Final answer:
Bulk transport is an active transport mechanism that cells use to transfer large molecules like proteins and polysaccharides across the plasma membrane using energy. It involves two primary methods, endocytosis and exocytosis, which require vesicles to carry substances into or out of the cell.
Step-by-step explanation:
Bulk transport is a type of active transport used by cells to move very large molecules across the plasma membrane. This process requires energy because it involves moving substances against the concentration gradient or engulfing large particles. There are two main types of vesicle transport involved in bulk transport: endocytosis and exocytosis.
In endocytosis, cells engulf substances to bring them inside. This can happen through phagocytosis, where large particles like bacteria are consumed, or pinocytosis, where liquids are brought into the cell. In exocytosis, vesicles inside the cell fuse with the plasma membrane to release their contents to the exterior of the cell. This is how cells export large molecules such as proteins and polysaccharides.
Molecules such as proteins, polysaccharides, and other macromolecules pass through the cell membrane by bulk transport. Unlike smaller molecules like oxygen or carbon dioxide, which can pass freely via passive transport, these large molecules cannot easily move through the plasma membrane or through transport proteins without the assistance of vesicle transport.