AQA A-Level Biology: Paper 1 2024 Questions With Complete Solutions

1.1 Describe the induced fit model of enzyme action and how an enzyme acts as a catalyst. - ANS - The substrate binds to the active site and forms an ES complex. - The active site changes shape slightly so it's complimentary to the substrate. - This reduces the activation energy. 1.2 Tick one box to show which substrate the scientists must add to the reaction mixture to produce ATP. - ANS - Adenosine diphosphate. 1.3 Suggest and explain a procedure the scientist could have used to stop each reaction. - ANS - The nature of the enzyme by putting it in ice. 1.4 Explain the change in ATP concentration with increasing inorganic phosphate concentration - ANS - With increasing phosphate concentration more ES complex is formed. - And at 40 mol dm3, all active sites are occupied. 2.1 Explain the advantage for large animals of having a specialised system that facilitates oxygen uptake. - ANS - Large organisms have a smaller surface area to volume ratio. - This means they overcome a long diffusion pathway. 2.2 Suggest how the environmental conditions have resulted in adaptations of systems using model A rather than model B. - ANS - Water is more dense than air. - So it supports the gills. 2.3 A student studied figure 3 and concluded that the fish gas exchange system is more efficient than the human gas exchange system. Use figure 3 to justify this conclusion. - ANS - The difference of oxygen concentration between the artery and vein is larger in the fish than the human. - So the fish remove a greater amount of oxygen that they intake. 2.4 Explain how the countercurrent principle allows sufficient oxygen uptake in the fish gas exchange system. - ANS - Blood and water continuously flow in opposite directions. - So the concentration gradient is maintained along the length of the lamellae. 3.1 Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation. - ANS - TRNA brings the specific amino acid to the ribosome. - The anticodon on the tRNA binds to the codon on the mRNA. - The amino acids join to form a peptide bond using ATP. 3.2 Use information in table to to suggest why this amino acid replacement changes the properties of crystallin. - ANS - The hydrogen bonds form instead of the ionic bonds. - And it changes the tertiary structure of the crystallin. 3.3 MRNA codon for the non-mutant triplets. mutated mRNA codon. Mutated DNA triplet. - ANS - AGG - GGG - CCC