The Golgi apparatus is the cellular organelle responsible for the modification, sorting, and packaging of proteins that are synthesized in the endoplasmic reticulum and destined for secretion or delivery to other organelles. It processes proteins by adding carbohydrate groups and tags them for their specific destinations. Unlike the lysosome or mitochondrion, the Golgi functions as the cell’s central protein trafficking hub. The endoplasmic reticulum primarily synthesizes proteins but does not sort or package them for secretion.

Reference:
Molecular Biology of the Cell, 6th Edition, Bruce Alberts, Chapter 15: The Golgi Apparatus and Intracellular Transport