Biology 11: Immune System and Disease Worksheets

Urine and vaginal secretions are too acidic for many pathogens, and semen contains zinc, which most pathogens cannot tolerate. Hydrochloric acid secreted by mucous membranes lining the stomach kills pathogens that enter the stomach in food or water. Biological Barriers. Biological barriers involve living organisms that compete with pathogens. ................
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