I expect my hypothesis to be correct as it is accorded to my background information. Osmosis is defined as the net movement of water or any other solution is 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 diagram below shows osmosis taking place.
At school we carried out a preliminary experiment where we done this experiment. The results were:
The lower the molar solution of the sucrose was, the larger and heavier the potato chip got. The percentage mass increase was higher than the potato chip in the high molar sucrose solution. I decided to measure the potato chips in the solutions of 1, 0.8, 0.6, 0.4, 0.2 and 0 molar solutions.
Background information
Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
Semi-permeable membranes are very thin layers of material (cell membranes are semi-permeable) which allow some things to pass through them but prevent other things from passing through.
Cell membranes will allow small molecules like Oxygen, water, Carbon Dioxide, Ammonia, Glucose, amino-acids, etc. to pass through. Cell membranes will not allow larger molecules such as Sucrose, Starch, protein, etc. to pass through.
A region of high concentration of water is either a very dilute solution of something like sucrose or pure water. In each case there is a lot of water: there is a high concentration of water.
The Internet is quite a key source to help my planning. The actual website to help me obtain my knowledge of osmosis is . I also used my biology text book provided to me by the school as it had a good definition of osmosis.
Method
Firstly I will use a cylinder cutter, in which will be utilised to cut 18 cylinder shapes out of a potato. After piercing the cylinder cutter in the potato, a metal rod was be used to push the cylinder-shaped potato out. I will repeat this action 18 times. When I have cut the required amount of potatoes chips, I will use a ruler to measure each piece. To ensure that the potato chips are the same size, I will cut each equally in length, which is 4 centimetres. After cutting each chip on a tile with a knife, I will weigh each individually. Subsequently, I will acquire 6 paper towels and label each from 1 to 6. There will be three sets of experiments going on at the same time do there will be 3 sets of test tubes labelled from 3 to 6. Then I will place each potato chip on each number and write the mass of each chip underneath the chip. Also, by placing the potato chips on paper towels, the paper can absorb the excess water after the chips are removed from the solutions; this makes the experiment fairer. I will also be cautious of preventing the potato from making contact with the ink used to write the masses, which could affect the results.
I will then obtain 3 test tube racks, which will hold the 18 test tubes. Following this, I will prepare the solutions. All the solutions will have the volume of 40millilitres.
Firstly, in the preparation of the solutions process, I will pour 40ml of sugar solution into a measuring cylinder. Then, after getting an accurate measure of the sugar solution, I will pour the solution into a test tube and label it 1. Then, after washing out the measuring cylinder, I will repeat the process. However this time I will pour 32ml of sugar solution and 8ml of water into the measuring cylinder. Next I will pour the mixture into a test tube and label it 2. I will repeat the process making sure that each time the measuring cylinder is cleansed, 8ml less of sugar solution is used and the rest of the mixture will be water, making a total of 40ml³. Every time each test tube contains 40ml³, it will be labelled with a number from 1 to 6. The last tube (tube 6) will contain 40 ml of tap water.
After preparing all the solutions, I will place each potato chip in each test tube. Hence each test tube will contain 40ml of solution and a potato chip. I will leave each test tube for 25 minutes, according to my stopwatch. After this time I will put each potato on the paper towels using tweezers. The potato chips extracted from the sucrose solutions will be dried in practically the same way. Each chip will be rolled across a paper towel and equal amount of times, which ensures that each chip receives the same intensity of drying. Lastly I will reweigh and measure the length of each potato chip. Then I will work out the average mass increase or loss for each different molar solution.
Variables
Turgidity
Size of the potatoes
The time in which the potatoes are in the solution
Strengths of the solution
Amount of solution
The shape of the potatoes
The amount of sugar solution or water in the potato
How to make it a fair test
I will try to make the experiment a fair test:
The potato chips remain in their solutions for the same time
The potato chips will be equal in length
Each solution will be of the same volume
No extra pressure is exerted on the weighing scales whilst the potato chips are being weighed
Preventing ink from making contact with the ink
Preventing water being on the weighing scales when being used
Using the same potato
Using the same cylinder cutter to cut each potato chip
Taking the excess solution off the potato chips
The potato chips are submerged at the same time
Make sure the potatoes are submerged all the time
Obtaining Evidence
Results
I did the experiment 3 times and then I could work out the average mass loss for all 3 experiments. This would make the results much more accurate.
Experiment 1
Before:
After:
Experiment 2
Before:
After:
Experiment 3
Before:
After:
Here are the averages for my results:
Graph
Analysis
I found out that osmosis movement of water molecules from a region of their high concentration to a region of their low concentration; this diffusion however takes place only over a partially permeable membrane (which was the potato), which separates 2 solutions of different concentrations. Therefore the potato in the strong sugar solution was the smallest in size and had the highest percentage decrease in mass. In addition the potato in the distilled water was the biggest in size and had the highest percentage increase in mass.
Furthermore, the sugar solution in low in concentration and the potatoes were high in concentration. As a result the water diffused out. Hence the stronger the solution, the higher the decrease of mass by the potato. The potato also became smaller in size.
My results fitted a general pattern but a few results were inaccurate as you can see on the graph. The graph should be negative straight line but there is a jerk in the graph. This inaccurate result may be because the potato was not submerged the whole time or because it was not weighed properly. This was probably caused by human error.
According to my results I found out that the potato in the strong sugar solution was the smallest in size and had the highest percentage decrease in mass. This was because of the fact that water molecules from a region of their high concentration move to a region of their low concentration. In this case the water molecules diffused into the potato, increasing the mass and size of the potato.
From the results that I had gathered it is fair to say that my hypothesis was correct as my results are in a patter and agree with my prediction. The graphs also make this point clear. They agree with my hypothesis as they are in a comprehensible pattern showing that osmosis clearly took place. This was proved by looking at the results; the stronger the solution the less increase in mass, and the weaker the solution the bigger increase in mass.
Evaluation
The method I used was reliable and accurate. From the method that I used I could distinguish whether my hypothesis was incorrect. The method I used was relatively straightforward yet I was able to produce a conclusion from it.
From the results obtained in this particular experiment it is clear to see that the results are in relative agreement of one another. However it is clear to me that to ensure accuracy in the future a greater number of repeats should be taken for each sucrose concentration (should a similar experiment be conducted). Also we can see that in the future a greater range of concentrations should be examined to allow for a suitable graph to be plotted and any trends in result to be examined. Altogether the experiment has been a valuable one, as it has identified the general pattern of results, which we should be looking out for in any future results as well as the improvements that can be made to this experiment.
The method utilised was a good one. It was accurate to a certain extent, depending on the variables and the number of repeated results. From the method I used I could gather a conclusion which would concur with my hypothesis.
The results were reliable as I followed my plan and the tried to abide by the fair test factors.
The evidence can support a conclusion but not a firm one as further work still needs to be undertaken. On the other hand the results followed my sensible hypothesis in which I supported with my scientific knowledge. I repeated the experiment to produce an average, preventing the attainment of anomalous results. Because of this valid reason I have decide to produce a conclusion based on the evidence I have presently.
The improvements that I propose are:
A greater range of concentrations should be examined
A greater number of repeats should be taken for each sucrose concentration
I can also propose further work. After undertaking my improvements I would use a variety of concentrations and observe how each concentration would affect the potato.
Navninder Singh Sandhu Page of