During early human development, a fertilised egg divides by mitosis to form an embryo. The cells in the early embryo are embryonic stem cells. As development continues, these cells become specialised. Explain how stem cells in the early embryo are different from the specialised cells found in an adult, and explain why embryonic stem cells are considered more useful for medical treatments than adult stem cells.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Researchers studying human development have noted that the cells of a two-day-old embryo can give rise to any type of cell in the body, whereas stem cells found in adult bone marrow can only produce a limited range of cell types.
Model answer (5 marks)
Embryonic stem cells are unspecialised – they have not yet differentiated and retain the capacity to become any cell type. They are totipotent/pluripotent, whereas specialised adult cells can only perform one specific function. Specialised cells possess structures adapted to their role, e.g. red blood cells lack a nucleus and muscle cells contain many mitochondria. Because embryonic stem cells can differentiate into a wider range of cell types than adult stem cells, they can be used to replace many different kinds of damaged tissue and treat a broader spectrum of diseases.
Examiner tips
- Use the terms ‘unspecialised’ and ‘totipotent/pluripotent’ to show understanding of stem‑cell potential.
- Explain the structural adaptations of specialised cells to link function and form.
- Show that the wider differentiation capacity of embryonic cells makes them more useful for therapy.
- Keep the answer concise – 5 marks can be earned with 4–5 short points.
Common mistakes
- Confusing embryonic stem cells with adult stem cells; not stating the totipotent/pluripotent nature.
- Failing to mention the specific structural features of specialised cells.
- Over‑extending the answer with irrelevant details, losing focus on the key comparison.
Mark scheme (5 marks)
- Embryonic stem cells are unspecialised / have not yet differentiated
- Embryonic stem cells can differentiate into any type of cell (are totipotent/pluripotent) whereas specialised adult cells can only carry out one specific function
- Specialised cells have specific structures / features suited to their function (e.g. red blood cells lack a nucleus; muscle cells have many mitochondria)
- Embryonic stem cells can differentiate into a wider range of cell types than adult stem cells
- This makes embryonic stem cells more useful for treating a greater variety of diseases / replacing more types of damaged tissue
Key terms in this question
stem cells · specialised cells · embryonic stem cells · adult stem cells
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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