The red poppy, *Papaver rhoeas*, and several species of daisy of the family Compositae often co-exist as weeds of wheat fields. Fig. 5.1 shows changes in the percentage frequency of red poppies and daisies in an area of wheat fields over a six year period from 1998 to 2003. From 1985, the herbicide metsulfuron-methyl was used to control weeds in this area of wheat fields. This practice continued throughout the six year period. 1998 showed the first occurrence of a red poppy known as biotype X. This red poppy had a specific mutation not present in normal red poppies. [Figure 5.1]

1. (a)Describe how the percentage frequencies of daisies and red poppies changed over the six year period.[4]
2. (b)(i)Metsulfuron-methyl acts by inhibiting an enzyme called acetolactate synthetase, which is needed for the daisies and red poppies to synthesise three amino acids essential for growth. The specific mutation carried by the red poppies of biotype X occurred within the gene coding for this enzyme. The mutation changed amino acid 197 of acetolactate synthetase from proline to leucine. Suggest the effect of this mutation on the structure and activity of the acetolactate synthetase enzyme of biotype X red poppies.[3]
3. (b)(ii)Suggest the effect of this mutation on the biotype X red poppies in the presence of metsulfuron-methyl.[1]
4. (b)(iii)With reference to Fig. 5.1, predict and explain the effect of biotype X red poppies on the relative proportions of weeds and wheat in the area of wheat fields in 2003 compared to 1998.[3]
5. (c)Suggest how stopping the use of the herbicide metsulfuron-methyl and replacing it with a herbicide that inhibits a different target enzyme in weeds would affect the abundance of red poppies of biotype X.[3]

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