Question

Oxidative phosphorylation occurs in
A) Outer membrane of mitochondria
B) Inner membrane of mitochondria
C) Stroma of chloroplast
D) Grana of chloroplast

Answer 1

Hint: Oxidative phosphorylation can be defined as the metabolic pathway through which ATP is produced by ADP and Pi using energy released due to oxidation of NADH and FAD through transfer of electrons via ETS to oxygen.

Complete Answer:
As we know, oxidative phosphorylation is the fourth step of cellular respiration and is responsible for producing high amounts of energy (ATP). It is also known as electron transport linked-phosphorylation.

1) Option A: The outer membrane of mitochondria is similar to that of a cell membrane. It acts as a semipermeable membrane and has various porin and protein complexes to allow entry of small and big particles respectively. Various reactions of the citric acid cycle and Krebs cycle take place in the matrix, but oxidative phosphorylation does not. Therefore, this is the incorrect option.

2) Option B: It is in the inner membrane of the mitochondria where oxidative phosphorylation occurs. The ETS or the Electron Transport System is present in the inner mitochondrial membrane. The inner membrane is generally impermeable to most of the molecules as the proton gradient needs to be maintained because that is what drives the process of oxidative phosphorylation. Therefore, this is the correct option.

3) Option C: In the stroma of chloroplast, three processes occur namely- carbon fixation, regeneration and reduction. But oxidative phosphorylation does not occur. Therefore, this is the incorrect option.

4) Option D: Grana is nothing but bundles of thylakoid discs. In plants, photophosphorylation occurs in the grana of chloroplast whereas oxidative phosphorylation occurs in the mitochondria. Therefore, this is the incorrect option.

Thus, the correct option is, B) the inner membrane of mitochondria.

Note: Do not confuse photophosphorylation and oxidative phosphorylation, as though both the processes are same the latter occurs in both light and dark and in the inner membrane of mitochondria. But, photophosphorylation occurs only in light and in grana.