For my experiment, I used a skewer to take samples of potato, cutting off the skin on a plate with a knife and measuring each one to exactly 2 cm in length with a ruler. I then weighed each one individually with scales and then in groups of three, which is the amount I put in each sample of solution. I measured and poured out exactly 20 cm³ of each sucrose solution with a measuring cylinder, including Distilled Water, or 0.0 Molar, 0.2 Molar, 0.4 Molar, 0.6 Molar, 0.8 Molar and 1 molar. I labelled each beaker of solution, so I did not make any mistakes and made notes on the appearance and texture of each solution and potato tuber. From my trial run, I saw that it was best to put in at least three samples of potato in each solution and that they should be weighed and measured individually as well as in a group, so I could calculate the averages. I also saw that it is better to handle the tuber samples using tweezers, so I do not squash them. I put the groups of tubers in the solutions and left them for two days before checking the results and measuring the solutions and the tuber cells.
I put all of my data into a set of tables and then made neater copies with keys explaining the highlighting I made on the table, which indicated the first and second run of the experiment and the outliers I identified. Outliers are results that can be very different or do not fit the pattern of the rest of the set of results. When they are identified, they are taken out of any statistical manipulation and reasons for their occurrence should be found. So as to improve the reliability of the data collected, the test should have multiple samples or be repeated so that the data can be trusted. I came across several outliers in my experiment’s results. Many of them occurred in the first run of my experiment, particularly in the weight of the tuber’s in the stronger solutions before and in the results from the weight of the tuber’s after I left them. The outliers before I left the tubers could be explained by the fact that I changed potatoes for the experiment because my first ran out, as it was a small potato. The one I used for the rest of the tubers would have had a different weight and density than the previous. The outliers from after I left the tubers could be down to where I placed the beakers on the shelf, which was different the second time round and so the environment was different, or could be dependant on the outliers that had already occurred before I left them as these may have been the tubers which came from the second potato. The outliers I found in the lengths of the tubers after the experiment could be down to my change in potato or a different rate of reaction from the cells in these samples.
I worked out the averages, percentages of decreases or increases, medians and ranges for the information available, excluding any outliers, from the different groups of information. With this information, I was able to make several graphs on the different information. These allowed me to analyse the data and identify any existing patterns. I calculated the averages on all the graphs by adding the individual measurements and then divided the total by the number of measurements there were. Some of them are lower than others and appear to be outliers on the graphs because there are only two measurements as opposed to three. For the percentages I used, I divided the result after I left the beakers by the result I had before I left them and then times it by 100. This showed me what percentage of the original was left and so I was able to calculate the percentage difference. The median values are just the middle value of those provided when put into ascending order. If there were two values instead of three, I chose the lower value as the median instead of deciding to choose the middle value between them. Finally, to work out the range of the values, I subtracted the lowest value from the highest. I used each form of these in at least one of my graphs as well as lines of best fit for each data set I used, which helped me see the overall pattern in the data. To find out the gradient of the lines, I divided the difference between the value on the line at the first and last molar concentration and divided it by 5, which was the number of concentrations I used. The outliers in the graphs could usually be explained by outliers being excluded from the calculations to make them or could be the result of human error or faulty equipment.
My first two graphs were on the percentage difference in the weight of the potato tubers after the experiment. I chose to do one from the group totals and the other from the averages for each molar because these would show the overall change that took place and was simpler than making the graphs from each individual measurement. I added on the lines of best fit and calculated the gradient of the graph, which in graph A showed that the higher the concentration of sugar, the greater the decrease in the weight of the potato tubers. This could be the result of the water molecules leaving the potato and moving into the solution because it was a stronger concentration than the potato and needed to reach equilibrium with the potato tubers. This is supported by graph B, which shows a very similar line of best fit and similar gradients. The gradients could show a fast rate of reaction, as the steeper the line, the faster the reaction was in the experiment.
Graphs C and D show the percentage difference in the length of the tuber cells, which supports the conclusion I made about graphs A and B, as the lengths decreased at a greater level with the higher concentrations and increased with the lower concentrations. This could also mean that water left the cells at a more rapid rate at the higher concentrations and entered the tuber cells at the lower concentrations until the solution and the potato were at a concentration equilibrium.
Graph E shows the percentage difference in the volume of solution after I left the beakers. The data in this graph shows that a large amount of the solution was lost at the lower concentrations, whilst only a little was lost at the higher concentrations. This could prove that the water molecules in the weaker samples moved to the potato by osmosis because the potato was at a higher concentration than the solution. In my preliminary results, the solution even gained some volume at the higher concentrations, but this did not happen here, possibly because of the solution I used or the concentration of the potato was higher, meaning that it would need more water molecules to reduce it to the solutions concentration. However, some of the solution could also have evaporated at a different rate that the preliminary trial run because of warmer temperatures at the windowsill I put the beakers on. However, this should have affected all of the solutions equally and would only have been a small amount.
In graph F, I have plotted the range and averages of the weight of the tubers I collected using error bars. I have added the data from before and after I left the beakers, meaning that I can see any patterns in the data. Both runs of the experiment show that the weights of the tubers were higher in the lower concentrations after the reaction and lower in the higher concentrations. This could mean that the tuber cells have gained water molecules at the lower concentrations as the potato was at a higher concentration that the solution and lost water molecules at the higher concentrations, as the potato was lower than the solution. This would have been the opposite with the sugar molecules in the potato, which would have moved from the potato to the solution at the lower concentrations and vice versa at the higher concentrations. The gradients of the two lines show that the reaction seemed to be quite fast, which was supported by the fact that I saw a big change in only two days.
Graphs G and H show the values for the lengths of the tubers after I left them, on average and as a group. The results were not as dramatic as the weight results, but did support the idea that the tubers in the higher concentrations lost water molecules from their cells, as they were shorter than those at the lower concentrations. The gradient shows a fairly slow reaction, which could be explained by the fact that a lot of water molecules would have to be lost for enough cells to begin to lose their shape and change the overall size of the tuber cells.
Finally, graph I shows the medians of the weights of the tuber cells groups both before and after the reaction. This is the most useful graph for showing the overall change in the reaction, followed by graph F, as it displays what happened to the tubers in general by showing the middle value. Both of the lines of best fit for the after results support my conclusion from the other graphs, particularly graph F, which appears to be very similar to this graph as both show greater weights at the lower concentrations after the reaction and lower weight before. They both also show lower weights at the higher concentrations after the reaction.
The descriptions I took of the tuber samples before and after the reaction support the idea that more water molecules were lost at the higher concentrations, as the tubers are shrivelled and brown. This means that water molecules have been lost as these make up the shape of the cells in the potato so it is stiff and large. When lost, the cells shape and consistency change so that the tuber cell changes as well. Also the solution description shows that sugar molecules have moved from the potato to the solution at the lower concentrations as the colour is opaque and there are thick strings of what must be sugar or sucrose, whilst the higher concentrations are clearer with no residue as water molecules have moved into these samples.
In conclusion, I believe that, form my results the concentration of the potato I used was around 0. 2 or possibly 0.4 as this is where there seem to be a change in the pattern of the results, according to graphs C, F, G, H and I. From these graphs and from the data I collected, it seems that this is the point where the water molecules in the solution stopped moving to the potato through osmosis because it was a higher concentration than the solution and the water molecules in the potato began moving to the solution because it was at a higher concentration. Therefore, the concentration of sugar in the potato was at this point because there was a change in the pattern. My prediction was right as the potato was at the concentration I predicted and the effect of the solution on the potato was how I predicted, with the potato in the lower concentration becoming hard and white through water molecule intake, and the potato in the higher concentration becoming squishy, browning and small. My predictions about the effect on the solution were also right as the lower solutions became opaque and stringy through sugar molecules intake through diffusion and the higher solutions became clearer through the extraction of sugar molecules and the intake of water molecules.
To make my experiment a fair test and reliable, I only changed the solution sugar concentration, as that was the factor being tested. However, as I ran out of potato, my results from this potato could jeopardise my overall findings. But, as I only used 3 or 4 samples form this potato, I have chosen to include them as a rough guideline to my conclusion. When I conducted the experiment, I used 3 samples of potato in each solution and repeated the experiment. This means that the results are fairly reliable as they are repeatable with the same pattern found each time. If I were to improve my experiment, I would use more accurate measurements so that I could make more specific conclusions. I would do this more specifically by using more samples of sugar solutions; preferably going form distilled water to 1 Molar up in 0.1 each time, so that I could have a more accurate conclusion as to the concentration of the potato. Also, I would use multiple samples of potatoes so I can tell the concentration of each in the beakers and repeat it a few more times to be completely certain about my findings.
