Final answer:
Mature B cells typically express surface IgM and IgD. The lifespan of a B cell is variable, from days to years, and can be extended if the cell is activated and differentiates into a plasma cell.
Step-by-step explanation:
The mature B cells usually have IgM and IgD on their surface, which function as antigen receptors. Naive B cells are mostly of the IgM class, which can also be found as pentameric IgM molecules secreted by plasma cells during an immune response. Additionally, plasma cells produce these antibodies in large quantities, playing a crucial role in the body's defense against pathogens. Regarding the lifespan of a B cell, it varies greatly and can range from a few days to many years. B cells may have a short life unless they become activated by antigen exposure, undergo clonal expansion, and differentiate into plasma cells.