Which process is responsible for trafficking substances from inside the cell to the extracellular space?

• A. Exocytosis
• B. Endocytosis
• C. Pore transport
• D. Ion pairing

Answer: (A)

Exocytosis is the mechanism that moves substances from inside the cell to the outside. In this process, secretory vesicles carry cargo—such as neurotransmitters, hormones, or enzymes—to the plasma membrane, fuse with it, and release their contents into the extracellular space. This fusion is often triggered by calcium signals and is guided by proteins like SNAREs, and it can occur in a constitutive or regulated manner depending on the cell type. Endocytosis does the opposite, bringing material into the cell. Pore transport isn’t a typical mechanism for releasing large cargo across the membrane, and ion pairing describes a chemical interaction, not a trafficking process.