In a blood transfusion, it is important that the donor's blood and recipients blood are compatible. If they are not what will happen to the recipients blood?

It causes the body to form antibodies that attack the new blood cells, causing them to break open and release harmful substances into the blood stream.

Explanation:

For blood transfusion to be successful, the blood group of the donor must be compatible with that of the recipient. If not, the donors red blood cells will clump in the recipients blood vessels, causing serious harm and release of harmful substances into the recipients blood stream. Usually blood used in blood transfusions contains very little of the donors plasma.