Question 18M.3.SL.TZ1.8
| Date | May 2018 | Marks available | [Maximum mark: 6] | Reference code | 18M.3.SL.TZ1.8 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Distinguish, Explain, Identify, State | Question number | 8 | Adapted from | N/A |
Citric acid is produced industrially from sugars in continuous fermenters using the fungus Aspergillus niger and with date syrup as a growth medium. Citric acid is a byproduct of the metabolism of this fungus. The fungus requires a nitrogen source for optimal growth and the impact of different nitrogen sources on citric acid production was investigated. The control received no additional nitrogen.
Identify the nitrogen source that results in the highest yield of citric acid.
[1]
NH4NO3 / ammonium nitrate
State two uses for industrially produced citric acid.
[1]
food preservative, flavouring, (stabilizer) in alcohol production
Two answers for 1 mark.
Citric acid can be produced by either batch fermentation or continuous fermentation. Distinguish between these two methods.
[2]
Answer does not need to be in a table.
Explain the significance of pathway engineering in the industrial use of microorganisms.
[2]
a. used to produce specific metabolites/chemicals/substances
b. used to create/maintain optimum conditions for microorganism growth/maximum yield
c. remove by-products / block competing pathways
d. introduce new genes that increase efficiency/yield