cells need a way to protect themselves. This job is done by the cell membrane, which is also known as the plasma membrane.
Controlling the Cell Contents
The cell membrane is semipermeable, or selectively permeable, which means that only some molecules can pass through the membrane.
Composition of the Cell Membrane
Molecules in the cell membrane allow it to be semipermeable. The membrane is made of a double layer of phospholipids (a “bilayer”) and proteins.
A single phospholipid molecule has two parts:
A polar head that is hydrophilic, or water-loving.
A fatty acid tail that is hydrophobic, or water-fearing.
Due to the composition of the cell membrane, small molecules such as oxygen and carbon dioxide can pass freely through the membrane, but other molecules, especially large molecules, cannot easily pass through the plasma membrane. These molecules need assistance to get across the membrane. That assistance will come in the form of transport proteins.
The cell membrane is selectively permeable, meaning only some molecules can get through.
The cell membrane is made of a double layer of phospholipids, each with a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail.