Edexcel IGCSE Biology: Double Science 复习笔记 5.1.3 Yeast in Food Production

Edexcel IGCSE Biology: Double Science 复习笔记 5.1.3 Yeast in Food Production

Yeast in Food Production


  • 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