Plan
Because we are experimenting with the effects of temperature on the membrane, samples of beetroot must be placed into water baths of varying temperatures. After this, the beetroot must rest in water and then % transmission of the water measured with a colourimeter. Although temperature is going to be the variable in this is experiment, it is just one of many possible variables. The integrity of the cell membrane can be tested using poisonous substances such as alcohol and other various solvents. The dependant variable in this experiment is colour change in water caused by betalain leakage. The dependant variable in this experiment is the colour change in the water caused by betalain leakage. In order for this experiment to be done, the following equipment is needed:
1xbeetroot, plant corers, white tile, heat proof mat, Bunsen burner, tripod, gauze, beaker, thermometer, 5 test tubes with a test tube rack, a colorimeter, 5 test tubes with a test tube rack, tongs and stop-watch.
Hypothesis
I believe that the higher the temperature that the beetroot is boiled at, the more dye will be released and therefore the lower the % transmission on the colourimeter will be. This is because at higher temperatures, protein denaturing will occur and the cell membrane will have large holes in it, which will let betalain out and will colour the water and increase the opacity of the water.
Method
Preparation: Before the experiment was started, the beetroot was prepared. Firstly, the white tile and corer were used to cut cylinders out of the beetroot (note: the same diameter corer was used for all the pieces so keep the surface area of each beetroot piece fairly similar so only one corer was needed). Five uniform cylinders were cut from the beetroot, trimmed to a uniform length and collected in a beaker of water. As the beetroot was cut, some of the outer cells membranes had been ruptured meaning that some of the betalain dye leaked out (as seen by the red dye on the white tile). This external dye had to be washed off in order to maintain the reliability of the results. This was done by leaving the beaker of beetroot cylinders in a running water bath over night.
Diagram: After the preparation, the apparatus was set us as below.
Main Experiment: A water bath was made using the beaker and water. This bath was heated to 85oC using the Bunsen burner. Once the water bath reached 85oC (measured using the thermometer) the Bunsen burner was turned off and the water bath allowed to cool. When the bath dropped to 80oC one piece of beetroot was placed directly into the hot water and left in for exactly 1 minute (timed by the stop-watch). When the minute was up, the beetroot cylinder was removed using the tongs and placed into one of the 5 test tubes along with some water to just cover the cylinder. The water bath was cooled to 70oC and the procedure repeated. This procedure was repeated with the other four cylinders of beetroot with varying water bath temperatures. The temperatures used were 60oC, 50oC and 40oC.
Colourimeter: The fluid in each of the test tubes will be analysed using a colourimeter and compared against the control (distilled water). The results were recorded.
Results
Conclusion
As we can see from the results, the hypothesis that I stated earlier is correct. This is because the graph shows that with increased temperature, there is decreased transmission in the solution that implies that more dye has been released as more cell membranes were been ruptured. This is because with increased temperature, more cell membranes were denatured which caused the cytoplasm and other substances in the cell such as the dye betalain in the vacuole to leak out.
The results decreased fairly smoothly with the exception of the cylinder which was heated at 60oC where the % transmission is too high, which shows that the amount of betalain actually reduced (which is incorrect). This anomalous result is due to experimental error, which I will talk about in my evaluation.
The betalain is released from the cells because phospholipids that make the cell membrane break down, which causes gaps to appear in it. These gaps allow fluids such as betalain to pass out freely into the cells surroundings (in this case water). However, when the temperatures increases to around 60oC, the proteins in the cells begin to denature, which blocks some of the holes created in the first place. This naturally slows down the release of betalain. This effect may have produced the ‘anomalous’ result at 60oC.
Evaluation
As there is an anomalous result at 60oC, it is possible to assume that the experiment could have been done more accurately. There are several ways which this could have been achieved.
Firstly, the results could have been made more reliable by repeating the experiment (triplicates), and also by taking more measurements (10 rather than 5).
The results could also be made accurate in several ways. Firstly, the beetroot cylinders were not cut accurately, but only estimated. If the beetroot was cut more accurately, there would be a similar surface area on each cylinder and each cylinder would have the same potential to release betalain.
Also, if the same volume of water was used to bathe the cylinders on each occasion (about 10ml), the amount of betalain released by each cylinder would be diluted equally and thus producing fair readings on the colourimeter. Also, the cylinders were left to stand for different amounts of time. For example, as the 80oC cylinder was done first, it was left to stand for the longest period of time, however the 40oC was left to stand for a very short period of time. In the future, the amount of time the cylinders are left to stand for should be measured (30 minutes seems like a good amount of time).
If the colourimeter used was digital (not analogue), the reading of the % transmission could have been measured more accurately.
