required practical 4: to investigate effect of named variable on the permeability of cell surface membranes

Question 1

describe method to investigate the effect of named variable on the permeability of cell-surface membranes

Answer 1

cut equal sized cube of plant tissue - tissue of the same age and type -
rinse/blot to remove excess pigment
add cubes to test tubes with the same volume of water
place each test tube in water baths of different temperatures and leave for the same amount of time
remove and measure colour released using a colorimeter -> draw a calibration curve

Question 2

what are issues with comparing colour to standards

Answer 2

subjective and does not give an accurate result

Question 3

why is beetroot rinsed before experiment

Answer 3

wash off any excess pigment on surface to ensure any pigment released is due to temp only

Question 4

how is temp of each water bath controlled

Answer 4

take readings of temp in intervals

Question 5

what does a high absorbance suggest about the cell-surface membrane

Answer 5

the membrane is more permeable due to damage caused by temp

Question 6

how does temp affect permeability of the cell-surface membrane

Answer 6

as temp increases, permeability increases
phospholipids gain kinetic energy so fluidity increases
transport proteins denature and H bonds break changing the tertiary structure

Question 7

how does pH affect permeability of the cell-surface membrane

Answer 7

high/low pH increases permeability
transport proteins denature changing the tertiary structure

Question 8

how do lipid-soluble solvents affect permeability of the cell-surface membrane

Answer 8

as concentration increases, permeability increases
lipid soluble solvents e.g. ethanol, may dissolve the phospholipid bilayer