Here's why:
* Phospholipid Bilayer: The cell membrane is primarily composed of a phospholipid bilayer. This bilayer has a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. The tails form the inner part of the membrane, creating a barrier that is difficult for polar molecules to cross.
* Non-polar Molecules: Small non-polar molecules, such as oxygen (O2), carbon dioxide (CO2), and lipids, can easily dissolve in the hydrophobic tails of the phospholipids. This allows them to pass through the membrane without needing any special transport mechanisms.
In summary: Small non-polar molecules pass through the cell membrane by simply diffusing across the phospholipid bilayer.
