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  • Level: GCSE
  • Subject: Science
  • Essay length: 3002 words

The aim of my experiment is to investigate the effect of osmosis via potato tubers.

Extracts from this essay...


Biology Coursework Investigation The aim of my experiment is to investigate the effect of osmosis via potato tubers. I have chosen to investigate how the concentration of salt solution affects the rate of osmosis via potato tubers. I have chosen this factor because it is a relatively simple experiment to conduct and there is minimal risk of something going wrong, compared to other variables. Also from my research I have been informed that this experiment produces substantial results. To ensure my experiment is a fair test the following factors must be considered: * Concentration of the solution * Size of the potato tuber (and mass) * Volume of the solution * Duration of time left in the solution * Surface area of the potato tuber * Age and type of potato used * Temperature of the solution To create a fair test all aspects of the experiment will have to be kept the same whilst one key variable is changed. For this experiment that means the concentration of the solution that the potato tubers are left in. If any of the non-variables (factors written above) are not kept constant it would mean it would not be a fair test. For example if one of the potato tubers was slightly longer, then the surface area of the tuber would be larger and there would therefore be more space for osmosis to occur. Other non-variables can be monitored, for example the temperature of the solution in which the tubers are left. Doing all the tests at one temperature; room temperature (around 22-25°C) would control it. The volume of the solution can be controlled using measuring cylinders and the duration of the experiment can be controlled using a stopwatch. I will also be using the same balance throughout the experiment. This is because the measurements may slightly vary between scales. All these controls must be made in order to get accurate and reliable results. The science involved in this investigation will be osmosis and plant cells.


I will measure the masses using an electronic scale, which is very accurate and easy to use. I will repeat the experiment 2 more times, exactly as before, so that I have 3 sets of results. This is so that I can improve the reliability and accuracy of my data, and I can see any anomalies. After getting all 3 sets of results I will take the average. This leaves me with a set of very reliable results that are conclusive. Preliminary Results Before doing the actual experiment we did a simulation practise experiment. Here are our results: Repeat Experiment: From this preliminary experiment we cannot see any obvious patterns in the results apart from the fact that most of the results are negative percentage mass changes. This may be due to the fact that we encountered many problems throughout the experiment, which have all stemmed from my method. Because of these faults I will have to change my method so that I don't have the same problems in my actual experiment. These are the changes I will make to the method: * Leave each tuber in the solution for 10 minutes instead of 5 minutes. This is so that the surface area of the tuber is increased, and more osmosis can take place and provide me with more reliable results. * Cut the tubers so that they are 4cm long instead of 2.5cm long. This is so that there will be more of a mass change, making it easier for me to analyse my results. * Place the first potato tuber in the solution at the same time as you start the stopwatch, i.e. 0 seconds, then carry on putting one into its corresponding test tube at minute intervals. This is so that I don't have to try and put them all in at the same time, which is very difficult. This will also give me more time at the end to take them out, and it will not be such a rushed procedure.


In my results table I found an anomaly that doesn't follow the trend of the other results. It is printed in red ink in the results table, and was not used when taking the average percentage mass change. I did not include this result because it is far too different from the other results, and if used would totally change the shape of the patter shown in my graph. It may have been caused by a number of different things: * Me writing the mass wrongly into my table. * The solution I was using may have got contaminated with tap water, or another concentration of the salt solution. * I may have not wiped off all the excess water from the tuber before I weighed it. * I might have mixed up the result with another result by accident. * I might have accidentally used the same potato tuber again from a previous repeat. My table of results shows that the readings did vary a bit, but this was consistent and followed a visible pattern. To make them more reliable I could take more readings of the same result and take an average. The only result that was too different was the anomaly highlighted, which was ignored and not included to make the graph. To improve the reliability of my results further I could change my method so that the tubers are in the salt solution for longer period of time. This would allow more osmosis to take place. I also could use a larger volume of salt solution, and put the solution into a beaker instead of a test tube. This would mean that the tuber would not touch the side of the container it is in, unlike when they were put into test tubes. This experiment can be extended or get additional evidence by changing the vegetable used, for example a carrot could be used instead, and then you could compare the 2 results and come to a conclusion about osmosis via vegetable tubers and see if osmosis is the same in all vegetables. 1

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