Heterotrophic organisms primarily use the process of cellular respiration to release energy. This process involves the breakdown of organic compounds, such as carbohydrates, fats, and proteins, to produce ATP (adenosine triphosphate), which serves as the main energy currency in cells.
During cellular respiration, glucose is often the starting molecule. It undergoes glycolysis, where it is broken down into pyruvate in the cytoplasm. Then, in the presence of oxygen, the pyruvate enters the mitochondria and participates in the Krebs cycle, producing electron carriers that are used in the electron transport chain. This series of reactions generates a significant amount of ATP involved in various cellular processes.
In the absence of oxygen, some heterotrophs can use anaerobic respiration or fermentation to generate energy, albeit less efficiently than aerobic respiration.