In this experiment I am intending to investigate the concentration of sugar in the cell sap of a potato-cell's vacuole. I will discover this using my knowledge of the biological process ofOsmosis.Osmosis is the movement of solvent (usually w...

Method

1. First use the potato corer to extract fifteen pieces of potato.
2. Cut each piece to 2.5cm in length.
3. Weigh each piece of potato and make a note of the results.
4. Place one piece of potato in each beaker of solution.
5. Leave for 24 hours.
6. Remove each piece of potato from the solution.
7. Wipe of all excess liquid.
8. Re-weigh each piece of potato.
9. Record the results.

Constants and Variables.

In this experiment there should only be two changing variables:

1. Different strengths of sugar solution.
2. Changing weight of the potato samples.

To be sure that these are the only variables I must:

1. Keep the potato samples the same length.

This is because a sample with a larger surface area will absorb, or expel more water than a shorter sample.

2. Use the same potato.

This is because a different potato will have different cell sizes and will absorb, or expel more water in a shorter length of time.

3. Stop any water from evaporating from the beaker.

This is because if the water level drops bellow the level of the potato it will have a lower surface area exposed to the solution.

4. Prevent contamination.

This is because the solutions are precise in concentration and any form of change will render the experiment void.

5. Keep the amount of solution the same.

This is because the higher the amount of solution, the higher the amount of sugar, and therefore the faster the rate of osmosis.

Accuracy

For this experiment to be accurate I must chose a suitable range of results (to be sure I capture the approximate concentration) and I must repeat each concentration (so that I can identify any anomalous results and repeat that concentrate). I have chosen to repeat each stage three times, and I will look for the potato concentrate between 0% and 40% sugar concentrate (with a separate experiment for each 10%) as I thought is more likely that concentration of the cell sap will be under 50% concentrate than over.

I chose to record the weight change in the potato sections to a 2 decimal place maximum as that will be close enough to detect any change in mass. I will measure the length of each piece of potato to only one decimal place, this measurement does not need to be too accurate as a difference of 0.1cm will not vary the results too much.

Safety

This experiment does not include any dangerous chemicals therefore it safe enough to not wear safety goggles. To ensure safety any sharp equipment that is needed during the experiment, i.e. Scalpels and potato corers, are to be used carefully on the surface of cutting tiles or boards.

Previous Knowledge

Through my previous knowledge I know that if the concentration of water surrounding the potato sector is greater than that contained within each potato cell’s vacuole, through the process of osmosis water will pass over semi-permeable membrane and enter the potato cell thus increasing the weight of the potato sector. However if the water concentration surrounding the potato sector is lower than that contained within then, thorough the process of osmosis, water will leave the potato cells through semi-permeable membranes into the surrounding solution thus decreasing the weight of the potato sector.

Prediction

 

In this section I will state what results I except to receive from each sugar concentration I have chosen to include in this particular experiment.

0%

This solution contains 0% sugar so it must contain 100% water, with a high concentration such as this I expect the cylinder of potato to increase greatly in weight.

I believe the potato will increase in weight because, in my opinion, it is impossible for the concentration of the surrounding solution, pure water, to have lower water content than that of the sugar solution contained within the cell cap of the potato. Therefore, due to Osmosis the water molecules will move from where they are in high concentration to where they are in low concentration: leaving the solution and entering the potato.

10%

This solution contains 10% sugar; therefore it must contain 90% water. As with the above concentration, this is also a very high concentration of water, so I predict that the cylinder of potato will increase in weight.

I believe the potato will increase in weight. I believe this because, as is my opinion, it is unlikely that the solution contained within the cell sap exceeds 90% water content. As the solution surrounding the potato cylinder is of 90% concentration, the water concentration it is higher outside the potato cylinder than inside. Therefore, due to Osmosis the water molecules will move from where they are in high concentration to where they are in low concentration: leaving the solution and entering the potato.

20%

As there is 20% sugar there is 80% water I estimate that the water to sugar ratio is approximately equal inside and outside the potato cells. Therefore I believe that there will be no weight change whatsoever.

 

I predict that at this point the potato will neither increase nor decrease in weight because I believe that it is at this point that the concentration of water in the surrounding solution, 80% water, is equal to that contained within each individual cell vacuole. Therefore there is no area of high concentration and no area of low concentration; this means there is no movement.

30%

At this concentration I believe that the potato will begin to decrease in weight because there is once again very little difference between the concentration of water inside the cell and the concentration outside the cell.

I believe the potato will decrease in weight because the concentration of water is now a higher inside the cell than outside. Therefore, due to Osmosis, the water molecules will move from where they are in high concentration to where they are in low concentration: leaving the cells and entering the solution.

40%

At this concentration I believe that the potato will decrease in weight because there is a high difference between the concentration of water inside the cell and the concentration outside the cell.

I believe the potato will greatly decrease in weight because water is now at a much higher concentration inside the cell than outside. Therefore, due to Osmosis, the water molecules will move from where they are in high concentration to where they are in low concentration: leaving the cells and entering the solution.

Collection of Results

To be sure that my results are collected and recorded in the correct manner, one which is easy to both understand and compare, I have constructed four results tables which can be seen overleaf. I have crated a separate table for every experiment and one in which I can record the average result of each aspect of those experiments.