# 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.

> OCR A-Level Biology B — Advancing Biology (H422) — 3.1 Cell division and stem cells · Explain · 5 marks

> 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.

## Mark scheme (5 marks)

1. Embryonic stem cells are unspecialised / have not yet differentiated
2. Embryonic stem cells can differentiate into any type of cell (are totipotent/pluripotent) whereas specialised adult cells can only carry out one specific function
3. Specialised cells have specific structures / features suited to their function (e.g. red blood cells lack a nucleus; muscle cells have many mitochondria)
4. Embryonic stem cells can differentiate into a wider range of cell types than adult stem cells
5. This makes embryonic stem cells more useful for treating a greater variety of diseases / replacing more types of damaged tissue

## Key terms

- [stem cells](https://www.gradenine.co.uk/glossary/stem-cells)
- [specialised cells](https://www.gradenine.co.uk/glossary/specialised-cells)
- [embryonic stem cells](https://www.gradenine.co.uk/glossary/embryonic-stem-cells)
- [adult stem cells](https://www.gradenine.co.uk/glossary/adult-stem-cells)

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/during-early-human-development-a-fertilised-dccafe19) · Published by Druglandscape Ltd.