Final answer:
The barrier phases of the immune response prevent the entry of pathogens into the body. The skin, mucosal surfaces, and stomach are all barrier phases that help protect against pathogens. Monocyte is not a barrier phase.
Step-by-step explanation:
The barrier phases of the immune response are the initial defense mechanisms that prevent the entry of pathogens into the body. The skin acts as a physical barrier, preventing pathogens from entering the body. Mucosal surfaces, such as those in the respiratory and digestive tracts, produce mucus and have mucociliary escalator mechanisms that help trap and remove pathogens. The stomach also plays a role in the immune response by producing stomach acid that helps kill pathogens.
Therefore, the correct answer is monocyte. Monocytes are actually a type of white blood cell that plays a role in the adaptive immune response, not a barrier phase.
Learn more about Barrier phases of the immune response