| Date | May 2012 | Marks available | 1 | Reference code | 12M.3.SL.TZ1.15 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | State | Question number | 15 | Adapted from | N/A |
Question
The sludge produced in sewage treatment plants contains pathogenic microorganisms. In a study, sludge was heated to 80°C in order to kill the pathogens and the effectiveness of this treatment was compared using viruses (coliphages) and bacteria (Salmonella choleraesuis) which were added as indicators. The level of activity of either of these two indicators shows whether pathogenic microorganisms may have survived in the sewage sludge.
The resistance of the indicators to heat treatment was studied and their level of activity is shown in the following graph.
State which indicator was more resistant to the heat treatment.
Markscheme
coliphages/viruses
Examiners report
The correct indicator was generally given.
Syllabus sections
Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics) » B.3 Environmental protection
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