What qualities characterize acquired immunity?

Acquired immunity is characterized primarily by specificity and memory. Specificity refers to the ability of the immune system to recognize specific antigens, which are typically foreign substances like pathogens or toxins. This allows the immune response to target and eliminate specific threats effectively.

Memory indicates that once the immune system has been exposed to a particular antigen, it retains the information about that antigen. If the same pathogen is encountered again in the future, the immune system can respond more rapidly and effectively thanks to these memory cells. This characteristic is fundamental to the effectiveness of vaccines, which aim to train the immune system to recognize and remember specific pathogens.

The other options describe qualities relevant to different aspects of the immune system or different types of immune responses. Innate and adaptive functions, for instance, refer to the two main branches of the immune response, with innate immunity being the first line of defense and adaptive immunity being the more specialized and acquired response. Immediate response and flexibility are features more commonly associated with innate immunity, which acts quickly upon infection. Speed and efficiency pertain to the overall performance of the immune response but do not specifically capture the defining traits of acquired immunity like specificity and memory do.