Effect of lipid solubility on permeability of plasma membrane

: To study the effect of lipid solubility of molecules on permeability of plasma membrane of animal cell.

Introduction :
Diffusion: In general, diffusion process occur when there is a concentration gradient between two region .Molecules (other than water) will move by diffusion as long as there is a concentration gradient. A concentration gradient exists when a particular type of molecule (like food coloring dye molecules) is not spread out in an even concentration, but exists in a higher concentration at some point.

Discussing about the movement across the plasma membrane of cell, diffusion is the simplest type of passive transport, whereby diffusion does not require the cell to use energy. Only small molecules can cross the cell membrane by simple diffusion. Diffusion is the movement of molecules from an area of high concentration to one of low concentration. This difference in the concentration of molecules across a space is called the concentration gradient. Diffusion is driven by the kinetic energy of the molecules.

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Because of their KE, molecules are in constant motion. Diffusion occurs when molecules move randomly away from each other in a liquid or gas.

The rate of diffusion depends on the temperature, size and the type of molecules that are diffusing. Molecules diffuse faster at higher temperatures than at lower temperatures, and smaller molecules diffuse faster than large molecules. Most transport of materials into and out of cells occurs by diffusion. The concentration gradient is the difference between the concentration of a solute in one place and its concentration in an adjacent area.

We would just compare the solutions inside and outside of the cell for their concentrations of the molecule in question. For example, if glucose (a monosaccharide) is in equal concentrations inside and outside of the cell, there is no glucose concentration gradient and glucose will not move. But, if glucose is in a higher concentration outside of the cell than inside of the cell, the glucose concentration gradient is from outside to inside the cell, and glucose will move into the cell. There is no need to expend any energy in order for glucose to enter the cell. The concentration gradient for the movement of molecules other than water is always from high concentration to low concentration.

SITI ALIA IZZANI ISMAIL
M13D

Research question :
How does the solubility of lipid-soluble molecules affect the permeability of plasma membrane by measuring the time taken for hemolysis to occur in red blood cells. Hypothesis

: The higher lipid solubility of molecules, the higher the permeability of plasma membrane Variables

: Independent : Solubility of lipid-soluble molecules. To obtain different solubility of lipid-soluble molecules, we use different type of lipid-soluble substances which the lipid solubility of them vary from each other.

 Dependent

: Permeability of plasma membrane. It is measured by recording the time taken by red blood cells to hemolysis, whereby the ‘X’ print on paper become clearly visible in sight as in distilled water.

 Controlled

: i) Volume of red blood cells suspension – All 3 test tubes containing different type of lipid-soluble substances each is dropped by the same volume of red blood cells suspension, which is 5 ml.
ii) Volume of lipid-soluble substances – The lipid-soluble substances is
taken in same volume, 5ml each .
iii) Concentration of lipid-soluble substances – The lipid-soluble substances are diluted to the same concentration, 0.3 M.
iv) Temperature of experiment environment – The experiment is carried out in the same room, so that all 3 set of experiments will have the same temperature.
v) Type of cells – The cells used in the 3 sets of experiments are of the same type of cell that is red blood cells.

SITI ALIA IZZANI ISMAIL
M13D

Materials

: No

Materials

Quantity

Size/Volume (ml)

1.
2.
3.
4.
5.
6.

Stock blood suspension
Distilled water
Methyl alcohol
Ethyl alcohol
Propyl alcohol
n-Butyl alcohol

5
5
1
1
1
1

5
5
5
5
5
5

Table 1 : List of materials used in experiment, with quantity and volume used. Apparatus

:

No

Apparatus

Quantity

Size/Volume (ml)

1.
2.
3.
4.
5.
6.

Test tubes
Measuring cylinder
Syringe
Paper with ‘X’ print
Timer
Dropper

5
1
1
5
5
1

25
10
5
-

Table 2 : List of apparatus used in experiment, with quantity and volume used. Diagram

A

:

B

C

D

Diagram 1 : The set up apparatus for the experiment

E

SITI ALIA IZZANI ISMAIL
M13D

Label for set up apparatus :
A : Red blood cell suspension + distilled water
B : Red blood cell suspension + Methyl Alcohol
C : Red blood cell suspension + Ethyl Alcohol
D : Red blood cell suspension + Propyl Alcohol
E : Red blood cell suspension + n-butyl Alcohol
Methodology :
1. Measure 5 ml distilled water using 10 ml measuring cylinder. 2. Put 5 ml of distilled water in a test tube.
3. Add 5 drops of red cell suspension and mix gently.
4. Repeat the procedure using 5 ml of 0.3M methyl alcohol, ethyl alcohol, propyl alcohol, nbutyl alcohol. 5. As the first drop of blood reaches the solution, start the timer . 6. Determine the time required for hemolysis to occur. Do this by holding the tube in front of the print on this page; as hemolysis occurs, the print will appear more and more clear. 7. If the hemolysis process occur too fast, chill all the 5 solution containing red blood cells in ice water to slow down the process of hemolysis

8. Record times for hemolysis of red blood cells in a table. Suggestion of data tabulation
Type of
substance

: Partition Coefficient
(solubility)

Distilled water
Methyl Alcohol
Ethyl Alcohol
Propyl Alcohol
n-butyl Alcohol
Table 3 : Suggestion for tabulated data

Time taken for hemolysis of red
blood cell (minutes)
Trial
1st
2nd
3rd
4th
5th

SITI ALIA IZZANI ISMAIL
M13D

Safety and Precaution

:

1. Stop the timer promptly as soon as the ‘X’ print on the paper is clearly visible as can be seen in control experiment to ensure the time recorded is more accurate. 2. Measure all the 5 solutions properly using measuring cylinder, so that all the solution used are relatively of the same amount. Ensure the eyes’ of observer are perpendicular to the scale of measuring cylinder to minimize parallax error. 3. Be careful when handling the red blood cell suspension, so that it will not spill and leave dirty stain on cloth.

References
1.
2.
3.
4.

:

http://www.nuffieldfoundation.org/practical-biology/
http://www.biology-online.org/
Biology for IB Diploma by C.J. Clegg published by Hodder Education in 2008. Student handbook for Biology HL Year 1, Kolej Mara Banting, International Baccalaureate
5. Heinemann Baccalaureate Higher Level Biology; Alan Damon, Randy McGonegal , Patricia Tosto, William Ward 2007