Air and Water as Respiratory Mediums

What are the advantages / disadvantages of a) air and b) water, as a respiratory medium?

So far all I have is that air has a 21% oxygen content compared with water which has less than 1%.

Can anyone come up with anything else?

Thanks

Reply 1

dfghj

Anyone?

Reply 2

iceman_jondoe

oxygen diffuses much faster in air than it does in water this is why fish have specialised gills to enable to draw out the oxygen content in the water.

Reply 3

nikk

Water is more dense than air and therefore requires more energy to keep it flowing over the exchange surface.

Although the high oxygen content of air supports organisms with higher metabolic rates, oxygen is also toxic.