Question 19M.3.HL.TZ1.a.iii
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.3.HL.TZ1.a.iii |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Suggest | Question number | a.iii | Adapted from | N/A |
Discs were soaked in different antibiotics and were placed on a culture of Bacillus subtilis spread on sterile agar in a Petri dish. The Petri dish was left in an incubator, after which zones of inhibition were observed surrounding some of the discs. The photograph is to scale.
[Source: Tasha L. Sturm. 2009. Kirby-Bauer disk diffusion susceptibility test. Visual Resources. American Society for
Microbiology, Washington, DC. www.microbelibrary.org Accessed 29 September 2014]
Suggest a reason for the result with disc X.
[1]
a. it contained no antibiotic ✔
b. it was a control «with only water» ✔
c. the antibiotic it contained was not effective against the bacterium/bacterium is resistant to antibiotic ✔
This question was also well answered, with most students recognising the disc as a control or the fact that the bacteria were resistant. Weaker students struggled with subject-specific terminology and mistakenly used terms such as “antibodies” (instead of “antibiotics”) and “immune” (instead of “resistant”).
