| Date | May 2016 | Marks available | 2 | Reference code | 16M.3.HL.TZ0.10 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Outline and Suggest | Question number | 10 | Adapted from | N/A |
Question
Annual ryegrass (Lolium rigidum) is a weed species that has been successfully controlled by the application of the herbicide glyphosate. The graph shows the number of confirmed cases of glyphosate resistant ryegrass across Australia between 1996−2012.
(i) Outline the pattern of change in resistant populations of ryegrass over time in Australia.
(ii) Suggest one reason for the pattern.
State two environmental benefits from the use of genetically modified glyphosate resistant soybeans.
Explain the role of the Agrobacterium tumefaciens Ti plasmid in genetic modification.
Markscheme
(i) Resistance is «exponentially» increasing (OWTTE)
(ii) Increased growth/differential survival of resistant population
OR
Natural selection for glyphosate resistance
Evolution of resistance is possible due to pre-existing variability
«Strong» selective pressure «by application of glyphosate»
Increased crop yields
OR
Reduced demand for more land
Less application of other herbicides «to control weeds»
OR
Glyphosate can replace more toxic/persistent herbicides
Less need for tilling/plowing/ploughing
OR
Less soil erosion
«Less plowing/herbicide application» uses less fuel/less emissions produced
Agrobacterium tumefaciens «Ti» plasmid causes tumours in the plant it infects
Donor gene inserted into Ti plasmid
Along with antibiotic resistance gene
Construct/recombinant Ti plasmid re-inserted into an A. tumefaciens bacterium
Infect leaf with bacterium «and grow on antibiotic medium»
«Some surviving» cells contain the gene/are glyphosate resistant
Examiners report
Most were able to identify the pattern of change in the graph in (i) but suggesting a reason for the pattern (ii) was more discriminating with fewer candidates able to express clearly why this was happening.
Most seemed able to give two environmental benefits and thus earned the 2 marks.
Most candidates were also able to explain the use of Ti plasmids in genetic modification, although some steps were left out, such as the reinsertion of the Ti plasmid in the bacterium or the role of the antibiotic resistant gene.
