Question 19M.3.HL.TZ1.9b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.HL.TZ1.9b |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | b | 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]
Explain how it could be determined that B. subtilis is a Gram-positive bacterium.
[2]
a. use the Gram staining procedure ✔
b. Gram-positive bacteria take up/retain «crystal violet» stain ✔
c. «Gram-positive bacteria» appear purple-coloured seen through a microscope ✔
Most candidates who attempted this option were familiar enough with the technique to score at least 1 mark.
