MPI

Red cabbage leaf epidermal cells are pigmented purple with anthocyanins. The pigments are held in their sap vacuoles. If the membranes of the cell are damaged these pigments will leak from the cell.

Heat will denature proteins, including those in the cell membranes. At what temperature do red cabbage cell membranes breakdown?

Materials

Method

Cut discs from the red cabbage and select 30 which are of uniform thickness. Place three discs in each test tube and add 10cm3 of distilled water to each tube.

Put the tubes in the water bath and set the temperature to 40°C. When the temperature reaches 40°C remove a tube. Continue raising the temperature and remove a tube at 5°C intervals.

Suck up liquid from a test tube and fill a colorimeter cuvette until it is 1 cm from the top. Wash the pipette, take a sample from the next tube and fill a fresh cuvette. When labelling the cuvettes mark one side only near the top. Handle the cuvettes near the top too.

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Starting the DataMate Program and calibrating the sensor

1.      Use the following steps to start the DataMate program on your calculator: Press (for TI-73, 82 and 83 press ), then press the calculator key for the number that precedes DATAMATE. Press . An introductory screen will appear, followed by the main screen.
2.      Plug  the colorimeter probe into channel CH 1 on the CBL2 interface.
3. Start the DataMate program. Press to reset the program. DataMate will detect the sensor and display the current sensor reading.
4. To calibrate the colorimeter set up a blank tube containing distilled water. Select the appropriate light source (remember red cabbage is purple) and press the calibration button on the colorimeter probe. There are four light sources to choose from: red (635nm), yellow (565nm), green (470nm) and blue (430nm).
5. Using the cursor buttons,  or  (be patient it’s a bit sluggish!) select MODE, press (scroll up to get to the last item on the menu).
6. In the SELECT MODE menu press : EVENTS WITH ENTRY
7. Press : OK to return to the main screen.
Collecting data 1. Set the cuvette with the first sample in the colorimeter, take care not to touch the sides where the light will pass.
2. Select : START to begin data collection. Press to record your measurement. When you are asked to enter value, enter the temperature of your first sample. Press again.
3. Place the next cuvette in the colorimeter and press . Then type in the next temperature. Press again and you will find the calculator producing an autoscaled scattergram of the measurements.
4. Continue to take measurements of all your samples.
5. You may stop data collection at any time by pressing the key. Remember for line graphs you should have at least 5 data points (10 is even better). When you stop data collection  you will see the complete auto-scaled graph.
6. To store your data, if you are satisfied with it, return to the main screen by pressing Press: TOOLS, then select : STORE LATEST DATA RUN. This stores the data in lists. In this case “temperature” in L1 and the colorimeter “absorbance” in L2 with a copy of it in L3. To check this press : QUIT, then , then and, finally, select : EDIT… You will see a spread sheet with your data in it in L1, L2 (and L3).

Trouble shooting

If you get readings that appear strange or impossible try the following:

(a)   Press and reboot the Datamate program.

(b)   Check the liquid that you have sampled. Is it homogeneous?

(c)   Check the cuvette that you are using is not dirty or wet on the outside.

(d)   Check the cuvette holder in the colorimeter. Is it clean and dry?

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