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OCR 21st Century Biology B7 and fermentation

Discussion in 'Science' started by ScienceAndPlants, Mar 11, 2011.

  1. ScienceAndPlants

    ScienceAndPlants New commenter

    Have you tried asking on the OCR forums? I think they're monitored quite closely by OCR team members and it might alert them to the problem, even if you don't get a response.
     
  2. phlogiston

    phlogiston Lead commenter

    Presumably you're relying on dissolved CO2 reducing the pH. This may take a while or a lot of fermentation.
    I don't know whether the OCR team will be able to help since the practicals were written by the people at York University.

    Best wishes,
    P
     
  3. One would imagine it could take a while but the problem is the reverse. We get positive results for all three sugars, even lactose when all the literature I've found states that yeast does not produce lactase. Also, fructose tends to go almost immediately whereas sucrose takes a while. This should not be the case as yeast should break sucrose into glucose and fructose easily using sucrase. It should begin anaerobic respiration of the glucose causing a pH drop (due to CO2 production) while in the meantime converting the remaining fructose to glucose using isomerase. The conversion of fructose to glucose should take several minutes as it is a more complex process. We've even had positive results with distilled water that contains no nutrient for the yeast at all.
    I have had to succombe to a complete cheat and demo it using a hugely concentrated sucrose solution, a weak fructose solution and having 2M NaOH in conical flasks labelled as 'lactose' and 'water'.
     
  4. Apparently not, although it might be worth testing. A yeast solution is alkaline.
     

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