Required Practical 3

Question 1

Explain why it is important to control the volume of water in the beetroot experiment (2 marks)

Answer 1

• If there’s too much water, the concentration of pigment will be lower/the solution will appear lighter (or vice versa)
• And so that the results are comparable

Question 2

Describe how you could monitor the temperature of the water in each tube (1 mark)

Answer 2

• Take readings during the experiment using a thermometer

Question 3

Suggest how an increase in the temperature of water causes the release of the red pigment in a beetroot (2 marks)

Answer 3

• Damages cell surface membrane
• So membrane proteins denature
• So increased fluidity/damage to the phospholipid bilayer

Question 4

Explain why it is important to wash the beetroot discs at the start of the experiment (1 mark)

Answer 4

• To remove any betalin pigment on the beetroot

Question 5

Suggest two variables you should control when investigating the effect of temperature on the rate of breakdown of a protein by the protease (2 marks)

Answer 5

• Enzyme concentration
• Substrate concentration
• pH

Question 6

Explain how decreasing the pH affects enzyme activity (4 marks)

Answer 6

• Increases H+ ions
• Hydrogen/ionic bonds broken - this changes the tertiary structure
• Changes shape of active site so E-S complex cannot form
• Decreases rate of of reaction

Question 7

Explain why increasing temperature causes more pigment to leak out from the beetroot tissue (2 marks)

Answer 7

• Increased fluidity of the phospholipid bilayer

- Since membrane proteins denature

Question 8

State the variables you would control in the beetroot experiment (3 marks)

Answer 8

• Volume of water
• Diameter and thickness of beetroot
• Type of beetroot

Question 9

Describe how you could use colour standards to estimate the concentration of a sample of pigment if provided with a solution of known concentration (3 marks)

Answer 9

• Prepare a dilution series from a pigment solution of known concentration
• Carry out the calorimetry experiment
• Compare the unknown sample with colour standards

Question 10

Describe how you could use a calibration curve to estimate the concentration of a sample of pigment (4 marks)

Answer 10

• Produce known concentrations of the substance
• Measure the absorbance of each concentration
• Plot a graph of absorbance on the y-axis against
  concentration (on x-axis) and draw a curve
• Use absorbance of sample to find protein concentration from curve