Summary:
- The plasma membrane contains molecules other than phospholipids, primarily other lipids and proteins.
- Many of the proteins in the plasma membrane assist other substances in crossing the membrane.
- The plasma membrane may have extensions, such as whip-like flagella or brush-like cilia.
- For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose.
- It is the semipermeable plasma membrane that determines what can enter and leave the cell.