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Membranes are important structural features of cells. They serve diverse functions in both eukaryotic and prokaryotic cells. One important role is to regulate the movement of materials into and out of cells. The phospholipid bilayer structure (fluid mosaic model) with specific membrane proteins accounts for the selective permeability of the membrane and passive and active transport mechanisms. In addition, membranes in prokaryotes and in the mitochondria and chloroplasts of eukaryotes facilitate the synthesis of ATP …

…transfer hydrogen atoms to components of the electron transport chain. During transport, hydrogen and electrons are transferred to acceptors in such a way that protons are pumped across the inner mitochondrial membrane. This results in an electrochemical gradient which is later used to phosphorylate ADP as protons diffuse back across the membrane. This whole process, collectively, is known as chemiosmosis. Hence, oxidative phosphorylation results because of the membranes present inside the cell and the mitochondria.