Why can oxygen diffuses across a cell membrane but a proton cannot?

Oxygen can diffuse across a cell membrane because it is a small, nonpolar molecule that can easily pass through the lipid bilayer of the membrane. In contrast, protons (H⁺ ions) are charged and polar, making it difficult for them to traverse the hydrophobic core of the membrane without assistance. Protons typically require specific transport proteins, such as ion channels or pumps, to facilitate their movement across the membrane. This difference in size and polarity explains why oxygen can diffuse freely while protons cannot.