Polar molecules cannot pass through the cell membrane by simple diffusion and require a carrier protein to facilitate their transport. This restriction is primarily due to the presence of:

Step-by-step solution

The cell membrane is composed of a lipid bilayer where the lipids are arranged with their polar hydrophilic heads towards the outer sides and non-polar hydrophobic tails towards the inner part. This arrangement creates a non-polar hydrophobic core. Polar molecules cannot interact with or pass through this non-polar lipid bilayer by simple diffusion. Therefore, polar molecules require a carrier protein to facilitate their transport across the membrane. The restriction is primarily due to the non-polar hydrophobic co