Osmosis. The results show that when a high concentration of sucrose is used, the potato loses water and when a low concentration of sucrose is used the potato takes in water

Osmosis makes plant cells swell up when they are surrounded by a weak solution and they become turgid. Turgid cells give the plant structural support. Animal cells have no cell wall and so burst if they take in too much water.

I will investigate osmosis with an experiment using pieces of potato is differing concentrations of solution.

The potatoes will be in the solution for FILL THIS BIT IN then weighed. The difference between the starting mass and the end mass will be calculated and converted into a percentage. The above experiment will be done 3 times, the average result of which will be used. In order to make it a fair test:-

* All the test tubes will be washed between experiments so that there is no sucrose from the last experiment.

* The potato pieces will all come from the same potato as factors like freshness would affect the water content.

* The same amount of solution will be in each test tube so that pressure is not an issue.

* The potato pieces will all be the same size and shape so that surface area is not a variable.

* All the experiments will be done on the same day so that temperature does not affect the rate of diffusion.

Equipment List

* 5 Test tubes

* Test tube holder

* Electronic scales

* Hard board mat

* FILL THIS BIT IN

* Knife

I have done a preliminary experiment.

% Sucrose

Mass before

Mass after

Change in mass

20%

2.45

2

-0.4g

2.5

2.1

-0.4g

0%

2.2

.8

-0.4g

2.2

2.0

-0.2g

5%

.8

.8

0

.8

.6

+0.2g

2%

2.0

.9

+0.2g

2.0

.9

+0.15g

Distilled water

2.3

2.3

0 (anomalous)

.8

.9

+0.1

I predict that the 20% sucrose solution will make the potato lose mass and the pure water will make it gain mass. From my prelim work I predict that the isotonic solution will be around 5%.

Obtaining Evidence

Sucrose in solution

Mass after experiment

Change

% Change

Average

20%

0.7

-0.3g

-10

-23.33

0.8

-0.2g

-20

0.8

-0.2g

-20

0%

0.9

-0.1g

-10

-6.66

.0

0g

0

0.9

+0.1g

+10

5%

.1

+0.1g

+10

+10

.1

+0.1g

+10

.1

+0.1g

+10

2%

.1

+0.1g

+10

6.66

.2

+0.2g

+20

.2

+0.2g

+20

None

.1

+0.1g

+10

23.33

.3

+0.3g

+30

.3

+0.3g

+30

Analysing and Conclusions

The results show that when a high concentration of sucrose is used, the potato loses water and when a low concentration of sucrose is used the potato takes in water. The point where the solution and the potato are isotonic is 7.6% sucrose solution, which means that potato cells contain approximately 92.4% water depending on if I left them in the solution for long enough. The line of best fit has a negative correlation and a gradient of

2/-5 = -0.4.

When the solution is 0% - 7.6% sucrose it is hypo tonic and the potato cells are hyper tonic, when the solution is above 7.6% it is hyper tonic and the potato cells are hypo tonic.

When both sides are 7.6% no net movement of water molecules occurs because the movement of water molecules from the solution to the potato is the same speed as the movement of water molecules from the potato to the solution.

Evaluating

I think that the results are definitely strong enough to carry the conclusion because there were no anomalous results are the negative correlation on the graph was very strong. This is probably because the process of osmosis is too slow for the results to be affected by things like somebody stopping the stopwatch to early or too late. If I were to do any further work I would investigate osmotic pressure. I could have improved the experiment by using a water bath, so that osmosis would happen quicker (because the molecules are moving around faster) and all the test tubes would be exactly the same temperature.