Which part is responsible for the class of immunoglobulin?

Ans. is 'a' i.e. Heavy chain * There are five immunoglobulin classes (isotypes) of antibody molecules found in serum: IgG, IgM, IgA, IgE and IgD. They are distinguished by the type of heavy chain they contain.* IgG molecules possess heavy chains known as g-chains; IgMs have m-chains; IgAs have a-chains; IgEs have e-chains; and IgDs have d-chains. The variation in heavy chain polypeptides allows each immunoglobulin class to function in a different type of immune response or during a different stage of the body's defense.