Answer:
The nature(hydrophilic or hydrophobic) of the molecule to be transported across the membrane determines whether that molecule can cross the cell membrane or not.
Step-by-step explanation:
Plasma membrane composed of lipid bilayer in which hydrophilic glycerol head groups of phospholipids in each monolayer are arranged oppositely with respect to each other whereas the nonpolar hydrophobic tail of both the monolayer faces each other.
The plasma membrane only allow the hydrophobic or nonpolar molecules to pass through its phospholipid bilayer but resist the passage of hydrophilic molecules or polar molecules through it.