Microorganisms are very tiny organisms that can only be seen in detail using a microscope. Many microorganisms are unicellular which means they exist as a single cell.

Examples of microorganisms include:

  • bacteria
  • yeast (a type of fungus)

Microorganisms can be used by humans to produce foods and other useful substances. They are suitable for this role because they grow rapidly, may have simple nutrient requirements and can produce a wide range of products.

Using yeast to make bread and beer

Yeast is a single celled, microscopic fungus that uses sugar as food. In bread making, the carbon dioxide produced by the yeast during respiration is trapped in the dough, causing it to rise.

You can see a significant rise once the dough has been baked.

Two bread tins with dough. One has risen more than the other.

In brewing, carbon dioxide and ethanol (alcohol) are produced by the yeast during fermentation (respiration without oxygen).

Beer contains alcohol and the carbon dioxide gives the beer its characteristic fizz.