• Microorganisms can be used by humans to produce foods and other useful substances
• One example of this is the?production of bread using yeast
• Yeast is a?single-celled fungus?that can carry out both?aerobic?and?anaerobic?respiration

Yeast is a single-celled fungus, similar to the one shown in the diagram above

Making bread

• When yeast carries out?anaerobic respiration, it produces an?alcohol (ethanol)?and?carbon dioxide
• Yeast will respire anaerobically if it has access to?plenty of sugar, even if oxygen is available
• This is taken advantage of in bread making, where the yeast is mixed with?flour?and?water
• The yeast produces?enzymes?that break down the?starch?in the?flour, releasing?sugars?that can then be used by the yeast for anaerobic respiration
• The?carbon dioxide?produced by the yeast during anaerobic respiration is trapped in small air-pockets in the dough, causing the dough to?rise?(increase in volume)
• The dough is then?baked?in a hot oven to form bread
• During baking, any?ethanol?produced by the yeast (as a?waste product?of anaerobic respiration) is?evaporated?in the heat
  • This is why bread doesn't contain any alcohol

   

• The yeast is killed by the high temperatures used during baking
  • This ensures there is no further respiration by the yeast

   

• Once cooled, the bread is ready to be eaten

The carbon dioxide produced by the anaerobic respiration of glucose is what makes bread dough rise

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