Optometry Admission Test (OAT) Practice 2025 - Free Optometry Admission Test Practice Questions and Study Guide

Oxidative phosphorylation is a crucial step in cellular respiration that primarily occurs in the mitochondria. Its main function is to utilize the electrochemical gradient of protons (H⁺ ions) across the inner mitochondrial membrane to drive the synthesis of adenosine triphosphate (ATP). During this process, electrons are transferred through a series of protein complexes known as the electron transport chain. As electrons move along the chain, they release energy, which is used to pump protons from the mitochondrial matrix into the intermembrane space, creating a proton gradient.

This proton gradient generates potential energy, akin to water held behind a dam. The return flow of protons into the mitochondrial matrix, facilitated by the enzyme ATP synthase, allows for the phosphorylation of adenosine diphosphate (ADP) to ATP. This process is highly efficient and is responsible for producing the majority of ATP generated during cellular respiration.

The other options presented describe different biochemical processes that do not accurately capture the role of oxidative phosphorylation. For instance, glucose synthesis from carbon dioxide is characteristic of photosynthesis, not oxidative phosphorylation. The direct reduction of NAD+ to NADH is part of glycolysis and the citric acid cycle rather than oxidative phosphorylation. Lastly, la