Each time a piece of beetroot is removed from the heated water, it will be left in the distilled water for exactly 30 minutes, before being discarded.
The fluid in each of the test tubes will be analysed using a colorimeter and compared against the control, which is distilled water to check for any variations in the colour of the water.
The variables kept constant
∙ The same diameter corer is used so to keep the surface area of each beetroot piece the same size.
- When the beetroot has been cut some of the cell membranes are broken, which means some anthocyanin will leak out. This must be completely washed off in order to maintain the reliability of the results.
- I will use distilled water to so that I have a reliable substance to test with a colourimeter.
Results Table
To be added as I can't do one on my computer ( not good enough software)- I will use a computer at school.
Analysis
The reason why the amount of betalain pigment released (colourimeter reading) from the vacuole increased directly proportionally to the temperature of the water bath (from 20oC to 40oC) is because the amount of random movement of betalain molecules out through the cell membrane depends on the amount of heat energy the betalain molecules are given to convert into kinetic energy- hence the higher the temperature the more betalain lost from the vacuole.
This is because the betacyanin pigment of beet root cells is normally sequestered in the vacuole and by means of the cell membrane which maintains the integrity of the cell and the tonoplasts, it does not leak into the cytosol or the extra-cellular sap of the beet root. However when we increase the temperature the relatively weak forces holding the different parts of the polypeptide chains together (like hydrogen bonds, sulphur bridges and ionic bonds) can be disrupted very easily- this damages the vacuole and makes holes in the cell membrane, inducing leakage.
The cell membrane is also damaged and so diffusion of betalain occurs through the partially permeable membrane by osmosis- the betalain molecules move by diffusion from an area where they are more highly concentrated to an area where they are at a lower concentration, along a concentration gradient.
The reason why the amount of betalain pigment increases rapidly (from 40oC to 60oC) is because most mammalian protein's denature and tertiary structure unravels (the strong covalent bonds between the R groups of amino acids in the polypeptide chains are destroyed) at temperatures over 40oC.
The reason why the curve starts to flattens out (between 60oC and 80oC), is because although the denaturing of the protein causes a rapid rise in the amount of betalain released to start with, when the temperatures begin to get higher still, the protein's tertiary structure blocks some of the holes in the cell membrane and therefore slows down the release of betalain.
Evaluation
There were a number of sources of error that may have affected the accuracy of my results. Firstly I had one stopwatch and timed all the water baths for fifteen minutes, so was a slight delay however between the placing of the tubes in each water bath, as I had to walk to each water bath so it would have affected my reults slightly. This would only have had a small effect on my results, because the vacuole of the beetroot would have only released slightly more betalain, as the molecules would have only had a very small amount more heat energy to convert into kinetic energy.
Secondly I when I washed each of the beetroot pieces I may not have removed all of the red pigment on the outside, so this would have affected my results very slightly. Again this would only have had a small effect on my results, because a very slight increase in betalain molecules would not have changed the reading on the colourimeter.
There were also limitations of my experiment. Firstly I only had an hour in which to conduct my experiment- this did not give me time to collect a suffient number of results. A larger number of results taken at different temperatures between 20oC and 60oC would have allowed me to find out more accurately where the point of denaturation occured.
It would also have been better to have had the time to repeat each temperature more times to make the results more reliable and so I could be sure the results were not gained through chance. This may have eliminated my anomaly, but I did repeat the experiment twice and the two results on each temperature were almost identical, so this would have had very little effect on the accuracy of my results.
Another limitation was cutting the beetroot into pieces. The pieces cut had roughly the same surface area to volume ratio- but not exactly the same. This would have had a slight effect on my results because the rate of diffusion of betalain particles across the plasma membrane is increased, as the surface area of the beetroot increases. So the slightly thinner and smaller pieces of beetroot I cut would have released more betalain from their vacuole.
I only looked at one type of plant cell, so I can not be sure that every plant cell and indeed eykaryote- which have different plasma membranes, that may be adapted to cope with heat better or worse than beetroot cells willl have the same results.
I can firmly conclude that there are no apparent anomalies in my results and none of my sources of error or limitations of my experiment are enough to deem my results unreliable. However the sources of error and limitations in my results may have made my results slightly less accurate, but other students in my class found the same patterns occuring and roughly the same results- which would vary slightly between each beetroot anyway.
