97 points | define antigen and antibody and explain why they create reactions between blood types.

An antigen is any substance unnatural (not natural to your blood cells) that enters your body triggering the production of antibodies.

An antibody is a protein found in the blood that is produced in order to "fight" antigens.

And this is how they create reactions between blood types: the self-antigens (natural antigens found in your blood cells) are not the same that is found in another blood type (since blood types are defined by the antibodies and antigens encountered). So, when a different blood type enters your body (obviously carrying different antigens), your antibodies will respond.

Hope it helped,

Happy homework/ study/ exam!

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."