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, unlike animal cells ie. cheek cells, which explode if they take up to much water. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen, stiff 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 salt solutions they lose water by osmosis and they become "flaccid." This is the exact opposite of "turgid". The content 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".
Diagram:
Apparatus list:
1. Core Borer
2. 3 / 4 potatoes
3. 35 ml of concentrated salt molar 0.2, 0.4, 0.6 0.8 1.0
4. White tile
5. Lab coat
6. Beaker
7. Scalpel
8. Accurate ruler
9. Accurate scale
10. Six petri dishes
11. Blotting paper
12. Weighing boats
13. Tweezers
14. 1 stop watches
15. Glass rod or thermometer
16. Measuring cylinder
17. Marker pen
18. Labels
19. 35 ml Distilled water
Method:
1. Use the core borer & bore out five cylinders out of a potato
2. The variables that are being controlled are size, weight, time and concentration of the salt.
3. Put these five pieces on a white tile and cut them to 4 cm and remove the skin if necessary.
4. Weigh each piece individually and record the weight on the table.
5. Put these cores into a beaker of water so they do not dry before the others.
6. Do this five times for each petri dish
7. Keep adding each piece in too a beaker of water
8. Blot the potato with paper towel to remove excess water only when they have all been cut
9. Weigh each piece individually and take note (add the results to the table)
10. Pour distilled water into petri dish
11. Set stop watches in front of each petri dish
12. With a permanent marker write the concentration of [mola] in each petri dish
13. Note the time and put the five potato cylinders into each petri dish
14. Put each five cores in the petri dish at five minutes interval
15. Wait 25 minuets (while waiting you may prepare the apparatus for the next face)
16. Each petri dish with his contents will be in for 25 minutes
17. Weigh each potato individually and take note (add the results to the table)
18. Record the new mass next to the old one
Risk assessment:
1. Lab coat most be worn at all times to avoid stains and cuts on clothes. Also getting clothes tangled or attached to the set apparatus, which may cause it to fall or break.
2. While using the scalpel always put white tile underneath, never use the scalpel on the top of bench or while holding sharp object it in hand because it may cause an injury or damage the furniture.
3. Whenever using the core bore make sure that no item of clothing, furniture or person is directly under the core bore when the perforation of the potato is about to occur.
4. If any beaker or glass item falls on the floor and breaks make sure that no one goes near or try’s to touch it and that the glass is brushed away into a non plastic bin liner.
TO BE CONSIDERED DURING THE EXPERIMENT
Variables
(To be allowed)Non-Variables
(To be controlled)
Solution concentrationSurface area
Solution volume
Duration of experiment
Temperature
Solution
Weighing scales
Conditions
Results:
The Formula for the Mean of the Percentage Change:
%change = weight before – weight after x100
weight before
Table to show the results of the affect of different salt solutions on potato cells.
0.0 mola concentrationmass before (g)mass after(g)change in mass(g)% change in mass
11.461.520.064.10
21.641.750.116.70
31.721.850.137.55
41.641.890.2515.24
51.631.850.2213.49
61.751.950.211.42
Mean1.641.800.169.75
0.2 mola concentrationmass before (g)mass after (g)change in mass(g)% change in mass
11.561.46-0.1-6.41
21.661.64-0.02-1.20
31.601.610.010.62
41.511.15-0.36-23.84
51.631.680.053.06
61.341.390.053.73
Mean1.551.48-0.06-4.00
0.4 mola concentrationmass before (g)mass after (g)change in mass(g)% change in mass
11.361.380.023.71
21.551.47-0.08-3.57
31.491.42-0.06-2.33
41.651.21-0.44-34.62
51.421.460.044.51
61.521.36-0.16-9.46
Mean1.621.50-0.11-7.05
0.6mola concentrationmass before(g)mass after(g)change in mass(g)% change in mass
11.651.45-0.2-12.12
21.661.52-0.14-8.43
31.881.71-0.17-9.04
41.421.36-0.06-4.22
51.661.51-0.15-9.03
61.601.52-0.08-5.00
Mean1.641.51-0.13-7.97
0.8m concentrationmass before(g)mass after(g)change in mass(g)% change in mass
11.641.36-0.28-17.07
21.491.34-0.15-10.06
31.871.74-0.13-6.95
41.391.26-0.13-9.35
51.801.63-0.17-9.44
61.381.18-0.20-14.49
Mean 1.591.41-0.17-11.23
1.0m concentrationmass before(g)mass after (g)change in mass(g)% change in mass
11.521.19-0.33-21.71
21.641.39-0.25-15.24
31.661.49-0.17-10.24
41.611.46-0.15-9.316
51.661.49-0.17-10.24
61.561.42-0.14-8.974
Mean 1.601.40-0.20-12.62
Table that shows the mean of the percentage of plasmolysed cells in each solution
Molar concentration of salt solutionMean of the percentage change
0.09.75
0.2-4.00
0.4-7.05
0.6-7.97
0.8-11.23
1.0-12.62
Graph:
Anomalous results:
From my graph it shows how I did not get any anomalous results except for the isotonic solution. That was a surprise because it was around 0.15 mola while the prediction was 0.4 molars.
There are no other visible anomalous results.
Analysis:
The results were surprising. It was not expected that the isotonic solution would be so low. The experiment did not follow the hypothesis fully although when the potato cylinders were placed in a solution that was weaker than that of the isotonic solution water entered the cells and the cylinder did gain weight and increase in mass. When the potato was put in a solution that was stronger than that of the isotonic solution then the potato cylinder lost mass as water left the cell.
When the experiment was first attempted time ran out because of lesson clashes. The following lesson a new bag of potatoes was opened meaning that the potatoes in the second bag might have been different. The results were different from the hypothesis because the potatoes in the new bag were very new and fresh. This was shown by the fact that the potato cracked when the core borer was put into it. It was also very hydrated or turgid, the water on the cylinders that came out of the potato helped in the answer to this it showed that the cells were very turgid. This is one explanation is that the potatoes were so turgid due to being watered a lot during growth.
This effected a major change in the results. The isotonic solution was found to be roughly 0.15 when it was predicted to be 4.0. The reason that it affected our results so much was that the potato could hardly absorb any more water because the cell wall was stopping it. In an animal cell the cell would probably have burst because animal cells do not have a rigid cell wall like the plant cells.
The reason that the potatoes were losing water at 0.2 molars was that it had a stronger concentration of water in its cells and therefore a weaker solution of sucrose in it. Therefore water left the potato cells, to go down the concentration gradient and dilute the stronger sucrose solution outside the cells.
The reason that the potato gained water at 0.0 molar is that even though the potato was fully turgid it would have to have other chemicals in it that make up the potatoes. So it is impossible for a potato or any other organism to have an isotonic solution of 0.0 molar. This is why even though the potato was nearly fully turgid, water entered it when it was put in this solution.
Unfortunately due to time shortage only one control was done. It was submerged into distilled water. If more class time would have been available the experiment would have not been over a two day period but just one lesson that means that the experiment could have been more easily controlled.
Evaluation:
The experiment was very successful in my opinion. I obtained a large quantity of very accurate results, by replicating the experiment, from which I was able to create an informative graph. This ensured the reliability of results and did not point out any anomalies. I think I recorded 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 this was done over a twenty five minutes periods. I thought the procedure was very suited to laboratory conditions and was effectively carried out by myself. In this way the results were most pleasing.
Accuracy was needed during the experiment.
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. 0.15 morality,0.25 morality and so on. This way would have allowed find out the isotonic point far more accurately as the one that I estimated is very approximately.
Errors:
It is hard to control errors because when you are concentrating on the experiment you actually not thinking about the errors that may occur though it may be a subconscious thought. This meant that the strength of the solutions inside the potatoes, were significantly weakened and there was a high water potential in the potatoes. This affected our results by making the isotonic solution significantly lower. To stop this from happening in the future the potatoes could be left for a few days so that they are not so hydrated when the test is carried out. A core sample could be taken to see if the potato was suitable.
Evaporation would have affected the results. The solutions that were made for the experiment were left for a couple of hours without anything on top of them this meant that evaporation would have occurred and the solutions strength would have actually been larger than written on the beaker. This is because the water would have evaporated without the salt.
To stop this the petri dishes containing the solutions should be covered with cling film. The petri dishes tubes should also be covered for the 15-minuet duration that they are being used.
The petri dishes might have also been contaminated by another uncontrollable variable like a fly landing on your solution and wasting all of your experiment or even when cutting some waste might easily fall into the petri dish. Using a layer of cling-film over the petri dish can prevent this.
Cross contamination would have affected the results. This could have happened many times when placing the potato on the waiting boat for example. The first time it would have had no problems though it may leave some sucrose residue and next potato you place on the waiting boat it may not be its real weight. Either drying or cleaning the weighting boat each time can avoid this, but that could waste time, crucial to this experiment. Alternatively having lots of clean weighting boats could solve the problem but this could be very expensive. If there are pipettes being used then mark on the pipette which solution it is being used for.
Human error would have affected the results. Humans are not naturally perfect and mistakes are made when measurements are being taken, sums worked out wrongly, timings mist, lengths not cut accurately. This would contribute to all the inaccuracies in the results. To stop this all that can be done is very through investigation. This could have been avoided if highly mechanical technology is used though errors may still occur because humans make machines.
Temperature during the experiment temperature was not kept constant. This was one variable that was not controlled. If the temperature is high then osmosis will occur more quickly as molecules have more kinetic energy and are moving more quickly. If the temperature is very high then osmosis will not occur as the membrane will be broken down and sucrose molecules will be able to get through. If the temperature is low then osmosis will happen very slowly, as there will be little kinetic energy. This means that the rate of osmosis could have been different for each reading. This is quite likely as the room temperature changed due to lab equipment such as bunsen burner radiators and body heat. To prevent this experiment could be done in a water bath this way the temperature would remain constant and therefore the rate of osmosis.
In this experiment the amount of solution that was put into each petri was not the same because it was not seen as a variable. It is however possible that it could affect the results. It is possible that if the two identical potato cylinders were put into identical petri dishes but different amounts of an identical solution were put in the results may be different. (If the potato was put in a solution below its isotonic solution) The one with the least solution will lose more water through osmosis and will become a stronger solution before the other with more solution. This will stop osmosis more quickly as the water potential outside the potato will fall more rapidly and affect the result.
Further experiments and improvements:
This experiment had problems with the potatoes being turgid. This could be studied in detail as to what affect the amount of water in the potato affects the isotonic solution. Hydrated and dehydrated potatoes could be tested for their isotonic solution this would give an indication on the affect that the amount of water in the potato cell has on the isotonic solution.
The experiment could include other foods such as apples. This would show the difference between a vegetable and a fruit. The amount of water in the cells would have to be kept constant if possible to get an accurate reading however. This was not done in this experiment and the results were surprising due to it. The most obvious way of doing this is to take a core sample and look at the amount of water in it and measure it visually and by estimation.
The experiment could include different types of potato this would show the isotonic solution and the affect of different sucrose solutions on different potatoes and the results could be put in graph form. Again the amount of water in the cells would have to be kept as constant as possible to make it a fare test.
Another problem is that the potatoes being used could have been abnormal to prevent this having a great affect amalgamating sets of results, for example of a whole class, where each experimenter used a different potato of the same type.
It would make the investigation more accurate if the potato was left in the solutions for longer this would allow the solution more time to reach the core of the sample. It would be better if there were more solutions so maybe 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and all the way up to 1.0 molers. It would be better for accuracy if more replicates could be done this would mean that errors would have less affect on the over all result.
A different solution could be used instead of salt. This would show if the isotonic solution was different in a potato for different solutions.
Appendix:
Osmosis, in botany and chemistry, the flow of one constituent of a solution through a membrane while the other constituents is blocked and unable to pass through the semi permeable-membrane. Experimentation is necessary to determine which membranes permits 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. In a classic demonstration of osmosis, a vertical tube containing a solution of sugar, with its lower end closed off by a semi-permeable membrane, is placed in a container of water. As the water passes through the membrane into the tube, the level of sugar solution in the tube visibly rises. A semi-permeable membrane that may be used for such a demonstration is the membrane found just inside the shell of an egg, that is, the film that keeps the white of the egg from direct contact with the shell. In this demonstration, the water moves in both directions through the membrane; the flow is greater from the vessel of pure water, however, because the concentration of water is greater there, that is, fewer dissolved substances exist in this solution than in the sugar solution. The level of liquid in the tube of sugar solution will eventually rise until the flow of water from the tube of sugar solution, under the influence of hydrostatic pressure, equals the flow of water into the tube. The hydrostatic pressure establishing this equality of flow is called osmotic pressure.
A variety of physical and chemical principles are involved in the phenomenon of osmosis in animals and plants.
Conclusion:
From all these facts and figures we can ascertain that osmosis has taken place because it has a semi-permeable membrane. As quoted in the hypothesis, the solution is stronger than the isotonic solution then the cell will lose water.
The amount of water in the cells of a potato has an effect on its isotonic solution. The isotonic solution of the potato in this experiment was 0.08. The results showed that as the strength of the solution increases the % mass difference falls.
Water has left the cell to go and try to dilute the stronger solution that is outside the cell. It has tried to make the concentration gradient the same. As the strength of the solution increases, the more water leaves the potato. The potato cell has a cell wall, however, so the cell has only become dehydrated or plasmolysed to a certain extent because of this unlike animal cells.
The prediction of a change, for higher and for lower, at about 0.4 on the concentration solution was not close, but, as the results of the experiment show, that it was inaccurate by 3.8 molar. Perhaps the water potential of the particular potatoes was slightly higher than average. Even though the prediction was inaccurate i can deduct that it was a highly successful experiment.
