The Golgi apparatus plays a critical role in protein modification and transport within the cell. After proteins are synthesized in the rough endoplasmic reticulum, they are sent to the Golgi apparatus for further processing. This includes the modification of carbohydrate groups through glycosylation and sorting proteins into vesicles for delivery to their final destinations, such as secretion outside the cell or incorporation into cell membranes. Its function is vital for proper cellular communication and material transport.