What is a buffer solution? Explain the types of buffer solutions with examples and state their biological importance.

(N/A) buffer solution is a solution that resists changes in $pH$ upon the addition of small amounts of acid or base.
Types of buffer solutions:
$1$. Acidic Buffer: $A$ mixture of a weak acid and its salt with a strong base. Example: $CH_3COOH + CH_3COONa$ $(pH < 7)$.
$2$. Basic Buffer: $A$ mixture of a weak base and its salt with a strong acid. Example: $NH_4OH + NH_4Cl$ $(pH > 7)$.
Biological Importance:
$1$. The $pH$ of human blood is maintained at approximately $7.4$ due to the $H_2CO_3/HCO_3^-$ buffer system.
$2$. Many biochemical reactions in cells occur only within a specific $pH$ range,which is maintained by intracellular buffer systems.