Closely stacked flattened membrane sacs are called the Golgi apparatus or body. The Golgi apparatus of plant or animal cells consists of five to eight flattened sacs called cisternae. The Golgi apparatus packages substances such as proteins and fats to transport them within the cell or out of the cell.
The Golgi apparatus is closely associated with another structure called the endoplasmic reticulum, which produces the substances that the Golgi apparatus packages. Each Golgi apparatus has two sides: the cis face and the trans face. The cis face is the entrance point for substances made in the endoplasmic reticulum. Substances are then packaged into vesicles that exit from the trans face of the Golgi apparatus. The Golgi apparatus usually has its cis face close to the endoplasmic reticulum, whereas its trans face is positioned near the cell membrane.