For this particular investigation I think that the lower concentration of the salt 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 ie. In the water itself, to a low concentration, i.e In the potato chip. Therefore, the chips in the higher water concentrations will have a larger mass than in higher salt concentrations.
Further information on potato plant cells:
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 works against osmosis. Turgidity is very important to plants because this is what make the green parts of the plant stand up into the sunlight.
When plant cells are placed in concentrated salt 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.
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 salt solution. This will give me a very 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 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 same type of potato will be used, 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. The 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.
Method
Equipment
Potato
Scalpel
Boiling tubes
Salt water
Water
Measuring cylinder
Test Tube rack
Knife
A range of salt solutions will be prepared with concentrations of 100%, 80%, 50%, 20%, 0% (pure water) salt solution. This will be done by adding varying amounts of distilled water to varying amounts of salt solution. Sections of potato will be cut using a scalpel and then weighed on an electric balance and recorded, the weight was made as close as possible on the two potato chips to be averaged. Two chips will be placed in each test tube each time so that I can take an average for each tube. I will use 50ml of each concentration of salt solution and once in test tubes each will be labeled. The potato pieces will then be placed in different test tubes and left for 30 minutes, I will time this using a stopwatch. Then the potato pieces will be removed, the surface solution removed using paper towels and then they will be reweighed.
Results
2.16g
2g
2.485g
2.56g
2.665g
The results I got are mainly accurate apart from one on 20% the second set of results the change is supposed to decrease instead of increase.
