Effect of different temperatures on the permeability of beetroot cell membrane.

                     Phospholipids make up the basic structure of the membrane, forming a bilayer. They have hydrophilic heads and hydrophobic tails, with the tales being non polar its very difficult for ions and polar molecules to pass through the membrane, so the phospholipids act as a barrier to water soluble molecules.

            Therefore the only way water-soluble molecules can get through the membrane is through the protein. Protein in the membrane acts as hydrophilic passage ways or transport route for ions and polar molecules to diffuse into the membrane. Protein control what substances enter and leave the membrane. There is specific protein types for different substances, these are known as protein carrier cells.

              Cholesterol role is different compared to protein and phospholipids, its role is to give the membrane support and strength. Cholesterol determines how fluid the membrane is. It helps to control the fluidity, stopping it from becoming too fluid or too rigid, preventing the membrane from bursting. Cholesterol structure is very similar to a phospholipid, it too has a hydrophilic head and hydrophobic tale, which allows it to fit neatly in the phospholipids.

            Glycolipids and glycoproteins role is to help stabilise the membrane, with their carbohydrate chains that extend out into the water surface forming hydrogen bonds with the water molecules.

In the experiment the diffusion between the beetroot membrane and the solution stayed the same in terms of the kinetic energy being the same having no effect on the leakage of the membrane. So the kinetic energy of the diffusion never changed and didn’t affect the experiment. So the leakage was at room temp as the beetroot cylinders was only heated for 1 minute, so they cooled back down when the leakage occurred. But the reason why the leakage was different for the beetroots at different temperature was during the 1 minute they were heated a molecule in the membrane was permanently damaged.

                         I believe the molecule that was permanently damaged was the proteins in the membrane. My reason for this is a protein is affected by temperature, when temperature is increased the 3D shape of the protein is changed causing it to become denatured. Proteins are hydrophilic channels for ions and polar molecules, also allowing certain substances enter and leave the membrane and if the proteins specific shape is changed this will cause the cytoplasm and other substances contained within the membrane to leak out. This has been shown by a steady increase in anthocyanin (polar molecule) leaked out of plant cells as the temperature increases. So this is what has caused more leakage from beetroot cells. The higher the temperature the more the protein has changed in shape, which is the reason for the absorbance increasing when beetroot is heated at higher temperatures. At low temperatures such as 35ºC-45ºC the 3D shape of the proteins isn’t changed too much, so not much leakage takes place. So there was more diffusion of the anthocyanin in higher heated beetroot cells, but that was due to the shape of the protein being changed, not the kinetic energy.  

Also during the 1 minute the beetroot membrane was heated the phospholipids were changed but this was only temporary, once the beetroot was back at room temperature the phospholipids changed back to their original form. What happens is at high temperatures the phoispholipids don’t fit together as easily, as the membrane becomes more fluid. This means there is a slight chance of substances getting through past gaps between the phospholipids, but most of the time they still acted as a barrier to ions and polar molecules even if there was gaps between them. If any anthocyanin did leak out through the gaps of the phospholipid or if the phospholipid burst when heated it would have leaked into beaker, which wasn’t measured. Only leakage at room temperature was measured.

Evaluation

Evaluation of procedure

The things that were kept the same to be a fair test are:

1. The beetroot was cut 21mm every time to allow the same surface area at each different temperature.
2. Using a thermometer to check the temperature at the start of when the beetroot was put in the boiling water and at the end of the minute when taking the beetroot out. This meant an average was taken for each temperature.
3. Each beetroot was washed before being put in hot water, this was so the beetroot juice was washed out.
4. Keeping each beetroot in the solution for the same amount of time, which was 25 minutes.
5. Using the same sized cork borer when cutting up the beetroot.

Evaluation of evidence

In my average absorbance graph/table there is no anomalous/ odd results.

But in group 2 absorbance at 65°C to 85°C the absorbance was 2 abilitrary units. This means there was an error in the colorimeter. This could have been caused by many of faults during the method.

But I believe it may be due to the cutting of the beetroot discs not being cut straight, and being cut diagonally which increases the surface area therefore increase the result.

                Another anomalous result was in group 3 at 35ºC where the absorbance decreases. I believe this could have been caused by the beetroot not being left in the water at  35ºC for one minute and was taken out to early. Also it may not have been at 35ºC and the temperature was lower.

            Also I think same reason applies for the anomalous result at 45ºC in group 2 and group 1.

         Overall the average absorbance results looked good, as there was a nice pattern, which formed a nice joined line on the graph and seem to be reliable. The reason why I think this is group 1 absorbance had excellent results, and group 3 absorbance was good it was only group 2 absorbance that had a lot of anomalous results. There was no mistakes in group 1 as that was my group, we did every thing the best we could and being very careful.

Percentage of errors

The formula that is used to find out due to measuring equipment is:

Minimum measurement

Actual measurement  

Errors due to thermometer

25ºC

So you apply the formula above:

Now add and subtract 4% of 25ºC (which is 1) to 25ºC.

1 + 25=26

1- 25=24

85ºC

Now add and subtract 1.2% of 85ºC (which is 1.02) to 85ºC

1.02 + 85= 86.02

1.02 + 85=84.02

Errors due to absorbance

Many instruments contribute to absorbance error, these are::

                                     Lowest point                                    Highest point

• Ruler (21mm)                4%                                                      4%
• Syringe (10cm3)            5%                                                      5%
• Clock (1min)                 2%                                                       2%
• Colorimeter                   7%                                                       0.53%

 

                                    Lowest point                                          Highest point

Compound error                18%                                                       11.53%

The percentage of error of the thermometer isn’t too bad, it doesn’t effect the results that and shows the thermometer is quite reliable.

The absorbance compound error at my highest point had a major effect on the result, it shows the equipment used for absorbance cause a massive error, as show on my average absorbance graph. While at the lowest point shows the compound error is high (17%), and has a major effect on the result. The percentage of errors of the equipment puts a question mark on the accuracy and reliability of the results.