RP4 - effect of named variable on permeability of cell membranes

Question 1

explain why it is important to wash beetroot discs

Answer 1

• to wash off pigment
• to show that any pigment released is due to alcohol

Question 2

describe a suitable control of this experiment

Answer 2

distilled water with beetroot discs instead of alcohol

Question 3

describe why using beetroot discs with water is important as a control

Answer 3

to conclude alcohol is causing leakage of pigment

Question 4

explain why it is important to shake test tubes every minute

Answer 4

increase surface contact with alcohol with all beetroot discs

Question 5

explain why it is important to pour alcohol directly from experimental test tube into a clean test tube

Answer 5

to limit variation of time discs were left in the alcohol

Question 6

explain why results would be different if using cooked beetroot instead of fresh beetroot

Answer 6

• cooking/heating would damage plasma membrane
• would denature proteins in phospholipid bilayer
• pigment released during cooking

Question 7

explain why a decrease in temperature of 5 degrees would affect the results

Answer 7

• less KE
• molecules move slower = lower diffusion rate
• membranes less fluid

Question 8

experiment was repeated using same procedure and accurately but differences in results were found. suggest why

Answer 8

variation in judging colour OR variation in beetroot type

Question 9

a student identified an anomaly. what can be done to check this

Answer 9

• repeat at same concentration
• check to see if results are similar

Question 10

suggest why the curve levels out

Answer 10

maximum membrane damage

Question 11

student was investigating effect of temperature on membrane permeability. beetroot discs were added to test tubes of same water volume. suggest why

Answer 11

• too much water = pigment may appear lighter
• so results from different temperatures are comparable

Question 12

suggest a way a student can monitor temperature of water in each tube

Answer 12

take readings using digital thermometer throughout experiment

Question 13

suggest how increase of temperature caused release of red pigment from beetroot

Answer 13

• increase temperature = damages phospholipid bilayer
• proteins denatured
• increased fluidity/permeability

Question 14

suggest one reason why temperature stayed constant

Answer 14

so permeability of phospholipid membrane is unaffected