♦The amount of time the pieces of beetroot are in the water baths, as different lengths of time will change the amount of dye released.
Other variables which I am aware of but do not need to be controlled in this particular experiment are:
♦The pH level of the beetroot. If I needed to control the pH of the beetroot then I could do so by using a pH probe at various times throughout the experiment.
♦The amount of oxygen available
♦The passage of ions
♦The amount of mitochondria in the cells
I will not need to control any of the above variables, as they will be the same throughout my experiment.
To make my experiment fair I will be controlling the variables I need to control as well as doing the following things:
♦I will leave the boiling tubes of water in the water baths for 5 minutes before I add the beetroot pieces to them, so that they have reached the required temperatures.
♦I will leave the boiling tubes containing water and beetroot in the water baths for 30 minutes, so that they all have had a chance to release dye.
♦I will measure the water/solutions I am using from the bottom of the meniscus at eye level, so that I get accurate readings.
♦I will do three readings for each temperature and then repeat the whole experiment twice so that I have done it with three different beetroots.
♦I will be using a colorimeter to measure the light absorbency of the pigment, in order to tell me how much dye has been released, as this is more accurate and precise than comparing the amount of dye released with my eyes. This will reduce the chance of human error as well as giving me a set of quantitative data.
♦Instead of using a thermometer to measure the temperature of the water baths, I will be using a temperature probe. This will give me a set of reliable results as it will stop any chance of systematic errors and reduce the chances of human error.
♦To measure the diameter of the pieces of beetroot I will not be using a ruler. Instead I will be using a vernier calliper, as this will measure the beetroot accurately because I can place it right up to the edge of the beetroot. This will stop any systematic errors from occurring and will reduce the chances of human error.
Apparatus:
♦Raw beetroot-To measure the effect of temperature on membrane structure on.
♦Size 4 cork borer-To accurately cut sections from the beetroot
♦A white tile-To cut the beetroot on so the workbenches are not stained or damaged.
♦A knife-To cut the beetroot into smaller bits once you have cut it into sections.
♦A vernier calliper-To accurately measure the diameter of the beetroot
♦Water baths at roughly 20°c, 30°c, 40°c, 60°c and 70°c-To measure the effect that temperature has on the amount of dye released from the beetroot.
♦5 boiling tubes-To put the water and beetroot in.
♦A temperature probe-To measure the temperature of the water baths.
♦A colorimeter-To measure the amount of light absorbed by the beetroot pigment.
♦Cuvette’s-To put the dye solution in.
♦A stopwatch-To measure the amount of time the water and beetroot has been in the water baths.
♦Distilled water-To put the beetroot in.
♦Pipette-To measure 2cm³ of the dye solution.
♦Small measuring cylinders-To measure the amount of distilled water.
Diagram:
Method:
First cut up sections of a beetroot using a size four cork borer. Now cut eight, 1cm length slices from these sections, making sure you do not spill any beetroot juice on your skin or clothes. Weigh each beetroot section to make sure they all weigh the same. Once you are sure they do, pour 5cm³ of distilled water into 8 labelled boiling tubes and place these into water baths at roughly 20°c, 30°c, 40°c, 60°c and 70°c. Leave for 5 minutes and then using your temperature probe measure the temperature of the water in each boiling tube. Now write these temperatures into your results table. Next place one of the beetroot sections into each boiling tube and leave in the water baths for exactly 30 minutes. When the 30 minutes are up remove the boiling tubes from the water baths and put them into a boiling tube rack. Now remove the beetroot sections and shake each boiling tube gently to disperse the dye. After you have shaken all eight boiling tubes switch on the colorimeter, set it to read % absorbance, and set the filter dial to the blue/green filter. Next use a pipette to measure 2cm³ of distilled water into a cuvette, and place the cuvette into the colorimeter making sure that the light is shining through the smooth sides. Now adjust the colorimeter to read 0 absorbance fir clear water, and do not alter the setting again during the experiment. After removing the cuvette with clear water, place 2cm³ of the dye solution into a colorimeter cuvette and take a reading for absorbency. Write this result into your results table. Now repeat these readings for all of the temperatures, making sure you write them into your results table. Finally repeat the whole experiment at least once more with another beetroot.
Results:
A results table to show how temperature affects the release of dye from beetroot one
A results table to show how temperature affects the release of dye from beetroot two
Conclusion:
By looking at my graph I can see that as the temperature increased, the amount of light absorbed by the pigment in the beetroot also increased. I can also see that my results were fairly accurate as my range bars were quite small, meaning that my results were consistent. The aim of my experiment was to see whether temperature affects membrane structure and my results show that it does. The higher the temperature the more the membrane structure broke down meaning that more dye was released from the beetroot.
My results prove my null hypothesis is incorrect, meaning my alternate hypothesis is correct. An increase in temperature does cause an increase in the amount of dye released from the beetroot. This is because heat denatures the phospholipids bilayer, so the betalain in the vacuole (the pigment) is able to diffuse out of the bilayer.
Evaluation:
My results are fairly accurate and this is shown by the closeness of the two sets of results, which where taken from different beetroots. My range bars on my graph also show this as they are quite small meaning that there wasn’t a big range in my results. I don’t seem to have any anomalies, however the result for 60°C for beetroot one is very high. This could be because I may have left the beetroot in the distilled water for longer after it had been taken out of the 60°C water bath, as I had to take each piece of beetroot out and this took me a little while. It could also be because the temperature may have fluctuated slightly over time meaning that the water bath wasn’t exactly the same temperature throughout the experiment.
The procedure I used was quite good, however if I were to carry out the experiment again I would carry out it out on three different beetroots. I would do this because when you use two sets of data either one could be a ‘fluke’ so by using three you can definitely see that your results are reliable.
Further work I could do is to see how pH level affects membrane structures. To do this I would leave the beetroot in different pH’s for 30 minutes and then use a colorimeter to measure the light absorbed by the dye that has been released from the beetroot. Other further work I could do is to see how surface area affects the amount of dye released. To do this I would change the surface area of the beetroot pieces and put them in different temperatures. This would allow me to have confidence in my results, as I would have backed them up with some more data. It would also allow me to further test my hypothesis.
Summary:
I have proved my alternate hypothesis correct as an increase of temperature breaks down the membrane structure causing an increase in the amount of dye released from the beetroot. My results are fairly accurate as I followed my plan precisely and made adjustments where necessary.
