Yeast fungi, which include around 600 different species, can utilise the energy in sugar without using oxygen. This process is called fermentation. Sourdough bakers almost always bake with wild yeast, i.e. yeast cells found in the air around us, but the yeast you can buy in the shop is of the species Saccharomyces Cerevisiae. The yeasts contribute at least 600 different chemical components, which strongly contribute to the characteristic flavour of the bread. It is the carbon dioxide released by the consumption of sugar that makes the dough grow during baking.
Yeast fungi have also proved helpful in the energy sector. Since we produce ethanol when yeasts process sugar, bioethanol is produced from sugar beet and sugar cane, for example.
Sources
Scientific American – The Mycelium Revolution Is upon Us 
Sciencedirect – Contribution of yeast and its biomass for the preparation of industrially essential materials: A boon to circular economy
Marcus Rosenlund (2022) – Det stora lilla livet
February 2024, TÄNKOM | Revised March 2024 RETHINK
