Investigation on Osmosis

Safety

To make sure the test is safe, I will keep my fingers away from the scalpel and make sure I carry it responsibly to avoid unavoidable cutting of flesh. When using the borer I won't put my fingers, or anyone else's, under the sharp metal, and I will handle only the wooden handle. On top of this I will clear up all spillage in order to avoid any dangerous slippage.

Prediction

Here is my prediction, in a simple, easy to view table, for each molar sugar solution I will be using:

Molar Solution

Prediction: - The weight and length will...

0.2

Increase

0.4

Stay the same

0.6

Decrease

0.8

Decrease more than 0.6M decreased

.0

Decrease more than 0.8M decreased

I have made my prediction, as in my previous learning experiences I discovered that the molar sugar solution of a potato is on average around 3-4 moles. Assuming that osmosis occurs in potatoes (which it should as I wouldn't be doing this project otherwise) then the water concentrations should equal out between the two solutions either side of the semi-permeable membrane (IE the potatoes cell membrane) that is separating the potato from the sugar solution.

I got some preliminary results from our teacher for 3 different molar solutions, at length 2cm. Below is the table with them in:

Moles

Weight before (grams)

Weight after (grams)

Length before (grams)

Length after (grams)

0.2

3.0

3.2

2.0

2.1

0.4

3.1

2.4

2.0

.8

0.8

3.2

2.2

2.0

.9

We it seems quite obvious to me that 0.4 was an anomalous result. I think that the molar sugar solution is more 0.4 than it is 0.3.

If so I think that the following should happen:

Molar Solution

What will happen

0.2

Since in the preliminary results it grew longer and weighed more I am going to use my knowledge to explain why I think that this will happen. The water should pass into the potato as the potato is the stronger solution and this should give it a higher weight. It should also become a greater length, as with the potato full of water it is turgid. This means that it is stiff and due to the excess fluid, should stretch out (IE a larger length)

0.4

There shouldn't be much passage of water as it is similar to the molar solution of a potato. I think this, as I believe that the preliminary test for 0.4M was very anomalous. This makes me believe that there may have been something wrong with the solution I used.

0.6

This solution should definitely be larger in moles than the potato. This means that a lot more of the water should pass from the potato to the solution so then the potato will lose even more weight. This shall cause it to become flaccid. When things are flaccid (opposite of turgid) they have lost fluid, and this should make it shrivel. This is why I think that the potato may shrink in size, and therefore it will shrink.

0.8

This will be the same as 0.6 moles but slightly more to the extreme. Knowing that in my preliminary results it lost weight (the potato in the 0.8 molar sugar solution) I have to explain why and have done in the boxes for 0.6, 0.8 and 1.0 molar solution. This helped me realise that it is likely that all of the molar solutions above 0.4 should lose weight and shrink. More water will be lost compared to 0.6 moles, so it will lose even more weight and shrink even more than 0.6 for the same reasons stated in the boxes for the 0.6 molar solutions.

.0

I don't want to bore you by repeating the same sort of things so I'll make this brief. For the same reasons as in the above 2 boxes, this one should weigh the least, and should be the shortest.

Obtaining

Solution

st Length cm (before)

st Length cm (after)

2nd Length cm (before)

2nd Length cm (after)

3rd Length cm (before)

3rd Length cm (after)

Average change in length (cm)

0.20

2.00

2.00

2.00

.80

2.00

2.20

0.10

0.40

2.00

2.20

2.00

.90

2.00

.80

-0.03

0.60

2.00

2.00

2.00

.60

2.00

.80

-0.20

0.80

2.00

.60

2.00

.80

2.00

.60

-0.33

.00

2.00

.60

2.00

.70

2.00

.60

-0.36

st Weight grams (before)

st Weight grams (after)

2nd Weight grams (before)

2nd Weight grams (after)

3rd Weight grams (before)

3rd Weight grams (after)

Average change in weight (cm)

.80

.80

.60

.70

.20

0.90

0.10

.80

.70

.60

.40

.00

0.90

-0.13

.80

.40

.60

.20

.20

0.90

-0.36

.80

.30

.60

.20

.10

0.90

-0.43

.80

.00

.60

0.80

.10

0.70

-0.73

Analysis

Below is the graph showing the average change of weight:

This graph shows that if the molar solution is more than 0.3 it loses more weight, and the higher it goes the more weight it loses. Above below 0.3 it gains weight, with the lower the molar solution, the higher the weight. This is because an excess sugar solution of 0.3 moles causes potatoes to lose water as the concentrations of each solution need to be equal. This is also why under 0.3 moles causes it to gain water. (Remember that a potatoes sugar concentration is 0.3-0.4 moles)

Now here is my graph showing the average change in length:

This graph shows that the higher the molar solution, the shorter the length. , Above 0.3 moles it loses water as in osmosis the concentrations have to be equal and it decreases in length. This is why below 0.3 it gets more water and increases in length.

Conclusion

I thought that it would be easier to put my results in a chart so you can easily check the scientific reasoning I have used in order to not have to back read through everything in order to check on the results:

Molar Solution

Why

0.2

At 0.2 moles, the potato had a lower concentration of water than the sugar solution it was submerged in. In osmosis the water moves from a region of higher concentration to a region of lower concentration, in this case from the surrounding solution to the potato. This is what made it gain more weight than it had before. This gain of water made the potato turgid, so it became full of water, so it had to make extra space for the water so it must have stretched out and that is why it had a longer length than before. I am glad because this agrees with my earlier prediction as I said that it would gain weight and grow longer.

PREDICTION CORRECT

0.4

The rate in osmosis must be a lot closer to 3 moles than it is to 4 moles. I say this as if the potato was of a molar sugar solution of 0.4 moles then it should have stayed the same, or at least less than what it would need to be in order to keep it even. But it shrank; as the water must have passed into the solution in order to make the potato and the sugar solution equal concentrations. It lost some water and lost weight, and it also shrunk, as it became a little bit flaccid. As it lost water it shrink's in order to make it more solidified, with less air in it.

PREDICTION WRONG

0.6

In this solution the potato became lighter and shorter. This is because it lost water and became flaccid. As it was flaccid it shrunk, as it was make it more solid. It became more flaccid than the potato at 0.4M did, so it was lighter and shorter.

PREDICTION CORRECT

0.8

In this solution the potato was lighter and shorter than in 0.6M as it lost more water as there was a greater difference in the solutions, so it had to make up for it by making it equal, therefore using more water to equal the solutions

PREDICTION CORRECT

.0

In this solution the potato was lighter and shorter than in 0.8M as it lost more water as there was an even greater difference in the solutions than before. For the same reasoning above it had to level out between two concentrations with even greater difference.

PREDICTION CORRECT

Evaluation

My results could tell me quite a lot but I don't think either sets of results were perfectly accurate as in each one I obtained an anomalous result.

There is one anomalous result, for weight, which was for the 0.8 molar sugar solutions. This does not fit in with my line of best fit, as it should be somewhere around -0.50 grams lost, as that is approximately what it is on my graph where I have drawn my curved line of best.

For the 0.6 molar solution of length, I had an anomalous result that also does not fit in with my line of best fit. It should have been somewhere around -0.30cm.

Probable reasons for obtaining these anomalous results are that the experiment may have gone wrong, it might have accidentally had the wrong specifications against my method, and it may have been fiddled with. It is hard to tell what goes wrong, maybe it just went wrong, or had the wrong solution in. It is unlikely that we will ever know.

I think my method was reasonably good, but If I had more time I would do it again to get more reliable results. I would use more accurate apparatus such as a burette to get more accurate readings, a sharper, thinner scalpel to cut the potatoes or even not use a funnel so the solution will go straight into the test tube from the burette. All these implemented would definitely make the experiment more reliable

I think I obtained a suitable range of results and I think they were good enough to help me find a solid, concrete conclusion. On the weight graph, the weight seems to decrease by around 0.20 grams for every time the molar sugar solution increases by 0.2M. To make my conclusion better, I could try to do the experiment for each 0.1 moles of sugar solutions (IE 0.1M, 0.2M, 0.3M, 0.4M etc.) and with distilled water as well. This would let me check to see if these results supported my conclusion and if they did, they might also match my theory that it would decrease by 0.2 grams every 0.2M gained (so 0.1 grams would be lost every 0.1M gained)

If I had more time, I would like to do some further work in order to investigate if osmosis would have a different affect on the potatoes if instead of being just 2.0cm long, there would be 2? 1.0cm pieces of potato. I would be interesting to see what the similarities are of the two experiments.

That comes to the conclusion of my report into "Osmosis in Potatoes" I hope you enjoyed it, and I hope that you found it more than just satisfactory

THIS REPORT WAS BY:

JAMIE MORRIS

CANDIDATE NUMBER 5094

CENTRE NUMBER 13330

Jamie Morris Biology Coursework