Final answer:
Potassium ions (K+) would pass through a K+ channel protein in the lipid bilayer, which provides selective permeability for K+ ions in response to voltage changes across the membrane.
Step-by-step explanation:
If a lipid bilayer were to contain a K+ channel protein, potassium ions (K+) would pass through the membrane. This allows the cell to maintain its electrical balance and important functions like generating an action potential. A K+ channel selectively permits the passage of K+ ions, thanks to its specific structural design, which differentiates it from other ions and molecules.
The cell membrane's phospholipid bilayer is generally impermeable to charged particles, since they are hydrophilic. However, transmembrane proteins such as channel proteins and pumps facilitate their transport. The sodium/potassium pump actively moves Na+ out of the cell and K+ into it, while voltage-gated ion channels allow ions to pass in response to changes in membrane potential.
Specifically, voltage-gated K+ channel proteins open in response to a voltage change across the cell membrane, allowing a precise and timely flow of K+ ions during processes such as nerve impulse transmission.