The expulsion or secretion of materials from the cell.

The process you are referring to is known as "exocytosis." ### Explanation of Exocytosis: 1. **Definition**: Exocytosis is a cellular process in which substances are expelled from the cell. This is achieved by the fusion of vesicles containing the materials with the plasma membrane, leading to the release of their contents outside the cell. 2. **Steps Involved**: - **Vesicle Formation**: Materials to be expelled are packaged into vesicles, which are small membrane-bound sacs. - **Transport to Membrane**: The vesicles are transported to the cell membrane. - **Fusion with Membrane**: The vesicle membrane fuses with the cell membrane. - **Release of Contents**: The contents of the vesicle are released into the extracellular space. 3. **Functions**: - **Secretion of Hormones**: Many hormones are released from cells via exocytosis. - **Neurotransmitter Release**: In neurons, exocytosis is crucial for the release of neurotransmitters into the synaptic cleft. - **Cell Membrane Repair**: Exocytosis can help in the repair of the cell membrane by adding new membrane material. 4. **Types of Exocytosis**: - **Constitutive Exocytosis**: This is a continuous process where materials are secreted without any external signal. - **Regulated Exocytosis**: This occurs in response to specific signals, such as the release of neurotransmitters in response to an action potential. Exocytosis is essential for various physiological processes, including communication between cells, nutrient absorption, and waste removal.