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