Osmosis in Potato Cores

GCSE Coursework – Osmosis in Potato Cores

Aim

To see how different concentrations of sucrose solutions affect the rate of osmosis in potato cores.

Hypothesis

Osmosis is the net movement of water molecules from a solution with a high concentration of water molecules across a partially permeable membrane to a solution with a low concentration of water molecules. This process can be seen in living cells. The cell membrane in cells is partially permeable, and the vacuole contains a sugar solution. If a cell is placed in distilled water which has a high water molecule concentration, the water will move across the partially permeable membrane of the cell from the sugar solution and into the potato and make it swell. The cell becomes turgid. If the cell is placed in a solution with a low water molecule concentration, the water will move across the partially permeable membrane from the potato and into the solution. The cell is plasmolysed.

In this experiment, the tiny holes in the potato membrane will allow the water molecules to pass through in and out of the solution depending on the concentration of the sugar solution used. If the concentration of water molecules in the potato is less than the concentration of water molecules in the solution, such as in sucrose solutions of molarity 0.0M (distilled water) and 0.2M, the water molecules in the solution will move into the potato, and increase it’s mass. If the concentration of water molecules in the potato is higher than the concentration of water molecules in the solution, such as in sucrose solutions of 0.6M, 0.8M and 1.0M, the water molecules in the potato will move into the solution, and decrease the mass of the potato. As the potato cores have been soaked in 0.4M sucrose solution, and I am also using 0.4M sucrose as one of my solutions, there should be very little or no change in mass as the concentration of water molecules in the potato and solution is equal.

Diagram of Osmosis

From the diagram above we can see how the water molecules travel from an area of high water molecule concentration to a low water molecule concentration.

Equipment List

18 x 8mm potato cores soaked in 0.4M sucrose
Potato corer
Sugar solutions of 0.2, 0.4, 0.6, 0.8 and 1.0M
Distilled Water
6 x Boiling Tubes
Measuring Cylinder
Digital Balance
Knife

Method

Potatoes will be cored with an 8mm corer.
The cores will be soaked in 0.4M sucrose solution.
The cores will be cut to 5cm lengths, measured ...

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Diagram of Osmosis

From the diagram above we can see how the water molecules travel from an area of high water molecule concentration to a low water molecule concentration.

Equipment List

18 x 8mm potato cores soaked in 0.4M sucrose
Potato corer
Sugar solutions of 0.2, 0.4, 0.6, 0.8 and 1.0M
Distilled Water
6 x Boiling Tubes
Measuring Cylinder
Digital Balance
Knife

Method

Potatoes will be cored with an 8mm corer.
The cores will be soaked in 0.4M sucrose solution.
The cores will be cut to 5cm lengths, measured with a ruler.
The cores will be weighed and their masses recorded.
The cores will be marked using an indelible marker pen with different symbols, no dots for the 1st repeat, 1 dot for the 2nd repeat, and 1 line for the 3rd repeat.
6 boiling tubes will be filled with 30ml of different concentrations of sugar solutions, 0.2M, 0.4M, 0.6M, 0.8M and 1.0M and distilled water.
After 10 minutes the cores shall be removed with tweezers and placed on the top pan balance, and the new mass recorded.
The cores will be put back into the boiling tubes for a further 10 minutes, and then the final mass recorded.

In this experiment, the timing is going to be quite challenging. It is obvious that I cannot take the mass of all the repeats at the same time, so the experiment shall be spread over 2 days, and the weighing staggered by 5 minutes for each boiling tube.

In this experiment the only 2 variables that should change are the different sugar solutions, and the change in mass of the potato samples. To make the experiment a fair test I must make sure that the potato cores at the start of the experiment are all the same lengths. If one is longer than the others, it will have a larger surface area, and osmosis will take place faster. I will use the same potato, as the age and size may affect the amount of water is in the potato cells, and therefore affect osmosis. I must make sure the amount of sugar solution is exactly 30mls, and a measuring cylinder shall be used to achieve this. I must also stop contamination, so the measuring cylinder must be washed after filling every boiling tube, to stop the sugar solutions from becoming contaminated.

Safety is an important aspect in every experiment, and I must take that into consideration when performing this one. I will be very careful that the solutions don’t get into my body internally, especially via my hands, as we do not know the damage it could do. This will be prevented by washing hands after the experiment to avoid the sucrose solution getting into contact with my mouth or getting wiped into eyes. I will wear a science overall to protect my clothes and my body. The knife being used to alter the lengths of the potato cores is also incredibly sharp, and I must take extreme caution when using this equipment.

Results

Percentage Changes

Average Percentage Changes

Analysis & Conclusion

Unfortunately, my results are not accurate enough for me to make a fair conclusion. My results for the solutions of concentration 0M (distilled water), 0.2M and 0.4M are reasonably accurate. In 0M AND 0.2M the potato cores gained mass, as the concentration of water inside the core was lower than that in the solutions and in osmosis water molecules travel from a high concentration to a low concentration. In 0.4M sucrose solution the percentage change was only 0.71%, which is very low and as the solutions are the same this is what I predicted would happen, where I said, “As the potato cores have been soaked in 0.4M sucrose solution, and I am also using 0.4M sucrose as one of my solutions, there should be very little or no change in mass as the concentration of water molecules in the potato and solution is equal.” My results for 0.6M, 0.8M and 1.0M sucrose solutions were however not accurate. In every repeat the potato cores gained mass, which is not correct, as the concentration of water in the solution is less than that in the potato, so the water molecules should have passed through the partially permeable membrane that is the potato cell wall, and into the solution, therefore decreasing the mass of the potato core.

I could have gained inaccurate results because of many reasons. The potato cores may not have all been the same lengths. I used a sharp knife to cut the cores, using a ruler to measure their length. If the ruler had been misread, then the cores could have had a too large or too small surface area. The surface area of the cores is important as the larger the surface area, the quicker osmosis will occur, because there will be more of the partially permeable membrane for the water to diffuse across. The potatoes were all collected together in a large container, so there was no way in which I could tell whether they were from the same potato or not. The age and size of the whole potato may affect the amount of water that is in the potato cells, and therefore that would affect osmosis. The amount of sugar solution used in the boiling tubes may have not been entirely accurate, due to careless reading of the measuring cylinder. Also when removing the cores for their 15 minute weighing the amount of solution in the boiling tube will have been decreased slightly as when I dried the potatoes liquid was lost to the tissue. Even though I washed the measuring cylinder in tap water after filling each different boiling tube, it was difficult to dry it, and therefore some water in the measuring cylinder could have mixed with the 0.6M, 0.8M and 1.0M sucrose solutions and diluted them making them have a higher concentration of water molecules. The experiment was done on 2 different days, and the room temperature in the lab on those 2 days could have varied, and affected the rate of osmosis. Temperature is a key factor as the higher the temperature, the more kinetic energy the water molecules have, and they will then move and diffuse faster.

I do not feel that an accurate conclusion may be drawn from my results in this experiment, as the 0.6M, 0.8M, and 1.0M sucrose solutions results are all against what is said about osmosis.

Evaluation

I am disappointed that my experiment did not go well. I worked hard in obtaining my results, and if I have the chance to repeat the experiment I would work harder to control the variables which affected and made my results random and wrong.

If I were able to do further work on osmosis in potato cores I would firstly repeat this experiment and try to gain some results from which I could make a sensible conclusion. I would also want to try the experiment with the cores in the solutions of different molarity but without soaking the cores in the 0.4M sucrose solution. By doing this I could discover the natural water concentration in a potato cell with a partially permeable membrane.