Chapter 9.10, Problem 9.36P

Consider a buffer prepared from the weak acid ${\text{HCO}}_{\text{3}}{}^{-}$ and its conjugate base ${\text{CO}}_{\text{3}}{}^{\text{2-}}.$
${\text{HCO}}_3{}^{\text{-}}(aq){\text{ + H}}_{\text{2}}\text{O}(l)\rightleftarrows {\text{ CO}}_3{}^{2-}(aq)+{\text{ H}}_3{\text{O}}^{\text{+}}(aq)$
Explain Why both ${\text{HCO}}_{\text{3}}{}^{-}$ and ${\text{CO}}_{\text{3}}{}^{\text{2-}}$ are needed to prepare the buffer.
What happens to the concentrations of ${\text{HCO}}_{\text{3}}{}^{\text{-}}$ and ${\text{CO}}_{\text{3}}{}^{\text{2-}}$ when a small amount of acid is added to the buffer?
What happens to the concentrations of ${\text{HCO}}_{\text{3}}{}^{-}$ and ${\text{CO}}_{\text{3}}{}^{\text{2-}}$ when a small amount of base is added to the buffer?