Virus

• Another category of microorganisms is Viruses.
• They are neither living nor non-living, hence comes at the border line of living and non living organisms.  

Virus under Microscope:

• They need a living system to grow which serves as a host system.
• When they are outside the host they cannot grow, hence are non-living then.
• They reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.
• Common ailments like cold, influenza (flu) and most coughs are caused by viruses.
• Serious diseases like herpes, AIDS, polio and chicken pox etc are also caused by viruses.
• The host of these viruses is human being.

Herpes virus

HIV Virus

• Bacteriophage is also a type of bacterial virus.

Bacteriophage