The function of vesicles in a cell is to transport materials within the cell and to the outside environment. They are small, membrane-bound sacs that can enclose various substances, including proteins, lipids, and waste products. Vesicles facilitate processes like exocytosis (release of materials) and endocytosis (uptake of materials), allowing for communication and nutrient exchange between cells. This transport mechanism is vital for maintaining cellular organization and function, contributing to overall cellular homeostasis.