OCR GCSE Biology A: Stem cells, gene technology and genomics in medicine (J247) – Revision Notes

These revision notes condense statements B6.3v, B6.3w and B6.3x of OCR GCSE (9-1) Gateway Science Biology A (J247), specification Version 4.0 (August 2026), for first assessment in 2018. For full explanations and worked examples, read the study guide. Test yourself with the practice questions, tick off points on the printable checklist, see the OCR GCSE Biology hub and take a free diagnostic to find weak spots. None of these three statements is marked Higher Tier only in the specification text.

Definitions to learn

Term	Meaning
Stem cell	An unspecialised cell that can divide and differentiate into specialised cell types
Embryonic stem cell	Taken from an early embryo; can become almost any cell type
Adult stem cell	Found in tissues such as bone marrow; makes a narrower range of cell types
Antigen	A surface protein that the immune system can recognise as self or foreign
Rejection	The recipient’s immune system attacking transplanted cells or tissue as foreign
Immunosuppressant	A drug that weakens the immune response, so rejection is less likely but infection is more likely
Therapeutic cloning	Making embryonic stem cells that are genetically identical to the patient
Gene technology	Changing the genes of cells or organisms
Gene therapy	Giving a patient’s cells a working allele to treat a genetic disorder
Vector	The carrier, often a modified virus, that delivers the allele into cells
Genome	All the genetic material of an organism

B6.3v: Stem cells

Benefits

• Replace tissue that is damaged or lost.
• Bone marrow or blood stem cell transplants restore blood cell production after leukaemia treatment.
• Possible future repair of nerves, eyes, heart muscle and insulin-making cells (research stage).

Risks and issues

• Tumours if cells keep dividing.
• Viruses can pass from donor material to recipient.
• Cells may not differentiate or work as intended.
• Rejection of donor cells.
• Embryonic stem cells: an embryo is destroyed, which some people reject.
• Cost and access.

Rejection: chain of events

1. Donor cells carry different antigens.
2. The recipient’s lymphocytes recognise them as foreign.
3. The immune response attacks the donor cells.

Method: reducing rejection

1. Match the tissue type, often using a relative.
2. Use immunosuppressants, and watch for infection.
3. Use the patient’s own adult stem cells.
4. Use therapeutic cloning to make genetically identical embryonic stem cells.

In bone marrow transplants, donor white blood cells can attack the recipient (graft-versus-host disease).

Quick calculation reminders

• Chance of at least one match among n siblings, if each has a 1 in 4 chance: 1 − (3/4)ⁿ. For 2 siblings this is 1 − 9/16 = 7/16, which is 44% (nearest whole number).
• Percentage = part ÷ whole × 100. If 9 of 48 grafts are rejected, that is 18.75%, so 19%.
• Compare risks using the same group size. If 3 of 45 grafts are rejected with an immunosuppressant, that is 6.7%, against 18.75% without it.

B6.3w: Gene technology in medicine

Use	How it works	Main benefit	Main risk or issue
Making human insulin	Human insulin gene put into bacteria, which make insulin in fermenters	Large, reliable supply; no animal pancreas needed	Needs strict control and safety testing
Gene therapy	Vector delivers a working allele into the patient’s cells	Treats the cause of a genetic disorder	Allele may insert badly and cause cancer; immune reaction; effect may fade; cost
Gene editing (for example for sickle cell disease)	Cells have their DNA altered, then are returned to the patient	Possible lasting treatment	Long-term effects not known; very costly

Ethical points to be able to state

• Somatic changes affect only the patient. Changes in eggs, sperm or embryos would be inherited and the future person cannot consent.
• Fear that treatment could slide into choosing traits.
• Cost and fairness: who gets treated?
• Patients with fatal disorders may accept more risk than those with mild ones.

Worked reminder: percentages in a trial

Of 40 cultures of embryonic stem cells put into mice, 6 formed tumours. Percentage = 6/40 × 100 = 15%. A statement such as “the cells cause tumours” is too strong. A better statement is that tumours formed in 15% of cultures, so the risk needs reducing before human use.

B6.3x: The human genome and medicine

Predicting disease likelihood

• Genetic tests find alleles linked to a higher risk of disease.
• The result is a risk, not a certainty. Environment and lifestyle also matter.
• Benefits: early screening, lifestyle advice, early treatment.
• Concerns: anxiety, effects on relatives, privacy, misuse by insurers or employers, wrongly reassuring or wrongly alarming results.

Targeted drugs

• Alleles differ between patients, so responses to drugs differ.
• A test can show who is likely to benefit, so the right drug and dose are chosen.
• Benefits: fewer wasted treatments, fewer side effects.
• Some cancer drugs work only on tumours with a particular genetic change.

Method: reading a risk table

1. Find the risk for the whole population and the risk for carriers.
2. Compare them as a multiple (carrier risk ÷ population risk) and as a difference in percentage points.
3. Scale to a group size, for example 500 people.
4. State what the data cannot show, such as the effect of lifestyle.

Worked reminder: scaling a risk

Allele Z raises the lifetime risk of a disease from 8% to 40%. In a group of 500 carriers, 40% of 500 = 200 are expected to develop the disease. With the population risk it would be 8% of 500 = 40. The test therefore points to 160 extra cases among 500 carriers, but 300 carriers (60%) do not develop it.

Method: a “discuss” answer in four steps

1. Give a benefit and explain why it matters to patients.
2. Give a risk or a limit and explain the harm it could cause.
3. Use any figures supplied, with the group each belongs to.
4. Finish with a judgement and the reason for it, for example “acceptable for a fatal disorder with no other treatment, but more evidence is needed on long-term safety”.

Must-know distinctions

Compare	Point
Embryonic and adult stem cells	Embryonic: wider range, ethical objections. Adult: narrower range, fewer ethical objections
Stem cell therapy and gene therapy	Stem cells replace cells; gene therapy corrects the genes in cells
Somatic and heritable changes	Somatic: not passed on. Heritable: passed to future generations
Risk and certainty	A genetic risk is a probability, not a diagnosis

Quick self-test

1. State what is meant by rejection.
2. Name two ways of reducing rejection after a stem cell transplant.
3. Why is a patient’s own adult stem cell less likely to be rejected?
4. Give one risk of using embryonic stem cells that is not an ethical objection.
5. Give one ethical objection to embryonic stem cells and one argument in favour.
6. What is the role of a vector in gene therapy?
7. Describe how bacteria can be used to make human insulin.
8. In a trial, 4 of 25 patients have a serious side effect. Calculate the percentage.
9. A genetic test shows a person has a 30% lifetime risk of a disease, compared with 6% for the population. How many times higher is the risk?
10. Explain why a drug targeted to a genome can reduce side effects.

Answers

1. The recipient’s immune system attacks transplanted cells or tissue because it sees their antigens as foreign.
2. Any two of: match the tissue type; give immunosuppressants; use the patient’s own cells; use therapeutic cloning.
3. It carries the patient’s own antigens, so the immune system does not see it as foreign.
4. Any one of: it may form tumours; it may not differentiate correctly; donor material may carry a virus.
5. Objection: an embryo is destroyed and some people think it has the rights of a person. In favour: the embryos are often spare IVF ones that would be discarded, and treatments could relieve suffering.
6. It carries the working allele into the patient’s cells.
7. The human insulin gene is put into bacteria, which are grown in fermenters, make the insulin, and the insulin is collected and purified.
8. 4/25 × 100 = 16%.
9. 30 ÷ 6 = 5 times higher (a difference of 24 percentage points).
10. A test shows which patients are likely to respond or likely to react badly, so the drug is given only to those who benefit and a different treatment to the rest.

Where marks are usually lost

• Answering “discuss” with only benefits or only risks.
• Saying “the body rejects it” without naming antigens or the immune response.
• Describing immunosuppressants without the risk of infection.
• Writing that gene therapy “cures” with no mention of risks or limited evidence.
• Confusing gene therapy with making insulin in bacteria.
• Stating a genetic test as a diagnosis, not a probability.
• Quoting a percentage without saying which group it refers to.
• Giving an ethical view without explaining the reason behind it.

Official syllabus

OCR GCSE (9-1) Gateway Science Biology A (J247), specification Version 4.0 (August 2026), for first assessment in 2018, published by OCR. Statements B6.3v, B6.3w and B6.3x.