The concentration of oxygen molecules in water is higher than the concentration of oxygen molecules in gills. As a result, oxygen molecules diffuse from water (high concentration) to blood (low concentration).

Can oxygen be diffused?

This chapter discusses the facilitation of oxygen diffusion in hemoglobin solutions. It is found that when oxygen diffuses through a flat layer containing hemoglobin, the oxygen flux is enhanced by the simultaneous diffusion of oxyhemoglobin.

Does oxygen diffuse rapidly?

Oxygen has a partial pressure gradient of about 60 mmHg (100 mmHg in alveolar air and 40 mmHg in deoxygenated blood ) and diffuses rapidly from the alveolar air into the capillary.