The endomembrane system fills the cell and divides it into compartments; in other words, it includes the different membranes suspended in the cytoplasm. The structures are tiny and visible only through electron microscopy. It includes lysosomes, Golgi apparatus, endoplasmic reticulum, and other related structures.

Overall, this system allows macromolecules to diffuse or be transferred from one of the components of the system to another. In particular, it processes proteins specified by the DNA within the nucleus and assembles sterols, sorting and sending them to their final destinations. Thus, in part, it is responsible for protein synthesis, modification, sorting, and transport.