Theory of Osmosis:
Process of Osmosis:
In osmosis, a solvent (often water) moves from a region of low concentration to a region of high concentration through a semi-permeable membrane. In the picture above, water molecules diffuse into the concentrated sugar solution because the water molecules are small enough to move through the membrane. The larger sugar molecules are unable to move through the membrane into the water solution. Osmosis will stop when the two solutions reach equal concentrations on either side of the membrane.
All plant cell membranes are differentially permeable, which means that they will allow some substances to penetrate them but not others. Water can freely penetrate all membranes. The cellulose cell wall does not act as a differentially permeable membrane and will allow most substances that are dissolved in water to freely pass through it.
When the concentration of sucrose is the same inside the potato as it is outside, i.e. when the potato neither gains or loses mass, this is called the isotonic point.
Original Results
These results are not accurate, as, due to circumstances beyond my control, I had to leave them for too long. Also, I did not have time to complete all the concentrations in my plan, therefore I am going to use results given to me.
Results
Graph
I have drawn a line graph to show my results. I have drawn a line of best fit and included error bars.
Analysis
My graph shows a downward trend, which means that as the concentration of the solution was increased, the loss in mass declined. With both the 0% and the 2% sucrose solutions the potato chips gained in mass, but when the concentration of the solution was increased to 5% the potato chips started to lose mass. The higher the concentration of the sucrose solution, the more the potato chips lost in mass.
My graph is not particularly accurate as most of the error bars are quite large, like the 5%, 10% and 15% solutions. The 2% solution is by far the most accurate as there is no error bar, the results were exactly the same for all three experiments. The 0% solution seems quite accurate, as there is only a small error bar, showing the results from the three experiments varied very little.
My results supported my prediction that:
“ in the 0% sucrose solution, the potato chip will gain mass. In the 20% sucrose solution… the potato chip will gain mass.”
The isotonic point in the experiment is between 2% and 4%, I would estimate it to be about a 3% concentration of sucrose.
Evaluation
There were 2 main problems that I encountered, these were:
- the lack of time in the lesson to complete my plan
- the fact that, due to circumstances beyond my control, the experiment had to be left for a longer amount of time than I wanted.
The amount of time in the lesson was not sufficient for me to complete my method. This was also due to the lack of equipment, meaning that my experiment was incomplete. I had originally intended to leave the experiment for 24 hours, but, due to unforeseen circumstances, this time was doubled, making my results very inaccurate. I think that, because I left the potato chips for so long, the cells may have dies, thus making the potato chip lose mass. I did not manage to overcome these problems and had to use a set of results given to me for my analysis.
There are a number of other experiments that I could have done, but my preliminary work showed that this was the best one. The experiments that I tried, and the reasons that they didn’t work as well as this one are listed below:
- using raisins instead of potato chips – this doesn’t give enough change in mass because the raisins are too small
- visking tubing – this is too hard to measure and is unreliable
So, in conclusion, although my experiment went wrong, I have found out that in very low concentrations of sucrose, the effects of osmosis are very little and the cells gain mass slightly, whereas in higher concentrations, the effects are greater and the cells lose mass.
