Question 19M.3.HL.TZ1.9c.ii
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.HL.TZ1.9c.ii |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | State | Question number | c.ii | 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. State three possible advantages to B. subtilis of forming a biofilm.
1.
2.
3.
[3]
a. allows a broader range of habitat «for colonization» ✔
b. biofilms are resistant to physical forces/heat shock/desiccation/physical wiping ✔
c. biofilms can withstand nutrient deprivation ✔
d. resistance to changes in pH ✔
e. resistance to antibiotics ✔
f. avoid phagocytosis ✔
For two years in a row, option B questions about biofilms have been well answered. The most commonly identified advantages of forming a biofilm were resistance to antibiotics and resistance to physical forces, such as wiping.
