Final answer:
Immunity is the body's ability to resist infection by pathogens through both active and passive means. The immune system has several lines of defense that work like a castle's fortifications. Vaccination is a method used to induce active immunity, resulting in the production of memory cells.
Step-by-step explanation:
Immunity is the ability to resist infection by a pathogen. Active immunity is a type of immune response where the body produces memory lymphocytes (B or T cells) following exposure to a pathogen, enabling the body to respond more efficiently to subsequent exposures to that same pathogen. Passive immunity, on the other hand, involves the transfer of antibodies from one individual to another, providing immediate, but temporary protection against disease or can be used to treat active disease.
As part of the body's defense system, the immune system functions much like a medieval castle with multiple lines of defense. The first line of defense includes barrier defenses such as the skin and mucous membranes that instantly block pathogenic invasion into the body's tissues. If pathogens bypass these barriers, they encounter the innate immune response which is rapid and nonspecific, followed by the adaptive immune response which is slower but highly specific and effective, mostly involving lymphocytes that control immune responses.
Vaccination is a deliberate form of exposure to a pathogen aimed at inducing active immunity, often resulting in the formation of memory cells that will recognize and fight the pathogen upon future exposures. Finally, a person may be born with certain immune responses, known as innate immunity, which provides nonspecific protection against pathogens.