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7.2 The formula below shows Fick’s law. Rate of diffusion = (area of diffusion x difference in concentration) ÷ ( thickness of surface area over which diffusion takes place) Use the information in the formula to explain how the rate of diffusion is affected by asthma. (2)

8.3 Explain what determines the shape of the active site of an enzyme. (1)

8. Proteases are enzymes used in biological washing powders.  

  TOTAL QUESTION 4 [8]

5.2 The diagram shows the structure of thymine and four other bases, P, Q, R and S. Bases P and S can form three hydrogen bonds each and bases Q and R can form two hydrogen bonds each.     Explain which of the four bases P, Q, R or S is adenine. (2)   Right-click on the blue button to open Fig 5.2        

5. Nucleic acids include DNA and RNA.  Each single strand of a DNA molecule is synthesised from mononucleotides.      Right-click on the blue button to open Fig 5.1        

6.2.3 The phospholipid bilayer plays an important role in this control of movement of molecules. Explain why the phospholipid molecules form a bilayer. (3)

2. The walls of arteries and veins include endothelium, smooth muscle tissue and elastic tissue. The graph below shows the relative thickness of these tissues in the walls of two blood vessels with a similar diameter.     Right-click on the blue button to open Figure 2.1        

2.3 Warfarin is an anticoagulant drug that can be used to treat cardiovascular disease (CVD).    2.3.1 Explain the benefits of warfarin in the treatment of CVD. (3)

7. The complexity of the respiratory system is correlated with the size of the organism. As animal size increases, diffusion distances increase and the ratio of surface area to volume drops. Animals therefore adapted with a unique gaseous exchange and blood circulatory system.