Final answer:
The statement is false (option b) ; lymphocytes including B cells and T cells play key roles in both adaptive and innate immune responses, with B cells producing antibodies and T cells directing cellular immune responses or killing infected cells.
Step-by-step explanation:
The statement that lymphocytes only function in adaptive immune responses is false. Lymphocytes, including B cells and T cells, are indeed crucial in the adaptive immune system. B cells are responsible for producing antibodies in what is known as the humoral immune response. These antibodies bind specifically to antigens to neutralize or mark pathogens for destruction.
In contrast, T cells are involved in cell-mediated immunity, where they either help regulate immune responses by secreting soluble factors or directly destroy cells infected with intracellular pathogens. Both B cells and T cells develop from bone marrow and mature in different locations before performing their functions in the adaptive immune response. It is important to understand that while their primary role is in the adaptive immunity, some lymphocytes like natural killer cells are also part of the innate immune system.