What organelles are membrane sacs used to transport molecules?

mitochondria

vacuoles

ribosomes

thylakoids

The answer is vacuoles. It can be be found in plants, fungal and some protist cells. It is responsible for several functions such as transport of molecules, nutrients, and unwanted substances. It can also contain or store toxic substances.

A vacuole is a membrane-bound organelle which found in plants and but also in some protist, animal and bacterial cells Vacuoles are filled with water and contains inorganic and organic molecules. There are a few different functions of this organelle, such as water and other storage functions, maintenance of turgor pressure, transport. Transport of molecules can occur via vacuoles during the exocytosis process. The vacuoles carry different substances to and from the cells.