Explain why the endoplasmic reticulum, Golgi apparatus, endosomes, and lysosomes are functionally related and comprise the endomembrane system.

The endoplasmic reticulum, Golgi apparatus, endosomes, and lysosomes are functionally related because they work together in a coordinated manner to synthesize, modify, package, and transport proteins and lipids within the cell. Proteins and lipids synthesized in the endoplasmic reticulum are transported to the Golgi apparatus for further modification and sorting. From the Golgi, these materials are then packaged into vesicles that can become endosomes for internalizing substances or lysosomes for cellular waste degradation, demonstrating a continuous flow and interconnectedness of their functions.