Micro organisams - 4learning http://www.channel4.com/science/index.html There are many small organisms in the world that we call micro-organisms or microbes. Some are harmful - they may cause illness. Bacteria and viruses may carry diseases.
Other micro-organisms help in the production of food. Yeast is a micro-organism - a kind of fungus that produces bubbles of gas that makes bread rise. Bacteria are essential to making yoghurt and cheese.