A student states: 'Every cell in a human body contains the same genes, so every cell must make the same proteins.' Explain why this statement is incorrect.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
All cells contain the same genes, but genes can be switched on or off in different cell types. Only the genes that are switched on (expressed) are transcribed and translated into proteins in that cell. Therefore, different cell types produce different proteins because they have different sets of genes switched on, giving them different functions.
Examiner tips
- Use the phrase ‘genes can be switched on or off’ to show understanding of gene expression.
- Show that only expressed genes produce proteins, linking to cell function.
- Mention that different proteins give different cell functions.
Common mistakes
- Assuming all genes are always expressed.
- Confusing DNA with RNA or protein production.
Mark scheme (4 marks)
- All cells contain the same genes / same DNA / same genetic information
- Genes can be switched on or off in different cell types
- Only the genes that are switched on / expressed are used to make a protein in that cell
- Different cell types produce different proteins because they have different genes switched on / expressed, giving them different functions
Key terms in this question
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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