IB Practical                               International Schoool of Toulouse                  Centre 1203         
Assessment of DC, DA, CE

Investigating membrane permeability in Beetroot

Aim:  To try to identify the thermal death point of the plasma membranes of beetroot cells.  This is the point where the integral proteins denature and causes breaks in the phospholipid bilayer.

To evaluate the accuracy of the equipment in an error analysis

Apparatus

  • Cork borer
  • Scalpel
  • Tweezers
  • Stopwatch
  • 1/2 beetroot per group
  • pipette
  • measuring cylinder
  • thermometer
  • access to water bath at 50°C and 80°C

Error Analysis

Look carefully at the scales on the ruler, thermometer and the colorimeter.  What is the size of the smallest unit of accuracy.

Method

Preparation of washed beetroot cylinders

  1. First it is important to prepare 10 identical sized cylinders beetroot and wash them in tap water.
  2. Cut them with a "cork borer", wash them and use a scalpel to make them all the same length.  Aim to have them all 2cm long but you might have to use shorter pieces.  the key is that they are the same length.

Prepare 10 diffusion solutions

  1. Set up 10 test tubes into 2 test tube racks.
  2. Put 5cm3 of distilled water into each test tube.
  3. Label them with the temperatures; 70°C, 65°C, 60°C, etc to 25°C.

Heat Treatment

  1. Make a "water bath" using 150ml of hot water in a 250ml beaker and thermometer.
  2. Fill it with water at 80°C from the electronic water bath.
  3. When the water cools to 70°C put the first beetroot cylinder in for exactly 60 seconds.
  4. Take out the beetroot and put it into the diffusion solution labelled 70°C for 15 minutes. (note the time).
  5. Repeat step 3 when your water bath cools to 65°C, then 60°C etc. to 25°C.
  6. Ensure that all the beetroot samples have 15 minutes diffusion time to make a fair test.
  7. Take the beetroot out of your diffusion solutions exactly 15 minutes after you put it in.
  8. Save the labelled diffusion solution for the colorimeter.

Measuring the Pigment Loss from the tissue

The more the pigment which has diffused out of the cells of the beetroot the deeper the purple colour will be in the diffusion test tube. We can measure exactly the colour intensity using a colorimeter.

  1. Fill the little plastic colorimeter cuvette 2/3rds full and put it into the slot in the colorimeter.
     (The machine needs careful calibration first to get good results)
  2. Note down the reading which you get.  Beware! you could be measuring the amount of light passing through your solution or you could be measuring the amount of light absorbed by the colour pigment.
  3. Repeat with all the other solution and record your results in a table of your own.

Results and Conclusion  (DA & EV)

Present your results and error analysis in a clear table of results.

Plot a graph of your experiment results.  Identify the thermal death point of the membrane, if you can.  
Write a conclusion which explains what you have found out.  
Find something in a text book which either supports or disagrees with your conclusion.  
Write a paragraph to explain the contribution

Collect results from 2 or 3 groups in your class present the data in tables and plot graphs of all the data.

Evaluate the limitations, weaknesses of the experiment and your data and suggest ways to improve the experiment.