Final answer:
The process where a particle or substance leaves a cell in a vesicle that merges with the cell membrane is called exocytosis, a type of active transport requiring energy.
Step-by-step explanation:
When a particle or substance leaves a cell in a vesicle that merges with the cell membrane, this process is known as exocytosis. Exocytosis is a form of active transport where vesicles containing substances fuse with the cell membrane, releasing their contents outside the cell. It requires energy, often in the form of ATP, because it's involved in transporting materials against their concentration gradient or large molecules that cannot pass through the cell membrane unassisted.