| Date | May 2018 | Marks available | 2 | Reference code | 18M.3.SL.TZ2.8 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Describe | Question number | 8 | Adapted from | N/A |
Question
Vinegar is a water-based solution of ethanoic acid. Acetobacter aceti is used in the production of vinegar. This bacterium has the ability to convert ethyl alcohol, C2H5OH, into ethanoic acid, CH3COOH.
In the generator method of ethanoic acid fermentation, Acetobacter aceti are grown over wood shavings in a fermenter to the point where they form a biofilm.
At the base of the fermenter oxygen is bubbled in, which then rises through the wood shavings. Ethanol drips through the wood shavings. At a suitable temperature the ethanol is converted to ethanoic acid, which is withdrawn from the bottom of the fermenter, and new ethanol is added at the top.
A. aceti is a Gram-negative bacterium. If a Gram staining procedure were carried out on a sample of A. aceti, predict the result that would be observed after decolourization.
A. aceti is a Gram-negative bacterium. If a Gram staining procedure were carried out on a sample of A. aceti, predict the result that would be observed after counterstaining.
List two abiotic variables that would need to be monitored during this fermentation process.
Describe one way in which microorganisms in this fermenter could be limited by their own activities.
Distinguish between batch fermentation and continuous fermentation.
Outline the concept of an emergent property.
Markscheme
the bacteria would be clear/colourless
would stain pink
Do not accept “violet” or “lilac”.
a. oxygen
b. temperature
c. pH levels
d. CO2
a. name of a factor
b. description
eg
a. pH
b.lowered by «ethanoic» acid production.
eg
a. increase in temperature
b. due to metabolism.
eg
a. increased population size/reproduction
b. would limit resources.
eg
a. increased metabolic waste
b. reduce population.
Table format is not required.
a. emergent properties arise from the interaction of the elements of a system
b. behaviours exhibited which are not shown by individuals
c. quoroum sensing
OR
matrix production
OR
water channels
OR
antibiotic resistance
OR
other correct example
Examiners report
