Micro-organisms mean small living things. These creatures are so small that can’t see with naked eyes. in order to see it first scientists used light microscope but is can’t shoe its interior but as the upgrades of scientists show a new microscope known as electron microscope. This microscope shows the exterior of the organisms as well as interior of the organism.

Micro-organisms form a diverse group which includes different kinds of organisms like viruses, bacteria, unicellular plants and animals, algae and some kinds of fungi. Some micro-organisms are good for the health of mankind but most are harmful for the humans and also for animals like some bacteria are very useful for humans because they are used to make antibiotics medicines and some used for fermentation but some type of viruses are the cause of SARS, AIDS, Hepatitis B & C in humans and they are also harmful for plants.

Micro-organisms are different from one another in structure and according to the mode of nutrition. On the basis of structure viruses are not cellular while other microbes are cellular. According to the mode of nutrition algae and a few bacteria are autotrophs while fungi and most unicellular animals are heterotrophs. Due to these physiognomies microbes form a various group of organisms which includes different kinds of creatures.