Oxidative systems refer to biological processes that use oxygen to produce energy in cells. These systems primarily occur in the mitochondria, where nutrients like carbohydrates and fats are broken down. The process generates adenosine triphosphate (ATP), the energy currency of the cell, through a series of reactions known as cellular respiration. In oxidative systems, electrons are transferred through a chain of proteins, known as the electron transport chain. This transfer releases energy, which is used to pump protons across the mitochondrial membrane, creating a gradient. The flow of protons back into the mitochondria drives the synthesis of ATP via an enzyme called ATP synthase.