CBSE Class 9 Answered

An antibody is a protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target.

An antigen is any molecule that is recognised by antibodies. Usually, an antigen is a protein or a polysaccharide, but it can be any type of molecule, even small molecules if coupled to a large carrier (haptens).

The antigen causes the disease, the antibody acts against the disease.

Antibody is produced by the body whereas antigen is a foreign body.