Question

In ETS, terminal electron acceptor is

• A. Cytochrome
• B. H${}_2$
• C. O${}_2$
  
• D. H${}_2$O

Answer 1

The correct option is C O${}_2$

Electron transport chain (ETC) or Electron transport system (ETS) or respiratory chain is present in the inner membrane of mitochondria. It consists of different enzymes and co-enzymes, all of which act as hydrogen and electron carriers. The electron carriers are arranged according to their increasing positive potential.

Hydrogen from NADH is first transferred to Co-Q via Flavin Mono Nucleotide or FMN. Co-Q release protons and electrons. From Co-Q, only the electrons are transferred through ETS and the protons are released into the surrounding medium. The electron then passes to cytochrome-b from Co-Q and then to cytochrome-c1 and then to cytochrome-c. From cytochrome-c, electrons are transferred to cytochrome-a and finally to cytochrome-a3.

Cytochrome-a3 finally donates the electrons to free molecular oxygen and thus, oxygen acts as the last electron acceptor at the end of ETS. Oxygen also receives two protons from the aqueous medium and form one molecule of water.

So, the correct answer is C.