Topic 2

Question 1

Describe the permeability of cell membrane experiment: stage 1, obtaining beetroot solution

Answer 1

• Use a scalpel to cut 5 equal sized pieces of beetroot on a cutting board
• Rinse pieces to remove pigment released in cutting
• Use a measuring cylinder to measure out 5cm3 of water
• In 5 different test tubes
• Place the test tubes into water baths at different temperatures
• Place 5 pieces of beetroot in 5 different test tubes for same length of time using stopwatch
• Remove beetroot from tubes leaving just coloured liquid

Question 2

Describe the permeability of cell membrane experiment: stage 2, using the calorimeter

Answer 2

• Switch calorimeter on and allow 5 minutes for it to stabilise
• Set up calorimeter using blue filter
• Use pure water to calibrate machine to zero
• Use pipette to transfer sample of liquid from first of beetroot test tubes to clean cuvette [3/4 full]
• Put cuvette in calorimeter and record absorbance of coloured solution
• Repeat for remaining test tubes
• Plot graph of temperature vs absorbance

Question 3

What is the relationship between light absorbance and permeability of the membrane? 4

Answer 3

• The higher the absorbance reading
• Less light passed through
• More pigment released
• Higher permeability of membrane

Question 4

Why is beetroot used to investigate cell membrane permeability?

Answer 4

It has a purple pigment that leaks out of the cell membrane according to its permeability

Question 5

Explain how to investigate the effect of enzyme/substrate concentration on enzyme controlled reactions

Answer 5

• Set up five concentrations of catalase/hydrogen peroxide depending on what’s tested
• Add a set volume and known concentration of hydrogen peroxide to a boiling tube
• Keep pH constant by adding buffer solution
• Set up apparatus with upside down measuring cylinder in trough of water connected to boiling tube with delivery tube
• Use pipette to add known concentration and volume of catalase
• Quickly attach bung and tube
• Measure volume of oxygen produced in measuring cylinder every 10 seconds for first minute of reaction
• Use stopwatch to measure time
• Plot data on graph of volume of oxygen produced vs time
• Draw tangent to determine initial rate of reaction