The immune system spans nearly every organ and tissue in the human body.

A. 5:Hemoglobin molecules do not bind five oxygen molecules; this exceeds their structural capacity.

B. 4:Each hemoglobin molecule has four heme groups, and each heme can bind one oxygen molecule. Therefore, one hemoglobin molecule can carry a maximum of four oxygen molecules.

C. 2:Hemoglobin can carry more than two oxygen molecules; two would only represent half-saturation of the molecule.

D. 6:Six oxygen molecules exceed the binding capacity of hemoglobin and are not physiologically possible.

E. 3:Hemoglobin can bind three oxygen molecules, but this is not the maximum capacity. Four is the full complement when fully saturated.

A. Lymph node:Lymph nodes are important for filtering lymph and mounting immune responses, but their removal does not typically cause severe harm because other nodes can compensate, even in young children.

B. Appendix:The appendix contains lymphoid tissue but is not essential for immune function. Its removal rarely causes significant immunologic compromise at any age.

C. Palatine tonsil:Tonsils contribute to local immune defense in the oral and pharyngeal region, but their removal in young children is usually well tolerated, with other lymphoid tissues compensating.

D. Spleen:The spleen is important for filtering blood and responding to certain pathogens, particularly encapsulated bacteria. While removal increases infection risk, children can often survive post-splenectomy with vaccinations and prophylaxis.

E. Thymus:The thymus is crucial in early life for T lymphocyte maturation and the establishment of adaptive immunity. Removal in a one-year-old would severely impair immune system development, making it much more harmful than thymectomy in adults, whose T cell repertoire is already largely established.