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Investigating the permeability of plant cells.

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Muddeha Waraich U.6.5. Investigating the permeability of plant cells. Abstract. This investigation has set out to look at how the permeability of plant cells is affected by temperature changes between 250C and 850C. This was done using beetroot as the plant cell under investigation, and the use of a colorimeter. For this investigation it was necessary to carry out research into plant cell membranes and the transport mechanisms used by these membranes. Background Knowledge. The permeability of a plant cell is dependant on the membrane of the cell. Therefore factors affecting the cell membrane are factors that will affect the permeability of the cell. The Cell Membrane. The cell membrane is the boundary of the cell. They regulate the molecules that cross the boundary and are extremely thin, approximately 12 nm, but very strong and flexible. In 1972 Singer and Nicholson put forward the 'fluid mosaic model' of the cell, which is still held to be true. The model incorporates a lipid bilayer, which forms the main continuous part of the membrane. A key feature of the model is the various specialised proteins inserted into the lipid membrane which carry out lots of important functions. Proteins located largely within the lipid bilayer, known as integral proteins are normally arranged with one end of the protein buried in the membrane and the other sticking out of the surface. Some of the integral proteins span the whole membrane and extend into the watery environments on both sides. Some of the other membrane proteins, known as peripheral proteins do not penetrate the lipid bilayer at all, but associate with the hydrophilic surfaces of the lipids of the membrane, to which they are anchored by a covalent bond. Another important constituent of membranes is carbohydrate, which is attached to proteins, forming glycoprotiens, or lipids to from glycolipids, and is always on one side of the membrane. All membranes have this basic structure, which is shown in the diagram, Figure 1. ...read more.


Whilst the water is being heated the other partner should measure out 6cm3 of distilled water using a 10cm3 measuring cylinder. Measure out 6cm3 for two test tubes per temperature, and label them by temperature. Cut 2 pieces of beta vulgaris, per temperature, length 3cm When the water is at the correct temperature place in the pieces of beetroot into the beaker of water. Start the stop watch simultaneously. After one minute, use forceps to transfer the pieces of beetroot into the appropriate test tubes. Note the time. Leave each piece of beetroot in the distilled water at room temperature for 30 minutes exactly. After the time has elapsed, shake the test tubes and place the two solutions in separate 100cm3 beakers. Remove the beetroot. Syringe 3cm3 of solution and pour directly into the Cuvettes. Using a colorimeter compare the amounts of red pigment which have diffused out of the beetroot and into the water. Repeat this for all the temperatures, i.e. 20. 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85OC. The Calibration. A calibration is carried out due to the fact that it is not possible to measure the exact number of betacyanin molecules, and thus are unable to work out the permeability. It is thus important to obtain a set of values experimentally. This can be done by following the procedure below: Make a highly concentrated solution of beetroot pigment using a pestle and mortar. Set the colorimeter on the blue filter. Pour 3cm3 of distilled water into a cuvette and put into the colorimeter. The light transmission should come to 100% If so proceed, otherwise use the button that resets it, until it does read 100% with distilled water. Then measure out the amount of pigment solution that has been made and pour the measured amount in to the cuvette. Put this into the colorimeter, the light transmission should come to 1%. ...read more.


This I think is untrue and must be where my main sources of error come in. Trends. The main trends are those expressed above. I.e. that of the graph structure. However, I had several anomalies, at 65OC, 80OC and 85OC. The general trends expressed are those in my prediction, apart from the last two results. This is probably due to errors in the colorimeter and age of beetroot, mainly, or to do with some human error. At 75OC I get the death point of the cell to be reached, higher than expected. It is at 450C that the rapid loss in pigment begins this must be when the membrane and cell wall of the beta vulgaris become disrupted. Comparisons. The shape of the graph expected is similar however, there are several differences, and I have only been able to see the general pattern emerge. The disrupting of the cell was predicted at 45OC and was found to lie at45OC according to my graph. However, I expected the death point of the cell to be lower than 75OC, I expected it to be 65OC.Also. I was expecting levelling off at the end of the graph once all the pigment had come out however, my results seem to have been affected by the source of errors. Other explanations could only be discussed after further experimentation. Hypothesis and Data. Even though there is a link between my prediction and that of the data collected, it is difficult to say whether my hypothesis is correct, this can only be found out by further experimentation. Further experimentation would include repeating this experiment with the modifications suggested and a look at further factors that should affect the permeability of plant cells. One example would be to look at other plant cells apart from Beta vulgaris, or to loo at how factors such as surface area and age of Beta vulgaris affect the permeability of their cells. ...read more.

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