Osmosis in Potato Cells

*** Rob Shanley ***

Osmosis in Potato Cells

Aim:

In this investigation I will be investigating the amount of osmosis in potato cells and whether osmosis and potato mass changes in different strengths of sugar solutions.

I will do this by putting a constant amount of potato in solutions with steadily increasing sugar contents.

Preliminary:

I decided to under take a preliminary experiment to find out whether there are any problems or hitches that would have to be sorted out before the real experiment.

For this preliminary experiment I took three Potato chips each made by a borer. My partners (Alex and Dan) and I made the chips 5cm in length with a diameter of 9mm and an average mass of 4.2 grams measured on a balance accurate to 2 decimal places. We then added each of the potato chips into a different solution in boiling tubes. The three solutions were 100% sugar solution with no distilled water, 50% water and 50% sugar solution, and finally 100% distilled water. We then left these Potato chips for 45 minutes and recorded are results in the table below:

What we found out after the experiment was that the stronger the sugar solution the more mass the potato lost. The Potato chip in 100% water and the 50% water and 50% sugar gained mass during the 45 minutes. We concluded that we would have to test a wider selection of solutions showing a greater variety of sugar strengths. Also we have decided to make the test fairer by using three Potato chips in each of the solutions, so in all we will have 15 Potato chips and therefore will have a large enough sample to take an average from each solution so we can find the average change in mass. This will make our results more reliable

Method:

For the experiment I have decided to take the borer and make the potato chips 5 cm long and 9mm wide. We decided to not make the mass of each potato chip the same. We used the boiling tubes and filled them up with 100ml³ of each solution strength. As we found out that we needed a greater selection of solutions we used the following strengths: 0.0 M, 0.2M, 0.4 M, 0.6 M, 0.8 M and 1M. This means we will have 6 different solution strengths and three chips for each solution, therefore we have 18 chips overall, this should be enough information to find out an average mass change.

For the Molar strengths we had to make sure that they were equal and fair amounts so we used the measuring cylinder and made the percentages according to the amounts i.e. 0.4 M would be 40% sugar and 60% water of the 60 ml cubed in the boiling tube. After we have cut and made the potatoes in the borer and massed each of them we will place them into the boiling tubes and leave them on the windowsill for 24 hours and then take each of them out of the solution individually starting with the ones we added first and lay them down on a paper towel to remove any excess solution that could effect the mass of the chip for the results table. We will then mass each chip on the balance with 2 decimal places to be as accurate as possible. After that we will fill in the results table and draw graphs to show all our results.

This is a simple table to show you how to do the solutions:

Fair Test:

This is a preview of the whole essay

This is a simple table to show you how to do the solutions:

Fair Test:

To make it a fair test you must look at all areas, which could be varied, then check how you could make it fair. To make our test fair we made all of the Potato chips the same length and diameter, 5 cm length and 9mm diameter. We decided to vary the mass of each potato chip to see if any effect on how much the mass changed after the experiment had. To make sure that all of the potatoes have the same conditions to carry out Osmosis in, we made sure that all of the test tubes which had the same sugar strength in all stood together in one beaker in the same place on the windowsill facing the outside so that they have the same room conditions. I tried to make sure that no artificial or Luna light (moonlight) would come into the room during the night so that this could not influence the result. The temperature in the room where the chips were left will vary although all of the Potato chips will be in the same place so the slight change in temperature should affect all of the samples equally.

Prediction:

I predict that the Potato chips that are placed in 100% distilled water will have a larger mass than the initial mass and that the Potato chips put in 100% Molar will have a smaller mass after the experiment. This is because of Osmosis, which is, the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane. Water passes through a cell membrane but the solute (sugar molecules) can’t pass through the partially permeable membrane. Osmosis will also be taking place within the Potato. Water moves from cell to cell in plants by osmosis. The cell membrane of a plant cell is a semi permeable membrane. So if a cell containing a weak solution is next to a cell with a stronger solution, water moves by osmosis from the weak to strong solution to balance them out.

So for the 0.0 M chip the water molecules will move into the Potato chip to make the cell and outside solution equal in water molecules this will fill the potato with water so the chip would have an increased mass and make the Potato chip turgid. Where as the chip in the 100% Molar solution will move the water molecules from inside it self into the solution to try and make the solution and chip have the same water particles making the Potato chip very flaccid. Shown below is the process of Osmosis:

This is what is happening in the Potato experiment. The water is trying to balance out the solution so is moving from a low concentrate to a higher concentrate. This is different to diffusion because in diffusion the molecules move from a high concentrated area to a low concentrated area.

My prediction of the change in mass is that the higher molar % in the solution the more negative mass change you will get however for the middle Molar strength solutions I believe that there will be little if no change in the mass and therefore will be a center mark for the rest of the results. A graph showing the average mass change should show the largest positive change for the 0.0 M then a steady decline to the biggest negative change in mass for the 1 M solution.

Apparatus:

10ml measuring cylinder - to measure out exactly 10ml of each sugar solution

15 test tubes - what the experiments will be held and carried

out in.

Electric Balance - to measure mass at the begging and end of the

experiment to find the increase in mass of the

potato.

Borer (1cm diameter) - to cut the right size potato chips

Ruler - to measure the length is 5cm and make sure the

diameter is 1cm.

Knife - to cut the potato chips down to 5cm in length.

Obtaining the Evidence

After carried out the experiment and weighed each of the potato chips to find out their mass change, we recorded them in a results table. We also decided to add in the percentage mass change so that we could see how they measured up in comparison to the others, as we did not make them have the same start mass. As we did three potatoes in each solution we have enough results to have an averages table. We added up the three potatoes masses from each solution and then did the mass change, divided by the original mass to find out the percentage change. Then filled in the average table and plotted a graph to show the average percentage change between potato chips in different solution strengths. As we used a balance correct to two decimal places we feel that we have accurate enough results to plot a sensible and fair graph. The results are shown in tables and graphs below:

Results

This is a table to show the results of my investigation.

This is a table to show the average result for each strength.

The graphs shows that the higher molar % in the solution the more negative mass change you will get however you can see for the middle Molar strength solutions that there is little if no change in the mass but for just pure water the mass increases. This is because water molecules will move into the Potato chip to make the cell and outside solution equal in water molecules this will fill the potato with water so the chip would have an increased mass and make the Potato chip turgid

Evaluation:

This experiment went well, and I have collected enough valuable data to produce a conclusive set of results, that are shown in the graphs. The results followed my prediction so I suppose it all went well.

Although it is impossible for me to have completed a perfect experiment, I feel that I have managed to collect reliable enough results to prove that solution strength does effect the mass change in potato chips by osmosis.

If I did this experiment again I would have made the potato chips the same length, width and the same mass, so that I could have been surer of my results. This would have made my conclusion stronger and I predict that I would have found that the 0.4 M solution would have showed even less change in mass than it did in the experiment.

If I repeated the experiment again I would make more potato chips for each of the solutions, and make sure that the potato chips were all the same size and mass. This could be achieved by using the borer two make holes as close as possible to each other on the potato, and try to use the same sized potatoes so that they have the similar make up. Another option to consider if I did this experiment again is to different fruits to see if osmosis occurs in them.

I would also make tables and graphs for each of the solutions individually instead of just taking the average, and try to get a larger sample size so that my average could have been based on a wider sample size. My results could have been more accurate by using a balance that was accurate to more than two decimal places. This would be more accurate but possibly not necessary as two decimal places I believe are enough to give me a good result. More accurate results may have been achieved by being more precise with the measuring out of the solutions, whilst I measured as accurately as I could, with different equipment I may have been able to be more precise.

I could have tried to be more accurate in the final stages of the experiment for example, I could not reliably measure how much water I dried off each potato chip before their mass was collected so this may have affected the results. Other things that may have varied include trying to keep the same mass of the chip at the start, the amount of time that I left the potatoes in the solution and the conditions that each of the solutions were left in. These adjustments may only be tiny changes but they may affect the final result.

So to conclude I think that the experiment was a success but there are many areas that I could improve. If I did it again I know that I would expect to see a greater variety of results and graphs.