In the case of oxygen, by binding oxygen to a protein and thus holding much more in the blood than a simple solution can hold. Carbon dioxide may also bind to protein and it can exist in water in a number of different forms which helps it to be in higher concentrations. Also to keep flow rates of gasses high, the surface areas of the gas exchange surfaces must be huge and the air or water at this surface must not be allowed to become stagnant. Diffusion All cells exchange gases with their environments by diffusion . Oxygen must diffuse in sufficient quantities to sustain life, and carbon dioxide must diffuse out rapidly enough to not poison the cell.
More oxygen is needed in cells that are larger and have more metabolizing mass.
This may limit the size of cells. The amount of diffused gas varies inversely with distance. This means that active cells would have diffusion advantages only if small and if their environment were replaced rapidly. Diffusion rates increase directly with difference in concentration, increased temperature, diffusion surface area, and inversely with the square root of the molecular weight of the gas and with the square of the distance diffusion must travel. It is not very soluble in water.