An Investigation into the process of Osmosis
Paul Scanlon 26/1/2002
BIOLOGY SCIENCE COURSEWORK:
"An Investigation into the process of Osmosis."
Situation:
"A chip shop owner wants to pre-prepare chips and soak them overnight without affecting their size. He has noticed that their size after soaking depends on the concentration of the glucose solution they have been left in."
Aim:
Therefore, my aim in this investigation is to find out the exact glucose concentration of a potato to help solve this situation. By doing this I should be able to determine the concentration of the potatoes themselves.
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 my predictions. This would leave way for me to figure out a way to make this investigation fair and safe.
Planning ahead would help me find out how to do what and when to do it, which in turn should lead me to a set of good reliable results at the end of the experiment.
Factors affecting the investigation:
At this point in time, I cannot foresee many factors that could affect my experiment. But, there are some:
* As there are no two identical potatoes anywhere in the world, it would be hard to try to equal the glucose concentration of the two chips taken from different potatoes.
Therefore, I shall take all my chips from the same potato and hopefully, the single potato should have a glucose concentration equally throughout it.
* Different temperatures may affect my experiment. If I was to perform this experiment in a high temperature, then the rate of evaporation would increase and in turn, this would cause the concentration and amount of glucose solution to differ. If I were to perform this experiment in cooler conditions, then the rate would slow down more. Different temperatures will affect the rate of osmosis. The reason for this is that if there is a high temperature and some of the water is evaporated, amount of water being evaporated from each solution will vary because of the molar of the solution. This in turn will send my whole experiment wrong and give me a false set of results making my experiment a complete failure.
There fore I shall keep the temperatures constant throughout my experiment. I will do this by keeping everything at room temperature. I can check this throughout the experiment by putting a thermometer in the solution. I shall use a different one in each solution so not to mix them all up and
contaminate the different molar solutions.
Fair testing will play a big part in my experiment, as it should in everyone's. If my 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 millimetre. 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 steps in the fair testing is to make sure that the potato is fully covered by the solution. This is because the potato should be fully submerged, by having total contact with the solution. This would give the potato complete contact with the solution and make the test fair because both potatoes then have 100% of the surface area in contact with the solution.
When using the balance, I will make sure that the balance is reading zero with the bowl on top before I put the 3 potatoes ...
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But I believe one of the most important steps in the fair testing is to make sure that the potato is fully covered by the solution. This is because the potato should be fully submerged, by having total contact with the solution. This would give the potato complete contact with the solution and make the test fair because both potatoes then have 100% of the surface area in contact with the solution.
When using the balance, I will make sure that the balance is reading zero with the bowl on top before I put the 3 potatoes individually on it. This is so that I don't get a false reading with the weight of my potato with the reading it was present on the previous reading. After the experiment, I will measure the 3 potatoes again that should be dried as much as possible, and weigh it the same way, taking the reading to the nearest 2 decimal places.
Also, I will be taking the measurements from the measuring cylinder by reading from the bottom of the meniscus.
As I have mentioned earlier, I will be carrying out the experiment under a constant temperature. To avoid any temperature change that might affect my 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 means that I 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 is quite impossible because we lack the number of balances. Also there are obviously too many sets to go through at such a fast time. Therefore, I will try my best to weigh the potatoes as quickly and as safely as I can. I have devised a method to record the mass of each potato chip in an accurate and efficient way. I shall place the first potato chips in the 0.2 molar glucose solution and then exactly two minutes later, I shall add the next potato chip to the 0.4 molar solution. I shall do this for each of the chips in order to give me a two-minute lapse between each of the tests when they are finished and are then required to be weighed.
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, this will affect the pattern of my results later on.
I will also make sure that the potato is fully covered by the 6 different kinds of solutions. This is because if the potato isn't fully covered up by the solutions, the effect of osmosis might not occur to the fullest it can.
Small things such as a dirty test tube, and a slightly cracked measuring cylinder could still affect the results I gain, so therefore I will take these into account as well.
Table showing the different variables that will be considered during the experiment:
Variables
Non-Variables
. Solution concentration
2. Surface area of potato in contact with solution
3. Volume of solution
4. Duration of experiment
5. Temperature
6. Weighing scales
Reasons for the above:
. I have chosen to vary the concentration of the sugar solution. This will give me a very varied set of results from which I hope to make an accurate conclusion.
2. For instance, if one of the potato chips was 1cm longer than all the others, the surface area of the chip would be larger and there would, therefore, be more space for osmosis to occur.
3. 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.
4. By keeping the length of the time of the experiment the same, all the potato chips will have the same amount of time for osmosis to occur. If the times were varied, then osmosis could occur in one chip more than the other due to the time and the end results would be misleading and draw the reader to the wrong conclusion.
5. For the purpose of my experiment I am going to do all the experiments at room temperature. I have explained this earlier.
6. I am also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between different scales.
My Prediction:
I predict that if the concentration of the water that the potatoes are submerged in is greater than that of the potato, the potato will swell up. If the concentration of the water solution is less than that of the potato, the cells in the potato will become plasmolysed.
Hypothesis:
Osmosis is the movement of water molecules from a weaker solution into a stronger solution, through a semi-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. And if there is very little different in the two water concentrations, there shouldn't be such a big change in mass. But if there is a higher concentration of water in the potato than outside, 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 both light and water. With both of these sources, the potato will keep on living until it dies of either the lack of water or 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 than 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 possibly can.
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. A turgid cell is a cell that is 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 cell shrinks and pulls away from the cell wall. These cells are said to be plasmolysed.
When plant cells are placed in a solution that 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".
Safety:
Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. I will be using a very sharp knife, which could injure someone if it's not handled properly. But other than that, there aren't any bigger matters that I should be too cautious of.
Apparatus:
Apparatus-
Reason for this piece of apparatus-
Stop Clock
To time our experiment
Cutting tile
To cut the potato on
Knife
To cut the potato
250ml Measuring cylinder
To measure the solutions
Distilled water
Part of the experiment
Glucose
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
Method:
I believe this task is very simple and it should be very easy to carry out the experiment. The investigation is very straightforward.
The one control I will have throughout the experiment is the amount of solution I will use on each potato. This will be kept constant.
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 I will put the 6 sets of 3 potatoes in the 6 test tubes at the same time and start the clock running for 30 minutes.
After 10 minutes, I will take all of the potatoes out of the test tubes, so that the actual osmosis action stops, and then I will put the potatoes onto one piece of dry towel, 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. I will repeat the experiment three times so that I can make sure that all of my results are similar, and so that I will be able to take the average of the 3 experiments. This makes sure that I get accurate results. Repeating the experiments are important, because I will be able to receive valid results, and look for any anomalous results. Not to mention that I will take the fair testing into account.
In short, I have produced the following list to follow in a step-by-step way:
. I will take two average sized ground potatoes and check that they are both healthy and hard.
2. Using a standard kitchen knife, I will peel the potatoes and cut into each of them with a cork borer on a white tile.
3. Taking the cylindrical potato chips and ruler, I will cut the potato chips into exactly the same lengths; 5 cm long. I will have to be very careful whilst cutting the potato, as the knife is exceptionally sharp. I will then have 18 chips.
4. Taking a test tube rack I will place 6 test tubes and then label them 0 molar: distilled water, 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar and 1 molar.
5. Using a measuring cylinder I will measure out different amounts of glucose solution and distilled water that I can then pour into the test tubes in a percentage ratio giving me the various molar concentrations.
6. I can then weigh every potato chip on an electronic balance and recorded the weights.
7. I will swiftly put 3 potato chips into each of the different molar concentrated beakers at two-minute intervals and then start my stop clock. The 3 chips that I am using for each of the different solutions will give me an average which will give me a better set of results and more accurate graphs. I will take the average of the three results for each of the individual solutions.
8. Whilst waiting, I can set out some paper towels with which I can dry the potato chips when they are done. Also, I can draw up a basic table for my results.
9. After 30 minutes I will drain out the solutions in the sink and place 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 will dry each chip with the paper towel and then place each one on the scales so that I can weigh them.
1. Each potato will be measured accurately on the electronic scales and then the weights are to be recorded in my table of results.
2. If I have time after doing the first set of results, I can redo the experiment under exactly the same conditions. This would give me a secondary set of results that would give me a more accurate view on the changes.