My aim for this experiment is to see the results of potato tissue's mass difference, when placed in different concentrations of sugar solutions.
Planning:
My aim for this experiment is to see the results of potato tissue's mass difference, when placed in different concentrations of sugar solutions.
Variables involved:
For this experiment I would expect to have 3 different variables, Independent, Dependent, and fixed variables, which all helps me to plan and explain the experiment thoroughly.
The Independent variable (things you change), the thing that I will be changing in this investigation into the factors affecting osmosis, is the concentrations of the solution that helps me to investigate osmosis with potato tissues. The different sugar concentrations will be changed to see the result of the potatoes when placed in sugar solutions placed in different molarities (strengths).
Dependent Variable (things that you measure) the things that I'll be measuring in this experiment on osmosis is the mass change and length change of the potatoes placed in different molarities of sugar solutions. I will record the masses in grams by using a balance and the length changes by using a ruler.
Fixed Variables (Things that you keep the same) the things that I have chosen to keep the same in each individual experiment to keep it a fair test is to keep the same sizes of each potato tissue the same by using the same cork borer and same ruler. I will be keeping the same amount of solution placed in the test tubes for each different experiment, which I will measure using a measuring cylinder. I will also be keeping the same potato through out the whole experiment to as using a different one might give me anomalous results as some might have more water in it then others.
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 mass. If there is very little different in the two water concentrations, there shouldn't be such a big change in mass. Also if there is a higher concentration of water in the potato, then the water will go out of the potato and into the liquid solution, as osmosis is the movement of water molecules from a region of high concentration to a region of low concentration, through a partially permeable membrane.
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 or too much water, or will stop, as both sides would become equal, making no more reactions. When the concentration gradient is lower in the potato, the water will transfer from the solution into the potato.
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 0.25 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 0.50 molar solutions of sucrose, similar to the 0.25 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.
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 0.25 molar solutions of sucrose and greater.
Scientific explanation of what would happen:
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.
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 ...
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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.
Using this information a graph and prediction can be made, which can be seen below:
At point A the graph suggests that no osmosis has occurred, suggesting that the concentration of water inside the cell is equal to the solution outside.
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.
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.
Apparatus I will need:
· Cork Borer (diameter of 0.5cm),
· Water,
· Forceps,
· Timer,
· Measuring cylinder,
· Tile,
· Potato,
· 0.25m, 0.5m, 1 molar of sugar solutions,
· Boat,
· Weighing balance,
· Stirring rod,
· Test tubes,
· Test tubes rack,
· Paper towels,
· Sticky labels,
· Ruler,
Fair Testing:
In this experiment on osmosis there should only be two changing variables:
: Different molarities of sugar solution,
2: Change in mass of the potato samples.
To keep these two variables the only variables in the experiment I must:
: Keep the potato samples the same length (5cm). 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 osmosis 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 and sizes might be different, which means one potato might have more water in them then another.
3: Stop the evaporation of any of the molar solution. This is because if the sugar solution evaporates past the level of the potato, then the potato sample will have less surface area in the solution so this would make osmosis happen much slower. To stop any solution evaporating a cork 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 his from happening, 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 the 6 sets of 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 and at the same time of the one-hour experiment.
Safety procedures:
Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. This is why I'll be taking this into consideration.
I will be using a very sharp knife, which could injure someone if it's not handled properly. I will also be very careful that the solutions don't get into our bodies internally, just in case, because I am not fully aware of the damage it could do to us. I will also be wearing an apron due to any solutions getting to my clothes.
But other than that, there weren't any bigger matters to be cautious of.
Method:
I plan to carry out this experiment by using all the safety issues and fair testing procedures to give me the most reliable and most accurate set of results.
I plan to have a range of sugar solutions prepared with concentrations from 0.1M to 1.0M, in intervals of 0.1, (but I will only be taking 6 of these 10 molarities, as this should be more than enough to explain the effects of the potato on osmosis). Then sections of potato will be cut using a cork borer and knife to equal lengths (5cm) keeping the surface area constant. I will then measure each tissue of potato using a measuring scale, measured in grams, when I do this I will place the boat on the scale and resetting the scale so that I only get the weight of the potato and not with the boat. I will then add 20ml of each concentration of sugar in two test tubes, giving me a total of 12 test tubes, and labelling each molar reading. Then to each test tube a cut piece of potato will be added and its concentration added to the label. These will be left for 1 hour. Then the potato pieces will be removed from the test tubes, and surface solution on the potato will be removed using paper towels. I will then measure the potatoes again, recording its change in mass by weighing them. I will then be taking the two readings of each molar concentration. This is because I will be doing a repetition of the experiment, as it will save me valuable time. These results will be taken for each concentration in order to get an average and reduce the effect of anomalous resulting.
As it is difficult to get the cut potato pieces to the same mass it was decided that I would use a percentage change in mass that will be used to compare the data in the results, as this would be far more accurate. I will do this by taking the difference in mass, divide it by the mass before of the potato and multiplying it by 100.
After looking at my preliminary work it suggested that there wasn't enough concentrations of sugar to compare each result to each other, so their will be 8 different sugar concentrations to choose from for the actual experiment. The timing of the potatoes weren't left for enough time in the preliminary experiment, as the results didn't have much change, therefore I will leave them for an hour instead of half an hour to give a greater mass change. I will also be and measuring the mass change as a percentage as it will be more appropriate so that reasonable results could be obtained.
I will also be using the same raw data table I used in my preliminary results seen below:
Solution Mass Before Mass After Length Before Length After Change of mass Percentage of change
in grams in grams in cm in cm in grams
0.25m
0.50m
1m
Water
Results of first experiment
Solution Mass Before Mass After Length Before Length After Change of mass Percentage of change
in grams in grams in cm in cm in grams
0.25m 1.49 1.55 5 4.9 0.06g 4%
0.50m 1.57 1.38 5 4.7 -0.19g -12%
1m 1.53 1.12 5 4.6 -0.41g -27%
Water 1.58 1.74 5 5.3 0.16g +10%
Results of repetition experiment
Solution Mass Before Mass After Length Before Length After Change of mass Percentage of change
in grams in grams in cm in cm in grams
0.25m 1.51 1.60 5 5.2 0.09g 6%
0.50m 1.52 1.35 5 4.8 -0.17g -11%
1m 1.58 1.11 5 4.5 -0.47g -30%
Water 1.44 1.61 5 5.1 0.17g +11%
Average set of results from the two experiments
Solution Mass Before Mass After Length Before Length After Change of mass Percentage of change
in grams in grams in cm in cm in grams
0.25m 1.50 1.575 5 5.05 0.075g 4%
0.50m 1.545 1.365 5 4.75 -0.18g -12%
m 1.555 1.115 5 4.55 -0.44g -28%
Water 1.51 1.675 5 5.2 0.165g +11%
Conclusion:
The evidence obtained from this investigation supports the prediction I made. It also 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.
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 there own category. This tells us that my experiment was successful.
The graphs and the results show that:
· Osmosis actually took place in the experiment.
· As the molars increased, the percentage of the weight difference decreased.
There doesn't seem to be any results, which undermine my predictions, and I didn't find any anomalous results, which means I didn't have to repeat any of our experiments more than twice times.
Having the results, which backs up my hypothesis, proves that this investigation was fully accomplished, and was an achievement.
In the table seen on the last page, 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 (mass). This means that the percentage will also be higher, increasing with the grams.
Evaluation:
I believe I gained accurate and sufficient enough results, shown on our graph and tables that concludes 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.
Looking at the overall experiment I have thought of a number of improvements to give me more and better accurate results. Firstly 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. Another thing I could have to improve my resulting was to measure the diameter change of the potato, which would have helped me to find out the volume before and after of the potatoes, which would also help me to explain the results obtained.
To make this experiment better, I believe that I could have done one test at a time, so that I can reduce the time difference, when I have to move the potato from the test tube to the balance. Between this, I have to dry the potatoes just enough, and then put it on the balance. When I'm 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, I would be able to concentrate more on one of the sets, instead of trying to finish all of them as quickly as I can.
I also could have got more people to do the experiment with me, so that I can organise the tasks, and I would then be able to divide the tasks helping us to get more accurate results.
Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results, so that I 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 tells us how much water could be transferred for each solution.
Further work could be carried out to include concentrations that increased in 0.05 M rather than 0.1. 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, apple.
I could also extend this experiment by repeated exactly as before. However this time I could take more 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 mass of the potato the species of the potato could be changed. For example I could use a new potato and a really old potato.
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 10Cº, 20Cº, 30Cº, 50Cº and 60Cº. 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 osmosis 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.
But overall, given the apparatus that I got to carry out the test, I think this experiment turned out to be very successful, and I'm very please with my results.
biology course work, feb 2003
