Master the Biology Bash: 2025 MCAT Biological Systems Practice Challenge!

B cells play a critical role in the immune system primarily through their ability to produce antibodies. These antibodies are proteins that specifically recognize and bind to antigens, which are foreign substances like pathogens (bacteria, viruses) or toxins, allowing the immune system to neutralize or eliminate these threats. When B cells encounter an antigen, they can differentiate into plasma cells that secrete large quantities of antibodies. These antibodies can mark pathogens for destruction by other immune cells, block pathogen entry into cells, or neutralize toxins directly.

This antibody-mediated response is crucial for adaptive immunity, which is characterized by a targeted and specific response to pathogens that the body has encountered previously. As a result, the adaptive immune system also leads to immunological memory, which is why subsequent exposures to the same pathogen often elicit a faster and more robust immune response.

The other options describe functions associated with different components of the immune system or biological processes. For example, the destruction of infected cells is primarily carried out by cytotoxic T cells, while engulfing pathogens is a function of phagocytes such as macrophages and neutrophils. Regulating hormone levels pertains to the endocrine system, not the immune system. Therefore, the production of antibodies by B cells is the clear and major