The Effect of Ethanol Concentration on the Permeability of Beetroot Cell Membranes to Betalain

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AS Biology Coursework 2007                                                                      

Experiment to Investigate the Effect of Ethanol Concentration on the

Permeability of Beetroot Cell Membranes to Betalain.

Preliminary Experiment:

        I have undergone my preliminary experiment to help me decide on how I am going to do my actual experiment. My preliminary experiment has helped me investigate all the variables for my final experiment. I have found out a suitable length and diameter for my beetroot cylinders, the volume of ethanol I should use and the appropriate concentration range to use, I have also identified a suitable timing for: how long the cylinders should be washed for, how long the cylinders should be submersed in the ethanol for and how long each boiling tube should be shaken for.

        The method to my preliminary experiment was as follows:

  1. Take a beetroot, with a cork borer (6mm diameter) and a cutting mat; bore 6 cylinders out of the beetroot.
  2. With a scalpel cut the cylinders into lengths of 30mm, ensuring all are equal and cut at 90°.
  3. Heat thermostatically controlled water bath to 40°C.
  4. Take 6 boiling tubes; fill with 20 cm³ of each concentration within the range 0% to 80% ethanol solution.
  5. Put boiling tubes into water bath and leave to heat for 5 mins.
  6. After 5 mins, take temperature of boiling tubes, if at correct temperature, put in cylinders in each boiling tube and start the time.
  7. Every 1min of the 5mins submersion, remove each tube and shake.
  8. After 5 mins remove all boiling tubes, place in boiling tube rack, remove all cylinders from boiling tubes and shake each tube thoroughly to distribute betalain (as betalain is denser than water).
  9. Calibrate colorimeter using distilled water.
  10. Take colorimetry tube (use same tube, and position exactly the same for each measurement due to change in thickness around glass and in differing tubes)  and pour the solution of 0% to a cm off the top, wipe dry the boiling tube and insert in colorimeter, record reading.
  11. Repeat 10. for each concentration, in between each concentration ensure the boiling tube is cleaned and dried before and after pouring solution into it.
  12. Repeat 10. and 11. two times, take average for each concentration of ethanol.

My results from my preliminary experiment were as follows:

From my results I have learnt the following: The variable measurements I have decided on are as follows:

  • I have learnt that there are some safety issues to be addressed in this experiment. I will be using sharp instruments and so will use with care and use a cutting board. Also, ethanol is flammable and poisonous so will make sure it is not near a naked flame or able to affect me and so  I will be wearing lab coat and goggles.
  • To have the temperature of my water bath at 40°C, this is suitable as it is warm enough to allow the ethanol to take affect and not take too long but I have previously found that temperature can also damage the cell membrane so this temperature is not so hot that the it takes effect on the cell membrane as well as the ethanol, causing the results to be proving the wrong point.
  • To rinse each cylinder 6 times, each time for 2mins, and to roll them for 30 seconds each time. This is because the cutting of the cylinders caused outer split cells to secrete betalain, if the cells are not washed thoroughly enough the 0% ethanol solution still shows some pink pigment proving the washing technique to be not good enough, see my results above: 0% ethanol solution had only 72.5 transmission proving some pink pigment was present when it really should have been 100%, if washing was adequate, as there is a lack of ethanol to effect the membrane.
  • I have decided to repeat each concentration 10 times so that I can get a good average transmission reading.
  • I have decided on the boiling tubes to warm up for 5mins and on a submersion time of 5mins for the cylinders when in the solution. This time proved to be a good time for the ethanol to take affect and leave a good range of colours across the concentrations.
  • The range of concentrations I will be using is from 0%-80% ethanol.
  • The volume of the solutions in the boiling tubes will be 20cm², this also proved to be an appropriate amount as it covered the cylinders and was not too much so the pink pigment dispersed too much making visible change difficult to see. Also it was enough to pour into the colorimeter boiling tube.
  • My beetroot cylinders will be 6mm in diameter and 30 mm in length.
  • I have decided that with the colorimeter I will be using a blue filter because it is opposite to red in the spectrum and so the red will absorb the blue giving a measurement.
  • I intend to have a staggered start to the experiment to give time for me to put all the cylinders in the test tubes and remove at the same time afterwards too; I will wait 15 secs in between each boiling tube.
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The Final Experiment

Diagrams of Apparatus and Equipment Required:

Apparatus List:

Method for Final Experiment:

  1. Take cork borer (6mm diameter) and bore 90 cylinders out of the beetroots using ...

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This is a well written report that includes a lot of detail. 1. The introduction section should be at the start and the variables and safety section should be before the preliminary test 2. The sources of information need to be referenced using either the Oxford or Harvard systems 3. The running commentary should be removed as well as the demonstration table of results ***