Q.What is immunity? Explain the mechanism of acquired immunity.

An antibody is a Y-shaped H2L2 molecule: the two arm tips are the antigen-binding sites, the two short outer chains are light chains, the two long chains are heavy chains, and the chains are held together by disulphide bonds — matching option (c).

In the CBSE/NCERT Human Health and Disease chapter, an antibody (immunoglobulin) is written as H2L2:

• A – Antigen-binding sites: the two tips of the Y (the variable regions) where the specific antigen binds.
• B – Light chains: two short polypeptide chains.
• C – Heavy chains: two long polypeptide chains. …

An antibody (immunoglobulin) molecule is a Y-shaped protein made of four polypeptide chains: two identical heavy chains and two identical light chains.

Each antibody unit consists of two long, identical heavy (H) chains and two short, identical light (L) chains, held together by disulfide bonds to form a characteristic Y-shaped structure. Each chain has a variable region (which determines antigen spec …

Lymphocytes (B-cells/plasma cells) secrete antibodies.

Antibodies (immunoglobulins) are the proteins of humoral immunity. They are produced by B-lymphocytes, which on activation differentiate into plasma cells that secrete large amounts of antibody into the blood. Monocytes, neutrophils and basoph …

The study of antigen–antibody interactions in blood is serology, so the answer is (A).

Serology is the branch of science dealing with blood serum and, in particular, with immune reactions between antigens and antibodies. Serological tests (such as agglutination and ELISA) detect specific antibodies or antigens in the blood and are used to diagnose infections and determine blood groups.

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Immunoglobulins (Igs) are the technical name for the antibody proteins produced by the immune system's B-cell lineage to specifically recognise and neutralise antigens.

Reasoning

Immunoglobulins are a class of glycoprotein molecules produced by plasma cells (differentiated B-lymphocytes) as part of the humoral (antibody-mediated) immune response. Each immunoglobulin/antibody molecule is Y-shaped and specifically recognises and binds to a particular antigen, helping neutralise it or mark it for destruction by other components of the immune system. Immunoglobulins are, by def …

Allergic responses are mediated by IgE antibodies.

Concept. An allergy is a hypersensitive immune reaction to allergens such as pollen, dust mites or certain foods. The KSEAB Class-12 syllabus (aligned with NCERT/CBSE) covers this under human health and disease.

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