Table 1.2: Table shows the recorded data for the initial length of the potato strips, cm and the final length of the potato strips, cm.
By using the data in the table 1.1 and 1.2 the difference in length of the apple and potato strips are calculated by using the formula below.
Difference of length of each apple/potato strips, cm:
Initial length of each apple/potato strips, cm – Final length of each apple/potato strips, cm
For example:
The following shows the calculation for the potato strips immersed in 0.2 M of glucose solution.
Difference in length for the first potato strip, cm:
= (4.50 ± 0.05 cm)-(4.50 ± 0.05 cm)
= (0.00 ± 0.1 cm)
Difference in length for the second potato strip, cm:
= (4.50 ± 0.05cm)-(4.50 ± 0.05cm)
= (0.00 ± 0.1cm)
Difference in length for the third potato strip:
= (4.50 ± 0.05cm)-(4.50 ± 0.05cm)
= (0.00 ± 0.1cm)
- The other values of difference in length for the apple and potato strips are recorded in table 2.1 and 2.2 respectively.
Table 2.1: Table shows the difference in length of the potato strips, cm immersed in different concentration of the glucose solution, M.
Table 2.2: Table shows the difference in length of the apple strips, cm immersed in different concentration of the glucose solution, M.
By using the same data in table 2.1 and 2.2, the average difference in length of the apple/potato strips are calculated using the formula below:
Average of difference in length of the apple/potato strips:
Sum of all the apple/potato strips that is immersed in the same concentration of glucose
3
=Average difference ± Standard deviation
For example:
The following shows the calculation of the average difference in length of potato strips for 0.2 M of glucose solution.
= (0.20 cm + 0.10 cm + 0.20 cm) 3
= 0.1667 ± 0.0470
-
For other values of average difference of potato strips, cm for each glucose concentration, mol/dm-3 please refers to the table 3.1.
Table 3.1: Table shows the recorded data for the average difference of the potato strips, cm for each glucose concentration mol/dm3.
- Note that all the standard deviation value is in bold state.
Graph 1.1: Shows the difference in length of potato strips against the concentration of sucrose solution.
Graph 1.2: Shows the difference in length of apple strips against the concentration of sucrose solution.
Graph 1.3: Shows the comparison between the apple and potato line graph.
- Note that the number in the x-axis represents the following:
1 = 0.2 mol
2 = 0.3 mol
3 = 0.4 mol
4 = 0.5 mol
5 = 1.0 mol
Qualitative quantity:
Table 4.1: Table shows the observational data of physical condition of each apple strips and level of glucose solution after being immersed in sucrose solution for 240 minutes level of glucose solution
Table 4.2: Table shows the observational data of physical condition of each potato strips and level of glucose solution after being immersed in sucrose solution for 240 minutes level of glucose solution
Conclusion:
Based on the apple strips result:
0.2M, 0.3M, 0.4M and 0.5M glucose solutions can be conclude that they are hypotonic to the cell sap of apple strips. This is because the length of the apple strips increases as the strips are immersed in the glucose solutions with those concentrations.
1.0M glucose solution is hypertonic to the cell sap of the apple strips. This is proven when the length of the strips decreases when they are immersed in 1.0M concentration of glucose solution. Based on the graph, it is believed that the concentration of glucose that is isotonic to cell sap of apple strips is approximately 0.75M.
Based on the potato strips result:
The solutions in 0.2M and 0.3M of glucose solutions are hypotonic or less concentrated than the cell sap of the strips of potato. Water diffuses into the cells by osmosis. This causes the potato strips to become turgid and firm.
The solutions in 0.5M and 1.0M of glucose solutions are hypertonic or more concentrated than the cell sap of potato tissues. Water leaves the cell by osmosis. This causes the potato strips of potato to decrease.
- The movement of substances across the plasma membrane depends on the difference gradient of the concentration between the surrounding solution and the cell sap of potato tissue.
- If the surrounding solution is hypotonic to the concentration of cell sap, then water enters the potato cells by osmosis.
- If the surrounding solution is hypertonic to the concentration of cell sap, then water leaves the potato cells by osmosis.
- If both the surrounding solution and the cell sap of potato tissue have the same concentration which is isotonic to each other, then the rate of water movement in and out of the cell is the same. The cells maintain their normal appearance.
The solutions in 0.2 and 0.3M of glucose solutions are hypotonic or less concentrated than the cell sap of the strips of potato. Water diffuses into the cells by osmosis. This causes the potato strips to become very turgid and firm. The solutions in 0.5 and 1.0M of glucose solutions are hypertonic or more concentrated than the cell sap of potato tissues. Water leaves the cell by osmosis. This causes the potato strips of potato to decrease.
Proven by the data and the graph represent the difference in length of the strips, the strips are actually decreasing as the concentration of the glucose increase.
Thus, the hypothesis stated above is not accepted.
Limitations and ways of improvement:
-
The volume of all solution in this experiment is measured by using 100cm3 measuring cylinder which is inappropriate in measuring small volume of solution such as 20ml of 1.0 mol of glucose solution. It is suggested that the 20ml of the difference concentration of the glucose solution measured by 10ml pipette which has smaller uncertainties.
- The potato and the apple strips were prepared by using different tuber or fruit which is then have difference concentration from one another. This will affect the rate of osmosis. It is suggested that the sample should be taken from the same part of the potato. As example the centre part of the apple fruit or the centre part of the potato tuber only. So that the concentrations of the strip will be the same.
- Because of the human limitations, the cutting of the tuber or apple strips might not be constant. This next can be avoided by placing a ruler at near the specimen to make sure the probability for the cutting to be slanting reduced.
- There might be parallax error during the reading of the volume of the water. This can be avoided by making sure that the eye levels are the same with the meniscus of water during the reading.
- The shape of the boiling tube is round which based on human limitations there might be a little slanting thus affect the reading of the volume taken. This is hardly avoided, but it can be reduced by placing the boiling tube on a flat surface by a straight ruler to make sure that there will be less slanting.
- The time of the experiment should be lengthening. The more the time might bring to more clear and precise result. The time 240 minutes should be lengthening to 480 minutes.
Appendix:
The preparation of 0.2, 0.3, 0.4, 0.5 mol/dm3 of glucose solution from 1.0 mol/dm3 of glucose solution.
Using the formula:
M1V1 = M2V2
M₁= Molarity of standard solution
V₁= Volume of standard solution
M₂= Molarity of desired solution
V₂= Volume of desired solution
Example: prepare 20cm³ 0.2mol dm ̄³ glucose solution.
1.0 mol dm ̄³ (V₁) = 0.2mol dm ̄³ (20cm³)
V₁ =
V₁ = 4.0cm³20cm³