Yeast is used in bread making. Flour is combined with water and yeast to make dough. The yeast breaks down the starch in the flour to form sugar. It then uses this sugar in respiration, releasing bubbles of carbon dioxide. These bubbles become trapped in the dough, causing it to rise in volume before baking.
Some students investigated the effect of yeast in four doughs made from different types of flour: wheat, rye, buckwheat and maize. They assessed the action of the yeast by measuring the amount by which the dough increased in volume.
The same mass of each flour was mixed with the same volume of water and the same mass of yeast to make a dough. Four 100 cm3 measuring cylinders were labelled and dough was placed into each one. The volume of dough in each cylinder was measured and written down at 15-minute intervals. Some of the results are shown in Table 2.1.
Table 2.2 presents some of the biological molecules in the four flours.
(a(i))[1]
Fig. 2.1 shows the measuring cylinder containing wheat flour dough after 30 minutes. Enter the dough volume in Table 2.1.
(a(ii))[2]
Complete Table 2.1 by finding the total increase in volume for each dough after 45 minutes.
(a(iii))[4]
Use the grid to draw a bar chart showing the total increase in volume of the four doughs after 45 minutes.
(a(iv))[3]
Using Table 2.2, your bar chart and the information about bread production, suggest and explain how these biological molecules affect the total increase in volume of bread dough.
(b)[2]
Describe how you would show that each of the four flours contained starch.
(c)[6]
The students made more dough from wheat flour, yeast and water. Using this dough, plan an investigation based on the method in 2(a) to find out the effect of temperature on the increase in volume of dough at temperatures between 20^{\circ}C and 80^{\circ}C. Predict your expected results.