Chemiosmotic coupling — During oxidative phosphorylation in most multicellular eukaryotes, ATP synthesis is driven primarily by which gradient and location?

Introduction / Context:
Peter Mitchell’s chemiosmotic theory explains how electron transport is coupled to ATP synthesis. The electron transport chain pumps protons to one side of a membrane, creating an electrochemical potential that ATP synthase converts into chemical energy in ATP.

Given Data / Assumptions:

• In mitochondria, Complexes I, III, and IV pump protons from matrix to intermembrane space.
• The inner mitochondrial membrane is impermeable to protons without channels, preserving the gradient.
• ATP synthase (F1F0-ATPase) spans the inner membrane and synthesizes ATP in the matrix.

Concept / Approach:
Identify both the correct ion and the correct membrane. In animal and plant mitochondria, the proton motive force across the inner mitochondrial membrane drives ATP formation. While some bacteria use the plasma membrane for a similar purpose, eukaryotic oxidative phosphorylation occurs in mitochondria, not the outer membrane or plasma membrane.

Step-by-Step Solution:

Verification / Alternative check:
Uncouplers dissipate the proton gradient and collapse ATP synthesis despite continued electron flow, confirming the gradient’s central role.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing bacterial respiratory chains (plasma membrane) with mitochondrial chains (inner membrane) in eukaryotes.

Final Answer:
A proton gradient across the inner mitochondrial membrane.