The endomembrane system encompasses the organelles that mediate the importa, export of molecules, that is, the transport of molecules from the environment to the cytoplasm and from the cytoplasm to the environment, respectively. The organelles that participate in such activities are the endoplasmic reticulum, the golgi apparatus, vacuoles and the cell membrane. Mithocondria's main purpose is energy production through oxidation of the carbohydrates/lipids we consume, thus, it is not related to molecule transport, and it can not be part of the endomembrane system.