ANATOMY

Detailed explanation-1: -Chemical barriers-such as enzymes in sweat, saliva, and semen-kill pathogens on body surfaces. Biological barriers are harmless bacteria that use up food and space so pathogenic bacteria cannot colonize the body.

Detailed explanation-2: -Sweat and skin secretions contain a mixture of molecules that kills or limits the growth of many types of microbes. This control of microbes is an example of what type of immune response? a nonspecific defense against infection. an enzyme-catalyzed biochemical reaction.

Detailed explanation-3: -Skin is a barrier that serves as one of the body’s first lines of defense against harmful microbes. Specialized immune cells within skin tissue help to fight invading organisms. Yet the skin hosts diverse communities of beneficial bacteria, collectively known as the skin microbiota.

Detailed explanation-4: -Dendritic cells (Langerhans cells and macrophages), or antigen–presenting cells (APCs), identify antigens and present them to immature T cells.