Which process involves gas exchange between the atmosphere and the cells of the body and the resulting chemical reactions that provide the cells with energy to function.

A. Filter lymph: lymph nodes physically and biologically filter lymph, trapping pathogens and debris.
B. Immune surveillance: lymph nodes house lymphocytes and antigen-presenting cells that monitor for and respond to foreign antigens.
C. Produce macrophages: lymph nodes contain macrophages (and support their activity), but macrophages differentiate from monocytes in tissues; nodes are not typically described as producing macrophages de novo.
D. Filter blood: the spleen primarily filters blood; lymph nodes filter lymph, not systemic blood.

A. The movement of white blood cells through blood vessel walls: diapedesis (transmigration) is when leukocytes squeeze between endothelial cells to leave the bloodstream and enter tissues.
B. The formation of platelets from megakaryocytes: that process is thrombopoiesis (platelet production), not diapedesis.
C. The squeezing of red blood cells through narrow capillaries: RBCs deform to pass through capillaries, but that is not called diapedesis.
D. The filling of red blood cells with hemoglobin: hemoglobin synthesis and RBC maturation are separate processes, not diapedesis.