In this investigation, I plan to see which factors would affect the rate of osmosis in potato cells

Osmosis

Introduction:

In this investigation, I plan to see which factors would affect the rate of osmosis in potato cells. Osmosis is the concentration gradient moving from a high concentration to a low concentration through a partially permeable membrane. I will weigh the potato chips before and after, if the weight increases, it shows that the potato chip has a lower concentration than the liquid it is in. Therefore, osmosis has taken place.

Vocabulary (Taken From the Internet- Check Bibliography)

Osmosis- the diffusion of fluids through a semi-permeable membrane or porous partition.

Concentration Gradient- The change in solute concentration per unit distance in solute. Concentration gradients cause Fickian diffusion (spreading) of solutes from regions of highest to regions of lowest concentrations. In slow-moving groundwater, this is the dominant mixing process.

Partially Permeable Membrane- A semi permeable membrane (or more accurately a selectively permeable membrane) is a membrane which will allow certain molecules or ions to pass through it by diffusion (sometimes "facilitated diffusion"). The rate of passage depends on the pressure, concentration and temperature of the molecules (or "solutes") on either side, as well as the permeability of the membrane to each solute.

Factors that affect osmosis:

Temperature- if the temperature is high, the particles will gain kinetic energy. This would increase the rate of osmosis. Because the particles have kinetic energy, they move around. This could result in them bumping into the membrane. If this does happen, the chance of molecules getting through the membrane increases, therefore; the rate of osmosis does too.

Water Potential- water tends to move from one place to another, as it is a liquid. This is water potential. It could be affected by two factors, one being if a solute is added, and the water potential decreases.

Concentration- this is the factor that I am investigating in this experiment. If there was no concentration difference, the molecules would not have anywhere to move to. This is because during osmosis, molecules move to a lower concentration.

Prediction:

I predict that when the potato chip is in water, the mass will increase because the water molecules will enter the chip. When it is in a high concentration of sugar, I think that it will decrease as the molecules will move from the chip to the solution. I think this because water has more molecules than the potato; and the molecules will move to a lower concentration. But with the sugar solutions; there are less water molecules than inside the chip. This means that the molecules will move outside of the chip and into the solution. The water and sugar solutions will loose/gain molecules of water until the equilibrium is reached.

Equipment Needed:

Potato – To make the potato chips which I will use for the experiment
Knife – To cut the potato into chips
Test Tubes – which the potato chips will be left in
Test Tube Racks - To hold the test tubes
Water – one of the solutions
Sugar solutions of different moles – the other solutions
Scales – to see how much the potato chips weigh
Tissue- to dry the potato so no access solution is left on it before weighing
Measuring Cylinder – so that the solutions used are an exact amount

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Equipment Needed:

Potato – To make the potato chips which I will use for the experiment
Knife – To cut the potato into chips
Test Tubes – which the potato chips will be left in
Test Tube Racks - To hold the test tubes
Water – one of the solutions
Sugar solutions of different moles – the other solutions
Scales – to see how much the potato chips weigh
Tissue- to dry the potato so no access solution is left on it before weighing
Measuring Cylinder – so that the solutions used are an exact amount

Method:

To make the experiment a fair one, I must do several things. These things include using the same potato for all of my chips; potatoes are of different sizes, ages and weights. This means that one potato may be heavier than another due to how much water is inside. Another thing to keep the same is the size of the potato chip. This is so all of my chips have the same surface area. The temperature of the room and all of the solutions must be kept the same; this is because temperature may be a factor which effects osmosis. Also, the amount of solution, if one potato chip has more than the rest, it may give unreliable results as it could also affect the rate of osmosis. Everything in the experiment should be the same for each potato chip, except the changing variable. In this case, the molarities of the sugar solutions.

The potato chips will need light and water to survive; this will need to be considered when choosing a place to leave them over the set period of three days. By having these two sources, it will prolong the time before the potato cells die. One of the reasons they could die; are too much or lack of water. If the concentration of the potato changes, the molecules will move to the water or sugar solution.

I will cut potatoes up into smaller potato chips. They will then be weighed, and cut so that they each weighed exactly 1.5g. Three were put into test tubes full of water, three into a 0.2m sugar solution, three into a 0.5m sugar solution and another three into a 0.7m solution. Each solution was 10mm³ to make it fair. The different solutions were chosen to see if the concentration of sugar affected the experiment in any way. The test tubes were left for three days then weighed again. The method was repeated thrice for each different solution the potato chip was put into. This is so that an average could be obtained to make sure my results were as accurate as possible.

A simple guideline to follow:

Cut the potato up into chips of the same size
Weigh them, make sure they all weigh the same
Measure out 10mm³ of every solution used
Put the solutions into a test tube each, then put the test tubes into a test tube rack
Leave the test tubes for three days
Dry the potatoes with tissue so no water is left on them
Weigh them again to see the difference

Potato chip in test tube.

Safety

Although the experiment seems extremely safe, all things must be considered.

Knife- the knife may be unsafe if not used properly whilst chopping the potato. It could cut you or someone around you. If this does happen, apply pressure to the cut for ten minutes and elevate the part of body which has been cut.

The Solutions- although the solutions are not extremely dangerous, we do not know the affect of the solutions if they somehow entered our body. If this did happen, and irritation began, you would have to notify your doctor.

Results:

Averages:

Analysis of individual graphs:

Graph 1- water-

All of the masses are around the same; this shows that my results are fairly accurate as no results are extremely different. No correlation is shown.

Graph 2- 0.2m sugar solution-

Again, all of the points plotted are extremely similar; this is another good sign showing that my results are accurate. No correlation is shown.

Graph 3- 0.5m sugar solution-

The points aren’t spread far apart; concluding precise results once again. And no correlation.

Graph 4- 0.7m sugar solution-

The points are in the same region which means the results are again; accurate. This graph shows weak positive correlation.

Conclusion:

By looking at the results I can see that the mass of the potato chips decreased when it was in a solution of a high concentration and the mass increased when the potato was in a low concentration. This means that my hypothesis was correct.

I think that the experiment was successful because the results complimented my prediction and also proved to be correct. The graphs and results gave me enough information to see that water leaves the potato chips when they are in a sugar solution; which is higher and water molecules enter the potato chip when they are in a water solution which, understandably, has more water molecules than the chip.

It was a good idea to use water and sugar solutions as it gave me an understanding of what would happen to a potato chip in different concentrated solutions. It was also easy to get water and the sugar solutions which made the experiment simple for the short amount of time we had to do it in.

The chip that was in water, increased most by weight whereas the 0.7m solution lost most mass. It became limp, possibly because of the amount of water and the water potential. The experiment helped me see that if there are two liquids, one of a higher concentration, the water molecules will move to the liquid with the lower concentration. This is osmosis, which is a case of diffusion. Also, I found out that the higher the concentration, the higher the mass will be.

Evaluation:

I think that the experiment I did gave me extremely good results and an excellent insight as to why and what could change the rate of osmosis. I think that one of the reasons my results were so reliable was because I was careful whilst doing the experiment and made it as fair as possible.

The experiment was quite easy to do which is a good thing but there are several ways in which it could have been improved to make it even more precise. One way is that instead of using a measuring cylinder, we could have used a more scientific method. An example of this could be titration. Also, I could have measured and recorded the size of the potato before and after and the diameter. This would have helped the investigation along even more.

There are parts of the experiment which I think could have been particularly unsuccessful. This would include drying the potato chip with tissue. Because tissue is a fibrous material, part of the tissue could have stuck onto the potato. This would not affect the weight a lot, but there is a possible chance of it changing the results.

Also, if we had used more types of sugar solutions and possibly other types of solutions, it would have given me more results and maybe even more accurate results.

Another way we could have improved the experiment is by doing all of the different solutions one after the other. This would mean three days of a water solution, three days of a 0.2m solution, and a further three days each for a 0.5m and 0.7m solution. This would make it easier and would mean that it is not as confusing to see which solution is which if some people did not label theirs.

However, if we did change the measuring method, how we dried the potato and how many solutions we used; it would prolong the experiment and make it more complicated than it actually has to be. It would also mean the time scale would be longer as the experiment would take much longer to do.

If the molarity levels were more precise, this would mean even more accurate results. I used 0.2m, 0.5m and 0.7m solutions but more could have been used. This too, would have made the experiment a lot more complicated. Also, the things I kept consistent such as the temperature would have affected the rate of osmosis. It would be good if I could have changed these to see what would have happened.

Considering the method and equipment used, I believe this to have been a very successful experiment and my results to be helpful and accurate. I am satisfied with how I did the practical and the results obtained.

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