Multiple Choice
Which of the following metabolic pathways requires a proton gradient?
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8. Respiration
Chemiosmosis
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During photosynthesis, which molecule is responsible for converting the proton gradient across the thylakoid membrane into chemical energy in the form of ATP?
A
NADP\textsuperscript{+} reductase
B
ATP synthase
C
Photosystem II
D
Rubisco
Verified step by step guidance1
Understand the context of the problem: Photosynthesis is the process by which plants convert light energy into chemical energy. During the light-dependent reactions, a proton gradient is established across the thylakoid membrane.
Recall the role of the proton gradient: The proton gradient is created by the movement of protons (H⁺ ions) into the thylakoid lumen during electron transport. This gradient represents potential energy that can be used to synthesize ATP.
Identify the molecule responsible for converting the proton gradient into ATP: ATP synthase is the enzyme embedded in the thylakoid membrane that uses the energy from the proton gradient to catalyze the formation of ATP from ADP and inorganic phosphate (Pi).
Clarify why other options are incorrect: NADP⁺ reductase is involved in the reduction of NADP⁺ to NADPH, Photosystem II is responsible for splitting water and initiating the electron transport chain, and Rubisco is an enzyme involved in the Calvin cycle, not the light-dependent reactions.
Conclude the explanation: ATP synthase is the correct answer because it directly converts the energy stored in the proton gradient into chemical energy in the form of ATP during the light-dependent reactions of photosynthesis.
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