Final answer:
The skin is the body's first line of defense against infection, acting as a physical barrier and producing antimicrobial substances to prevent pathogen entry. When injured, it forms a scab to seal the wound.
Step-by-step explanation:
The structure that represents the body's first line of defense against infection is the skin.
The skin acts as a physical barrier, preventing pathogens from entering the body. It also produces antimicrobial substances that help kill or inhibit the growth of microorganisms.
For example, when you get a cut or scrape, the skin forms a scab to seal the wound and prevent pathogens from entering.
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