DP Biology (last assessment 2024)

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Question 23M.3.SL.TZ1.8

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Date May 2023 Marks available [Maximum mark: 5] Reference code 23M.3.SL.TZ1.8
Level SL Paper 3 Time zone TZ1
Command term Explain, State Question number 8 Adapted from N/A
8.
[Maximum mark: 5]
23M.3.SL.TZ1.8

The graph shows the changes in the composition of biogas inside a fermenter.

[Source: Náthia-Neves, G., de Alencar Neves, T., Berni, M., Dragone, G., Mussatto, S., Forster-Carneiro, T., 2018. Start-up phase
of a two-stage anaerobic co-digestion process: hydrogen and methane production from food waste and vinasse from
ethanol industry. Biofuel Research Journal, [e-journal] 5(2), pp. 813–820. https://dx.doi.org/10.18331/BRJ2018.5.2.5.]

(a)

Explain the changes in biogas composition from day 40.

[3]

Markscheme
  1. increase in methane;
  2. produced by methanogens/archaeans;
  3. in anaerobic conditions/absence of oxygen;
  4. decrease in carbon dioxide which is converted into methane;
  5. some methane and carbon dioxide produced by breakdown of organic acids/alcohol/organic compounds;

Ignore any data from 0 to 40 days Ignore any comments on hydrogen – it is 0 from 40 days

Accept correct formulae

Examiners report

There were references to gases increasing or decreasing without an explanation.

(b)

State one source of organic matter that can be used to produce biogas.

[1]

Markscheme

manure/animal dung/household waste/sewage/farm waste/bagasse;

Examiners report

Generally correctly answered, usually with household waste.

(c)

Solid and liquid waste are generated during biogas production. State how this waste can be used.

[1]

Markscheme

(slurry) can be used as fertilizer;

Accept other verified examples

Examiners report

Generally correctly answered, usually with household waste.