A Level Biology Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

The primary immune response is characterized by the slow and gradual production of antibodies following the first exposure to a specific pathogen. During this initial encounter, the immune system has to recognize the pathogen, activate B cells, and then differentiate these cells into plasma cells that secrete antibodies. This entire process takes time, typically days to weeks, which is why the production of antibodies is considered slow compared to subsequent immune responses.

In contrast, the response does not involve a rapid production of antibodies, nor does it lead to immediate neutralization of pathogens—those aspects occur in the secondary immune response when the immune system has already been exposed to the pathogen and has "memory" cells in place. Additionally, the primary immune response does not occur with every subsequent exposure; this repeat exposure triggers a more rapid and robust response because of memory cells formed during the primary response. Thus, option B accurately reflects the nature of the primary immune response.