Mucous membranes line body cavities and passages serving as barriers to microorganisms. The secretions produced inhibit microbial growth.

• A. The circulatory system
• B. Mucous membranes act as barriers to microorganisms
• C. The liver filters pathogens
• D. The kidneys remove toxins

Answer: (B)

Mucous membranes act as a physical barrier and deliver chemical defenses that slow or stop microbial growth. The mucus lining traps pathogens, and its secretions contain antimicrobial substances like lysozyme and IgA that create an environment hostile to microbes. This combination directly describes how these membranes help protect the body, making it the best description of the concept in the statement. The circulatory system mainly transports blood and immune cells, the liver filters pathogens but isn’t the lining barrier described, and the kidneys remove wastes rather than serving as a barrier to microorganisms.