Blood types (A, B, O, AB, etc.) are based on antigens on the surface of your blood cells. Being "A" means you have the A antigen on your blood cells. Being "B" means you have the B antigen on your blood cells. AB means you have both. Being O means you have neither.


Also, there are Rh positive and Rh negative (like if you here that someone is A+, then they have the A antigen and also the Rh antigen).



BTW, you should put questions like that into "Homework Help" instead of "Test Prep" - at least I think so!

The blood groups are based on antigens on the glycoprotein cell surface. This determines who you can get blood from if you need a transfusion. There is a good chart on Wikipedia: http://en.wikipedia.org/wiki/Blood_type

This should be in homework help but anyway.... blood groups are classified based on proteins on the exterior-facing surface of a cell. Cells have many of these proteins which are used by other cells/compounds to determine how to interact with these cells. Red blood cells have these and some common types include A, B, AB, and O. There is also something called Rh + and Rh - and Rh + is much more common.