Scientists investigate two genetically uniform lines of freshwater snails. All the snails within a line have the same genome, but line R and line S have different genomes.
The snails are raised in water with different calcium concentrations. All other conditions are controlled, and the results are repeatable.
| Line | Mean adult shell thickness at 20 mg/dm³ calcium / mm | Mean adult shell thickness at 50 mg/dm³ calcium / mm | Mean adult shell thickness at 80 mg/dm³ calcium / mm |
|---|---|---|---|
| R | 0.32 | 0.43 | 0.54 |
| S | 0.40 | 0.43 | 0.46 |
A scientist makes this claim:
‘Line S produces a thicker shell than line R, and shell thickness in line S is less affected by calcium concentration.’
Evaluate the scientist's claim. Use calculations in your answer.
The scientists carry out another investigation using only snails from line S. One group is kept at 15 °C and another group is kept at 25 °C. The calcium concentration and all other conditions are controlled.
Suggest a possible result that would provide evidence that temperature affects adult shell thickness. Explain why this result would not prove that the genome has no effect on shell thickness.
80 exam-style questions on AQA GCSE Biology 6.2 Variation and evolution, covering 6.2.1 Variation, 6.2.2 Evolution, 6.2.3 Selective breeding, 6.2.4 Genetic engineering, and 6.2.5 Cloning. Each one has a worked solution and a mark scheme showing where the marks go.