Safety Precautions – I will take care when using the scalpel to cut up the potato, all stools will be under desks and safety goggles will be used if necessary.
Equipment –
- Potatoes
- A corer to core out the potato
- Scalpel
- Test tubes
- Test tube holder
- Solutions needed
- Pins
- Cling film
- White tile
- Weighing Scales
Method – First I got the potatoes needed and cored them out, we then cut lots up so they were all pretty much the same size/mass (if all the pieces of potato were not all similar, the rate of osmosis would vary from a small piece to a large piece), I weighed all pieces of potato that were used . I prepared test tubes (labelled) with 7 different concentrations of salt solution (0, 0.5, 1, 1.5, 2, 2.5 & 3) all with the same amount of solution in each, and then put 3 pieces of potato in each of the test tubes (so and average of the 3 can be made), but so we could identify each piece of potato had: 1 pin, 2 pins or none. The test tubes were then sealed up with cling film so no air can get in or out (hence they will all be the same and then left in a suitable place for a couple of days. Next each piece of potato was dried then weighed, and the results were recorded.
Observations: 0 – Hard, 0.5 – Fairly Hard, 1 – Hard, 1.5 – Soft, 2.0 – Slightly Soft, 2.5 – Very Soft and 3 – Very Soft.
The graph clearly shows as I increase the concentration of the salt solution, the weight change (%) on the graph drops every time the concentration is increased, backing up my prediction.
Evaluation - The experiment was very successful in my opinion. I obtained a good set of accurate results. I think I took easily enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow a sufficient amount of osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results. The cutting of the potatoes was the most difficult part of the experiment 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 have possibly found a device to cut the potato as it would ensure that all potatoes would be the same weight and dimensions. As well as the potato I could have found a more accurate way to measure out the solutions. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g.
Conclusion - By using my scientific knowledge of osmosis I know that if a potato is placed in a solution where the concentration of salt is more than the concentration of water then the potato will increase size/mass, but if I increase the concentration of water this will result in the plant tissue increasing in size/mass more quickly compared. For example if have two potato cylinders and I place each of them in a beaker, but the concentration is different then I would expect the beaker which contains plant tissue of 5% salt to decrease slightly compared to the plant tissue which decreases more in size and mass because it was placed in a solution of 10% salt. This is because water molecules move from a high concentration i.e. the solution, to a low concentration i.e. the plant tissues. Therefore, the potatoes cylinders in higher water concentrations will become swollen and increase in mass compared to the salt concentrations. After a certain period of time I predicted that the plant tissue will not be able to increase in size any further this is because the plant tissue is completely swollen. And the opposite will happen if I place the plant tissue in a solution with higher salt concentration than water concentration. I predict that the potato tissue will have become soft and weak, and its size will decrease more according to the concentration. This is because osmosis is the diffusion of water from a region of high concentration of water i.e. plant tissue, to a region of low concentration i.e. salt solution. Using this I can say that my prediction was correct.