Final answer:
B cells are produced in the red bone marrow where they undergo maturation to become part of the adaptive immune system.
Step-by-step explanation:
B lymphocytes, or B cells, originate from lymphoid tissue of the GI tract and the bone marrow. Specifically, B cells are produced from stem cells in the red bone marrow. Unlike T cells, which mature in the thymus, B cells undergo their maturation process in the bone marrow itself where they grow larger and get ready to produce antibodies involved in humoral immunity. Once they are fully matured, B cells can circulate in the bloodstream and lymph, and reside in secondary lymphoid organs such as the spleen and lymph nodes.