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ICT IN BIOLOGY
MEMBRANE INTEGRITY IN RED CABBAGE LEAF
CELLS
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.
What will be the effect of heat on the membranes of
red cabbage tissue?
MATERIALS
- Computer with Logger pro installed
- Lab Pro interface
- Colorimeter sensor
- 10 cuvettes and caps
- Electronic water bath
- Thermometer or temperature probe
- 10 test tubes in a rack
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- Test tube holder
- 10 cm3 syringe
- 1cm diameter cork borer
- Red cabbage
- Distilled water
- Marker pen
- Dropping pipette
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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.
- the tubes in the water bath
and set the temperature to 40°C. When the temperature
reaches 40°C remove a tube. Monitor the temperature of the water using a
thermometer or a temperature probe. 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 (about 2/3rds full). 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.
Starting the DataMate Program and calibrating the
sensor
KEEP YOUR LIQUIDS AWAY FROM THE COMPUTER AND ITS MOUSE
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Connect the LabPro interface to the mains via the mains adaptor. Connect the
LabPro to the US-B socket of the computer.
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Plug the colorimeter probe into channels
CH 1on the LabPro interface.
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Start the Logger Pro program.
Logger Pro will detect the
auto-ID sensor, set the data collection parameters, and display the current
sensor reading.
Remove the graph window leaving the data set spread sheet alone.
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Click on Setup
icon to open the data collection menu. Select Mode
and choose Events with entry.
The Column entry is
Temperature and the
Unitsare
°C
Click Done.
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To calibrate the colorimeter set up a blank tube
containing distilled water. Select the appropriate light source. Remember red
cabbage is purple. This is the light that is transmitted. You want to choose a
wavelength of light that is absorbed by the liquid.
Press the calibration button
on the colorimeter probe. A LED will flash on the colorimeter to show it is
calibrating.
Collecting data
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Put a cap on the cuvette with the first sample. Set the
cuvette in the colorimeter, take care not to touch the sides where the light
will pass.
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When everything is ready:
Select Collect (the green arrow) to begin data collection.
Click on the wheel symbol Keep current value. Enter the temperature the
sample was heated to and click Done.
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Remove the cuvette and replace it with the next. Collect
the data for every 5°C from 40 to 80°C. The data will appear in the spread
sheet of the data set. Click on Stop to end the data collection.
DO NOT LEAVE THE LAST CUVETTE IN THE COLORIMETER
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Copy the data set. Present your data in an appropriate
way, process the data to determine the effect of temperature on the
membranes of this tissue. Discuss and evaluate your results.
Trouble shooting
If you get readings that appear strange or impossible try the
following:
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Check the liquid that you have sampled. Is it homogeneous
and transparent?
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Check the cuvette that you are using is not dirty or wet
on the outside.
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Check the cuvette holder in the colorimeter. Is it clean
and dry?
| Note: You should try to keep your
results between 0.050 – 0.550 absorbance. Outside this range the
calibration curve is not linear. If your results are outside this range
try a different wavelength (light source) or the liquid may need
diluting by a known factor. |
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