The figure given below represents a molecule present in the body of a mammal.

(a) Name the parts labelled 'a' and 'b' in the molecule shown above.
(b) Name the type of cells that produce this molecule.

Explanation

(a) Antigen binding site : It is made up of `V_(L)` (Variable light) and `V_(H)` (Variable heavy) domain of the antibody molecule.
Heavy Chain : It is the heavier chain of the polypeptide present in the antibody molecule.
(b) B-lymphocytes when come in contact with pathogen (antigen) starts producing antibodies.