Multiple choice

In living organisms, gases like oxygen and carbon dioxide cross the plasma membrane mainly by

  1. passive diffusion through the lipid bilayer

  2. primary active transport

  3. specific gas transport proteins known as cotransporters

  4. secondary active transport

  5. proton pumps

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Gases are non-polar and can cross the lipid bilayer with ease. They therefore, do not need specific mechanisms to cross the plasma membrane. The lipid bilayer is permeable to water molecules, oxygen and carbon dioxide. They diffuse freely in and out of the cell.