AQA A-level BIOLOGY (7402/1) Paper 1 Mark scheme 2021 SPECIMEN V1

AQA A-level BIOLOGY (7402/1) Paper 1 Mark scheme 2021 SPECIMEN V1 1.1 Describe the induced fit model of enzyme action and how an enzyme acts as a catalyst. - - 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 are the substrate the scientists must add to the reaction mixture is to produce ATP. - - Adenosine diphosphate. 1.3 Suggest and explain a procedure the scientist could have used to stop each reaction. - - The nature of the enzyme by putting it in ice. 1.4 Explain the change in ATP concentration with increasing inorganic phosphate concentration - - With increasing phosphate concentration more ES complex is form. - 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. - - 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. - - Water is more dense than air. - So it supports the gills. 2.3 A student studies 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. - - 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 countercurrents principle allows sufficient oxygen uptake in the fish gas exchange system. - - Blood and water continuously flow in opposite directions. - So the concentration gradient is maintained along the length of the lamellae. 3.1 Describe