Question 23M.3.SL.TZ2.9
| Date | May 2023 | Marks available | [Maximum mark: 5] | Reference code | 23M.3.SL.TZ2.9 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Outline, State | Question number | 9 | Adapted from | N/A |
State the scientific name of the microorganism used commercially to produce citric acid.
[1]
Aspergillus niger/A.niger;
The majority of students were unable to identify the microorganism used to produce citric acid.
State one use of the citric acid produced.
[1]
used as a preservative/flavouring;
A few could identify one use.
The image shows two petri dishes with bacteria growing on the surface of agar, one of them testing the effect of a certain substance as an inhibitor of the growth of the bacteria.
[Source: Stalons, D., 1972. Staphylococcus aureus (AB Test). [image online] Available at:
https://commons.wikimedia.org/wiki/File:Staphylococcus_aureus_(AB_Test).jpg
[Accessed 14 February 2022]. Public domain.]
Outline how the experiment is carried out.
[3]
- the bacteria are spread over the surface of the agar of the petri dishes;
- a disc is soaked in the substance to be tested and then placed on the agar;
- the plates are incubated for a certain time (for bacterial growth);
- the greater the diameter/radius of the clear area, the greater the inhibiting effect of the substance;
- must have a control with no inhibitor
OR
the experiment should be replicated;
Most candidates could score some marks for outlining the growth of bacteria on agar plates with answers tending to be vague.
