| Criteria | Marks |
|---|
| Demonstrates a thorough understanding of the trends observed in the graph and the role of Pasteur’s work | 5 |
| Demonstrates a sound understanding of the trends observed in the graph and the role of Pasteur’s work | 4 |
| Demonstrates some understanding of Pasteur’s work with reference to trend(s) in the graph | 3 |
| Demonstrates some understanding of Pasteur’s work or a trend in the graph | 2 |
| Provides some relevant information | 1 |
Sample answer:
Pasteur’s work involved disproving spontaneous generation. This understanding of microbes explains that organisms in the milk could be causing the disease outbreaks.
Pasteur’s work also showed that heating substances to high temperatures causes microbes to be killed. Similarly, increasing the temperature of the milk to 70°C kills many bacteria in milk.
The knowledge that there are microbes in milk and that heating the milk would kill the microbes explains why pasteurised milk would reduce the likelihood of disease outbreaks. This is seen with the number of outbreaks due to pasteurised milk generally being much lower compared to raw milk – it can be seen that after 1945 the number of raw milk disease outbreaks decreased significantly.
The low number of outbreaks after 1945 may also be due to fewer people drinking raw milk. There were some outbreaks due to pasteurised milk – this could be due to problems during the pasteurisation, storage or transport of the pasteurised milk.
