The organelle being observed is the endoplasmic reticulum (ER). There are two types of ER: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The ER is the port of entry of protein synthesis and modification of proteins and is characterized by membranous tubules and sacs. Since there are smaller structures (called ribosomes) near the organelle, it is most likely the RER.
ANSWER: A. modification of proteins. From the ribosomes where the proteins are made, it goes to the endoplasmic reticulum for refinement or modification. Once the modified protein is complete, it leaves the endoplasmic reticulum inside a sac that detaches off the organelle.
