Which structure is described as a stack of flattened membrane-bounded compartments?

The Golgi apparatus is described as a stack of flattened membrane-bounded compartments because it consists of a series of cisternae, which are stacked parallel to each other. These compartments are involved in modifying, sorting, and packaging proteins and lipids that have been synthesized in the endoplasmic reticulum. The structure's organization allows for sequential processing of materials as they move through the stack, with enzymes located in specific compartments playing key roles in the modification process. This distinct structure underlies its function in receiving vesicles from the endoplasmic reticulum on one side, processing their contents, and then dispatching them in new vesicles on the other side to various destinations within the cell or for secretion outside the cell.

In contrast, lysosomes are membrane-bound organelles containing digestive enzymes, the endoplasmic reticulum is a network of membranes involved in protein and lipid synthesis, and vesicles are small membrane-bound sacs that transport materials within the cell. These structures do not have the specific stacked and flattened configuration characteristic of the Golgi apparatus.