Kitchen towel – to dry potato pieces, so water does not make them weigh more, as this would not make it fair
Pipette – measure solution
Test tube rack – to put test tubes in
Variables
- Temperature – The warmer the solution, the quicker the osmosis will go. This is because the water molecules will be moving more quickly. Careful though, if you heat something like the potato chip up too much then you will simply destroy all the cells.
- Difference in concentrations – This will speed up the rate of osmosis because there will be more particles that’ll have to change places.
- Surface Area – This will speed up the rate of osmosis because there will be more space on the potato for osmosis to take place.
- Concentration of water in potato – the higher the concentration of water in the potato the quicker osmosis will happen because less water will have to diffuse into the potato to even the amounts of water inside and outside the potato.
Prediction
I predict that the mass of the chips will increase as the concentration of the glucose solution increases. I predict that as the solution then becomes more concentrated, the increase in mass will begin to decline and eventually the chips mass will decrease from its original weigh. Therefore more concentrated the solution is, the lower the mass gain should be. The reasons for my predictions are that when the solutions concentration is low the water in the solution (outside the potato and its cells) is greater than that inside the potato cells. Therefore osmosis occurs and the potato cells take in the water in the solution. If the solution is a stronger concentration of glucose osmosis will work in reverse in that water will be drawn out of the potato cells into the solution. The cells will become plasmotised as it loses mass. When the water osmoses into the potato chip cell they become turgid. The potato chip will become rigid when turgid.
Fair test.
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 sucrose solution.
For the purpose of my experiment I am going to carry out all the experiments at the same time so the temperature is kept almost the same throughout.
The mass of the potato is a dependent variable. 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 the same. The potato chip must be totally covered in the solution, and the amount of solution will be kept the same because
all the potato chips will be the same size. I am also going to use the same scale to weigh my potato chips. This is because the measurements may slightly vary between different sets of scales.
Analysis
From these experiments, I have found out that my predictions were correct. In lower concentrations of sucrose, Osmosis takes place and the potato chips become turgid. In higher concentrations of sucrose, Osmosis takes place but the potato chips become plasmolysed.
The results show that, in accordance with our hypothesis, the cylinders will expand when external solute concentration is low (high water concentration), and contract in strong solutions (low water concentration). This is due to osmosis, where water passes from weak solutions to strong solutions across a semi-permeable membrane, such as a cell membrane.
Conclusion
The prediction made is supported by the evidence obtained from this investigation. It shows that the potato cells increase mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration.
The evidence obtained from this investigation supports the prediction I made. It also shows that the potato cells increase mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration. I have been able to identify a pattern in my results, in the difference in weight.
In this experiment, I believe that I have collected enough data to support my hypothesis. This investigation was, I think, successful. Successful meaning my results collaborated my predictions. The potato cells, working to stay alive, took in, or gave out the water depending on the concentration of the tissue and the concentration of the solution it is surrounded in. I have been able to record sufficient results by repeating the experiment three times.
Evaluation
There was one anomalous result this could be improved by altering the experiment, for example by measuring the sizes of potato cylinders before and after with a more accurate method, e.g. accurate weight measurement. The test might also be more accurate if the potato cylinders were left in the solutions for a longer period of time to allow the solution to penetrate fully to the core of the sample. The test could also be repeated more times for each concentration of solution, and with a greater number of concentrations, as this would decrease the error - a disadvantage of our experiment was that one anomalous result affected the others significantly.
Results that were not as I would have expected occurred, the range of results appeared too low. However, although this is apparently an anomalous result, it could have been caused by either experimental error - more significant when a small number of results are used, or a difference in the potato for those cylinders. Either of these would easily be recognized if a larger number of results were collected and used.
For future experimentation we could repeat this experiment using a range of solution strengths very close to the value discovered here of sap osmolarity, to define more exactly its true value. We could also extend the experiment to use tissue samples from other plants, to discover whether the hypothesis is also correct for other tubers, and even for other plant tissues. We would then also be able to compare osmotic pressures inside different plants.
