All these organisms come diverse forms in terms of shapes, colours, behaviours and many more differences.  Also the organisms have certain features that are similar  and can therefore be grouped together. To study these diverse forms of life biologists sort them into groups based on similarities and give them a collective name for example plants and animals. These two have distinct differences.

To distinguish the differences, the scientists must examine them, however some are too small to be examined with naked eyes. Biologists require specialised apparatus to observe them.

      

Some  of the  apparatus is a Hand lens (left) and Microscope (right).