Bacteria are minute and microscopic. They are the simplest organisms. Like fungi most of them are parasites and saprophytes. Some of them are however, autotrophs. There is a good deal of controversy about their taxonomic position in the living world. Bacteria comprise 2500 varieties.
Viruses have been a highly controversial group of tiny microscopic objects which have been rightly termed the most perfect obligate parasites of the world. They are absolutely inert outside a living host but once inside the host they are capable of growing, multiplying and undergoing even mutation. They are, therefore, supposed to represent a transitional form of life lying on the border line between the non living and the living world.
Viruses have been a highly controversial group of tiny microscopic objects which have been rightly termed the most perfect obligate parasites of the world. They are absolutely inert outside a living host but once inside the host they are capable of growing, multiplying and undergoing even mutation. They are, therefore, supposed to represent a transitional form of life lying on the border line between the non living and the living world.