Report
Name :
Liew Shirene
Sudent ID :
J14015081
Title of experiment :
Water Potential of Potato Tuber Cells
Results:
Diagram of potato strip before immerse in the solution:
Diagram of potato strip after immerse in S1 solution:
Diagram of potato strip after immerse in S2 solution:
Diagram of potato strip after immerse in S3 solution:
Diagram of potato strip after immerse in 90% ethanol and S3 solution:
Questions:
1. Explain as fully as possible what had happened to the strips in dishes 1, 2 and 3.
Length of strips in dish 1 becomes shorter than before. Water potential in potato cells of the
strips is higher than water potential of S1 (1 mol dm^-3) solution. There is a net movement
of water molecules from potato cells of the strips into the S1 solution. This cause the
decrease in length of potato strips.
Length of strips in dish 2 remains unchanged. Water potential in the potato cells of the strips
is the same as the water potential in S2 (0.5 mol dm^-3) solution. There is no net movement
of water molecules.
Length of the strips in dish 3 becomes longer than before. Water potential in S3 (0.01 mol
dm^-3) solution is higher than water potential in the potato cells of the strips. There is a net
movement of water molecules from S3 solution to potato cells in potato strips. This cause
the increase in length of potato strips.
Sucrose molecules (solute) does not affect the length of strip because it is too big pass
through the cell membrane of potato cells of potato strips.
2. How do you account for the differences between the strips in dishes 3 and 4?
The length of potato strips in dish 4 is longer than the length of potato strips in dish 3.
Potato cells of strips in dish 4 can take in more water molecules from S3 solution than
potato cells of strips in dish 3. This is because the cell membrane has been broken and burst
open. Cholesterol that provide mechanical stability of cell membrane has been dissolved in
ethanol.
3. Why was it important that the lids were kept on all the dishes during this investigation?
To prevent oxidation of potato cells and also evaporation of sucrose solution.
4. State two properties of the sucrose solution which account for the effects it had on the
potato strips.
Sucrose molecules are unreactive so it does not interfere the cell activity. It is also large in
size and so it can not pass through the cell membrane.
5. What deduction could be made about the water potential of potato if a similar strip did not
change its shape when it was placed in a solution of known molarity of sucrose?
The water potential of the potato cells of potato strip is the same as the water potential of
the solution of known molarity of sucrose.
B) In a similar investigation, involving a range of sucrose concentrations, the results shown in Table
1.2 were obtained.
Table 1.2
Sucrose solution concentration
/mol dm^-3
0.0 (water)
0.25
0.50
0.75
1.00
i)
Mean length of strips /mm
52.0
49.0
47.0
43.5
41.5
Percentage change in length of
strips
+4
-2
-6
-13
-17
On the grid provided, plot a graph of the percentage change in length of the strips,
against the molar concentration of the sucrose solutions.
ii)
Use the graph to determine the concentration of the solution that is equal to the water
potential of the potato tissue.
0.175 mol dm^-3
iii)
Explain in terms of water potential, the percentage change in length of the potato chips
that occurred in water.
Water potential of the sucrose solution is the highest when its concentration is 0.00 mol
dm^-3 and it is higher than water potential in potato cells of the strips. There is a net
movement of water molecules from sucrose solution to potato cells of the strip. Thus,
potato strip increase in length and the value of percentage change in length is positive.
Water potential of the sucrose solution decrease as its concentration increase. This
cause the increase of length of potato strips and positive value of percentage change in
length becomes lower. When the concentration of sucrose solution is more than 0.175
mol dm^-3, water potential in it is lower than in potato cells of the strips. There is a net
movement of water molecules from potato cells of the strips to the sucrose solution.
Thus the length of the potato strip will become shorter and the percentage change in
length decrease.
C) In another investigation involving a range of sucrose concentrations, the results in Table 1.1 were
obtained.
Table 1.1
Sucrose solution concentration / mol dm^-3
0.00 water
0.20
0.40
0.60
0.80
1.0
i)
Percentage change in length of strips
+5.0
+2.5
-1.0
-1.5
-6.3
- 8.8
At 1.0 mol dm^-3 sucrose concentration, the mean length of the strips before the
experiment was 80.0 mm and after the experiment was 73.0 mm.
Calculate the missing value for the percentage change in length of the strips and
complete Table 1.1.
You may use the space below to show your working.
X 100%
=
=
= - 8.75 %
= - 8.8 % (2 s.f)
ii)
When the student first performed this experiment the percentage change in length in a
0.8 mol dm^-3 solution was +3%. Suggest what the student did when this result was
obtained and explain why.
Repeat the experiment using the 0.8 mol dm^-3 sucrose solution. This first experiment
must has an error. The percentage change in length in 0.8 mol dm^-3 should be in a
negative value according to the trend of the percentage change in length of strips in
different sucrose solution shown in Table 1.1. The +3 % is a anomous value.
iii)
Plot a graph of the percentage change in length of the strips against the concentration of
the sucrose solution using the student’s results.
e) The concentration of sucrose solution that would give no change in length was not found very
precisely in the experiment. Suggest how it could be improved to give this more precisely.
Use a wider range of different concentration of sucrose solution. Increase the immersion time of the
potato strips in sucrose solution. Prepare 2 set of experiment by placing same length of the potato
strip, which is obtained from the same potato into two petri dish for each different concentration of
sucrose solution and use the mean value of the final length of the potato strip to calculate the
percentage change in length of potato strips.
f) The student’s hypothesis was
- the more concentrated the solution, the smaller the potato strips became.
Draw an appreciate conclusion to the student’s experiment.
You should include in your conclusion whether the experimental data support the hypothesis and
produce a revised or new conclusion if necessary.
It is acceptable according to the experimental data. The percentage change in length of potato strips
decrease as the concentration of sucrose solution increase. This shows that the final length of the
potato strips decrease as the concentration of sucrose solution increase.
g) Other than temperature, suggest how the student could improve the experiment to reduce errors.
Obtain the potato strips from the same potato so that water content of potato cells of each strip is
the same. Use potato strips with the same diameter. Put the potato strips in water first or place it in
a refrigerator to prevent oxidation of the potato cells of the strips.