Here's why:

* Stack of slightly curved saccules: The Golgi apparatus is indeed composed of flattened, membrane-bound sacs called cisternae that stack upon each other.

* Packaging and secretion: The Golgi apparatus plays a crucial role in modifying, sorting, and packaging proteins and lipids synthesized by the endoplasmic reticulum. These molecules are then packaged into vesicles for transport to other parts of the cell or for secretion outside the cell.

Let me know if you have any other questions about cell structures!