What types of transport does the cell membrane regulate?

To understand what types of transport the cell membrane regulates, let us first discuss what the cell membrane is. The cell membrane is a lipid bilayer that separates the inside of the cell, the cytoplasm, from the outside of the cell, the extracellular space. Within this bilayer, a number of different membrane proteins, which each serve various functions, exist. Because this bilayer is tightly packed, only small molecules such as oxygen, carbon dioxide, and water are able to easily pass through it. Larger molecules, such as ions, like calcium, sodium, and potassium can not pass through the lipid bilayer directly, and instead can only cross into (or get out of the cell) through the regulated opening of channel proteins. These channel proteins are regulated by other signaling molecules that tell them when to open and close. This opening or closing then allows molecules to either leave or enter the cell. Another mechanism of transport through the lipid bilayer is through carrier proteins, which are able to bind large molecules and physically move them across the lipid bilayer membrane and into the cell. Hope this helps!