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Date May 2017 Marks available 3 Reference code 17M.3.SL.TZ1.8
Level Standard level Paper Paper 3 Time zone Time zone 1
Command term Outline Question number 8 Adapted from N/A

Question

The graph shows the development of biogas production and substrate utilization at Svensk Biogas (Sweden) from 1997 to 2009.

Biogas production in a fermenter requires a substrate. State another requirement for this process.

[1]
a.i.

Suggest reasons based on the data in the graph for increases in biogas production at Svensk Biogas.

[2]
a.ii.

Outline the principles of fermentation by continuous culture.

[3]
b.

Markscheme

lack of oxygen/anoxic/anaerobic conditions / acidic pH / warm temperature / methanogens / acidogenic bacteria

a.i.

a. increased variety of substrates used 

b. change in the proportion of substrates used
OR
from 1997 to 2004 increase in slaughterhouse waste 

c. less reliance on manure/increase use from food industry 

d. waste from food industry results in higher biogas yield

a.ii.

a. microbial population can be maintained in a state of exponential growth for a long time
OR
concentration of microorganisms in fermenter stable 

b. «balanced growth is» maintained by keeping nutrients/medium/pH/ temperature/ oxygen level constant 

c. nutrients are added AND products removed «at steady rate» 

d. probes used to monitor conditions within fermenters 

e. open fermentation/fermenter

b.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
b.

Syllabus sections

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