Question 19M.3.HL.TZ1.9c.i
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.3.HL.TZ1.9c.i |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Define | Question number | c.i | 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]
B. subtilis colonies form biofilms through quorum sensing. Define quorum sensing.
[1]
«a system of» behaviours triggered as a function of population density ✔
This question was a good discriminator, as weaker students were unable to use correct terminology such as “population density,” instead resorting to vague phrases like “when the bacteria sense something.”
