Question

Why is it essential to match blood groups of the donor and the recipient before blood transfusion

Answer 1

It is essential to match blood groups because, receiver has a specific type of proteins and carbohydrates and donor should also have same blood group of receiver's blood group because they all are useful for body and immune system. If donor's blood group doesn't match with receiver's blood group then that proteins and carbohydrates present in the receiver's blood group is destroyed by the blood plasma of donor's plasma.
It causes blood clots and may the receiver die 

Answer 2

It is imp to match blood of the donor as well as the recipient coz if the blood group does'nt matches clumping of cells in the recipient's blood takes place that could be fatal.