Diagram:
Prediction:
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.
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
Apparatus: Solutions:
Measuring cylinder Sucrose Solution
Tile
Knife
Balance
Borer
Boiling tubes
Test tube rack
Ruler
Constants:
Solution type
Duration
Temperature
Conditions
Weighing scales
Variables:
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 give me a varied set of results from which I hope to make a sufficient conclusion. If any of the non-variables below were not kept constant it would mean it would not be a fair test. For instance if one of the potato chips was 1cm longer the surface area of the chip would be larger and there would therefore be more space for osmosis to occur.
For the purpose of my experiment I am going to do all the experiments at room temperature.
The water potential of the potato 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 chip 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. They must be totally covered in the solution, and the amount of solution will be kept the same because all the potato chips are the same size.
I am also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between scales.
Diagram:
Safety:
Goggles will be worn at all times
Caution will be taken when cutting potato
Method:
A range of sucrose sugar solutions will be prepared This will be done by adding varying amounts of distilled water to varying amounts of sucrose solution. Sections of potato will be cut using a borer. 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 weight of each chip will be measured the experiment will be repeated with different concentrates of solution. The potato pieces will then be placed in the different test tubes and then left over night. Then the potato pieces will be removed, the surface solution removed using paper towels and then they will be re-weighed and measurements will be taken again. I will repeat this experiment again as to obtain a second set of results and to obtain averages. This will hopefully produce more accurate results from which I will be able to draw a more accurate conclusion and graphs.
Fair test:
I have to keep all of the different non-variables the same, to make sure that none of them are affect the results of the experiment in any way.
The measurements for the solutions have to be perfect as to not change the out come of the experiment.
I will ensure that every time I handle the potatoes my hands are clean and dry. This will stop any kind of contamination and make sure that I don’t pass on any extra water onto the potato
Results:
These preliminary results give me an overall impression on the change in mass gain or loss when placed in varying concentrations of sucrose solution.
Potato 1
Potato 2
Averages
Increase or Decrease in mass and length
Conclusion:
From the results obtained in my experiment I found out that a cell is only turgid if its surrounding fluid is more watery than the fluid in the cell vacuole. I also discovered that a cell is plasmolysed if its surrounding fluid is less watery than the cell vacuole. I.e. the solution contains a lot of dissolved substances like salt or sugar. I noticed that as the concentration of the solutions increased, the potato chips decreased in mass and length. This is due to that Plasmolysis occurs when the external medium is more concentrated than the cell vacuole. The results obtained show that my original prediction was correct I thought that the lower the concentration of the sugar solution in the test tubes 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
Evaluation:
The experiment was very successful in my opinion. I obtained a large quantity of very accurate results from which I was able to create informative graphs. However if I was to repeat the experiment I might increase the time of the result to allow more osmosis to happen and possibly find out the saturation point of the chips. The range of concentrations was adequate but I would use more concentrations if I repeated the experiment so that I would have more varied results. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g. The concentrations 3% and 5% we experimented gave inaccurate results. They were above the line of best fit. This may have been caused by a human error. 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. I would also measure the flaccidity of the potato chip. This would allow me to examine if there was any connection between osmosis and the flaccidity of the potato chips. However with all this said I think that the experiment was truly successful and I was very pleased with my results.