What Is Permeability of Cell Membrane?

Each living cell is enclosed by a cell membrane. The cell membrane mainly consists of lipids and proteins. Lipid molecules form the bilayer with the polar head outside and their hydrophobic tails inside. Proteins are integral and peripheral, which are buried in the membrane and present on the surface of the membrane, respectively.

Cell Membrane

Cell membrane permeability

Permeability of cell membrane refers to the ease with which a molecule can pass through a cell membrane. It is the rate at which the passive diffusion occurs through the membrane. Transporting molecules across the cell membrane is one of the important functions of the cell membrane. The cell membrane is selectively permeable, i.e. they allow only certain molecules to enter and leave the cell. It is an important aspect to maintain the integrity of the cell.

The permeability of molecules across the cell membrane depends on the polarity, charge and size of molecules. Neutral molecules can pass through the cell membrane without requiring energy by passive transport, whereas polar molecules cannot cross the nonpolar lipid bilayer and require carrier proteins for their transport, i.e. facilitated transport. Molecules are transported from higher concentration to lower concentration in passive transport and do not require energy, e.g. simple diffusion and facilitated diffusion.

When molecules and ions are transported across the cell membrane against the concentration gradient, i.e. from lower concentration to higher concentration, it is called active transport. Active transport requires energy, e.g. Na+/K+ pump. Water can also diffuse through the cell membrane by osmosis.

Recommended Video: Evolution of Cell Membrane

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