Final answer:
The key difference between the adaptive and innate defenses is the ability of the adaptive immune system to remember specific antigens, leading to the formation of memory lymphocytes that enable a faster and more efficient response in future encounters with the same pathogen.
Step-by-step explanation:
The ability to remember specific antigens is one of the key differences between the adaptive and innate defenses. The adaptive immunity is characterized by its ability to target specific pathogens through a process that involves the recognition of antigens by B and T lymphocytes. Whenever the immune system encounters a particular pathogen for the first time, it initiates what is known as a primary response, during which plasma cells and T cells increase their activity against the pathogen. After this initial encounter, the body produces memory lymphocytes, such as B and T memory cells, which remember the pathogen and enable a faster and more powerful response upon subsequent exposures, known as the secondary immune response.
On the other hand, the innate immune system does not have the ability to form such immunological memory. This is why vaccinations, which are a form of active immunity, are effective; they exploit the natural function of the adaptive immune system to create a memory of specific pathogens, thus preparing the immune system for potential future encounters with those pathogens.