O-LevelBiologyRespiration5090/22 · Oct/Nov 2016 · Q110 Marks

Two separate strains, A and B, of the same species of microorganism are used in the making of bread and beer (a drink that contains alcohol).

(a)(i)Name this type of microorganism[1]
(a)(ii)Name the gas released by this microorganism during the production of bread and beer.[1]
(b)(i)Fig. 1.1 shows the volume of gas released by the strains while they are being used. [Figure 1.1] Fig. 1.1 shows the gas released by strain B at a temperature of 18°C. Draw a curve on Fig. 1.1 to show the effect on strain B of increasing the temperature by 10°C.[3]
(b)(ii)Name two other external factors that would change the shape of the curves shown in Fig. 1.1.[2]
(c)Strain A has a sweet taste and strain B has a bitter taste. Suggest which strain is used for making bread. Give reasons for your answer. strain used in making bread reasons[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2016). The mark or mark type is shown in brackets.

[1] yeast/fungus / Saccharomyces ;
[1] carbon dioxide/CO2;
[3] starting at zero ;
line above that on graph at least up to (the drawn line's) peak;
peaking earlier (than dotted line on graph) ;
reaches same height as dotted line ;
[2] pH;
substrate (or named carbohydrate) concentration/amount ;
toxins / named toxin;
amount of yeast/microorganism/strain A/strain B;
competing microorganism AW ;
pressure/(presence of) oxygen ;
[3] (strain A):
produces high volume/amount+CO2/gas;
quick(er) process;
CO2 / gas makes the dough rise AW/trapping of CO2/trapping of gas/improves texture ;
flavour suitable for bread AW;

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