What is the body's first line of defense against infection by foreign organisms?

The first line of defense against infection are the surface barriers. The surface barriers include intact skin, secretions of skin and mucous membrane. Skin protects external or outside boundaries and mucous membranes protect internal boundaries. Both the skin and mucous membranes release chemical secretions which restrict the growth of microbes on their surfaces if pathogens cannot cross the first line of defense body, they cannot disrupt normal functioning of and cannot cause disease.

all matter is made up of atoms

in any element all atoms are the same

elements in a compound are always in a constant ratio: apex

the endomembrane system i think