Why can oxygen diffuse across a cell membrane but a protein cannot

Polar molecules and large ions dissolved in water cannot diffuse freely across plasma membrane due to the hydrophobic nature of the fatty acid tails of the phospholipids that make up the lipid bilayer only small non popular molecules such as oxygen and carbon can diffuse easily across the membrane

Oxygen is much smaller than a protein. proteins are too large, A protein cannot diffuse across a cell membrane because as the pore radius of the membrane approaches the protein radius, the mobility of the protein is significantly reduced