| Criteria | Marks |
|---|
| Demonstrates a thorough understanding of the links between the use of Bt cotton, insecticides, disease control and natural selection; provides a comprehensive analysis of the data; interprets inter-relationships between the use of genetically engineered crops and insecticides for disease control; makes an informed judgement based on the data | 5 |
| Demonstrates a sound understanding of the use of Bt cotton, insecticides, disease control and/or selective pressures; provides an analysis of the data; provides a suitable judgement based on the data | 4 |
| Demonstrates an understanding of the use of Bt cotton and disease control; outlines the benefit(s) and limitation(s) of using Bt cotton for disease control; supports answer with reference to the data | 3 |
| Outlines a benefit or a limitation of the use of Bt cotton for disease control AND provides link(s) to the data | 2 |
| Provides some relevant information | 1 |
Sample answer:
The introduction of Bt cotton initially resulted in less insect damage and disease and a saving in application of insecticides.
As Bt cotton was introduced, the amount of insecticides applied to kill bollworm decreased, eventually to zero, suggesting that Bt cotton was effectively controlling disease due to bollworm. However, the data show that once most of the cotton crops grown were Bt cotton, insecticide use to kill hemiptera increased markedly to a higher level than before Bt cotton was introduced. These increased amounts of insecticides were needed to maintain high yields.
A conclusion that can be drawn is that Bt toxin killed bollworms but did not kill hemiptera. Removal of bollworms provided a survival advantage for hemiptera which became the dominant pest. Therefore, a new cause of disease in cotton was dominant and the benefit of Bt cotton for disease control was temporary.
The data show that use of a genetically engineered crop such as Bt cotton can control disease due to one pest, but removal of that pest opens the way for other pests to survive and reproduce so that disease in the crop persists due to insects. It can be concluded that Bt cotton only has short-term benefits and needs to be complemented by use of pesticides.
