Biology 5090/62 — October/November 2017
Cambridge O-Level · Alternative to Practical · worked solutions for every part, with the mark scheme
Topics Experimental Contexts · Analysis, Conclusions and Evaluation · Planning Experiments and Investigations · Microscopy and Biological Drawing · Use of Techniques, Apparatus and Materials · Observations and Measurements
Glucose is a reducing sugar. Benedict's solution is used to test for the presence of reducing sugar.
Describe how you would use Benedict's solution to test for reducing sugar in a piece of potato. Include details of a safety precaution in your answer.
Some students were given a 1.0% glucose solution and some distilled water. They diluted the glucose solution to produce five solutions of different concentrations.
The students tested each of the solutions they had prepared with Benedict's solution. The concentrations of the solutions and the results of their tests are shown in Table 1.1.
Table 1.1
| glucose solution concentration (%) | result of Benedict's test |
|---|---|
| 0.0 (distilled water) | ______ |
| 0.1 | slightly green |
| 0.2 | green |
| 0.3 | yellow |
| 0.4 | orange |
| 0.5 | red |
The students also decided to test the distilled water with Benedict's solution.
Write the result of this test in Table 1.1.
Explain why the students tested the distilled water.
The students compared the colour of their solutions after the same length of time. State three other variables that the students should have controlled to make their results comparable.
- ______
- ______
- ______
The students were then provided with a glucose solution X of unknown concentration which they tested with Benedict's solution. The result was a yellowish-orange colour.
Use Table 1.1 to suggest what the students may have concluded about the % concentration of glucose in solution X.
Suggest how the students could determine a more accurate % concentration for glucose solution X.
You are given a 1.0% glucose solution. Describe in detail how you would use it to produce of a 0.5% glucose solution.
After the students had tested the glucose solutions in Table 1.1 with Benedict's solution, they noticed that a solid (precipitate) had collected at the bottom of the test-tubes.
They decided that finding the mass of the solid was another way of measuring the concentration of glucose in the solution.
Suggest how the students could separate this solid from the solution and obtain its mass.
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