The main reason why a Individual with type AB, Rh-negative blood cannot donate blood to an individual with type A, Rh-positive blood

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.

A. It is a cause of anemia: Sickle cells are fragile and hemolyze prematurely, producing a chronic hemolytic anemia.
B. It is cause of malaria: Malaria is caused by Plasmodium parasites; sickle-cell disease does not cause malaria (in fact, sickle-cell trait provides some protection against severe malaria).
C. It is due to a hereditary hemoglobin defect: Sickle-cell disease is inherited and results from a mutation in the β-globin (HBB) gene producing hemoglobin S.
D. It is advantageous in that it can protect carriers against malaria: Heterozygous carriers (sickle-cell trait) have relative resistance to severe forms of Plasmodium falciparum malaria.
E. It is caused by excessive allele that modifies the structure of hemoglobin: The disease is caused by a point mutation (a single nucleotide change) in the β-globin allele that alters hemoglobin structure (Glu→Val at position 6). Saying “excessive allele” is misleading -the cause is a specific mutant allele, not an “excessive” one.