8) blot potatoes dry with paper towels
9) Weigh and measure the potatoes using scales and a ruler
10) Record findings on the results table
Apparatus
7 x test tube
3 x beakers
Scalpels
Borer
White cutting tile
Measuring cylinder
Stop watch
Sieve
Goggles
Sugar solutions
21 x potato tubes
Experiment to investigate osmosis
Conclusion of preliminary testing
From the results I found, I can clearly see that using level 0 molar changed the length of the potato tube by 0.3cm and the mass by 0.03g. After looking at the second set of results it shows that using level 1.25 molar makes the potato tubes decrease in size and weight.
The reason why potatoes held in level 1.25 molar both decrease in length and weight is because of plasmolysis, this is where the contraction of cells within plants reduce due to the loss of water through osmosis. It is the cell membrane peeling off of the cell wall and the vacuole collapsing. This now proves the prediction I made, stating that the biggest change will be within the 0.25 molar sugar solution results.
Main Investigation
After carrying out our first investigation into osmosis, I am going to do a further investigation to see if I can get my results more accurate.
For the main investigation, I am going to use all 7 of the sugar solutions at levels 0, 0.25, 0.50, 0.75, 1.0, 1.25 and 1.5 molar to help me determine the best way sugar solutions effect potato cells.
I predict, as same as before, that as the sugar solutions rise the number of change will become greater but will develop into a negative number.
I will be controlling the amount of sugar solutions, length and weight of the potatoes. I am doing this so the result can be as accurate as possible.
In order to find the most accurate way of measuring the change I studied the results I found in the preliminary investigation and finally decided to weigh the mass of the potatoes before and after to find out the best way the effect the sugar solutions have on potato cells.
To carry out the main investigation I am going to:
1) Cut all potatoes to 4.5cm using a scalpel and borer
2) Weigh potatoes using scales, fill in data on table
3) Mark the potatoes ‘A,B,C’ with a marker pen
4) Pour 30cm3 of all 7 levels of sugar solutions (0, 0.25, 0.50, 0.75, 1.0, 1.25 and 1.5 ) into 7 test tubes using measuring cylinders.
5) Place 3 potato tubs in each solution
6) Leave them for 20 minuets timed using a stop watch
7) Take potatoes out of tubes using a sieve
8) blot potatoes dry with paper towels
9) Weigh and measure the potatoes using scales and a ruler
10) Record findings on the results table
Main Investigation
Conclusion
By looking at my line of best fit it shows the average change in mass against sugar solution strength. I can see that it has a negative correlation. My line of best fit tells me that the cell sap (a dilute fluid that is found in the large central vacuole of many plant cells. It contains water, amino acids, glucose, and salts. The sap has many functions, and also helps plant-cells in the process of osmosis.
) concentration is equivalent or some what equal to level 0.75 molar. This is because it has an average change of 0. This means it is isotonic — a solution with exactly the same water concentration as the cell. There will be no net movement of water across the cell membrane.
I have found that as the sugar solution began to get stronger the changes between the mass decreases gradually. As the solutions begins to get stronger the mass of the potatoes decrease. This happens because the amount of water in the potato becomes greater than the quantity of water in the solution as the solution strengthen. So the water from the potato moves from a region of low concentration(hypotonic) to a region of high concentration(hypertonic) through a partially permeable membrane to even out water balance making the potato shrink and the solution to become less concentrated.
As an extension to this investigation, I would run two experiments in parallel. All cores would be from the same potato, but one would run for an hour, as this one did and for the other the cores would be left in the solutions for longer, perhaps 24 hours, to establish if one hour is the end point of the osmotic diffusion.
Evaluation
The experiment worked somewhat to what was expected and the method was fairly reliable and produced reasonably dependable results. There are a few things that I could have changed - I think we could have had a better method for drying the potato tubes because if a potato tube isn't dried properly then there is much more water on the tube at the start than another tube. This may affect the results and therefore may end up affecting the conclusion. Another thing we could have improved was to try and do each individual solution at the very same time. The problem with this is that we simply didn't have enough people to do this.
As an extension to this investigation, I would run two experiments in parallel. All potato tubes would be from the same potato, but one would run for an hour, and for the other the potato tubes would be left in the solutions for longer, perhaps 24 hours, to see if one hour is the end point of the osmotic diffusion. I would also experiment with different temperatures to see if there was any more change.
