This table shows the variables that I will control in order to keep the experiment a fair test:
Equipment
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Raw beetroot provides betalains
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Size 4 cork borer cuts beetroot into precise cylinders of the same diameter
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White tile protects desk when beetroot is cut
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Knife cuts beetroot into 1cm pieces
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Ruler (with 1mm intervals) measures 1 cm pieces of beetroot
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Constant temperature water baths with thermostats set to 20, 30, 40, 50, 60 and 70°C provide constant temperature for water surrounding beetroot
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Boiling tube rack holds boiling tubes while pipette is filled
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6 boiling tubes hold beetroot and surrounding water
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Thermometers (100°C) check temperature of water baths
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Colorimeter (and cuvettes) measures colour of water objectively
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Stopwatches monitors time beetroot has been heated
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Distilled water allows betalains to diffuse out of beetroot
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5cm3 pipette (and filler) measures solution for cuvettes
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10cm3 measuring cylinder measures distilled water to surround beetroot
Method
- Using a size 4 cork borer, cut sections from a raw beetroot. Cut each section into 1cm lengths, discarding the skin.
- Allow the beetroot pieces to soak in distilled water for 5 minutes, then drain them, refill with fresh distilled water, and allow to soak for another 5 minutes to wash off surface betalains from damaged cut cells.
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Using the measuring cylinder, place 5cm3 distilled water in each boiling tube, and place each boiling tube in a different water bath. Leave until the distilled water has heated to the correct temperature.
- Add one piece of beetroot to each boiling tube and start the stopwatch. Leave for 30 minutes.
- Remove the beetroot piece and shake the solution to disperse the dye.
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Calibrate the colorimeter to read 0% absorbance with a cuvette filled with 2cm3 distilled water, measured out with the pipette.
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Measure out 2cm3 of each of the beetroot pieces’ water into separate cuvettes, and take a reading for % absorbency.
Ethical issues
There are no ethical issues related to this experiment as no animals are being used.
Safety issues
Using the cork borer and knife presents a risk of cutting oneself, so care should be taken not to slip with these pieces of equipment, and a white tile should be used.
Glassware is being used in this experiment, so if it chips or breaks, it will be swept up with a dustpan and brush and disposed of in a broken glass bin.
If water is spilt, it will be mopped up with tissue. If it is hot, it will be allowed to cool until it is safe to touch before being mopped up.
Results
Conclusion
My results fit with my hypothesis (although we did not manage to do the experiment at 70°C). This is because extra heat energy given to the beetroot by the water causes the channel proteins in the cell membrane and tonoplasts to de-nature and therefore malfunction, letting more of the betalain pigments diffuse into the water. However, my graph did not seem to level off
However, the pattern changes after 60°C. This could be an anomaly, if the water bath had been set at the wrong temperature so everyone had an increased absorbance, or because the rate at which the betalains break down is greater than the rate at which the increased number of betalains leaked out above 60°C.
The half-life of betalain pigment is 413 minutes at 25°C but only 83.5 minutes at 60°C.
Beetroot Pigments and Membranes – Ian White, Godalming College, 2003.
This could mean that even though more betalains were leaked, some broke down before we tested the absorbance.
Evaluation
As the beetroot at 70°C was not in a water bath – the test tube was placed in a beaker of water which had to be topped up with boiling water if it cooled down – the temperature was not kept constant. This will have affected the results, as the hydrogen bonds in the carrier bonds may have re-broken and re-formed many times. This probably meant the results for the absorbance were too low, since the hydrogen bonds reforming would restrict the diffusion of the betalains.
The beetroot pieces were left in the water for different times, since only one cuvette of solution could be tested at any one time. This will also have affected the results. The higher temperatures were left in for longer, so the percentage absorbance is probably too high because of this factor.
The use of the ruler incurred a 5% error when measuring 1cm pieces of beetroot. This was unlikely to have heavily influenced the results. Measuring out the 5cm3 distilled water carries an error of ±0.05cm3. This is a 10% error, which may have affected the results by making the solution either too dilute or too concentrated, which in turn would have made the percentage absorbance either too high or too low.
References
Beetroot Pigments and Membranes – Ian White, Godalming College, 2003.
Y12 practicals help sheet – G Hartland and A Warrick, September 2006