AP BIOLOGY

Detailed explanation-1: -Memory B cells can survive for decades, which gives them the capacity to respond to multiple exposures to the same antigen. The long-lasting survival is hypothesized to be a result of certain anti-apoptosis genes that are more highly expressed in memory B cells than other subsets of B cells.

Detailed explanation-2: -Figure: B memory cells: B lymphocytes are the cells of the immune system that make antibodies to invading pathogens like viruses. They form memory cells that remember the same pathogen for faster antibody production in future infections.

Detailed explanation-3: -IgG is the only class of immunoglobulin capable of crossing the placenta; consequently, it provides some degree of immune protection to the developing fetus.

Detailed explanation-4: -Memory B cells are generated during primary responses to T-dependent vaccines. They persist in the absence of antigens but do not produce antibodies (i.e., do not protect), unless reexposure to antigen drives their differentiation into antibody-producing plasma cells.