Question

which of these is human body first line of defense against invading pathogens such as bacteria and viruses

Answer 1

Your first line of defense against pathogens include your skin and hair (first line) and actions such as sneezing, coughing, vomiting, producing ear wax, lacrimation (tears). Some of these actions are enhanced by the type of cells in your respiratory tract (cells with teeny tiny hair, beating in a synchronized direction to help get stuff out), the hairs in your nose to "catch" pathogens before they are swallowed or inhaled, or the swift action of tears washing away potential irritants.

Once a pathogen has gotten around these barriers, your immune system (comprised of both general and specialized cells), will do what it can to fight off infection.