# Explain why cells in the same organism can have very different structures even though they all contain the same DNA.

> OCR A-Level Biology A (H420) — 2.6 Cell division, diversity and organisation · Explain · 4 marks

> During development, a single fertilised egg divides repeatedly by mitosis to produce all the cells of an organism. Despite containing identical genetic information, cells such as erythrocytes, goblet cells and neurones differ dramatically in their structure and function.

## Mark scheme (4 marks)

1. All cells contain the same genes but only certain genes are expressed (switched on) in a given cell type
2. Gene expression leads to transcription of specific mRNA molecules in that cell type
3. The mRNA is translated to produce specific proteins (e.g. structural proteins or enzymes) characteristic of that cell type
4. This selective gene expression is the basis of cell differentiation, resulting in cells with different structures adapted to their function

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