Answer:
Facilitated diffusion
Explanation:
Oxidative phosphorylation, involving the Electron transport chain and Chemiosmosis is the third stage of cellular respiration. The main purpose of the ETC is to build an electrochemical (electrical and concentration) gradient across the inner mitochondrial membrane. It does this by using energy to pump protons (H+ ions) from the matrix to the inter-membrane space of the mitochondria.
Facilitated diffusion, also known as passive transport through channels, is a form of facilitated transport involving a passive movement of molecules along their concentration gradient, through channels called membrane proteins.
During Chemiosmosis of Oxidative phosphorylation, protons (H+) flow back down their concentration gradient (from inter-membrane space to matrix) due to the chemiosmotic gradient that has been formed in ETC. However, hydrogen ions (H+) cannot pass through the inner mitochondrial membrane except through an enzyme (protein) found in the inner mitochondrial membrane called ATP synthase. This protein acts as a machine powered by the force of the H+ diffusing through it, down an electrochemical gradient. This movement of H+ via ATP synthase further catalyzes the conversion of ADP to ATP.
It is an example of facilitated diffusion because H+ ions are diffusing across the inner mitochondrial membrane (from inter-membrane space to matrix) via a protein channel or membrane protein called ATP synthase.
