Biology 5090/31 — May/June 2023
Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme
Topics Observations and Measurements · Experimental Contexts · Analysis, Conclusions and Evaluation · Planning Experiments and Investigations · Use of Techniques, Apparatus and Materials · Microscopy and Biological Drawing
You are going to investigate the movement of water by osmosis using potato tissue. You are provided with:
- four cylinders of potato tissue with equal diameters
- four different concentrations of sodium chloride (salt) solution at room temperature
- four test-tubes
- sharp knife
- white tile
- marker pen/pencil
- paper towels
- stop-watch/timer
- ruler.
Use the following method:
- label the test-tubes 0.0%, 2.0%, 4.0% and 6.0%
- on the white tile, cut each of the four cylinders of potato to exactly in length
- place one potato cylinder in each test-tube
- pour the concentration of salt solution matching the label into each test-tube so that the potato cylinders are covered as shown in Fig. 1.1
- start the timer and leave the potato cylinders in the solutions for 40 minutes
After 40 minutes you are going to remove the potato cylinders from the test-tubes, measure their final lengths and calculate any change in length.
While waiting you may continue with Question 1(b) and Question 2.
- after 40 minutes pour off the salt solution from each test-tube into the container labelled waste but leave each potato cylinder in its test-tube.
Complete the column headings in Table 1.1.
Table 1.1
| percentage concentration of salt solution | starting length / ______ | ______ / ______ | ______ / ______ |
|---|---|---|---|
| 0.0 | 40 | ||
| 2.0 | 40 | ||
| 4.0 | 40 | ||
| 6.0 | 40 |
For each potato cylinder:
- remove the potato cylinder from its test-tube
- measure its length
- record this final length in Table 1.1.
Calculate the change in length of each potato cylinder and record it in Table 1.1.
Water can move into and out of potato cells by osmosis. Salt cannot move into and out of potato cells.
Use this information to explain the results in the test-tube containing 6.0% salt solution.
______
Explain why it is important that all the potato cylinders were cut to the same length at the start of the investigation.
______
A student used a similar method to investigate the movement of water by osmosis in potato cylinders. Instead of length, changes in mass were measured for each potato cylinder. The cylinders each had the same mass when first placed in the salt solutions.
Fig. 1.2 shows the results in the student's notebook:
Use the data in Fig. 1.2 to construct a graph of percentage concentration of salt solution used against change in mass. Join your points with ruled lines.
Each potato cylinder had a starting mass of .
Use your graph to determine the final mass of a potato cylinder placed in 3.0% salt solution.
Show your working on your graph.
final mass = ______
The concentrations of salt solution were made by using different volumes of a 10.0% salt solution and distilled water.
Calculate the volumes of 10.0% salt solution and distilled water needed to make of a 4.0% salt solution.
volume of distilled water = ______
volume of 10.0% salt solution = ______
The student dried the potato cylinders before obtaining their final mass. Explain why this was important.
______
Design an investigation to determine the concentration of salt solution in which movement of water into and out of potato tissue is equal.
Your investigation should be based on the method described on page 2 but using changes in mass of the potato tissue and not changes in length.
Give full experimental details.
Identify the dependent variable in the investigation you have designed.
______
The rest of this paper
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