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Date	May 2018	Marks available	2	Reference code	18M.3.SL.TZ1.8
Level	Standard level	Paper	Paper 3	Time zone	Time zone 1
Command term	Distinguish	Question number	8	Adapted from	N/A

Question

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]

a.

State two uses for industrially produced citric acid.

[1]

b.

Citric acid can be produced by either batch fermentation or continuous fermentation. Distinguish between these two methods.

[2]

c.

Explain the significance of pathway engineering in the industrial use of microorganisms.

[2]

d.

Markscheme

NH₄NO₃ / ammonium nitrate

a.

food preservative, flavouring, (stabilizer) in alcohol production

Two answers for 1 mark.

b.

Answer does not need to be in a table.

c.

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

d.

Examiners report

[N/A]

a.

[N/A]

b.

[N/A]

c.

[N/A]

d.

Syllabus sections

Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics) » B.1 Microbiology: organisms in industry

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