8. Demonstrate Osmosis using RBCs
An experiment was carried out to investigate the effect of different concentrations of sodium chloride on human red blood cells. Equal amounts of blood were added to equal volumes of the salt solution but of different concentrations. The results are shown in the table below:
|
Set-up |
Solution |
Number of red blood cells |
|
|
|
Sodium chloride concentration |
At start of experiment |
At the end of the experiment |
|
A |
0.9% |
Normal |
No change in number |
|
B |
0.3% |
Normal |
Fewer in number |
(a) Account for the results in the set-up
A
- No change in; number because 0.9% sodium chlorine solution is isotonic to RBC;
B
- Fewer in number because 3% sodium chloride solution is hypotonic to RBC therefore some water was drawn into RBCs by osmosis; leading to haemolysis of RBCs
(b) If the experiment was repeated using 1.4% sodium chloride solution, state the expected results with reference to:
(i) The number of red blood cells
- Number remains constant;
(ii) The appearance of red blood cells if viewed under the microscope
- RBC become crenated/shrunk;
9. Demonstrate Osmosis using Plant Cells
Cells of the Tradescantia plant were found to have an average diameter of 2.5ɥm. The cells in each solution were determined and results obtained are shown below.
|
Percentage (%) sugar concentration |
1 |
5 |
10 |
15 |
20 |
25 |
|
Diameter of cells (ɥm) |
5.0 |
4.0 |
3.0 |
2.0 |
1.5 |
1.0 |
(a) Draw a graph of diameter of cells (y-axis) against percentage sugar concentration (x-axis). (6marks)
(b) From the graph determine the concentration of cell sap. (1 mark)
(c) Give an explanation for the average diameter of cells placed in 2.5% sugar. (3 marks)
