Aim
The aim of this experiment is to either or both the cytoplasm and the cell wall of a plant cell are selectively permeable, to discover at which temperature the permeability of the cell membrane is affected and how much it is affected.
Pilot study
Before doing the actual experiment I did a pilot study to make the final decisions as to the temperatures I was to use, the amount of beetroot and the amount of time it would be exposed to these temperatures, and also the equipment that would be needed.
The pilot study showed that although there was a lot of spare time while the beetroot was left standing after they had been exposed to these temperatures, there is a rush to make sure they are all put in the water at close proximity. This made it clear that when I do my final experiment I must prepare everything before beginning, from slicing and counting the beetroot to putting the right amount of water in each test tube.
Having done the pilot study, it made me alter some of the measurements for each factor. Initially, I was going to start the temperature of the water baths at thirty Degrees Celsius, but this seemed unnecessary as a temperature this low had no effect on the permeability of the cell membrane, so I changed the temperatures to a smaller range Originally I was going to use six discs of beetroot and six milliliters of water but I have now decided on five discs of beetroot and five milliliters of water in each test tube. This merely simplifies the numbers to make the experiment easier to do and therefore improving the chance of accurate results.
Hypothesis
I predict that my results will support the theory that it is part of the cytoplasm, rather than the cell wall that selectively permeable. I believe that the temperature will have to be reasonably high (at least over fifty-five Degrees Celsius) before there is a great change in the permeability of the cell. After this point the permeability will worsen and the cell membrane will have lost its selective permeability.
Plan
Before beginning the experiment I will set up all the apparatus carefully and precisely. I will set up six test tubes all containing five milliliters of water, (by using a graduated pipette) and put them into a test tube rack. I will label each test tube according to the temperature that the beetroot has been exposed to. I will also measure the temperature and pH of the water to ensure that the variables are kept constant and it is a fair test.
I will prepare the water baths, keeping them at a constant temperature top insure the accuracy of the experiment. There will be six water baths of different temperatures, fifty Degrees Celsius, fifty-five Degrees Celsius, sixty Degrees Celsius, sixty-five Degrees Celsius, seventy Degrees Celsius and eighty Degrees Celsius. To avoid the temperature of the water baths falling I will place tin foil over them to keep the heat in.
I will slice all the beetroot and place them onto the mounted needle. When slicing the beetroot I will ensure that each slice is exactly the same so that there is no increase in surface area as that could alter the experiment. To do this I will use a cork borer to cut the diameter of the cylinders, and a ruler and scalpel to cut the width, which will be about three millimeters thick.
I will then place these discs (thirty altogether) into a petri dish full of water, wash them and then leave them for about five minutes. This is because when the beetroot is cut, it will cut through cell membranes, this will mean the contents of the cell will leak out. The pigment will leak out and then show up on the colorimeter, it will be mistaken for pigment leaked out due to the distortion of cells because of temperature. Therefore it is important that this is washed off so that the only pigment recorded is that which has been freed because of the high temperatures.
Once the beetroot has been washed I will impale five discs, evenly spread onto a mounted needle and line them up ready to begin the experiment. Then all the preparation will be done and the experiment is ready to begin.
I will place the mounted needle into the first water bath, making sure that all the slices of beetroot are covered. I will set a timer for two minutes and once the timer goes off I will taker the mounted needle out and place the beetroot in to the appropriate test tube. I will then continue to do this with the other five water baths as quickly as possible, afterwards placing the beetroot in to the beaker according to which temperature it was exposed to.
I will then leave the beetroot to stand, in the water for twenty minutes so that the pigment can diffuse throughout the water. Once the twenty minutes is up I will place some of the liquid from each test tube into a vial and then put it into the colorimeter, which will give me a reading for each test tube. To make the readings as accurate as possible, before putting each vial into the colorimeter I will put an empty one in and make sure that it reads zero so that I know it is working correctly.
When doing this experiment I shall follow all the regular lab rules, this includes wearing a lab coat and lab specs, taking great care when cutting the beetroot and when handling hot water.
Results
Experiment 1
Experiment 2
Experiment 3
Analysis
These results, both in the tables and on the graph show that as the temperature increased the Color percentage went further and further down. This means that as the temperature increased the less transparent and the more pigment the water became. Therefore each time the temperature was increased the plasma membrane’s permeability worsened and became less selective. This theory was supported by the group results.
As I stated in my hypothesis, there was not a very noticeable decrease in the permeability until the temperature reached sixty degrees Celsius, however it was at seventy that it plummeted, decreasing as much as forty-nine point six from sixty-five degrees Celsius. This shows that this was the point at which the protein cell became so denatured that gaps occur in the lipid layer creating space for a great deal of diffusion.
The graph is beginning to illustrate a pattern in which suggests the percentage of transparency is directly in proportional to the increase in temperature.
Evaluation
Although this experiment did contain some errors and areas that have some room for improvement I believe that on the whole these results are accurate and reliable. They give a clear idea of effect of temperature on the permeability of the plasma membrane, which I believe to be a productive experiment.
If I were to repeat this experiment I would cut out some of the errors that were made to make it more accurate. Some of which were human errors, for instance in timing the amount of time in the water bath, the amount of water in the test tubes possibly diluting the pigment in the vial, and also reading the colorimeter accurately. Additionally, the test tubes were not all left to stand for exactly the same amount of time, as the ones I did first would stand for longer while I was doing the others, this also may have affected the dilution of the pigment.
To further this experiment I would investigate the permeability of plant cells beside beetroot, and perhaps also some animals’ cells, and see if the effect on the permeability differs. I could also do the experiment using different variables and see what affect they have.
Equipment list
- Thirty slices of beetroot
- Six test tubes each containing six milliliters of water
- Six water baths ranging from fifty to eighty Degrees Celsius
