Fermentation: To prepare and show the production of alcohol by yeast:

Fermentation (Anaerobic Respiration): To prepare and show the production of ethanol by yeast:
Yeast is used to break down glucose in anaerobic conditions (no oxygen present) to show fermentation taking place with the production of ethanol.
• Two flasks are set up with a glucose solution and with dissolved yeast. Flask A has glucose mixed with yeast while flask B has glucose mixed with yeast that has already been boiled (denatured) for 5 mins and left to cool.
• The water that was used to dissolve the glucose was boiled first to ensure there was no oxygen present. Once the water cooled the yeast solutions were added and a layer of oil (acts a barrier to stop oxygen entering the water) was added to ensure anaerobic conditions were maintained.
• Both flasks are then placed in a water bath at 25°C for the reaction to take place.
• The reaction is over when CO2 bubbles stop being produced, this can be tracked by placing the tube coming out of the flask into limewater. This limewater will also show the presence of CO2 as it will turn cloudy is CO2 is present.
• Once the reaction is finished the product is removed and tested for the presence of ethanol by carrying out the Iodoform test. The colour of the solution will change to yellow when heated if ethanol is present.
Result: The product from flask A contains ethanol the product from flask B doesn’t (yeast had been killed).