Investigation on how the concentration of ethanol would affect the plasma membrane in a beetroot cell

AS and A Level Science

Aim

My aim is to find out how ethanol affects the plasma membrane of a beetroot cell. When the plasma membrane is broken, then the liquid in the cytoplasm come out. Because the liquid is purple, I can measure the intensity of the colour using a colorimeter. I can therefore know how much damage different concentration of ethanol would do to the plasma membrane of a beetroot cell.

Planning

The following apparatus are needed:

A beetroot

A cork borer

A ruler

A cutter

6 small cylinders

5 different concentration of ethanol (I have decided to use 80%, 60% 40% 20% 10% and distilled water)

A syringe (10ml)

6 cuvettes

A colorimeter

Method:

Before doing the experiment, apron and safety specs should be wearied.
First of all, I need to cut my beetroot into cylinder shapes using a cork borer
Then I need to cut the cylinders of beetroot into 25 5mm slices.
After that, I need to rinse the beetroot cells several times until the purple colour is washed away.
Place 5 slices of beetroot cells into 5 different cylinders
The total volume of the solution is going to be added to 25ml
For the distilled water one, use a syringe to add 25ml of distilled water in a cylinder. In the other 5 cylinder, pour different concentration of diluted ethanol in. The diluted ethanol should be made.

Method of making diluted ethanol: For example if I am making a 25ml solution that contains 20% of ethanol, I need to syringe 5ml of ethanol into the cylinder, then 20ml of distilled water in the solution, Now, I have made a diluted ethanol containing 20% ethanol and 80% water.

After the solution is ready, I need to pour the solution in at the same time so the result will not be bias.
Use a stop watch to time it, after it reached 2 minutes, shake the cylinder gently, so that all the colour of the solution ...

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After the solution is ready, I need to pour the solution in at the same time so the result will not be bias.
Use a stop watch to time it, after it reached 2 minutes, shake the cylinder gently, so that all the colour of the solution in the cylinder should be evenly spread out.
Pour the solution from different cylinder into 6 different cuvettes.
Filled one of the cuvette with distilled water and use I as a control.
Put the control cubic in the colorimeter, and, then put the cuvette in once at a time, record the reading shown in the screen.

I need to control some variables that would affect the intensity of the solution in order to it a fair experiment and therefore have a reliable result.

The surface area of the slices of beetroot must be the same and I also need to make sure that they are not overlap during the experiment as this could also differ the surface area. The slices are cut into the same size, so the surface area should be the same.

The temperature should also be the same; I can use a water bath and place the cylinders in it to make sure the temperature of every cylinder are the same.

The volume of diluted ethanol should also be the same. Using a 20cm3 to measure the volume and that should give a degree of accuracy of ± 0.5cm3

The time that each experiment took should be the same. I can ensure that the reaction time is the same using a stopwatch.

To make my result more reliable, I could repeat each of the experiment 3 times if time is unlimited.

There are my results:

From my graph shown above, it can be clearly seen that the higher percentage of ethanol I used in the solution, the higher the color intensity. So, the more concentrated the ethanol I used, the more damage (cut open) the plasma membrane, therefore the more the cytoplasm leaks out, making the colour more intense.

The data plotted on the graph are all very close to the line of best fit drawn above, except one. The ‘outlier’ shows that if it is pure water we used (0% of ethanol), then the colour intensity will be zero, suggesting that there will be no damage do to the plasma membrane as the purple liquid inside the cytoplasm did not leak out.

Ethanol is able to damage the plasma membrane of beetroot cell because I know that cell wall consists of 2 layer of phospholipid. It can be shown clearly in a fluid mosaic model:

Ethanol is therefore able to dissolve the lipid on the plasma membrane, destroying it, causing the contents in the cytoplasm to leak out.