CP 5

Question 1

State 2 factors that affect the permeability of cell

membranes.

Answer 1

Temperature

Concentration of solvents (ethanol)

Question 2

IV

Answer 2

Temp of water

Question 3

DV

Answer 3

% transmission of light through resulting solution

Question 4

What variables to control

Answer 4

• volume of distilled water
• time left in water
• size of beetroot piece
• source of beetroot

Question 5

How is beetroot used to measure the permeability of

cell membranes?

Answer 5

The higher the permeability, the more red pigment that leaks out into the surrounding solution within a given time.

A colorimeter can be used to determine the absorbance, hence concentration of pigment

Question 6

Outline the procedure to investigate the
effect of temperature on permeability of
cell membrane.

Answer 6

● Using cork borer and knife, cut pieces of beetroot into 1 cm length cylinders.

● Place in distilled water overnight to remove any dye released on preparation. Wash and blot dry.

● Place 8 boiling tubes of distilled water into 8 water baths of different temperature. Once at temperature, add a piece of beetroot to each and leave for 30 mins.
● Remove beetroot and shake tubes to disperse dye.

● Set colorimeter to % absorbance on blue/green filter.

● Calibrate using distilled water in a cuvette first then add 2cm3 of beetroot solution from the first temp to a new cuvette. Place into colorimeter to read
% absorbance

Question 7

EVALUATION POINTS

Answer 7

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

Question 8

What are the safety hazards involved in testing the
effect of ethanol concentration on membrane
permeability?

Answer 8

Ethanol is an irritant and is flammable, keep away
from naked flames, wear eye protection.

Keep sharp scalpel away from fingers.

Handle hot liquid with care

Question 9

What is the effect of temperature on membrane

permeability?

Answer 9

As temperature increases, percentage transmission increases slightly increased to a point at which its greatly increased due to membrane molecules gaining more heat energy, vibrating more to a point where the vibrations caused large gaps in the membrane enabing the release of dye

Also proteins in membrane denatured leaving large pores

Question 10

What is the effect of ethanol concentration on

membrane permeability?

Answer 10

Increasing ethanol concentration leads to
increased membrane permeability, as
ethanol causes gaps to form in the
membrane.

Question 11

Give a reason why the beetroot discs were placed in the same volume of ethanol solution.
(1)

Answer 11

Volume affects pigment concentration / absobance

Question 12

Explain why the boiling tubes were kept in a water bath.

2

Answer 12

temperature afffects diffusion / permeability

temp affects pigment release / aborbance

Question 13

Explain the effect of increasing ethanol concentration on membrane permeability.

Answer 13

increases permeability

because affects phospholipid bilayer

Question 14

The student then investigated the effect of ethanol concentration on leaves from different
plant species.
Justify the modifications to the procedure in part (a) that will be required to obtain valid data.
(5)

Answer 14

• Leaves of same age as this affects conc of pigment
• Obtain leaves discs from same part of leaf because this affects conc of pigment
• Use same cork borer / diameter of leaf disc because this affects conc of pigmet
• Use same temp because temp affects rate of diffusion
• same volume of ethanol so cholorphyll is diluted the same
• wash discs to remove pigment
• replicate each ethanol conc to identify anomalies

Question 15

Analyse the data to explain the effect of ethanol on beetroot cell membranes.
(3)

Answer 15

• ethanol dissolves phopholipids in cell membrane
• therefore pigment released as a result of damage to cell membrane
• conc that causes most damage is between

Question 16

A student investigated the effect of ethanol on beetroot cell membranes.

The following method was used.
-a beetroot was cut into small cubes
-one of the small cubes of beetroot was then placed into a test tube of ethanol solution
-this test tube was incubated for 20 minutes
-a colorimeter was used to measure the absorbance of the red pigment released from the
-beetroot tissue into the ethanol solution
this procedure was repeated using four other ethanol concentrations
-a control was also carried out using water alone
the investigation was repeated three times

Describe how the method could be improved so that a valid conclusion could be made

Answer 16

• use control to zero colourimeter
• cut cubes to same shape and size so they have same surface area :vol ratio
• all test tubes must be same temperature because diffusion affected by temperature
• same vol ethanol solution/ all cubes must be submerged to diuite the pigment equally
• smaller range of concentrations between 20/40 to identify critical value

Question 17

improvements

Answer 17

• We could perform the test with more replicates, and more temp intervals
• use cutter to ensure all slices same size and mass
• weigh them before immersing them in soution

Question 18

Explain why beetroot needs to be washed before starting the experiment

Answer 18

the washing prevents any pigment leaking from cells damaged in the cutting

If this pigment is not removed it will affect the light transmittance read by the colourimeter, and provide inaccurate results