Q.Why does the secondary immune response occur faster and stronger than the primary immune response?

During a person's very first exposure to a particular antigen, the immune system has to identify the antigen, select and activate the small number of matching B- and T-lymphocytes, and allow them time to multiply before an effective antibody response is mounted — this slower, first-time reaction is the primary immune response. However, some of the activated lymphocytes from this first encounter do not disappear once the infection is cleared; instead, they persist for years as memory B- and T-cells. …

Anchor the answer on the single word 'memory' — every part of the explanation should trace back to m …

Do not say the secondary response is faster simply because 'the body is used to it' — the precise biological reason is the pre-existence …