A student investigated how to extract anthocyanins from blueberries. She mixed 10 g of crushed, fresh blueberries with 100 cm³ of extraction solvent for 1 hour. She investigated three different extraction solvents: E – Ethanol, water and acid F – Ethanol and water G – Water When making up extraction solvent E, the student used a volume ratio of 70:30:1 ethanol:water:acid. Tick (✓) one box that shows the most appropriate volumes she would use to make up 100 cm³ of extraction solvent E. 69.3 cm³ ethanol, 29.7 cm³ water, 1.0 cm³ acid The student kept constant: 1. The mass of fresh blueberries 2. The time of the mixture to stand. Name two other variables the student should have kept constant during this investigation. 1 2 After 1 hour, the student filtered the samples. She placed the filtrate in a colorimeter and measured the light absorbance. Her results are shown in Figure 4. Use your knowledge of membrane structure to explain the results in Figure 4. A different student did this investigation. He did not have a colorimeter. Describe a method this student could use to prepare colour standards and use them to give data for the total anthocyanin extracted.

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A student investigated how to extract anthocyanins from blueberries - AQA - A-Level Biology - Question 4 - 2020 - Paper 1

Question 4

A student investigated how to extract anthocyanins from blueberries. She mixed 10 g of crushed, fresh blueberries with 100 cm³ of extraction solvent for 1 hour. Sh... show full transcript

Worked Solution & Example Answer:A student investigated how to extract anthocyanins from blueberries - AQA - A-Level Biology - Question 4 - 2020 - Paper 1

Step 1

When making up extraction solvent E, the student used a volume ratio of 70:30:1 ethanol:water:acid.

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Answer

The most appropriate volumes to use for 100 cm³ would be:

Ethanol: 69.3 cm³
Water: 29.7 cm³
Acid: 1.0 cm³ This ensures the proper ratio is maintained.

Step 2

Name two other variables the student should have kept constant during this investigation.

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Answer

Temperature during the extraction to ensure consistent enzyme activity and extraction efficiency.
Agitation/mixing speed to maintain uniform extraction across all samples.

Step 3

Use your knowledge of membrane structure to explain the results in Figure 4.

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Answer

Higher absorbance indicates more anthocyanin released during extraction, which can be attributed to solvent effectiveness. Ethanol enhances membrane permeability, allowing for better extraction of anthocyanins. Water's lower ability to permeate membranes results in lower absorbance, while the combination of ethanol and acid (solvent E) maximizes extraction through enhanced solubility of pigments and disruption of membranous structures.

Step 4

Describe a method this student could use to prepare colour standards and use them to give data for the total anthocyanin extracted.

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Answer

Use known concentrations of blueberry juice or extract to prepare standard solutions with varying anthocyanin concentrations.
Compare sample absorbance with that of standard solutions using a colorimeter once available.
Establish a standard curve to correlate absorbance with concentration, enabling quantification of anthocyanin in unknown samples.

A student investigated how to extract anthocyanins from blueberries - AQA - A-Level Biology - Question 4 - 2020 - Paper 1

Worked Solution & Example Answer:A student investigated how to extract anthocyanins from blueberries - AQA - A-Level Biology - Question 4 - 2020 - Paper 1

When making up extraction solvent E, the student used a volume ratio of 70:30:1 ethanol:water:acid.

Name two other variables the student should have kept constant during this investigation.

Use your knowledge of membrane structure to explain the results in Figure 4.

Describe a method this student could use to prepare colour standards and use them to give data for the total anthocyanin extracted.

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