My preliminary work was to cut the chips out of the potato and removing the skin. I cut them of various sizes and weights to see what would be best to use in my experiment.
My conclusion to the work of above was that a long and thin which weighs about 2.8g chip would be best as they fit in the test tube easy and the results are more visible and reliable.
The thing that I am going to measure are: the size of the chips when they are cut to make sure they are all of equal length, and the weight before and after the tests to see which have increased or decreased in weight. I will also measure the size of the chips after they have been in the solution and see if they go firm and rigid or floppy and smooth after they have been in the solution. From the results I should be able to tell where the isotonic point is on my graph. This will be wear the chip has not gained weight as the concentration will be equal on the inside and outside of the chip so osmosis can not occur.
This diagram will show how I plan to set up my investigation.
In order to make sure my investigation is safe I am going to follow the following guidelines: I will not use a sharp knife; this should avoid me cutting myself. I will stand up for the duration and handle the equipment carefully. I will put the test tubes in a test tube rack in order to limit the chances of them being broken. I will move all coats and bags and put them in a safe place in order to stop me from falling over them. I will move all used equipment out of the way so I don’t break anything.
Method
- Firstly I collected a potato and all the formentioned equipment. These were six test tubes, a test tube rack, knife, weighing scales, the different types of molar solution and water.
- Next I filled up 6 test tubes with the different types of molar solution. The solutions ranged from 0molar, 0.2molars, 0.4molars, 0.6molars, 0.8molars and 1.0 molar. I labelled each test tube so I didn’t get confused.
- I then cut 12 chips out from the potato, these were long and thin as I mentioned earlier because of the preliminary test. I then weighed them and they were approximately 2.8g in weight.
- I then put two chips in each test tube as this would ensure the results are more reliable.
- We put them in a test tube rack and left them over night until the next lesson.
- Finally I removed all the chips and weighed them separately. I then recorded all my results and calculated the increase or decrease in weight and drew the results up on a graph to find out where the isotonic point is.
My results
My graph is on a separate sheet and reveals 2 anomalous results. But the isotonic point is at about 2.3 molars.
The pattern in my results shows that when the solution was Hypotonic the weight increased but when the solution was Hypertonic it decreased in weight. When the weight stayed the same it showed that must be the isotonic point. You can tell this as when the chips gained weight it was in the hypotonic solution which has more water in it and therefore the cell vacuole would gain weight as the concentration is lower inside the cell so that proves that osmosis takes place as the solution moved from a higher concentration to a lower concentration. In the hypertonic solution which is a salty solution the opposite occurred. The cell had a higher concentration so it moved out into the lower concentration which resulted in the loss of weight.
In my investigation I found that the isotonic point is at 2.3 molars and the above when the chips increased and decreased in weight according to whether or not it was in a higher or lower concentred solution. If it was in hypotonic it increased and if it was in Hypertonic it decreased.
I think this because osmosis will occur which is when the water inside the test tube goes to a level of lower concentration which would be inside the vacuole if it is a hypotonic solution which makes the cell become turgid but outside the cell if it is hypertonic so the cell would lose weight and become flaccid. Isotonic is equal to the cell strength sap so there would be no movement as the concentrations are equal.
My predictions and results are very accurate as I had already predicted the correct outcome. The chips in the hypotonic solution increased in weight and the chips in the hypertonic solution lost weight because of osmosis.
Evaluating my evidence
I think that my investigation went well and I carried out a thorough test. The test was accurate because the chips were the same weight except to one or two which probably resulted in two of the anomalous results. The only other problem which could have been the reason behind the anomalous result is that the chips were different sizes although they were all long and thin and weighed the same they were different sizes.
In my investigation I feel the results are quite reliable as they were all near the line of best fit and I think it would be almost impossible to get them absolutely right and they all fit into the pattern of that they increased if they were Hypotonic and decreased if they were Hypertonic.
I had two anomalies in my test and they are the increase of 5.4% at o.2 molars and the decrease of 16.1% at 0.6 molars. They should be able to fit into the lines of best fit.
I think these anomalies might have occurred because I cut the sizes different although they were the same weight and long and thin. Or they might be because of two of the chips were the wrong weights.
If I had to use my results as evidence then I think they give a great example of osmosis occurring and water entering and leaving the vacuole and that in different types of solutions cells can become turgid or flaccid.
The reason I think this is because my results fit with osmosis and show that in a dilute solution the chip will get bigger as water enters the vacuole as it is of a lower concentration but in a concentrated solution the chips shrink as water leaves the vacuole to go to a place of lower concentration.
If I did my investigation again I would improve it by being as accurate as I can in cutting my chips and make sure they are long, thin, the same size and the same weight and if I did this then I think I wouldn’t get any anomalous and therefore my results would be reliable and perfect.
In order to try and get further evidence I would try different types of food instead of chips like peas, bits of apples or carrots.