| Date | May 2013 | Marks available | 1 | Reference code | 13M.3.SL.TZ1.16 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Deduce | Question number | 16 | Adapted from | N/A |
Question
The yeast Brettanomyces bruxellensis is a contaminant of wine which when present produces acetic acid, the main component of vinegar. The presence of acetic acid can lead to economic losses as it alters the taste of the wine and inhibits the growth of Saccharomyces cerevisiae, thus decreasing the ethanol production. Scientists investigated the effect of changing the temperature in fermentation tanks containing only Brettanomyces bruxellensis and a growth medium containing glucose in order to understand the dynamics of this contaminant.
State the concentration of glucose at 20°C after 110 hours of incubation, giving the units.
State the effect of increasing temperature from 20°C to 30 °C on the rate of production of ethanol.
Deduce one reason why there were no more rises in ethanol concentration after 120 hours at 30°.
Deduce one reason why the concentration of ethanol and acetic acid at 35°C does not rise after 80 hours despite the fact that the concentration of glucose is still high.
Discuss the idea of producing wine using a lower temperature range to avoid economic losses due to contamination by yeasts other than S. cerevisiae.
Markscheme
20 g l–1 (Accept answers from 20 to 21. Units required.)
at 30 °C ethanol produced more quickly/increased rate of production/positive correlation
glucose ran out
cells are dying / enzymes denatured
Arguments against low temperature
a. high temperatures kill B. bruxellensis;
b. high temperatures results in low acetic acid in wine;
c. high temperature results in low alcohol content;
Arguments for low temperature
d. rate of fermentation/use of glucose/alcohol production is higher;
e. no real arguments for low temperature as B. bruxellensis growth rate/acetic acid production high;
Must include at least one for and against point for full marks.
Examiners report
Few candidates answered this option.
In F1 the data was a challenge for students who attempted this option and responses to this section were quite poor.
Few candidates answered this option.
In F1 the data was a challenge for students who attempted this option and responses to this section were quite poor.
Few candidates answered this option.
In F1 the data was a challenge for students who attempted this option and responses to this section were quite poor.
Few candidates answered this option.
In F1 the data was a challenge for students who attempted this option and responses to this section were quite poor.
Few candidates answered this option.
In F1 the data was a challenge for students who attempted this option and responses to this section were quite poor.
