Question: 106: Which one of the following is not true regarding the release of energy during ATP synthesis through chemiosmosis? It involves:
(1) Movement of protons across the membrane to the stroma
(2) Reduction of NADP to NADPH { }_{2} on the stroma side of the membrane
(3) Breakdown of proton gradient
(4) Breakdown of electron gradient
Answer: Option (4)
Explanation:
Chemiosmosis is the mechanism by which ATP is synthesized using the energy stored in a proton gradient across a membrane.
During photosynthesis, protons accumulate in the thylakoid lumen and then move across the membrane into the stroma through ATP synthase.
This movement of protons to the stroma leads to the breakdown of the proton gradient and provides energy for ATP synthesis.
Reduction of NADP to NADPH { }_{2} occurs on the stroma side of the thylakoid membrane and is associated with the light reactions.
Chemiosmosis involves only the proton gradient and not an electron gradient.
Electrons move through the electron transport chain to help generate the proton gradient,
but ATP synthesis does not occur due to breakdown of an electron gradient.
Therefore, breakdown of electron gradient is not involved in ATP synthesis through chemiosmosis.
Hence, option (4) is the correct answer.