Memory is a key feature of adaptive immunity because it:

• A. It is immediate and non-specific
• B. It develops memory and is specific
• C. It is identical to innate immunity
• D. It is primarily passive

Answer: (B)

Memory is a defining feature of adaptive immunity because, after first exposure to an antigen, the system creates memory B and memory T cells that are specific for that antigen and persist long-term. These memory cells were generated through clonal expansion and differentiation, so they remain ready to respond. If the same antigen appears again, the response is much faster and stronger, often neutralizing the threat before it causes disease. This combination of specificity (each cell recognizes a particular antigen) and memory (long-lived cells ready for rapid reactivation) is what sets adaptive immunity apart.

In contrast, innate immunity acts quickly but is non-specific and does not leave behind memory cells for a targeted future response. Passive immunity involves receiving antibodies rather than generating memory through the body's own immune activation.