Which one of the following is not true regarding the release of energy during ATP synthesis through chemiosmosis? It involves:
Answer: (B) Breakdown of electron gradient. In chemiosmosis, ATP synthesis is driven by the breakdown of a PROTON gradient: protons move from the thylakoid lumen across the membrane to the stroma through ATP synthase, and NADP+ is reduced to NADPH on the stroma side.
- A.Breakdown of proton gradient
- B.Breakdown of electron gradient✓
- C.Movement of protons across the membrane to the stroma
- D.Reduction of NADP to NADPH2 on the stroma side of the membrane
Correct Answer
(B) Breakdown of electron gradient
Solution & Explanation
In chemiosmosis, ATP synthesis is driven by the breakdown of a PROTON gradient: protons move from the thylakoid lumen across the membrane to the stroma through ATP synthase, and NADP+ is reduced to NADPH on the stroma side. There is no 'electron gradient' involved in the energy release during ATP synthesis. Hence 'breakdown of electron gradient' is the statement that is not true. NCERT: Class 11 Ch 11, p.141 [141:019-022]: "This gradient is important because it is the breakdown of this gradient that leads to the synthesis of ATP. The gradient is broken down due to the movement of protons across the membrane to the stroma through the transmembrane"