Final answer:
The structure of a phospholipid molecule contributes to the partial permeability of a cell surface membrane by creating a hydrophobic interior and allowing certain molecules to pass through.
Step-by-step explanation:
The structure of a phospholipid molecule contributes to the partial permeability of a cell surface membrane in two main ways.
Firstly, the phospholipids are tightly packed together in a lipid bilayer with their hydrophilic heads facing outwards and their hydrophobic tails facing inwards. This arrangement creates a hydrophobic interior of the membrane, which allows only nonpolar and relatively small molecules to move through the lipid bilayer unaided.
Secondly, the hydrophilic heads of the phospholipids interact with water molecules on the outside and inside of the cell, maintaining the integrity of the membrane while still allowing certain molecules to pass through. The selective permeability of the cell membrane is crucial for regulating the movement of substances in and out of the cell.