To conduct an investigation to compare the osmotic behaviour of potato and Chinese radish chips in varying concentrations of sucrose solution.

* I shall then take a slice of potato and cut it down to around 5cm (the size does not matter exactly as I shall only be weighing it) using a scalpel, and then I will cut up six more slices of potato to around the same size. I will then cut up 7 more slices of potato but this time only about 2cm long.

* I will then do exactly the same thing with the Chinese radish.

* Then I shall take one 5cm potato chip and weigh it, I will then record the mass in my readily prepared table and then place the chip in tube A (potato, water). Then I will take a 2cm one and place it in the same test tube (see Diagram below). This process shall then be repeated with all the other potato chips, making sure there are no mistakes when writing down the weights.

* This whole process shall then be repeated in exactly the same way with the Chinese radish chips, making sure that I take as much care in weighing them.

* The Chips will then be left for 24 hours, so that any change that may occur will have time to take place.

* After 24 hours has passed I shall take out one of the chips from tube, A (potato, water) dab it off for 10 seconds on tissue paper and then weigh it, then I shall then record the weight of it and then discard of the chip. I will then take out the other chip from the same tube and repeat the procedure. This will then be done for all the other potato chips, making sure that I dry them for 10 seconds only to reduce the variables.

* This shall then be repeated for the Chinese radish chips and recorded on the table.

* When I have finally gathered all my data, I shall work out the percentage change of the 5cm chips and the 2cm chips and then work out an average.

Diagram showing what should happen to the cells when in water and when in weak molar sucrose solutions.

Sources:

Encarta Encyclopaedia Deluxe 2000

Preliminary work.

GCSE Biology (2nd Edition)

Obtaining Evidence (O)

Potato

Tube

Mass at Start/g

Mass After/g

Change/g

% Change

Av. % Change

-

2cm

5 cm

2 cm

5 cm

2 cm

5 cm

2 cm

5 cm

-

A-H2O

.27

2.65

.47

3.13

+0.20

+0.48

5.7

8.1

6.9

B-0.1

.25

2.63

.39

2.93

+0.14

+0.30

1.2

1.4

1.3

C-0.2

.13

2.90

.22

3.10

+0.09

+0.20

8.0

6.9

7.5

D-0.3

.22

2.67

.30

2.80

+0.08

+0.13

6.6

4.9

5.8

E-0.4

.17

2.87

.15

2.85

-0.02

-0.02

-1.7

-0.7

-1.2

F-0.5

.10

2.97

.02

2.66

-0.08

-0.31

-7.3

-10.4

-8.9

G-0.6

.12

2.65

0.95

2.12

-0.17

-0.53

-15.2

-20.0

-17.6

Radish

Tube

Mass at Start/g

Mass After/g

Change/g

% Change

Av. % Change

-

2 cm

5 cm

2 cm

5 cm

2 cm

5 cm

2 cm

5 cm

-

A-Water

0.95

2.58

.17

2.96

+0.22

+0.38

23.2

4.7

9.0

B-0.1

.10

2.61

.21

2.86

+0.11

+0.25

0.0

9.6

9.8

C-0.2

.02

2.39

.11

2.50

+0.09

+0.11

8.8

4.6

6.7

D-0.3

.09

2.56

.12

2.63

+0.03

+0.07

2.8

2.7

2.8

E-0.4

.03

2.71

.00

2.63

-0.03

-0.08

-2.9

-7.8

-5.4

F-0.5

.07

2.70

0.98

2.48

-0.09

-0.22

-8.4

-8.1

-8.3

G-0.6

.11

2.32

0.99

2.11

-0.12

-0.21

-10.8

-9.1

-10.0

Calculations:

% Change = Change / Mass at start * 100

e.g.% Change of Potato Tube A (2cm) = 0.20/1.27 * 100 = 15.74 = 15.7

Av. % Change = [Change (2cm) + % Change (5cm)] / 2

e.g. Av. % Change of Potato Tube A = [15.7 + 18.1] / 2 = 16.9

Analysing Evidence and Drawing Conclusions (A)

Analysis:

When the concentration of sucrose was low the chips gained mass and as the concentration of sucrose increased more mass was lost. In all of the cases, whether the chip gained or lost mass the water moved in or out of the cells by osmosis. Osmosis is the movement of water particles from an area oh high concentration to an area of Low concentration through a semi-permeable membrane.

From looking at my graphs, I can clearly see that there is a strong negative correlation, which again proves that the chips loose weight when there is more sucrose in the solutions. What the graph/line of best fit also shows is that at 0.33 molar sucrose solution for potato chips and 0.34 molar sucrose solution for Chinese radish chips, the concentration of molar sucrose solution has the same water potential as the plant tissue, so there is no change.

Another thing that is very clear when looking at my result tables is that the potato chips gained less mass in water and lost more mass in 0.6 molar sucrose solution then the Chinese radish chips. In water the potato chips gained 16.9% and the Chinese radish chips gained 19.0% and in 0.6 molar sucrose solution the potato chips lost 17.6% and the Chinese radish chips lost 10.0%.

With the chips in water, there was a higher water potential in the solution in the test tube then in the chips themselves, so water moved through the semi-permeable membrane (cell membrane) of all the chips cells causing them to increase in volume and push against the cellulose cell wall, so that no more water can enter and the chips becomes turgid and hard (see Diagram 1 below). With the chips in 0.6 molar sucrose solution, there was a higher water potential inside the chips then in the solution in the test tube, so water moved out of all the cells causing them to shrink and the chips became plasmolysed and soft (see Diagram 2 below)

Looking back at my predictions, I believe that my predictions were fairly accurate and that I was only a couple of percent at most. I shall just compare a couple of them, so in water I predicted that they would gain between 15- 20%, and in 0.5 molar sucrose solution I predicted that they will lose between 5-10%. Well, in water the potato chips gained 16.9% and the Chinese radish chips gained 19.0%, in 0.5 molar sucrose solution the potato chips lost 8.9% and the Chinese radish chips lost 8.3%.

1) Plant cell - Turgid 2) Plant cell- Plasmolysed

Evaluating Evidence (E)

Evaluation:

My procedure must have been reasonably reliable as it produced a good set of results, which show a clear negative correlation, as you can see on my graph.

The balance used to weigh the chips before and after was very accurate to two decimal places of one gram, which obviously helped a lot in keeping my experiment as accurate a possible. But undoubtedly there is places where I may have been inaccurate, it is very hard to fill the syringes accurately, even when being careful and reading the measurements from eye level. It can be very difficult to see if there are any air bubbles in the syringe and it doesn't help when you are trying to be really careful and you know that the measurement on the syringes are only accurate to about 1/4 of a cm, so add that together with my inaccuracies and every one of my measurements was probably about 1/2 a cm off. Another area where I had to be as careful as possible was when I took the chips out of the solutions and dried them, I had to be very careful to try and reduce the variables as much as possible, so I dried each chip for 10 second before weighing them.

After thinking about all the areas that I could have made mistakes and been inaccurate, I think I am lucky not to have any major anomalous results, but the percentage change in the potato chip that was in 0.3 molar sucrose solution does look slightly adrift from the line of best fit. This could be due to any of the reasons shown above and was most likely a mistake with the mixing of the solution with the syringes. The rest do look about right and were pretty much what I expected.

If I were to do this experiment again, I would try and seek new ways to make it as accurate a possible; firstly I think I would use four chips for each of the solutions and take an average out of the results, which would greatly improve the accuracy. Also instead of wasting lots of time measuring out the solutions in the syringes, I would use graduated pipettes instead; the measurements on them are far more accurate and would definitely make the concentrations more accurate. Finally, this is not necessary but I believe it would be very interesting to instead of just drying the chips for 10 seconds, to dry them for 10 seconds then weigh them, then dry them for 30 seconds then weigh them and finally dry them for 1 minute and weigh them and find out the percentage difference, which I suspect to be just a couple of percent at most.

But I believe my evidence as a whole to be very reliable, except for maybe the potato chip in 0.3 molar sucrose solution, and it is definitely sufficient enough to support me with a firm and correct conclusion.