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An investigation to examine the effects of temperature on membrane stability in beetroot, by assessing the degree of pigment leakage.

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An investigation to examine the effects of temperature on membrane stability in beetroot, by assessing the degree of pigment leakage. Aim: - to discover how temperature affects the stability of the cell membrane in beetroot. Introduction:- Plant cells contain a plant cell wall as well as a cell membrane, which surround the protoplast (everything that is within the cell) of the cells. All cell membranes consist of a phospholipids bilayer, which are made up of two layers of phospholipids, hence the name. The plasma membrane is a partially permeable barrier between the cell and the extra cellular environment. The plasma membrane mainly consists of phospholipids. These phospholipids are a phosphate head, which is attached to two fatty acid tails (hydrocarbon chain). The phosphate group is highly soluble in water and so hydrophilic; however, the fatty acid tails are not soluble in water and therefore are hydrophobic. In the plasma membrane, the phospholipids are in two layers (hence the name phospholipid bilayer). The hydrophobic regions of the phospholipids line up together in the middle of the membrane, whilst the hydrophilic regions are on the outside of the membrane. Due to the hydrophobic regions of the phospholipid bilayer, it is generally not possible for large charged molecules or ions to pas through the membrane freely. The phospholipids have a hydrophilic (water liking and so soluble in water) head, which is a phosphate group (PO4��) that is attached to two hydrocarbon tails (fatty acids, that are insoluble in water and so are hydrophobic). There are other components that can be found in the phospholipids bilayer; however, phospholipids comprise most of the membrane. The hydrophobic regions of the phospholipids are directed towards the interior of the membrane and the hydrophilic heads are directed towards the exterior. Fig 1. Diagram of the cross-section of a phospholipids bilayer within a plant cell. The phospholipids bilayer acts as a barrier between the protoplast and the surroundings of the cell as well as controlling what enters and leaves the cell. ...read more.


and cut down the beetroot cylinders to 2cm in length, using the ruler. * Record the temperature of the environments before placing any of the beetroot into them. * Place a piece of beetroot into each of the 3 boiling tubes in one of the environments, starting the stop clock as soon as possible. (the second and third pieces of beetroot are my repeats) * At 2 minute intervals, record the temperature of the environments and do so at the end of the 6 minutes as well. * After 6 minutes, take the boiling tubes out of the environments, shake them (so that the pigment becomes distributed evenly throughout the solution) and pour some solution from each boiling tube into a separate cuvette. * Zero the colorimeter by placing a cuvette with distilled water in it, then place the cuvette with the solution in it and read off the percentage of light that was able to pass through. Repeat this process for each of the solutions. * Repeat this entire process for the rest of the environments. By repeating the experiment twice, I will be able to find an average result for each of the temperatures and it will allow for any anomalies within my experiments and so make my results more reliable. Apart from temperature of the environments, there are many other variables that I must consider within this experiment, which could affect the results that I obtain. Therefore, I must control them in order to make my results as accurate as possible. Controlling these factors will help to ensure that my experiment is as fair a test as possible. Accuracy and precision of equipment used: * Stop-watch: this read the time correct to the nearest milli-second. * Thermometer: this reads the temperature correct to the nearest 0.5�C * Ruler: this measures correct to the nearest 0.5mm * 10cm� measuring cylinder: this reads correct to the nearest 0.5cm� * Colorimeter: reads correct to the nearest 1% None of the equipment that I will be using will allow my measurements to be 100% accurate. ...read more.


However, once all of these percentage uncertainties have been combined, it is possible that they will have a great affect on the end reading that I obtained. The validity of the results that I obtained will depend upon the accuracy of the equipment used. If there is an overall high uncertainty on the equipment used, then my results will not be as valid as they should or could be. Therefore, the points plotted on my results graph may be incorrect and so give a wrong impression of the affect that temperature has on the membrane stability of plant cell membranes. Table to show percentage uncertainties of equipment used and total percentage uncertainty. Equipment Percentage uncertainty (%) Stop-watch 0.0014 Thermometer 0.542 Ruler 1.250 10cm3 measuring cylinder 4.167 Colorimeter 0.931 Total percentage uncertainty 6.891 The total percentage uncertainty of all of the equipment used is 6.89%. The percentage uncertainties are relatively low and so the accuracy and precision of the equipment used is quite high. This also means that the results that I obtained, which led to the plotting of the points on my graph, are quite precise. However, I still need to look at the reliability of my results, as they can be precise without being accurate of reliable. Also, the equipment used could be exchanged for equipment that has a lower percentage uncertainty to ensure that the precision of results is as high as possible. To extend this investigation further I could look at the affect of temperature on the permeability of other plant cells, such as potato cells, carrot cells etc. I could analyse the trends that occur in each of these plant cells and comparing them to one another. I could also, do the same investigation again, only with a different set of temperatures, or more temperatures (e.g. 10, instead of 5). This would give me more data and so I would be able to see more clearly whether my results to this investigation were truly correct. ...read more.

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Here's what a teacher thought of this essay

3 star(s)

*** This is a lengthy report that contains very thorough consideration of the sources of experimental error. There is a good deal of background information included but this needs to be more selective and focus directly on the aspects relevant to the question being investigated. The key elements of an experimental report are included, (ie. there is an introduction, a procedure, data, a conclusion and an evaluation) but the positioning of these elements within the report is not helpful e.g the consideration of variables comes after the method.
Research and rationale
The background material for the investigation was extensive and the rationale for the investigation was clearly justified. It would help to list the references used within the text at the appropriate point.
This is a fairly well known investigation but there was sufficient thought and consideration given to the control of the key variables and the apparatus/method was modified to suit the project using the results of a trial run. A testable hypothesis was formulated and biological knowledge used to explain the prediction. The risk assessment was minimal and needs to be improved. The organization and order of each section needs more careful planning.
Observing and recording
The apparatus appeared to have been used competently with he results recorded in suitable tables. The headings of some columns could have been more informative.
Interpreting and evaluating
Summary tables were presented and calculation of statistical data was presented clearly. The graph was not included. The trends and patterns in the data were clearly recognized and commented on and the anomalies were discussed. The candidate is aware the results may not be entirely reliable and explored the possible sources of error. Suggestions for extensions of the investigation were very limited and this section could have been improved by proposing suitable extensions to the investigation.
The layout of the report could be improved and would benefit from the addition of subheadings. Appropriate technical terms were used throughout and spelling, punctuation and grammar were acceptable. More annotated images to illustrate key points would have made the report easier to read.

Marked by teacher Stephanie Wells 26/04/2013

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