The endomembrane system is a collection of membranes and organelles that work together in eukaryotic cells to package, alter, and transport proteins and lipids.
All eukaryotic cells, including plant cells, have an endomembrane system.
The nuclear membrane, Golgi apparatus, endoplasmic reticulum, and other cellular organelles are all included in the endomembrane system by definition.
The endomembrane system is required for intracellular protein processing, lipid modification, and transit.