Answer:
Small, nonpolar molecules (ex: oxygen and carbon dioxide) can pass through the lipid bilayer and do so by squeezing through the phospholipid bilayers. They don't need proteins for transport and can diffuse across quickly.
Explanation:
The channel proteins act like doors through the cell membrane.
They allow large polar molecules to move in and out of the cell.
The process is called passive diffusion or passive transport, because it does not need energy.
Sometimes the protein changes shape to help the polar molecules move through the channel.
It often uses a gated pore mechanism, in which the channel is never completely open.
