The fungus Aspergillus niger (A.niger) is used to produce citric acid in fermenters using sugars as substrates - Scottish Highers Biology - Question 10 - 2019
Question 10
The fungus Aspergillus niger (A.niger) is used to produce citric acid in fermenters using sugars as substrates.
Citric acid is an intermediate in a metabolic pathwa... show full transcript
Worked Solution & Example Answer:The fungus Aspergillus niger (A.niger) is used to produce citric acid in fermenters using sugars as substrates - Scottish Highers Biology - Question 10 - 2019
Step 1
Explain why the growth medium used to produce citric acid should not contain iron.
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Answer
The presence of iron in the growth medium could inhibit the activity of the aconitase enzyme. Iron can act as a cofactor for other enzymes, leading to competition for binding sites, or it could cause the formation of reactive species that adversely affect the metabolic pathways necessary for citric acid production.
Step 2
Explain why less citric acid would be produced if the temperature in the fermenter was reduced.
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Lower temperatures can decrease the activity of the enzymes involved in the metabolic pathway for citric acid production, leading to a reduced rate of synthesis. The optimum temperature allows the enzymes to work at their most efficient rate, maximizing citric acid production.
Step 3
Predict the pH at 10 days.
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The predicted pH at 10 days would be approximately 3-4, following the trend indicated in the graph.
Step 4
Suggest a reason for the change in the pH observed.
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The decrease in pH can be attributed to the production of citric acid as the fermentation process progresses, which increases the acidity of the medium.
Step 5
State a variable, other than temperature or pH, that should be monitored and controlled in this process.
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The concentration of oxygen or sugars in the substrate should be monitored and controlled to ensure optimal fermentation conditions.
Step 6
Explain why it was necessary to sterilise the fermenter before A.niger was added.
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Sterilization is necessary to eliminate any other microorganisms, bacteria, or fungi that could compete with A.niger for nutrients and resources, potentially contaminating and reducing the yield of citric acid.
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