Edexcel IGCSE Biology

Revision Notes

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

A typical fungal cell, IGCSE & GCSE Biology revision notes

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

Yeast bread, IGCSE & GCSE Biology revision notes

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

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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