Page 05 6. Over millions of years of evolution, mutations occur at a broadly constant rate within a gene. This allows genes to be used as molecular clocks. The diagram below shows how the base sequence in part of a gene changed as two evolutionary lineages diverged from an original base sequence. The base sequence in the gene has changed at a rate of 1 base per 5 million years as shown. Original base sequence 5 million years after diverging 10 million years after diverging Species Y Species X CAATTGATCG CAATTTATCG CGATTTATCG CAATTGCTCG CGGTTTATCG Assuming this rate of mutation continued, by how many bases would this part of the gene differ in Species X compared with Species Y 20 million years after diverging from the original base sequence? A 4 B 8 C 16 D 20 7. In metabolic pathways, the rates of reaction can be affected by the presence of enzyme inhibitors. Which row in the table below is correct? Type of inhibition Inhibitor binds to active site Effect of increasing substrate concentration on inhibition A competitive yes reversed B non competitive yes unaffected C competitive no unaffected D non competitive no reversed 8. Which row in the table below identifies the number of heart chambers and the type of circulatory system in amphibians? Number of heart chambers Type of circulatory system A 3 incomplete double B 4 incomplete double C 3 complete double D 4 complete double [Turn over