And ensure a fair test.
SURFACE AREA- I will keep the surface area the same
As it means that there is the same
Amount of space for osmosis to
Occur. I will use the same borer to
To do this and cut them to the same
Length.
VOLUME OF SURRONDING LIQUID- I will keep this the same
To ensure that it is a fair
Experiment and the potato
Chips are also the same.
Cling film lids could be used
To cover the tests to prevent
The evaporation of the liquid
TIME IN LIQUID- this shall be kept the same, so that each potato
Chip will have the same amount of time for
To occur
THE MASS OF THE CHIP- the mass of the chip will be measured
Before and after the experiment to
Ensure we get accurate results. I have
Decided to measure the loss or gain in
Water by mass as I did two experiments
In class one measuring length and one
Mass. We achieved the most accurate
Results with mass.
The key factors which I am going to control are going to be concentration of the solution, the mass of the potato chips, the temperature and the time that the potato chips spend in the liquid.
Method
A range of sucrose sugar solutions will be prepared with concentrations; 0M, 0.2 M , 0.4M, 0.6M, 0.8M, .I have chosen these values of sucrose solution because they will give me a wide range of results which will allow me to calculate an average. If there is an anomalous result I can use also still use the other two recordings that I will take which can form an average. Sections of the same variety of potato will be cut into cylinders of 3cm with a cork borer. This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur. The mass of each chip will be measured as well so that more results can be obtained. Three chips will be placed in each flask according to the colour of pen on the bottom of the chip. The flasks are filled with 75ml of a certain concentration of sucrose solution and then left for an arranged amount of time. The potato chips will then be weighed every hour on the same digital weighing scales for a substantial amount of time. The potato chips will be removed from the solution, the surface solution removed using paper towels and then they will be re-weighed.
The equipment that will be used is;
- Cork Borer
- Potato’s of the same variety
- 6 flasks of 75ml
- 0.0,0.2, 0.4, 0.6, 0.8, 1M sucrose solutions
- Weighing scales
- Three different coloured pens
- Cling film lid to cover the sucrose solutions.
There are certain safety precautions that will need to be taken to avoid danger within this experiment. Hair must be tied back to prevent any substances touching the hair. Overalls should be worn so that sucrose solution is not split on clothes. Precautions must be taken when using the cork borer to cut the potato chips to the right size.
I predict that the lower the concentration of the sugar solution in the flasks, the larger the mass of the potato chip will be. This is because the water molecules pass from a region of high concentration, i.e. in the water itself to a region of low concentration, i.e. in the potato chip. Therefore the chips in higher water concentrations will have a larger mass than in higher sugar concentrations. The greater the concentration of water in the external solution, the greater the amount of water that enters the cell by osmosis. The smaller the concentration of water in the external solution the greater amount of water that leaves the cell. However, there will be a point where the concentrations of water in inside and outside the potato cells are equal. At this point there will be no change in length, volume and mass of the potato, as the net movement of water will be zero, no osmosis has occurred.
At point A the graph suggests that no osmosis has occurred, suggesting that the concentration of water inside the cell is equal to the solution outside.
At point B (high water concentrations), there is no indication that the cell is increasing further in size. This is because the cell is fully turgid and no more water can enter
At point C (low water concentration), there is no indication that the cell is decreasing further in size. This is because the cell is fully plasmolysed and no more water can leave the cell.
The evidence obtained from this investigation supports the prediction that I made. It also shows that the potato cells increase mass in solutions with a higher water concentration and decrease in mass in solutions with a low water concentration. In this experiment I believe that I have collected enough data to support my hypothesis. This investigation was overall quite successful. Successful meaning that my results mostly agreed with my prediction. 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.
The results were fairly good and by looking at the weights measured during the experiment there is a definite trend that can be seen from the results table. I believe that are preparations before the experiment wee accurate enough, there were a few anomalous results but we were still able to collect an average.
The graphs and the results show that osmosis actually took place in the experiment. As the molars increased, the percentage of the weight difference decreased.
There seem to be the odd results that undermine my predictions and one or two anomalous results. These may have happened because one of the key variables that we planned was not completely correct and accurate.
Having most of my results agree with my prediction proves that the experiment was a success.
The experiment helped me to find out how osmosis occurs between two liquid substances with a partially impermeable membrane and that the higher the water concentration is the larger increase in grams. This means that the percentage will also be higher therefore increasing with the grams.
Looking at the overall experiment I have thought of a few ways in which I could improve the experiments so that I get better and more accurate results. Firstly the concentrations of sucrose solutions were measured out using a measuring cylinder. Although we tried to make this as accurate as possible there was still room for error. A burette could be used next time to measure the concentrations as a burette is far more accurate than a measuring cylinder. Secondly when the potato chip was remove from the solution and dabbed dry to remove any liquid on the surface this may not have been done the same on every potato chip. On some chips more liquid may have been removed that others therefore affecting the mass of the potato chip. A more accurate and uniform way of drying the chips would need to be looked into next time to make sure that exact results are obtained next time. Another way in which I could improve my results would be to measure the diameter change in the potato chip throughout the experiment; this would have helped me to find out the volume before and after of the potato chips which would also help me to explain the results that were obtained
To make this experiment even more accurate and successful I think perhaps if there were more people in each group then each person could be assigned to a job and that job could be done to a higher level of accuracy. It would also mean that less experimental errors might occur as each job will not be as rushed.
Using more types of molar sucrose solutions could give me a wider range of results which would then help me to make an easier conclusion whether the results complimented my predictions.
Further work could be carried out to include concentrations that increased in 0.05 M. this would increase the accuracy and improve the graph other investigations could include using a different variety of potato and compare the results. Even different plant tissue could be used e.g. carrot, apple.
I could change other key variables in the experiment not just the concentration e.g. the amount of time the plant tissue is left in the solution, the size of the plant tissue or perhaps the temperature that I do the experiment in could be varied.
The size and shape of the plant tissue could be varied but I doubt whether this will have a substantial effect on the results.
I think that temperature would be a good key variable to change, for example the samples could be placed in different water baths and brought up to different temperatures to see if temperature does affect the rate of osmosis. The same method could be applied to this as for the experiment I did except perhaps the plant tissues could remain in the water baths for 24 hours and then recordings could be done.
Overall I think that with the apparatus and method which I used the experiment was a fairly good success.
