14 6 Spider silk is a very strong and flexible natural fibre. It is of interest to humans as a possible fibre for protective clothing. Scientists have genetically modified a range of organisms to produce spider silk, including goats and plants such as alfalfa. (a) A gene for spider silk is copied. A gene for resistance to antibiotic A is also copied. The flow diagram shows some of the stages in genetically modifying alfalfa plants to produce spider silk using the copied genes. Stage 1 An enzyme is used to join each copied gene for spider silk to a copied antibiotic resistance marker gene to form pairs of joined genes Stage 2 Plasmids are cut open so that these joined genes may be inserted Stage 3 The plasmids are placed inside Agrobacterium tumefaciens bacteria, which are then exposed to antibiotic A Stage 4 Surviving Agrobacterium tumefaciens bacteria are used to infect cells of the alfalfa plant Stage 5 Infected alfalfa plant cells are grown on agar containing IAA Stage 6 Spider silk is extracted from alfalfa plants Turn over 15 (i) Explain how an enzyme is involved in joining the two different genes together in stage 1. 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(ii) Which one of the following enzymes can be used to cut open the plasmids in stage 2? (1) A DNA polymerase B RNA ligase C RNA polymerase D restriction endonuclease (iii) Explain why antibiotic A is used in stage 3. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 16 (iv) Give reasons why the infected alfalfa plant cells are grown on agar containing IAA in stage 5. 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(v) The table shows the mass of spider silk produced from the genetically modified alfalfa in stage 6. It also shows the mass of spider silk produced from the genetically modified goats. Organism Mass of spider silk produced per year Alfalfa 218 kg per acre Goat 10 kg per goat A typical number of goats that can be kept on one acre of land is 12. Calculate the percentage increase in spider silk produced by the alfalfa plants compared with the goats. (3) .............................................................. % Turn over 17 (b) Give two reasons why some people may be concerned about the use of genetically modified alfalfa as a source of spider silk. 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(Total for Question 6 = 13 marks) 18 BLANK PAGE