How does the concentration of glucose mass affect the mass of potato sticks?

Planning

For this investigation, I am going to investigate the process of osmosis. Osmosis is the net transfer of water, through a semi permeable membrane, from an area of high concentration to an area of low concentration. This continues until a point of equilibrium is reached, when equal amounts of water are coming in and out of the membrane, reaching a point of stalemate. This is a dynamic situation. I am going to investigate this reaction using potato sticks, which are left in a solution of glucose, to test whether the rate of osmosis changes with different concentrations of glucose, and to record the changes in mass of the potato sticks. The factor that I will be changing is the amount of glucose (g) present in the water solution.

Prediction

In this experiment, I predict that the potato stick will decrease in mass when there is a higher concentration of glucose present. I predict this because when there is a higher concentration of glucose than the water surrounding it, osmosis will take place in the potato, causing the mass to decrease until it becomes flaccid. This is when the potato stick looks shrunken and soft in appearance, and no more water can be drawn out. I predict this because when the concentration of glucose is higher than water in the solution, osmosis will occur. This is because water is moving the water molecules are moving from an area of high concentration to low concentration in the potato stick, and water will be lost through the partially permeable cell membrane in the potato, and the water will be diffused into the solution of glucose. Therefore, the contents of the cell have shrunk and pulled away from the cell way, becoming plasmolysed. This is when no more water can be extracted through a cell through osmosis.

However, when the concentration of glucose is more diluted, the mass of the potato sticks will increase until it becomes turgid. I predict this because there is a greater concentration in the water than the glucose solution. Therefore, the water is moving from an area of high concentration, in the solution, to an area of low concentration in the potato stick. I predict that the potato stick will become swollen and hard, as the cell has absorbed a large amount of water, making the cells expand, until no more water can enter the cell.

Method

In this experiment, I will have to be extremely careful and meticulous in the way I use the apparatus, so that I can obtain the most accurate results. To begin the investigation, I will cut ten potato sticks from a potato using a cork borer, and cut the skin off from either end. Each of these sticks will be roughly 5cm in length. I will then weigh each of these sticks and note down the original mass, intending to get all of the sticks to be approximately the same in mass. After I have done this, I intend to fill ten test tubes with 25ml of water. This will remain the same throughout the investigation. I will also add a varying amount of glucose powder into each of these test tubes. I will then place each of the ten potato sticks into the ten test tubes filled with water and glucose, which will have dissolved into the water. After roughly 24 hours, I will again measure the mass of the potato sticks, to see whether my initial prediction was correct, and to note down the affects of osmosis.

I will need to be careful when doing this experiment. I will need to maintain that none of the glucose and water solution spills from the test tube, as this could result in an inaccurate experiment. I will wear safety goggles as well, as the investigation involves chemical reactions.

In this investigation, I will need to measure, observe and record a great deal of different results and figures. I am going to investigate the changes in the mass of ten potato sticks, with different amounts of glucose in 25 ml of water. For this experiment, I intend to use the concentrations of glucose of: 0g, 0.5g, 1g, 2g, 3g, 4g, 5g, 8g, 12g and 15g. Hopefully, these different concentrations will enable the most accurate results. I will measure the starting mass of the potato sticks, and the final mass once they have been in the water solution for a period of time. I will do this using a scale. I will record these results on paper, and this enables me to present the final data in a table and graph at the end of my experiment.

The equipment that I intend on using for this experiment are:

Cork borer – This will enable me to cut the potato sticks from the potato.
Scale – This will enable me to record the starting and final mass of the potato sticks.
Test tubes – These ten test tubes will contain the 25ml of water and varying grams of glucose solution, to enter the potato sticks into.

To maintain that all results and evidence I collect during the experiment are accurate, I will ensure that I follow the same procedure every time I make an ...

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The equipment that I intend on using for this experiment are:

Cork borer – This will enable me to cut the potato sticks from the potato.
Scale – This will enable me to record the starting and final mass of the potato sticks.
Test tubes – These ten test tubes will contain the 25ml of water and varying grams of glucose solution, to enter the potato sticks into.

To maintain that all results and evidence I collect during the experiment are accurate, I will ensure that I follow the same procedure every time I make an observation of the mass of the potato sticks. I will collect the information in the same way, and this will ensure that all information I gather is completely accurate.

There are many factors that I need to take into account when ensuring that my experiment is a fair test. Firstly, I will need to make sure that the set up of the experiment was correct and fair. There will need to be the same volume of water in each of the ten test tubes, which I have set at 25ml. I will need to test that this is the case in all of the test tubes. The mass of the potato sticks will also need to be approximately the same, as this will prevent my final results from being slightly inaccurate, and I can come to a conclusion much quicker is my results are correct. All of the potato sticks will need to be as close to 5cm as possible, and the quality of all of the sticks will need to be similar.

Once the potato sticks are all set up in their individual test tubes, they will need to be all kept in the same conditions. The test tubes will be kept away from the sun, to prevent the sun from evaporating the water from the test tube, which would hamper the investigation. The test tubes will all need to be kept at room temperature, as colder or warmer temperatures could affect the rate of osmosis.

There are many factors which could affect my investigation. It is important that I regulate these closely, to prevent my experiment becoming pointless due to the conditions which would cause problems. The factors that I will need to keep constant throughout the investigation are, the temperature of the environment in which the test tubes are kept and the amount of light which is given to the test tubes. This will make sure that the rate of osmosis will remain the same, which is essential if I want the investigation to be completely accurate.

I will keep these conditions the same by making sure that the test tubes are kept in a well-lit room, but away from the constant glare of the sunlight. The room in which the test tubes are kept will hopefully remain at a suitable temperature also, as it is crucial that the rate of natural osmosis is not slowed down or sped up.

When I begin my investigation into osmosis, I will have to ensure that I make a suitable number of measurements, as this will give me the greatest chance of achieving accurate results for the experiment. I have chosen to do ten separate test tubes, each filled with 25ml of water. To this I will add ten different amounts of glucose powder. This is the factor that I am changing throughout the investigation. The ten different values I will be using are: 0g, 0.5g, 1g, 2g, 3g, 4g, 5g, 8g, 12g and 15g.

I feel that ten is a good number of measurements to take. This is because there is enough evidence to prove whether the investigation has worked, or if there is a correlation between the results that I find. Also, using values ranging from 0g to 15g, I feel this is a large enough gap to see whether the rate of osmosis is greatly different at both ends of the spectrum.

Results

These are the results that I recorded throughout this investigation. The table includes the starting mass of the potato stick, the amount of glucose added, the final mass after the experiment is over, and the percentage increase or decrease of the mass.

It will not be required for me to repeat any aspects of the investigation, because the results appear to be accurate and correct.

Analysis and Conclusion

For my investigation to be a complete success, I needed to collect together my final results for the experiment, and then show this information in two graphs to see what patterns would emerge. This will also help me when evaluating my investigation, as it clearly shows the patterns of my results.

On the line graph that I have drawn, there are several patterns that emerge from it. The graph plots the percentage difference that I worked out from the initial mass and final mass of the potato stick, against the varying concentrations of glucose that I added. The graph begins as a gently sloping gradient, and shows that the lower the amount of glucose that is added, the greater the positive percentage difference.

On the more important graph though, I have graphed the final masses of the potato sticks against the varying concentrations of glucose. The graph shows that the mass of the potato sticks decreases with the greater concentration of glucose. The graph sharply drops from 0g to around 6g, but then begins to straighten out, and shows little change from around 6g to where I finished obtaining evidence, at 15g.

The graphs I have done clearly show that that the further that the graph continues, the range in results is much smaller. The graphs show that when the amount of glucose present is increasing, the mass of the potato sticks is decreasing.

This proves that when a greater concentration of glucose that is added to the solution, the mass of the potato stick decreases. This much is clear on the graphs that I have produced, as there is a negative slope showing, which makes me come to this conclusion.

There is a scientific explanation as to why I have come to these results. The mass of the potato sticks is decreasing when a higher concentration of glucose is added because osmosis is taking place between the cells. When there is a higher concentration of glucose than the water surrounding it, osmosis will happen in the potato stick, as water is moving from an area of high concentration in the potato stick to an area of low concentration in the solution. The water molecules are moving out of the potato, through the partially permeable cell membrane that surrounds the cell, and the water is diffusing into the water and glucose solution. The contents of the potato stick cell have therefore shrunken, and the appearance of the potato stick is shrunken and soft, as it has become flaccid. This is because all water has been drained from the potato stick, causing the cell to become plasmolysed. This means that no more water can be drawn out through osmosis.

However, the mass of the potato stick is increasing when the glucose solution is more diluted. This is because the water is moving from an area of high concentration in the solution, to an area of low concentration in the potato stick. This is because there is a higher concentration of water than glucose in the solution. Therefore, water is absorbed into the stick, causing it to become turgid, swollen and hard in appearance. Therefore, the mass is greater when the concentration of glucose is more diluted.

As demonstrated on the graph, the line seems to level out once reaching a certain point. This is the point of equilibrium, when no water can be drawn out or absorbed during osmosis, when equal amounts of water are leaving and entering the cell.

This all proves that my prediction was correct. I predicted that the mass of the potato sticks would decrease when glucose concentration was higher, and this has proven to be the case for the reasons that are listed above.

Evaluation

For my investigation, I need to make an evaluation on how well I believe that it has gone. This will help me analyse how successful the experiment was, and how accurately I managed to complete it.

The obtaining evidence aspect of the investigation went reasonably well. I was able to measure the results without any major error, and this is reflected in the continuity of the final results. However, there were a few minor errors that could have affected the final outcome. When weighing the final mass of the potato sticks, I took them out of their test tubes, and weighed them individually, therefore allowing some of the potato sticks a longer amount of time in the water solution. Although it would have made no major difference to the outcome, this was slightly inaccurate. I also felt that perhaps I did not allow the potato sticks long enough in the water, and this was reflected in a handful of the results. If I were to repeat this experiment, I would ensure that all of the potato sticks had long enough for the full effect of osmosis to take place, by allowing a longer amount of time in which to gain or lose mass, which could have had a greater impact on my results.

The measuring instruments that I used were extremely useful in the outcome of this experiment. However, I took the option of using test tubes to fill with the 25ml of water, and the glucose powder in which to add the potato sticks. This proved to be quite awkward at times, and it became difficult at points to remove the potato stick. This was not ideal at all, and was posing the risk of the stick breaking, which would have severely disrupted the final outcome. A better alternative would probably have been a small beaker, as this allows a greater amount of room to remove things from. Also, the set of scales I used to measure the mass of the potato sticks was slightly erratic, meaning I was unsure that the weights were entirely correct. The results could have been a bit more accurate if I had used a reliable set of scales for this investigation.

Although these factors are, in the end, quite minor, they could have had a small outcome. In the future, I would have to ensure that the evidence I measured was accurate by re-testing the masses on a different set of scales to check whether they were correct, and to choose the apparatus I used more carefully.

After looking at the data I obtained during this investigation, and the graphs that I produced, I can conclude that the results fit the pattern that I expected. The data shows that when a higher concentration of glucose is added, the mass of the potato sticks decreased. I expected this pattern, although was perhaps a bit surprised by how rapidly this process began, and then reached the point of equilibrium after only a small amount of glucose was added, and the results seemed to remain fairly constant after this point. Apart from this, the pattern of the results appears to correspond with the conclusion that I have made.

The results that I have gotten appear to be reasonably consistent, although there could be one small blip in the results. After 12g of glucose is added, my percentage difference clearly notes that it is smaller than when 8g was added, but the results comply back to the trend at 15g. I would guess that this happened, perhaps because of the small inaccuracies of the experiment. It could be that the potato stick in this test tube was slightly smaller than the others, or that not exactly 25ml of water was added, or it could be that this test tube was left in the glare of a beam of sunlight. This appears to be the only real odd result I have gathered.

The evidence that I have obtained from throughout the investigation appears to be valid. The results that I got from it seem to match with the prediction I made, and they also appear to have a correlation, which would indicate that they are reasonably accurate.

However, I needed to make sure that the factors I noted earlier to ensure that it would be a fair test were met. I poured exactly 25ml of water into each test tube, and this meant the proportions for the glucose powder would be correct. However, I’m sure I could have improved the length and starting mass of the potato sticks. I stated that I would like the length to be as close to 5cm as possible. However, once I had measured one of the sticks to 5cm, I merely tried to make sure all of the sticks were similar to this one in length, and this could have affected the overall accuracy of the final results. The masses were also similar, but perhaps they could have been closer, and this could have also affected my overall outcome.

I was content that the test tubes were kept in a suitable environment whilst the experiment was taking place. There was no adverse reaction to sunlight, and the temperature of the classroom in which they were stored remained constant. The room was well-lit also, and this part of the obtaining of results appeared to come off as accurate.

However, I am confident that this aspect of the investigation could be improved. The beginning phases of preparing the apparatus and the potatoes could easily be improved, and this would have provided a slightly more accurate investigation, and where the investigation would remain on a level footing before it got underway. I’m confident that if I had met all of these criteria, my overall results would be extremely close to perfect.

I am reasonably confident that I have obtained enough evidence to support my overall conclusion. I believe that a set of ten results is enough, and that if I had done another set of experiments, this would have served little purpose other than to clarify what had already been confirmed.

However, I could possibly have done another set of experiments, where I double the concentrations of glucose in the solution, or double the amount of water in the test tubes. This would clarify my initial results, and hopefully the final outcome of a new experiment of this nature would reflect the results I had obtained in this one. Other than that, I am pleased with the amount of evidence I have gathered throughout this investigation.

I would not make a great deal of changes to my original method, although I would probably make some slight alterations to ensure that I could provide the best possible outcome. I believe it would probably have been best of me to use small beakers instead of test tubes in this experiment. It would have been less clumsy, and would probably have helped me in the obtaining of evidence. I would also perhaps use a slightly large volume of water, as 25ml seemed a slightly small amount to be using, for the size of potato sticks that I was entering into them.

Other than that, I am pleased that the original method that I had set out is correct, and I followed it completely. It enabled me to acquire a good final set of results, and to set out the investigation in such a way that I find difficult to fault.

Overall, during my evaluation, I have concluded that although there were some improvements I would make to the layout of my experiment, I am fairly confident that I completed it successfully, and enabled me to come to a final conclusion on osmosis in potato cells.