aqa a-level biology: RP4, effect of temperature on cell membrane permeability Questions & Answers(RATED A+)

What is the premise behind the experiment? - ANSWER- Cell surface membranes made of phospholipid bilayer selectively permeable. This can be changed by variables like temp and solvent conc. - As temp increases, enzymes like transport proteins lining the membrane may denature, allowing the red pigment to leave the membrane as it is now permeable to more susbstances. - Membrane permeability is measured using beetroot cells, which contain a purple pigment. When membranes are more permeable, more pigment leaks out. - Amount of pigment leaked from beetroot cells is measured in a colourimeter. Why is it important to put the same vol of water in each tube? - ANSWERHigher volume leads to the pigment concentration becoming diluted, which can affect how much leaves cells, leading to difference in results. Why do you equilibrate the test tubes in the water bath first before commencing the experiment? - ANSWERTo ensure experimental T = water bath T. What is the method? - ANSWER1. Beetroot cut into identical cubes using scalpel. 2. Wipe/rinse to remove any XS pigment. 3. Place each cube in equal vol of distilled water. 4. Each tube is placed in a water bath at range of temperatures. 5. Sample is left for 20 mins so pigment leaks out of beetroot. 6. Filter each sample into a cuvette using filter paper and measure absorbance for each solution. 7. High absorbance = high pigment conc = more permeable membrane. 8. Graph is plotted with absorbance on the y axis and concentration on the x axis.