The primary factors affecting cell membrane permeability are the electric charge and polarity of a molecule, says Physiology Web. The size and mass of a molecule also affect permeability, but to a lesser degree, notes Wikipedia.Continue Reading
Cell membranes are selectively permeable, allowing some substances to pass through while restricting the passage of others, says Physiology Web. This is essential for providing a cell with nutrients, eliminating waste and preventing unwanted molecules from entering a cell. The double phospholipid layers of a cell membrane include polar heads and non-polar tails, says WiseGeek. Cell membranes are very permeable to non-polar molecules, such as oxygen, nitrogen, carbon dioxide and steroids, says Physiology Web. Conversely, membranes are less permeable to small polar molecules, such as water, glycerol, urea and ethanol, and highly impermeable to large polar molecules, such as glucose and sucrose.
Electric charge also plays an important role in membrane permeability, says Physiology Web. Charged particles, or ions, cannot penetrate a cell membrane. These charged particles, such as sodium, potassium, calcium, hydrogen and chlorine ions, require specialized transport proteins to carry them across the membrane. Transport proteins also carry molecules like glucose, water and ethanol across membranes. This means that the cell has more control over how many of these molecules pass through, and how often.Learn more about Cells