What are vesicles?

Vesicles are small membrane-bound sacs that play a crucial role in the transport of materials within a cell. They are formed by the budding off of membranes from organelles such as the endoplasmic reticulum and the Golgi apparatus. These tiny structures can carry a variety of substances, including proteins, lipids, and other molecules, facilitating their movement to different parts of the cell or even outside of it through processes such as exocytosis.

The significance of vesicles lies in their ability to maintain compartmentalization within the cell, ensuring that substances are properly enclosed and protected during transport. This process is vital for cellular functions, including metabolism, communication between cells, and the secretion of hormones and neurotransmitters.

In contrast, the other options describe different cellular components or functions. For instance, proteins providing structural support are typically part of the cytoskeleton, rather than vesicles. The production of energy occurs in mitochondria, and the outer layer that protects the cell refers to the cell membrane or cell wall in some organisms. Thus, the definition of vesicles as transport carriers is clearly aligned with their role in cellular operations.