Controlled-Variables:
- Temperature – for the purpose of my experiment I am going to do all my experiments at room temperature.
- Type of potato – the potato chips should all be cut from the same potato, using the same tool and without being washed or peeled, to ensure that my experiment is fair.
- Size of potato chips – the mass of the potato should be measured throughout the experiment, and should be measured in Grams. The potato chip will be measured before and after it is put into the solution. This will allow me to see whether osmosis has occurred and to what extent.
- Volume of solution – the volume of the solution that the potato chips are kept in must be fair. The potato must also be totally covered in the solution and the amount of solution will be kept the same throughout.
- Weighing equipment – the same balance should be used to weigh my potato chips. This is because the measurements may slightly vary between scales.
Equipment List
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3 Test tube racks – These will be used to store my test tubes in, whilst osmotic activity occurs. They shall be clearly labelled so that I do not get mixed up.
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15 test tubes – These will be used to hold each potato chip and its chosen solution of sucrose concentration. These shall also be clearly labelled so that I do not get mixed up.
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1 borer – This shall be used to cut the potato chips, by using one borer it will ensure that all chips are of the same size, this will increase accuracy and the reliability of my experiment.
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1 Scalpel – This shall be used to cut the potato chips
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1 Ruler – This will be used to measure the potato chips to make sure they are all of the same length.
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1 Set of electronic Scales – These shall be used to weigh the potato chips both before and after the experiment. The fact that they are electronic increases accuracy.
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Sheets of blotting paper – These will be used to remove excess liquid from the surface of the potato chips before weighing after the experiment has been carried out.
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2 pipettes – These shall be used to extract the different liquids to make up the different concentrations. They will be thoroughly washed during usage as to not mix up solutions which could possibly damage the reliability of my final results.
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1 measuring cylinder – This will be used to measure out the distilled water, and the sucrose solution to make up the concentrations. It will be thoroughly washed during usage as to not mix up solutions which could possibly damage the reliability of my final results.
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1 roll of cling film – Small sections of cling film shall be placed tightly over the test tubes once they contain the chosen solution and potato chip. This is to ensure no evaporation occurs as this could affect the final results and reliability of the investigation.
Method Plan
Start by preparing a range of sucrose solutions with concentrations of 0 molar, 0.1 molar, 0.2 molar, 0.3 molar, 0.4 molar.This will be reached by adding the varying amounts of sucrose solution to the distilled water. Then, using a potato borer, cut out 15 cylinders of potato, and measure them using a ruler. This preparation must be done very accurately as a change in surface area will allow less or more osmosis to occur. The mass of each chip will be measured and recorded using the scales, in order to obtain more results. Place one potato chip into each test tube, resulting, with three potato chips for each solution (in different test tubes).
This should be recorded along with the weights, so as I know which chip went in which solution and in what order. This will make results even more accurate. And I will be able to take an average for each concentration of sucrose.
25ml of each sucrose concentration will be used, and once the potato chips are
In the test tubes they will be labelled so that they do not get mixed up. The potato pieces will be then placed in the different test tube racks, which will also be labelled and left for 2 hours. After this amount of time the potato pieces will be removed from the test tubes and surface solution will be removed using the blotting paper. The potato chips will now be re-weighed and their weights recorded.
Modifying Method
After carrying out my preliminary work, I modified my method plan. The main thing I changed was the amount of time that I left the potato chips in the sucrose solution from 24 hours to 2 hours. I also changed the sucrose concentrations that I used. Doing the preliminary work, helped me to improve my experiment and ensured that I got the best possible results.
Obtaining Evidence
Method:
1. I took three average sized ground potatoes and checked that they were both hard and not damaged.
2. Using a potato borer, I carefully cut out 15 cylinders of potato. The borer ensured that all my cylinders were the same shape and diameter.
3. Using a scalpel and ruler I cut the potato’s into chips so they were all equal length. I had to be very careful whilst cutting the potato’s as the scalpel is exceptionally sharp. I then had 15 chips and I placed them side by side, in groups of three, on a smooth white tile.
4. I took a test tube rack and placed 5 test tubes in each one and then labeled them 0.1 molar, 0.2 molar, 0.3 molar, 0.4 molar and 0.5 molar.
5. Using a measuring cylinder I measured out different amounts of sucrose solution and distilled water, so I could make my chosen concentrations. Which I then poured into the test tubes, putting one of each concentration in each test tube rack. I then had, three test tubes containing 25ml of each concentration. This will allow me to make an average of each sucrose concentration.
6. I then weighed every potato chip on an electronic scale and recorded the weights.
7. I quickly, but carefully, put 1 potato chip into each test tube. 3 chips were used for each concentration to create an average which gave me a better set of results and more accurate graphs.
8. I then tightly covered the top of each test tube with a small piece of cling film, to prevent any evaporation, which cold ruin my results.
9. I then placed my three test tube racks, (containing my test tubes) on a table, away from direct sunlight.
9. After 2hours minutes I drained out the solutions one at a time, in the sink and placed the chip on the blotting paper in the order I had put them in the test tubes as to not confuse myself as to which chip came from which solution.
10. I removed excess solution using the blotting paper and then placed each chip on the scales so that I could weigh them.
11. Each potato chip was measured accurately on the electronic scales and then the weights were recorded.
Precautions
- I had to keep all of the controlled-variables the same and constant throughout, to ensure that none of them affected the final results of the experiment.
- Whilst cutting the potato, I had to take care and precision with the scalpel and the borer, as it is very sharp and could cause cuts.
- The concentrations for the solutions had to be exact as to not damage the results of the experiment.
- I had to make sure that every time I came into contact with the potatoes my hands were clean and dry. This was to prevent contamination and made sure that I did not pass on any extra water or sucrose onto the potato chips as this would affect the accuracy of my results.
Results
Average results
Analysis and Conclusion
My graph supports my prediction of the experiment.
The reason my hypothesis is right is because, there is a large amount of water inside the potato chip and a small amount outside, as there is small amount outside, therefore water moves through the process of osmosis from inside the potato chip to outside, until the concentrations are equal. This is because the definition of osmosis states that water moves through a semi permeable membrane (the potato) from an area where it is in high concentration to an areas where it is in low concentration.
The simple trend that my graph shows is that as the concentration of sucrose increases, the mass of the potato chip decreases.
The gradient does change in my graph. It gets less steep as the X axis gets bigger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in mass of each concentration is becoming closer and closer together. From the line of best fit that has been added in, it can be seen that most of my points were very close to making a smooth curve. This shows that my results are very reliable.
When I put a potato chip in the solution of 0.1 Molars sucrose solution the potato chip increased in weight by an average of 0.14 g. This was due to the difference in concentrations between the sucrose solution and the water. When a chip was placed in a solution of 0.2 molars there was an increase of weight but only by the average of 0.04 g. This was a lot less than the increase of weight when the chip was in the solution of 0.1 molars. Reasons being that the 0.2 molar solutions must be closer to the solution inside the potato chip. Looking at the graph I can see that when the potato chip was placed in the solution of 0.3 molars, the potato chip decreased by 0.02g. This was due to the water concentration inside the potato cell was less than the 0.3 molar concentrations. Therefore water moved out of the potato cell causing it to decrease in weight. From then on the potato chip decreased in weight as the molars increased to 0.4 and 0.5 molars. I didn’t have any anomalous results which gives the impression that I successfully made up my molar solutions and accurately cut up the potato chips in the right lengths. From the graph an estimate to the concentration of the potato cell can be made as 0.26 M, as this is the point where the potato is not increasing or decreasing in mass, this is known as the isotonic point. This is called the isotonic point, where there is no net movement of water. At the isotonic point, there are equal concentrations of water on both sides of the membrane. However, it is important to realize that this is only an estimate.
Whilst I was recording my results, before discarding of each potato chip after weighing them, I gently felt them with my fingers and I noticed that the potato chips that had been in a higher concentration of sucrose felt softer, and were obviously flaccid. I knew this because, the fact that they had been in a higher concentration of sucrose told me that they had lost water, and were therefore flaccid. These cells had undergone plasmolysis because a more concentrated solution existed on the outside so water was drawn out.
Contrastingly the potato chips which had been in the lower concentrations, felt hard and tough, they were turgid. They had gained water.
Because water molecules have kinetic energy, they are constantly moving around in gaseous or liquid form, moving randomly from one place or another. The greater the concentration of water molecules in a system or solution, the greater the total kinetic energy, and the higher its water potential. This means, that as the concentration of glucose increases in a solution, the concentration of water decreases, lessening the solution’s water potential, and lessening its ability to move between solutions by osmosis. Relating this to the potato chips: basically, as the concentration of sucrose in each solution increases, the water in that solution is less able to move to the potato, causing water from the potato to move to the solution, decreasing its weight.
Evaluation
In my opinion the experiment went well. I gained a fine set of results and overall I am pleased with the investigation. The graph from the results strongly agrees with my prediction. This suggests that the experiment was fairly accurate. Although 3 repetitions of each concentration were sufficient, there was an anomalous result (circled on graph). This part of the experiment would need to be repeated, to guarantee further accuracy. A possible factor affecting my results is that the cylinders were bored from 2 different potatoes. Or perhaps it was caused by me, when the potato chips were removed from the test tubes, I could have possibly blotted the potato chips too much, causing then to loose too much weight thus affecting my results, making them unreliable.
However, there are small ranges between the results from each of the 3 test tubes used for each concentration. For example, for the sucrose concentration 0.1m, the first potato chip gained +0.14(g),the second potato chip gained +0.13(g) in mass, and the third potato chip gained +0.14(g) in mass. These small margins allow me to conclude that my experiment was accurate.
To improve the experiment if I repeated it in the future, I would possibly create more concentrations of sucrose solution so that I would have more varied results, i.e. 0.05m, 0.15m, 0.25m, etc. This will enable me to find out the isotonic point far more accurately as the one that I estimated is approximate. I measured the concentrations using a measuring cylinder; in the future the concentrations could be made more accurately using titration.
Further more, I used a scalpel to cut the potato’s, it was very difficult to do and un-precise cutting, could well have affected the surface area and so the overall rate of osmosis, in further experiments I could possibly find a machine to cut the potato chips as it would make sure that all the potato chips would have exactly the same dimensions. I could also weigh each chip on a more accurate scale, to improve accuracy further. E.g. not to 0.00g but 0.000g.
Another way of improving the results would have been to leave the experiment running longer, this would have enabled me to find the saturation point (when the potato can no longer take in any more water) and dehydration point (when the potato cannot lose any more water)and therefore get a more accurate result.
Finally, I could extend the experiment to a more exact level by looking at the potato cylinders under a microscope, and then I would be able to see the cells in greater detail and draw some more observational results.
Further investigations that I could carry out in the future are, using a different variety of potato, for example, a ‘king Edward’ rather than a ‘maris piper’. Also I could use a different plant tissue, for example, a carrot or an apple. Then I could find out whether osmosis occurs with the same patterns and trends with any vegetable.
Conclusion
However despite this, I think that the experiment I carried out, (given the apparatus I was given to carry out the test) was successful, my results were consistent, and I was pleased with the comparison of my results with my previous prediction. I followed the method plan correctly; I believe I gained accurate and sufficient enough results to conclude the experiment, and to prove my initial prediction.