True or False: The adaptive immune system can only respond to pathogens it has previously encountered, making it ineffective against new infections.

False. The adaptive immune system can recognize and fight new infections, not only ones it has seen before, because it contains many naive lymphocytes that are ready to respond to unfamiliar antigens. When a new pathogen enters, these naive cells are activated, multiply, and produce antibodies that target the invader. Over time, some of those cells become memory cells, giving the body a faster, stronger response if the same pathogen returns. For example, when you first get chickenpox, your immune system learns to fight it, and later when you encounter the same virus, you recover much more quickly.