I aim to find out at what strength of salt solution there is not a net change in mass of the plant tissue.

To find out at what strength of salt solution there is not a net change in mass of the plant tissue

Teyfide Hassan AT1:OSMOSIS

PLAN

AIM:I aim to find out at what strength of salt solution there is not a net change in mass of the plant tissue. I will find out the water potential of the plant tissue by using different salt solutions. The water potential will be found when a plant cell is immersed in a solution, which has the same concentration of solute as the cell; there is no net loss or gain of water.

METHOD

1 Get out all the equipment

2 Using a knife cut six equal mass of plant tissue

3Measure the mass of the tissue – ORIGINAL MASS

4 Measure out 30ml of solutions into labelled petri dishes

5 Place the plant tissue into each dish

6 Leave for at least half an hour

7 With filter paper wipe off any excess water before measuring the mass of each piece of plant tissue

8 Put results into a table

EQUIPMENT

Here is a list of all the equipment I shall be using:

Tile

Knife

Petri dish

Stop clock

Filter paper

Measuring cylinder

Solutions: distilled water, 0.1,0.2,0.3,0.4,0.5 molar

FAIR TEST

To make this a fair test I will always use 30ml of salt solution. The potato will be cut into equal sizes. I will leave the potato chips in for half an hour and make sure they will come out at the same time. I will repeat the experiment twice to make sure my results are correct as the first time I do the experiment something might go wrong so by doing the results again I can check for anomalous results.

NUMBER AND RANGE

I will use six different concentrations in the first petri dish I will have distilled water in the second petri dish I will have 0.1 molar salt solution, petri dish 3 will contain 0.2 molar, petri dish 4 contains 0.3 molar. In petri dish 5 I will have 0.4 molar, in the last petri dish I will have0.5 molar salt solution. So there is a whole range of different concentrations.

RELIABLITY

To make my experiment reliable I shall conduct my experiment twice to make sure that my results match up. The results also rely on whether you take out the potato tissue out you might not wipe off all the excess water and for another tissue you did, so I will make sure that all the excess water is wiped off with filter paper. I will also make sure that I keep all six pieces of tissue in for the same amount of time. This experiment is not very reliable as the results all depend on how big the pieces of potato tissues are, as the smaller the pieces the more accurate the results will be.

PREDICTION

I predict that the potato tissue in the distilled waters mass will increase because of osmosis. I also predict that the new mass of the potato tissues in the concentrations 0.1,0.2,0.3,0.4 and 0.5molar will lose mass because of osmosis as the water moves from a high water concentration (potato) to an region of low water concentration (solution 0.1,0.2,0.3,0.4,0.5molar).

SECONDARY SOURCES

I made this prediction because I have read from books that osmosis is a special type of diffusion. Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration. This explains why my prediction might be correct. I also know that osmosis can happen in the guard cells. Guard cells draw in water by osmosis, swell and become turgid and the stomatal aperture is wide. When water is scarce, they become flaccid and they change shape which closes the stomatal pores.

PRELIMINARY WORK

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SECONDARY SOURCES

PRELIMINARY WORK

My teacher did the same experiment as a demo and from this we knew how to conduct the experiment and know what results to expect. I knew that the potato chip in distilled water would gain and the salt solutions from 0.1 to 0.5 would loss mass.

ANALYSE

Experiment1

Text Box: PATTERNS I noticed a few patterns the new mass of the potato in distilled water went up as water was taken in as the inside of the potato was a lower concentration then the distilled water so by osmosis water is taken in to even out the concentration. But the potato chips in the other concentrations all loosed mass and the stronger the concentration the loo is more. PREDICTION RIGHT OR WRONG? My prediction that the distilled water would gain weight and the 0.1 to 0.5 concentrations would lose mass and this is correct as osmosis is about evening up the concentration. The water molucles actually pass both ways through the membrane in a two-way traffic. But because there are more on one side than the other there’s a steady net flow into the region with fewer water molecules i.e. into the stronger solution. This causes the salt solution region to fill up with water. The water acts like it is trying to dilute it, so as to “even up” the concentration ether side of the membrane. GRAPHS From my first graph I know my results are not that accurate as my results are scattered about I did a line of best fit to make my results as close as possible. The water potential in my first graph is 0.16. The water potential is when no more concentration or water will enter the potato to even up the concentration in the potential as the concentration both inside and outside the potato are equal so nothing happens. My second graph of experiment 2 is more accurate as the results are nearly all on a straight line and I showed this as I did a line of best fit. The water potential of graph 2 is 0.025. CONCLUSION From my graphs and results and secondary sources I have found out what osmosis is and at what strength of salt solution there is not a net change in mass of the plant tissues. I Know the water potential of the potato 0.18 and 0.025 from both my results.

Concentration of salt solution

Results

This is a table to show the mass of the potatoes at the start of the experiment. Each weight was carried out three times.

The next table shows the weights of the potatoes after the experiment

Next I produced a table to show the average results in a table and then I displayed them as a percentage.

Interpretation of Results

By looking at the graph that I have plotted I can see that more often then not the percentage change gets lower the more concentrated the salt solution is. This is because the potato absorbed the water due to Osmosis and therefore gained weight. But if the solution contains sodium chloride the water potential of the potato is more negative then the water potential of the potato therefore water is drawn out of the potato and in to the solution caused by Osmosis. This is what caused the potato to lose or gain weight. It can be seen from looking at the results that the perfect concentration for the potato to be placed in without gaining or loosing any water is somewhere between 0 and 0.2 mol/dmֿ³.

Using the graph I can predict that it will be 0.1 as this is where the line crosses the Y-axis (I’ve put a ring around this area to indicate it more clearly). Once the line on the graph reached 1.0, the line straightened out and levelled off.

Conclusion

From the experiment I can conclude that the Change in mass decreases the more concentrated the solution is. This is because of the process osmosis. The concentration levels of the potatoes change due to the molecules moving from an area of high concentration to an area of low concentration. Therefore either entering or leaving the potatoes causing them to either gain or decrease in weight.

Evaluation

During the experiment, the following sources of error could of occurred which could of affected the results

The first source of error is related to when I took the potato out of the solution and placed it on a paper towel to get rid of the excess water. This could of allowed water to be absorbed by the paper towel from in the potato, or it may not of entirely absorbed of all the excess water from the outside of the potato.
Inaccurate measuring could have been a source of error, as the measuring cylinders may not have been read correctly. And because of excess water that may be left behind in the measuring cylinder when the solution is poured.
Another source of error could have been the temperature that the potatoes were exposed to. Depending on whereabouts in the room the potatoes were left could have allowed more sunlight on some pieces and not on others.
When measuring out the weight of the potato the scale would never really give one single measurement and so made it very difficult to read from. This could of lead to the wrong weight being read off.

From looking at my graph I would have to say that there is only one real anomalous result, and that would be the point at the 1.4 mol solution. This result could of come from any of the above sources of error. The anomalous result is approximately 3-4% less then what it should be. I made this assumption using my line of best fit.

The experiment did not really give a conclusion as to the exact concentration of salt solution required to equal the concentration of the potato therefore if I were to do the experiment again I would use readings that were closer together and that were between 0 and 0.2 Mol/dmֿ³ as this was the concentration that the potato was nearest to in the experiment. Carrying out the experiment again will allow you to get a very

accurate reading as to what the concentration of the potato actually is.