What organelles are small bubbles of membrane that transport materials throughout the cell?

The answer is secretory vessicles. They transport the modified proteins and lipids from the Golgi apparatus to the outside of the cells. They are especially abundant in secretory cells. They bud from the trans side of the Golgi apparatus. Golgi apparatus are flattened disks of the membrane with cisternae. They transport, fold and modify proteins and lipids in a cell. The cis side of Golgi apparatus is located in close proximity to the endoplasmic reticulum that manufactures the proteins and lipids.