Final answer:
The first line of immune defense involves physical, chemical, and biological barriers such as skin, secretions, and beneficial bacteria, providing non-specific protection. The second and third lines consist of the innate and adaptive immune responses, including inflammatory responses, phagocytosis, and specific antibody production.
Step-by-step explanation:
The question, "How does the first line of defense differ from the second and third lines of defense?", pertains to the body's immune system, particularly its layered defense mechanisms against pathogens. The correct answer to the question is A) The first line involves physical barriers, while the second and third lines involve chemical and cellular responses. The body's first line of defense includes mechanical, chemical, and biological barriers that are non-specific and always ready to protect the body from infection. These include the skin and mucous membranes, enzymes in secretions like sweat and saliva, and beneficial bacteria that inhibit the growth of pathogens.
If pathogens breach these barriers, the second line of defense is triggered, which includes inflammation and innate immune responses like phagocytosis by neutrophils and macrophages, as well as the complement system. This second layer is still part of the innate immune system but involves physiological defense mechanisms that act rapidly albeit non-specifically.
The third line of defense is the adaptive immune response, characterized by specificity and memory. This includes the production of antibodies by B cells and the targeted responses of T cells, which are tailored to the specific pathogens that have been encountered by the immune system previously. The adaptive immune response is slower to initiate than the innate response but provides a long-term and highly specific defense against pathogens.