How would a polar molecule like water travel through the plasma membrane?

Answer 1

The structure of cell membrane allows nonpolar molecules to diffuse, but not polar molecules. Membrane architecture is in the form of a phospholipid bilayer. A single phospholipid has a "head" composed of a polar NH3 group, and two "tails" composed of nonpolar fatty acids. The lipids spontaneously arrange themselves into bilayers with the hydrophilic heads directed outward, and the hydrophobic tails facing inward. Because nonpolar solvents can only dissolve nonpolar solutes, polar molecules cannot mix with the nonpolar inside of the lipid bilayer. A polar molecule cannot cross the cell's lipid membrane without aid from a carrier protein. While this is true, there are multiple forces that dictate whether or not a molecule can cross a phospholipid membrane, including electrochemical gradients and size. Very small and non-polar molecules have a very easy time crossing the phospholipid bilayer. However, very small, polar molecules like water can also cross the phospholipid bilayer due to hydrostatic pressure and concentration gradient differences. Water will, but with some difficulty because of it's polarity. Aquaporins, protein channels embedded into cellular membranes allow for sufficient amounts of water to diffuse into cells.

Answer 2

Polar molecules are hydrophylic. Because the inner portion of the phospholipid bilayer (plasma membrane) consists of hydrophobic interactions, generally polar molecules cannot pass directly though. These molecules require protein channels to actively or passively move between the cytosol and the plasma membrane.

Non-polar molecules,due to their hydrophobic, nature can pass directly though the cell membrane.

Answer 3

The polar molecule movement across the membrane is because of diffusion. In this process, energy is not required and it occurs in kinetic movement randomly.