The potato cells in my experiment when placed in solutions that contain less water then the water content in the potato will lose water via the osmotic gradient. The Solution will have higher water (ψ).
In pure water potential is 0. Water potential (ψ) is the tendency of water molecules to move from one place to another. Water potential will always move from a place with high water potential to a place where there is less water potential until a equilibrium is reached. If a solute is added to water then it will have a negative effect on the water by lowering its water potential and making it negative (less then 0). So the more solute is added to water the more lower the water potential becomes. The amount that the solute molecules lower the potential of a solution is known as the solute potential (ψs).
My predictions in correlation to the different concentration levels of my solution.
The potato will be cut up into 21 pieces; each will be the same size, they will need h20 to survive for longer or they will dehydrate quicker. I will provide the potato with sunlight and obviously each different potato piece will have its won different molar level of sugar solution. With these sources the potato will keep on working until in naturally dies. When the concentration gradient is lower in the potato, the water will transfer from the solution to the potato and vice versa. With my 21 pieces of potatoes I will place them in sets of three in seven different molar levels of sucrose solution.
Conclusion of prediction
I predict that the higher the concentration of the solution will have a weight, turgidity and water losing effect upon the potato pieces. This is because if there is a lower concentration of sucrose and inside the potato cells the water will flow outwards across the permeable membrane to the higher water potential, in this case this could be the higher concentrated solution in the Petri dish.
The lower the sucrose solution Is I predict that there will be more water entering the cells of the potato pieces. This will increase the sizes and weight of the potato pieces no to mention the turgidity. The water will move to the potato cells as there would be greater water potential there.
Fair test.
Making the test fair is essential; if we don’t insure this factor then it could give us false results and even more a wrong, inaccurate and incorrect conclusion which we can easily avoid by taking simple procedures.
I will make sure that the test is as fair as possible by making sure that I do the following things.
1) firstly I will make sure that when I cut out my 14 pieces of potato that the pieces are all equal of size. I will firstly cut one out with a sharp scalpel knife and a ruler and use It as a template to cut out the other pieces from the potato. All my pieces should be of diameter of 2x1x1 cm. To make sure of this I will measure each and every piece with a ruler with capabilities of reading the sub multiples of the centimeter, I.E the millimeter.
2) I will make sure that all the pieces and any necessary apparatus are weighed with an electronic weighing scale to make sure I get the most accurate of readings. I will also record the weight of the potato pieces and the solution amount.
3) I will weigh each and every potato on the weighing scale before we put them in the experiment. I will make sure that the scale has no dirt on it and I will make sure that it is reset to 0.0g before I place the potato pieces onto it.
4) One of the factors that I think that will truly affect the experiment and the results is the amount of solution I use in the Petri dish. I shall make sure I completely submerge the pieces of potato to insure that osmosis occurs to a decent degree. I will make sure that the solution submerges the potato by 1 cm. The solution should have total contact with the solution with the potato pieces.
5) I will time the osmosis period using a stop clock to make sure all the pieces have the same amount of time. I will make sure that I will weigh all the pieces as soon as all the pieces have had their 20mins inside the Petri dish. I will be careful not to damage or drop any of the pieces I will take down the reading on the weighing scale to insure there are no miss complications in readings.
6) Temperature is another factor that can affect my results. I will always monitor my Petri dish temperature using a non lead/mercury thermometer. I will be first handedly supervising the experiment to make sure the temperature doesn’t exceed result effecting temperature. Ideally I think the temperature should moderate around 20c which is room temperature. I will keep the dishes away from any heat sources e.g. light bulbs and heaters.
7) Getting the exact number of molars and water content to each Petri dish is vital to this experiment. If one Petri dish has the incorrect molar placed in it, it could affect my results and patterns later on.
8) I will also make sure that all my apparatus is clean especially my Petri dishes. I will clean them to make sure no impurities are not effecting the experiment and more specifically the osmosis process in the Petri dishes.
Safety
Even though this experiment doesn’t use any dangerous chemicals its still vital that I and my fellow class mates follow safe procedures and never forget the importance of safety.
Be carefully with the scalpel knife and do not run or walk with it. Use it accurately and softly to prevent miss control.
Apparatus
Potatoes
Ruler
Scalpel
Various concentrations of glucose – 0 M/dm3, 0.1 M/dm3, 0.2 M/dm3, 0.3 M/dm3,
0.4 M/dm3, 0.5 M/dm3, 1.0 M/dm3.
Distilled water
Petri Dishes
Stopwatch
Plan of Method
The practical part of this investigation is very easy and merely time consuming
- Firstly I will make a template from a potato. I will cut the potato up into many slices which are 1 cm thick. With them slices I will use a ruler and a scalpel knife to cut out a template potato which I will use to cut out the other potato pieces from the potato slices. I will make sure that piece is 2cm x 1 cm x 1cm
1cm (not drawn to scale)
2cm
- I will then measure each potato piece with a metal ruler with the sub multiple of the centimeter which is the millimeters.
- I will make sure that all the potato pieces measure 2x1x1cm.
- I will then place the 21 pieces into 21 different petri dishes. i will make sure the Petri dishes have been cleaned of any dirt or any impurities that may effect my results.
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I will then make pour the sucrose solution in all of the pieces. I will pour 7cm3 of the molar solutions in all the Petri dishes. Each molar level solution will be tested on three potatoes so I get the most accurate of results.
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When the 7cm3 of solution is placed in every single Petri dish I will place the lids on the solution to prevent evaporation and I will place the dishes in sunlight which will sustain the rate of osmosis. I will then immediately start the stop clock and I will supervise the room temperature and as well as the potato pieces to make sure they aren’t disturbed.
- I will make sure that the potato is completely submerged in the solution so osmosis is happening to its fullest.
- I will make sure that I place all the potato pieces in the Petri dishes as quickly as possible to make sure that they don’t get different times for the osmosis process to occur. One that has happened I will shut all the Petri dish lids to prevent any dirt or the pices being disturbed.
- I will then start the stop clock.
- I will then monitor all the Petri dishes to insure that the that they aren’t disturbed and that I will have a thermometer and I will be constantly monitoring the temperature in the room to make sure it moderates around 20 c.
- After twenty minutes I will stop the clock and then measure the pieces of potato accurately with my metal ruler. Once I have measured the length of the potato pieces I will then note down the results immediately on paper.
We will be using 3 pieces of potato to make sure that all our results are similar, and so that we will be able to take the average of the sets of three. This makes sure that we get accurate results. In a way I am repeating the experiment but at the same time and three times. I am doing this because I think it is important, because we 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.
Apparatus
Potatoes
Ruler
Scalpel
Various concentrations of glucose – 0 M/dm3, 0.1 M/dm3, 0.2 M/dm3, 0.3 M/dm3,
0.4 M/dm3, 0.5 M/dm3, 1.0 M/dm3.
Distilled water
Petri Dishes
Stopwatch
Obtaining results – method
1) I will cut the potato up into slices 1 cm thick, with a scalpel knife. I will be careful and accurate while I do this to get the exact thickness of the slice 1cm.
2) Now I will cut out a template with a ruler and scalpel knife. I will do this carefully by engraving a dotted stencil with the scalpel knife before I cut out the template I made sure that it was of correct dimensions (2cmx1cmx1cm) by measuring it with a ruler. I measure the cut out template is well to insure it was of correct size.
I cut out 20 more pieces and place them in the labeled Petri dishes and then insert the designated molar glucose solution.
1 got 21 Petri dishes and labeled each one is correlation to the molar solution I was put in it.
5) I then carefully measured 7cm3 of solution and water and poured them carefully in the dishes making sure the potato pieces were fully submerged.
6) Once the potato pieces were in place I then started the stop clock immediately trying to save time.
7) During the experiment I was observing the Petri dishes and a thermometer analyzing the temperature moderated at 20 Celsius.
8) After 20 minutes I stopped the stop clock and I immediately took them out of the petri dishes and started measuring them in molar order, starting from 0.0 dm3.
All 21 pieces got measured with the metal ruler, at the same time I will be hand writing the results. I will be careful to measure the pieces in sets due to the amount of concentrated solutions they were put in so I don’t get results confused.
My results
Results from the 21 pieces of potato in my experiment.
Here are the averages for the changes in length in cm and the percentage change of length.
Conclusion – based on results.
From the 21 sets of results I got from my experiment I worked out the average change in length, the average length of pieces after the experiment as well as the average change in length in percentage. I have plotted a graph above to show the average change in length. The graph shows that the higher the glucose concentration the lower the length the potato ship will become.
In my graph we can see that from the molar levels from 0 to 0.3 we see a increase or no change in length of the potato. This proves my prediction as I said water particles will move from lower water potential to a higher water potential. The highest change in length has happened to the potato pieces that were placed in distilled water, this happened as there was a higher water potential in the potato then in the distill water itself as there was less water in the potato. The potato length is highest at 0.0 dm3 because the water potential is the greatest, the water potential decreases as the concentration level increases.
At the molar level of 0.3 we see that there I no change in length because the water potential in the solution and in the potato is equal (or has reached a equilibrium). The concentration of glucose in the potato and the solution is equal and therefore they have the same water potential.
From the molar levels from 0.3, 0.4, 0.5 and 1.0 we see a decrease in length. This again proves my prediction that water will move to a place with higher potential from a place of lower water potential. The cells of the chips became plasmolysed and therefore the chips become soft because the cells had lost water. The reason that there is a decrease in length of the potato pieces is because there is a higher water potential outside the potato pieces and its cells.
I overall conclude that my predictions were correct and that my results are strong enough to prove my predictions.
Evalutation
Aim - To determine the water potential (ψ) of a potato.
My experiment went according to plan, I had no anomalous results and my implementation of my method went according to plan. I followed all the fair test procedures to insure that my results were accurate. Even though my results were conclusive and accurate I do think the whole experiment could have been improved to obtain better results.
If the potato pieces came from the same place and they were cut with a machine to insure that they were perfectly identical in size and volume, then I could of obtained more conclusive results. Some of my potato pieces had slight grooves on them altering the size of the surface area which would inevitably effect osmosis and my results.
As I said in my conclusion my results directly correlated into my trend and proved my predictions correct. If I were to change the experiment and find out any other factors which effect osmosis I would change the size and surface area of the potato pieces and see the effect that it has on osmosis. I would also change the time I let osmosis occur from 20 minutes to one hour. I would do this because osmosis would occur to a better and more fulfilled degree. I could also analyze the effect of temperature on osmosis.
I would change the factors above if I was to further extend my investigation. I would also use molar solutions that were more consistent in there concentration as I jumped four molar levels in my experiment 0.6, 0.7, 0.8, 0.9 were all left out. I could also use different types of plant, like specially adapted plants for instance.