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The effect of temperature on the cell membrane of a beetroot

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In this experiment I will be testing the effect of temperature on the plasma membrane of a beetroot. I will do this by measuring the percentage light transmission using a spectrophotometer. Once I have obtained my results, I will justify them using scientific knowledge explaining what I have observed whilst carrying out the experiment.

Factors to be controlled

“« The pH concentration

“« Regular use of distilled water

“« Ensuring that the surface area of each piece of beetroot is the same

“« Use the same volume of water

“« Start with the required temperature before placing the beetroot into the boiling tube.

“« Use a new piece of beetroot for each experimental temperature

“« Ensuring that the boiling tubes are left in the water baths for the same amount of time

Through secondary research I found that if I were to prevent the structure of the protein from altering in any way, I would need to keep the pH level constant. Subsequently, I decided to will be using distilled water throughout the experiment as it has a pH 7 and is neutral; neither acid nor alkali. By surrounding the beetroot with distilled water the protein will not have been altered, and the concentration gradient will be fairly constant for each of the temperatures also. This is because I will be exposing the beetroot to the surroundings of the same type of water, maintaining a fair test as distilled water may contain less or more impurities as other types of water, for example: tap water. I will have to control the amount of distilled water I use to place the beetroot pieces in and control this by using a measuring cylinder. I will measure 15cm3 of distilled water each time. It is important to keep the amount of water constant, as the dilution will affect the rate of diffusion, therefore affecting the results.

Another factor that I will be controlling is the surface area and mass of the beetroot pieces used. This is because the surface area affects the rate of diffusion, thus affecting the results. This will be done with the aid of a cork borer with which I will measure each beetroot piece with a ruler to 20mm. It is unlikely that their masses will be identical but I will do a visual check to make sure they are the same size, however I will later evaluated how this may or may not have affected my results.

As one particular section of beetroot will only contain a certain amount of pigment, I will be using a separate section for each test tube. As no two pieces of beetroot can be identical, possible differences in permeability and temperature can occur. Therefore, I will make note of this when evaluating my results, and consider how this may have reflected on my results.

Another factor I will need to take into consideration to create a practical and fair test, is to assure that the pigment is not left to stand for too long. This would cause the pigment to settle at the bottom of the test tube giving me an inaccurate reading of light transmission. Another way to prevent this from happening would be to shake the test tube in order to dissolve any pigment that has settled at the bottom of the tube.

I will also be controlling the amount of time the solutions are left at their designated temperatures, as unequal time spans will results in unfair results. In order to do this, I will be using a stop clock and allowing each solution to be at the desired temperature for 3 minutes.


The main variable in this experiment will be temperature as I am trying to find out how this specifically affects the cell membrane. In order to certify that the results obtained differ due to the changes in temperature, I will repeat the same experiment three times, in the same temperature of water, for the same amount of time. This precaution of repeating my results is used to ensure that my results are reliable, and to identify any anomalies. These experiments will be set up at room temperature. The percentage light transmission for these three test tubes will be expected to be the same. If this is apparent, then I will know that the change in my results is due to temperature.

Equipment to be used:For what purpose:

Measuring cylinders:to accurately measure the amount of distilled water

Boiling tubes:to place the beetroot pieces in

Ruler:to measure the beetroot pieces

Scalpel: to cut beetroot into 20mm segments

White tile: to use as cutting surface

Stop clock:to measure the amount of time the solutions are left at each temperature

4 water baths:for each temperature used

Safety goggles:to protect eyes



Thermometer:to measure temperature


Firstly I will obtain the correct equipment, and set the experiment up correctly. I will then cut 4 pieces of beetroot ensuring they are of the same size. I will do this by placing each beetroot piece onto the white tile and cutting it into small pieces measuring 20mm each. To do this I will be using a scalpel and a ruler for accuracy. I will visually decide whether the beetroot pieces look as if they are of the same mass. I will then measure 15cm3 of distilled water with the help of a measuring cylindered, and pour it into a boiling tube. I will do this for 4 boiling tubes, each now containing the same amount of water. One test tube will be placed a water bath of the following temperatures resulting in 4test tubes at different temperatures;

“« Room temperature ( 25 )

“« 45

“« 65

“« 85

The beetroot will then be added for 3 minutes exactly, and this will be accurately timed with the use of the stop clock. This will ensure that my test is fair. Once the beetroot has been soaked for 3 minutes in the desired temperatures, I will take the solution out of the test tubes and place it into separate test tubes. Separating the beetroot piece from the water will prevent any excess pigment from diffusing further. I will then repeat this experiment three times to gain a more reliable set of results. I will then record my results in a table in order to gain an average and make a clearer evaluation. I will take the averages by taking the mean of the data, putting it into a table to obtain accurate data. This will also allow me to identify any anomalous results.

Data analysis

My results will be recorded in the following table:


( C)Transmission of light absorption (%

Room temp




Once the results have been collected, I can then record the data into the table and draw a graph. This will make it easier for me to spot any correlation and trends between the light transmission and temperature. For example, if there is a positive correlation between the results, I will be able to conclude that with a positive increase in temperature, there will be greater light absorption. Negative correlation would conclude the opposite. After my results have been collected and analysed, I will be ready to predict further results, including the effect on light absorption at various other temperatures for which I have not tested. I can then prove this with a test at that particular experimental temperature. This would be able to tell me whether or not my prediction is correct, and assure me of the reliability of my results. If my prediction is proved to be accurate, then this would suggest that the results I have obtained are correct, and are a true reflection of the effect of temperature on the permeability of the plasma membrane of a beetroot.

In my graph I will be analysing the general trend of the line (or curve) of best fit to investigate the relationship between x (whatever it is) and y, as x varies to form a quantitative relationship.


As the temperature increases, the transmission of light absorption decreases. Diffusion is the movement of molecules from a region where they are at a high concentration to a region of lower concentration. The difference is referred to as a concentration gradient. There will be a net movement down the concentration gradient until equilibrium is reached that is a uniform distribution of the molecules. The process is passive as it does not require metabolic energy. The diagram below shows diffusion;

Diffusion of molecules occurs down the concentration gradient, from high to low



The procedure I have planned will be carried out to a fine degree of safety. I will insure this by implementing the following;

“« Insure the work area does not get over crowded; work away from other people

“« Before starting, tidy your books and create a clear and tidy area to prevent any accidents

“« Push stools in, in case of somebody tripping over.


Details- safety precautions, measurements, ranges

Measuring cylindersTo measure distilled water (mm)

Boiling tubesThese are used to hold water and must be handled carefully because they are made of glass which can be dangerous if broken.

RulerTo measure the beetroot pieces, using ranges for every tenth of a centimetre in mm

ScalpelI will make sure I am careful when handling the scalpel and keep it away from other people and away from my body. I will be using the scalpel to cut the beetroot

White tileUsed as a cutting surface

Stop clockUse to measure time in the range of 0.5 of a second

4 water bathsI will make sure that water does not spill and away from me

Safety gogglesTo protect eyes from hot water


ThermometerI will make sure that the

I will be using these ranges, as they are small enough for me to see any relationship between the variables within the given time.

Fair test

Insuring a fair test is extremely important. Without a fair test you will not receive accurate results, in turn, making the conclusions drawn from this investigation inaccurate. To insure a fair test I will do the following;

“« I will only change one variable, which is the one I am investigating;

“« I will repeat the experiment to increase reliability. s

“« I will take measurements and readings extremely accurately

“« I will keep factors to be controlled, controlled


During the practical, I encountered a few problems which I had to modify to ensure a smooth running investigation, with more precise results and therefore, reliable data.

I decided to


I have collected my results and presented them in a graph and table. I chose theses methods as they clearly communicate the information. In addition, they clearly show the obvious patterns; for example, the line (or curve) of best fit shows any anomalies.

Experiment One


( C)Transmission of light absorption (%)

Room temp88.5




Here, I noticed an irregularity at 85 degrees, therefore, I specifically repeated this temperature and obtained 61.5%. This anomaly is explained in the conclusion.

Experiment Two


( C)Transmission of light absorption (%)

Room temp89




Experiment Three


( C)Transmission of light absorption (%)

Room temp88




Averages Table


( C)Average transmission of light absorption (%)

Room temp88.5




Calculation of average:

= Sum of averages__

Sum of frequencies

I used a table of averages, disclosing the anomaly as it did not fit the general trend, therefore, I regarded that as unvalid data.

Analysis and Conclusion


The graph clearly shows a negative correlation, which reflects the fact that as I increase the temperature, the diffusion rate decreases. This supports my hypothesis, which will be further stated in my conclusion. I have drawn a line of best fit, which identifies the fact that this is a non-linear graph. The reason for this curve occurring is because of the rate of diffusion of the anthocyanin is decreasing, as there is less left to diffuse as time goes on.


My hypothesis was correct, stating that the general trends in the results would be in a negative correlation. The biological theory behind this is explained in context below:

The cell surface membrane consists mainly of lipids and proteins. Carbohydrates are also present, but are always found in association with lipids and proteins, as glycolipids and glycoproteins respectively. Many proteins and lipids have short, branching carbohydrate chains attached to external surface of the membrane, thus forming glycoproteins and glycolipids repectively.

Diagram of the fluid mosaic model of membrane structure

The carbohydrate chains project out into the watery fluids surrounding the cell, where they form hydrogen bonds with the water molecules and so help to stabilise the membrane structure. They also act as receptor molecules, binding with particular substances such as hormones or neurotransmitters. Different cells have different collections of receptor molecules in their membranes that will bind with particular substances. One group of glycoproteins known as antigens are important in allowing cells to recognise each other.

As the temperature is increased, an increasing number of extrinsic, intrinsic and glycoproteins imbedded in the cell plasma membrane of beetroot cells, become denatured.


The reasons for anomalous data;

In my results, overall I had one anomaly (I did not count this anomaly as a part of my average results, as it was not valid, and it was too far from the general trend), which did not fit the general trend). I highlighted it in my table. All the other results showed that it was too low to fit in the general trend. Based on scientific knowledge I have explained possible reasons for this anomaly;

“h There may have been a slight variation in temperature- going down e.g. a draft etc.

“h The readings may not have been read off correctly by me

“h Instrumental calibration- faulty instruments caused an upset in the results

“h Because I used visual verification, I may not have accurately judged the mass of the beetroot pieces

Though I feel that my results are reliable and that my conclusion is secure, I know that there are areas for improvement, that could further enhance my conclusion and to make me more confident with my results, and to be more precise. Additionally, to avoid any further anomalies, and reduce errors to the absolute minimum I would:

Areas for improvementsHow these could be implemented

Use more accurate equipment, limitations of equipmentInstead of visually judging the mass of the beetroot pieces, I would use a weighing machine, this would help to avoid instrumental calibration error

Avoid precision errorA higher degree of precision in measuring percentage light intensity

Avoid an operator errorMake sure equipment is used carefully

Ensuring reliability

For the curved graph, I could have calculated an equation by

More tests could be taken ensuring an extremely reliable average to back up my theory, and therefore I will be more precise

Avoid any uneven surfaces (i.e. table surface)Avoid areas where uneven surfaces as they could affect my experiment

Other experiments that could be carried out to further study and enhance the conclusion;

Clearly by simply doing one type of experiment, you can never be 100 percent sure of your conclusion. Further study needs to be carried out. This would act as additional or more reliable evidence for my conclusion. This further study would entail;

Another modification I would do is to heat up the water to the desired temperature before adding the beetroot pieces as this will prevent any diffusion from occurring before the water is at a desired temperature.

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