Membrane Permeability

Question 1

What is a colorimeter, and how does it work?

Answer 1

 Colorimetry is a technique that measures the absorbance of light passing through a solution.

 A cuvette is filled with the solution and placed in the colorimeter.

 A more concentrated solution (that has more colour in it) will absorb more colour.

Question 2

What are the independent variables in the membrane fluidity experiment?

Answer 2

: temperature of water

Question 3

What are the dependent variables in the membrane fluidity experiment?

Answer 3

: % transmission of light through resulting solution

Question 4

Name the equipment needed for the membrane fluidity experiment.

Answer 4

Raw beetroot,
size 4 cork borer,
white tile,
knife,
ruler,
beaker, 8
forceps,
water baths,
boiling tubes,
thermometer
colorimeter &
cuvettes,
stop clock,
distilled water,
syringe

Question 5

What are the other variables that we need to control in the membrane fluidity experiment?

Answer 5

Volume of distilled water
Time left in water
Size of beetroot piece

Question 6

What are some Possible evaluation issues during the membrane fluidity experiment?

Answer 6

• Some beetroot may have skin on affecting surface area.
• Difficulty in maintaining temperature
• Accurate reading of the colorimeter
• From the different parts of the root
• Accurate size of beetroot
• Ensuring same amount of time at the different
  temperatures

Question 7

Explain the effect of temperature on membrane fluidity.

Answer 7

 As temperature increases, the kinetic energy of molecules also increases so they move faster.

 The phospholipids in the membrane vibrate/
move more.

 Membrane proteins can be denatured by high
temperatures. As the temperature increases
(over 40 degrees) there is more denaturation and
disruption of membranes.

 The betalain pigment can escape from the cell/
vacuole when the membrane is disrupted.

 For the dye to be released, the vacuole
membrane also needs to be disrupted.

Question 8

Explain the effect of ethanol on membrane fluidity.

Answer 8

 Ethanol is a polar solvent that can dissolve the
phospholipids.

 Thus, ethanol causes the membrane to be disrupted.

 Ethanol can also cause membrane proteins to be
denatured. Similarly, it can disrupt the vacuole membrane.

 Thus, the pigment can escape from the cell/ vacuole when
the membrane is disrupted.