A student carried out two investigations into the action of yeast. (a) In the first investigation, the student dissolved 20.0g of glucose in 100cm³ of water in a beaker. The student then added 3.5g of yeast and used a balance to measure the loss in mass from the beaker over the next 24 hours. The results of this investigation are shown in the graph. [Figure 3.0 showing a graph of mass lost /g vs time/hours, with data points up to 24 hours.] (i) Calculate the rate at which mass was lost during the first 6 hours. Space for working. ....... g per hour [2] (ii) Explain why mass was lost during the investigation. [3] (iii) The student then repeated this first investigation changing only the mass of yeast. Draw a line on the graph on page 6 to show the pattern of results you would expect the student to obtain when using 7.0 g of yeast. [2] (b) In a second investigation, the student prepared three samples of bread dough. Each sample of dough had a volume of 50 cm³ and contained: • 1 g of yeast • 25 cm³ of water • 40 g of flour. (i) Starch molecules in the flour are used to provide the yeast with a source of glucose. Describe how the action of a named chemical, produced by yeast cells, makes glucose available from starch. [2] Each sample of dough was placed at the bottom of a 200 cm³ measuring cylinder. The three measuring cylinders were then placed in water-baths at different temperatures for 60 minutes. The temperatures chosen were 20°C, 40°C and 80°C. After this time, the student measured the volume of dough in each measuring cylinder. The diagram shows the volume of dough in the measuring cylinder from the water-bath at a temperature of 20°C at the end of the investigation. [Figure 3.1 showing a measuring cylinder with dough volume at 60 cm³] (ii) Estimate the volumes of the dough at the end of the investigation in the other two measuring cylinders, from water-baths at temperatures of: 40°C ..................................................... cm³ 80°C ..................................................... cm³ [2] (iii) Explain the results of this investigation. [3]

1. (a)(i)Calculate the rate at which mass was lost during the first 6 hours. Space for working. ....... g per hour[2]
2. (a)(ii)Explain why mass was lost during the investigation.[3]
3. (a)(iii)The student then repeated this first investigation changing only the mass of yeast. Draw a line on the graph on page 6 to show the pattern of results you would expect the student to obtain when using 7.0 g of yeast.[2]
4. (b)(i)Starch molecules in the flour are used to provide the yeast with a source of glucose. Describe how the action of a named chemical, produced by yeast cells, makes glucose available from starch.[2]
5. (b)(ii)Estimate the volumes of the dough at the end of the investigation in the other two measuring cylinders, from water-baths at temperatures of: 40°C ..................................................... cm³ 80°C ..................................................... cm³[2]
6. (b)(iii)Explain the results of this investigation.[3]

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