Pilot
The pilot allows me to concentrate around the concentration which caused the least increase or decrease in the chip this will give me an area wear the isotonic point is. I will take concentrations above and below this figure depending on if there is an increase or decrease.
From my pilot I learned that the isotonic solution should be approximately 0.375.therefore I decided my range should be from 0.1M to 0.5M. From this hopefully I can find, using the range of concentrations, the isotonic solution and therefore the exact osmotic potential of water.
Method
My original method has changed due to my pilot experiment that I have already completed.
- The first step of my method is to cut 15 chips out of 1 potato, measure and cut them so they are all the same length.
- Next put enough distilled water, to cover the chips, in a beaker.
- Now cut 15 chips roughly the same length with a cork borer, measure and cut all of the chips to the same size and make sure there is no skin left on the chip.
- After put them in a beaker of distilled water that is already out.
- Next you need to calculate the amount of sugar you need for your stock sugar solution, put it in the flask and add distilled water up to the line marked on the flask.
- Now you need to make up the different solutions of 0.M1, 0.2M, 0.3M, 0.4M, and 0.5M.Put all of the chips in and measure each chip and write which solution it is going in so you can calculate the percentage increase later.
- Now leave them for approximately 5hours.
- Take out the chips and measure the length and then record it.
Prediction
I predict that in my experiment the chip will increase in length as the water potential increases. Some chips will increase in length and some will decrease this is because of osmosis. Osmosis is when water passes through a partially permeable membrane from a region of high water potential to a region of lower water potential.
This table shows the average percentage increase of a potato chip when it is left in sucrose solution.
The trends in this table are what I was expecting, as the concentration goes up the average increase in length goes down. This is what I predicted at the beginning of the experiment. I have some anomalies in my data; these are ringed and were discounted for the averages. For example the average increase for 0.1M was 2.45, so according to my prediction the average increase should go down because the water potential is lower; the average increase for 0.2M is 1.85. My prediction was correct.
The results of this experiment show that the isotonic point of the potato is 0.29 molars. This is the point that there is no net movement of water into the potato cells. Some chips increased in length and some decreased this is because of osmosis. Osmosis is when water passes through a partially permeable membrane from a region of higher water potential to a region of lower water potential. From my research I found that the osmotic water potential of a potato is 0.375 ( ).
Evaluation
The limitations of my method were I didn’t leave the chips in for exactly the same time because I can’t take them out all at the same time. Also all of the class were doing the experiment all at the same time so there was a delay when I wanted to use some of the equipment. I have quite a lot of anomalous results I think it is because I didn’t measure my chips accurately before I put them in the solutions.
Appendix
This table shows the raw data from my experiment.
