What is the most abundant protein in plasma?

A. Type AB: Type AB has both A and B antigens.
B. Type O: Type O has neither A nor B antigens.
C. Either Type A or Type B, there is not enough information to distinguish between them: Presence of A antigens and absence of B antigens identifies Type A (unless testing error or weak expression, but standardly it’s Type A).
D. Type B: Type B would have B antigens (and no A).
E. Type A: A antigens present and B antigens absent - Type A.

A. alpha chains in hemoglobin: alpha chains are globin polypeptides that contribute to hemoglobin’s structure; O₂ binds to the heme prosthetic groups, not directly to the alpha globin chain.
B. delta chains in hemoglobin: delta chains (found in small amounts as HbA₂) are globin subunits; oxygen binding still occurs at heme groups, not the delta polypeptide.
C. beta chains in hemoglobin: beta chains are globin subunits that help form the O₂-binding pocket, but O₂ binds to the heme group (iron), not directly to the beta chain.
D. heme groups in hemoglobin: each hemoglobin has four heme groups (each with an Fe²⁺) that reversibly bind O₂; ~98–99% of blood O₂ is carried bound to hemoglobin’s heme.
E. the plasma membrane of erythrocytes: the RBC membrane does not bind O₂; O₂ diffuses across the membrane and is carried by hemoglobin inside the cell.