1. Which of the following is a primary physical barrier in the body's defense system against pathogens? A) Mucous membranes B) T lymphocytes C) Antibodies D) Fever Answer: A) Mucous membranes Rationale: Mucous membranes line various cavities in the body and are one of the first lines of defense in the immune response, trapping pathogens and preventing further entry into the body. 2. During an infection, which cells are responsible for presenting antigens to T cells? A) Neutrophils B) Macrophages C) Erythrocytes D) Platelets Answer: B) Macrophages Rationale: Macrophages are antigen-presenting cells that engulf pathogens and present their antigens on their surface to T cells, initiating an adaptive immune response. 3. What is the role of natural killer (NK) cells in pathogen elimination? A) Production of antibodies B) Phagocytosis of pathogens C) Destruction of virus-infected cells D) Activation of the complement system Answer: C) Destruction of virus-infected cells Rationale: NK cells are a type of lymphocyte that can recognize and destroy cells infected by viruses, playing a crucial role in the innate immune response. 4. Which complement pathway is activated directly by pathogens without the need for antibodies? A) Classical pathway B) Lectin pathway C) Alternative pathway