A Level Biology Practice Exam 2025 - Free A Level Biology Practice Questions and Study Guide

B cells play a crucial role in the immune system's response to pathogens. When they encounter an antigen, they primarily respond by producing antibodies. These antibodies are specific proteins designed to bind to the antigen, which helps neutralize pathogens or mark them for destruction by other immune cells. This process is essential for the adaptive immune response and contributes significantly to the body's ability to remember and effectively fight off infections.

While B cells may undergo rapid proliferation in the process of creating a robust immune response, the key and defining action that characterizes their response to an antigen is the production of antibodies. This differentiation between actions is important, as the generation of antibodies is the primary outcome that directly targets the antigen, while replication is part of the overall immune response but not the purpose of B cell activation. The other options do not accurately describe the function of B cells; they do not create toxins or differentiate into T cells, as T cells are a separate type of lymphocyte with different roles in the immune response.