5. Microorganisms

What you need to know...
  • What are microorganism?
  • What are the properties of microorganisms?
  • How is yeast used in baking and brewing?
  • How is bacteria used to make yoghurt, cheese and biofuels?
What are microorganisms?
What are microorganisms? Well it is all in the name:
There are three main groups of micro-organisms: These are bacteria, viruses and fungi. The ones that we need to know about for now are are bacteria and a particular fungus called yeast.
As you can see from the pictures, these living things are made of a single cell.
Microorganisms are so useful because they growth very quickly, they use many different types of food and they produce a wide range of products.
Yeast is useful in many industrial processes because when it feeds on sugar it makes alcohol and carbon dioxide.
  • Beer and wine making - Yeast used in beer and wine making because when it feeds on sugar is makes alcohol.
  • Breadmaking - Yeast produce carbon dioxide which is used in dough to make the dough rise. When the bread is baked the spaces created by the yeast keep the break light and fluffy. Baking also gets rid of the alcohol which evaporates off.
Bacteria are used in lots of industrial processes:
  • Yoghurt making - Some bacteria are added to milk to make yoghurt. The bacteria feed on the lactose sugar in milk to make lactic acid. This lactic acid thickens the milk and makes it sour to give yoghurt its characteristic taste and texture.
  • Cheese making - When making cheese, bacteria are added to milk (along with the enzyme rennet) to make cheese. The enzyme acts with bacteria to clot the milk and make curds and whey. The whey is the liquid bit which is just drained off. The curds is the solid bit which is used to make cheese.