Final answer:
The correct sequence for protein transport in the endomembrane system is ER → Golgi → Plasma Membrane, where proteins are synthesized in the RER, modified in the Golgi apparatus, and then transported to their final destination.
Step-by-step explanation:
In the context of the endomembrane system, the correct order for protein transport is ER → Golgi → Plasma Membrane. This process begins with the synthesis of proteins on ribosomes associated with the rough endoplasmic reticulum (RER). From the RER, proteins enter the interior space or become part of the RER membrane. These proteins are then packaged into transport vesicles that bud off and fuse with the Golgi apparatus at the cis face. After modifications within the Golgi, the proteins are sorted and packed into new vesicles that bud from the trans face and are transported to their final destination, which may be the plasma membrane or other organelles.
The correct answer to the question is thus 'a) ER → Golgi → Plasma Membrane' as this sequence follows the protein's journey from synthesis to the point at which it may be embedded in the plasma membrane or secreted outside of the cell.