What is the difference between an antibody and an antigen?

Another difference between antigen and antibody is where they are. Antigens are “hooks” on the surface of cells and are found in nearly every cell. You can find IgA antibodies in the vagina, eyes, ears, digestive tract, breathing passages, and nose, as well as in blood, tears, and saliva.

Hope this helps!

materials water oxygen those are the things i can think of in this moment.

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link: