Question 19M.3.SL.TZ1.8b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.SL.TZ1.8b |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | b | Adapted from | N/A |
Hexochlorophene (HCP) and ortho-phenylphenol (OPP) are two ingredients of handwashing formulations. The antiseptic effectiveness of the two agents was tested by soaking discs in the agents and applying them to plates inoculated with Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. The resulting zones of inhibition are depicted.
[Source: © International Baccalaureate Organization 2019]
E. coli and P. aeruginosa are both Gram-negative bacteria and S. aureus is Gram-positive. Explain how it could be verified that S. aureus 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 ✔
Some answers referred back to the experiment, but where there was knowledge of Gram staining there were good answers.
