Question 23M.3.HL.TZ2.10
| Date | May 2023 | Marks available | [Maximum mark: 6] | Reference code | 23M.3.HL.TZ2.10 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Distinguish, Explain, Outline, State | Question number | 10 | Adapted from | N/A |
Distinguish between batch and continuous fermentation.
[2]
| batch | continuous | ||
| a. | substrate/nutrients added | only at the beginning | all the time; |
| b. | product harvesting | at the end | at periodic intervals / constant; |
| c. | waste removal | no | yes; |
| d. | chance of contamination | less | more; |
Most candidates could distinguish batch and continuous fermentation, but many did not include sufficient elements in their distinction or organized their answer with non-comparable elements.
Biogas production was investigated in batch and continuous fermentation. A semi-liquid mixture containing animal feces (slurry) was added to the continuous fermenter once a week.
State one type of organism that can produce methane in a fermenter.
[1]
archaeans/methanogenic bacteria/methanogens;
Accept named examples.
Most could state archaeans or methanogens.
Outline the need for slurry in the fermentation.
[1]
substrate/reactant / source of nutrients / organic matter for bacteria;
Most could outline the need for slurry correctly.
Explain how growth of microorganisms in fermenters can become limited.
[2]
- changes in temperature/heat affect metabolic rate/limit enzyme activity;
- production of CO2/carbonic acid decreases pH/increase acidity which denatures enzymes;
- high levels of toxins/ammonia/sulphur inhibit growth;
- increase in salt/organic matter/ethanol concentration can affect osmoticpotential/metabolism;
- lack of nutrients prevents reproduction / OWTTE;
Explaining the microorganisms' growth limitation was difficult for most, and many provided only a list instead of an explanation.