An example of a preformed chemical barrier is:

Correct Answer: B

Rationale: Step-by-step rationale: 1. Lysozyme is an enzyme that destroys bacterial cell walls. 2. This action acts as a preformed chemical barrier against pathogens. 3. Mucus (choice A) is a physical barrier, not a preformed chemical one. 4. Tight junctions (choice C) and cilia (choice D) are structural components, not chemical barriers. Summary: - Choice B, Lysozyme, is correct as it actively targets and destroys pathogens. - Choices A, C, and D are incorrect as they do not directly function as preformed chemical barriers.

Correct Answer: D

Rationale: The correct answer is D, "All of the above." Immunoglobulins are antibodies produced by the immune system to recognize and bind to foreign molecules called antigens. These antigens can be proteins (choice A), carbohydrates (choice B), or lipids (choice C). Therefore, immunoglobulins can bind to all classes of biological molecules. Choices A, B, and C are incorrect as they each represent individual classes of molecules that can be targeted by immunoglobulins, but the correct answer encompasses all of them.

Correct Answer: D

Rationale: Rationale: 1. A is correct as lymph is taken up from tissues by lymphatic capillaries. 2. B is correct as lymph carries antigens and mature dendritic cells to lymph nodes. 3. C is incorrect as lymph is not secreted by lymphocytes. 4. Therefore, D is correct as both A and B accurately describe the components and functions of lymph.

Correct Answer: D

Rationale: Dendritic cells play a crucial role in the immune system. Firstly, they provide costimulation to activate naïve T cells (A). Secondly, they process protein antigens into peptides for antigen presentation (B). Finally, dendritic cells present peptide-MHC complexes to T cell receptors for immune response activation (C). Therefore, the correct answer is D, as dendritic cells are involved in all these processes essential for initiating and regulating immune responses. Choices A, B, and C are incorrect as they are individual roles of dendritic cells and do not encompass the full range of functions that dendritic cells perform.

Correct Answer: B

Rationale: The correct answer is B: Opsonization. Both IgG and IgA antibodies can participate in opsonization, which involves tagging pathogens for destruction by phagocytes. IgG and IgA have specific receptors on phagocytes that recognize the tagged pathogens, enhancing their clearance. Neonatal immunity (choice A) is primarily mediated by IgG antibodies transferred from mother to fetus. Antibody-mediated degranulation of mast cells (choice C) is mainly associated with IgE antibodies in allergic reactions. Complement activation (choice D) mainly involves IgM and IgG antibodies, leading to a cascade of reactions for pathogen elimination.