The invention of the microscope opened up the world of very minute living organisms called micro organisms. Known commonly as germs or microbes, they are found almost everywhere in nature:
• in air , water and soil;
• on surfaces of objects and living organisms; and
• within living organisms, where they are able to invade living cells.
They are commonly dreaded as disease causing agents. These are known as pathogens and are mainly the parasitic micro organisms. Many micro organisms, however, benefit us greatly, especially the saprophytic ones that bring about the decay if organic matter. We have also learnt to ude certain micro organisms for our benefit.
