Question

Assertion (A): Oxidation of one molecule of ${\mathrm{FADH}}_2$ produces two molecules of $\mathrm{ATP}$, while that of one molecule of $\mathrm{NADH}$ gives rise to three molecules of $\mathrm{ATP}$.

Reason (R): The number of $\mathrm{ATP}$ molecules synthesised depends on the nature of the electron donor.

• A. Both assertion and reason are true and the reason is the correct explanation of the assertion
• B. Both assertion and reason are true but the reason is not the correct explanation
• C. The assertion is true but the reason is false
• D. Both assertion and reason are false

Answer 1

The correct option is A Both assertion and reason are true and the reason is the correct explanation of the assertion

Oxidation of one molecule of ${\mathrm{FADH}}_2$ produces two molecules of $\mathrm{ATP}$, while that of one molecule of $\mathrm{NADH}$ gives rise to three molecules of $\mathrm{ATP}$ because the number of $\mathrm{ATP}$ molecules synthesised depends on the nature of the electron donor.

The electrons from $\mathrm{NADH}$ pass through three proton pumps (Complex I, III and IV) which generate proton gradient. The $\mathrm{NADH}$ proton gradient, in turn, gives 3 $\mathrm{ATP}$ molecules.

While, the electrons from ${\mathrm{FADH}}_2$ pass through two proton pumps (Complex III and IV) which gives only 2 $\mathrm{ATP}$ molecules from the proton gradient generated.