The graph below compares the primary and secondary immune responses to the same pathogen. The secondary response may eliminate the pathogens before any damage occurs.

In reference to the graph above, which peak A or B represents secondary response?

Explanation

Peak B
During the primary immune response to the first encounter with a specific pathogen, some lymphocytes called memory cells develop with the ability to confer long-lasting immunity to that pathogen, often for life. These memory cells recognise antigens on the pathogens they have encountered before, triggering the immune system to respond faster and more effectively than on the first exposure. Hence, the response is more effective as the antibodies produced in second exposure are much larger as compared to the first exposure to same antigen.