why is there never any aggultination between red cells and serum obtained from the same student?

Answer 1

Red cells contain antigen and plasma contains antibodies to antigens of other blood groups. That is why there is agglutination between plasma and cells of an incompatible blood group. Plasma cannot have antibodies to the individual's own blood group, therefore there is no agglutination.

Answer 2

coz its from the same person. agglutination only takes place if theres a conflict between the the anibodies and the antigens present in the blood, this can only happen f the blood types are different and incompatible. If its from the same person it will be 100% compatible and no prob is present.