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