Final answer:
The proton gradient starts off at the mitochondrial matrix and moves down a chemical gradient to the intermembrane space through the process of chemiosmosis.
Step-by-step explanation:
The movement of protons (H+) from the mitochondrial matrix to the intermembrane space can be experimentally demonstrated by studying the process of chemiosmosis. The proton gradient starts off at the mitochondrial matrix and moves down a chemical gradient to the intermembrane space through the process of chemiosmosis. Chemiosmosis is the flow of ions across a semipermeable membrane down their electrochemical gradient.
In the case of the proton gradient in mitochondria, protons are pumped from the matrix to the intermembrane space by complexes I, III, and IV of the electron transport chain. This creates a proton concentration gradient and an electrical gradient across the membrane.