Biology 5090/31 — October/November 2021
Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme
Topics Observations and Measurements · Experimental Contexts · Use of Techniques, Apparatus and Materials · Planning Experiments and Investigations · Analysis, Conclusions and Evaluation · Microscopy and Biological Drawing
The tissue of a peeled potato tuber is composed of many similar cells.
You are going to investigate the effect of varying concentrations of sucrose solution on some potato tissue.
You are provided with some potato tissue, distilled water (A) and three sucrose solutions (B, C and D).
Solutions B, C and D are different concentrations of sucrose solution.
- Label four test-tubes A, B, C and D.
- Cut four strips from the potato each measuring in cross-section and long. This is their starting length, which must be identical for each strip.
- Place one strip in each of the four test-tubes.
- Add solution A to the test-tube labelled A so that it covers the potato strip.
- Do the same for test-tube B with solution B, test-tube C with solution C and test-tube D with solution D.
Record the time. ______
- Leave the potato strips in the solutions for 25–35 minutes.
Continue with Questions 1(b) and 2 while you are waiting.
- After the strips have been in solutions A, B, C and D for 25–35 minutes, pour away the solutions. Remove the strips and place them on a white tile, making sure that you can identify each strip. Record the time.
time strips were removed from solutions = ______
Calculate how long the strips had been left in the solutions, to the nearest minute.
total time that strips were left in the solutions = ______
Describe what you did to make sure that, when you removed the strips from the test-tubes, you knew which potato strip had been in which solution.
Measure the lengths of strips A, B, C and D. Record the lengths of each strip at the start and end of the investigation and calculate the changes in length. Enter your results in the table.
| solution | start length / | end length / | change in length / | flexibility of strip |
|---|---|---|---|---|
| A | ||||
| B | ||||
| C | ||||
| D |
Gently bend each strip to see how flexible it is. The more easily it bends, the more flexible it is. Decide the order of decreasing flexibility and use the scale to record this in the table. Record the most flexible strip as ++++ and the least flexible as +.
| most flexible/bendable | ++++ |
| +++ | |
| ++ | |
| least flexible/bendable | + |
Describe and explain the changes in length and flexibility in the potato strip that had been in solution A.
Identify two problems with the method used in this investigation that might have led to unreliable conclusions. Suggest a way in which each could have been improved to make the results more reliable.
problem 1 = ______
improvement 1 = ______
problem 2 = ______
improvement 2 = ______
Another student investigated the effect of varying concentrations of sucrose solution on some potato tissue by measuring changes in the mass of the tissue.
He placed five pieces of potato tissue, each with a mass of , in five separate test-tubes.
The test-tubes contained either distilled water or one of four concentrations of sucrose solution.
Later he poured away the solutions.
State two factors, apart from the mass of tissue, that should have been kept constant when using this method.
- ______
- ______
When he removed the pieces of tissue from the test-tubes, he carefully dried them on a paper towel.
Explain why it was important to dry them.
The table shows the measurements at the end of the investigation.
| sucrose concentration / | mass at end of investigation / |
|---|---|
| 0.0 | 5.7 |
| 0.2 | 5.2 |
| 0.4 | 4.6 |
| 0.5 | 4.3 |
| 0.8 | 3.3 |
Construct a line graph of the data in the table on the grid below. Join your points with ruled, straight lines.
Use your graph to determine the concentration of sucrose which will produce no change in mass.
concentration = ______
Describe the method you used to determine this concentration of sucrose.
The rest of this paper
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