So you want to investigate fermentation in yeast. Here are some ideas for you.

The factors that might affect the rate of fermentation are the:

  1. sugar concentration,
  2. temperature,
  3. oxygen concentration,
  4. amount of yeast and,
  5. amount of alcohol produced.

You could investigate any one of these factors.

Do some research on yeast to decide how you think that these factors affect yeast. Here are a few clues:

  1. If there is plenty of oxygen, yeast will respire aerobically; absolutely NO alcohol will be produced, i.e. there is no fermentation. Fermentation is a kind of anaerobic respiration, so it only happens in the absence of oxygen.
  2. Alcohol is a toxic chemical. As the yeast ferments sugar, more and more alcohol is produced so that it will eventually stop fermentation.
  3. You already know that putting food in the fridge stops it going mouldy and that putting something in boiling water will sterilise it. It is fair to assume that between 0 and 40 C fermentation will speed up as temperature is increased.

When you have done your research, you will be able to write a prediction: a hypothesis with a scientific explanation.

So you can now plan:

  1. vary the temperature ~ take measurements at a minimum of 5 different temperatures,
  2. measure the rate of fermentation by counting bubbles of carbon dioxide,
  3. make sure that all the other variables are constant.

In this experiment, temperature would be the independent variable. the rate of fermentation (number of bubbles per minute) would be the dependent variable. All the other variables are fixed; i.e. use the same amount of sugar each time, run the experiment for the same length of time.

When you have completed your investigation, you should think about things like accuracy. Would it have been better to measure the volume of carbon dioxide produced rather than just counting bubbles? Should you repeat the experiments? Did you get any anomalous results (ones that did not fit into the pattern)?

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