If yeast cells are kept in anaerobic conditions alcohol (ethanol) and another substance are produced - Leaving Cert Biology - Question c - 2005
Question c
If yeast cells are kept in anaerobic conditions alcohol (ethanol) and another substance are produced.
(i) Describe, with the aid of a diagram, how you would keep ye... show full transcript
Worked Solution & Example Answer:If yeast cells are kept in anaerobic conditions alcohol (ethanol) and another substance are produced - Leaving Cert Biology - Question c - 2005
Step 1
Describe, with the aid of a diagram, how you would keep yeast under anaerobic conditions in the laboratory.
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Answer
To keep yeast under anaerobic conditions in the laboratory, a fermentation vessel can be used. The diagram should depict a closed container with yeast and a carbohydrate source, featuring an airlock system to prevent oxygen from entering. It is important to ensure that the vessel is sealed appropriately, hence allowing fermentation to occur without contamination from external oxygen.
Step 2
Name a carbohydrate that you would supply to the yeast as an energy source.
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Glucose is a common carbohydrate that can be supplied to yeast as an energy source.
Step 3
Give an account of a chemical test to demonstrate that alcohol (ethanol) has been produced. Include the initial colour and final colour of the test.
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To test for the presence of alcohol (ethanol), use potassium dichromate in an acid solution. The initial color of the potassium dichromate solution is orange. Upon the reaction with ethanol, the solution will change color to green, indicating that alcohol has been produced.
Step 4
What is the other substance produced under anaerobic conditions?
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The other substance produced under anaerobic conditions is carbon dioxide.
Step 5
Alcohol (ethanol) production is an example of fermentation. How would you know when fermentation has ceased?
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Fermentation is considered to have ceased when no more bubbles are produced in the fermentation vessel, indicating that the process of gas release has stopped.
Step 6
Why does fermentation eventually cease?
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Fermentation eventually ceases because the alcohol produced can inhibit the activity of yeast cells, leading to their death or a depletion of the available sugar, which halts the fermentation process.
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