Variables
Variables, which could affect my collected data include:
- When cutting beetroot into 1cm strips using a ruler may not be accurate enough.
- The amount of distilled water the beetroot is left in could effect how much dye is released over night, affecting the experiment.
- There is a certain degree of inaccuracy with measuring 5cm³ and 2cm³ by eye.
- Temperature in water baths should be kept constant.
- The time each test tube spends in each water bath should be kept equal.
Independent Variables
My independent variable will be the temperature to see what effect this has on the membrane structure of beetroot causing it to release dye into the distilled water. I am going to be able to control this variable by using water baths set at certain temperatures and leaving thermometers in the water, I will make regular check to make sure that the water temperature is staying constant.
Constant Variables
As much as I can I will make sure my experiment is a fair test and that each beetroot strip is cut accurately that each are kept under the same conditions until the experiment and that time keeping is done so that each have equal opportunity to release the dye into the water.
Equipment
To heat up my section of beetroot I am going to place them in the freezer, fridge, in the room, at 50 C and 70 C. The two above room temperature will be put in water baths, this will enable me to keep them at a constant temperature and is a far more accurate way to do this than heating them for example with a Bunsen burner. I am going to use a colorimeter to measure the change in colour from ordinary distilled water to the different concentrations of beetroot juice. The piece of equipment measures to an accuracy of 0.005 and so my results will be quite reliable from this perspective. My results will therefore be quantitative but measuring a qualitative colour change.
Fair test
I have been as careful as possible when measuring and timing to make sure that my results are reliable. To improve on the accuracy I could use a laser cutter to cut the beetroot and a weighing scale to measure the amount of distilled water to get my results more accurate.
Safety precautions
During this experiment I have use a cork borer, a knife and water baths measuring 50 and 70 Centigrade in temperature. To ensure I cause no harm to others or myself, I cut the beetroot on a tile on the desk, whilst standing up. I also made sure no bags or books were on the floor in case I tripped with the glass beakers. When putting the test tubes in the water baths I held the top carefully and securely to ensure I didn’t touch the water.
Results
After leaving the test tubes at different temperature for 30 minutes I took them out if their locations and took a sample of 2cm³ and placed it in the colorimeter. I repeated my experiment 3 times as this will ensure I can work out an average for the 3 results and plot the average reading on a graph, this way my will be more valid.
To ensure I collected the most accurate results possible I used the correct measuring instruments for each measurement, although they all have a certain degree of inaccuracy the equipment for instance my pipette, was 5cm³ and I used this for the measuring of 2cm³ and 5cm³ as this is more accurate than using a 10cm³ pipette.
These are the results I have collected for each of the experiments I carried out
This is a graph to show the results for the average leakage of dye.
My null hypothesis was; that the temperature will have no effect on the amount of dye, which is released from the beetroot. As you can see from the graph there was a variation in colorimeter readings and so as temperature was the only variable in my experiment it must have had an effect.
From the chart you can see that my results are reliable, fairly precise and quite accurate as they are not all in the centre but in the same area.
Discussion
My results prove that my hypothesis was correct and that temperature has an effect on the amount of dye released from beetroot. The graphs show that as the temperature increased more dye leaks out.
I know that the trend of the data is correct because when you heat a beetroot, you disrupt the cell membranes, which are made up of a phospholipid bilayer. These are formed because the phospholipids that make it up have a polar "water-loving" (hydrophyllic) head and a “water-hating” (hydrophobic) tail. The tails pack together, exposing only the polar heads to the water. In a cell they form sacks; one goes all around the cell (the plasma membrane), others may form vacuoles. In these lipid seas, there will be a number of proteins in various degrees of submersion. Some span all the bilayer, thus being exposed on both sides. Others just drift on either of its surfaces. Typically, you will find that about 70% of a cell membrane is protein, they're formed of coiled and folded strings of amino-acids, held together by hydrogen bonds and disulphide bridges. If you heat them too much, they will untangle and break apart. When this happens to the proteins spanning a lipid membrane, they will form holes that will destroy the delicate structure.
The water around the and within the compartments formed by the phospholipid bilayers is also crammed with protein (cytoplasm). When you heat the bilayer the molecules behave like any other and start to spin and vibrate faster. The water will expand too, causing a disruptive effect on any membrane in its way. To make things worse, lipids become more fluid as temperature goes up so the membranes become more fragile. This is why 70 C has a more drematic effect on the amount dye leak out than the others.
My results have a particular flaw. I placed one of my samples in the freezer, instead of providing me with a slow or no dye leakage it produced the highest colorimeter reading. This is because freezing the beetroot first bursts the cell membranes as the water inside expands and then kills the cells, allowing the pigment to be extracted much more quickly.
Errors that may have occurred in my practical are the measuuring of the different components.
From the table you can see that the majority of the equipment was to a high standard of accuracy and so my results can be relied apon to be fairly certain representative of events.
The main limiting factors of my results was not enough different temperatured water baths if more had been tested I could have been more able to come to a valid conclusion as the trend would be more sound.
Summary
In this experiment I tested the effect different temperature had on the permeability of a beetroot membrane structure. I found out that as the temperature increases the more dye leaks out due to the bonds vibrating in the structure. This breaks apart the phospholipid bilayer creating larger holes in the membrane substainsial enough to allow the red pigments called betalains in the cell vacuole that do not normally pass through the membrane.
References
As Unit 1 book (See for detailed method)
