The reason why an increase in temperature causes an increase in the total concentration of pigment that has been released, is due to the workings of the cell membrane itself. Membranes are composed of lipids (more often known as fat). Lipids compose the main bulk of membrane mass, so what happens if you heat fat up? Think of melting butter, this is mostly fat, and consequently melts when you heat it up. Likewise with a membrane, when you heat them up they consequently loose their structure. Membranes obviously have lots of proteins in them as well, they are much less stable over a range of temperatures than lipids. That’s' one reason why many organisms live only at certain ranges of temperature and why organisms like us maintain a constant body temperature, so proteins will be relatively stable. In addition to proteins, the membrane is in part 'held' together by interaction of proteins and lipids in the membrane with the cell's cytoskeleton (microtubules and filaments). These fall apart also as temperature is raised and therefore the cell structure is damaged resulting in greater permeability. This greater permeability will henceforth let more beetroot pigment diffuse through the membrane and into the surrounding solution. So the reason the membrane becomes permeable as the temperature is increased is because it is falling apart. There's no semi-rigid structure packed tightly together like there is in an intact membrane.
For the definition of osmosis, whereby water flows from an area of high concentration to an area of low concentration through a semi-permeable membrane, it is appropriate to make use of it in this situation. This means that as the water flows into the beetroot cells, they become turgid, then as excess water flows into the cells, the cell bursts releasing the pigment into the water. The higher the temperature the faster the water molecules move because they have more kinetic energy thus the process occurs faster and effects more cells. It is worth mentioning that as the temperature increases by every 5 degrees, denaturisation is having more of an impact, as the percentage of absorption in the colorimeter increases. It was important to have washed the beetroot before carrying out the experiment, in order to wash out pigment from the cells that were damaged when using the cork borer and knife.
For this experiment to have been more successful then the variables would need to be kept more constant, although this is incredibly difficult to master, so it is not really an option when trying to improve upon the investigation. A good way to help make the experiment more worthwhile is to attempt each temperature several more times to ensure that you get a more reliable result, which you can also work out an average figure. The anomaly was the sample placed in the fridge, which seemed to give a rather large percentage of beetroot pigment concentration, due to the fact that the cell membrane could not work at such a cold temperature, and therefore the pigment was easily diffused. As an overall conclusion it is acceptable to establish the fact that as the temperature is increased the permeability of the cell membrane increases resulting in more beetroot pigment diffusing into the surrounding solution. This then causes the percentage of absorption to increase as well, which is measured using the colorimeter. The beetroot pigments incidentally are anthocyanins, it is soluble in water and OH- ions, but not chloroform and paraffin oil, this means that even when the cell membrane is damaged, the red pigment will not diffuse out into the chloroform or oil.
Evaluation:
If you look at the results in the above table you can see that for the samples measured at 35 C and 40 C there is a slight error. The percentage of absorbance at 35 C was 0.15%, whereas at 40 C it was 0.14%. This has to be an anomaly as well, as it does not conform to the general overall pattern. This slight inaccuracy is probably due to either the water bath not being at the correct temperature, but this is probably not the reason as a thermometer was used in the water baths for insurance. This slight error could also be a result of the person themselves, in this case me, as I may have left the sample in the bath for the wrong amount of time, or I could have easily misread the colorimeter reading. It is not certain why this inaccuracy occurred but as the difference is so small, it is not a major problem. I have also taken into account the difference in absorbance between each sample, as there is no distinct trend here. I have included a table of the absorbance difference as follows;
Temperature ( C) Difference in absorbance (%)
fridge 0
30 -0.18
35 0.07
40 -0.1
45 0.04
50 0.03
55 0.02
60 0.02
65 0.13
70 0.03
- 0.05
As you can see there are some distinct similarities betwixt these figures, but also some differences. Excluding the fridge sample and the small error between 35 and 40, you can see that an increase of about 0.02% - 0.03% is common across the board, but there with one exception, and that is the difference between 60 C and 65 C. The difference here is much larger, a clear source of error, but to be quite certain of this, I would have to carry out another test. This concept of error is quite interesting and would be worth having a closer look at. Another matter to take into account is the water baths themselves, the temperature although being measured by a thermometer and a digital reading, it could be for example at a temperature of 35.4 C, but be rounded off to 35 C. This minor judgement will probably have little effect upon the overall result. One of the main sources of error is mostly due to the beetroot itself, they are all cut into relatively the same dimensions, but this could have an effect, due to the idea that if the beetroot is bigger then it has more surface area and will hence release a greater amount of beetroot pigment.
DUNCAN BEARD
