Explain why a cell from a multicellular organism, such as a muscle cell, contains the same genetic information as a liver cell from the same organism, yet the two cell types look and function very differently.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
During development, a fertilised egg divides repeatedly by mitosis to produce all the specialised cells in the body. Muscle cells are adapted to contract, while liver cells carry out chemical reactions such as breaking down toxins.
Model answer (5 marks)
Both muscle and liver cells arise from the same fertilised egg and therefore contain identical DNA.
Mitosis copies the genome exactly, so every cell in the body has the same genes.
During development cells become specialised (differentiated).
In each cell type only a specific subset of genes is switched on (expressed).
The proteins produced from these genes give muscle cells their contractile structure and liver cells their detoxifying enzymes, so the cells look and function differently.
Mitosis copies the genome exactly, so every cell in the body has the same genes.
During development cells become specialised (differentiated).
In each cell type only a specific subset of genes is switched on (expressed).
The proteins produced from these genes give muscle cells their contractile structure and liver cells their detoxifying enzymes, so the cells look and function differently.
Examiner tips
- State that all cells have the same DNA and that differentiation is due to gene expression.
- Explain that mitosis produces identical genomes and that specialised functions arise from different proteins.
- Use the terms "differentiation" and "gene expression" to show understanding.
- Keep the answer concise and directly linked to the marks scheme points.
Common mistakes
- Confusing mitosis with meiosis; mention only mitosis.
- Saying cells have different DNA – they have the same DNA but different gene expression.
- Failing to mention that proteins produced are what give different structure and function.
Mark scheme (5 marks)
- Both cell types originate from the same fertilised egg / the same original cell by mitosis
- Mitosis copies DNA exactly, so every body cell contains identical genetic information / the same genes
- Cells become specialised / differentiated during development
- Only certain genes are switched on / expressed in each cell type
- Different proteins are therefore produced in each cell type, giving them different structures and functions
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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