Question

Antibodies which stick to the surface of microbes are:
A. Antitoxins
B. Agglutinins
C. Opsonins
D. Precipitins

Answer 1

Antibodies are special protective proteins which are produced by the immune system of the body in response to a foreign substance referred to as an antigen. Antibodies are essentially immune-globulin chains which react and nullify an antigen.

Complete answer:
The primary response to a pathogen or any foreign particle is produced by the interaction of antibodies with the antigen molecule present in the pathogen. Opsonins are basically proteins used to mark antigens to make the antigens more distinguishable to phagocytic cells which leads to their destruction. These opsonins mark an antigen by binding to the membrane or surface of an antigen. One of the main mechanisms by which opsonin facilitates phagocytosis or cell lysis, is due to the ability of receptors in the phagocytic cells to identify and bind to the opsonins on the marked antigens.
Considering other options:
A. Antitoxins refers to certain antibodies which have the ability to neutralize a toxin. These are usually produced by certain animals, plants and even some bacteria. Although they act on toxins, they sometimes can be used to kill various microbes too.
B. Agglutinins are proteins in the blood which help aggregate or coagulate. Incase of antibodies these are the proteins which help to form aggregates of antigens by binding at the antigen binding sites present in the antibodies.
D. Precipitins are the type of antibodies which usually form a visible precipitate upon binding to an antigen. These are usually employed in various diagnostic tests.

So, the correct answer is “Option C”.

Note:
Antibodies which are produced by B-lymphocytes are classified into 5 different types based on their molecular composition such as IgG, IgA, IgM, IgE and IgD. All of these carry out the same function of defending the body against a foreign particle and successful elimination of such a threat. Antibodies are also referred to as immuno-globulins.