Diffusion cell membrane

 Before moving on, you need to review the gases that can diffuse across a cell membrane. 

Because cells rapidly use up oxygen during metabolism, there is typically a lower concentration of O₂ inside the cell than outside.

 As a result, oxygen will diffuse from the interstitial fluid directly through the lipid bilayer of the membrane and into the cytoplasm within the cell. 

On the other hand, because cells produce CO₂ as a byproduct of metabolism, CO₂ concentrations rise within the cytoplasm; therefore, CO₂ will move from the cell through the lipid bilayer and into the interstitial fluid, where its concentration is lower. 

This mechanism of molecules moving across a cell membrane from the side where they are more concentrated to the side where they are less concentrated is a form of passive transport called simple diffusion (

Figure 3.5 Simple Diffusion across the Cell (Plasma) Membrane The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion.