Explain $ETS$.

(N/A) $ETS$ or electron transport system is located in the inner mitochondrial membrane. It facilitates the release and utilization of energy stored in $NADH + H^+$ and $FADH_2$,which are formed during glycolysis and the citric acid cycle. $NADH + H^+$ is oxidized by $NADH$ dehydrogenase (complex $I$). The electrons generated are transferred to ubiquinone through $FMN$. Similarly,$FADH_2$ (complex $II$) generated during the citric acid cycle transfers its electrons to ubiquinone. The electrons from ubiquinone are received by cytochrome $bc_1$ (complex $III$) and further transferred to cytochrome $c$. Cytochrome $c$ acts as a mobile carrier between complex $III$ and the cytochrome $c$ oxidase complex,which contains cytochrome $a$ and $a_3$ along with copper centers (complex $IV$).
During the transfer of electrons through these complexes,the process is coupled with the synthesis of $ATP$ from $ADP$ and inorganic phosphate by the action of $ATP$ synthase (complex $V$). The amount of $ATP$ produced depends on the molecule being oxidized. Generally,the oxidation of one molecule of $NADH$ yields $3$ $ATP$ molecules,and the oxidation of one molecule of $FADH_2$ yields $2$ $ATP$ molecules.