Q. What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?
In the aquatic habitat the concentration of oxygen is good up to a certain depth only. Moreover, as oxygen is available as dissolved in water, so taking oxygen from there is not a very efficient method to that.
In terrestrial habitat oxygen is available in free form so it is easier to absorb by organisms. This is more efficient so terrestrial organisms can facilitate better utilization of food by way of respiration.