Foundations of energy transduction — Which of the following processes contribute directly to cellular ATP production in respiration?

Introduction / Context:
ATP synthesis in oxidative phosphorylation depends on a sequence of energy-converting events. Understanding how electron flow, proton pumping, and chemical transformations are coupled clarifies how cells harvest energy efficiently from nutrients.

Given Data / Assumptions:

• Electron carriers shuttle electrons through membrane-bound complexes.
• Energy released from redox reactions is used to pump protons, forming an electrochemical gradient.
• ATP synthase uses this gradient to phosphorylate ADP to ATP.

Concept / Approach:
Each listed process is a link in the same energy chain: redox reactions (b) power proton pumping (a), creating the proton-motive force. The underlying thermodynamic drive is conversion from high-energy substrates to lower-energy products (c). Together they enable ATP generation via chemiosmosis.

Step-by-Step Solution:

Verification / Alternative check:
Uncouplers collapse the gradient and abolish ATP production despite continued electron transport, demonstrating the essential roles of (a) and (b). Substrate-level phosphorylation also exists but does not replace oxidative phosphorylation in most tissues.

Why Other Options Are Wrong:

Common Pitfalls:
Overlooking the chemiosmotic coupling; assuming electron transport alone, without proton pumping, would produce ATP.

Final Answer:
All of the above.