Select the false statement about the function of antibodies. a. antibodies may bind to and block specific sites on viruses or bacteria thereby neutralizing the pathogen's effects. b. antibodies may cause the formation of cross linked antigen-antibody complexes resulting in agglutination. c. antibodies directly destroy antigen-bearing invaders by releasing potent toxins. d. the main antibody defense is triggering complement fixation.

C. Antibodies directly destroy antigen-bearing invaders by releasing potent toxins.

Explanation:

An antibody is part of the host cell defense and it’s made by B-cells (white blood cell).  The structure of the antibody consists of two light chains and two heavy chains, and at the very tip of the antibody is a hyper variable region, which is the antigen binding site that recognizes lots of different types of antigens.  An antigen is anything that is foreign to the human body (the body does not recognize it as self), it can be a virus, bacteria,  fungi, some foods and particles like dust that cause allergies and in some cases your own body will appear as foreign.

Antibodies act like small keys looking for the perfect lock, once they find their target they alert the immune system to mount a full immune response.  Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by the immune system or it can neutralize its target directly for example, by blocking a part of a microbe needed for entering and invading a cell.  Depending on the antigen the antibody binding may impede the biological process causing the disease or may activate macrophages to destroy the foreign substance, it does not release potent toxins.  Antibody binding can cause the clumping (agglutination) of large particles (viruses, bacteria etc.) making it a large complex, making phagocytosis more efficient (as they eliminate lots of clumped up viruses or bacteria in one go, and not one by one).