Biological Molecules
1. This question has 4 part(s).
1.1. Yeast cells are often used when making bread.
A student uses this method to investigate the effect of temperature on the height that bread dough rises.
Place dough containing flour, sugar, water and yeast into a measuring cylinder
Measure the height of the dough
Place the measuring cylinder in a 25 °C water bath
Measure the height of the dough after two hours
Repeat the experiment at temperatures of 35 °C and 65 °C
The diagram shows the student’s apparatus.
The table shows the student’s results.
Temperature in °C | Height of dough in mm | Percentage (%) increase in height of dough | |
|---|---|---|---|
At start | After two hours | ||
25 | 25 | 35 | 40 |
35 | 25 | 45 | |
65 | 25 | 27 | 8 |
Calculate the percentage increase in the height of the dough after two hours at a temperature of 35 °C.
1.2. Explain why yeast causes the bread dough to increase in height.
1.3. Explain why the dough rises to a different height at 25 °C compared with the height at 35 °C.
1.4. Explain why the dough rises to a different height at 35 °C compared with the height at 65 °C.
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