and the use of embryos created specifically for research (therapeutic cloning).
In the UK, research on human embryos is regulated by law and licensed (the HFEA) and limited to the first 14 days of development.
When evaluating, give balanced points, state who might benefit or be harmed, and use evidence rather than opinion.
Section 5 of 9Exam skills
Questions may give data on, for example, a trial comparing patients treated with stem cells and with a placebo.
Exam skills
Look for the size of the sample, the presence of a control group, the statistical significance, how long the patients were followed up and any side effects.
The problem of tumour formation arises because stem cells divide in an uncontrolled way if not properly differentiated; link this with 8.2.10-8.2.11. Link with totipotency and potency (8.2.1) and with the use of tissue culture (8.2.4).
Section 6 of 9Evaluating a treatment
When asked to evaluate a stem cell therapy, structure the answer around benefits, risks, and evidence.
1
Benefits include replacing damaged cells that the body cannot regenerate and reducing the need for organ donors.
2
Risks include rejection, tumour formation, infection from culture, and possible failure of cells to integrate.
3
Evidence should come from controlled clinical trials with large samples, randomised allocation, a placebo or standard-treatment control group, and long-term follow-up.
4
Treatments at an early stage of testing should not be marketed to patients as proven cures, and clinics that offer unregulated stem cell injections raise concerns about safety and exploitation of vulnerable patients.
5
A balanced answer ends with a justified judgement, such as that adult and iPS sources are preferable where they work, because they raise fewer ethical objections.
Section 7 of 9Exam-style questions
Explain why iPS cells could be considered better than embryonic stem cells for treating a patient. [3]3 marks
Exam-style questions1. iPS cells are made from the patient's own body cells, so are genetically identical and not rejected. [1]2. No embryo is destroyed so there are fewer ethical objections. [1]3. They are pluripotent so can develop into many tissue types. [1]Give two ethical objections to the use of embryonic stem cells and one argument in favour. [3]3 marks
Exam-style questions1. The embryo is destroyed / considered a potential human life. [1]2. Embryos may be created solely for research / informed consent issues. [1]3. For: treatments could cure serious diseases, and the embryos used are surplus from IVF that would be discarded. [1]Describe how a bone marrow transplant treats leukaemia. [3]3 marks
Exam-style questions1. The patient's cancerous bone marrow cells are destroyed by chemotherapy or radiation. [1]2. Healthy haematopoietic stem cells from a matched donor are transplanted. [1]3. These divide and differentiate into healthy blood cells. [1]
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Embryonic stem cell | A pluripotent cell from the inner cell mass of an early embryo. |
| Adult stem cell | A multipotent or unipotent cell found in mature tissue. |
| iPS cell | A pluripotent cell produced by reprogramming a body cell. |
| Cord blood | Blood from the umbilical cord, rich in haematopoietic stem cells. |
| Immunosuppressant | A drug that reduces the immune response to prevent rejection of transplants. |
| Therapeutic cloning | Producing an embryo genetically matched to a patient to provide stem cells. |
| Haematopoietic stem cell | A multipotent stem cell that gives rise to blood cells. |
Section 9 of 9Exam technique
1
Saying that stem cells always produce tumours; the risk exists but is managed.
2
Forgetting that adult stem cells have a limited potency.
3
Giving ethical views without a reason or evidence.
4
Thinking that iPS cells are made from embryos.
5
Failing to mention rejection and immunosuppression when comparing sources.
Marked practiceQuizzes for this lesson
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