Biology · Respiration in Plants · NEET
No. The ETS is the chain of complexes (I to IV) that passes electrons and pumps protons. Oxidative phosphorylation is the final step where ATP synthase (Complex V) uses that energy to make ATP. The ETS builds the energy; oxidative phosphorylation spends it to phosphorylate ADP. NEET often couples them, but they are separate ideas.
'Phosphorylation' means adding a phosphate group to ADP to form ATP. 'Oxidative' means the energy for this comes from oxidation-reduction (redox) reactions in the ETS, not from light. NCERT states clearly: in respiration it is the energy of oxidation-reduction that is used to make the proton gradient, so the process is called oxidative phosphorylation.
Oxygen acts as the final hydrogen (electron) acceptor at the terminal stage. It combines with hydrogen to form water and removes hydrogen from the system, which keeps the whole ETS running. NCERT says oxygen's role is limited to the terminal step, but its presence is vital because it drives the whole process.
In substrate-level phosphorylation (glycolysis and Krebs cycle) ATP is made directly by transferring a phosphate from a substrate to ADP. In oxidative phosphorylation ATP is made indirectly, using energy from the proton gradient built by the ETS. Most ATP in aerobic respiration comes from oxidative phosphorylation.
No, this is a common trap. Oxygen does not directly make ATP. It only accepts electrons and hydrogen at the end. ATP is actually made by ATP synthase (Complex V) using the proton gradient. Oxygen keeps the electron flow going so the gradient can form.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
On the inner mitochondrial membrane, where the ETS complexes (I to IV) and ATP synthase (Complex V) are embedded.
Per NCERT, oxidation of one NADH gives 3 ATP and one FADH2 gives 2 ATP through oxidative phosphorylation.
ATP synthase, also called Complex V. Electrons passing through Complexes I to IV are coupled to Complex V to make ATP from ADP and inorganic phosphate.
It is aerobic. It needs oxygen as the final hydrogen acceptor, so it does not occur in fermentation (anaerobic respiration).
The energy released in the ETS pumps protons and builds a gradient. Chemiosmosis is how this proton gradient drives ATP synthase, so chemiosmosis is the mechanism behind oxidative phosphorylation.
