• Yeast can respire?anaerobically?(without oxygen), breaking down glucose in the absence of oxygen to produce?ethanol?and?carbon dioxide
• Anaerobic respiration in yeast cells is called?fermentation
• Fermentation is economically important in the manufacture of?bread?(where the production of carbon dioxide makes dough rise) and alcoholic drinks (as ethanol is a type of alcohol)
• It is possible to investigate?the effect of temperature on yeast fermentation, by seeing how temperature affects the?rate of anaerobic respiration?in yeast

The process of anaerobic respiration in yeast

Apparatus

• Boiling tubes
• Capillary tubes
• Bungs
• Yeast
• Sugar solution
• Oil
• Stopwatch
• Water bath
• Limewater

Method

• Mix yeast with sugar solution in a boiling tube
  • The sugar solution provides the yeast with?glucose?for anaerobic respiration

   

• Carefully add a layer of oil on top of the solution
  • This prevents oxygen from entering the solution (prevents aerobic respiration in the yeast)

   

• Using a capillary tube, connect this boiling tube with another boiling tube that is filled with?limewater
• Place the boiling tube with yeast and sugar solution into a?water bath?at a?set temperature?and?count the number of bubbles produced in a fixed time?(e.g. 2 minutes)
  • The rate that carbon dioxide is produced by yeast can be used to measure the?rate of anaerobic respiration?(i.e. the?rate of fermentation)

   

• Change the temperature of the water bath and repeat

Experimental set up for investigating anaerobic respiration in yeast

Results and Analysis

• Compare results at?different temperatures?to find out at which temperature yeast?respires fastest
• The?higher the temperature, the?more bubbles?of carbon dioxide should be produced as higher temperatures will be closer to the?optimum temperature?of enzymes in yeast,?increasing enzyme activity
• As respiration is an?enzyme controlled reaction, as enzyme activity increases, the rate of anaerobic respiration will increase
• If the temperature is?too high?(beyond the optimum temperature), the enzymes will?denature?causing carbon dioxide production to?slow down?and eventually?stop

Applying CORMS to practical work

• When working with practical investigations, remember to consider your CORMS evaluation

CORMS evaluation

• In this investigation, your evaluation should look something like this:
  • C?– We are changing the temperature in each repeat
  • O?– The type (species) of yeast we are using must be the same
  • R?– We will repeat the investigation several times at each temperature to make sure our results are reliable
  • M1?– We will measure the number of bubbles (of carbon dioxide) produced
  • M2?– in a set time period (e.g. 2 minutes)
  • S?– We will control the concentration, volume and pH of the sugar solution, as well as the mass of yeast added

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