Osmosis experiment
Aim: My main aim in this experiment is to find out if osmosis occurs in a potato, and how it affects the potato in different molar solutions of sucrose and water.
Introduction: Osmosis is the diffusion of water molecules, down a water potential gradient, across a partially permeable membrane. If the solutions on each side of the partially permeable membrane are equally concentrated then there will be no net movement of water across the membrane. If the solution outside the cell has a low concentration of solute, this causes cells to become turgid as water flows into them, or if the solution outside the cell is of high concentration the cells become plasmolysed as the water flows out.
Even if the solute concentration external to the cell is low relative to the vacuole contents, cell will not continue to take in water by osmosis for ever. The cellulose cell wall prevents this. A cell that is full of water is said to be turgid and cannot expand further as the outward pressure on the cell wall is balanced by the inward force of the stretched wall.. At the other extreme, a cell placed in a solution that is high relative to the cell contents will lose water by osmosis. The cytoplasm will cease to exert a pressure on the cellulose cell wall and the cell, described as flaccid, will lack support. Water loss can continue to such an extent that the cytoplasm, and attached cell membrane, contracts and detaches from the cell wall. A cell in this condition is said to have undergone plasmolysis. This very rarely, if ever happens in nature.
Apparatus: For the experiment we will require:
A potato
A potato chipper
Sugar (Sucrose) solution of known strength.
Tap water (to produce a range of sucrose concentrations) from
Test tubes
Test tube holder
Scalpel
Cutting tile
Tissue paper
Measuring Cylinder
Marker pen
Electronic top pan balance
Prediction: Osmosis is the flow of particles from a high concentration to a low concentration.
So I predict if you place a potato in a high concentrated solution the potato shall shrink
And if you place a potato in water the potato shall increase in size and mass.
As the potato is a plant cell, it contains a vacuole and a cytoplasm. The cell membrane also partially permeable i.e. it lets some substances in but not all substances.
This means that water particles diffuse into cells by osmosis if the cells are surrounded by a weak solution. Therefore the cell shall increase this is know as turgidity. If the cells are surrounded by a stronger
Solution, e.g. salt water, the cells may loose water by osmosis it shall decrease in size. This is called flaccidity.
If the potato is present in the solution for to long (strong solution) then the cell membrane shall rip of its cell. This formation is call plasmolsyed.
Shape of potato
This must be kept the same, because if different shapes are used, it will affect the end result.
Starting mass of potato: The starting mass must be the same to insure the test is fair, if they are all different masses, it will be hard to say which solution created the most mass change.
Temperature: The temperature must stay the same to insure that the solutions are not affected by the change in temperature. Volume of sucrose solution used each time. The volume must stay the same so one can monitor the mass change accurately. If these variables are not kept the same it would influence our results and make them inaccurate. However, we will ...
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Starting mass of potato: The starting mass must be the same to insure the test is fair, if they are all different masses, it will be hard to say which solution created the most mass change.
Temperature: The temperature must stay the same to insure that the solutions are not affected by the change in temperature. Volume of sucrose solution used each time. The volume must stay the same so one can monitor the mass change accurately. If these variables are not kept the same it would influence our results and make them inaccurate. However, we will also be changing some variables to enable us to obtain the results we need. We will be changing the concentration of sucrose in the sucrose solution, so that we can see how the change in mass varies depending on the concentration of sucrose in the solution.
Variables:
* The concentration of sucrose (sugar) solution.
* The temperature of the solution
* The size of the potato chips
* The type of potato (pore size)
Key factors: In this investigation the key things which are possible to change are the concentration of the sucrose solution surrounding the potato; the size, length, weight and surface area; whether or not you leave the skin on at the two ends and the volume of the various concentrations of sucrose solution. Also you can control how much of the surface area of the potato is exposed to the solution.
Fair test: To make this a fair test I am going to make sure that the volume of the sucrose solution the same at 20ml. I will change the concentration of this 20ml solution. I will keep the size of the potato the same. Also the sort of potato will remain the same. I will control the size of the potato by using the same size of cork borer and I will cut the length to 3cm.
Safety: For this experiment I made sure all the glassware was away from the edge of the table to avoid knocking them off and smashing them. Also I was careful whilst using the scalpel and made sure I was sitting down when I was using it and I was careful carrying to and from the tray. When cutting the potato tubers to equal length of 4 centimetres, I will make sure to hold it from the blunt end and be careful not to cut my fingers. I will place the potato on a platform or board and not on my hand when inserting the cork borer inside; if I do not, then the cork borer may cut through the hand.
Reliability: I have tried to make the results as reliable as possible by using distilled water to eliminate any sort of variation in the water. Also the measuring cylinder was washed and cleaned between measuring to prevent the next mixture being inaccurate. I used two 15ml measuring cylinders rather than larger ones so there was little room for error. Also the same type of potato etc (see fair test).Also I will repeat the experiment three times and take the average measurement in an attempt to get the most reliable and accurate results possible. Also I rolled the potato in a tissue before weighing after it had been taken from the test tubes.
Method:
A cork borer and plunger used to make potato A weight scale.
Cylinders
I will now carry out my procedure using the apparatus that I have gathered. The steps of the procedure are listed below.
- I will first rinse and clean the Petri dishes and beakers to remove any droplets of previous solutions. so will be permanently banned.
- I will then label the Petri dishes, noting the morality of the solution that will be stored in it. Therefore, the concentrations should read 'Water', 0.125M, 0.25M, 0.5M, 0.75M, and 1M.
- I will label the six beakers, noting the concentration of solution to be stored inside.
- I will then measure the volume of the solution inside the beaker by using a measuring jar. I will use a volume of 30mL for each solution.
- I will then wash the fresh potato and place it on a piece of paper. I will then use the No.2 Cork borer and No 3. Cylinder plunger to form potato tubers.
- I will plunge twenty-four tubers, four for each Petri dish.
- I will then place the potato tubers onto a graph paper.
- I will use a washed razor blade to cut the potato tubers to exactly four centimetres. I will remove the potato skin in the process.
- I will now place each potato tuber onto filter paper and measure its mass on the weight scale. I will record these readings.
- I will now place four potato tubers into each Petri dish.
- I will then pour 30mL of each solution into its corresponding Petri dish, noting the time when the solution is poured.
- I will close each Petri dish and keep them aside for twenty-four hours.
- After a day, I will check the potato tubers and note its appearance; if there are any differences.
- I will then note the mass of each potato tuber and will take the average.
- I will also take the length of each potato tuber and note the difference in length.
Method 2:
) I will cut out twelve potato chips, with a scalpel, all with the identical dimensions of 8x7x20mm.
2) I will weigh each of the potato chips and record their masses in a table, labelling half of them A and the other half B, a pink streak of felt tip pen will denote B.
3) I will attach all the A chips to their corresponding B chips with a pin.
4) At one minute intervals I will place each of the pairs into six different boiling tubes containing sucrose solutions, varying from a concentration of 0.1M to 0.6M and increasing in 0.1M intervals. do not redistribute this work. We work very hard to create this website, and we trust our visitors to respect it for the good of other students. Please, do not circulate this work elsewhere on the internet. Anybody found doing so will be permanently banned.
5) After twenty minutes is up for the first pair I will carefully remove them with a mounted needle and dry each chip with three strokes of filter paper to remove excess solution.
6) I will separate the A chip the B chip, weigh them and record their new masses in a table.
7) I will reattach A to B and replace it in the sucrose solution.
8) I will repeat numbers 5-7 for each of the six chip pairs.
9) I will leave the solutions for approximately two days then return and repeat steps 5-6 then dispose of everything.
0) I will work out the changes in mass for each result, percentage change in mass and average percentage change in mass and record the results in my table.
1) I will plot a graph of concentration against average percentage mass change after two days and look for patterns in it. I will also plot the same graph but for the results after twenty minutes and compare the two sets of data,
Data recording: There are various ways of presenting the data I have achieved and each has individual qualities. The first way I have presented them is in a table format, this is useful for obtaining exact numerical values for calculations and so forth. But from the table it is difficult to identify certain trends, so I plotted graphs with the data, so I was able to identify the above trends.
Anomalies: There were no anomalies that I could see from the table, although the graph may reveal one or two.
Conclusion: From my investigation I can conclude that it was an accurate investigation, due to the graphs which all fall in line with a certain degree of consistency. My conclusions are that as the concentration increases the amount of weight lost by the potato increases. This statement is backed up by my results. It is easier to see in the graphs. They prove that as the concentration increases, so will the amounts of mass lost by the potato. All of this evidence backs up my initial prediction. "Essentially what I am saying is that as the concentration increases, so will the amount of mass lost by the potato. However I did not expect a straight line graph. I thought that the cell wall was so rigid that any sort of large expansion or decrease would not be possible without the cell bursting or caving in. I was unaware that the cell wall would be quite flexible. However nearer the edges of the curved line graph the line starts to flatten out. I think this is because the cell wall was starting to put up a bit of resistance. I would be interested to go further with the concentrations. I anticipated the cell wall making a resistance but I expected it to allow a certain amount of loss or gain of mass. This is backed up by my prediction of " I feel that nearer the extremes of concentration the results will be more closely grouped." . This was because of the rigidity of the cell walls that I mentioned.. I predicted that the cell wall would affect the loss of mass much more severely. But in the light of the results I would have to say that the cell wall had a lot less effect than I previously anticipated. All in all I would say that the experiment was well conducted and to a good deal of accuracy.
Evaluation: I do believe that my results were accurate. The proof for this is in the graph I have drawn entitled "What Affect Changing the Concentration of Sugar Solution Has On The % Of Weight Loss". This shows results from all three of my experiments, and as you can see all three are consistently together. This proves that I am consistently accurate with my experiments. There is little chance that they were all wrong as they were done on separate days to each other.
There are however many places and ways that errors could occur. First starting with the concentration. It was possible that the concentration of the sucrose was not already precisely 2molar when I got it. Also there is the large possibility that I measured the quantities wrongly. To make this aspect more accurate I would use a smaller measuring cylinder and be sure to measure from the meniscus of the liquid (the dip in the liquid). This allows for any residue of liquid remaining in the cylinder after pouring. Also a major factor was the cutting. I could have easily left a larger surface area on one than the other. Therefore one would be at an advantage as a larger surface area induces more osmosis to occur. One way to avoid this would be to use complicated machinery to weigh and cut the potato; although beneficial, this wasn't practical. So just taking extra time and care with the cutting would make it more accurate.
I could have done more work. I could have done the experiment more times to gain a more accurate result . Also I could test more of a range of concentrations - again to obtain a more accurate result. Also I could experiment with exposing the same weight pieces, but with different surface areas. This would be interesting to do. The results were perhaps a bit undetermined here and there. I think this could have been from one, if not more of the above factors.
If I was to repeat the experiment again then I would go to a higher concentration to see what happens in relation to the cell wall. And exactly how much osmosis is able to occur and what would happen to the cell and its wall when it reached the limit. The reason I would do this as I think it would be both interesting and beneficial to see what the capabilities of the cell and its cell walls were. Also if I were to do it again I would test more values of concentration. For example I tested 0,0.5,1,1.5,2. Then I would go in to more values like 0,0.25,0.5,0 .75,1, 1.25.....etc. The reason for this is I feel it would provide me with more accurate results to base my graph and theories on. Also I would like to see how the surface area would affect osmosis. This is because I feel that it would be interesting to know what affect it has and to compare it to the other set of results I obtained.
