Why can oxygen diffuses across a cell membrane by a protein cannot?

Oxygen can diffuse across a cell membrane because it is a small, nonpolar molecule that easily passes through the lipid bilayer of the membrane. In contrast, proteins are larger and often charged or polar, making it difficult for them to traverse the hydrophobic core of the membrane without assistance. Proteins typically require specific transport mechanisms, such as channels or carriers, to facilitate their movement across the membrane. This difference in size and polarity accounts for the varying transport methods between oxygen and proteins.