Final answer:
The correct spelling of the word is 'immunity.' This term refers to the ability to resist pathogens because of memory lymphocytes in the immune system. Active immunity, gained through exposure to a pathogen or vaccination, is longer-lasting than passive immunity.
Step-by-step explanation:
The correct spelling of immunity is option 2) immunity. Immunity is the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells. Memory cells play a crucial role in immunity; they are a type of lymphocyte that remains in the body after an initial infection and enables a rapid response to subsequent infections by the same pathogen.
Active immunity is the immunity that results from the production of antibodies by the immune system in response to the presence of an antigen. It lasts longer than passive immunity, which is provided by administering antibodies, because the body produces memory cells during active immunity that lead to a quicker and more effective response upon future exposures to the same antigen. Immunization works by simulating infection, causing the body to produce its own antibodies and memory cells, thus preparing the body to fight off real infections, such as the virus that causes measles.