Question 20N.3.HL.TZ0.c
| Date | November 2020 | Marks available | [Maximum mark: 1] | Reference code | 20N.3.HL.TZ0.c |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | State | Question number | c | Adapted from | N/A |
Disinfectants can be used to break up the biofilms. One of the most commonly used disinfectants is chlorine. Hypochlorous acid forms when chlorine mixes with water. Two different disinfectants were tested experimentally: monochloramine and hypochlorous acid. The concentration of disinfectant needed to kill 99 % of the bacteria was determined, both for free bacteria and for bacteria in biofilms. The table shows the results.
[Source: LeChevallier, M W et al. “Inactivation of biofilm bacteria.” Applied and environmental
microbiology vol. 54,10 (1988): 2492–9. doi:10.1128/AEM.54.10.2492-2499.1988 reproduced/amended with
permission from American Society for Microbiology.]
State how viruses could be used to treat water systems, in order to avoid the use of a disinfectant.
[1]
viruses/(bacterio)phages that are specific to the bacterium are used to kill it;
Most knew that viruses were used but could not specify that they were specific to the biofilm bacteria; few stated that they were bacteriophages.
