Here's why:
* Smaller size: Oxygen molecules are smaller than carbon dioxide molecules. Smaller molecules generally diffuse faster.
* Higher concentration gradient: Typically, there's a higher concentration of oxygen in the lungs (where it's inhaled) than in the blood and tissues, creating a steeper concentration gradient that drives diffusion.
* Lipid solubility: While not as soluble as carbon dioxide, oxygen has some solubility in the lipid membranes of cells, aiding its diffusion.
While carbon dioxide (CO2) is also important for gas exchange, it diffuses slower due to its larger size and lower concentration gradient.
