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4. A person touches a sharp pin.     The diagram shows the reflex arc involved in the response to this stimulus.     Right-click on the following button to open Figure 4.1         4.1.1 Name the parts labelled A, B, C and D.     [partA] [partB] [partC] [partD] (4)

  TOTAL QUESTION 9  [16]

6.2.1 Use the information in the diagram to compare the Davson-Danielli model with the fluid mosaic model. (2)

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)