Q.On what property is the principle of immunization/ vaccination based? Explain briefly. OR Explain the importance of fungi and cyano bacteria as bio fertilizers.

Vaccination exploits the immune system's memory property: prior exposure to an antigen primes memory cells for a rapid, effective response upon real infection.

Property underlying immunization/vaccination: Vaccination is based on the property of "memory" of the immune system. When the immune system first encounters an antigen (a foreign pathogen or its component), it mounts a relatively slow, weaker primary immune response, and importantly, generates some memory B-cells and memory T-cells specific to that antigen.

Explanation: In vaccination, a preparation of antigenic proteins of a pathogen, or an inactivated/weakened (attenuated) form of the pathogen itself, is deliberately introduced into a healthy individual's body (the vaccine). This does not typically cause disease, but it does stimulate the immune system's primary response and, crucially, generates memory cells. If, at a later time, the vaccinated person is naturally exposed to the actual live/virulent pathogen, these memory cells enable the immune system to recognise it immediately and mount a very rapid and highly effective secondary immune response, producing large amounts of antibody quickly enough to neutralise/eliminate the patho …