Osmosis is defined as 'the movement of water molecules from an area of high water concentration to an area of low water concentration, across a semi-permeable membrane' (Collins, 1999).
Prediction
Osmosis is defined as 'the movement of water molecules from an area of high water concentration to an area of low water concentration, across a semi-permeable membrane' (Collins, 1999).
If you get information from books put the copied text in brackets and at the end put the authors surname and date the book was published in brackets. Then put the full details of the book at the end of the course work in the 'References'
In a high concentration of water the amount of solute (e.g. sugar) is low. This could be called a weak or dilute solution.
In a low concentration of water the amount of solute (e.g. sugar) is high. This could be called a strong or concentrated solution.
When two such solutions are divided by a semi-permeable membrane the water will move from the area of high concentration to the area of low concentration, until both sides are equal (have reached equilibrium).
This can be seen in living cells. The cell membrane in cells is semi-permeable and the vacuole contains a sugar/salt solution. So when a cell is placed in distilled water (high water concentration) water will move across the semi-permeable membrane into the cell (lower water concentration) by osmosis, making the cell swell. This cell is now referred to as turgid. If done with potato cells the cells would increase in length volume and mass because of the extra water.
If these potato cells were placed in a solution with a low water concentration, then the opposite would happen. Water would move out of the cell into the solution. In extreme cases the cell membrane breaks away from the cell wall and the cell is referred to as plasmolysed. The potato cells will have decreased in length, volume and mass.
The greater the concentration of water in the external solution the greater the amount of water that enters the cell by osmosis. The smaller the concentration of water in the external solution the greater the amount of water that leaves the cell.
However, there will be a point where the concentrations of water inside and outside the potato cells are equal (isotonic). At this point there will be no change in the length, volume and mass of the potato, as the net movement of water will be zero, no osmosis has occurred.
Conclusion
The prediction made is supported by the evidence obtained from this investigation. It shows that the potato cells increase mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration. At concentrations above 0.6 M, there appears to be no further water loss, suggesting that the cell is fully plasmolysed.
From the graph an estimate to the concentration of the potato cell can be made as 0.132 M. As this is the point where the potato is not increasing or decreasing in mass. However, it is important to realize that this is only an estimate as the potato cells will not be uniform in their concentration.
Evaluation
The accuracy of the investigation was adequate, however the concentrations were measured using a measuring cylinder and could be made more accurate using titration. Also when the potato was dried to remove surface liquid it was not necessarily done the same on each potato, a more accurate and uniform way of drying would improve the accuracy further.
Further work could be carried out to include concentrations that increased in 0.1 M rather than 0.2. This would increase the accuracy and improve the graph. Other investigations could include using different varieties of potato or different plant tissues e.g. carrot.
Fair test:
In this experiment there should only be two changing variables: 1: Different molarities of sugar solution. 2: Changing weight of the potato samples. To keep these two variables the only variables in the experiment I must:
: Keep the potato samples the same length (2cm). This is because if one potato sample is 1cm long and one is 3cm long then the 3cm long sample will have a larger surface area and will osmosise much more quickly.
2: Use the same potato. This is because many factors due to the potato may affect the experiment. For example the age, species e.g. King Edward, size and any imperfections in the potato can be kept to a minimum.
3: Stop the evaporation of any of the molar solution. This is because if the sugar solution evaporates past the level of the of the potato then the potato sample will have less surface area in the solution so may osmosise slower. To stop any solution evaporating a foil lid can be placed on top of the test tube.
4: Accurate amount of sugar solution: More Bathing solution may affect the rate of solution. To make the amount of solution placed in the test tube as accurate as possible a syringe will be used to measure out the exact amount needed.
5: Contamination: As each test tube is filled up with the different molar solutions the syringe which would measure the amount of solution placed in the test tube may become contaminated with different molarities. To stop this the beaker and syringe must be washed every time they are used.
6: Average: To make the experiment as accurate as possible an average will be taken out of 5 results taken. Also any clearly anomalous results will be ignored.
7:Temperature: The temperature may affect the reliability of the experiment for example at extreme temperatures the cells of the potato may die and at less extreme temperatures the experiment may be speeded up. To keep this from happening all the test tubes will be kept in the same place
Prediction:
I predict that at around the 0.3 molarity solution there will be not much change. This is because on a pilot test done before hand there was not much change at around this point. I also predict that if a sample floats in the solution then it will gain weight and osmosise and if it sinks then the potato will ex-osmosise.
Revised Procedure.
. Set up Test tubes, five for each molarity level, making sure they are labelled.
2. Prepare the potato samples, cut out tubes using the same cork borer and then cut them to 2cm long using a scalpel. Making sure you clean your equipment to prevent contamination.
3. Immediately weigh each sample, and then place in the bathing solution.
4. Leave for 24 hours.
5. Remove samples; wipe off excess water on dry tissue paper.
6. Immediately re-weigh the samples and record the results.
Number and Range:
There will be 7 different molarity levels 0, 0.5, 0.1.15, 0.2, 0.25, and 0.3. The results will also be taken five times per molarity level and an average taken this will help reduce anomalous results.
Appropriate Equipment.
. 5 test tubes for each molarity level (35).
2. Bungs for test tubes (35).
3. Labels for test tubes (35).
4. Test tube rack for each molarity level (7).
5. Bungs for test tubes (35).
6. Scalpels for cutting potato samples.
7. Cork borer.
7. Cutting board.
8. Weighing machine.
9. Beakers for measuring solution.
0. Tissue for drying potato samples.
Diagram:
Procedure:
Use a syringe to measure out 50 mls of a molarity level of a sugar solution and fill up five test tubes with 50mls of the solution. This will give a range of results and if the average is taken then. Cut out five samples of potato for each molarity level all from the same potato as if the potatoes are different then their cellular make up will be to and therefore they would have different osmotic properties. Make sure that they are two cm in length. Then place them in the test tube and cover with foil so that the solution does not evaporate over the 24 hours you have to leave it. <INSERT OSMOSIS DEFINITION HERE>During this 24 hours if the potato gains wait it is osmosising and the water molecules in the solution will be able to pass through the semi-permeable membrane of the potato sample. However the sugar molecules will not be able to pass through and therefore if no sugar molecules pass through the potato will become equally balanced with the water outside and as it needs to get water into its cells to do this then it will gain wait. On the other hand if there is more of a concentration of water in the potato then the water will ex-osmosise into the sugar solution therefore losing weight. Therefore if the sugar concentration in the solution is high the water inside the potato will pass through the potatoes semi-permeable membrane and into the sugar solution.
Prediction:
The weight of the potato should not change at some point just below or above 0.25m. This was worked out using preliminary tests.
Preliminary work:
Prior to this experiment I did an experiment to help with a prediction and also to help indicate a number and range for the main experiment. The experiment was done quickly using the molarity levels 1, 0.5, 0.25 and 0. There was no average taken but it helped identify a closer range to work with. The potato sample did not gain or lose much weight at around the 0.25 mark. This meant that we could now produce a more accurate experiment at around the 0.25 molarity mark and instead of having several molarity all the way up to 1% I could be more accurate and pin point at around what position exactly I would do the experiment. This also helped establish that if the potato sunk then it would probably lose weight and if it floated then it would gain weight and therefore showed me whether it would osmosise or ex-osmosise.
Section O:
Safety: To make the experiment safe the equipment that was sharp i.e. Scalpels and core borers were used carefully and a cutting tile or board.
Table to show the average loss/gain in % of a sample of potato tissue submersed in Sugar solution for a period of 28 hours (to 2dp).
Molarity Sample Weight
Original: New: Loss/Gain (g): Loss/Gain (%): Average Loss/Gain (%):
0.0m 1 1.17 1.34 + 0.17 + 14.53 +12.66
2 1.05 1.18 + 0.13 + 12.38
3 1.11 1.25 + 0.14 + 12.61
4 1.07 1.20 + 0.13 + 12.15
5 1.03 1.15 + 0.12 + 11.65
0.05m 1 1.06 1.17 + 0.11 + 10.38 +9.70
2 1.25 1.36 + 0.11 + 8.80
3 1.13 1.24 + 0.11 + 9.73
4 1.01 1.10 + 0.09 + 8.91
5 1.22 1.35 + 0.13 + 10.66
0.10m 1 1.13 1.20 + 0.07 + 6.19 +6.97
2 1.13 1.21 + 0.08 + 7.08
3 1.11 1.20 + 0.09 + 8.11
4 1.11 1.19 + 0.08 + 7.21
5 1.12 1.19 + 0.07 + 6.25
0.15m 1 1.15 1.20 + 0.05 + 4.35 +4.40
2 1.14 1.20 + 0.06 + 5.26
3 1.01 1.05 + 0.04 + 3.96
4 1.13 1.18 + 0.05 + 4.42
5 1.00 1.04 + 0.04 + 4.00
0.20m 1 1.14 1.18 + 0.04 + 3.51 +3.26
2 1.01 1.04 + 0.03 + 2.97
3 1.03 1.06 + 0.03 + 2.91
4 1.11 1.15 + 0.04 + 3.60
5 1.20 1.24 + 0.04 + 3.33
0.25m 1 1.03 1.05 + 0.02 + 1.94 +0.40
2 1.01 1.00 - 0.01 - 0.99
3 1.01 1.00 - 0.01 - 0.99
4 1.00 1.00 +/- 0.00 +/- 0.00
5 1.02 1.04 + 0.02 + 1.96
0.30m A 1.03 0.99 - 0.04 - 3.88 -5.94
B 1.02 0.96 - 0.06 - 5.88
C 1.01 0.93 - 0.08 - 7.92
D 1.00 0.93 - 0.07 - 7.00
E 1.00 0.95 - 0.05 - 5.00
The range was close to being inaccurate but showed that the potato samples solute content was between 0.25 and 0.3.
Flow diagram of how we obtained the results:
Fill a test tube with the sugar solution
ê
Cut out potato samples with an apple corer
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Cut each sample to 2cm in length
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Place a sample inside the test tube
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Place a foil lid over the neck of the test tube
ê
Leave for 28 hours
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Remove potato sample from the test tube and wipe off excess water
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Re-weigh and record the results
Scatter graph to test the accuracy of the results:
Section A:
Table of results showing molarity level and % loss/gain in the potato samples weight.
Molarity Sample Weight
Original: New: Loss/Gain (g): Loss/Gain (%): Average Loss/Gain (%):
0.0m 1 1.17 1.34 + 0.17 + 14.53 +12.66
2 1.05 1.18 + 0.13 + 12.38
3 1.11 1.25 + 0.14 + 12.61
4 1.07 1.20 + 0.13 + 12.15
5 1.03 1.15 + 0.12 + 11.65
0.05m 1 1.06 1.17 + 0.11 + 10.38 +9.70
2 1.25 1.36 + 0.11 + 8.80
3 1.13 1.24 + 0.11 + 9.73
4 1.01 1.10 + 0.09 + 8.91
5 1.22 1.35 + 0.13 + 10.66
0.10m 1 1.13 1.20 + 0.07 + 6.19 +6.97
2 1.13 1.21 + 0.08 + 7.08
3 1.11 1.20 + 0.09 + 8.11
4 1.11 1.19 + 0.08 + 7.21
5 1.12 1.19 + 0.07 + 6.25
0.15m 1 1.15 1.20 + 0.05 + 4.35 +4.40
2 1.14 1.20 + 0.06 + 5.26
3 1.01 1.05 + 0.04 + 3.96
4 1.13 1.18 + 0.05 + 4.42
5 1.00 1.04 + 0.04 + 4.00
0.20m 1 1.14 1.18 + 0.04 + 3.51 +3.26
2 1.01 1.04 + 0.03 + 2.97
3 1.03 1.06 + 0.03 + 2.91
4 1.11 1.15 + 0.04 + 3.60
5 1.20 1.24 + 0.04 + 3.33
0.25m 1 1.03 1.05 + 0.02 + 1.94 +0.40
2 1.01 1.00 - 0.01 - 0.99
3 1.01 1.00 - 0.01 - 0.99
4 1.00 1.00 +/- 0.00 +/- 0.00
5 1.02 1.04 + 0.02 + 1.96
0.30m A 1.03 0.99 - 0.04 - 3.88 -5.94
B 1.02 0.96 - 0.06 - 5.88
C 1.01 0.93 - 0.08 - 7.92
D 1.00 0.93 - 0.07 - 7.00
E 1.00 0.95 - 0.05 - 5.00
The weight increased in each potato sample until just above 0.25 and below 0.30. This shows the solute content of the potato is equal with the concentration of the bathing solution. How ever the last results at 0.3 have a difference of 4%. This may produce anomalous results.
To find the exact solute content of a potato a graph will have to be plotted showing molarity against % weight change. The point at which the potato does not gain or lose any weight should be just above 0.25m. This is because there was little weight gain at 0.25 and a loss at 0.30m.
Graph of weight (%) change vs. Molarity of bathing solution (m):
Conclusion:
The graph above shows that at 0.23 there is 0% loss or gain in the weight of the potato. This shows at this point the solute content of the potato is exactly equal to the concentration of the sucrose bathing solution. Therefore no water moves between the potato and the bathing solution. This means that the weight of the potato sample does not change. So the concentration of the solute content of potatoes must be 0.23%.
Prediction:
In Section P. I predicted that the potatoes would have a solute content at around 0.25%. The real solute content of the potato was 0.23%. This proves my prediction was accurate.
Section E:
Accuracy and general comments:
The evidence obtained was accurate. Most anomalous results were cancelled out by the averages taken. The scatter graph in section A shows that the results taken were accurate and the results were all quite close to the line. This means that the results were accurate enough to make a reliable conclusion. However there were some anomalous results at some point as the table suggests that the solute content of the potato would be between 0.25 and 0.30, however the best fit line on the graph shows that this is not true and that the actual solute content of a potato is around 0.23%.
The accuracy of the experiment was accurate to suit our purpose to make it more accurate several steps could have been taken.
: Human error: Human error could have been reduced by taken more accurate measurements to a uniform result. This could be attempted by using a tool which could be set to a set length to cut the potato.
2: Instead of the range of the potato being 0.0 to 0.30 the range could be decreased to 0.20 to 0.30. This would produce more accurate results. Also increasing the number of results so instead of taking results from 7 different molarity levels 10 molarity levels could be taken. This would make the lines of best fit on the graphs more accurate, therefore the end results would be more accurate.
3: If the potatoes did not rest against the sides then they would all have the same amount of surface area. This is the same for the potato samples that float therefore exposing themselves to air and the samples that sink stopping osmosis occurring on the areas that are touching the bottom of the test tube.
Reliability: The results were reliable to take a reasonably accurate result. However the steps above (1,2 and 3) would produce an even more accurate result.
Further work: To extend this experiment it could be repeated exactly as before. However this time results at the molarity levels 0.20, 0.21, 0.22,0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30. This would produce much more accurate results.
Other variables in the experiment could be changed for example instead of changing the weight of the potato the species of the potato could be changed. For example New potatoes, King Edwards etc could be used.
Also the shape and size could be changed. However this would not affect the results much. This is because the variable would only change the rate of osmosis because of a different weight and size.
Temperature could also be changed for example the samples could be placed in different water baths and brought up to different temperatures to see if temperature played its part in the osmosis of potatoes. 5 sets of 5 potatoes could be placed in water baths at 10oC, 20oC, 30 oC, 50 oC and 60 oC. Then leave them for 24 hours making sure all the variables in the first experiment still apply however just using one molar solution. Then after 24 hours re-weigh the samples and record the result. I would expect that at high temperatures the potato samples would osmosise the most. This is because at high temperatures the solutions water molecules would move faster and therefore equal the concentration faster. A preliminary experiment could be set up beforehand to find out how long the experiment should be kept going because if the concentration of the potatoes equalises then the weight of the potatoes will be almost exactly the same.
Introduction
Knowing that osmosis (a diffusion of water) will occur across a semi-permeable membrane whenever there is a difference between the water concentrations on the two sides of the membrane, and knowing that when this happens to cells they will either become turgid if water flows into them, or plasmolysed if water flows out of them, and thus change their volume, we want to test the hypothesis that:
If the concentration of a solution into which a cylinder of potato is placed is greater than a certain level the cylinder will contract, and if the concentration is less than that level it will expand.
We have studied turgidity and plasmolysis in a textbook (Key Science-Biology, pages 143-144) and in a preliminary experiment, where we first added 2% sucrose solution to rhubarb epidermal cells, and saw them become plasmolysed, and then added water, and saw them become turgid. However, we did not use different solution concentrations, and did not measure the amount of contraction or expansion that took place. From our results in the main experiment, we should be able to work out not only the amount of contraction or expansion caused by each strength of solution, but also the concentration of the sap inside the cells.
Apparatus
For the experiment we will require:
Either cylinders of potato with a diameter of 6.5mm and a height of 5mm, or a potato, a borer with a diameter of 6.5mm and a scalpel. (To allow us to make our own).
Solutions of varying strengths (of sucrose and NaCl), or a solution of a known strength and distilled water. (To allow us to make our own).
Pins (To ensure that cylinders remain separate while in the solutions.)
Test-tubes
Callipers (To measure cylinder height and diameter.)
Diagram
One of the test-tubes during the experiment.
Three potato discs on a pin, not touching.
Method
We take a cylinder of potato, with a diameter of 6.5mm, from the potato, and cut it into separate cylinders each with a height of 5mm. We then thread at least three of the cylinders, to make the experiment fair (in case one of the cylinders is abnormal or damaged), on to a pin, keeping them apart from each other. We then make up solutions of either sucrose or sodium chloride, either by % strength or by molarity, and place 4 millilitres of each strength into a separate test-tube. We used a range of % sucrose solutions, going from distilled water (0%) to 2% (which we knew from earlier experiments would plasmolyse the cells), and a range of sodium chloride solutions from distilled water (0) to 0.4 molar (which would again be enough to plasmolyse the cells). We then place each of the sets of three cylinders on a pin into each of the different solutions, making sure that the cylinders are covered by the solution, and leave all of the test-tubes close to each other for 24 hours.
We assume that this means that the pressure and temperature in each case is the same, as these are factors which could affect osmosis, and we know that the volume, size and surface area of each cylinder is the same, and as they are all from the same potato, the only variable that we are altering is the concentration of the solution. Although ideally the experiment would be repeated several times, we were not able to do this as we did not have sufficient time.
After 24 hours we remove the cylinders from solution and, with callipers, which are more accurate than a ruler and would cover the likely range of sizes (from 4mm to 7mm), measure the new diameter and height of the cylinders. The results, in table and graph form are recorded below in the Results section.
Results
Concentration Cylinder Diameter/mm Cylinder Height/mm Volume/mm3 (2dp) Ave. Cylinder Volume/mm3
Pre-immersion 6.5 6.5 6.5 5 5 5 165.92 165.92 165.92 165.92
Sodium Chloride solution
0.0 Molar 6.8 6.6 6 5.5 6.4 5.2 199.74 218.96 147.03 188.58
0.1 Molar 6 6.5 6.8 4.4 4.9 4.9 124.41 162.6 177.95 154.99
0.2 Molar 5.6 5.9 5.7 5 4.5 4.5 123.15 123.03 114.83 120.34
0.3 Molar 6 6.1 5.9 4.9 4.9 4.5 138.54 143.2 123.03 134.92
0.4 Molar 5.9 6 5 5.6 5.4 5 153.1 152.68 98.17 134.65
Sucrose Solution
0% 6.8 7 6.8 5.7 5.5 5.3 207.01 211.66 192.48 203.72
0.25% 5.5 6 5 5 5.5 5 118.79 155.51 98.17 124.16
0.50% 5 5.2 5 5.5 6.6 5 107.99 140.17 98.17 115.44
% 5.5 5 4.9 5.9 5.1 5 140.17 100.14 94.29 111.53
2% 4.4 4.6 4.4 4.8 5.2 4.4 72.99 86.42 66.9 75.44
Concentration of Solution Average % Change in Volume From Original
NaCl solution
0.0 Molar 13.66
0.1 Molar -6.59
0.2 Molar -27.47
0.3 Molar -18.68
0.4 Molar -18.84
Concentration of Solution Average % Change in Volume from Original
Sucrose Solution
0% 22.78
0.25% -25.17
0.50% -30.42
% -32.78
2% -54.53
Analysis
The results show that, in accordance with our hypothesis, the cylinders will expand when external solute concentration is low (high water concentration), and contract in strong solutions (low water concentration). This is due to osmosis, where water passes from weak solutions to strong solutions across a semi-permeable membrane, such as a cell membrane. The graphs of % change against solution strength show that the results tend to form a curve, crossing the x axis (where there is no change in volume), at approximately 0.07 molar concentration for the sodium chloride solution, and at approximately 0.2 % for the sucrose solution. This concentration is the osmolar concentration (the total solute concentration) of the sap inside the cell. The volume change forms a curve when plotted against solute concentration because the cells, which have cellulose cell walls in addition to a cell membrane, will not expand or contract indefinitely, and will be held in shape within certain limits. However, the relatively low number of solutions tested (5) means that there is a range of possible values for the osmolar concentration of sap in the cell, and means that we cannot accurately predict values for volume change at different concentrations. To conclude, therefore, the results support our hypothesis, and we were also able to discover the approximate concentration of the sap in the cell.
Evaluation
Although the results of the sodium chloride and sucrose experiments support the hypothesis, there are several anomalous results and a large deviation for each result. These could be improved by altering the experiment, for example by keeping the test-tubes in a water bath at a set temperature, by keeping them at a constant pressure, and by measuring the sizes of potato cylinders before and after with a more accurate method, e.g. accurate weight measurement or volumetric displacement. The test might also be more accurate if the potato cylinders were left in the solutions for a longer ...
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Evaluation
Although the results of the sodium chloride and sucrose experiments support the hypothesis, there are several anomalous results and a large deviation for each result. These could be improved by altering the experiment, for example by keeping the test-tubes in a water bath at a set temperature, by keeping them at a constant pressure, and by measuring the sizes of potato cylinders before and after with a more accurate method, e.g. accurate weight measurement or volumetric displacement. The test might also be more accurate if the potato cylinders were left in the solutions for a longer period of time to allow the solution to penetrate fully to the core of the sample. The test could also be repeated more times for each concentration of solution, and with a greater number of concentrations, as this would decrease the error - a disadvantage of our experiment was that one anomalous result affected the others significantly (e.g. NaCl 0.2 molar concentration). Another factor is that the potato from which the cylinders are taken could be abnormal - this could be prevented by amalgamating sets of results, for example of a whole class, where each experimenter used a different potato.
Results that were not as I would have expected occurred with NaCl solution at 0.2 molar concentration (see above), where the range of results appeared too low. However, although this is apparently an anomalous result, it could have been caused by either experimental error - more significant when a small number of results are used, or a difference in the potato for those cylinders. Either of these would easily be recognised if a larger number of results were collected and used. Another result that appeared unusual was the ¡¥step¡¦ in the graph for the sucrose solution between 0.25% and 1% solutions - here different results for each cylinder pulled the average upwards by a noticeable amount, a problem that possibly would not occur if more measurements were taken.
For future experimentation we could repeat this experiment using a range of solution strengths very close to the value discovered here of sap osmolarity, to define more exactly its true value. We could also extend the experiment to use tissue samples from other plants, to discover whether the hypothesis is also correct for other tubers, and even for other plant tissues. We would then also be able to compare osmotic pressures inside different plants.
Planning
We have been asked to investigate the effect of osmosis on monkeys. Osmosis is the diffusion of water from a lower concentration of solute to a higher concentration of solute, through a membrane.
I have chosen to investigate the effect of the water potential/concentration of solution on potato chips. This means that I will put potato chips into salt solutions of different concentrations. These concentrations would be ones such as these; 0.25mola, 0.5m, 0.75m, 1.0m, 1.25m, 1.50 and distilled water.
There are other factors involved and these are;
¨ Temperature
¨ Water potential of potato initially
¨ SIZE of potato
¨ Light intensity
¨ Mass of potato dependent variable
¨ Volume of solution potato chip is in
¨ Type of potato
¨ Time left in solution
¨ Surface area of potato chip
¨ Use the same balance to measure chip
If I am going to conduct a fair test, then I am going to have to control these other factors. Doing all the tests at one temperature will control the temperature. For the purpose of my experiment I am going to do all the experiments at room temperature.
To keep the water potential of the potato initially will be kept the same by using the same type of potato, which have been treated in the same way, e.g. have all been cut without being washed and peeled.
The size of the potato is very important. This is because if the size of the potato varies,
so will the amount of mass is looses or gains. I will cut all the pieces of potatoes, to the
same size. We will be given potato chips with the same width and dimensions, but the
length of them will differ, (due to potatoes being of uneven shapes). The potato chip will
be 3cm in length.
The light intensity will be kept the same by doing all the experiments in the same room,
with the same light intensity, (no extra light will be shone on the experiments, nor will
there be any experiments kept in the dark).
The mass of the potato is a dependent variable, and this means that it will be measured
throughout the experiment. I will measure the mass in grams. The potato chip will be
measured before it is put in the solution, and after. This will allow us to see whether
osmosis has taken place, and to what extent.
The volume of the solution that the potato chips are kept in must be fair. The must be
totally covered in the solution, and the amount of solution will be kept the same because
all the potato chips are the same size. The amount of solution I cover each chip in will be
50ml.
The type of potatoes we use are going to be kept the same, because different potatoes
may absorb at different rates. For this experiment I am going to use the same brand
The time the potato chip is left in the solution must be kept the same in each
experiment. This is because more or less solution may be absorbed depending on time. I
am going to keep each potato chip in each solution for 10 minutes, in a boiling tube.
The surface area of the potato chips will be kept the same by having all the chips the
same size. This must be kept the same because the amount of surface area exposed to
the solution may effect the rate of osmosis. The thickness of the chip will already be the
same, so I will cut the length so that each chip is 3cm long.
To make the mass readings more fair, I will take each chip of the solution, roll all the surfaces gently on a paper towel, (2 seconds on each surface), to remove all excess solution, and I must not squeeze the chip.
I am also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between scales.
I predict that the higher the concentration of salt solution the more water will move out of the potato chip. We know that osmosis the flow of one solvent, (water) of a solution through a membrane while the other constituents are blocked and unable to pass through the membrane. Experimentation is necessary to determine which membranes permit selective flow, or osmosis, because not all membranes act in this way. Many membranes allow all or none of the constituents of a solution to pass through; only a few allow a selective flow. As the potato is a plant cell, it contains a vacuole and a cytoplasm. The cell membrane is also partially permeable i.e. it lets some substances in but not all substances. This means that water paeticalscan diffuse into cells by osmosis if the cells are surrounded by a weak solution. (Osmosis is the movement of water molecules from a high area of water potential to an area of low water potential through a selectively permeable membrane.) If the cells are surrounded by a stronger solution, e.g. salt water, the cells may loose water by osmosis.
To ensure safety , the boiling tubes will be kept in beakers so that they can not be knocked over. The potato chips will be cut on a white tile with a scalpel so that no one will be cut. Also while using scalpels everyone will have to wear safety goggles.
My experiment is not experimenting the how permeable the membranes are, but it is testing the rate of osmosis with different solutions. We also know that diffusion of water will occur from a lower concentration of solute to a higher concentration of solute. I am saying that the higher the concentration that the potato chip is exposed to, the more water will move out of it making it flaccid. Here are some diagrams to help explain.
Distilled water Salt solution (0.25m)
Potato Chip Potato chip
Water has a lower Water moves out, from
concentration than lower to higher con-
potato chip, therefore centration.
water moves into chip
and it becomes turgid.
The graph above is my prediction graph. This is how I think my final results will fit into a graph. As you can see, the change in mass for distilled water is positive (y-axis measures % gain/loss in mass), and all the rest are negative, below the x-axis, and the best fit line is a curve, showing that the loss/gain in mass is not proportional to the concentration of the fluid.
I will take readings of the concentration of the salt solution, which will have already been made. I could also take a measurement of the temperature of the room using a thermometer. I will also have to measure each potato chip I use, and make sure that they are all of the same size. The mass of the potato chip will be weighed before and after the experiment to show whether water moved in or out of the chip, and also to what extent, (in grams). I will measure the time the potato chip is left in the solution with a stopwatch, and this will be measured in minutes, (10). The volume of solution the chip is put in can be kept the same because the chips are all of the same size, and seeing as they all must be totally covered, I will have each chip in 100ml of solution. I will cut 7 (multiplied by the number of repeats (3)) chips into equal lengths of 3cm. After I weigh them and record these results, I will place them into pre-labeled test tubes of which are already containing 25ml of the relevant solution. I will place all the chips as quickly as I can and then saturate the stop watch, for 10 mins. I will then remove all the solutions from the test tubes as quickly as I can, (so that the chips do not carry on changing weight, and the test is kept as fair as possible), and I will then weigh them and record the results. These will then be put into tables and will be used in graphs. I will also measure the temperature in the room.
I am going to do the experiment three times, in each solution, and I will then take an average to have a fairer reading. One result may not be accurate because of human error, so to eliminate all possibilities of inaccuracy I will repeat it. I must also do at least 5 types of concentrations, to have sufficient results and to see if my prediction is correct, and I am going to do 7.
Here is a diagram to show the equipment I am going to use:
Test-tube rack
test tube filled with solution
Stopwatch
Tile and Scalpel
Paper towel
Prongs holding chip
Preliminary Results
Concentration of solution Mass Before Mass After % Change in Mass
Distilled Water: 1st attempt 1.66 1.74 4.819277108
2nd attempt 1.58 1.66 5.063291139
0.25m: 1st attempt 1.7 1.62 -4.705882353
2nd attempt 2.06 2.07 0.485436893
0.50m: 1st attempt 1.69 1.62 -4.142011834
2nd attempt 1.78 1.67 -6.179775281
0.75: 1st attempt 1.76 1.6 -9.090909091
2nd attempt 1.71 1.56 -8.771929825
.0m: 1st attempt 1.74 1.59 -8.620689655
2nd attempt 1.4 1.25 -10.71428571
.25m: 1st attempt 1.65 1.44 -12.72727273
2nd attempt 1.4 1.25 -10.71428571
.50m: 1st attempt 1.79 1.41 -21.22905028
2nd attempt 1.75 1.42 -18.85714286
Concentration Average
Distilled water 4.94128412
0.25m -2.11022273
0.5m -5.16089356
0.75m -8.93141946
.0m -9.66748768
.25m -11.7207792
.50m -20.0430966
The room temperature was 26ºC.
From my preliminary results I have decided that the length of my potato chip should remain 10 cm. Each chip will be left in each solution for 10 minutes. I could have a number of experiments going on at once so that I save time. The range of my variable is suitable, because I have at 7 concentrations, and thus I will have more results to make more accurate conclusions. I will remove any excess water by rolling the chip on a paper towel, keeping each surface on the towel for 2 seconds, making sure that I do not squeeze the chip so that my results are fair. I have decided that I am no longer going to use 50ml of solution for each chip, because this is proved to be too large, therefore I will only need to use 25ml. I also must make sure that the solutions must be removed from all the test tubes after 10 minutes to have a fairer test. I am going to have three experiments going on at one times, and then I will wash the test tubes and re-use them. I must wash them so that no salt solution is left in them that might change my results. When weighing the weight of the potato chip on the scales, you must not lean on the bench because it affects the weight. I noticed that I had enough time left in the double lesson to do my whole experiment again, which means that I would have 6 sets of results. The more results you have the more accurate you graph will be, so when I come to do my actual experiment I will repeat it. I must also make some labels to label my test tubes with so that the test tubes do not get mixed up. I can also see that there will be some anomalous results, so if I do take a wider set of results, (by repeating the experiment), I will get a more reliable average. Also changing the other aspects e.g. such as emptying out all the solutions after 10 mins, will hopefully produce less anomalous results.
Results
Distilled water mass before (g) mass after (g) change in mass (g) %change in mass
1.46 1.52 0.06 4.109589041
2 1.64 1.75 0.11 6.707317073
3 1.72 1.85 0.13 7.558139535
4 1.64 1.89 0.25 15.24390244
5 1.63 1.85 0.22 13.49693252
6 1.75 1.95 0.2 11.42857143
average 1.64 1.801666667 0.161666667 9.757408672
0.25m mass before (g) mass after (g) change in mass (g) %change in mass
1.56 1.46 -0.1 -6.41025641
2 1.66 1.64 -0.02 -1.204819277
3 1.6 1.61 0.01 0.625
4 1.51 1.15 -0.36 -23.8410596
5 1.63 1.68 0.05 3.067484663
6 1.34 1.39 0.05 3.731343284
average 1.55 1.488333333 -0.061666667 -4.005384557
0.5 mass before (g) mass after (g) change in mass (g) %change in mass
1.65 1.45 -0.2 -12.12121212
2 1.66 1.52 -0.14 -8.43373494
3 1.88 1.71 -0.17 -9.042553191
4 1.42 1.36 -0.06 -4.225352113
5 1.66 1.51 -0.15 -9.036144578
6 1.6 1.52 -0.08 -5
average 1.645 1.511666667 -0.133333333 -7.976499491
0.75 mass before (g) mass after (g) change in mass (g) %change in mass
1.64 1.36 -0.28 -17.07317073
2 1.49 1.34 -0.15 -10.06711409
3 1.87 1.74 -0.13 -6.951871658
4 1.39 1.26 -0.13 -9.352517986
5 1.8 1.63 -0.17 -9.444444444
6 1.38 1.18 -0.2 -14.49275362
average 1.595 1.418333333 -0.176666667 -11.23031209
m mass before (g) mass after (g) change in mass (g) %change in mass
1.52 1.19 -0.33 -21.71052632
2 1.64 1.39 -0.25 -15.24390244
3 1.66 1.49 -0.17 -10.24096386
4 1.61 1.46 -0.15 -9.316770186
5 1.66 1.49 -0.17 -10.24096386
6 1.56 1.42 -0.14 -8.974358974
average 1.608333333 1.406666667 -0.201666667 -12.6212476
.25m mass before (g) mass after (g) change in mass (g) %change in mass
1.68 1.38 -0.3 -17.85714286
2 1.65 1.37 -0.28 -16.96969697
3 1.63 1.44 -0.19 -11.65644172
4 1.75 1.57 -0.18 -10.28571429
5 1.6 1.37 -0.23 -14.375
6 1.73 1.58 -0.15 -8.670520231
average 1.673333333 1.451666667 -0.221666667 -13.30241934
.5m mass before (g) mass after (g) change in mass (g) %change in mass
1.81 1.56 -0.25 -13.8121547
2 1.87 1.38 -0.49 -26.20320856
3 1.57 1.35 -0.22 -14.01273885
4 1.56 1.26 -0.3 -19.23076923
5 1.63 1.46 -0.17 -10.42944785
6 1.61 1.37 -0.24 -14.9068323
average 1.675 1.396666667 -0.278333333 -16.43252525
Concentration of salt solution Average %change
Distilled water 9.76
0.25m -4.01
0.50m -7.98
0.75m -11.23
.0m -12.62
.25m -13.3
.50m -16.43
The temperature when I was doing my actual results was 27ºC.
Analysis
My graph is a git that slopes downwards and does not go through the origin. Because the line is not straight and does not pass through the origin, it means that the percentage gain/loss in mass and morality are not directly proportional. However, there is a pattern on my graph, and this is, as the morality of the salt solution increases, the percentage change in mass decreases. The gradient does change in my graph. it gets less steep as 'x' gets bigger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in mass of each morality are becoming closer and closer together. All of my results lie close to my best-fit curve. This shows that my results are fairly reliable. My graph fits in with my prediction of the experiment graph.
The percentage gain/loss in mass homosexual are not directly proportional
are not directly proportional to each other, so I decided to test another simple way of seeing whether the results are related. This is to see if they are indirectly proportional. This is where you get the results and, x, and put 1 over them, 1/x. The graph is not a straight line through the origin which shows that the percentage gain/loss in mass and morality are not directly proportional either.
The average distilled water gains in mass. This means that osmosis takes place and that the water moves from the beaker into the potato. The matches my initial predictions, and fits in with my prediction graph as well. The point where the line crosses the x-axis is the isotonic point. This is where no osmosis is taking place, i.e. no water is moving in or out of the potato. The next point, 0.25 mola looses approximately 4.0g. This shows that the water potential of the salt solution in the beaker is weaker than that of the potato chip. The next, 0.50 m, looses approximately 8.0g in mass. This shows that the salt solution has an even weaker water potential than 0.25 m and that osmosis took place. This is why the potato lost even more mass, and it shows that the water potential in the beaker is less than that of the potato chip. Also that the potato is trying to make the water potential of the fluid on both sides of the semi permeable membrane the same, (osmosis from the potato to the salt solution, from a higher water potential to a lower one). This pattern carries on through the graph, and even more mass is loss, as more water moves out of the potato. My results tally with my initial predictions. These were that osmosis would take place, and as the water potential decreases, morality increases, the percentage change in mass will decrease.
Evaluation
The experiment was easy to do , but all the results I had to take had to be accurate had to change my plan several times. Things like having the potato chip 5cm long changed to 3cm because it was it was hard to have all the chips 5cm long, and 3cm was sufficient. Also, I changed the amount of solution I would keep the potato chips in, because I only needed enough to cover the potato chip. These changes were easy to make, because I did a preliminary experiment, so I could iron out any errors that may have occurred in my actual experiment.
I think I took enough results for the amount of moralities that I was given, and the time restrictions that I had to follow, (1h20 mins). The range was big enough, but to fill in the gaps in my graph, I could have taken results of more moralities, i.e. 0.10m, 1.15m, 1.20m, etc. This way I could have found the isotonic point by there being no change in mass. This would show the water potential of the potato , and this result could then be used further. Also to make my experiment better I could have repeated it more, and possibly have worked with someone else, or with the whole class. I could have also used cloned potatoes, so that they would have all been the same. I could have also cut the potatoes into doughnut shapes, because the cells in the center of the potato may have a different capacity of water and the intake, or distribution of it, or different water potentials. If I had cut the potato into doughnuts, I would have only been using the out side of the potato, leaving out the middle. I could have also used a machine to cut the potato chips.
My results did lie close to the curve, and therefore were fairly accurate, but if I was doing the experiment again I could make changes, some as mentioned above. I could also use a burette measure out my solutions. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each chip on a digital and more accurate scale, e.g. not to 0.00 but to 0.0000g.
There were not any anomalous results, but some results were not as close to the line as others. This may have been caused by human error, or on out of my six results could have been inaccurate, and changed the average drastically. Or perhaps the potato chip was not cut accurately, or that part of the potatoes, cells did not loose/gain mass well. My results did vary a lot for the same concentration. The fact that a certain part of the potato may not be the same as another was shown as the chips all of the same length were not the same weight, or even close. This is another reason to use cloned potatoes. My results were consistent, and there were no results that they were ignore .
I could extend my enquiry by testing the percentage change in mass with morality using a different substance. By this I mean using a different vegetable, perhaps celery or cucumber. Then I could find out whether osmosis occurs with the same patterns and trends with any vegetable.
Aim:
My main aim in this experiment is to find out if osmosis occurs in a potato, and how it affect the potato in different molar solutions of sucrose and water.
Apparatus
· Stop Clock - to time our experiment
· Cutting tile - to cut the potato on
· Knife - to cut the potato
· 25cm Measuring cylinder - to measure the solutions
· Distilled water - part of the experiment
· sucrose - part of the experiment
· Potatoes - part of the experiment
· Tissue paper - to dry the potatoes after the osmosis takes place
· Balance - to weigh the potatoes
· Cork borer - to cut out potato cylinders
Planning
Before actually planning the experiment, I will do some research to find out about osmosis, and matters related to it, so that I can make predictions. And figure out a way to make this investigation fair and safe.
Planning ahead would help me find out how to do what, when, which should lead me to good results at the end of the experiment.
Hypothesis
Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane. In this case, the tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration gradient of the two substances. So in this case, when the water concentration is lower in the tissue, the water will go inside the tissue of the potato, and the potato will gain weight. And if there is very little different in the two water concentrations, there shouldn´t be such a big change in weight. And if there is a higher concentration of water in the potato, the water will go out of the potato.
The potato, cut up into pieces, will need some sort of element to survive, and in this experiment, it would be light and water. With both of these sources, the potato will keep on working, until it dies of either lack of water, too much water. When the concentration gradient is lower in the potato, the water will transfer from the solution to the potato. And vice versa.
In the distilled water, I believe that the water is more concentrated in the potato, and therefore the water should transfer from the water to the potato, making the potato bigger in size, and heavier in weight. The potato tissues, being surrounded by a weak solution, will be most likely to swell up and become turgid, taking in all the water it can possibly take in.
With the potato in molar solutions of sucrose, I don´t think there will be much change in the weight of the potato. This is because there isn´t much difference between the two substances. I believe that the weight and the size of the potato won´t be altered much.
The 0.4 molar solutions of sucrose, similar to the 0.2 molar solution of sucrose, compared to the potato, both substances have very close concentration gradients. And that is why I am predicting that the weight of the potato in this experiment should be decreased by only a fraction.
The 0.6 molar solution of sucrose, I think, should make a big difference now, noting that it should be a large difference between the two concentration gradients. And there fore the weight should decrease, at least noticeable for us to notice.
The difference between the water concentration in the potato and the 0.8 molar solution of sucrose is big, and the water in the potato should be transferred from the potato, through the permeable membrane, to the solution surrounding the potato. And as a result, I am sure that the weight of the potato will increase largely. And because the potato tissues are surrounded by a stronger solution, it will probably become smaller, and shrink. But because of such high molars of sucrose, the water can diffuse all the way, throughout the two substances, equalling the concentration gradient of the two substances.
My theory in this experiment is that, due to the difference in the water concentrations of the two substances, I believe that the weight of the potato will start decreasing when it is tested on 0.2 molar solutions of sucrose and greater. By researching information about osmosis, and making predictions of the results, I believe the graph would look something like this:
Fair Test
Fair testing should play a big part in this experiment. If this experiment isn´t a fair test, we will be obtaining the wrong results, which could lead us to the wrong conclusions.
First of all, and most importantly, we will have to get the measurements and the weights of the solutions and the potatoes as exact, and as accurate as possible. We will try and get the measurements of the potatoes as accurate as possible for every single potato, evenly cutting the potato pieces, and making a record of the length to the nearest millimetre. And we will be using a very sensitive balance so that we can get the best readings possible.
But I believe one of the most important step in the fair testing is to make sure that the potato is fully covered by the solution. This is because the potato should fully submerge, by having total contact with the solution.
When using the balance, we will make sure that the balance is reading zero with the small foam bowl, before we put the 3 potatoes on it. This is so that we don´t get a false reading, with the weight of our potato with the reading it had before. And after the experiment, we will measure the 3 potatoes that should be dried as possible, and weigh it the same way, taking the reading to the nearest 2 decimal places.
And we will also be reading the measurements of the measuring cylinder by reading the bottom of the meniscus.
Carrying out the experiment in a constant temperature for the three hours of experiment is important. And to avoid temperature change, which might affect our 3 different sets of results, we will take the temperature of the solution into account.
Another important factor of a fair test is to start and stop the clock as quickly as possible. This meaning that we should start the clock as soon as the potato is put inside the test tube, and stop the clock as soon as 20 minutes have passed. Stopping the clock, taking them out and measuring it all in less than a minute us quite impossible because we lack the number of balances. And there are obviously too many sets to go through at such a fast time. Therefore, we will try our best to weigh the potatoes as quickly and as safely as we can.
Getting and experimenting with the exact measurements of molars and water is vital to this task. If the volume of one solution in a test tube is higher or lower than another, will affect the pattern of results later on.
We will also make sure that the potato is fully covered by the 6 different kinds of solutions. This is because, is the potato isn´t covered up by the solutions, the effect of osmosis might not occur to the fullest.
Small things such as a dirty test tube, and a slightly cracked measuring cylinder could still affect the results, and therefore we will take these into account as well.
Safety
Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. And that is why we take this into consideration, no matter what.
We will be using a very sharp knife, which could injure someone if it´s not handled properly. And we will also be careful that the solutions don´t get into our bodies internally, just in case, because we are not fully aware of the damage it could do to us.
But other than that, there weren´t any bigger matters to be cautious of.
Method
I believe this task is very simple and should be very easy to carry out the experiment. The investigation is very straightforward.
There won´t be any control for this experiment, because the weight would vary depending on the potato pieces. And therefore, it might affect the results, which we are going to take in after the experiment.
First I will have to get the pieces of potatoes ready. I will push the cork borer through the potato, cutting it into long cylinders with a diameter of 6mm. And then I will cut the potatoes into cylinders of 40mm, and weigh 6 sets of 3 potato cylinders. I will have 6 sets because we will have to test the potatoes in 6 different types of solutions; 0.2, 0.4, 0.6, 0.8, 1.0 molar solutions of sucrose, and distilled water.
I will weigh each set and have them ready for us to put into the test tube.
Then we will put the 6 sets of 3 potatoes in the 6 test tube at the same time and start the clock running for 10 minutes.
After 10 minutes, we will take all of the potatoes out of the test tube, so that the actual osmosis action stops, and we will put the potatoes onto one piece of dry towel, in their own groups. We will dry them with the tissue paper, in sets of 3, and weigh and measure the potatoes taking in the average reading of the 3 pieces.
We will repeat the experiment three times so that we can make sure that all our results are similar, and so that we will be able to take the average of the 3 experiments. This makes sure that we get accurate results. Repeating the experiments are important, because we will be able to receive valid results, and look for any anomalous results. Not to mention that we will take the fair testing into account.
Obtaining evidence
After the experiment, I had to dry the potatoes first, so that the water outside the tissue of the potatoes won´t alter the weight of what it is supposed to be. I quickly took all of them out, and put them onto a piece of tissue paper, into their own groups.
When obtaining my results, I reset the balance, so that it would read zero with the small foam bowl on top of it. This was because, if I had weighed the potatoes with the bowl, then I would have to take the weight of the bowl away from that result.
Table of results
In the table below, it shows the 'solution´ column, which are the 6 different types of solutions. The 'number of test´ column, which shows the number of tests that took place, and the average of the three tests. The weight before and after the experiment represents the 3 sets of results and the average taken out of the three. The increase/decrease of the weight is calculated by taking the weight after, minus the weight before. The percentage increase/decrease of the weight of the potato is calculated by taking the weight increase/decrease divided by the original weight multiplied by a hundred. This should help us lead to a more accurate result, and the average percentage will be used to present the graph.
solution no. weight Weight percentage change
In Water Before after weight + or - (%)
1 5.87 5.89 0.02 0.41
2 5.81 5.84 0.03 0.62
3 5.85 5.88 0.03 0.62
AVERAGE 5.84 5.87 0.03 0.55
0.2 molar
1 5.85 5.85 0.00 0.00
2 5.83 5.84 0.01 0.21
3 5.84 5.84 0.00 0.00
AVERAGE 5.84 5.84 0.00 0.07
0.4 molar
1 5.87 5.69 -0.18 -3.70
2 5.66 5.51 -0.15 -3.22
3 5.74 5.62 -0.12 -2.53
AVERAGE 5.76 5.61 -0.15 -3.15
0.6 molar
1 5.87 5.63 -0.24 -4.93
2 5.86 5.57 -0.29 -5.97
3 5.88 5.55 -0.33 -6.76
AVERAGE 5.87 5.58 -0.29 -5.89
0.8 molar
1 5.81 5.49 -0.32 -6.65
2 5.62 5.22 -0.40 -8.66
3 5.86 5.53 -0.33 -6.79
AVERAGE 5.76 5.41 -0.35 -7.35
1 5.64 5.23 -0.41 -8.84
2 5.86 5.51 -0.35 -7.20
3 5.80 5.39 -0.41 -8.54
AVERAGE 5.77 5.38 -0.39 -8.18
Analysis
On the graph shown below, I have made the 'different solutions´ as my independent variable, since it won´t be changing on any event. And I have made the 'percentage´ as my dependent variable, because it doesn´t change in any particular order or a pattern. I have decided to make it a bar graph, because the independent variables aren´t exactly in the same category. For example, I would have used a line graph if the independent variable in my experiment was time, which is changed deliberately, but these is different subjects of matter. And also, the results were very different, as well as the columns and there wouldn´t be any advantages of using a line graph to view the results. I have taken the average result of the 6 different solutions and put it on the graph to be more accurate.
Conclusion
In this experiment, I believe that I have collected enough data to support my hypothesis. This investigation was, I think, successful. Successful meaning my results collaborated my predictions.
The potato cells, working to stay alive, took in, or gave out the water depending on the concentration of the tissue, and the concentration of the solution it is surrounded in.
The results were fine and by looking at the weights measured before the experiment, you can see that there is no reading which seems to be out of the line. As the weights before the experiment range between 5.62g and 5.87g, this tells us that the potato pieces were cut well, and I believe accurate enough. There were, I believe, no anomalous results after the experiment as the weights were very similar in their own category. And this tells us that my experiment was successful.
The graphs and the results show that:
v Osmosis actually took place in the experiment.
v As the molars increased, the percentage of the weight difference decreased.
There doesn´t seem to be any results, which undermine my predictions, and our group didn´t find any anomalous results, which means we didn´t have to repeat any of our experiments more than three times.
Having the results which backs up my hypothesis, proves that this investigation was fully accomplished, and was an achievement.
Solution Weight Weight Weight + or - Percentage change
Before(g) After(g) (g) (%)
water 5.84 5.87 0.03 0.55
0.2 5.84 5.84 0.00 0.07
0.4 5.76 5.61 -0.15 -3.15
0.6 5.87 5.58 -0.29 -5.89
0.8 5.76 5.41 -0.35 -7.35
5.77 5.38 -0.39 -8.18
In the table above, the percentage shows a steady decrease, telling us that the percentage of the difference decreases as the water concentration decreases.
This experiment helped me find out that osmosis occurs between 2 liquid substances with a partially impermeable membrane, and that higher the water concentration is, the larger increase in grams. This means that the percentage will also be higher, increasing with the gram.
Evaluation
We followed the plan correctly, I believe we gained accurate and sufficient enough results to conclude the experiment, and to prove our hypothesis.
My final results were very reliable, due to the precautions I took to make this a fair test.
To make this experiment better, I believe that we could have done one test at a time, so that we can reduce the time difference, when we have to move the potato from the test tube to the balance. Between this, we have to dry the potatoes just enough, and then put it on the balance. When we are doing this for one set, writing down the results at the same time, while the other 5 sets are on the tissue paper, the water outside the potato tissue is going to vary for all. Therefore, we would be able to concentrate more on one of the sets, instead of trying to finish all of them as quickly as we can.
We also could have got more people to do the experiment with us, so that we can organize the tasks, and we would be able to divide the tasks.
Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results, so that we can make sure the results are totally correct.
Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tell us how much water could be transferred for each solution.
Repeating the same tasks many other times wouldn´t have been very useful, since we had already done the result 3 times, and ALL the results were reliable.
Even though we didn´t use these experimental plans, we still got results which were correct, according to my hypothesis, and backed up my predictions.
But overall, given the apparatus that we got to carry out the test, I think this experiment turned out to be very successful, and I´m very please with my results.
Planning
I am investigating the effect of osmosis on a potato. Osmosis is the diffusion of water down a concentration gradient through a semi permeable membrane.
I am investigating the effect of water concentration on the potato chips. This means that I will put potato chips into salt solutions of different concentrations. There are also other factors involved, these are:
- Temperature of water
- Size of chip
- Light
- Mass of potato
- Volume of solution potato is in
- Type of potato
- Time left in solution
- Surface area of potato chip
- Using the same balance to measure chip
If I am going to make this a fair test, then I will have to control these other factors. Doing the tests at one fixed temperature will control the temperature of the water. For the purpose of my experiment I am going to do all the experiments at room temperature.
The size of the potato is very important. This is because if the size of the potato varies, so will the amount of mass it can loose or gain. I am going to try to cut all the pieces of potatoes, to the same size. Because of the 'chipper´ I will have chips with the same width and height, but the length of the chips will differ. I am going to cut the chips to 3cm in length.
The light intensity cannot really me measured or kept the same, as the chips will be moved from one room to another, for storage. However I will try to keep the chips in the same place when I am storing them.
The mass of the potato is a variable, and this means that it will be measured throughout the experiment. I will measure the mass in grams. The potato chip will be measured before it is put in the solution, and after. This will allow us to see whether osmosis has taken place, and how much osmosis has occurred.
The volume of the solution that the potato chips are kept in must be the same. The chip must be totally covered in the solution, and the amount of solution will be kept the same because all the chips are the same size. The amount of solution I cover each chip in will be 25ml.
The type of potatoes I will use is going to be kept the same, because different potatoes may absorb at different rates. For this experiment I am going to use the same potato.
The time the potato chip is left in the solution must be kept the same for each chip. This is because more or less solution may be absorbed depending on time. I am going to keep each potato chip in each solution for nine days.
The surface area of the potato chips will be kept the same by having all the chips the same size. This must be kept the same because the amount of surface area exposed to the solution may effect the rate of osmosis. The thickness of the chip will already be the same, so I will cut the length of each chip to 3cm long.
To make the mass readings more fair, I will take each chip, roll the chip gently on a paper towel, to remove all excess solution, and I must not squeeze the chip.
I am also going to use the same balance to weigh my chips. This is because the measurements may vary slightly between scales.
I predict that the higher the concentration of salt in the solution, the more water will move out of the potato chip. We know that osmosis is the flow of water in a solution through a membrane while the other molecules are unable to pass through the membrane. Experimentation is needed to discover which membranes allow osmosis, as not all membranes act in this way. Some membranes may allow all or none of the molecules of a solution to pass through, only a few may allow a selective flow. The cell membrane of the potato is partially permeable (it lets some substances in but not all substances). This means that water particles can diffuse into the cells, via osmosis. This occurs if the cells are surrounded by a weak solution e.g. Vimto. If the cells are surrounded by a stronger solution, e.g. very salty water, the cells may loose water by osmosis.
To ensure safety, I will keep my boiling tubes in a large glass beaker so they cannot fall over. The potato chips will be carefully cut on a white tile using a scalpel, so that no one will be cut.
My experiment is not testing how permeable the chip´s membrane is, but it is testing the rate of osmosis of the salt solution. I am predicting that the higher the concentration that the chip is exposed to, the more water will move out of the chip; making it flaccid.
I am going to set up the experiment so I have three results per concentration, I will then take an average to make the test fairer. One result may not be accurate because of human error, so to get rid of the errors, I will repeat it. I will also do at least 3 types of concentrations, to have enough results and to see if my prediction is correct. I am probably going to do 4, these being;
- Water
- 3 x 2g salt
- 3 x 3g salt
- 3 x 4g salt
The equipment I am going to use will be:
- A chipper
- A white tile
- A scalpel
- 10 boiling tubes
- A large beaker
- A measuring cylinder
- A large potato
- Salt
- Water
- Weighing scales
Preliminary Results
My preliminary results were a bit rubbish, as I could not really think of anything to do except find out how many spatulas of salt or sugar went into 25ml of water. However these are my results:
Sugar into 50ml water = 15 spatulas
Salt into 50ml water = 15 spatulas
Although pointless I did decide that sugar took longer to dissolve into the water, so would I use salt instead (to save time). I also decided my concentrations. ( I do not understand the language used when talking about concentrations i.e. molars etc. so I will use ratios instead )
The ratio is water (ml) : salt (g) and the letters are what I labelled the boiling tubes as.
A 25 : 0
B 25 : 2
C 25 : 2
D 25 : 2
E 25 : 3
F 25 : 3
G 25 : 3
H 25 : 4
I 25 : 4
J 25 : 4
I am going to measure the weight of the chip (before and after) to the nearest .01g (the nearest the scales will allow)
Obtaining Evidence
Here is my table of results:
Tube Salt Mass Before (g) Mass After (g) Change in Mass (g) Change in Mass %
A 0g 5.25 5.13 -0.12 -2.339181287
B 2g 5.16 4.52 -0.64 -14.15929204
C 2g 5.42 4.62 -0.8 -17.31601732
D 2g 5.61 4.83 -0.78 -16.14906832
E 3g 5.99 5.16 -0.83 -16.08527132
F 3g 5.68 4.74 -0.94 -19.83122363
G 3g 5.71 4.78 -0.93 -19.45606695
H 4g 6.15 5.25 -0.9 -17.14285714
I 4g 6.01 5.74 -0.27 -4.703832753
J 4g 5.72 4.92 -0.8 -16.2601626
Average 2.7g 5.67 4.969 -0.701 -14.34429734
The average for 2g salt is -15.875
The average for 3g salt is -18.458
The average for 4g salt is -12.702
Analysis
My first graph is just there to show comparisons between the mass before and the mass after. This is quite useful, as it shows that the chips with 2g salt lost around the same mass, whereas with the chips in 3g salt G and F lost more mass than E.
The second graph shows the change in mass of the chips. In theory this graph should be quite useful as I can guess the change in mass of the chip that has 5g salt in the water. However this will probably not be happening with mine, as it is quite wrong. I don´t know if my results are wrong or not, but the graph looks very wrong. From the graph I have noticed that I have one anomalous result per gram of salt. B, E and I are all anomalous, and this changes the bottom line of the graph, but the top two still look dodgy. If J had a .87g change in mass (or a figure around .9g) then the top two lines of the graph would have been quite good.
Evaluation
The experiment was easy to do, but all the results I took had to be accurate. Unfortunately I had to change my plan several times. There are several reasons for this, these being that someone stole my boiling tubes, which I had spent 2 weeks getting exactly the right amount of salt into. There were also other things, like having the chips 5cm long. I changed this to 3cm because I couldn´t find 10 5cm long chips. Also, I changed the amount of solution I would keep the potato chips in, because otherwise the water spilled out of the tube, and I only needed enough to cover the chip (it was 100ml). These changes were easy to make, as they were only minor, however the case of the stolen boiling tubes meant that I had to spend several lunchtimes taking my results again.
I think I took enough results for the coursework. The range was big enough, but to fill in the gaps in my graph I could have taken different results, i.e. 1g, 1.2g, 1.4g etc. or even smaller. This way I could have found more accurate results. Also to make my experiment better I could have repeated it more, and possibly have worked with someone, as I was working on my own, or even with the whole class. I could have also cut the potatoes into doughnut shapes, because the cells in the middle of the potato might have different properties, making them react differently to osmosis. I could have also used a machine to cut the potato chips. I could also weigh each chip on a digital and more accurate scale, e.g. not to 0.00 but to 0.0000g.
There was one main anomalous result, this is highlighted in red and is two sizes bigger (tube I), but there is one more, but it is not that far out (tube B). This may have been caused by human error, or one out of my ten results might have been inaccurate, and changed the average. Or perhaps the chip was not cut accurately, or I added the wrong amount of salt. concentration.
I could extend my coursework by testing the same brand of chip using a different substance. By this I mean using a different thing instead of salt, i.e. sugar or coffee or even vimto. Then I could find out whether osmosis occurs differently with different things diluted in the water. I could even use different vegetables.
Essaybank
Method
A potato was taken, and using a hollow cylindrical tube many long potato tubes were made. Using a ruler and knife these were cut into 3.5cm tubes. These were weighed individually on the scales and then placed into test tubes, as well as this the total weight of all three potatoes to be placed into a test tube was calculated. Water baths were heated to the correct temperatures, this was ensured using a thermometer. Then taking a bottle of distilled water, the test tubes with potatoes in them were filled half way and then placed in a water bath. Using a stopwatch this was timed for eighteen minutes. Once eighteen minutes had passed the test tube was emptied above the sink and the potatoes were dried using tissues. Once dry their weights were taken again on the scales. The weight before and after was taken. This was recorded in a table.
Fair and Reliable Test
To guarantee that the test was fair as well as reliable the following measures were taken:
* All the Potato tubes were made the same length
* The same amount of water was placed into each test tube
* Potatoes were left in water baths for the same amount of time
* It was made sure that the scales were reading "0" before the potatoes were placed on them to take the weight
* The potatoes were dried after the experiment so the mass of residue water on the potato was not included in the final weight
Aim My main aim in this experiment is to find out if osmosis occurs in a potato, and how it affect the potato in different molar solutions of sucrose and water. Apparatus À 6 petri dishes û for all of the six solutions À Marker pen û to label the petri dish, just in case of a mix up À Beakers û to pour the solutions into the petri dish À Stop Clock û to time our experiment À Cutting tile û to cut the potato on À Knife û to cut the potato À 25cm Measuring cylinder û to measure the solutions À Distilled water û part of the experiment À 2, 0.4, 0.6, 0.8, 1.0 molar solutions of sucrose û part of the experiment À Potatoes û part of the experiment À Tissue paper û to dry the potatoes after the osmosis takes place À Balance û to weigh the potatoes À Cork borer û to cut out potato cylinders Planning Before actually planning the experiment, I will do some research to find out about osmosis, and matters related to it, so that I can make predictions. And figure out a way to make this investigation fair and safe. Planning ahead would help me find out how to do what, when, which should lead me to good results at the end of the experiment. Hypothesis Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane. In this case, the tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration gradient of the two substances. So in this case, when the water concentration is lower in the tissue, the water will go inside the tissue of the potato, and the potato will gain weight. And if there is very little different in the two water concentrations, there shouldnÆt be such a big change in weight. And if there is a higher concentration of water in the potato, the water will go out of the potato. The potato, cut up into pieces, will need some sort of element to survive, and in this experiment, it would be light and water. With both of these sources, the potato will keep on working, until it dies of either lack of water, too much water. When the concentration gradient is lower in the potato, the water will transfer from the solution to the potato. And vice versa. In the distilled water, I believe that the water is more concentrated in the potato, and therefore the water should transfer from the water to the potato, making the potato bigger in size, and heavier in weight. The potato tissues, being surrounded by a weak solution, will be most likely to swell up and become turgid, taking in all the water it can possibly take in. With the potato in 0.2 molar solutions of sucrose, I donÆt think there will be much change in the weight of the potato. This is because there isnÆt much difference between the two substances. I believe that the weight and the size of the potato wonÆt be altered much. The 0.4 molar solutions of sucrose, similar to the 0.2 molar solution of sucrose, compared to the potato, both substances have very close concentration gradients. And that is why I am predicting that the weight of the potato in this experiment should be decreased by only a fraction. The 0.6 molar solution of sucrose, I think, should make a big difference now, noting that it should be a large difference between the two concentration gradients. And there fore the weight should decrease, at least noticeable for us to notice. The difference between the water concentration in the potato and the 0.8 molar solution of sucrose is big, and the water in the potato should be transferred from the potato, through the permeable membrane, to the solution surrounding the potato. And as a result, I am sure that the weight of the potato will increase largely. And because the potato tissues are surrounded by a stronger solution, it will probably become smaller, and shrink. But because of such high molars of sucrose, the water can diffuse all the way, throughout the two substances, equaling the concentration gradient of the two substances. My theory in this experiment is that, due to the difference in the water concentrations of the two substances, I believe that the weight of the potato will start decreasing when it is tested on 0.2 molar solutions of sucrose and greater. By researching information about osmosis, and making predictions of the results, I believe the graph would look something like this: Fair Test Fair testing should play a big part in this experiment. If this experiment isnÆt a fair test, we will be obtaining the wrong results, which could lead us to the wrong conclusions. First of all, and most importantly, we will have to get the measurements and the weights of the solutions and the potatoes as exact, and as accurate as possible. We will try and get the measurements of the potatoes as accurate as possible for every single potato, evenly cutting the potato pieces, and making a record of the length to the nearest millimeter. And we will be using a very sensitive balance so that we can get the best readings possible. But I believe one of the most important step in the fair testing is to make sure that the potato is fully covered by the solution. This is because the potato should fully submerge, by having total contact with the solution. When using the balance, we will make sure that the balance is reading zero with the small foam bowl, before we put the 3 potatoes on it. This is so that we donÆt get a false reading, with the weight of our potato with the reading it had before. And after the experiment, we will measure the 3 potatoes that should be dried as possible, and weigh it the same way, taking the reading to the nearest 2 decimal places. And we will also be reading the measurements of the measuring cylinder by reading the bottom of the meniscus. Carrying out the experiment in a constant temperature for the three hours of experiment is important. And to avoid temperature change, which might affect our 3 different sets of results, we will take the temperature of the solution into account. Another important factor of a fair test is to start and stop the clock as quickly as possible. This meaning that we should start the clock as soon as the potato is put inside the petri dish, and stop the clock as soon as 20 minutes have passed. Stopping the clock, taking æem out and measuring it all in less than a minute us quite impossible because we lack the number of balances. And there are obviously too many sets to go through at such a fast time. Therefore, we will try our best to weigh the potatoes as quickly and as safely as we can. Getting and experimenting with the exact measurements of molars and water is vital to this task. If the volume of one solution in a petri dish is higher or lower than another, will affect the pattern of results later on. We will also make sure that the potato is fully covered by the 6 different kinds of solutions. This is because, is the potato isnÆt covered up by the solutions, the effect of osmosis might not occur to the fullest. Small things such as a dirty petri dish, and a slightly cracked measuring cylinder could still affect the results, and therefore we will take these into account as well. Safety Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. And that is why we take this into consideration, no matter what. We will be using a very sharp knife, which could injure someone if itÆs not handled properly. And we will also be careful that the solutions donÆt get into our bodies internally, just in case, because we are not fully aware of the damage it could do to us. But other than that, there werenÆt any bigger matters to be cautious of. Plan I believe this task is very simple and should be very easy to carry out the experiment. The investigation is very straightforward. There wonÆt be any control for this experiment, because the weight would vary depending on the potato pieces. And therefore, it might affect the results, which we are going to take in after the experiment. First I will have to get the pieces of potatoes ready. I will push the cork borer through the potato, cutting it into long cylinders with a diameter of 10mm. And then I will cut the potatoes into cylinders of 30mm x 10mm x 10mm, and weigh 6 sets of 3 potato cylinders. I will have 6 sets because we will have to test the potatoes in 6 different types of solutions; 0.2, 0.4, 0.6, 0.8, 1.0 molar solutions of sucrose, and distilled water. I will weigh each set and have them ready for us to put into the petri dish. We will then get 25cm of the solutions and the water with help of the measuring cylinder, and pour them into the petri dish, naming them to make sure that they donÆt get mixed up. Then we will put the 6 sets of 3 potatoes in the 6 petri dishes at the same time and start the clock running for 20 minutes. After 20 minutes, we will take all of the potatoes out of the petri dish, so that the actual osmosis action stops, and we will put the potatoes onto one piece of dry towel, in their own groups. We will dry them with the tissue paper, in sets of 3, and weigh and measure the potatoes taking in the average reading of the 3 pieces. We will repeat the experiment three times so that we can make sure that all our results are similar, and so that we will be able to take the average of the 3 experiments. This makes sure that we get accurate results. Repeating the experiments are important, because we will be able to receive valid results, and look for any anomalous results. Not to mention that we will take the fair testing into account. Method In the actual experiment, instead of using a cork bearer of 10mm diameter, we had to use a cork bearer of 8mm diameter. Although there was a change in plans, I donÆt think this change would affect neither my hypothesis, nor my results that we got. As for the experiment that we carried out, no changes were made in the experiment. Obtaining evidence After the experiment, I had to dry the potatoes first, so that the water outside the tissue of the potatoes wonÆt alter the weight of what it is supposed to be. I quickly took all of them out, and put them onto a piece of tissue paper, into their own groups. When obtaining my results, I reset the balance, so that it would read zero with the small foam bowl on top of it. This was because, if I had weighed the potatoes with the bowl, then I would have to take the weight of the bowl away from that result. Table of results In the table below, it shows the æsolutionÆ column, which are the 6 different types of solutions. The ænumber of testÆ column, which shows the number of tests that took place, and the average of the three tests. The weight before and after the experiment represents the 3 sets of results and the average taken out of the three. The increase/decrease of the weight is calculated by taking the weight after, minus the weight before. The percentage increase/decrease of the weight of the potato is calculated by taking the weight increase/decrease divided by the original weight multiplied by a hundred. This should help us lead to a more accurate result, and the average percentage will be used to present the graph. SOLUTION NUMBER WEIGHT INCREASE OR PERCENTAGE OF TEST BEFORE (g) AFTER (g) DECREASE (g) (%) DISTILLED 1 4.87 4.89 0.02 0.41 WATER 2 4.81 4.84 0.03 0.62 3 4.85 4.88 0.03 0.62 AVERAGE 4.84 4.87 0.03 0.55 0.2 1 4.85 4.85 0.00 0.00 2 4.83 4.84 0.01 0.21 3 4.84 4.84 0.00 0.00 AVERAGE 4.84 4.84 0.00 0.07 0.4 1 4.87 4.69 -0.18 -3.70 2 4.66 4.51 -0.15 -3.22 3 4.74 4.62 -0.12 -2.53 AVERAGE 4.76 4.61 -0.15 -3.15 0.6 1 4.87 4.63 -0.24 -4.93 2 4.86 4.57 -0.29 -5.97 3 4.88 4.55 -0.33 -6.76 AVERAGE 4.87 4.58 -0.29 -5.89 0.8 1 4.81 4.49 -0.32 -6.65 2 4.62 4.22 -0.40 -8.66 3 4.86 4.53 -0.33 -6.79 AVERAGE 4.76 4.41 -0.35 -7.35 1 1 4.64 4.23 -0.41 -8.84 2 4.86 4.51 -0.35 -7.20 3 4.80 4.39 -0.41 -8.54 AVERAGE 4.77 4.38 -0.39 -8.18 Analysis On the graph shown below, I have made the ædifferent solutionsÆ as my independent variable, since it wonÆt be changing on any event. And I have made the æpercentageÆ as my dependent variable, because it doesnÆt change in any particular order or a pattern. I have decided to make it a bar graph, because the independent variables arenÆt exactly in the same category. For example, I would have used a line graph if the independent variable in my experiment was time, which is changed deliberately, but these is different subjects of matter. And also, the results were very different, as well as the columns and there wouldnÆt be any advantages of using a line graph to view the results. I have taken the average result of the 6 different solutions and put it on the graph to be more accurate. Conclusion In this experiment, I believe that I have collected enough data to support my hypothesis. This investigation was, I think, successful. Successful meaning my results collaborated my predictions. The potato cells, working to stay alive, took in, or gave out the water depending on the concentration of the tissue, and the concentration of the solution it is surrounded in. The results were fine and by looking at the weights measured before the experiment, you can see that there is no reading which seems to be out of the line. As the weights before the experiment range between 4.62g and 4.87g, this tells us that the potato pieces were cut well, and I believe accurate enough. There were, I believe, no anomalous results after the experiment as the weights were very similar in their own category. And this tells us that my experiment was successful. The graphs and the results show that: v Osmosis actually took place in the experiment. v As the molars increased, the percentage of the weight difference decreased. There doesnÆt seem to be any results, which undermine my predictions, and our group didnÆt find any anomalous results, which means we didnÆt have to repeat any of our experiments more than three times. Having the results which backs up my hypothesis, proves that this investigation was fully accomplished, and was an achievement. SOLUTION WEIGHT INCREASE OR PERCENTAGE BEFORE (g) AFTER (g) DECREASE (g) (%) DISTILLED 4.84 4.87 0.03 0.55 WATER 0.2 4.84 4.84 0.00 0.07 0.4 4.76 4.61 -0.15 -3.15 0.6 4.87 4.58 -0.29 -5.89 0.8 4.76 4.41 -0.35 -7.35 1 4.77 4.38 -0.39 -8.18 In the table above, the percentage shows a steady decrease, telling us that the percentage of the difference decreases as the water concentration decreases. This experiment helped me find out that osmosis occurs between 2 liquid substances with a partially impermeable membrane, and that higher the water concentration is, the larger increase in grams. This means that the percentage will also be higher, increasing with the gram. Evaluation We followed the plan correctly, except for the little change that we had to do, which was to use the cork borer with a diameter of 8mm instead of 10mm. But I believe that it wouldnÆt have made much difference to the conclusion. Apart from that small modification in the planning, I believe we gained accurate and sufficient enough results to conclude the experiment, and to prove our hypothesis. My final results were very reliable, due to the precautions I took to make this a fair test. To make this experiment better, I believe that we could have done one test at a time, so that we can reduce the time difference, when we have to move the potato from the petri dish to the balance. Between this, we have to dry the potatoes just enough, and then put it on the balance. When we are doing this for one set, writing down the results at the same time, while the other 5 sets are on the tissue paper, the water outside the potato tissue is going to vary for all. Therefore, we would be able to concentrate more on one of the sets, instead of trying to finish all of them as quickly as we can. We also could have got more people to do the experiment with us, so that we can organize the tasks, and we would be able to divide the tasks. Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results, so that we can make sure the results are totally correct. Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tell us how much water could be transferred for each solution. Repeating the same tasks many other times wouldnÆt have been very useful, since we had already done the result 3 times, and ALL the results were reliable. Even though we didnÆt use these experimental plans, we still got results which were correct, according to my hypothesis, and backed up my predictions. But overall, given the apparatus that we got to carry out the test, I think this experiment turned out to be very successful, and IÆm very please with my results.
Skill Area P: Planning
Aim: To investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato chip of a given size.
Hypothesis: Osmosis is defined as the net movement of water or any other solution¡|s molecules from a region in which they are highly concentrated to a region in which they are less concentrated. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water through but does not allow bigger molecules to pass through. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other.
For this particular investigation I think that the lower the concentration of the sugar solution in the test tube the larger the mass of the potato will be. This is because the water molecules pass from a high concentration, i.e. In the water itself, to a low concentration, i.e. In the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations.
The graph above shows a simple curve obtained when the concentration of the solution is plotted against the percentage change in mass.
"Y At point A the graph tells the viewer that no osmosis has occurred, suggesting that the concentration of water inside the cell is equal to the solution outside.
"Y At point B (high water concentration), there is no indication that the cell is increasing further in size. This is because the cell is fully turgid and no more water can enter.
"Y At point C (low water concentrations), there is no indication that the cell is decreasing further in size. This is because the cell is fully plasmolysed and no more water can leave the cell.
Further information on potato plant cells:
Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what make the green parts of the plant "stand up" into the sunlight.
When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid." This is the exact opposite of "turgid". The contents of the potato cells shrinks and pulls away from the cell wall. These cells are said to be plasmolysed.
When plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. "Incipient" means "about to be".
Variables:
To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. I have chosen to vary the concentration of the sugar solution. This will give me a vary varied set of results from which I hope to make a decent conclusion. If any of the non-variables below are not kept constant it would mean it would not be a fair test. For instance if one of the potato chips was 1cm longer the surface area of the chip would be larger and there would therefore be more space for osmosis to occur. Doing all the tests at one temperature will control the temperature.
"X For the purpose of my experiment I am going to do all the experiments at room temperature.
"X To keep the water potential of the potato initially will be kept the same by using the same type of potato, which have been treated in the same way, e.g. have all been cut without being washed and peeled.
"X The mass of the potato is a dependent variable, and this means that it will be measured
throughout the experiment. I will measure the mass in grams. The potato chip will be
measured before it is put in the solution, and after. This will allow us to see whether
osmosis has taken place, and to what extent.
"X The volume of the solution that the potato chips are kept in must be fair. The must be
totally covered in the solution, and the amount of solution will be kept the same because
all the potato chips are the same size.
"X I am also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between scales.
TABLE SHOWING THE DIFFERENT VARIABLES THAT WILL
BE CONSIDERED DURING THE EXPERIMENT
Variables Non-Variables
Solution concentration Surface area
Solution volume
Duration of experiment
Temperature
Solution
Weighing scales
Conditions
Preliminary Results
Concentration of solution Mass Before Mass After % Change in Mass
0.00m: 1st attempt 1.66 1.74 4.819277108
2nd attempt 1.58 1.66 5.063291139
0.25m: 1st attempt 1.7 1.62 -4.705882353
2nd attempt 2.06 2.07 0.485436893
0.50m: 1st attempt 1.69 1.62 -4.142011834
2nd attempt 1.78 1.67 -6.179775281
0.75: 1st attempt 1.76 1.6 -9.090909091
2nd attempt 1.71 1.56 -8.771929825
.0m: 1st attempt 1.74 1.59 -8.620689655
2nd attempt 1.4 1.25 -10.71428571
Percentage change in accordance to the varying solutions
Concentration Average % change
0.00m 4.94128412
0.25m -2.11022273
0.5m -5.16089356
0.75m -8.93141946
.0m -9.66748768
These preliminary results give me an overall impression on the change in mass gain or loss when placed in varying concentrations of sucrose solution.
Planned method:
A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.25 molar, 0.5 molar, 0.75 molar and 1 molar. This will be done by adding varying amounts of distilled water to varying amounts of sucrose solution. Sections of potato will be cut using a scalpel and will be measured using a ruler. This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur. The mass of each chip will be measured as well so that more results can be obtained. Three chips will be placed in each test tube each time so that I can take an average for each tube. I will use 10 ml of each concentration of sugar solution and once in the test tubes they each will be labelled. The potato pieces will then be placed in the different test tubes and then left for 30 minutes. Then the potato pieces will be removed, the surface solution removed using paper towels and then they will be re-weighed. If I then have time afterwards I will repeat this experiment again as to obtain a second set of results. This will hopefully produce more accurate results from which I will be able to draw a more accurate conclusion.
Skill Area O: Obtaining evidence
Method:
. I took two average sized ground potatoes and checked that they were both healthy and hard.
2. Using a standard kitchen knife I peeled the potatoes and cut each one into an even block approximately 7cm by 5cm by 4cm on a white tile.
3. Using a scalpel and ruler I cut the potato into ¡§chips¡¨ which were 5 cm long. I had to be very careful whilst cutting the potato as the scalpel is exceptionally sharp. I then had 15 chips.
4. Taking a test tube rack I placed 5 test tubes and then labelled them 0 molar, 0.25 molar, 0.5 molar, 0.75 molar and 1 molar.
5. Using a measuring cylinder I measured out different amounts of sucrose solution and distilled water which I then poured into the test tubes in a percentage ratio giving me the various molar concentrations.
6. I then weighed every potato chip on an electronic balance and recorded the weights.
7. I swiftly put 3 potato chips into each beaker and then started my stopwatch. 3 chips were used to create an average which gave me a better set of results and more accurate graphs.
8. Whilst waiting I set out some paper towels with which I was going to dry the paper and I drew up a basic table for my results.
9. After 30 minutes I drained out the solutions in the sink and placed all the chips on the paper towel in the order I had put them in the test tubes as to not confuse myself as to which chip came from which solution.
0. I dried each chip with the paper towel and then placed each one on the scales so that I could weigh them.
1. Each potato was measured accurately on the electronic scales and then the weights were recorded.
2. As I had time after doing the first set of results I redid the experiment under exactly the same conditions. This gave me secondary set of results which gave me a more accurate view on the changes.
Precautions:
"h As was stated in my planning section of the coursework, I had to keep all of the different non-variables the same, to make sure that none of them affected the results of the experiment in any way.
"h Whilst cutting the potato, extreme care and precision had to be taken with the scalpel as it is very sharp and could easily cause a serious wound.
"h The measurements for the solutions had to be perfect as to not change the out come of the experiment.
"h I had to ensure that every time I handled the potatoes my hands were clean and dry. This was to stop any kind of contamination and made sure that I did not pass on any extra water onto the potatMain Tables of Results for all Concentrations
0.00m concentration mass before (g) mass after (g) change in mass (g) % change in mass
1.46 1.52 0.06 4.109589041
2 1.64 1.75 0.11 6.707317073
3 1.72 1.85 0.13 7.558139535
4 1.64 1.89 0.25 15.24390244
5 1.63 1.85 0.22 13.49693252
6 1.75 1.95 0.2 11.42857143
average 1.64 1.801666667 0.161666667 9.757408672
0.25m concentration mass before (g) mass after (g) change in mass (g) % change in mass
1.56 1.46 -0.1 -6.4102
2 1.66 1.64 -0.02 -1.2048
3 1.6 1.61 0.01 0.625
4 1.51 1.15 -0.36 -23.841
5 1.63 1.68 0.05 3.06748
6 1.34 1.39 0.05 3.73134
average 1.55 1.48833 -0.0616 -4.0053
0.5m concentration mass before (g) mass after (g) change in mass (g) % change in mass
1.65 1.45 -0.2 -12.121
2 1.66 1.52 -0.14 -8.4337
3 1.88 1.71 -0.17 -9.0425
4 1.42 1.36 -0.06 -4.2253
5 1.66 1.51 -0.15 -9.0361
6 1.6 1.52 -0.08 -5
average 1.645 1.51166 -0.1333 -7.9764
0.75m concentration mass before (g) mass after (g) change in mass (g) % change in mass
1.64 1.36 -0.28 -17.073
2 1.49 1.34 -0.15 -10.067
3 1.87 1.74 -0.13 -6.9518
4 1.39 1.26 -0.13 -9.3525
5 1.8 1.63 -0.17 -9.4444
6 1.38 1.18 -0.2 -14.492
average 1.595 1.41833 -0.1766 -11.230
.00m concentration mass before (g) mass after (g) change in mass (g) % change in mass
1.52 1.19 -0.33 -21.71
2 1.64 1.39 -0.25 -15.243
3 1.66 1.49 -0.17 -10.240
4 1.61 1.46 -0.15 -9.3167
5 1.66 1.49 -0.17 -10.240
6 1.56 1.42 -0.14 -8.9743
average 1.60833 1.4066 -0.2016 -12.621
This graph shown above gives the line of best fit for the percentage change in mass of the potato chips over the course of the thirty minute experiment. The graph is a curve that slopes downwards and does not go through the origin. Because the line is not straight and does not pass through the origin, it means that the percentage gain and loss in mass and concentration are not directly proportional. However, there is a pattern on my graph, and this is, as the concentration of the solution increases, the percentage change in mass decreases. The graph shows that the percentage gain and loss in inversely proportional to the concentration. The gradient does change in my graph. It gets less steep as X axis gets bigger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in mass of each molar concentration is becoming closer and closer together. From the line of best fit that has been added in, it can be seen that all of my points were very close to creating a perfectly smooth curve. This shows that my results are fairly reliable. My graph fits in with my prediction of the experiment graph.
It shows that the potato cells increase in mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration. When the concentration reaches above 0.75 M, there appears to be no further water loss, suggesting that the cell is fully plasmolysed. From the graph an estimate to the concentration of the potato cell can be made as 0.13 M, as this is the point where the potato is not increasing or decreasing in mass, this is known as the isotonic point. This is where no osmosis is taking place, both the potato and the solution have an identical molar concentration. The next point, 0.25 M looses approximately 4.0 %. This shows that the water potential of the salt solution in the beaker is weaker than that of the potato chip. The next, 0.50 M, looses approximately 8.0 % in mass. This shows that the salt solution has an even weaker water potential than 0.25 M and that osmosis took place. This is why the potato lost even more mass, and it shows that the water potential in the beaker is less than that of the potato chip. This pattern carries on through the graph, and even more mass is lost, as more water moves out of the potato into the solution. My results also match with my initial predictions.
This graph of the change in mass helps prove the point of complete plasmolysis, whereby the potato cannot expand and take in any more water. As you can see as the molar concentration increases the change in mass decreases. From right to left the first two points on the graph are very spread out indicating that there was a large change in the mass. This decreases throughout the increasing molar concentration until the change is minuscule (about 0.02g).
This graph above shows a clear indication that there was an overall decrease in mass during the experiment. At the point 0.00 M the line for after the experiment is above the line for before the experiment unlike any of the others. This is because the water potential of the sugar solution is higher than that of the potato chip.
Skill Area E: Evaluation
The experiment was very successful in my opinion. I obtained a large quantity of very accurate results from which I was able to create informative graphs. I think I took easily enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen and possibly find out the saturation point of the chips. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. 0.10m, 1.15m, 1.20m, and so on. This way would have allowed me to also find out the isotonic point far more accurately as the one that I estimated is very approximate.
The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine to cut the potato as it would ensure that all potatoes would be the same weight and dimensions. As well as the potato I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. Perhaps I could have used a burette. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g.
There were not any out of the ordinary results, but some were not as close to the line as others. This may have been caused by human. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction.
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Osmotic activity in potato cylinders
Skill Area P: Planning
Aim: To investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato cylinders.
Hypothesis: Osmosis is defined as the net movement of water or any other solutions molecules from a region in which they are highly concentrated to a region in which they are less concentrated. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water through but does not allow bigger molecules to pass through. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other.
For this particular investigation I think that the lower the concentration of the sugar solution in the test tube the larger the mass of the potato will be. This is because the water molecules pass from a high concentration, i.e. in the water itself, to a low concentration, i.e. in the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations.
Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what makes the green parts of the plant "stand up" into the sunlight.
When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid." This is the exact opposite of "turgid". The contents of the potato cells shrinks and pulls away from the cell wall. These cells are said to be plasmolysed.
When plant cells are placed in a solution, which has exactly the same osmotic strength as the cells, they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. "Incipient" means, "about to be".
Variables:
Variables Non-Variables to be considered
) Solution concentration Surface area
2) Solution volume
3) Duration of experiment
4) Temperature
5) Solution
6) Conditions which experiment is kept in
To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. I have chosen to vary the concentration of the sugar solution. This will hopefully give me a varied set of results from which I hope to make a decent conclusion. If any of the non-variables below are not kept constant it would mean it would not be a fair test. For instance if one of the potato cylinders was 1cm longer the surface area of the chip would be larger and there would therefore be more space for osmosis to occur. Doing all the tests at one temperature will control the temperature, so it cannot effect the results, so i am going to carry out my experiment in a controlled environment. To keep the water potential of the potato initially will be kept the same by using the same type of potato, which have been treated in the same way, e.g. have all been cut without being washed and peeled. The mass of the potato is a dependent variable, and this means that it will be measured
throughout the experiment. I will measure the mass in grams. The potato cylinder will be measured before it is put in the solution, and after. This will allow us to see whether
osmosis has taken place, and to what extent.
The volume of the solution that the potato chips are kept in must be fair. The cylinders must be totally submerged in the solution, i will make sure the amount of solution will be kept the same to make it a fair test.
.
Planned method:
A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.25 molar, 0.5 molar, 0.75 molar and 1 molar.
Sections of potato will be cut using a scalpel and will be measured using a ruler. This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur.
The mass of each chip will be measured as well so that more results can be obtained. Three chips will be placed in each test tube each time so that I can take an average for each tube.
I will use 10 ml of each concentration of sugar solution and once in the test tubes they each will be labelled.
The potato pieces will then be placed in the different test tubes and then left for 24 hours.
Then the potato pieces will be removed, the surface solution removed by gently blotting paper towels over surface at the same pressure to keep it a fair test and then they will be re-weighed.
Skill Area O: Obtaining evidence
Method:
. Using a cork borer i cut cylinders out of the potato
2. Using a scalpel and ruler I cut the cylinders down to roughly the same size. I had to be very careful whilst cutting the potato as the scalpel is exceptionally sharp. I then had 15 chips. 3.Taking a test tube rack I placed 5 test tubes and then labelled them 0 molar, 0.25 molar, 0.5 molar, 0.75 molar and 1 molar.
4. Using a pipette I put the same amount of each different concentration of solution and put each test tube in the right place in the rack
5.I then weighed every potato chip on a top pan balance and recorded the weights in a table.
6. I put 3 potato chips into each test tube and placed the rack in a controlled environment. 3 chips were used to create an average which gave me a better set of results and more accurate graphs.
7. After 24 hours I drained out the solutions in the sink and placed all the chips on the paper towel in the order I had put them in the test tubes as to not confuse myself as to which chip came from which solution.
8. I dried each chip with the paper towel and then placed each one, one by one, on the top pan balance to weigh them and their weights were recorded in a table.
Precautions:
>Whilst cutting the potato, extreme care and precision had to be taken with the scalpel as it is very sharp and could easily cause a serious wound.
>The measurements for the solutions had to be perfect as to not change the out come of the experiment.
>I had to ensure that every time I handled the potatoes my hands were clean and dry. This was to stop any kind of contamination and made sure that I did not pass on any extra water onto the potato.
RESULTS
This graph shown above gives the line of best fit for the percentage change in mass of the potato cylinders. The graph is a curve that slopes downwards and does not go through the origin. Because the line is not straight and does not pass through the origin, it means that the percentage gain and loss in mass and concentration are not directly proportional. However, there is a pattern on my graph, and this is, as the concentration of the solution increases, the percentage change in mass decreases. The graph shows that the percentage gain and loss in inversely proportional to the concentration. The gradient does change in my graph. It gets less steep as X axis gets bigger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in mass of each molar concentration is becoming closer and closer together. From the line of best fit that has been added in, it can be seen that all of my points were very close to creating a perfectly smooth curve. This shows that my results are fairly reliable. My graph fits in with my prediction of the experiment graph.
It shows that the potato cells increase in mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration. When the concentration reaches above 0.75 M, there appears to be no further water loss, suggesting that the cell is fully plasmolysed. From the graph an estimate to the concentration of the potato cell can be made as 0.13 M, as this is the point where the potato is not increasing or decreasing in mass, this is known as the isotonic point. This is where no osmosis is taking place, both the potato and the solution have an identical molar concentration. The next point, 0.25 M looses approximately 4.0 %. This shows that the water potential of the salt solution in the beaker is weaker than that of the potato chip. The next, 0.50 M, looses approximately 8.0 % in mass. This shows that the salt solution has an even weaker water potential than 0.25 M and that osmosis took place. This is why the potato lost even more mass, and it shows that the water potential in the beaker is less than that of the potato chip. This pattern carries on through the graph, and even more mass is lost, as more water moves out of the potato into the solution. My results also match with my initial predictions.
Skill Area E: Evaluation
This experiment was very successful in my opinion. I obtained accurate results from which I was able to create informative graphs. I think I took enough results for the concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur.
However if I was to repeat the experiment I could possibly try to find out the saturation point of the potato. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have a larger amount of results to test this idea further.
The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would take more care when cutting the potato to ensure that all potatoes would be the same weight and dimensions. I will also use the same balance to weigh my potato chips. This is because the measurements may slightly vary between the top pan balances. I would have liked to repeat this experiment again to obtain a second set of results. This will hopefully produce more accurate results from which I will be able to draw a more accurate conclusion.
There were not any out of the ordinary results, but some were not as close to the line as others. This may have been caused when the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction.
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