MCQ Detailed View

Yeast is a microscopic, single-celled fungus widely used in the baking industry, particularly in making bread. The main reason yeast is added to bread dough is because it produces carbon dioxide gas through a process called fermentation.

When yeast is mixed with flour, water, and sugar, it begins feeding on the sugars present in the dough. During this process, yeast breaks down the sugar into carbon dioxide (CO₂) and alcohol (ethanol). The carbon dioxide gas gets trapped in the dough, forming tiny bubbles that cause the dough to rise and become soft and fluffy. The alcohol produced evaporates during baking, leaving behind the pleasant aroma and texture of fresh bread.

Without yeast, bread would remain dense and flat because there would be no gas to create the airy structure inside the dough. This is why yeast is considered a leavening agent, meaning it helps the dough expand and rise.

Other options are incorrect:

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  Sugar: Yeast consumes sugar; it does not produce it.

  
  


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  Bacteria: Yeast is a fungus, not a bacterium, and does not create bacteria.

  
  


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  Oxygen: Yeast does not release oxygen; it consumes oxygen initially but produces mainly carbon dioxide in fermentation.

  
  

This process is an example of biological fermentation, an important topic in Everyday Science and Biology, as it explains how microorganisms are used in food production. Apart from bread, yeast is also used in making cakes, pastries, beer, and wine due to its fermentation ability.

In conclusion, carbon dioxide production by yeast is the key factor that makes bread light, soft, and porous, making it an essential ingredient in baking.