All cells have cell membranes. A cell membrane surrounds the cell to separate its internal things, and allows interaction with external things controlled way.
composition
The cell membrane is a plasma membrane. For information on the composition, structure and permeability of the cell membrane, see phospholipid , vesicle , bilayer , plasma membrane.
membrane transport
passive diffusion
Passive diffusion is the movement of molecules over time by random motion (also called Brownian motion) from regions of higher concentration to regions of lower concentration. Significant passive diffusion across cellular membranes is limited to a few molecules, mostly gasses like O2, CO2, and N2, that can freely cross the hydrophobic phospholipid barrier.
carrier proteins
When a carrier protein binds a solute that must cross the membrane, it undergoes an allosteric change. During transport, the carrier protein undergoes another change in shape. When the solute reaches the other side of the membrane, it no longer has a high affinity for the carrier protein. After release of the solute, a final allosteric change restores the original conformation of the transport protein. These sequential conformational changes are illustrated on the next page.
channel proteins
active transport
active transport is making molecules against their passive diffusion direction with proteins, using ATP as power
bulk export
the Golgi apparatus produces vesicles to wrap the contents in a plasma membrane, and merges with the cell membrane so that the contents can be released outside of the cell.