Practical: Investigating Anaerobic Respiration in Yeast (Edexcel IGCSE Biology (Modular))

Practical: Investigating Anaerobic Respiration in Yeast

• 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