Which cell structure is a membrane-bound sac involved in transport within the cell?

• A. Nucleus
• B. Mitochondrion
• C. Golgi apparatus
• D. Vesicle

Answer: (D)

Vesicles are small membrane-bound sacs that shuttle materials inside the cell. They bud off from membranes such as the endoplasmic reticulum or Golgi apparatus and carry cargo like proteins and lipids to various destinations—another organelle, the plasma membrane, or outside the cell. The vesicle’s membrane protects the cargo and helps the cargo reach the right place through specific docking and fusion with target membranes. This makes vesicles the primary carriers for intracellular transport. By contrast, the nucleus houses genetic material, mitochondria generate energy, and the Golgi apparatus, while involved in processing and packaging, is a stack of sacs rather than a single transport vesicle.