Question
Yeast is used in bread-making. It respires anaerobically, producing carbon dioxide.
(a) Write the balanced chemical equation for anaerobic respiration of yeast in bread-making. [2]
A baker wants to increase the rate of carbon dioxide production in the bread-making process.
The baker trialled different concentrations of glucose solution in the bread dough.
Fig. 3.1 shows the results.
(b) (i) Predict the rate of carbon dioxide production if the concentration of the glucose solution
was 7.0%.
…………………………………………………………………………………………………… cm3 per min [1]
(ii) The baker carried out the trials at 30 °C.
The trials were repeated at 20 °C.
Draw a line on Fig. 3.1 to show the rate of carbon dioxide production at 20 °C. [2]
(iii) The baker carried out another trial at 80 °C. No carbon dioxide was released.
State why no carbon dioxide was produced. [1]
(c) Name one other industrial process that uses yeast. [1]
(d) During the production of penicillin, large fermenters are used. Fig. 3.2 shows a fermenter
(i) Explain the functions of the following parts of the fermenter:
stirrer
water-filled jacket
probes [3]
(ii) The air and nutrients that are added to the fermenter are sterile.
State why they must be sterile. [1]
[Total: 11]
Answer/Explanation
Ans
3 (a) C6H12 O6 → 2C2H5OH + 2CO2 ;;
(b) (i) 4.1 (cm3 permin) ;
(ii) a single line below the original curve on the graph and following the same shape ;
line starts at origin ;
(iii) enzymes denatured/ yeast died ;
(c) (named) alcohol production ;
producing biofuels / ethanol ;
production of yeast extract ;
GM yeast ;