Beetroot Practical Write up

Ali Attalla

Biology Coursework

Beetroot

Hypothesis: To investigate the effect of different concentrations of ethanol on the permeability of beetroot cell membranes.

Prediction: By exposing a membrane to a solvent, ethanol, it will affect its permeability. Therefore higher the concentration of the solvent, the more permeable the membrane will be. But by increasing the concentrations of the ethanol beyond a certain point it may have no affect on the cell membrane because the ethanol would have broken down the cell membrane completely. This is because of the effect of ethanol on the lipids in the membrane. Also, more dye would be present as the lipids are essential to the structure of the cell membrane as they control the substances that enter and leave the cell. Ethanol could also destroy some the proteins or denature the structure because protein has a tertiary structure. The ethanol would destroy the hydrogen bonds that hold the protein structure. Therefore, with the lipids and proteins destroyed in the cell membrane, the pigment is allowed to escape from the cell due to there being no cell membrane holding substances in the cell.

Scientific Knowledge:

Transfer across cell membrane structure:

There are many ways that ions and molecules are transported across the cell membrane. By this, the cell must acquire the ions and molecules they need from their surrounding ‘’. With the cell membrane being in contact with ethanol in the extracellular fluid, there is direct contact with the solvent. Therefore, by diffusion the ethanol is secreted into the cell and along the way destroys the permeability of the cell membrane.

The cell transports ions and small molecules across their membranes by the following means:

Osmosis:

By osmosis the diffusion of water through the plasma membrane is possible. Since the lipids bilayers are impermeable to essential molecules and also to a few small molecules like oxygen and carbon dioxide, these molecules and ions diffuse freely across the cell membrane.

Diffusion or Facilitated diffusion (Passive transport):
By diffusion the ions and molecules move spontaneously across their concentration gradient (from a region of higher to a region of lower concentration). Small, polar, hydrophilic molecules, like oxygen, and water, can pass through cell membranes by diffusion. Where as larger hydrophilic molecules, like glucose, can pass through the cell membrane by facilitated diffusion. In all cases of facilitated diffusion through channels, the channels are selective. Meaning that the structure of the protein admits only certain types of molecules through (hydrophilic pores). Where as non-polar, hydrophobic molecules are not impeded by the phospholipids in the cell membrane. This means that they are small enough to fit between the phospholipids layers. The factors that affect the rate of diffusion are: concentration gradient, temperature, pH (the charge), surface area, size of molecule and the width of the diffusing space.

Active transport:

By active transport, ions and molecules are forced by the use of metabolic energy to move against their concentrated gradient. Forms of active transport are:
Phagocytosis:

The ingestion of solids from outside of the cell is the process of phagocytosis. The cell membrane encloses a particle and buds off to form a food vacuole. Lysosomes with enzymes will fuse with it to enable digestion of the contents. Soluble products pass out of the vacuole and are assimilated.

Pinocytosis:

The ingestion of the fluid surrounding the cell is the process of pinocytosis. The cell membrane encloses some of the fluid and pinches off to form a vesicle. As the vesicle is closed off the materials are dispersed in the cell, which is referred to as assimilation.

Exocytosis:

Vesicles budded off from the Golgi apparatus or endoplasmic reticulum can fuse with the cell membrane, expelling their contents.

Endocytosis:

Where a substance attaches to the cell membrane, inducing it to slide or flow inwards forming a pouch.

Function and structure of cell membranes:

All cells have a cell membrane that forms the outer limit of the cell. In the fluid mosaic model, the membrane structure consists of a double layer of phospholipid molecules, which is called the lipid bilayer, with a hydrophilic head which is on the outside of the membrane and a hydrophobic tail which is on the inside of the membrane. The cell membrane is considerably quite fluid and this is helped by cholesterol, which help disturb the close packing of the phospholipids by breaking up the Van der Waals forces. The proteins that float in this bilayer are either on the surface or they completely penetrate the lipid layer. The proteins that penetrate the bilayer may control the entry and removal of specific molecules from the cell. The proteins that are on the outer edge or on the surface of the membrane have carbohydrates molecules attached, usually short sugar chains. These are called glycoproteins. The carbohydrates part of the glycoproteins is important in cell recognition, which is the ability of cells in the body to tell whether or not a cell is from another individual or another organism (invading pathogens), for example, in the immune system. Some substances, particularly carbohydrates and ions, are transported across the membrane via the proteins. Where as some substances, including water, are transported directly through the lipid layer.

The lipids in the bilayer are soluble to organic solvents with low molecular weight molecules, such as ethanol; therefore to have beetroot in ethanol would affect the lipids in the bilayer by destroying or dissolving them. Hence, more pigment would leak into the solution because there would be less, if any, structure to the cell membrane to hold in the pigment if the lipids have been damaged or destroyed.

Biological molecules and cell membrane:

The cell membrane can be seen as a fluid structure in which proteins can move about depending upon the fluidity of the lipids and the amount of cholesterol. The amount of fluidity of the membrane influences the function. By reducing the fluidity in the cell membrane it decreases the ability of proteins to move and interact, while enhancing the fluidity it may lead to a break down in the cell membrane. Cell membranes have been tested upon with ethanol, which have been shown to fluidise the membrane, which perhaps provides a basis for altered protein function. Protein in its tertiary structure has been affected and altered or even denatured which affects the overall fluidity in the cell membrane and the function or interaction of the proteins. “These influenced cellular function in the brain and body and led to the various symptoms of alcohol action.”

So not only does ethanol affect the soluble lipids in the cell membrane, it also affects the proteins in the cell membrane by altering their functions and interactions between each other. This is because the ethanol affects the hydrogen bonding in both the lipids and peptide bonds in proteins, as this is what holds the structure together.

Beetroot:

The betacyanin pigment of beetroot is located in the sap vacuole and, “by means of the properties of the tonoplast and cell membrane, does not leak into the cytosol or the extra-cellular sap of the beetroot.” When beetroot is cut, the cells are sliced and naturally pigment spills out. If the slices were thinner, thus providing a larger surface area it therefore speeds up the pigment leakage. But if the membrane is destroyed and the phospholipid bilayer and possibly proteins are altered, more pigment, betacyanin, and leaks by means of diffusion. The pigment serves as a marker for ...

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Beetroot:

The basic structure of betacyanins

Betacyanin: Structure and Solubility:

Betalaines are the red-purple pigments of beetroot, Beta vulgaris.
They are water-soluble and exist as internal salts in the sap vacuoles of plant cells. Betalaines are made up of red betacyanins and yellow betaxanthins. Betacyanines include about 90% of beetroot betalaines. The most important betacyanin is betain. This makes up 75-95% of the total colouring found in the beetroot.

Ethanol:

The general formula is C2H5OH with the structure as following:

Generally ethanol is an alcohol found in beer, wine, cider, spirits, and other alcoholic drinks. When pure, it is a colourless liquid with a pleasant odour, miscible with water or ether. It burns in air with a pale blue flame. The vapour forms an explosive mixture with air and may be used in high-compression internal combustion engines. It is produced naturally by the fermentation of carbohydrates in yeast cells. Industrially, it can be made by absorption of ethene and sub-sequent reaction with water, or by the reduction of ethanal in the presence of a catalyst, and is widely used as a solvent.

Ethanol is used as a raw material in the manufacture of ether, choral, and iodoform. It can also be added to petrol, where it improves the performance of the engine. Crops such as sugar cane may be grown to provide ethanol (by fermentation) for this purpose.

(Information from The Hutchinson: Dictionary of Science)

The pH affects proteins that make up about 70% of most cell membranes. Proteins are made of amino-acids with a variable number of nitrogen and oxygen atoms in the protein. These can form hydrogen bonds with the many hydrogen atoms found in the molecule.

When the pH of a solution is added or changed, then the position of some of these hydrogen atoms also change. This is because “amino-acids are amphoteric, and tend to stabilise pH. Thus, they can lose an H+ ion at the COOH part of the molecule at higher pHs, or gain an H+ ion at the NH2 end of the molecule at lower pHs.”

Therefore the overall shape of the protein molecule changes because of this change in the pH. However, unlike heat, the denaturing of a protein by changing its pH is normally reversible.

So, by adding ethanol, betalain in beetroot diffuses out of the cell when the membrane proteins are damged. This is because of the change in pH to the cell membrane.

Appropriate equipment:

Beetroot
Corer
Ceramic tile
Scalpel
Tweezers
10 Test tubes
10 Boiling tubes
Test tube and boiling tube racks
Measuring cylinder 25cm3
Colourimeter
Green filter
Cuvettes
Pipette

Choice of equipment:

Colourimeter:

The colourimeter is precise, reliable and accurate compared to a natural eye test comparison or a colour chart comparison. Statistical figures are given as percentage of transmission of light through the substance. This also gives a more accurate reading instead an eye test or colour test comparison. However a chart is considerable easier to read and the colourimeter is occasionally difficult to make a reading exactly 100% with a water filled cuvette. These readings fluctuate between 98% and 102%, which could possibly cause variations with the rest of the experiment results.

Corer:

Provides the same diameter throughout the beetroot and if done correctly could supply a constant length of beetroot. The length that will be subsequently used from analysing the preliminary experiment for the final work will be 9mm. The larger the surface area the more area exposed to the ethanol.

Green filter:

It is the complimentary colour, which would produce accurate readings compared to a red filter as this would read at 100% transmission of light.

Beetroot:

Size: The larger the surface area the greater the leakage of pigment from the beetroot cell membrane. Therefore with discs this would increase the surface area of the facings therefore more leakage of pigment. But with a section at a longer length for example at 2cm, this would have a smaller surface area on the facings which would initially cause pigment leakage, but would overall decrease the surface area.

Age: If the beetroot were too old, then several factors would affect the final results. These could include that the pigment has dried up and would consequently lead to no pigment leakage. Also if enough of the cell membrane die, then there would be no structure or support to keep the pigment in the cell, therefore would lead to more pigment leakage and not an accurate set of results.

Variables:

Volume of the solution:

The same ratio of ethanol and distilled water must be accurate and constant. This is because the results would not average scientifically well neither would it be considered a fair test as a larger amount of ethanol may have a larger affect on the cell membrane possible at a faster rate than it would be with a smaller amount.

Constant and compromised timing:

If the beetroot was left at a longer length of the time in one experiment and then at a shorter time the next, would not be considered accurate or constant. With the beetroot in at a longer length of time eventually the ethanol would have totally destroyed the cell membrane whatever the size of the beetroot or ratio with distilled water. This is because of the chemical properties of the solvent would affect the lipids in the cell membrane. If the beetroot was left in a shorter amount of time, then the ethanol would not have had it’s full affect on the cell membrane to gain any efficient results from.

Repeated experiment:

This experiment would be repeated three times overall to gain a correct scientific average and so the timing can be exact.

Filter colour:

Originally a colourimeter comes with three different filters, red, green and blue. For this experiment the green or blue filter would be acceptable. This would be because blue and green are the complimentary colours and if the red filter would be used then this would have an overall affect on the final results. This would not give correct readings as the colour of the natural pigment in beetroot is red and for the colourimeter to measure the light transmission, red liquid through a red filter would just read at 100% because it would not distinguish between the colour changes. Where as blue and green are the opposite colours could distinguish this. For accuracy reasons a green filter will be used for the final experiment as this was the same filter used in the preliminary experiment.

Accuracy:

No spillages or loss of solution from splashes as this would affect the volume and ratio of the ethanol and distilled water

Diameter of beetroot:

From preliminary results the diameter of the beetroot was changed between 8mm and 9mm, this didn’t affect the overall results, which suggests that for the final experiment would be to keep the diameter of the beetroot a constant factor at 9mm. This diameter was chosen for practical reasons so that it would comfortably fit into a boiling tube. If the diameter was changed and not kept at a constant variable then it would be considered that with a larger surface area the pigment leakage would be sped up, but this is not what is being measured and not needed to be furthered experimented with.

Size of the beetroot:

From the practical aspect of the preliminary experiment it would be considered very difficult to cut the beetroot at a long length, e.g. 60mm, as this would be because of the natural sizes of the beetroot which are small naturally and that the entire experiment may require more than one beetroot. Therefore for the final experiment lengths of 2mm are acceptable. From my preliminary results different lengths do affect the light transmission percentages, but considering that to cut beetroots at specific lengths accurately is time consuming. This might affect the speed at which the experiment is completed at and whether all aspects of safety and accuracy are induced.

Measurements:

Transmission of light through the cuvettes with the final results of the solution and colouring are being measured. Three consecutive experiments are carried out to find the final average. Each experiment would consist of 20 to 30 minutes each. For the final experiment, the concentrations of ethanol would be between 0 and 20: the range being 0, 5, 10, 15, and 20.

Safe working environment:

Ethanol:

Corrosive and highly flammable. Irritating to skin and eyes. Can be damaging if large amount is splashed into eyes. Intoxicating if ingested. If ingested in undiluted form, it has a severe drying effect on mucous membranes of mouth and throat. Intoxicating if continuously inhaled for a long period of time.

Spillages:

Safety hazard, inhalation if not cleared, corrosive and room needs to be well ventilated even without spillages.

Scalpels:

Cutting the beetroot – white tile needed and cautious of a sharp implement

Gloves:

Beetroot pigment stains clothes, therefore gloves are useful with the use of beetroot as well the usage of ethanol, as it is skin irritant.

Secondary source information to inform strategy:

The previous testing on the effect of temperature showed that at higher temperatures more pigment was left in the solution. This previous testing provided a basis for a method and suitable equipment that may have been needed for the preliminary and final experiment. For the preliminary work, a similar experiment will be investigating the effects of ethanol on the cell membrane of the beetroot instead of temperature. After completing the temperature investigation, a suitable prediction could be presented by employing the results. To justify length and shape of beetroot, the beetroot shape will be cylindrical because a large surface area to volume ratio would provide more cells exposed to the ethanol. The smaller the length the larger the surface area, however if the beetroot was too small then not enough pigment would be left to analysis. A colourimeter was used for the previous testing on the affects of the temperature and was reliable for statistical information instead of an eye test comparison. The qualitative information given from the colourimeter is precise; therefore a colourimeter will be used for the final experiment with the affects of ethanol on the beetroot membranes.

Why ethanol?

By studying the effects of ethanol or organic solvents on beetroot cell membranes can give scientists an idea how ethanol or organic solvents may have on a persons cell membrane. From this experiment the cell membrane from the beetroot would show how much ethanol would affect it’s cell membrane and the level of damage at what concentration or ratio with distilled water. From the results it would give scientist predictions of the effect of ethanol on a persons stomach or digestive lining. Therefore knowing these effects would help provide a wider knowledge of alcohol on the body’s cell membranes and perhaps how to overcome the dangers of drinking.

Preliminary Apparatus:

Beetroot
Corer
Ceramic tile
Scalpel
Tweezers
10 Test tubes
10 Boiling tubes
Test tube and boiling tube racks
Measuring cylinder 25cm3
Colourimeter
Cuvettes
Pipette

Preliminary Method:

Using a corer, cut strips of beetroot with the corers at 8mm and 9mm
Then using a ruler cut these sections into the following:

Five 8mm diameter at 2cm in length
Five 8mm diameter at 0.5cm in length
Five 9mm diameter at 2cm in length
Five 9mm diameter at 0.5cm in length

Thoroughly rinse cut beetroot so that excess pigment will not affect the overall results
Prepare boiling tubes for the sections of the diameter of 9mm as these do not fit into a normal test tube, and prepare test tubes for the sections of 8mm
Label clearly which test tubes and boiling tubes contain which ratio of concentration of the ethanol
Accurately measure with a pipette for the following percentages and correct measuring ratio of distilled water and ethanol

100% ethanol 0% water, ratio 12cm3 of ethanol : 0cm3 of water
75% ethanol 25% water, ratio 9cm3 of ethanol : 3cm3 of water
50% ethanol 50% water, ratio 6cm3 of ethanol : 6cm3 of water
25% ethanol 27% water, ratio 3cm3 of ethanol : 9cm3 of water
0% ethanol 100% water, ratio 0cm3 of ethanol : 12cm3 of water

Leave for 40 to 60 minutes for effects to happen
After this period of time, take out the beetroots from the boiling tubes or test tubes
Using a colourimeter, set up by placing complementary green or blue light filter into the designated position
Fill a cuvette of distilled water and place into the colourimeter with the clear sides facing the reader and the ridged edges facing the sides
By using the dial, set the percentage of transmittance of light on the reading to 100%, or get as close to 100% as possible
Then at one at a time fill a cuvette with the final results individually with each test tube or boiling tube substance
Record results by noting the percentage reading of the light transmittance

Preliminary Prediction:

By exposing a membrane to a solvent, ethanol, it will affect its permeability. The higher the concentration of the solvent, the more permeable the membrane will be. For preliminary results, the ranges of concentrations are going to range between 0% and 100%. From these results, observations may evidently show that at 50%, 75% and 100% concentrations the cell membrane of the beetroot has been totally broken down. This is because by increasing the concentrations of the ethanol beyond a certain point it may have no effect on the cell membrane.

Preliminary Results measuring the percentage of light transmittance:

Water = 101.8%

Preliminary Analysis:

From analysis of the results, it is to conclude that there is too large a range between concentrations and that the effects on the beetroot cell membrane happens between the concentrations 25 and 0. Therefore possible for the final experiment the range will be between 0 and 20: 0, 5, 10, 15, and 20. Consequently there will an average range between the stages where the cell membrane is most affected from the ethanol. To overcome these anomalies more accuracy and timing would be a factor, also possible only having one length and one diameter measurement. This would then provide a concentrated measurement and comparison. Also when returning to the beaker holding the cut beetroot, a lot of the pigment was still present which might have had an affect on the overall results. To overcome this, the cut beetroot would need all of the excess pigment absent from the beaker whilst in storage purposes. However from this experiment, it is clear that the length and possible even the diameter does effect the final pigment leakage.

From the preliminary work the final investigation with only need boiling tubes because in the preliminary the beetroot was 8mm in diameter, which fitted into test tubes but a 9mm diameter needed boiling tubes, now that for the final the beetroot is only a 9mm diameter and at 2cm length boiling tubes would be required.

Preliminary Graph Analysis:

From analysis and comparison of the graphs, it is apparent that the general trend of each graph is decreasing, ignoring any anomalies. The beetroot with the diameter of 9mm and the length of 2cm were devoid of anomalies, this could be because this was the first of the four experiments, and therefore accuracy and suitable timing were required, hence a better set of results compared to the other three. The results with the beetroot at 9mm in diameter went up at the end of the graph line; this could be accounted for as not the correct timing or enough accuracy. Similar inconsistent results occurred in both sets of results for the beetroot at 8mm in diameter. In particular with the length at 0.5cm, this sudden increase and then decrease is could also be because of timing or accuracy.

Experimental Graph Analysis:

From these results and general graph trends decreasing, for the final experiment, a similar pattern should occur with a decreasing trend. This is apparent with the original prediction made that the higher the percentage of ethanol exposed to the cell membrane, the permeability is affected enough to allow further pigment leakage.

Method Preparation:

Taking into consideration the final results of the preliminary experiment and the inadequate methods used during that experiment, the method will be altered slightly from the original preliminary made.

The changes will include the following:

Only need 15 boiling tubes rather than 10 boiling tubes and 10 test tubes, this is because the beetroot at a 9mm only fits in a boiling tube where as the 8mm fits in a test tube. Since the concentrations have been lowered to the range between 0 and 25, with a gap of 5 between each, then only 5 boiling tubes shall be needed for each experiment hence 15 altogether.
A corer for a diameter of 9mm instead of 8mm for the above reasoning.
Lengths only at 2cm instead at 0.5cm and 2cm, this would provide a constancy and accuracy.
Found that leaving the substances in for only 30-40 minutes was sufficient enough rather than 40-60 minutes. If the beetroot was left in for too long then no matter what concentration the beetroot was in with ethanol, all of the pigment would have naturally leaked out, or the ethanol would eventually have destroyed the entire membrane

Experimental Method:

Using a corer, cut strips of beetroot with the corers with a 9mm diameter
Then using a ruler cut ALL the beetroot at the length of 2cm
Thoroughly rinse cut beetroot so that excess pigment will not affect the overall results
Label clearly which boiling tubes contain which ratio of concentration of the ethanol
Accurately measure for the following percentages and correct measuring ratio of distilled water and ethanol

20% ethanol 80% water, ratio 2.5cm3 of ethanol : 9.5cm3 of water
15% ethanol 85% water, ratio 2cm3 of ethanol : 10cm3 of water
10% ethanol 90% water, ratio 1.5cm3 of ethanol : 10.5cm3 of water
5% ethanol 95% water, ratio 1cm3 of ethanol : 11cm3 of water
0% ethanol 100% water, ratio 0cm3 of ethanol : 12cm3 of water

Leave for 30 to 40 minutes for effects to happen
After this period of time, take out the beetroots from the boiling tubes
Using a colourimeter, set up by placing complementary green light filter into the designated position
Fill a cuvette of distilled water and place into the colourimeter with the clear sides facing the reader and the ridged edges facing the sides
By using the dial, set the percentage of transmittance of light on the reading to 100%, or get as close to 100% as possible
Then at one at a time fill a cuvette with the final results individually with each boiling tube substance
Record results by noting the percentage reading of the light transmittance

Method

Equipment:

Test tube rack
Boiling tubes
Graduated syringe
Measuring cylinders
Beakers
Ceramic tile
Cork borer
Razor blade
Thermometer
Forceps
Stop clock
Colourimeter

Method:

Cut enough cylinders from the taproots of fresh beetroot with a number 8 mm (diameter width) cork borer to make 35, 30mm cylinders.
Place the cylinders into a large beaker and rinse under running tap water until no more pigment is released into the water.
While the cylinders are rinsing collect 11 clean, dry boiling tubes and label them with the ethanol %’s you will be using; these should be 0% (distilled water), 5%, 10%, 15%, 20%, 25%, 30%, 40%, 45%, 50%.
Place 30ml of distilled into the corresponding tube and measure the temperature. Place 30ml of each solution of ethanol into the other tubes. These can be prepared by diluting the supplied 100% solution of ethanol.
Place one cylinder of rinsed beetroot into each of the tubes and start the stop clock. (It may be necessary to stagger the start time for each dilution to give you time to remove the cylinders at the end of the test) Stagger by 30 seconds.
Leave the cylinders in the boiling tubes for exactly 30 minutes
After 30 minutes have elapsed, shake the tubes and carefully remove the cylinders from the tubes taking care not the damage the cylinders. This will give you 11 tubes containing solutions stained with red pigment.
Calibrate a colourimeter using a clean cuvette of distilled water and a blue filter.
Transfer each of the solutions to a clean, dry cuvette and measure the transmittance using a colourimeter. (It may be necessary to recalibrate the colourimeter regularly with distilled water to ensure the accuracy of your results).
Repeat the experiment three times and calculate an average for each solution.
Carefully record all of your results in a table.

Analysis:

The results shown on a separate sheet show the mean slowly declining. From the graph, it shows a general trend of the mean decreasing. From this, it shows that the initial prediction made was correct. This was that the higher the concentration or the ratio of ethanol to distilled water, the larger leakage of pigment. This would also imply that ethanol does in fact affect the cell membrane to such an extent that it emulsifies the lipids to therefore cause pigment leakage.

The year’s results show that this also supports the initial prediction. With the experiments means taken, the calculations of standard deviation could also be taken and compared.

The formula used for standard deviation is shown below:

The standard deviation indicates the spread of results around the mean and gives an indication of the accuracy of the experiment. The standard deviation shows that the year’s results were quite accurate because each spread of data is considerably comparable.

Research of ethanol and the effects of this on the cell membranes of beetroot showed that the pH affects proteins that are essential on the cell membrane. To conclude the betalain pigment in beetroot diffuses out of the cell when the membrane proteins are damaged and the lipids are dissolved. This is because of the change in pH to the cell membrane which causes the proteins to denature and no longer hold a complete structure. Ethanol also dissolves lipids, so it would damage the membrane and cause it to become completely permeable. This also contributes to the leakage of the pigment from the cell membrane. Ethanol emulsifies the plasma membrane and therefore pigments are released from the membrane.

Cell surface membranes have a number of different functions within the cell, but their major role is to act as a selectively responsive barrier to control the entry and exit of particular substances. According to the fluid mosaic theory, the cell surface membrane consists of a double layer of phospholipids molecules the lipid bilayer, which is a fluid like structure and contains a ‘mosaic’ of protein molecules where movements of molecules can take place.

The plasma membrane also provides a boundary to cell cytoplasm separating it from other cells. Phospholipids have a polar head, which is hydrophilic and a non-polar tail, which is hydrophobic. Proteins have a hydrophobic part, which is buried in the lipid bilayer, and a hydrophilic part, which can be involved, in a variety of activities. Some proteins move freely where as some are fixed in one place. Some proteins only span the top bilayer, which is the extrinsic, or the bottom, which is the intrinsic, or they may span the entire membrane. Some proteins on the outer edge of the membrane have carbohydrates molecules attached, usually short sugar chains called glycoproteins or lipids with carbohydrates attached to them called glycolipids. These are important in cell recognition; therefore membranes are vital to cellular function.

Evaluation:

Whilst completing the experiment, the only possible way to get the beetroot out of the boiling tube was to stab the beetroot cylinder with a scalpel. After completing a set of results, pigment was obviously released whilst the scalpel was in contact, this would have in effect released more pigment as the cell membrane was cut instead of affected by the ethanol. However, only a few molecules of betalain would have been released, which would not affect the final results.

After washing the beetroot and clearing the excess dye of the pigment, the beetroot cylinders were left overnight in a container filled of distilled water so the beetroot does not dry out. Returning the next day to the apparatus, more pigment leakage was apparent in the container of water. This may have only affected my results slightly, but not significantly enough to influence the final result as only a few betalain molecules had leaked.

Anomalous results:

There were also limitations for the experiment, which included time. There was only 2 hours to repeat the experiment three times between the concentrations of 0% and 50%. A more accurate experiment would have included a longer time frame to carry out more experiments to gain a more accurate mean. This may have eliminated any anomalies, but generally the final results were acceptable and accurate enough to count. To repeat the experiment additional times would actually not have an effect on the accuracy of the final results.

Another limitation was cutting the beetroot to the exact length with the constant width with the cylinder. Many times it was difficult to cut the beetroot using a corer to have the exact diameter throughout. Sometimes the beetroot was exactly 30mm; so a few millimetres were lost because the skin had to be cut off either end. This wouldn’t have had much of an effect on the final results, as only a few molecules of betalain would have leaked because of this.

With this particular experiment, it was limiting since only one type of plant cell membrane was considered. Therefore to conclude that all cell membranes act in this way would be incorrect. Different plant cell membrane may be adapted to cope better or worse than beetroot cell membranes.

Another limitation was the range of concentrations. To have a better understanding of the effect of ethanol on cell membrane would to conduct a smaller range and then concentrate on where the cell membranes are most affected. This experiment was completed between the ranges 0% and 50%, and the main affect on the cell membrane was between 0% and 20%. Therefore to complete a more accurate result comparison would to have conducted an experiment between these results and then scale it down again to perhaps 10%, 11%, 12%, 13%, 14% and then 15%. This would gain a more specific set of results and a larger comparison to be possibly made. This limitation did not affect the final sets of results.

Getting the years results meant that the reliability of the results were high. This in general meant that a correct and accurate mean could be produced.

The readings from the colourimeter may have been incorrect because from a human factor using the dial to find 100.0% on the colourimeter was difficult to get exactly. Sometimes the readings of the distilled water would be between 101.3% or 100.5%, which was the closest reading possible to get and keep constantly. But this is not as accurate as it could have been, which would have been 100.0%. This was unreliable as 100.0% shows that there is 100.0% light transmission, which for distilled water it was. But if the figures were below or higher than 100.0%, then the rest of the results would be inaccurate as the light transmission was not at the correct figure.

Teacher Reviews

Here's what a teacher thought of this essay

Ross Robertson

1st of Mar 2013

Overall, this is a very considerable effort on the part of the writer. A great deal of thought has been put in to the overall structure of the report. A lot of experimental work was carried out, notably a very thorough preliminary investigation which proved very valuable. The only major weakness lies with the analysis of the data collected. This is a very common issue with A'Level assignment reports. IV/DV trends should have been discussed in detail with reference to data points on the graph. Any SD calculations could then have been used to examine the reliability of the final data. The evaluation section was thorough, but it is important to assess the validity of data by examining in detail whether all the control variables were indeed controlled (kept constant). In practice, this is very hard to do. Despite these misgivings, this is an impressive piece of work.

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