| Date | November 2019 | Marks available | 2 | Reference code | 19N.3.HL.TZ0.10 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| Command term | Explain | Question number | 10 | Adapted from | N/A |
Question
The diagram below represents a small-scale biogas fermenter.
[Source: © Science in Society. http://www.i-sis.org.uk/BiogasChina.php]
Suggest one material that could be loaded into the biogas fermenter from which biogas can be produced.
Identify the ideal temperature and oxygen conditions inside the fermenter for efficient biogas production.
Temperature:
Oxygen:
Distinguish between batch and continuous culture fermentation.
Explain how conditions in the fermenters are maintained to maximize penicillin production.
Markscheme
blackwater
OR
brownwater/sewage
OR
feces
OR
organic solid waste
OR
paper pulp
OR
other biodegradable material ✔
Do not accept methane and CO2.
temperature: warm
oxygen: low/anaerobic ✔
Both required.
a. in batch culture product is withdrawn at the end of the «organisms » growth phases whereas in continuous culture product is withdrawn while the organism is growing / OWTTE ✔
b. in batch culture all of the growth medium/nutrients are added at the beginning whereas in continuous culture, growth medium/nutrients are added at a constant rate / OWTTE ✔
c. batch culture is carried out in large scale fermenters whereas continuous culture could be in small scale ✔
d. continuous can run for a longer time than batch ✔
a. aerobic conditions achieved by stirring/aeration ✔
b. buffers maintain pH ✔
c. moderate temperatures maintained by cooling jacket ✔ Accept mention of 20-30°C.
d. product is collected during stationary phase ✔
Award marks for identification of the factor and description of the effect.
