The electron transport system (ETS) takes place in the inner mitochondrial membrane. This membrane is highly folded into structures known as cristae, which increase the surface area available for the electron transport chain proteins and enzymes.
During cellular respiration, electrons are transferred through a series of protein complexes embedded in this membrane. As these electrons move through the chain, they help pump protons (H+) from the mitochondrial matrix into the intermembrane space, creating a proton gradient. This gradient is crucial for the production of ATP, the energy currency of the cell, through a process called chemiosmosis, facilitated by ATP synthase.
In summary, the inner mitochondrial membrane is the site where the electron transport system occurs, playing a key role in cellular energy production.