At some point (when it is the same as the potato’s concentration), the potato chip will be placed in an isotonic solution, and that very little osmosis will take place. This is due to the fact that the concentration is equal on both sides, the same water molecules move from both sides to the other, reaching the point of equilibrium.
I predict that the graph will look like this: Foucault
Pre-Test
For my final experiment to run smoothly and for myself to attain the right sort of results to analyse, I needed to do a pre-test to find out how certain things will work during my experiment. For example, I could have tested what size potato 'chip' was most suitable for getting results, how much water I should put into the test-tube and how long I should leave the sample in the solution
A pre- test will now be performed to help me come to a decision of the best method to use for my main results. This will be as follows:
For my pre-test, I got 3 potatoes, cut them down to size using a cork borer- so that each chip will have the same surface area, then cut them to the same length as the surface hugely affects the weight of a potato. The potato chips were roughly 3.5cm in size and took their individual mass on the weighing machine, then, recorded their mass down. Now 3 solutions will be made- the spread of the concentrations will range from 0, 5, 10% salt solution, In order to make up the solutions for example lets take 5g of salt placed into 100ml of stilled water stir it around to dissolve the salt particles = a 5% salt solution, the same technique is used using the amount of salt required for the other two solutions. 25ml of the solutions is then poured into different boiling tubes- I choose 25ml as it covered the potato chip, not too much nor to little.
I then placed all the potato chips into the separate boiling tubes with the different salt solutions. Then, I started the stopwatch. After a lesson which lasts for about 55 minutes. I then took each potato chip out of the solutions dried them off to remove excess solution and then weighed each one separately on a top pan balance, to find out the mass difference, record and then calculate the mass difference and the mass change.
The results of my pre- test are:
The results tell me that the concentration of the potato cell must be approximately 1 point or so.
Prediction
What I now predict will happen when you change the concentration of the salt solution around the potato chip is that when the potato chip is placed in a hyper tonic solution (5%), the more water is lost from the potato. The water in the cell sap flows out until the salt to water solution is equal in and out of the cell sap. When the potato chip is placed in a hypotonic solution (0%) the more water the potato chip will gain. This is because of the semi permeable membrane which divides the two concentrations of the salt to water. The water moves in to the cell until the salt to water solution is equal on both sides. At some point (when it is the same as the potato’s concentration say about 0.5-1.5), the potato chip will be placed in an isotonic solution, and that very little osmosis will take place. This is due to the fact that the concentration is equal on both sides, the same water molecules move from both sides to the other, reaching the point of equilibrium.
Fair test
To make this a fair test I will make sure that the following factors are kept the same:
The type and how fresh the potato is may affect osmosis, age of the potato- in order to do this I will get the potato from the same bag and from the same potato. I will also try to keep the temperature roughly the same, though it will be difficult to keep exactly the same, as the temperature in the room will keep changing, therefore it will be changing the temperature of the water. The size and surface area of is also another one- I will do this by cutting the potato with the same cork borer and then cutting the chips to have an exact size of 3.5cm long.
Details of readings
To make my readings more reliable I will include more results, meaning a greater range or spread of concentrations with equal intervals so that it is much clearer to see the actual trend of the curve.
Therefore, I have decided to use the following rage of concentrations of salt solution 0 – 5 going up in 0.5 e.g. 0.5, 1, 1.5, 2 etc.
Method
To do the experiment, I will need 11 'chips' carved out of a potato, 11 solutions with different concentrations of solute, boiling tubes, a measuring cylinder, a ruler, a tile and a sensitive weighing machine- top pan balance. I will set the apparatus as shown below:
The solutions will be made, in total I will make 11 concentrations using the same method as above which was e.g. take 1g of salt placed into 100ml of stilled water stir it around to dissolve the salt particles = a 1% salt solution, the same technique is used using the amount of salt required for the other 10 solutions
Take a potato and a small cork-borer, cut the potato with the cork-borer, cut out as many pieces as you can from the potato- these will be your potato chips.
Take the skins off the sides of the potato chips. The skins add to the mass of the potato chip, which would give me unreliable results. Cut each potato chip to a length of 3.5cm long to get reliable results.
Pour 25ml of each salt solution into separate boiling tubes, label them 0.5 -5% etc
Weigh each potato chip on a top pan balance and record their weight before they are placed in the different salt solutions.
Then I will place the potato chips into 11 various concentrated solution, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5.
Leave for about a length of a lesson- 55minutes.
Take the potato chips out of the solutions.
I will dry with towels to remove nay excess solution off the potato chips.
Re-weigh each potato piece on the top pan balance as this will take Record the results and then calculate the mass difference and the mass change.
Results table
The formula I will use to find the percentage gain/ loss will be; Final Mass - Original Mass x 100 to (dp)
Conclusion
From my graph what I can see initially is that, as the concentration of the solute concentration increases, the percentage mass of the potato chip decreases.
Meaning that my prediction generally seemed to support
I think the reason for my evidence show this is as follows lower the point 0.5% concentration of salt solution the potato chips gain mass, concentration above 0.5% causes the potato chips to loose mass, the plots below show on the horizontal axis shows this.
Osmosis is the process when water diffuses across a selectively permeable membrane to an area of high solute concentration. This can also be said that it is the movement of water molecules, from a high concentration, to an area of low concentration of water. When there is a high concentration of water, it is also called 'high water potential.' The water molecules follow the salt molecules. When the potato chips were placed in a solution from 0-0.5 the potato chips gained in mass- water passes in by osmosis- water flows through the cell wall and the cell membrane into the cytoplasm and into the vacuole. The increased pressure of the water in the vacuole presses the cytoplasm against the cell wall. When the cell can take in no more water it is called fully TURGID. It is this turgor pressure which keeps the cells rigid and therefore provides support for the potato chip. When the potato chips were placed in a solution greater than 0.5, in a more concentrated solution, they loose mass- water passes out of the cytoplasm through the cell membrane and the cell wall and into the solution outside the cell, the pressure decreases and the cytoplasm pulls away from the cell wall, the cell becomes FLACCID. There was no net gain at about 6% where my line of best fit crosses the horizontal axis therefore I am able to say that there was the same number of water particles to salt particles- the salt concentration of the potato chip is the same of the salt concentration of my solution-EQUILIBRIUM.
The ways in which my conclusion/evidence supports my original prediction is that in still water the gradient levels out the potato chip takes on water until it is fully turgid, when reaching its equilibrium state/ isotonic state it loose water until the same salt particles to water particles in and outside of the cell. At the end of the graph it becomes flaccid/ plasmolysis - meaning no more water can be taken out.
Evaluation
I am confident that my experiment supports my prediction because the results fitted in line with everybody else’s-the same pattern occurred for everyone as did for mine. My experiment was accurate/inaccurate because most of the points were close to the line of best fit. Though at these points circled on the graph at salt concentrations of 0.4 and 0.5% the points seemed to clearly go up not fitting into the predicted pattern as these results were meant to level out.My results are reliable / unreliable because the points fitted the general pattern that was predicted, which were similar to other groups and their results except for the anomalous results which did not fit the predicted pattern.
I have highlighted the odd readings in my results table I think that these were due to: Either the solutions were not being made up probably with the use of inaccurate scales not being exact with how each chip was weighed as the scales only measured to 1dp e.g. if the actual weight of the potato was 1.09 the scales would read it as 1. This can also be said for the weight of the potato chips will also be inaccurate due to the fact that the scales only measured to 1dp. The way in which the potato chips were dried off, it could have been that some potato chips were dried off better than others therefore not drying them to the same extent. They were all dried off with the same towel so therefore instead of getting rid of excess solution it might have been gaining. If I were to redo this experiment again, I would change the following things, because of the following reasons: To improve the accuracy of the experiment I will use a new paper towel for each potato chip to dry off the excess solution-to be sure that each potato chip is being dried off thoroughly and that no excess solution is gained. A top pan balance that reads to the second dp more precise and accurate which is needed to find the actual mass gain or loss from the potato chip To improve the reliability of the experiment I will have smaller steps between the concentration which will make it a lot clearer to see the anomalous results and clearer for a line of best fit to be put in without a guessing as there will be more of a definite strong bold line that the points would give. Also repeat each concentration several times and then work out an average for them. Other ways I could collect more results to test my prediction are the length and gurth of the potato chip, because as the cell becomes turgid- this is where the potato chip has gained in less concentrated solution, so the water passes through the cell wall and into the cell membrane into the cytoplasm and into the vacuole, increasing the pressure of water inside the vacuole therefore pressing the cytoplasm against the wall. This turgor pressure keeps the cell rigid providing support for the cell making it fatter and stronger. Through proceeding the experiment this way we are able to see if changing the length and the gurth would make it more flexible as more water has been either lost or gained.
