We must remember that micro-organisms are living and share the characteristics associated with all living organisms including humans like yourself. Just think of a microbe as a "small person;" and then you will remember the characteristics of life or living organisms. Living organisms are composed of one or many cells; they carry on or perform cell metabolism or chemical activity; microbes grow, often increasing in size; microbes respond to the environment and any stimuli that might be present and or change; and thank goodness microbes reproduce. It is often during this reproductive process when microbes are most vulnerable and can be controlled. However, if not controlled, it is estimated that one bacterial cell would reach a number of 1,150,000 at the end of 10 hours of unlimited reproduction.