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Date	November 2016	Marks available	2	Reference code	16N.3.SL.TZ0.8
Level	Standard level	Paper	Paper 3	Time zone	TZ0 / no time zone
Command term	Suggest	Question number	8	Adapted from	N/A

Question

Sugar solution in a fermenter was inoculated with a culture of fungus, incubated at 30°C and left for 10 days to produce citric acid. The mass of sugar consumed and the mass of citric acid produced was measured daily.

State a suitable fungus for the production of citric acid in the fermenter.

[1]

Suggest a reason that fermentation is most successful at 30°C.

[1]

Suggest reasons for the changes in mass of sugar and citric acid after day 6.

[2]

State two uses of the citric acid produced.

[2]

Markscheme

Aspergillus/A niger/Aspergillus niger

enzymes work optimally/well/efficiently at this temperature

“Enzyme” is essential for the mark.

a. sugar consumption continues to increase because it is used in respiration / produces energy

b. products inhibit the reaction so no increase in citric acid
OR
negative feedback inhibits the reaction so no increase in citric acid
OR
decrease in pH may inhibit the enzymes

a. add a sour/acidic flavour to food/drink / change flavor / enhance taste

b. can act as a preservative in food/drink/cosmetics

c. controls pH in food/drink/cosmetics

Do not accept “food additive”.

Examiners report

[N/A]

Syllabus sections

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

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19M.3.SL.TZ2.8b:
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Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics)

Option B: Biotechnology and bioinformatics

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