Biology 5090/31 — May/June 2012
Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme
Topics Experimental Contexts · Observations and Measurements · Analysis, Conclusions and Evaluation · Planning Experiments and Investigations · Microscopy and Biological Drawing · Use of Techniques, Apparatus and Materials
Bread is made from dough composed of flour, water and active yeast.
You are required to investigate the action of active yeast in of each of two different types of flour, S1 and S2.
- Carefully add flour S1 to the beaker, labelled S1, containing active yeast, and stir until thoroughly mixed to make the dough.
- Level the top of the dough as much as possible by using the stirrer. Using a marker pen or label, mark this level on the outside of the beaker.
- Use the ruler to measure the height of the dough and record your measurement in Table 1.1 as the initial height.
- Record the start time in Table 1.1 and leave the beaker on the bench for 30 minutes.
- Clean the stirrer.
- Repeat the above procedure using flour S2 and the second sample of active yeast in the beaker, labelled S2. Record the initial height and the start time in Table 1.1.
While you are waiting you should continue with the other questions.
- After leaving each dough for 30 minutes, record the finish times in Table 1.1 for S1 and S2. Measure the maximum height of the dough in each beaker and record this in Table 1.1 as the final height.
Complete Table 1.1 by calculating the durations and changes in height for S1 and S2.
Table 1.1
| time | height of dough / | ||||
|---|---|---|---|---|---|
| S1 | S2 | S1 | S2 | ||
| at start | initial height | ||||
| at finish | final height | ||||
| duration / mins | change in height |
Describe any differences in the two dough mixtures after the 30 minutes.
Describe and explain how the metabolic processes of the active yeast have brought about the changes that you have observed.
Describe how you would carry out an investigation into the effect of temperature on the activity of yeast in dough made with flour S1.
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