To determine the concentration inside potato cells.

The experiment will be performed 3 times so an average can be obtained. The same conditions and equipment were used for each repetition. Repeating the experiment helps to correct any anomalies and make the results more accurate.

A stopwatch will be used to time each beaker to make sure they all get an equal amount of time. The potato will be blotted twice to ensure no excess sucrose solution is left on the surface of the sample.

Safety: Goggles must be worn to protect eyes and an apron must be worn to protect clothing. Loose hair should be tied back and loose clothing secured.

Factors affecting the experiment:

* Time-is relevant because it takes 30 minutes for the experiment to work and if some of the beakers were not left for that long then it would not really be a fair test.

* Volume- is relevant because you need the same amount of solution for each experiment to make it fair. I will be using 65ml of sucrose in each beaker.

* Concentration- is relevant because that is the variable I will be changing.

* Temperature- must be kept the same to ensure a fair test.

* The solution will be stirred at the beginning of each experiment for 10 seconds.

* Surface area- will be kept the same.

* Mass of potato- can be different for each experiment because the difference will be taken.

* The majority of variables will be kept the same during the experiment.

* Distance- is not relevant.

* pH- is not relevant.

* Drying- this is relevant because blotting the solution makes sure that there is no extra solution on the surface of the potato.

(The living world- Michael Roberts)

Obtaining

Results no 1

Molarity of sucrose (M)

Initial mass of potato (g) 2dp

Final mass of potato (g) 2dp

Difference in mass (g) 2dp

Change in mass (%)

0.0

3.87

3.99

0.12

3.10

0.2

3.53

3.59

0.06

1.70

0.4

3.88

3.91

0.03

0.77

0.6

3.76

3.68

-0.08

-2.13

0.8

3.70

3.62

-0.08

-2 .16

.0

3.67

3.57

-0.1

-2.72

Results no 2

Molarity of sucrose (M)

Initial mass of potato (g) 2dp

Final mass of potato (g) 2dp

Difference in mass (g) 2dp

Percentage change in mass (%)

0.0

3.39

3.60

0.21

6.19

0.2

2.81

2.87

0.06

2.14

0.4

2.45

2.44

-0.01

-0.41

0.6

2.51

2.48

-0.03

-1.20

0.8

3.28

3.17

-0.11

-3.35

.0

2.96

2.56

-0.40

-13.50

X = anomalous results.

Results no 3

Molarity of sucrose (M)

Initial mass of potato (g) 2dp

Final mass of potato (g) 2dp

Difference in mass (g) 2dp

Percentage change in mass (%)

0.0

2.21

2.29

0.08

3.62

0.2

2.64

2.69

0.05

1.89

0.4

.78

.74

-0.04

-2.25

0.6

.79

.70

-0.09

-5.03

0.8

.46

.33

-0.13

-8.90

.0

.91

.71

-0.20

-10.47

I used my three sets of data to obtain an average. The three figures were added together and divided by three to give an average of all the three results. Any anomalous results were ignored when finding the percentage change in mass

Molarity of sucrose (M)

Average change in mass

(%)

0.0

4.30

0.2

.58

0.4

-0.63

0.6

-2.79

0.8

-4.80

.0

-6.595

I decided to find the percentage mean because by using these figures I will be able to compare the water lost during each experiment relatively, taking into account the initial mass of the potato sample.

The graph plotted will use these figures.

Analysing:

My results and graph show that the exact molarity inside the potato cell is 0.34m. My graph is in the shape of a curve, which shows that there is trend. The trend is that as the molarity of the sucrose solution increases the percentage change in mass decreases. My graph shows that there is also a trend because a line of best fit can be drawn. There was an anomalous result in my experiment but I did not include it when working out the mean of the data because it would have affected the outcome of the graph. The line curves inwards towards the circle on the graph because this is the point where the potato did not lose or gain water due to osmosis - the theory that the concentration of the water molecules in the sucrose solution had reached the same as inside the potato cells. 0.34m is the molar of the potato cell, which in the sucrose will not lose or gain water through the semi permeable membrane. In the top half of my graph the solution was of lower concentration than the potato because it has lost water and in the bottom half of my graph the solution was of a higher concentration than the potato and so the potato has lost water. The graph corresponds well with the mean results or the line of best fit; they are very close together. There were no real anomalous results as they were very close together to begin with, also I plotted the mean results and I did not use the anomalous results to calculate the mean because this would have made the graph inaccurate. In sucrose solutions with a lower amount of water than in the potato the water moves along the cells from a low water potential in the sucrose solution to a high water potential in the potato cells, the cylinders lose mass because they have lost water. In a solution, which has the same amount of water as the potato cell the water moves in and out of the cells at the same rate, this is because the two areas are in equilibrium.

Evaluation:

My results do match my prediction as I stated that the sucrose solution where no water was gained or lost would be the concentration of the potato, however I was not very specific.

There were many ways in which the experiment could have been improved and could have affected the results.

The area that the sample of potato was extracted from could make a difference to the results because if the potato is taken from where a growth is occurring then the potato will have glucose in it, but if it is taken from where no growth is occurring then the potato will contain starch. If the glucose is taken with the potato it will make a difference as glucose is insoluble and therefore will affect the amount of water it can take up, if starch is taken then it will not affect the results because starch is insoluble. (Internet)

When the potato was blotted each time there was no way to make sure that we blotted exactly the same amount of water off each time and this would make it unfair.

If the samples were left for a long period of time then some of the water could evaporate and cause the results to be inaccurate.

If the samples were taken from two or three different potatoes then there is no way of knowing if they contained the same amount of water as each other to begin with.

Improvements:

Samples should be taken away from any growths to ensure there is no excess glucose in the potato.

The potato should be cut in more equal sizes because the surface area could affect the rate that osmosis works.

Potato samples should be taken from the same potato so the results are known to be more accurate.

My results match textbook ideas as they correspond with their findings.