Exocytosis
The reverse process of moving material into a cell is the process of exocytosis. Exocytosis is the opposite of the processes we discussed above in that its purpose is to expel material from the cell into the extracellular fluid. Waste material is enveloped in a membrane and fuses with the plasma membrane's interior. This fusion opens the membranous envelope on the cell's exterior, and the waste material expels into the extracellular space (Figure). Other examples of cells releasing molecules via exocytosis include extracellular matrix protein secretion and neurotransmitter secretion into the synaptic cleft by synaptic vesicles.
Methods of Transport, Energy Requirements, and Types of Transported Material | ||
---|---|---|
Transport Method | Active/Passive | Material Transported |
Diffusion | Passive | Small-molecular weight material |
Osmosis | Passive | Water |
Facilitated transport/diffusion | Passive | Sodium, potassium, calcium, glucose |
Primary active transport | Active | Sodium, potassium, calcium |
Secondary active transport | Active | Amino acids, lactose |
Phagocytosis | Active | Large macromolecules, whole cells, or cellular structures |
Pinocytosis and potocytosis | Active | Small molecules (liquids/water) |
Receptor-mediated endocytosis | Active | Large quantities of macromolecules |