A patient is diagnosed with leukaemia, a cancer of the blood. Doctors suggest a bone marrow transplant as a treatment. Bone marrow contains stem cells. Describe what stem cells are and explain how a bone marrow transplant could be used to treat leukaemia.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Leukaemia is a type of cancer in which the bone marrow produces abnormal white blood cells that cannot fight infection properly. A bone marrow transplant involves replacing the patient's damaged bone marrow with healthy bone marrow from a donor.
Model answer (5 marks)
Stem cells are unspecialised, undifferentiated cells that can divide by mitosis to produce more cells. They have the capacity to differentiate into many different cell types, including all types of blood cells. In a bone marrow transplant the donor’s stem cells are introduced into the patient’s marrow. These healthy stem cells then differentiate into normal white blood cells, replacing the abnormal, cancerous cells that are characteristic of leukaemia, allowing the patient to fight infection again.
Examiner tips
- Use the terms "unspecialised", "undifferentiated" and "mitosis" to describe stem cells.
- Show the chain: donor stem cells → differentiation → normal white blood cells → replacement of cancerous cells.
- Link the replacement of abnormal cells to the patient’s improved immunity.
Common mistakes
- Confusing stem cells with mature cells; not stating they are undifferentiated.
- Failing to mention mitotic division as the means of producing more cells.
- Omitting the replacement of cancerous cells by healthy ones.
Mark scheme (5 marks)
- Stem cells are unspecialised / undifferentiated cells
- Stem cells can differentiate into many different cell types / any type of cell
- Stem cells can divide (by mitosis) to produce more cells
- The donor stem cells in the bone marrow can differentiate into normal / healthy white blood cells
- This replaces the abnormal / cancerous white blood cells so the patient can fight infection
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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