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===The Nose===
: The [[nose]] has [[hair]]s hairs which act as a physical barrier as they can trap [[micro-organism]]s before they enter the [[lung]]s.
: The [[nose]] is full of [[mucus]] which acts as a physical barrier since it is a sticky substance which [[micro-organism]]s can get stuck in. This [[mucus]] is then swallowed into the harsh environment of the [[stomach]] which kills [[micro-organism]]s.