Safety
Usual lab safety rules were followed, as well as taking the fragile test tubes and potato peeler into care.
Fair Test Requirements
To make sure the experiment is fair and runs smoothly; I will have to monitor numerous factors very closely. For the experiment I will be using three pieces of potato (from the same potato) for each solution then taking the average result to plot my graph. I will not touch the potato cylinders with my hands as I might accidentally alter the mass and could affect the experiment. All the potato pieces will also be measured and weighed before hand so it doesn’t influence the results. The temperature of the lab will also be monitored and kept the same, if not, then this could influence the results. If I keep to my Fair Test guidelines I should receive accurate and reliable results. I will repeat the investigation and find averages to get the most accurate results as sometimes small mistakes can be made that cause anomalous results.
Prediction
I predict that as the concentration of sucrose solution increases, the potato chip after 24 hours will decrease in mass and length. I can make this prediction knowing how osmosis works. The definition of osmosis states that when there is a high sucrose solution concentration outside the potato chip it will be greater than that inside the potato cells. This means that the water from the cells will diffuse out into the surrounding solution which will balance the water and sucrose concentration. As the cells lose water through diffusion, the potato chips become plasmolysed, causing the chips to collapse, which will then obviously cause the chips to change in mass and length. The above can be reversed when the concentration in the potato chip is greater than the surrounding solution. Instead of the water diffusing out, it diffuses into the cell causing the chip to become turgid, making the potato chip swell. Using this principle, we will be able to find out the concentration of the potato cell, so when the mass or length of the potato is unchanged we know that no water has diffused in or out, so this means the concentration of the sucrose is equal to that inside of the potato chip.
Diagram
This diagram explains the experiment we are carrying out, when the solution outside the cell has a greater concentration than the cell inside.
Results Table
After obtaining these results I realised they weren’t good enough and also I didn’t have enough time to carry out all the sucrose solutions I said I would investigate. So because of this I will only be using the results I obtained in class to analyse and plot my graph.
Analysis
The results show that as the concentration of the sucrose solution increases, the mass and length of the potato chips decrease. This proves my earlier prediction. The reason being is because osmosis was taking place. Water of high concentration areas diffused to areas of low concentration. As the sucrose concentration increased the amount of water in the solution decreased. So the water from the potato chip diffused into the surrounding solution which is sucrose. Therefore the cells become plasmolysed and the chip decreases in mass and length. As I explained in my prediction, the above can be reversed when there is higher concentration inside the potato chip than outside. The water diffuses into the potato chip making it turgid; therefore the potato increases in mass and length.
Graph
The graph I have plotted gives the line of best fit for the percentage change in size of potato chips against the concentration of sucrose.
By using the graph we are able to find out the osmotic potential of the potato cell (where the sucrose concentration is neutral). This is found out by finding the point that both lines of best fit cross the X-axis. But because both the mass and length lines do not meet at the same point we must estimate the point on the line between the two. So on the graph, 0.305m is the reading between both the lines of best fit. So the osmotic potential of the potato chip is 0.305m.
Evaluation
The results and graphs obtained are roughly in line with my predictions. Although the results were fairly accurate, I still think the investigation went fairly well and they were good enough to prove our hypothesis. The accuracy of the investigation was adequate, however there are some improvements that could be made if we were to do the experiment again;
- Firstly carrying out more tests will enable us to obtain a more accurate average.
- We did not take the potato chips out at the same time allowing some chips more time in the sucrose; this could have affected the results and so should be taken into consideration if there were to be a next time.
- Use a wider range of sucrose solutions.
- When the potato was dried to remove surface liquid it was not necessarily done the same on each potato, allowing some to weigh more.
- Although the osmotic potential for this investigation was estimated, a more scientific approach would have been better.
- Selecting a better root vegetable to see how the results differ.
These points can all be taken into consideration for a re- test, but I believe this experiment went well and we obtained the results that proved my hypothesis and prediction.
