What describes naturally acquired active immunity?

Naturally acquired active immunity occurs when a person is exposed to a live pathogen, which can result in an infection. During this process, the body's immune system responds by generating a specific immune response, including the production of antibodies against the pathogen. This exposure leads to the development of lasting immunity, as the immune system retains memory cells that can respond more effectively if the same pathogen is encountered again in the future.

This type of immunity is fundamental because it not only protects the individual but also typically provides robust and long-lasting protection. The antibodies produced in response to the pathogen’s antigens help the body fight off future infections. The immune memory created through this process is the cornerstone of how the body learns and adapts to different pathogens over time.

The other answer choices describe different forms of immunity. For instance, receiving an injection of antibodies pertains to passive immunity rather than active immunity. Immunization with a killed pathogen involves the introduction of a non-live version of the pathogen to stimulate an immune response, which is a form of artificial immunity, not naturally acquired. Lastly, immunity developed through passive transfer of antibodies refers to another form of immunity that does not involve the individual's immune response creating its own antibodies.