(a) Explain the roles of (i) primary, and (ii) secondary lymphoid organs that are responsible for developing defence to combat the action of pathogen/foreign antigens which enter our body.
(b) Doctors generally advise not to undergo surgery of tonsils. Why?

(a) (i) The primary lymphoid organs produce blood and immune cells. The primary lymphoid organs are red bone marrow and thymus and the maturation of T-lymphocytes and B-lymphocytes takes place. Bone marrow has pluripotent stem cells and results in red blood cells and myeloid progenitors formation. Mature lymphocytes help in distinguishing between self and nonself cells as they have a specific receptor on the cell surface. (ii) Secondary lymphoid organs are lymph nodes and spleen. They recognise pathogens and maintain the number of mature lymphocytes.

(b) The palatine tonsils are the ones that are located near the opening of the oral cavity into the pharynx. They are secondary lymphoid organs which provide the site for interaction of lymphocytes with the antigen, which then proliferate to become effector cells. They defend against bacteria and viruses that enter the mouth. Since tonsils provide immunity, doctors generally advise not to undergo tonsillectomy.