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Potato Essay, Research Paper

Osmotic activity in potato cylinders Skill Area P: Planning

Aim: To investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato cylinders.

Hypothesis: Osmosis is defined as the net movement of water or any other solutions molecules from a region in which they are highly concentrated to a region in which they are less concentrated. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water through but does not allow bigger molecules to pass through. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other. For this particular investigation I think that the lower the concentration of the sugar solution in the test tube the larger the mass of the potato will be. This is because the water molecules pass from a high concentration, i.e. in the water itself, to a low concentration, i.e. in the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations. Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become “turgid” when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what makes the green parts of the plant “stand up” into the sunlight. When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become “flaccid.” This is the exact opposite of “turgid”. The contents of the potato cells shrinks and pulls away from the cell wall. These cells are said to be plasmolysed. When plant cells are placed in a solution, which has exactly the same osmotic strength as the cells, they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. “Incipient” means, “about to be”.

Variables: Variables Non-Variables to be considered

1) Solution concentration Surface area

2) Solution volume

3) Duration of experiment

4) Temperature

5) Solution

6) Conditions which experiment is kept in To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. I have chosen to vary the concentration of the sugar solution. This will hopefully give me a varied set of results from which I hope to make a decent conclusion. If any of the non-variables below are not kept constant it would mean it would not be a fair test. For instance if one of the potato cylinders was 1cm longer the surface area of the chip would be larger and there would therefore be more space for osmosis to occur. Doing all the tests at one temperature will control the temperature, so it cannot effect the results, so i am going to carry out my experiment in a controlled environment. To keep the water potential of the potato initially will be kept the same by using the same type of potato, which have been treated in the same way, e.g. have all been cut without being washed and peeled. The mass of the potato is a dependent variable, and this means that it will be measured

throughout the experiment. I will measure the mass in grams. The potato cylinder will be measured before it is put in the solution, and after. This will allow us to see whether

osmosis has taken place, and to what extent.

The volume of the solution that the potato chips are kept in must be fair. The cylinders must be totally submerged in the solution, i will make sure the amount of solution will be kept the same to make it a fair test.


Planned method: A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.25 molar, 0.5 molar, 0.75 molar and 1 molar.

Sections of potato will be cut using a scalpel and will be measured using a ruler. This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur.

The mass of each chip will be measured as well so that more results can be obtained. Three chips will be placed in each test tube each time so that I can take an average for each tube.

I will use 10 ml of each concentration of sugar solution and once in the test tubes they each will be labelled.

The potato pieces will then be placed in the different test tubes and then left for 24 hours.

Then the potato pieces will be removed, the surface solution removed by gently blotting paper towels over surface at the same pressure to keep it a fair test and then they will be re-weighed.

Skill Area O: Obtaining evidence


1. Using a cork borer i cut cylinders out of the potato

2. Using a scalpel and ruler I cut the cylinders down to roughly the same size. I had to be very careful whilst cutting the potato as the scalpel is exceptionally sharp. I then had 15 chips. 3.Taking a test tube rack I placed 5 test tubes and then labelled them 0 molar, 0.25 molar, 0.5 molar, 0.75 molar and 1 molar.

4. Using a pipette I put the same amount of each different concentration of solution and put each test tube in the right place in the rack

5.I then weighed every potato chip on a top pan balance and recorded the weights in a table.

6. I put 3 potato chips into each test tube and placed the rack in a controlled environment. 3 chips were used to create an average which gave me a better set of results and more accurate graphs.

7. After 24 hours I drained out the solutions in the sink and placed all the chips on the paper towel in the order I had put them in the test tubes as to not confuse myself as to which chip came from which solution.

8. I dried each chip with the paper towel and then placed each one, one by one, on the top pan balance to weigh them and their weights were recorded in a table.


>Whilst cutting the potato, extreme care and precision had to be taken with the scalpel as it is very sharp and could easily cause a serious wound.

>The measurements for the solutions had to be perfect as to not change the out come of the experiment.

>I had to ensure that every time I handled the potatoes my hands were clean and dry. This was to stop any kind of contamination and made sure that I did not pass on any extra water onto the potato.


This graph shown above gives the line of best fit for the percentage change in mass of the potato cylinders. The graph is a curve that slopes downwards and does not go through the origin. Because the line is not straight and does not pass through the origin, it means that the percentage gain and loss in mass and concentration are not directly proportional. However, there is a pattern on my graph, and this is, as the concentration of the solution increases, the percentage change in mass decreases. The graph shows that the percentage gain and loss in inversely proportional to the concentration. The gradient does change in my graph. It gets less steep as 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 molar concentration is becoming closer and closer together. From the line of best fit that has been added in, it can be seen that all of my points were very close to creating a perfectly smooth curve. This shows that my results are fairly reliable. My graph fits in with my prediction of the experiment graph. It shows that the potato cells increase in mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration. When the concentration reaches above 0.75 M, there appears to be no further water loss, suggesting that the cell is fully plasmolysed. From the graph an estimate to the concentration of the potato cell can be made as 0.13 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 where no osmosis is taking place, both the potato and the solution have an identical molar concentration. The next point, 0.25 M looses approximately 4.0 %. This shows that the water potential of the salt solution in the beaker is weaker than that of the potato chip. The next, 0.50 M, looses approximately 8.0 % in mass. This shows that the salt solution has an even weaker water potential than 0.25 M and that osmosis took place. This is why the potato lost even more mass, and it shows that the water potential in the beaker is less than that of the potato chip. This pattern carries on through the graph, and even more mass is lost, as more water moves out of the potato into the solution. My results also match with my initial predictions.

Skill Area E: Evaluation

This experiment was very successful in my opinion. I obtained accurate results from which I was able to create informative graphs. I think I took enough results for the concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur.

However if I was to repeat the experiment I could possibly try to find out the saturation point of the potato. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have a larger amount of results to test this idea further.

The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would take more care when cutting the potato to ensure that all potatoes would be the same weight and dimensions. I will also use the same balance to weigh my potato chips. This is because the measurements may slightly vary between the top pan balances. I would have liked to repeat this experiment again to obtain a second set of results. This will hopefully produce more accurate results from which I will be able to draw a more accurate conclusion. There were not any out of the ordinary results, but some were not as close to the line as others. This may have been caused when the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction.

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