A scientist is comparing embryonic stem cells and adult stem cells for use in treating patients with blood disorders such as leukaemia. Explain the differences between embryonic stem cells and adult stem cells, and suggest why adult stem cells found in bone marrow are particularly useful for treating blood disorders.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Leukaemia is a cancer in which the bone marrow produces abnormal white blood cells. One treatment involves replacing the patient's bone marrow with healthy donor bone marrow containing stem cells, which then produce normal blood cells.
Model answer (5 marks)
Embryonic stem cells are pluripotent (or totipotent) and can differentiate into any cell type in the body.
Adult stem cells are multipotent; they can differentiate into only a limited range of related cell types.
Embryonic stem cells are isolated from early embryos, whereas adult stem cells are found in tissues such as bone marrow.
Bone‑marrow stem cells can give rise to red blood cells, white blood cells and platelets, so they can replace the abnormal blood cells that are produced in leukaemia.
Using embryonic stem cells raises ethical concerns because the embryo must be destroyed; adult stem cells can be taken from a donor or the patient without destroying an embryo.
Adult stem cells are multipotent; they can differentiate into only a limited range of related cell types.
Embryonic stem cells are isolated from early embryos, whereas adult stem cells are found in tissues such as bone marrow.
Bone‑marrow stem cells can give rise to red blood cells, white blood cells and platelets, so they can replace the abnormal blood cells that are produced in leukaemia.
Using embryonic stem cells raises ethical concerns because the embryo must be destroyed; adult stem cells can be taken from a donor or the patient without destroying an embryo.
Examiner tips
- State the pluripotency of embryonic cells and the limited differentiation of adult cells. Mention the tissue source (embryo vs bone marrow). Explain the direct relevance of bone‑marrow stem cells to blood cell production. Note the ethical issue with embryonic cells but not with adult cells.
Common mistakes
- Confusing pluripotent with totipotent; not distinguishing the range of differentiation. Forgetting to mention the bone‑marrow source or the ethical issue. Using vague terms like "different" instead of "any cell type" or "limited range".
Mark scheme (5 marks)
- Embryonic stem cells can differentiate into any cell type (they are pluripotent / totipotent)
- Adult stem cells can only differentiate into many (but not all) cell types / a more limited range of cell types than embryonic stem cells
- Adult stem cells are found in bone marrow (whereas embryonic stem cells are found in early embryos)
- Bone marrow contains stem cells that can develop into red blood cells (and white blood cells / blood cells), making them directly useful for replacing abnormal blood cells in leukaemia
- Using embryonic stem cells raises ethical issues (e.g. the embryo is destroyed) whereas adult stem cells do not raise the same ethical concerns / adult stem cells can be taken from the patient or a donor without destroying an embryo
Key terms in this question
embryonic stem cell · adult stem cell · stem cell · bone marrow
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
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- Decode the mark scheme abbreviations →
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