1.2 Micro-organisms:

   Micro means small and organisms means living things. Micro-organisms are those organisms that are so small and they cannot be seen with naked eye. In order to observe them, we need a light microscope or an electron microscope.

      Micro-organisms form a diverse group which includes different types of organisms, viruses, bacteria, unicellular plants and animals, certain algae and fungi (Fig1.1)

Micro-organisms differ from one another with regard to structure and mode of nutrition. On the basis of structure viruses are not cellular while other micro-organisms are cellular. Bacteria are unicellular but they have no organized nucleus while other micro-organisms have organized nucleus. According to mode of nutrition algae and few bacteria are autotrophs while fungi and most unicellular animals are heterotrophs. Due to these characteristics micro-organisms form a diverse group which includes different types of organisms.