To Prepare And Show The Production Of Alcohol By Yeast Flashcards
Why must this investigation be carried out under anaerobic conditions?
(2)
Alcohol is only produced under anaerobic conditions
If aerobic conditions no alcohol will be produced
How did you ensure conditions were anaerobic?
Layer of paraffin oil on top of boiled glucose solution and yeast
Suggest a suitable control for this experiment.
Add no yeast
How did you know fermentation was taking place?
Bubbles of carbon dioxide will be seen in the limewater
Why might limewater be used in this experiment?
Limewater turns milky in the presence of carbon dioxide
Name the molecule from which lactic acid is produced by glycolysis.
Pyruvate (pyruvic acid)
In what part of the cell does the Krebs Cycle occur?
Mitochondrion
Suggest how you would know the glucose is used up.
No more bubbles are produced
Explain why boiled yeast is suitable as a control for this experiment?
Heat denatures enzymes
Give an alternative control other than boiled or no yeast.
Distilled/deionized water
What affect does the absence of limewater have on the experiment?
No affect on experiment
Explain why the absence of limewater doesn’t affect the experiment?
Limewater is only present to test for carbon dioxide
State one factor apart from temperature that must be kept constant when repeating the experiment, what needs to be the exact same when repeating the experiment.
(2)
Same concentration of glucose
Same concentration of yeast
Name one industry that depends on fermentation.
Brewing/baking
Name one end product of the brewing industry.
Alcohol
Name one substance that yeast can use to make ethanol.
Sugar
What substance, other than ethanol, is produced by the fermentation by yeast.
Carbon dioxide
Suggest a suitable temperature for this experiment.
30 degrees Celsius
Why does the production of ethanol eventually stop?
3
Sugar is used up
Alcohol kills yeasts
Yeast dies
Name the reagent(s) used to demonstrate that alcohol (ethanol) has been produced and the colour change associated with a positive test,
(2)
Acidified potassium dichromate - orange to green
Iodoform test -Potassium iodide solution - colourless - then sodium hypochlorite solution - brown -orange then colourless - heat at 50-60 degrees then yellow crystals form
Describe the iodoform test.
7
Filter the solution
Place some of filtrate into a test tube
Add an equal volume of potassium iodide solution - colourless
Add sodium hypochlorite solution - brown-orange colour then becomes colourless
Place test tube in a water bath at 50-60 degrees for 4 to 5 minutes
Remove test tube and allow to cool
Pale yellow crystals form of a chemical called iodoform which indicates ethanol is present
Describe the discontinued test for alcohol.
3
Acidified potassium dichromate is added to the filtered solution
The test tube is placed in a warm water bath
If alcohol is present the colour changes from orange to green
What substrate did you use?
Sugar/glucose
