Osmosis in potato cells

Planning

I am going to investigate the effect of different sugar concentrations on different pieces of potato, also I will be able to find the concentration inside the potato cells at the same time.

The concentration of the sugar solutions will affect the experiment, from preliminary work I have found this out, osmosis will occur differently depending on the sugar concentrations. The time the potato disks are left in the concentrations will also affect it, the concentration might not have equalled throughout, reaching the situation of net flow. So by preliminary work, I realised after 25 minuets the rate of change of mass either decreased considerably or stopped completely, meaning they were either at or very near the situation of net flow. The sizes and amount of surface area of the potatoes will affect the experiment. This is because, for example, if the piece of potato has a big surface area the water molecules will come in/out of it at a much less time than one that has a small surface area. Because different potatoes have different sugar concentration and cell density. Therefore this could also effect in the experiment.

I want to find the effect the different sugar solutions have on the potato cells, so I am only going to change this.

To make the experiment fair I will:

Use 5cm³ of the sugar solution for each test.
Use accurately the same size, shapes, weights of disks that I can in each test.
Use clean and the same size test tubes.
Dab off all excess solutions before weighing, making sure not to over dry the samples so that only weighing the potato discs and what they contain and nothing else.
Only change the sugar concentrations in each test tube.

To make it reliable I will:

Put batches of potato disks into each test tube, therefore if any are not accurate the others will cancel it out, so it doesn’t give erroneous result.

I am going to weigh the potato disks before and after I put them in the sugar concentrations, to do this I will use a sensitive weighing scale. I was going to measure the length and width of the potato too, but after doing some preliminary work, I found out that it would be too hard to firstly measure them all accurately with just a ruler as the potatoes are too small and also if they did change shape they would often sink inwards or bulge outwards, not being just a simple cylinder/disk shape anymore, therefore it would be really hard to measure it accurately.

Method

Peel one potato and remove any bad pieces with a scalpel. With the cork borer cut 4 cylinders, cut the ends off straight with a scalpel and also cut equal slices of disks out of them. Weigh them and separate them out equally into 6 batches. After that reweigh each batch and record the weights onto my table. Prepare 6 clean test tubes, all the same size and put them in the test tube holder. Then with a measuring cylinder measure 5cm³ of each concentration of 1-6 and put each one into a test tube, labelling the ...

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Method

After everything is ready put the potato batches into each test tube at the same time and start the stop clock. After 25 minuets pour the solutions out of the test tube, then get the batches of potato discs out, dry the surface areas with a paper towel, to take off any excess solution, so therefore not adding any extra weight but don’t over dry or it could take the solution out of the potato cells again. Then reweigh each batch again, recording the results on my table. Work out the change in mass from the original mass, then from that work out the percentage change of each.

Equipment

Cork borer, Scalpel,

Potato, 6 Test tubes,

Sugar solutions with Test tubes holder,

Concentrations from 1-6, Sticky labels,

10cm³ measuring cylinder, Paper towels,

Diagram

Prediction

By looking at textbooks ‘biology for you’ from pages 21-24, ‘biology, the revision guide’ page 6 and my own knowledge I have predicted this.

If the sugar solutions outside the potato cells are more concentrated than those inside the vacuole of the cells, the water will pass out of the cell by osmosis. Osmosis occurs when the concentration outside the potato cell is different from the concentration of the cells vacuole. When the concentration is higher outside the potato cell the water passes out of the cell, as a consequence the vacuole starts to shrink, becomes flaccid and therefore will decrease in weight. So when the concentration is lower outside the potato cell the water passes into the vacuole of the potato, as a consequence the cell swells up, becomes turgid and therefore the weight increases. I’m not quiet sure what the potato cells concentrations will be, all I know is, from my preliminary work, that it is somewhere roundabout 3(m), because that was where the weight hardly changed therefore the concentration was nearly the same. Therefore that being near the concentration in the vacuole of the cell.

Table of results

Obtaining evidence

I did the experiment safely by doing preliminary work before hand so I knew nothing could go drastically wrong, I didn’t break anything or nothing along those lines so I would say it was a safe experiment and suitable for what I wanted to find out.

I left the potatoes in the solutions overnight; this was because I didn’t have time to weigh them after 25 minutes so I had to leave them until the next day. When I weighed them the next day they had all decreased in weight (gone flaccid), I think this was because the water out of the sugar solutions had been evaporating while they was left so the concentration would have got stronger. Meaning that the results were inaccurate and I couldn’t draw a fair conclusion from them. So I had to use someone else’s results these consisted of more than 1 result for each experiment so this made it more reliable and was accurately measure to milligrams.

Analysing and concluding

From the results I can see that the sugar concentrations of 0.4m to 1.0m was more concentrated than in the vacuole of the potato cells. Therefore the water moves from a high concentration, the vacuole, into a low concentration, the sugar solution by osmosis. As water passes out, the vacuole starts to shrink. These cells are no longer firm, they are limp. We say they are flaccid. This is called plasmolysis and as more water leaves the cells the cytoplasm starts to peel away from the cell wall. I can see that these sugar concentrations was more concentrated than in the vacuole of the potato cells because the potatoes placed inn these solutions weight decreased.

And also from the results I can see that the sugar concentrations of 0.0m to 0.2m was less concentrated than in the vacuole of the potato cells. Therefore the water moves from a high concentration, the sugar solution, into a low concentration, the vacuole by osmosis. As water passes in, the vacuole starts to swell up. The water pushes up against the cell wall. Eventually the cell contains as much water as it can hold, as seen as it has a cell wall it doesn’t burst. We now say the cell is turgid I can see that these sugar concentrations was less concentrated than in the vacuole of the potato cells because the potatoes placed in these solutions weight increased.

This then means the concentration inside the vacuole of the potato cells must be between 0.3m and 0.4, I can tell this because when the concentration is the same the change of mass would be no different and the 0.4m concentation is only just under 0g (-0.45g) and the 0.2 is quite a lot different (6g).

I think the second result for the 0.0m concentrations was an anomaly because it was only 0.6g away from a result for the 0.2m concentration result and it was 2.5g difference from the other result obtained from the same experiment of 0.0m concentration.

The higher the concentration was away from 0.4m the more weight the potatoes gained and so the lower the concentration was away from the 0.4m the more weight the potatoes lost.

My results do agree with my prediction that basically if the concentration of the sugar solution was higher than the concentration inside the vacuole, water will pass out of the cell by osmosis and the weight of the potatoes will decrease. And so if the concentration of the sugar solution was lower than the concentration inside the vacuole, water will pass into the cell by osmosis and the weight of the potato will increase.

Evaluating

I am not happy on the way my experiment went because the results obtained were wrong as the concentrations changed for the reason that they were left too long in the open and so some of the water started to evaporate into the air.

The results were reasonably reliable to improve this I could have done each test 3 times, doing this you would be able to tell if there was a anomaly result and if so which one it was. The results that appeared very similar could be averaged and used for plotting the graph and the anomaly ignored if there were any so it wouldn’t ruin the final results.

To ensure the experiment was the most accurate that I could get it, I used accurate apparatus with the most suitable scale for setting up the experiment and obtaining the results. But I don’t think it was very accurate that when getting the potatoes out of the solution that you had to damp the excess water off, because you had to be careful not to dry it out too much or it could ruin the results by absorbing the water back out of the potato.

The second result for the 0.0m concentrations was an anomaly, this could have been caused by being dried too much therefore taking too much water off it, and so it would weigh less than it should of.

I collected enough evidence to draw a graph off and to see a pattern so I am confident about my conclusion.

The further work I could do is to do each experiment 3 times making it more reliable and to put corks on the end of the test tubes stopping any water from being evaporated from the solution. Do the concentrations in-between of 0.4 to 0.6 to see exactly and more accurately which concentration the potatoes are.