Question

A critical feature of the plasma membrane is that it is selectively permeable. This allows the plasma membrane to regulate transport across cellular boundaries--a function essential to any cell's existence. How does phospholipid structure prevent certain molecules from crossing the plasma membrane freely?

Type of molecule philic/phobic
- nonpolar able to cross bilayer
-polar transport protein required
-Ions

Answer 1

The hydrophobic interior of the phospholipid bilayer allows only nonpolar molecules to pass through freely, while polar molecules and ions are unable to cross without assistance from transport proteins due to their hydrophilic nature.

Step-by-step explanation:

The phospholipid structure of the plasma membrane provides a selectively permeable barrier due to its hydrophobic interior. Only small, nonpolar molecules can freely cross the lipid bilayer without the need for transport proteins. Polar molecules and ions, which are hydrophilic, are unable to pass through the hydrophobic core of the membrane on their own due to repulsion from the lipid tails. Transport proteins are required to facilitate the passage of these substances, and they can function via passive transport or might require energy (such as ATP) in some cases. Large molecules also cannot freely pass through and must transport with the help of these protein structures within the plasma membrane.