Osmosis. My main aim in this experiment is to find out if osmosis occurs in a potato, and how it affects the potato in different molar solutions of sucrose and water.
Introduction
Osmosis is the "movement of a solvent through a semipermeable membrane (as of a living cell) into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.
A semipermeable membrane is a membrane that will pass some atoms or molecules but not others.. The best common example of a semipermeable membrane would be the lining of the intestines, or a cell wall. Gore-tex is another common semipermeable membrane. Gore-tex fabric contains an extremely thin plastic film into which billions of small pores have been cut. The pores are big enough to let water vapor through, but small enough to prevent liquid water from passing
In a high concentration of water the amount of solute is low. This could be called a weak or dilute solution.
In a low concentration of water the amount of solute 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.
Aim:
My main aim in this experiment is to find out if osmosis occurs in a potato, and how it affects the potato in different molar solutions of sucrose and water.
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 - molar solutions
· Potatoes - to put in sucrose
· Tissue paper ...
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Aim:
My main aim in this experiment is to find out if osmosis occurs in a potato, and how it affects the potato in different molar solutions of sucrose and water.
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 - molar solutions
· Potatoes - to put in sucrose
· Tissue paper - to dry the potatoes after the osmosis takes place
· Balance - to weigh the potatoes
· Cork borer - to cut out potato cylinders
Prediction
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 sill up and become turgid, taking in all the water it can possibly take in.
Fair Test
Fair testing should play a big part in this experiment. If this experiment isn't a fair test, I will be obtaining the wrong results, which could lead me to the wrong conclusions.
First of all, and most importantly, i will have to get the measurements and the weights of the solutions and the potatoes as exact, and as accurate as possible. I 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 i will be using a very sensitive balance so that i 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, i will make sure that the balance is reading zero, before i put the 3 potatoes on it. This is so that i don't get a false reading, with the weight of our potato with the reading it had before. And after the experiment, i will measure the 3 potatoes that should be dried as possible, and weigh it the same way.
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, i 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 i should start the clock as soon as the potato is put inside the test tube, and stop the clock as soon as it is time to take the potato cylinders out. Stopping the clock, taking them out and measuring it all in less than a minute is quite impossible because i lack the number of balances. And there are obviously too many sets to go through at such a fast time. Therefore, i will try our best to weigh the potatoes as quickly and as safely as i 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, then this will affect the pattern of results later on, as there ill be anomalies result
I 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.
Safety
Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. And that is why I take this into consideration, no matter what.
I will be using a very sharp knife, which could injure someone if it's not handled properly. And i will also be 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 me.
But other than that, there aren'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 i am 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 i will have to test the potatoes in 6 different types of solutions; 0.0,0.2, 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 me to put into the test tube.Then i will put the 6 sets of 3 potatoes in the 6 test tubes at the same time and start the clock running for 10 minutes.
After 10 minutes, i will take all of the potatoes out of the test tube, so that the actual osmosis action stops, and i will put the potatoes onto one piece of dry toil, in their own groups. I 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.
Results
Molarity
Length
Initial
mass
of pot
Average
Potato 1
Potato 2
Potato 3
0
2 cm
5.5g
5.4g
5.6g
5.5g
0.2
2 cm
5.5g
5.3g
5.6g
5.4g
0.4
2 cm
5.6g
5.5g
5.3g
5.4g
0.6
2 cm
5.5g
5.3g
5.1g
5.3g
0.8
2 cm
5.1g
5.3g
5.4g
5.2g
2 cm
5.0g
5.2g
5.3g
5.1g
Molarity
Length
Final
mass
of pot
Average
Potato 1
Potato 2
Potato 3
0
2 cm
5.7
5.6
5.7
5.6g
0.1g
0.2
2 cm
5.4g
5.2g
5.5g
5.3g
-0.1
0.4
2 cm
5.7g
5.5g
5.3g
5.4g
-0.2
0.6
.9 cm
5.2g
5.0g
4.8g
5g
-0.3
0.8
.7 cm
4.7g
4.9g
5g
4.8g
-0.4
.5 cm
4.5
4.7
4.8
4.6g
-0.5
Analysis
Having studied the results graph, there seems to be a trend, I can see that, as the molarity increases the average weight of the potato cylinders decreases and length also decreases.
There is only an increase of weight then there is no molarity solution.
The potato pieces in 0mol solution increased, this is because the solution has a positive water potential, there were no solute molecules to get in the way of the collisions between the water molecules and selectively permeable membrane. The solute potential is negative.
Water in the tube will move from high concentration to low concentration of water molecules inside the potato, increasing weight
Conclusion
In this experiment, I believe that I have collected enough data to support my planning. This investigation was, I think, successful. Successful meaning my results corresponded 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. 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.
Evaluation
I followed the plan correctly, I believe i gained accurate and sufficient enough results to conclude the experiment.
My final results are very reliable, due to the precautions I took to make this a fair test.
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 was 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.
Having more types of molar sucrose solutions would have helped me obtain better results, and more accurate results, so that i can make sure the results are totally correct.
