(N/A) The $ABO$ blood grouping system is based on the presence or absence of two surface antigens on the red blood cells,namely $A$ and $B$. The plasma of individuals contains two natural antibodies,$anti-A$ and $anti-B$.
| Blood Group | Antigens on RBCs | Antibodies in Plasma | Donor Group |
| :--- | :--- | :--- | :--- |
| $A$ | $A$ | $anti-B$ | $A, O$ |
| $B$ | $B$ | $anti-A$ | $B, O$ |
| $AB$ | $A, B$ | $nil$ | $A, B, AB, O$ |
| $O$ | $nil$ | $anti-A, anti-B$ | $O$ |
$1$. Group $AB$ is known as the universal recipient because it can receive blood from all groups.
$2$. Group $O$ is known as the universal donor because it can donate blood to all groups.